Link Layer and Lans

ITTC © James P.G. Sterbenz Communication Networks The University of Kansas EECS 780 Link Layer and LANs

James P.G. Sterbenz

Department of Electrical Engineering & Computer Science Information Technology & Telecommunications Research Center The University of Kansas

[email protected]

http://www.ittc.ku.edu/~jpgs/courses/nets

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-2 ITTC © James P.G. Sterbenz Link Layer Hybrid Layer/Plane Cube

management Layer 2: data plane control plane hop-by-hop L8 social data transfer L7 application in data and p control planes L5 session l L4 transport a L3 network n e L2.5 virtual link L2 link L1.5 MAC L1 physical 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-3 ITTC © James P.G. Sterbenz Link Layer Link Definition

network CPU intermediate CPU system

M app M app end system end system

• Link is the interconnection between nodes – intermediate systems (switches or routers) – end systems (or hosts)

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-4 ITTC © James P.G. Sterbenz Link Layer Link Protocol application application session session transport transport network network network network link link link link end system intermediate intermediate end system network system system link network intermediate • Link protocol system – is responsible for per hop transfer of data frame – assume dedicated links for now: no MAC lecture MW

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-5 ITTC © James P.G. Sterbenz Link Layer Service and Interfaces

• Link layer is HBH analog of E2E transport layer – transport layer (L4) transfers packets E2E

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-6 ITTC © James P.G. Sterbenz Link Layer Service and Interfaces

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-7 ITTC © James P.G. Sterbenz Link Layer Service and Interfaces

• Link layer is HBH analog of E2E transport layer – transport layer (L4) transfers packets E2E • Link layer (L2) service to network layer (L3) – transfer frame HBH (hop-by-hop) • sender: encapsulate packet into frame and transmit • receiver: receive frame and decapsulate into packet – error checking / optional correction or retransmission • recall end-to-end arguments: E2E reliability with HBH error control only for performance

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-8 ITTC © James P.G. Sterbenz Link Layer Service and Interfaces

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-9 ITTC © James P.G. Sterbenz Link Layer Service and Interfaces

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-10 ITTC © James P.G. Sterbenz Link Layer Service and Interfaces

• Link layer frame encapsulates network layer packet – packet (NPDU – network layer protocol data unit) – frame (LPDU link layer protocol data unit) • frame = header + packet + (trailer) network layer network layer

NPDU packet NPDU link layer link layer

H NPDU T frame H NPDU T …10111001010… MAC/phy layer MAC/phy layer

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-11 ITTC © James P.G. Sterbenz Link Layer Functional Placement

switch end system routing forwarding mem CPU line card line card

network line card line card interface frames packets frames

• Link layer functionality per line interface – end system: network interface (NIC) – switch/router: line card

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-12 ITTC © James P.G. Sterbenz Link Layer and LANs LL.2 Framing and Delineation

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-13 ITTC © James P.G. Sterbenz Link Framing Structure and Fields

• Link protocols need to delimit link layer frame why?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-14 ITTC © James P.G. Sterbenz Link Framing Structure and Fields

• Link protocols need to delimit link layer frame – physical layer is coded bit stream – receiver needs to delimit frames

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-15 ITTC © James P.G. Sterbenz Link Framing Structure and Fields

• Delimits link layer frame – physical layer is coded bit stream – receiver needs to delimit frames • Header: what to do with the frame – beginning of frame – multiplexing information for multiplexed links – addressing information for multiple access links

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-16 ITTC © James P.G. Sterbenz Link Framing Structure and Fields

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-17 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation

• Key problem: how to detect start of frame ideas?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-18 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation

• Key problem: how to detect start of frame – in the presence of errors ideas?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-19 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation Techniques

• Synchronous clocks • Counting • Flags with – byte stuffing – bit stuffing • Preamble pattern • Special physical layer code

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-20 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Synchronous Clocks

• Synchronous links • Sender and receiver maintain tight synchronisation – receive clock carefully matched to sender – clock recovery • Example – SONET/SDH

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-21 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Counting

• Counting (bit, byte, or word) – count bytes to determine frame length – use length field in header for variable length frames 4 3 2 1 6 5 4 3 2 1 3 2 1 8 7 6 5 4 3 2 1 5 7 4 9

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-22 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Counting

• Counting (bit, byte, or word) – count bytes to determine frame length – use length field in header for variable length frames 4 3 2 1 6 5 4 3 2 1 3 2 1 8 7 6 5 4 3 2 1 5 7 4 9 Effect of errors?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-23 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Counting

• Counting (bit, byte, or word) – count bytes to determine frame length – use length field in header for variable length frames 4 3 2 1 6 5 4 3 2 1 3 2 1 8 7 6 5 4 3 2 1 5 7 4 9 • Effect of errors – difficult to maintain frame synchronisation – serious problem if length field is corrupted 4 3 2 1 2 1 8 7 6 5 4 3 2 1 2 1 6 5 4 3 5 3 9 4 9 3 7 – checksums don’t help why? 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-24 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Counting

• Counting (bit, byte, or word) – count bytes to determine frame length – use length field in header for variable length frames 4 3 2 1 6 5 4 3 2 1 3 2 1 8 7 6 5 4 3 2 1 5 7 4 9 • Effect of errors – difficult to maintain frame synchronisation – serious problem if length field is corrupted 4 3 2 1 2 1 8 7 6 5 4 3 2 1 2 1 6 5 4 3 5 3 9 4 9 3 7 – checksums don’t help • indicate error, but not the beginning of the next frame 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-25 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Flags

• Flags F H NPDU T F – special sequence of bits at beginning and end of frame problem?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-26 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Flags

• Flags F H NPDU T F – special sequence of bits at beginning and end of frame what if data stream contains flag bitstring? F H F NPDU T F

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-27 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Flags with Byte Stuffing

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-28 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Flags with Byte Stuffing

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-29 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Flags with Byte Stuffing

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-30 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Flags with Byte Stuffing

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-31 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Flags with Byte Stuffing

• Flags F H NPDU T F – special byte at beginning and end of frame – data transparency: flag byte must be allowed in data • Byte stuffing F H EF NPDU T F – escape byte stuffed when flag (or escape) is in data • Example: PPP 01111110 flag 01111101 escape – data B B B F B B E B B F F B B – sender insertion F B B B F E B B E E B B F E F E B B F – receiver strips B B B F B B E B B F F B B • escaped escape: remove escape E E  E • escaped flag: remove flag F E  F • flag: frame boundary F 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-32 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Flags with Bit Stuffing

• Flags F H NPDU T F – special byte at beginning and end of frame what if data stream isn’t byte stream? F H NPDU T F

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-33 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Flags with Bit Stuffing

• Flags F H NPDU T F – special sequence of bits : n 1s delineated by 0 bits – stuffing can be applied at bit level as well as byte level • Bit stuffing F H F NPDU T F – 0-bit is stuffed in data stream after n–1 bit sequence occurs

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-34 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Flags with Bit Stuffing

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-35 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Flags with Bit Stuffing

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-36 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Flags with Bit Stuffing

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-37 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Flags with Bit Stuffing

• Flags F H NPDU T F – special sequence of bits : n 1s delineated by 0 bits – stuffing can be applied at bit level as well as byte level • Bit stuffing F H F0 NPDU T F – 0-bit is stuffed in data stream after n–1 bit sequence occurs • Example: 01111110 flag (run of six 1 bits) – data 00111001111111111111101011 groups of 5 – insertion 01111110001110011111011111011110101101111110

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-38 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Flags with Bit Stuffing

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-39 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Flags with Stuffing

• Flags – special sequence of bits • Stuffing – add escape (byte or 0-bit) for data transparency Problem?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-40 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Flags with Stuffing

• Flags – special sequence of bits • Stuffing – add escape (byte or 0-bit) for data transparency • Data stream transformation – bits or bytes inserted problem?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-41 ITTC © James P.G. Sterbenz Link Framing Receiver Delineation: Flags with Stuffing

• Flags – special sequence of bits • Stuffing – add escape (byte or 0-bit) for data transparency • Data stream transformation – bits or bytes inserted – data rate non-deterministically altered – sufficient link-capacity headroom must be provided • Was used by PPP for dialup modem access – no longer common

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-42 ITTC © James P.G. Sterbenz Link Framing Preamble Pattern

• Preamble pattern – special pattern in header (like a flag) How to handle data transparency?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-43 ITTC © James P.G. Sterbenz Link Framing Preamble Pattern

• Preamble pattern – special pattern in header (like a flag) How to handle data transparency? without flags

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-44 ITTC © James P.G. Sterbenz Link Framing Preamble Pattern

• Preamble pattern preamble – special pattern in header (like a flag) • Significantly longer than flag header – lowers probability of bit error impacting

payload

trailer

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-45 ITTC © James P.G. Sterbenz Link Framing Preamble Pattern

• Preamble pattern preamble – special pattern in header (like a flag) • Significantly longer than flag header – lowers probability of bit error impacting length • Length field in header – allows preamble in payload

payload

trailer

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-46 ITTC © James P.G. Sterbenz Link Framing Preamble Pattern

• Error check in trailer payload – protects against errors – e.g. FCS (frame check sequence) FCS

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-47 ITTC © James P.G. Sterbenz Link Framing Preamble Pattern

10101010 10101010 10101010 10101010 • Preamble pattern preamble + SFD 10101010 10101010 10101010 10101011 – special pattern in header (like a flag) MAC header destination address • Significantly longer than flag 22B – lowers probability of bit error impacting source address length/type • Length field in header LLC/SNAP LLC subheader – allows preamble bits in payload 8B SNAP • Error check in trailer – protects against errors payload payload – e.g. FCS (frame check sequence) trailer • Example: Ethernet 10101010… 4B FCS

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-48 ITTC © James P.G. Sterbenz Link Framing Special Physical Layer Code

• Physical layer codes bits on within channel Lecture PL • Special physical code may be reserved for framing how to handle data transparency?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-49 ITTC © James P.G. Sterbenz Link Framing Special Physical Layer Code

• Physical layer codes bits on within channel Lecture PL • Special physical code may be reserved for framing – choose code symbol that doesn’t represent valid data

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-50 ITTC © James P.G. Sterbenz Link Layer and LANs LL.3: LAN Types and Topologies LL.1 Link layer functions and services LL.2 Framing and delineation LL.3 LAN types and topologies LL.3.1 LAN topologies LL.3.2 Point-to-point protocol LL.3.3 802 and Ethernet LL.3.4 Ring LANs LL.4 Multiplexing and switching LL.5 Per-hop error and flow control LL.6 Link layer components LL.7 VLANs, L2 tunnels, and ARP LL.8 Residential broadband

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-51 ITTC © James P.G. Sterbenz Link Types and Topologies Point-to-Point vs. Shared Medium

• Point-to-point links – one transmitter per medium • dedicated

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-52 ITTC © James P.G. Sterbenz Link Types and Topologies Point-to-Point vs. Shared Medium

• Point-to-point links – one transmitter per medium • dedicated • multiplexed (layer 2) more later

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-53 ITTC © James P.G. Sterbenz Link Types and Topologies Point-to-Point vs. Shared Medium

• Point-to-point links – one transmitter per medium • dedicated • multiplexed (layer 2) more later • Shared medium (multiple access) – multiple transmitters per medium implication?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-54 ITTC © James P.G. Sterbenz Link Types and Topologies Point-to-Point vs. Shared Medium

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-55 ITTC © James P.G. Sterbenz Link Types and Topologies Point-to-Point vs. Shared Medium

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-56 ITTC © James P.G. Sterbenz Link Types and Topologies Point-to-Point vs. Shared Medium

• Point-to-point links – one transmitter per medium • dedicated • multiplexed (layer 2) more later • Shared medium (multiple access) – multiple transmitters per medium – results in contention for medium • medium access control (MAC) needed lecture MW – examples • wireless networks • original Ethernet 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-57 ITTC © James P.G. Sterbenz Link Layer and LANs LL.3.1: LAN Topologies LL.1 Link layer functions and services LL.2 Framing and delineation LL.3 LAN types and topologies LL.3.1 LAN topologies LL.3.2 Point-to-point protocol LL.3.3 802 and Ethernet LL.3.4 Ring LANs LL.4 Multiplexing and switching LL.5 Per-hop error and flow control LL.6 Link layer components LL.7 VLANs, L2 tunnels, and ARP LL.8 Residential broadband

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-58 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Medium

• Early LANs used a shared medium among all stations – contention among station pairs for the medium – collisions when multiple stations transmit at the same time • Topology alternatives – bus – ring

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-59 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Medium Bus

• Bus topology problems?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-60 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Medium Bus

• Bus topology – topology constrained by medium • longest path • limited to LAN lengths due to delay

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-61 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Medium Bus

• Bus topology – topology constrained by medium • longest path • limited to LAN lengths due to delay Network scalability?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-62 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Medium Bus

• Bus topology – topology constrained by medium • longest path • limited to LAN lengths due to delay • Limited scalability – all hosts share capacity of bus

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-63 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Medium Bus

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-64 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Medium Bus

• Bus topology – topology constrained by medium • longest path • limited to LAN lengths due to delay • Limited scalability – all hosts share capacity of bus – contention for shared medium • collisions in shared medium • need MAC lecture MW

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-65 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Medium Bus

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-66 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Ring

• Ring topology advantages and problems?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-67 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Ring

• Ring topology – topology constraints station – interstation distance an issue • host is frequently called a station

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-68 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Ring

• Ring topology – topology constraints – interstation distance an issue Network scalability?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-69 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Ring

• Ring topology – topology constraints – interstation distance an issue • Limited scalability – all stations share capacity of ring

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-70 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Ring

• Ring topology – topology constraints – interstation distance an issue • Limited scalability – all stations share capacity of ring – contention for shared medium

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-71 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Ring

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-72 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Ring

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-73 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Ring

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-74 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Ring

• Ring topology – topology constraints – interstation distance an issue • Limited scalability – all stations share capacity of ring – contention for shared medium • possible to prevent collisions • need MAC lecture MW • Resilience – dual ring can survive cut • Example: token ring 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-75 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Medium Bus and Ring Comparison

Characteristic Bus Ring

Scalability ? ?

Contention

Resilience

Topology

• Ring vs. bus

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-76 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Medium Bus and Ring Comparison

Characteristic Bus Ring

Scalability poor moderate

Contention ? ?

Resilience

Topology

• Ring vs. bus

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-77 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Medium Bus and Ring Comparison

Characteristic Bus Ring

Scalability poor moderate

Contention collisions contention

Resilience ? ?

Topology

• Ring vs. bus

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-78 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Medium Bus and Ring Comparison

Characteristic Bus Ring

Scalability poor moderate

Contention collisions contention

Resilience poor single failure

Topology ? ?

• Ring vs. bus

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-79 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Medium Bus and Ring Comparison

Characteristic Bus Ring

Scalability poor moderate

Contention collisions contention

Resilience poor single failure

Topology linear ring

• Ring vs. bus

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-80 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Medium Bus and Ring Comparison

Characteristic Bus Ring

Scalability poor moderate

Contention collisions contention

Resilience poor single failure

Topology linear ring

• Ring vs. bus LAN debate – Ethernet vs. token ring: famous networking holy wars – token ring advocates touted superior capacity – Ethernet advocates claimed that differences not significant

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-81 ITTC © James P.G. Sterbenz Link and LAN Technologies Point-to-Point Dedicated Links

H payload T H payload T H payload T

• Point-to-point dedicated links – sequence of framed packets along a link

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-82 ITTC © James P.G. Sterbenz Link and LAN Technologies Point-to-Point Dedicated Links

H payload T H payload T H payload T

• Point-to-point dedicated links – sequence of framed packets along a link • No layer 2 multiplexing – higher layers are multiplexed onto a single link – packets belonging to different E2E flows

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-83 ITTC © James P.G. Sterbenz Link and LAN Technologies Point-to-Point Dedicated Links

H payload T H payload T H payload T

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-84 ITTC © James P.G. Sterbenz Link and LAN Topologies Switched Point-to-Point Links

• Point-to-point links between switches – space division mesh 2

2 2

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-85 ITTC © James P.G. Sterbenz Link and LAN Topologies Switched Point-to-Point Links

• Point-to-point links between switches – space division mesh Network scalability? 2

2 2

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-86 ITTC © James P.G. Sterbenz Link and LAN Topologies Switched Point-to-Point Links

• Point-to-point links between switches – space division mesh • Scalable: 2 – add links and expand switches

2 2

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-87 ITTC © James P.G. Sterbenz Link and LAN Topologies Switched Point-to-Point Links

• Point-to-point links between switches – space division mesh • Scalable: 2 – add links and expand switches

– add switches 2 2

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-88 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared Medium Bus and Ring Comparison

Characteristic Bus Ring

Scalability poor moderate

Contention collisions contention

Resilience poor single failure

Topology linear ring

• Ring vs. bus LAN debate – Ethernet vs. token ring: famous networking holy wars – token ring advocates touted superior capacity – Ethernet advocates claimed that differences not significant

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-89 ITTC © James P.G. Sterbenz Link and LAN Topologies Shared and Switched Link

Characteristic Bus Ring Switched excellent Scalability poor moderate if nonblocking Contention collisions contention very low excellent Resilience poor single failure if biconnected Topology linear ring mesh • Ring vs. bus LAN debate – became irrelevant – Ethernet won, but then became switched

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-90 ITTC © James P.G. Sterbenz Link Layer and LANs LL.3.2: Point-to-Point Protocol LL.1 Link layer functions and services LL.2 Framing and delineation LL.3 LAN types and topologies LL.3.1 LAN topologies LL.3.2 Point-to-point protocol LL.3.3 802 and Ethernet LL.3.4 Ring LANs LL.4 Multiplexing and switching LL.5 Per-hop error and flow control LL.6 Link layer components LL.7 VLANs, L2 tunnels, and ARP LL.8 Residential broadband

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-91 ITTC © James P.G. Sterbenz Point-to-Point Links PPP Overview

• PPP: point-to-point protocol [RFC 1557] – link protocol for modem access • Widely used for dialup Internet access – far more common than SLIP (serial line IP) [RFC 1055] • Diminishing importance with broadband alternatives – HFC (CATV) – DSL (PSTN) – 802.11 lecture MW – 802.16 and WiMAX lecture MW Details for reference in online notes

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-92 ITTC © James P.G. Sterbenz Link Layer and LANs LL.3.3: 802 and Ethernet LL.1 Link layer functions and services LL.2 Framing and delineation LL.3 LAN types and topologies LL.3.1 LAN topologies LL.3.2 Point-to-point protocol LL.3.3 802 and Ethernet LL.3.4 Ring LANs LL.4 Multiplexing and switching LL.5 Per-hop error and flow control LL.6 Link layer components LL.7 VLANs, L2 tunnels, and ARP LL.8 Residential broadband

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-98 ITTC © James P.G. Sterbenz LAN Protocols IEEE 802

• IEEE 802 LAN/MAN standards [IEEE 802.1] www.ieee802.org • Definition of LAN/MAN protocols for L1–L2 – does not align perfectly with conventional layers • L2 defined by LLC (logical link control) and MAC header

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-99 ITTC © James P.G. Sterbenz LAN Protocols IEEE 802

• IEEE 802 LAN/MAN standards [IEEE 802.1] www.ieee802.org • Definition of LAN/MAN protocols for L1–L2 – 802.2 : logical link control – 802.n : MAC and physical media dependent LLC sublayer link 802.2 logical link control layer MAC sublayer MAC medium access control layer 802.n MI sublayer media independent physical PMD sublayer layer PMD PMD PMD 1 2 k physical media dependent

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-100 ITTC © James P.G. Sterbenz Internet Protocols Important IEEE 802 Protocols Common name Standard Scope Technology architecture IEEE 802.1 LAN/MAN media independent LLC IEEE 802.2 LAN/MAN media independent Ethernet IEEE 802.3 LAN/MAN wire, fiber Token ring IEEE 802.5 LAN wire WLAN IEEE 802.11 LAN RF, (IR) WPAN IEEE 802.15 PAN RF WMAN IEEE 802.16 MAN RF • Many other 802.n protocols – some once important, but obsolete, e.g. 802.5 – some never important, e.g. 802.6 DQDB, 802.20 MBWA – some lost to competing standards, e.g. 802.14, 802.16 – the jury is still out on others, e.g. 802.17, 802.22

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-101 ITTC © James P.G. Sterbenz Shared Medium Links Ethernet

10101010 10101010 10101010 10101010 • Early LAN technology (1973) preamble + SFD 10101010 10101010 10101010 10101011 – DIX: Digital, Intel, Xerox MAC header destination address • IPv4 over DIX [RFC 0894] 22B – IEEE 802.3 using 802.2 LLC source address • IPv4 over 802.3 [RFC 1042] length/type LLC/SNAP LLC – note: DIX and 802.3 similar subheader 8B SNAP • but not identical

payload payload

trailer 4B FCS

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-102 ITTC © James P.G. Sterbenz Shared Medium Links Ethernet

10101010 10101010 10101010 10101010 • Early LAN technology (1973) preamble + SFD 10101010 10101010 10101010 10101011 – DIX: Digital, Intel, Xerox MAC header destination address – IEEE 802.3 using 802.2 LLC 22B • Initially shared coaxial medium source address length/type – CSMA/CD MAC lecture MW LLC/SNAP LLC subheader – performs well in light load < 50% 8B SNAP – performs poorly in heavy load > 80%

payload payload

trailer 4B FCS

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-103 ITTC © James P.G. Sterbenz Shared Medium Links Ethernet

10101010 10101010 10101010 10101010 • Early LAN technology (1973) preamble + SFD 10101010 10101010 10101010 10101011 – DIX: Digital, Intel, Xerox MAC header destination address – IEEE 802.3 using 802.2 LLC 22B • Initially shared coaxial medium source address length/type – CSMA/CD MAC lecture MW LLC/SNAP LLC subheader – performs well in light load < 50% 8B SNAP – performs poorly in heavy load > 80%

• Dominant 1980s LAN payload payload – token ring only significant competitor

– evolved 10 to 100 Mb/s to … trailer 4B FCS

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-104 ITTC © James P.G. Sterbenz Shared Medium Links Ethernet 10101010 10101010 10101010preamble 10101010 10101010+SFD 10101010 • Early LAN technology (1973) 10101010 10101011 MAC – DIX: Digital, Intel, Xerox destination header address 22B – IEEE 802.3 EECS 780 source address • Shared wire medium length / type LLC LLC/MAC – CSMA/CD MAC subheader SNAP 8B – performs well in light load < 50% – performs poorly in heavy load > 80% frame body • Dominant 1980s LAN 38 – 1492 B – token ring only significant competitor pad trailer – evolved 10 to 100 Mb/s to … FCS 4B

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-105 ITTC © James P.G. Sterbenz Shared Medium Links Ethernet

• Scaling to high data rates – 10 Mb/s  100 Mb/s  1 Gb/s  10 Gb/s  40/100 Gb/s –  802.3u  802.3ab  802.3an  802.3ba Cu –  802.3z  802.3ae  802.3ba fib. • fiber standards and deployment first for 1 and 10 Gb/s • consistent with aggregation for enterprise and metro use • More sophisticated coding – DSSS  OFDM  STBC • MAC and link framing enhancements – slot time increase, frame extension, and bursting for 1 Gb/s – elimination of CSMA/CD for 10 Gb/s: full duplex only

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-106 ITTC © James P.G. Sterbenz Shared Medium Links Ethernet 10101010 10101010 10101010preamble 10101010 10101010+SFD 10101010 • …Evolved to 1 Gb/s 10101010 10101011 MAC destination header Problems? address 22B source address length / type LLC LLC/MAC subheader SNAP 8B

frame body 38 – 1492 B

pad trailer FCS 4B

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-107 ITTC © James P.G. Sterbenz Shared Medium Links Ethernet 10101010 10101010 10101010preamble 10101010 10101010+SFD 10101010 • …Evolved to 1 Gb/s 10101010 10101011 MAC destination header • Problems: Ethernet design address 22B – not inherently scalable source address • 100 Mb/s: several-year standards battle length / type LLC LLC/MAC – designed for shared medium subheader SNAP 8B • thickwire and thinwire with taps • later hubs with half-duplex pt-to-pt links • CSMA/CD time constants and overhead frame body 38 – 1492 B

pad trailer FCS 4B

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-108 ITTC © James P.G. Sterbenz Shared Medium Links Ethernet 10101010 10101010 10101010preamble 10101010 10101010+SFD 10101010 • …Evolved to 1 Gb/s 10101010 10101011 MAC destination header • Problems: Ethernet design address 22B – not inherently scalable source address • 100 Mb/s: several-year standards battle length / type LLC LLC/MAC – designed for shared medium subheader SNAP 8B • thickwire and thinwire with taps • later hubs with half-duplex pt-to-pt links • CSMA/CD time constants and overhead frame body 38 – 1492 B • 802.3z decision pad – retain CSMA/CD trailer FCS – modify MAC for higher rates 4B

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-109 ITTC © James P.G. Sterbenz Shared Medium Links Ethernet 10101010 10101010 10101010preamble 10101010 10101010+SFD 10101010 • …Evolved to 1 Gb/s 10101010 10101011 MAC destination header • Modifications address 22B – still supporting CSMA/CD source address • slot time increased  8 length / type LLC LLC/MAC – 512b  512B subheader • extension trailer need for longer slot SNAP 8B problem?

frame body 38 – 1492 B

pad trailer FCS 4B ext extension 0-448B 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-110 ITTC © James P.G. Sterbenz Shared Medium Links Ethernet

frame1 • …Evolved to 1 Gb/s

• Modifications ext – still supporting CSMA/CD • slot time increased  8 frame2 – 512b  512B • extension trailer need for longer slot – larger minimum frame size ext – but very inefficient for small frames solution? frame3

ext

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-111 ITTC © James P.G. Sterbenz Shared Medium Links Ethernet

frame1 frame1 • …Evolved to 1 Gb/s

frame2 • Modifications ext

– still supporting CSMA/CD frame3 • slot time increased  8 frame2 – 512b  512B • extension trailer need for longer slot – larger minimum frame size ext – but very inefficient small frames • frame bursting frame3 – burst of frames in a single slot – significantly increased efficiency ext

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-112 ITTC © James P.G. Sterbenz Shared Medium Links Ethernet

• …Evolved to 10 Gb/s Problems?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-113 ITTC © James P.G. Sterbenz Shared Medium Links Ethernet

• …Evolved to 10 Gb/s • Problems? – CSMA overheads and time constants much bigger problem • further scaling of slot time and extension headers not practical Solution?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-114 ITTC © James P.G. Sterbenz Shared  Dedicated Links Ethernet

• …Evolved to 10 Gb/s • Solution – half-duplex shared medium probably never used at 1 Gb/s – 802.ae decided to completely eliminate CSMA/CD – only point-to-point full-duplex dual cables supported

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-115 ITTC © James P.G. Sterbenz Dedicated Links Ethernet

• …Evolved to 10 Gb/s • Modification – point-to-point only • initially fiber only (802.3ae) later copper (802.3ak / 802.3an) – full duplex only (separate xmit and recv cables required ) • no CSMA/CD or related slot and distance constraints • no extension trailer needed • frame bursting not needed nor supported – compatible with SONET coding and physical transmission • pacing for 10Gb/s (LAN)  9.95 Gb/s (WAN) • § in table

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-116 ITTC © James P.G. Sterbenz Dedicated Links Ethernet

• …Evolved to 40 Gb/s and 100 Gb/s – 802.3 HSSG (high speed study group) – 802.3ba: June 2010 standard issued • Objectives – 40 Gb/s for SONET OC-192 and OTN ODU3 compatibility • will probably see deployment before 10 Gb/s – 100 Gb/s for Ethernet order-of-magnitude trajectory – single- and multimode fiber and short-reach copper • 10-km multimode distance for MANs – full duplex only – 802.3 backward compatible framing

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-117 ITTC © James P.G. Sterbenz Dedicated Links Ethernet

• …Evolving toward 1Tb/s • IEEE 802.3bs-2017 – decision was made to initially target 400 Gb/s • interim 4 step before 10 level likely to persist – 200 Gb/s was added – 1 Tb/s will be considered later • probably ~2020

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-118 ITTC © James P.G. Sterbenz Dedicated Links Ethernet

• Ethernet also evolving from LAN to MAN technology – IEEE 802.3 retains control of MAC and PHY standards • ITU-T Ethernet transport networks – ITU-T G.8010 series specifications – specification of Ethernet in transport networks – relationship to SONET/OTN transport networks • Metro Ethernet service deployments – MEF: Metro Ethernet Forum • www.metroethernetforum.org • implementation agreements and specifications

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-119 ITTC © James P.G. Sterbenz Point-to-Point Links Ethernet ≤ 1 Gb/s Link Type Rate | Year Media Full Coding Range Topology Ovhd Payload 2.94 Mb/s PARC coax H Manchester shared 10 B  4K B 1972-1976

10Base5 10 Mb/s thick coax H 500 –2500* m shared 10Base2 DIX 1980 thin coax H Manchester 185 – 925* m shared 38 B 38–1492 B 10BaseT 802.3 1985 2 pair UTP-3 H | F *w/repeaters 100 m hub 100BaseTX 2 pair UTP-5 H | F 4B/5B 100 m 100 Mb/s star: 100BaseT2 2 pair UTP-3 H | F PAM5x5 100 m 802.3u hub/ 38 B 38–1492 B 100BaseT4 4 pair UTP-3 H 8B/6T †full duplex 100 m switch 100BaseFX 1995 mm fiber H | F 4B/5B 412 – 2000† m

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-120 ITTC © James P.G. Sterbenz Point-to-Point Links Ethernet ≥ 1 Gb/s Link Type Rate | Year Media Full Coding Range Topology Ovhd Payload

1000BaseT 1 Gb/s 4 pair UTP-6 H | F 4B/5B|PAM5 100 m 38 B 1000BaseCX twinax STP H | F 8B/10B FCS 25 m switch + 802.3z 38–1492 B 1000BaseLX  sber H | F 8B/10B FCS 316 – 5000 m pt-2-pt 448 1000BaseSX 1998  mm fiber H | F 8B/10B FCS 275 – 550 m /burst 10GBaseX 10 Gb/s parallel fiber F 8B10B FCS 65 m – 10GBaseR 802.3ae fiber F 64B/66B 40 km switch 38 B 38–1492 B 10GBaseW 2002 fiber F 64B/66B § pt-2-pt 10GBaseT 802.3an 4 pair UTP-7 F 100 m

40GBaseKR Cu backplane 1 m 40GBaseCR4 40 Gb/s Cu 7 m 100GB.CR10 100 Gb/s Cu 7 m 40GBaseSR4 100 m mm par. fiber switch 100GB.SR10 mm par. fiber F 100 m 38 B 38–1492 B 802.3ba pt-2-pt 40GBaseLR4 sm par. fiber 10 km 2011 100GB.LR4 sm par. fiber 10 km 100BaseER4 sm par. fiber 40 km 100BaseFX 802.3bg sm serial fiber 2 km 200 Gb/s 200GBase sm par. fiber switch 400 Gb/s F 400GBase sm par. fiber pt-2-pt 802.3bs 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-121 ITTC © James P.G. Sterbenz Link Layer and LANs LL.3.4: Ring LANs LL.1 Link layer functions and services LL.2 Framing and delineation LL.3 LAN types and topologies LL.3.1 LAN topologies LL.3.2 Point-to-point protocol LL.3.3 802 and Ethernet LL.3.4 Ring LANs LL.4 Multiplexing and switching LL.5 Per-hop error and flow control LL.6 Link layer components LL.7 VLANs, L2 tunnels, and ARP LL.8 Residential broadband

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-122 ITTC © James P.G. Sterbenz Ring Links Token Ring

• Early LAN technology (1972) – DCS and Cambridge rings provided foundation

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-123 ITTC © James P.G. Sterbenz Ring Links Token Ring

• Early LAN technology (1972) – DCS and Cambridge rings provided foundation – IBM LAN technology; standardised as IEEE 802.5

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-124 ITTC © James P.G. Sterbenz Ring Links Token Ring

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-125 ITTC © James P.G. Sterbenz Ring Links Token Ring

• Early LAN technology (1972) – DCS and Cambridge rings provided foundation – IBM LAN technology; standardised as IEEE 802.5 • Shared wire medium – token passing ring – performs well to heavy load > 80% • 16 Mb/s TR significantly outperformed 10Base5 • Significant 1980s LAN – but Ethernet had greater market share – evolved to 16 Mb/s (1988) – evolution to hubs required double STP to end systems 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-126 ITTC © James P.G. Sterbenz Ring Links Token Ring

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-127 ITTC © James P.G. Sterbenz Ring Links Token Ring

• Logical successor: FDDI – fiber distributed digital interface – only 100 Mb/s LAN technology of time • ANSI X3.139-1987 (MAC), X3.148.1988 (PHY) • 100BaseT vs. 100BaseVG wars hadn’t even begun • OC-3 ATM LANs were just appearing (and expensive) • Dual fiber token-passing ring – contra-rotating rings with automatic protection from cuts • single ring option with no protection – later adapted for STP and UTP-5: CDDI (copper DDI)

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-128 ITTC © James P.G. Sterbenz Ring Links Token Ring

• FDDI-II proposal for integrated services – slotted ring adds circuit service to basic FDDI packet service

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-129 ITTC © James P.G. Sterbenz Ring Links Token Ring

• FDDI-II proposal for integrated services – slotted ring adds circuit service to basic FDDI packet service • But 100BaseT killed FDDI (and ATM to the desktop)

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-130 ITTC © James P.G. Sterbenz Ring Links Token Ring

• FDDI-II proposal for integrated services – slotted ring adds circuit service to basic FDDI packet service • But 100BaseT killed FDDI (and ATM to the desktop) • High-speed token ring (HSTR) proposals DOA* – 100 Mb/s 802.5t 1998 draft (a few products) – 1Gb/s 802.5v working group

*dead on arrival 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-131 ITTC © James P.G. Sterbenz Ring Links Ring LANS

Link type Rate Media Coding Access Link Len Circum Topology Ovhd Payload

DCS 1972 2.5 Mb/s token ring

Cambridge 10 Mb/s 2 x TP slot ring 22 b 16 b 1979

Token Ring 0 – 4529 B 4 Mb/s 1981 IBM STP  Manch. token* 250 m† ring 21 B 0 – 18279 16 Mb/s 1985 802.5 B HSTR 802.5t 100 Mb/s {US}TP MLT-3 0 – 18279 1998 802.5t 100 Mb/s fiber 4B/5B DTR – star 21 B B 802.5v 1 Gb/s fiber 8B/10B FCS

FDDI 1988 100 Mb/s fiber 4B/5B token 2 km 200 km 2ring 28 B 0 – 4522 B

STP CDDI 100 Mb/s MLT-3 token 100 m 10 km 2ring 28 B 0 – 4522 B UTP-5

*DTR (dedicated token ring) for switched mode added in 1998 to 4 Mb/s and 16 Mb/s 802.5 some switch/NICs supported full duplex at 32 Mb/s †72 m for UTP

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-132 ITTC © James P.G. Sterbenz Ring Links SONET Rings

✄

• SONET links in ring configuration – dual rings provide fault tolerance – APS: automatic protection switching • restoration after fiber cut (aka backhoe fade) more on SONET later 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-133 ITTC © James P.G. Sterbenz Link Layer and LANs LL.4 Multiplexing and Switching

LL.1 Link layer functions and services LL.2 Framing and delineation LL.3 LAN types and topologies LL.4 Multiplexing and switching LL.4.1 Link-layer multiplexing LL.4.2 Link-layer switching LL.4.3 TDM transport networks: PDH, SDH/SONET, OTN LL.5 Per-hop error and flow control LL.6 Link layer components LL.7 VLANs, L2 tunnels, and ARP LL.8 Residential broadband 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-134 ITTC © James P.G. Sterbenz Link-Layer Multiplexing & Switching Overview

• Link-layer multiplexing – multiplexing multiple lower rate links  higher rate link – demultiplexing to lower rate links  higher rate link • Link-layer switching (L2 switching) – switching in space or time at the link layer – transparent to layer 3

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-135 ITTC © James P.G. Sterbenz Multiplexing and Switching LL.4.1 Link-Layer Multiplexing

LL.1 Link layer functions and services LL.2 Framing and delineation LL.3 LAN types and topologies LL.4 Multiplexing and switching LL.4.1 Link-layer multiplexing LL.4.2 Link-layer switching LL.4.3 TDM transport networks: PDH, SDH/SONET, OTN LL.5 Per-hop error and flow control LL.6 Link layer components LL.7 VLANs, L2 tunnels, and ARP LL.8 Residential broadband 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-136 ITTC © James P.G. Sterbenz Link-Layer Multiplexing Overview

• Link-layer multiplexing • PSTN evolution – synchronous multiplexing for traffic aggregation • Broadband Internet access – PONs (passive optical networks)

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-137 ITTC © James P.G. Sterbenz Link-Layer Multiplexing Scenarios

• PSTN and PON multiplexing – multiplexing for traffic aggregation

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-138 ITTC © James P.G. Sterbenz Link-Layer Multiplexing Scenarios

• PSTN and PON multiplexing – multiplexing for traffic aggregation • PSTN access to SONET rings – ADM: add-drop multiplexor – insert into ring – extract from ring

A D M

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-139 ITTC © James P.G. Sterbenz Link-Layer Multiplexing Multiplexing Schemes

• TDM: time division multiplexing – synchronous (e.g. PDH, SDH/SONET) – asynchronous or statistical (e.g. ATM) • FDM: frequency division multiplexing (typically RF) – WDM: wavelength division multiplexing (light)

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-140 ITTC © James P.G. Sterbenz Link-Layer Multiplexing Synchronous TDM Links

H1 H2 2 H3 T2

• Synchronous time-division multiplexing (STDM) – n  R/n rate signals combined – fixed-size slots round-robin: 0, 1,… n –1, 0, 1,… n –1, 0, … Advantages? Disadvantages?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-141 ITTC © James P.G. Sterbenz Link-Layer Multiplexing Synchronous TDM Links

H1 H2 2 H3 T2

• Synchronous time-division multiplexing (STDM) – n  R/n rate signals combined – fixed-size slots round-robin: 0, 1,… n –1, 0, 1,… n –1, 0, … + Simple multiplexing scheme – Difficult to efficiently use link – time slot allocation problem – wasted/oversubscribed slots

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-142 ITTC © James P.G. Sterbenz Link-Layer Multiplexing Synchronous TDM Links

H1 H2 2 H3 T2

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-143 ITTC © James P.G. Sterbenz Link-Layer Multiplexing Asynchronous TDM Links

• Asynchronous time division multiplexing (ATDM) – aka statistical multiplexing – variable size time slots Advantages? Disadvantages?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-144 ITTC © James P.G. Sterbenz Link-Layer Multiplexing Asynchronous TDM Links

• Asynchronous time division multiplexing (ATDM) – aka statistical multiplexing – variable size time slots – May be more complex – unless FIFO service discipline which is unfair + Better link efficiency + each sender uses proportion of link needed

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-145 ITTC © James P.G. Sterbenz Link-Layer Multiplexing Multiplexing vs. Multiple Access

• Multiplexing vs. multiple access • Link multiplexing – single transmitter – dedicated point-to-point link

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-146 ITTC © James P.G. Sterbenz Link-Layer Multiplexing Multiplexing vs. Multiple Access

• Multiplexing vs. multiple access • Link multiplexing – single transmitter – dedicated point-to-point link • Multiple access – multiple transmitters – shared medium – essentially physical layer multiplexing – MAC algorithm needed to arbitrate lecture MW

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-147 ITTC © James P.G. Sterbenz Link-Layer Multiplexing Higher Layer Multiplexing

• Higher layers multiplex into lower layers L7⇇⇒L4 multiple applications use E2E transport flow (port) L4⇇⇒L3 multiple transport flows use network paths (prot id) L3⇇⇒L2 multiple network path use links

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-148 ITTC © James P.G. Sterbenz Link-Layer Multiplexing Link Layer Multiplexing

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-149 ITTC © James P.G. Sterbenz Link-Layer Multiplexing Link Layer Multiplexing

• Higher layers multiplex into lower layers L7⇇⇒L4 multiple applications use end-to-end transport flow L4⇇⇒L3 multiple transport flows use network paths L3⇇⇒L2 multiple network path use links • Link layer multiplexing: L2⇇⇒L2 – some link layers also provide native multiplexing • mux/demux without network layer switching • Recall historical precedence – PSTN has minimal layer 3 switching – time division multiplexing from premises–CO–long-distance – digital hierarchy: T-carrier and SONET/SDH 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-150 ITTC © James P.G. Sterbenz Link-Layer Multiplexing Link Layer Simple Multiplexing

• Link layer multiplexing • Layer 2 combine/split

 OC-n

– of lower rate signals  OC-m • Examples  STS-n – SONET/T-carrier • OC-m ⇇⇒ OC-n , m < n

STS-n 

• T3 ⇇⇒ OC-3  – PONs (passive optical nets)  OC-n • residential broadband more later

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-151 ITTC © James P.G. Sterbenz Multiplexing and Switching LL.4.2 Link-Layer Switching

LL.1 Link layer functions and services LL.2 Framing and delineation LL.3 LAN types and topologies LL.4 Multiplexing and switching LL.4.1 Link-layer multiplexing LL.4.2 Link-layer switching LL.4.3 TDM transport networks: PDH, SDH/SONET, OTN LL.5 Per-hop error and flow control LL.6 Link layer components LL.7 VLANs, L2 tunnels, and ARP LL.8 Residential broadband 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-152 ITTC © James P.G. Sterbenz Link-Layer Switching Overview

• Traditionally switching is a network layer 3 function – but…

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-153 ITTC © James P.G. Sterbenz Link-Layer Switching Overview

• Traditionally switching is a network layer 3 function – but link layer switching and multiplexing is done by layer 2 Why do layer 2 switching?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-154 ITTC © James P.G. Sterbenz Link-Layer Switching Overview

• Link layer switching – switching done by L2 components – supported by link protocol • e.g. SONET • e.g. 802.1D bridging for Ethernet • Evolved with PSTN and Internet

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-155 ITTC © James P.G. Sterbenz Link-Layer Switching PSTN SONET Rings

• PSTN synchronous multiplexing – multiplexing for traffic aggregation • PSTN SONET switching – XC: inter-ring cross-connect – ADM: add-drop multiplexors

A XC A D D M M

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-156 ITTC © James P.G. Sterbenz Link-Layer Switching Internet LANs

• Internet LAN switching – shared-medium segments

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-157 ITTC © James P.G. Sterbenz Link-Layer Switching Internet LANs

• Internet LAN switching – shared-medium segments replaced by Ethernet switches • more on this evolution later – no awareness, involvement, or management of IP

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-158 ITTC © James P.G. Sterbenz Link-Layer Switching Evolution

• Link layer switching – native layer 2 protocol and device switching • Evolved with PSTN and Internet – migration from shared medium to switched LAN • e.g. Ethernet – add switching functionality to multiplexing structure • e.g. SONET cross-connects Advantages?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-159 ITTC © James P.G. Sterbenz Link-Layer Switching Advantages

• Potential advantages – simpler, cheaper switches than L3 (IP switch/router) • less important with fast IP lookup hardware – no need to manage IP in small networks • less important with DHCP and router auto-configuration – faster restoration on link failure • IP routing convergence much slower than ring restoration Disadvantages?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-160 ITTC © James P.G. Sterbenz Link-Layer Switching Disadvantages

• Potential advantages – simpler, cheaper switches than L3 (IP switch/router) – no need to manage IP in small networks – faster restoration on link failure • Disadvantages – duplication of L3 functions in L2 – where should functionality really go? • if IP converged rapidly, SONET APS might not be necessary

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-161 ITTC © James P.G. Sterbenz Link-Layer Switching Space-Division Switching i0 o0 example: switch i1 o1 inputs  outputs i o 2 2 i0  o2 i o 3 3 i1  o0

i2  o1 i o n–1 n-1 i3  o3

• Space division switches the links that frames traverse – multiple inputs links interconnected to multiple output links – switch fabric responsible for input  output interconnection • Variety of switching technologies – crossbar, shared memory, MIN, etc. Lecture NL

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-162 ITTC © James P.G. Sterbenz Link-Layer Switching Space-Division Switching

• Space-division switching sufficient for TDM-based link layers such as SONET?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-163 ITTC © James P.G. Sterbenz Link-Layer Switching Time-Division Switching

• Space-division switching – solves only part of the problems in TDM-based link layers • Time-division switching: – TDM networks also need to be switched in time – switching time slots for synchronous TDM

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-164 ITTC © James P.G. Sterbenz Link-Layer Switching Time Division Switching: TSI

i0 example: i1 i2 swap slots 2  3 i2 o3 i2  o3 i3 i3  o2

cn–1 • TSI: time slot interchange – switching time slots for synchronous TDM

todo: slot diagram before and after swap

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-165 ITTC © James P.G. Sterbenz Link-Layer Switching Time Division Switching: TSI

i0 example: i1 i2 swap slots 2  3 i2 o3 i2  o3 i3 i3  o2

cn–1 • TSI: time slot interchange – switching time slots for synchronous TDM • Reordered in switch memory

– received frames written into memory sequentially i0, i1,… in–1

– frames read in different order for transmission oj… 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-166 ITTC © James P.G. Sterbenz Link-Layer Switching Space- and Time-Division Switching

How to switch in both space and time?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-167 ITTC © James P.G. Sterbenz Link-Layer Switching Space- and Time-Division Switching

i0 o0

i1 o1

i2 o2

i3 o3

in–1 on-1

• Combination space/time switching – needed for interconnection of multiple TDM links • e.g. SONET cross-connect at intersection of two rings

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-168 ITTC © James P.G. Sterbenz Link-Layer Switching Space- and Time-Division Switching

i0 o0

i1 o1

i2 o2

i3 o3

in–1 on-1

• Combination space/time switching – needed for interconnection of multiple TDM links • e.g. SONET cross-connect at intersection of two rings • Multiple combinations possible, e.g. – T-S-T: time-space-time (shown): TSIs – space switch – TSIs – S-T-S: space-time-space : space – TSIs – space

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-169 ITTC © James P.G. Sterbenz Multiplexing and Switching LL.4.3 TDM Transport Networks

LL.1 Link layer functions and services LL.2 Framing and delineation LL.3 LAN types and topologies LL.4 Multiplexing and switching LL.4.1 Link-layer multiplexing LL.4.2 Link-layer switching LL.4.3 TDM transport networks: PDH, SDH/SONET, OTN LL.5 Per-hop error and flow control LL.6 Link layer components LL.7 VLANs, L2 tunnels, and ARP LL.8 Residential broadband 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-170 ITTC © James P.G. Sterbenz TDM Transport Networks Overview

• Transport networks – link layer (L2) infrastructure in the PSTN context – not to be confused with end-to-end (L4) transport • used in Internet protocol terminology • Transport network evolution – PDH: digital hierarchy, generally over wires (e.g. T-carriers) – SDH/SONET: digital hierarchy over optical fiber – OTN: optical transport network with WDM switches

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-171 ITTC © James P.G. Sterbenz TDM Transport Networks ITU Hierarchy

CBR IP control planes CBRk GFP AAL PNNI PDH ATM ETH GFP CBRk SDH/SONET GMPLS proprietary DWDM OTN ASON

PDH: pleisiochronous digital hierarchy SDH: synchronous digital hierarchy ATM/B-ISDN Ethernet PNNI GMPLS OTN: optical transport network ASON 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-172 ITTC © James P.G. Sterbenz TDM Transport Networks ITU Hierarchy

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-173 ITTC © James P.G. Sterbenz TDM Transport Networks ITU Hierarchy

• Data and management planes – OTN: optical transport network WDM links – SDH: synchronous digital hierarchy (SONET) links – Ethernet: long-haul point-to-point Ethernet links – ATM/B-ISDN: asynchronous transfer mode / broadband ISDN • Control plane (layer 2 switching) – ASON: automatically switched optical network • GMPLS: generalised multiprotocol label switching – RSVP-TE, CR-LDP (IETF deprecated) • PNNI: (ATM) private NNI signalling (layer 3 switching)

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-174 ITTC © James P.G. Sterbenz TDM Transport Networks LL.4.3.1 PSTN Digital Hierarchy

LL.1 Link layer functions and services LL.2 Framing and delineation LL.3 LAN types and topologies LL.4 Multiplexing and switching LL.4.1 Link-layer multiplexing LL.4.2 Link-layer switching LL.4.3 TDM transport networks: PDH, SDH/SONET, OTN LL.5 Per-hop error and flow control LL.6 Link layer components LL.7 VLANs, L2 tunnels, and ARP LL.8 Residential broadband 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-175 ITTC © James P.G. Sterbenz TDM Transport Networks PSTN Digital Hierarchy

• PSTN digital hierarchy – digital multiplexing structure to replace analog circuits – hierarchy of increasing rates for aggregation in network core – multiplexors and demultiplexors independent of switching • Plesiochronous – from the greek: πλησίος = nearly + χρόνος = time – digital signals are nearly synchronous – bit slips tolerated with bit-stuffing in frame structure – signals are bit streams – framing not visible to next-higher level – no relative synchronisation among signals below given level

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-176 ITTC © James P.G. Sterbenz PSTN Digital Hierarchy Relationship to Protocol Stack

CBR IP control planes CBRk GFP AAL PNNI PDH ATM ETH GFP CBRk SDH/SONET GMPLS proprietary DWDM OTN ASON

PDH: pleisiochronous digital hierarchy SDH: synchronous digital hierarchy ATM/B-ISDN Ethernet PNNI GMPLS OTN: optical transport network ASON 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-177 ITTC © James P.G. Sterbenz PSTN Digital Hierarchy Standards

• PSTN WAN/MAN near-synchronous electrical links – PDH: plesiochronous digital hierarchy (ITU-T) • E-carriers – DH: digital hierarchy (Bellcore, ANSI) • T-carriers (US) • J-carriers (Japan) • Standards suite: – format specification G.702, G.704, G.706, T1.107 – equipment G.705 – physical interfaces G.703, T1.102, T1.403, T1.404

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-178 ITTC © James P.G. Sterbenz PSTN Digital Hierarchy US Multiplexing Structure DS0 DS0

DS1

 24:1 DS2 DS2 1:24   DS3 DS3 4:1 1:4   DS4 7:1 1:7  3:1 1:3 T1 T1 T3 T3 • Digital signals (DS) on T-carriers (others for DS-4) – DS0: digital voice channel or 56 kb/s leased data line – DS1: 24  DS0 or 1.5 Mb/s T-1 data service – DS2: 4  DS1 – DS3: 7  DS2 or 45 Mb/s T-3 data service – DS4: 3  DS3 (historical – now replaced by SONET) 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-179 ITTC © James P.G. Sterbenz US Multiplexing Structure Frame Structure

• Framing – bit patterns distributed throughout frames • Alarms – indicate loss of signal or framing to other end of link – used by networking monitoring and management • Error detection – parity or CRC • Signalling and data channels – robbed from DS0 or distributed throughout frame Details for reference in online notes

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-180 ITTC © James P.G. Sterbenz PSTN Digital Hierarchy PDH Carrier Characteristics

Link type Frame Size Frame Media Coding Channels Rate Payload Rate Carrier Channel (super/multi) Overhd

DS-0 1 64 kb/s 8 b 56 kb/s

T1 DS-1 24 1.544 Mb/s 2316|4362 b 12|24 b 1.536 Mb/s J1 twisted pair bipolar 24 1.544 Mb/s E1 32 2.048 Mb/s T2 DS-2 96 6.312 Mb/s 1176 b 24 b 6.183 Mb/s twisted pair B6ZS E2 8.448 Mb/s T3 twisted pair 672 44.736 Mb/s 4760 b 56 b 44.210 Mb/s DS-3 FT3 fiber 672 44.736 Mb/s B3ZS J3 twisted pair 480 32.064 Mb/s E3 twisted pair 512 34.368 Mb/s WT4 waveguide T4M DS-4 coax 4032 274.176 Mb/s DR 18 RF

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-200 ITTC © James P.G. Sterbenz PSTN Digital Hierarchy Summary and Comparison

PDH SDH/SONET OTN DW OTN OTM

Transmission electronic

Mux & switching electronic

Multiplex domain TDM

Synchronisation plesiochronous

Levels* 4

Transparency opaque

Rates‡ 1.5 – 45 Mb/s

* as currently defined in standards, not including sub- and intermediate levels ‡ approximate as currently defined in standards, not including STS-1 and sub-rates (DS0 and VTs) 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-201 ITTC © James P.G. Sterbenz TDM Transport Networks LL.4.3.2 SDH and SONET

LL.1 Link layer functions and services LL.2 Framing and delineation LL.3 LAN types and topologies LL.4 Multiplexing and switching LL.4.1 Link-layer multiplexing LL.4.2 Link-layer switching LL.4.3 TDM transport networks: PDH, SDH/SONET, OTN LL.5 Per-hop error and flow control LL.6 Link layer components LL.7 VLANs, L2 tunnels, and ARP LL.8 Residential broadband 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-202 ITTC © James P.G. Sterbenz TDM Transport Networks Generic Framing Procedure (GFP)

• Framing for synchronous transport networks problem?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-203 ITTC © James P.G. Sterbenz TDM Transport Networks Generic Framing Procedure (GFP)

• Framing for synchronous transport networks – problem: synchronous networks designed for voice – CBR (constant bit rate) stream in TDM – IP packets need additional framing

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-204 ITTC © James P.G. Sterbenz TDM Transport Networks Generic Framing Procedure (GFP)

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-205 ITTC © James P.G. Sterbenz TDM Transport Networks Generic Framing Procedure (GFP)

• Framing for synchronous transport networks – problem: synchronous networks designed for voice – CBR (constant bit rate) stream in TDM – IP packets need additional framing • POS: packet over SONET – initial deployments: PPP framing of IP over SONET [RFC 2615] • Motivation for new solution – PPP not designed for this application – goal: new generic framing protocol • IP and CBR over synchronous links

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-206 ITTC © James P.G. Sterbenz TDM Transport Networks Generic Framing Procedure (GFP)

PLI • Framing for transport networks cHEC – ITU-T G.7041 over OTN, SDH/SONET type – 4B common header (length, check HEC) tHEC – client specific headers ext header

– FCS frame check eHEC • Transfer of: – variable size frames (GFP-F) • IP, PPP client payload information field • Ethernet MAC – block code (transparent – GFP-T) • FCS FCS • ESCON/FICON (IBM I/O channels) 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-207 ITTC © James P.G. Sterbenz TDM Transport Networks SONET/SDH Overview

• SONET: synchronous optical network – evolution of T-carrier digital hierarchy in the Bell System – extension of TDM multiplexing structure – higher data rates over fiber optic cable • OC: optical carrier – electronic multiplexing and cross-connects • O/E: optical to electrical conversion at inputs • E/O: electrical to optical conversion at outputs • SDH: synchronous digital hierarchy – ITU standard similar to SONET

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-208 ITTC © James P.G. Sterbenz TDM Transport Networks SONET/SDH Standards

• WAN/MAN synchronous optical links – SDH: synchronous digital hierarchy (ITU-T) – SONET: synchronous optical network (Bellcore*, ANSI) • Standards suite: – architecture G.803, T1.105, Bellcore GR-253 – framing and multiplexing G.707, T1.105.02 – equipment G.671, G.783 – physical interfaces G.691, G.692, T1.105.06, T1.106 – OAM&P G.784, G.831 – protection G.841, T1.105.01 * now Telcordia

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-209 ITTC © James P.G. Sterbenz TDM Transport Networks SONET Topology: Mesh

• SONET mesh – mesh of SONET links – switched at L3 IP • between ATM switches • between IP routers

IP IP

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-210 ITTC © James P.G. Sterbenz TDM Transport Networks SONET Topology: Rings

• SONET rings – multiplexed at L2 • 4:1 multiplexing for aggregation • ADMs for ring insertion/extraction – switched at L2 • cross-connects for ADM ring interconnection – fault tolerant • dual ring APS XC – automatic protection switching

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-211 ITTC © James P.G. Sterbenz TDM Transport Networks SONET Add/Drop Multiplexing OC-n • ADM: add/drop multiplexor – electronic device

– optical transceivers  STS-n OC-m  • Layer 2 insertion/extraction  – of lower rate signals • optical OC-m , m < n

• electrical T-k , typically T3   – to/from OC-n SONET  STS-n • Typically on SONET ring – but may be point-to-point link OC-n

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-212 ITTC © James P.G. Sterbenz TDM Transport Networks SONET Cross Connect OC-n OC-n • XC: Cross-connect – electronic switch • 22 switch shown STS-n STS-n • larger cross-connects possible – optical transceivers • Space division between: – point-to-point links – rings STS-n STS-n • Time division – multiplexing hierarchy OC-n OC-n

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-213 ITTC © James P.G. Sterbenz SONET Hierarchy US Multiplexing Structure DS-0

DS-3  24:1 DS-2

 STS-1

4:1  7:1 OC-3 3:1 OC-12 T1 OC-48 T3 4:1 OC-192 OC-3 4:1 OC-768 OC-12 4:1 OC-48 4:1 OC-192    • Synchronous transport signals (STS) on optical carriers (OC) – used for higher-level aggregation of voice circuits – OC-n data services 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-214 ITTC © James P.G. Sterbenz TDM Transport Networks SONET/SDH Sublayers

• Path (F3): links between L3 swithces DS0 – STS-n generation, HEC, and framing path VT • Tandem connection (optional) STS • Line / Digital Section (F2) tandem connection – de/multiplexing STS-n ↕ STS-N – concatenation 4STS-n  STS-4n line • Section / regenerator section (F1) – STS-n transport, framing, scrambling section • Physical / photonic section – between EO and EOE regeneration • Details for reference in online notes physical

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-215 ITTC © James P.G. Sterbenz TDM Transport Networks SONET/SDH Hierarchy

Link Type Payload rate Transport Rate Payload Overhead SONET SDH SONET ATMmax

STS-1 STM-0 51.84 Mb/s 27 B 774 B 49.54 Mb/s 44.87 Mb/s

OC-3c STM-1c 155.52 Mb/s 81 B 2 340 B 149.75 Mb/s 135.63 Mb/s

OC-12c STM-4c 622.08 Mb/s 324 B 9 387 B 600.77 Mb/s 544.09 Gb/s

OC-48c STM-16c 2.49 Gb/s 1 296 B 37 575 B 2.40 Gb/s 2.16 Gb/s

OC-192c STM-64c 9.95 Gb/s 5 184 B 150 327 B 9.62 Gb/s 8.71 Gb/s

OC-768c STM-256c 39.81 Gb/s 20 736 B 601 335 B 38.48 Gb/s 34.85 Gb/s

OC-3072c STM-1024c 159.25 Gb/s 82 944 B 2 405 367 B 153.94 Gb/s 139.42 Gb/s

OC-N c STM-(N/3)c N  51.84 Mb/s N 39 B N 879 – 9 B 1.0 SONET 48/53 SONET

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-227 ITTC © James P.G. Sterbenz TDM Transport Networks SONET/SDH Summary and Comparison

PDH SDH/SONET OTN DW OTN OTM

Transmission electronic optical

Mux & switching electronic electronic

Multiplex domain TDM TDM

Synchronisation plesiochronous synchronous

Levels* 4 5

Transparency opaque transparent

Rates‡ 1.5 – 45 Mb/s .155 – 40 Gb/s

* as currently defined in standards, not including sub- and intermediate levels ‡ approximate as currently defined in standards, not including STS-1 and sub-rates (DS0 and VTs) 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-228 ITTC © James P.G. Sterbenz TDM Transport Networks LL.4.3.3 Optical Transport Networks

LL.1 Link layer functions and services LL.2 Framing and delineation LL.3 LAN types and topologies LL.4 Multiplexing and switching LL.4.1 Link-layer multiplexing LL.4.2 Link-layer switching LL.4.3 TDM transport networks: PDH, SDH/SONET, OTN LL.5 Per-hop error and flow control LL.6 Link layer components LL.7 VLANs, L2 tunnels, and ARP LL.8 Residential broadband 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-229 ITTC © James P.G. Sterbenz WDM Transport Networks Wavelength Division Multiplexed Links

H1 payload T1

H2 payload T2

H3 payload T3

• Optical WDM: wavelength division multiplexing – FDM where frequencies are wavelengths (shades of IR) – number of wavelengths inversely proportional to distance • stimulated Raman scattering due to molecular vibrations • stimulated Brillouin scattering interacting with acoustic waves • carrier-induced cross-phase modulation causes phase shifts • four-wave mixing induces sum and difference frequencies much more about this in EECS 881

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-230 ITTC © James P.G. Sterbenz WDM Transport Networks OTN Overview

• All optical network motivation – increase capacity on fiber with multiple wavelengths – WDM: wavelength division multiplexing • OTN: optical transport network – evolution of transport network to WDM optical switches • no need for O/E/O conversion – matches SDH/SONET hierarchy • eases replacement of optical for electronic switches • SDH over OTN hierarchy – adds interfaces between service providers • SONET/SDH were designed before deregulation More in EECS 881 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-231 ITTC © James P.G. Sterbenz WDM Transport Networks OTN Standards

• OTN: Optical transport network • ITU-T standards suite: – architecture G.871/Y.1301, G.872 – OTH framing/multiplexing G.709/Y.1331 – equipment G.798 – physical interfaces G.694, G.959.1, G.8251 – OAM&P G.874, G.875 – protection G.873 – ASON G.8080/Y.1304 automatically switched optical network

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-232 ITTC © James P.G. Sterbenz WDM Transport Networks OTN Link Hierarchy

• Trails – undirectional and bidirectional – point-to-point and point-to-multipoint • Interfaces – OUNI (OIF implementation agreement) – IrDI / E-NNI interdomain (OIF implementation agreement) – IaDI / I-NNI intradomain • Framing and multiplexing hierarchy – digital wrapper •digital encapsulation with associated overhead – optical transport module (OTM) •optical/photonic with non-associated overhead

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-233 ITTC © James P.G. Sterbenz WDM Transport Networks OTN Service Provider Interfaces

OUNI ONNI IrDI E-NNI

OTNa OTNb

• ONNI: optical network node interface – Interdomain: IrDI (data) / E-NNI (signaling exterior NNI) • may or may not terminate OCh – Intradomain: IaDI (data) / I-NNI (signaling interior NNI) • IrVI/IaVI: inter-/intra vendor interface • OUNI: optical user–network interface 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-234 ITTC © James P.G. Sterbenz WDM Transport Networks OTN Multiplexing and Framing

• Digital over optical multiplexing hierarchy – client trail (SONET, ATM, GFP) – digital wrapper (in band) • OCh payload unit 2.4Gb/s, 10Gb/s, 40Gb/s – OTM n.m – optical transport module • OCh optical channel edge-to-edge lightpath • n = max number of wavelengths • m = rate identifier Details for reference in online notes

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-235 ITTC © James P.G. Sterbenz WDM Transport Networks OTN OTH Rates

Link type Payloads OPU OTU/Och rate DW OH FEC OPU rate Payload OTH SONET GFP+CRCmax Ethernet

– 51.84 Mb/s STS-1

– 155.52 Mb/s STS-3c

– 622.08 Mb/s STS-12c

OPU1 2.67 Gb/s 64 B 1024 B 15 232 B 2.49 Gb/s STS-48c 2.49 Gb/s 1000Base

OPU2 10.71 Gb/s 64 B 1024 B 15 232 B 9.95 Gb/s STS-192c 9.96 Gb/s =10GBase

OPU3 43.02 Gb/s 64 B 1024 B 15 232 B 39.81 Gb/s STS-768c

OPU4 172.80 Gb/s 64 B 1024 B 15 232 B 159.25 Gb/s STS-3072c 159.15 Gb/s 100G

255/(239–k) = SONET 65495 OPUk 164 B 2564 B 38084 B  SONET line rate 65535

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-241 ITTC © James P.G. Sterbenz WDM Transport Hierarchy Summary and Comparison

PDH SDH/SONET OTN DW OTN OTM

Transmission electronic optical optical optical

Mux & switching electronic electronic electronic optical

Multiplex domain TDM TDM TDM WDM

Synchronisation plesiochronous synchronous synchronous asynchronous

Levels* 4 5 3

Transparency opaque transparent transparent opaque

Rates‡ 1.5 – 45 Mb/s .155 – 40 Gb/s 2.5 – 160 Gb/s –

* as currently defined in standards, not including sub- and intermediate levels ‡ approximate as currently defined in standards, not including STS-1 and sub-rates (DS0 and VTs) 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-242 ITTC © James P.G. Sterbenz Link Layer and LANs LL.5 Per Hop Error and Flow Control

LL.1 Link layer functions and services LL.2 Framing and delineation LL.3 LAN types and topologies LL.4 Multiplexing and switching LL.5 Per-hop error and flow control LL.5.1 Error detection and correction LL.5.2 Error control LL.5.3 Flow control LL.6 Link layer components LL.7 VLANs, L2 tunnels, and ARP LL.8 Residential broadband 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-243 ITTC © James P.G. Sterbenz Link Layer Error Control Introduction

• Per-hop error control for frame transfers Why?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-244 ITTC © James P.G. Sterbenz Link Layer Error Control Introduction

• Per-hop error control for frame transfers • Recall end-to-end arguments: – if error checking and correction needed E2E … … it must be done end-to-end by transport (or application) • HBH link error control – improve overall performance for apps requiring reliability • in addition to E2E error control – improve performance over lossy links for loss-tolerant apps • Alternatives – e.g. ARQ for wireless links – e.g. FEC for satellite and fiber optic links 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-245 ITTC © James P.G. Sterbenz Per Hop Error and Flow Control LL.5.1 Error Detection and Correction

LL.1 Link layer functions and services LL.2 Framing and delineation LL.3 LAN types and topologies LL.4 Multiplexing and switching LL.5 Per-hop error and flow control LL.5.1 Error detection and correction LL.5.2 Error control LL.5.3 Flow control LL.6 Link layer components LL.7 VLANs, L2 tunnels, and ARP LL.8 Residential broadband 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-246 ITTC © James P.G. Sterbenz Link Layer Error Control Detection vs. Correction

• Error detection – generally useful at link layer to detect errors – corrupted frames typically dropped why?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-247 ITTC © James P.G. Sterbenz Link Layer Error Control Detection vs. Correction

• Error detection – generally useful at link layer to detect errors – corrupted frames typically dropped • useless data not sent through network consuming resources • transport layer detects (or signalled) and corrects as necessary – it needs to do this anyway – link layer checks frequently stronger than E2E • link frame CRC much stronger than TCP checksum

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-248 ITTC © James P.G. Sterbenz Link Layer Error Control Detection vs. Correction

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-249 ITTC © James P.G. Sterbenz Link Layer Error Control Detection Techniques

• Byte, word, or block – parity – 2-dimensional parity – Hamming codes • Frame – checksum – CRC

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-250 ITTC © James P.G. Sterbenz Block Error Detection Parity

What is simplest error detection method?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-251 ITTC © James P.G. Sterbenz Block Error Detection Parity

• Parity : detect single errors – no ability to correct errors – only an odd number of bit errors detected • only useful if bit error probability very low

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-252 ITTC © James P.G. Sterbenz Block Error Detection Parity

• Parity: detect single errors – no ability to correct errors – only an odd number of bit errors detected • only useful if bit error probability very low • Parity bit covers n bit block • Even parity: even number of 1s (including parity) – example: 0111 0001 1010 1011 ? • Odd parity odd number of 1s (including parity) – example: 0111 0001 1010 1011 ?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-253 ITTC © James P.G. Sterbenz Block Error Detection Parity

• Parity: detect single errors – no ability to correct errors – only an odd number of bit errors detected • only useful if bit error probability very low • Parity bit covers n bit block • Even parity: even number of 1s (including parity) – example: 0111 0001 1010 1011 1 • Odd parity odd number of 1s (including parity) – example: 0111 0001 1010 1011 0

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-254 ITTC © James P.G. Sterbenz Block Error Detection Parity

• Parity: detect single errors – no ability to correct errors – only an odd number of bit errors detected • only useful if bit error probability very low • Parity bit covers n bit block • Even parity: even number of 1s (including parity) – example: 0111 0001 1010 1011 1 • Odd parity odd number of 1s (including parity) – example: 0111 0001 1010 1011 0 Extension to detect which bit in error?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-255 ITTC © James P.G. Sterbenz Block Error Detection & Correction 2-Dimensional Parity

• 2-dimensional parity: correct single bit errors – detects which bit flipped and can therefore correct

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-256 ITTC © James P.G. Sterbenz Block Error Detection & Correction 2-Dimensional Parity

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-257 ITTC © James P.G. Sterbenz Block Error Detection & Correction 2-Dimensional Parity

• 2-dimensional parity: correct single bit errors – detects which bit flipped and can therefore correct • n + m parity bits covers n  m bit block – n row parity bits cover m data bits each – m column parity bits cover n data bits each • Example (odd parity) 0111 0 0001 0 1010 1 1011 0 1000 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-258 ITTC © James P.G. Sterbenz Block Error Detection & Correction 2-Dimensional Parity

• 2-dimensional parity: correct single bit errors – detects which bit flipped and can therefore correct • n + m parity bits covers n  m bit block – n row parity bits cover m data bits each – m column parity bits cover n data bits each • Example (odd parity) 0111 0 0111 0 0001 0 0001 0 1010 1 1110 1  detects and can correct flip 1011 0 1011 0 1000 1000 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-259 ITTC © James P.G. Sterbenz Block Error Detection & Correction Hamming Codes

• Hamming codes: correct single bit errors – detects which bit flipped and can therefore correct – k parity bits per block cover different sets of n data bits

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-260 ITTC © James P.G. Sterbenz Block Error Detection & Correction Hamming Codes

• Hamming codes: correct single bit errors – detects which bit flipped and can therefore correct – k parity bits per block cover different sets of n data bits • SECDED: single error correct double error detect

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-261 ITTC © James P.G. Sterbenz Block Error Detection & Correction Hamming Codes

– parity bits p2 p1 p0 interleaved with data bits d3 d2 d1 d0

1011010 d3 d2 d1 p2 d0 p1 p0

1-1-0-1 d3 d1 d0 covered by p0

10--00- d3 d2 d0 covered by p1

1011--- d3 d2 d1 covered by p2

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-262 ITTC © James P.G. Sterbenz Block Error Detection & Correction Hamming Codes

– parity bits p2 p1 p0 interleaved with data bits d3 d2 d1 d0

1011010 d3 d2 d1 p2 d0 p1 p0 1111010

1-1-0-1 d3 d1 d0 covered by p0 1-1-0-1

10--00- d3 d2 d0 covered by p1 11--00- p1 detects error

1011--- d3 d2 d1 covered by p2 1111--- p2 detects error

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-263 ITTC © James P.G. Sterbenz Frame Error Detection Checksum

• Detect errors in PDU • Binary addition of bytes/words – sender: compute checksum and insert in header/trailer – receiver: compute checksum and compare to header/trailer Advantages? Disadvantages?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-264 ITTC © James P.G. Sterbenz Frame Error Detection Checksum

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-265 ITTC © James P.G. Sterbenz Frame Error Detection Checksum

• Detect errors in PDU • Binary addition of bytes/words – sender: compute checksum and insert in header/trailer – receiver: compute checksum and compare to header/trailer • Advantage: – simple to compute • Disadvantage: – weak detection of errors – some bit-flip combinations may remain undetected

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-266 ITTC © James P.G. Sterbenz Frame Error Detection CRC

• Cyclic redundancy check CRC – stronger error detection for PDU

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-267 ITTC © James P.G. Sterbenz Frame Error Detection CRC

• Cyclic redundancy check D R – stronger error detection for PDU d r • View data bits, D, as a binary number – choose r + 1 bit pattern (generator), G • Goal: choose r CRC bits R such that – exactly divisible by G (modulo 2) – receiver knows G, divides by G if non-zero remainder: error detected – can detect all burst errors less than r + 1 bits

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-268 ITTC © James P.G. Sterbenz Frame Error Detection & Correction FEC

• Forward error correction FEC D – each PDU has error correcting header h d – combination of header/payload allows significant correction

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-269 ITTC © James P.G. Sterbenz Frame Error Detection & Correction FEC

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-270 ITTC © James P.G. Sterbenz Frame Error Detection & Correction FEC

• Forward error correction FEC D – each PDU has error correcting header h d – combination of header/payload allows significant correction • Open-loop error control – errors corrected at the receiver without retransmissions – reduces need over long delay links for: • retransmissions • sender buffers – statistical reliability good enough for some applications – e.g. G.975 (255,239) Reed Solomon code in SDH/SONET

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-271 ITTC © James P.G. Sterbenz Frame Error Detection & Correction FEC

• Forward error correction FEC D – each PDU has error correcting header h d – combination of header/payload allows significant correction • Open-loop error control – errors corrected at the receiver without retransmissions – reduces need for retransmissions over long delay links – statistical reliability good enough for some applications – e.g. G.975 (255,239) Reed Solomon code in SDH/SONET • Note: FEC can also be done end-to-end – but TCP doesn’t support it

todo: add HARQ 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-272 ITTC © James P.G. Sterbenz Frame Error Detection & Correction Hybrid

• Hybrid error correction – HARQ: hybrid ARQ • Each PDU covered by FEC – provides statistical reliability • Each PDU recovered after FEC covered by CRC – CRC detects uncorrectable payload – permits retransmission only when FEC doesn’t correct

todo: add HARQ 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-273 ITTC © James P.G. Sterbenz Per Hop Error and Flow Control LL.5.2 Error Control

LL.1 Link layer functions and services LL.2 Framing and delineation LL.3 LAN types and topologies LL.4 Multiplexing and switching LL.5 Per-hop error and flow control LL.5.1 Error detection and correction LL.5.2 Error control LL.5.3 Flow control LL.6 Link layer components LL.7 VLANs, L2 tunnels, and ARP LL.8 Residential broadband 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-274 ITTC © James P.G. Sterbenz Error Control Overview

• Error control mechanisms – detect lost or corrupted frames – retransmit as needed – generally only for very lossy links • satellite, wireless, optical with long inter-regen spans why?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-275 ITTC © James P.G. Sterbenz Error Control Overview

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-276 ITTC © James P.G. Sterbenz Error Control Overview

• Error control mechanisms – detect lost or corrupted frames – retransmit as needed – generally only for very lossy links • satellite, wireless, optical with long inter-regen spans • recall end-to-end arguments • Same as E2E mechanisms Lecture TL – unrestricted simplex (baseline no error control) – stop-and-wait: sufficient for short links such as WLANs – go-back-n – selective repeat

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-277 ITTC © James P.G. Sterbenz Per Hop Error and Flow Control LL.5.3 Flow Control

LL.1 Link layer functions and services LL.2 Framing and delineation LL.3 LAN types and topologies LL.4 Multiplexing and switching LL.5 Per-hop error and flow control LL.5.1 Error detection and correction LL.5.2 Error control LL.5.3 Flow control LL.6 Link layer components LL.7 VLANs, L2 tunnels, and ARP LL.8 Residential broadband 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-278 ITTC © James P.G. Sterbenz Link Flow Control Negotiation

• Flow control why?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-279 ITTC © James P.G. Sterbenz Link Flow Control Negotiation

• Flow control – sender transmits at a rate that will not overwhelm receiver

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-280 ITTC © James P.G. Sterbenz Link Flow Control Negotiation

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-281 ITTC © James P.G. Sterbenz Link Flow Control Negotiation

• Flow control – sender transmits at a rate that will not overwhelm receiver • Initial rate negotiation – automatic negotiation of parameters • e.g. modem rate • e.g. Ethernet rate (10M/100M/1G) b/s • Dynamic flow control – may be needed end-to-end – most modern links do not need HBH flow control

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-282 ITTC © James P.G. Sterbenz Link Layer and LANs LL.6 Link Layer Components

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-283 ITTC © James P.G. Sterbenz Link Layer Components Types

• Amplifiers and regenerators • Multiplexors and cross-connects • Optical wavelength converters • Hubs and bridges • Time slot interchangers (TSI) – time division switches

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-284 ITTC © James P.G. Sterbenz Link Layer Components Amplifiers and Regenerators

• Amplifiers: analog – example: optical EDFA (erbium doped fiber amplifier)

every few hundred km

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-285 ITTC © James P.G. Sterbenz Link Layer Components Amplifiers and Regenerators

• Amplifiers: analog – example: optical EDFA (erbium doped fiber amplifier)

every few hundred km • Regenerators: A/D/A – 2R: regeneration and reshaping preserves timing – 3R: regeneration, reshaping, and retiming

– examples: • optical 2R and 3R • microwave relays • bent-path satellite links EECS 881

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-286 ITTC © James P.G. Sterbenz Link Layer Components Multiplexors and Cross-Connects

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-287 ITTC © James P.G. Sterbenz Link Layer Components Multiplexors and Cross-Connects

• Multiplexors / demultiplexors – aggregate multiple virtual links onto a physical link • example: T-carrier, point-to-point SONET, WDM multiplexors • example: SONET ring add-drop multiplexors • Cross-connects – layer 2 switch with relatively static configuration • example: SONET cross-connect between rings

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-288 ITTC © James P.G. Sterbenz Link Layer Components Optical Wavelength Converters

• O/E/O: convert through electronic domain – expensive – lose advantages of all-optical lightpaths

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-289 ITTC © James P.G. Sterbenz Link Layer Components Optical Wavelength Converters

• O/E/O: convert through electronic domain – expensive – lose advantages of all-optical lightpaths • Optical domain: future technology – cross-modulation: input modulates laser output at new  – coherent effects: similar to four wave mixing • Small cheap DWDM multiwavelength converters will – reduce some lightpath assignment constraints – will require modification of lightpath routing algorithms EECS 881

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-290 ITTC © James P.G. Sterbenz Link Layer Components LAN Components

How to extend the reach of LAN segment? original shared medium bus or ring

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-291 ITTC © James P.G. Sterbenz Link Layer Components Bridges

• Bridges connect LAN segments – extend reach beyond limits – important for early LANS • e.g. Ethernet extension

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-292 ITTC © James P.G. Sterbenz Link Layer Components Bridges

• Bridges connect LAN segments – extend reach beyond limits – important for early LANS • e.g. Ethernet extension • Promiscuous – repeat (pass) all frames network scalability?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-293 ITTC © James P.G. Sterbenz Link Layer Components Bridges

• Bridges connect LAN segments – extend reach beyond limits – important for early LANS • e.g. Ethernet extension • Promiscuous – repeat (pass) all frames – all interconnected segments share intra-segment frames alternative?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-294 ITTC © James P.G. Sterbenz Link Layer Components Bridges

• Bridges connect LAN segments – extend reach beyond limits – important for early LANS • e.g. Ethernet extension • Learning bridge – learns local segment addresses • snooped on source MAC address in frame header – only repeat frames destined for other segments

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-295 ITTC © James P.G. Sterbenz Link Layer Components Hubs

• Early LANs dictated wiring topology – linear segments for Ethernet – loops for token ring Problems?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-296 ITTC © James P.G. Sterbenz Link Layer Components Hubs

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-297 ITTC © James P.G. Sterbenz Link Layer Components Hubs

• Early LANs dictated wiring topology – linear segments for Ethernet – rings for token ring • Office topology frequently didn’t match LAN topology – Ethernet bridges frequently needed to bridge hallways • End user could take down network – by disconnecting network interface • token ring • some Ethernet links (e.g. 10Base2) – sys/netadmins would have to run from office to office Response? 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-298 ITTC © James P.G. Sterbenz Link Layer Components Hubs

• Alternative – use a star wiring plan – host/station links all go to a hub in a wiring closet

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-299 ITTC © James P.G. Sterbenz Link Layer Components Hubs

• Alternative – use a star wiring plan – host/station links all go to a hub in a wiring closet • More flexible wiring plan • Central location for debugging

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-300 ITTC © James P.G. Sterbenz Link Layer Components Hubs

• Alternative – use a star wiring plan – host/station links all go to a hub in a wiring closet • More flexible wiring plan • Central location for debugging Network scalability?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-301 ITTC © James P.G. Sterbenz Link Layer Components Hubs

• Alternative – use a star wiring plan – host/station links all go to a hub in a wiring closet • More flexible wiring plan • Central location for debugging • Hub is still shared medium bottleneck alternative?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-302 ITTC © James P.G. Sterbenz Link Layer Components LAN Switches

• Alternative – replace hub with a space division switch

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-303 ITTC © James P.G. Sterbenz Link Layer Components LAN Switches

• LAN switch – switches on layer 2 (MAC address) header – full bandwidth of each link available • assuming non-blocking switch fabric

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-304 ITTC © James P.G. Sterbenz Link Layer Components LAN Switches

• LAN switch – switches on layer 2 (MAC address) header – full bandwidth of each link available • assuming non-blocking switch fabric – arbitrarily scalable with addition of additional switches

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-305 ITTC © James P.G. Sterbenz Link Layer Components LAN Switches

• LAN switch – switches on layer 2 (MAC address) header – full bandwidth of each link available – arbitrarily scalable with addition of additional switches Substitute for L3 (IP) switch (router)?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-306 ITTC © James P.G. Sterbenz Link Layer Components LAN Switches

• LAN switch – switches on layer 2 (MAC address) header – full bandwidth of each link available • Not a substitute for L3 (IP) switch (router) – no IP routing and forwarding capability – flat addressing: addresses randomly assigned to NICs – no ability to aggregate into hierarchy as with IP – fwd table must contain every randomly assigned L2 address

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-307 ITTC © James P.G. Sterbenz Link Layer and LANs LL.7 VLANs, L2 Tunnels, and ARP

LL.1 Link layer functions and services LL.2 Framing and delineation LL.3 LAN types and topologies LL.4 Multiplexing and switching LL.5 Per-hop error and flow control LL.6 Link layer components LL.7 VLANs, L2 tunnels, and ARP LL.7.1 Virtual LANs LL.7.2 Layer 2 tunnels LL.7.3 IP address resolution LL.8 Residential broadband 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-308 ITTC © James P.G. Sterbenz VLANs, L2 Tunnels, and ARP Motivation

• LANs operate as part of Global Internet – using IP • Several technologies needed for this – VLANs: Virtual LANs – L2 tunnels: link emulation over IP – ARP: IP address resolution protocol

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-309 ITTC © James P.G. Sterbenz VLANs, L2 Tunnels, and ARP LL.7.1 Virtual LANs

LL.1 Link layer functions and services LL.2 Framing and delineation LL.3 LAN types and topologies LL.4 Multiplexing and switching LL.5 Per-hop error and flow control LL.6 Link layer components LL.7 VLANs, L2 tunnels, and ARP LL.7.1 Virtual LANs LL.7.2 Layer 2 tunnels LL.7.3 IP address resolution LL.8 Residential broadband 05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-310 ITTC © James P.G. Sterbenz Virtual LANs Motivation

• LANs provide useful infrastructure at network edge – cheap and simple interconnection for workgroup – “plug-and-play” interfaces – no need to understand or configure IP routing What if workgroup doesn’t match physical topology? reasons?

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-311 ITTC © James P.G. Sterbenz Virtual LANs Motivation

• LANs provide useful infrastructure at network edge – cheap and simple interconnection for workgroup – “plug-and-play” interfaces – no need to understand or configure IP routing • Workgroup may not match physical topology – multiple workgroups share LAN infrastructure – workgroups scattered across wide area Internet

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-312 ITTC © James P.G. Sterbenz Virtual LANs VLAN Topology Alternatives

• Workgroup may not match physical topology – virtual LANs (VLANs) • Multiple workgroups share LAN infrastructure – VLANs segregate physical LANs – traffic isolation • separate L2 broadcast domain • security: prevent L2 frames to be visible across VLANs • Workgroup scattered across wide-area Internet – layer 2 tunnels extend LAN with L2 tunnel in IP datagram

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-313 ITTC © James P.G. Sterbenz Virtual LANs L2 Switch Configuration

How to configure VLANs in a L2 switch?

L2 0 1

3 4 5

05 November 2018 KU EECS 780 – Comm Nets – Link Layer & LANs NET-LL-314 ITTC © James P.G. Sterbenz Virtual LANs L2 Switch Configuration