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Telematics Chapter 5: Medium Access Control Sublayer User Server watching with video Beispielbildvideo clip clips Application Layer Application Layer Presentation Layer Presentation Layer Session Layer Session Layer Transport Layer Transport Layer Network Layer Network Layer Network Layer Prof. Dr. Mesut Güneş Data Link Layer Data Link Layer Data Link Layer Computer Systems and Telematics (CST) Physical Layer Physical Layer Physical Layer Distributed, embedded Systems Institute of Computer Science Freie Universität Berlin http://cst.mi.fu-berlin.de Contents ● Design Issues ● Metropolitan Area Networks ● Network Topologies (()MAN) ● The Channel Allocation Problem ● Wide Area Networks (WAN) ● Multiple Access Protocols ● Frame Relay ● Ethernet ● ATM ● IEEE 802.2 – Logical Link Control ● SDH ● Token Bus ● Network Infrastructure ● Token Ring ● Virtual LANs ● Fiber Distributed Data Interface ● Structured Cabling Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.2 Design Issues Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.3 Design Issues ● Two kinds of connections in networks ● Point-to-point connections OSI Reference Model ● Broadcast (Multi-access channel, Application Layer Random access channel) Presentation Layer ● In a network with broadcast Session Layer connections ● Who gets the channel? Transport Layer Network Layer ● PtProtoco ls use dtdtd to determ ine w ho gets next access to the channel Data Link Layer ● Medium Access Control (()MAC) sublay er Phy sical Laye r Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.4 Network Types for the Local Rang e ● LLC layer: uniform interface and same frame format to upper layers ● MAC layer: defines medium access - LLC IEEE 802.2 Logical Link Control ... s s kk g e n n u r e e b Layer ANSI ATM h e c 802.3 802.4 802.5 802.6 i Data Lin X3T9.5 Forum S S MAC ... CSMA/CD Token Token ATM LAN (Ethernet) Bus Ring DQDB FDDI Emulation ISO/OSI ExistingReale Network Netze Concepts Both concepts are implemented together in existing networks (as a device driver): 1. Packing of data into frames: error detection during frame transmission and receipt 2. Media Access Control: this contains the frame transmission and the reaction to transmission errors Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.5 Standardization: IEEE ● Institute of Electrical and Electronic Engineers (IEEE) ● Standardization of the IEEE 802.X -Standards for Local Area Networks (www.ieee802.org) www.ieee.org 802.1 Overview and Architecture of LANs 802.11 Wireless LAN (WLAN) 802.2 Logical Link Control (LLC) 802.12 Demand Priority (HP’s AnyLAN) 802.3 CSMA/CD (Ethernet) 802.14 Cable modems 802.4 Token Bus 802.15 Personal Area Networks ((,PAN, 802.5 Token Ring Bluetooth) 802.6 DQDB (Distributed Queue Dual Bus) 802.16 Wireless MAN 802.7 Broadband Technical Advisory 802.17 Resilient Packet Ring Group (BBTAG) 802.18 Radio Regulatory Technical 802.8 Fiber Optic Technical Advisory Advisory Group (RRTAG) Group (FOTAG) 802.19 Coexistence Technical 802.9 Integrated Services LAN Advisory Group (ISLAN) Interface 802.20 Mobile Broadband Wireless 802.10 Standard for Interoperable Access (MBWA) LAN S ecuri ty (SILS) 802.21 Media Independent Handover Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.6 Network Categories ● Local Area Networks (LAN): 10m - few km, simple connection structure ● Ethernet/Fast Ethernet/Gigabit Ethernet/10Gigabit Ethernet ● Token Bus, Token Ring LAN ● FDDI (up to 100 km, belongs to LANs nevertheless) ● Wireless LAN (WLAN, up to a few 100 m) ● Metropolitan Area Network (MAN): 10 - 100 km, city range ● DQDB ● FDDI II MAN ● Resilient Packet Ring ● [also used: Gigabit Ethernet] ● Wide Area Networks (WAN): 100 – 10,000 km, interconnection of subnetworks ● Frame Relay ● ATM WAN ● SDH Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.7 Network Topologies Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.8 Bus B Terminating resistor Example: Ethernet Ω Ω A ● Bus ● Broadcast Network: if station A intends to send data to station B, the message reaches all connected stations. Only station B processes the data, all other stations ignore it. ● Passive coupling of stations ● Restriction of the extension and number of stations to connected ● Simple, cheap, easy to connect new stations ● The breakdown of a station does not influence the rest of the network Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.9 Star ● Star ● Designated computer as central station: a message of station A is forwarded to station B via the B central station ● Broadcast network (Hub) or point- to-point connections (Switch) ● Expensive central station ● Vulnerability through central station (Redundancy possible) ● N connections for N stations A ● Easy connection of new stations Example: Fast Ethernet Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.10 Tree ● Tree ● Topology: Connection of several busses or stars ● Branching elements can be active (Router) or passive (Repeater) ● Bridging of large distances ● Adaptation to given geographical structure ● Minimization of the cable length possible Branch 1 Branch 2 A B C D Repeater Router Backbone Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.11 Ring ● Ring ● Broadcast Network ● Chain of point-to-point connections B ● Active stations: messages are regeneratdbted by the s ttitations (Repeater) ● Breakdown of the whole network in case of failure of one single station or connection ● Large extent possible A ● Easy connection of new stations ● Only N connections for N stations ● Variant: bidirectional ring Example: Token Ring, FDDI ● stations are connected by two opposed rings Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.12 Meshed Networks ● Fully Meshed Network ● Point-to-Point connections between all stations ● For N stations N(N −1) 2 connections are needed ● Connecting a new station is a costly process ● Redundant paths ● Maximal connection availability through routing integration Partly meshed network: cheaper, but routing, flow control, and congestion control become necessary (Wide Area Networks) Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.13 Examples ● Ethernet (IEEE 802.3, 10 Mbps) ● originally the standard network ● available in an “immense number” of variants ● Token Ring (IEEE 802.5, 4/16/100 Mbps) ● for a long time the Ethernet competitor ● extended to FDDI (Fiber Distributed Data Interface) ● Fast Ethernet (IEEE 802.3u, 100 Mbps) ● at the moment the most widely spread network ● extension of Ethernet for small distances ● Gigabit Ethernet (IEEE 802. 3z, 1000 Mbps) ● very popular at the moment; 10 Gbps are already in the planning phase at the moment Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.14 The Channel Allocation Problem Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.15 The Channel Allocation Problem ● The channel allocation problem ● Given N independent stations which want to communicate over a single channel ● Organize the sending order of the stations Medium Wire or wireless ● Approaches ● Static channel allocation ● Simple procedures ● Dynamic channel allocation ● Complex procedure, that adapt to changes Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.16 Static Channel Allocation ● Time Division Multiple Access ● Frequency Division Multiple (TDMA) Access (FDMA) ● Each user gets the entire ● Each user gets a portion of the transmission capacity for a fixed transmission capacity for the whole time interval time ● Baseband transmission ● Frequency range ● Broadband transmission Frequency Frequency User 1 User 2 Time User 3 111222333 Time Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.17 Static Channel Allocation ● Problems with static channel allocation ● Works only for a fixed number of users ● When number of users change, the allocation scheme does not work ● Data traffic is very often bursty, i.e., long time no data and for a short time high data ● Thus, users do not use their allocated channel capacity Most of the channels will be idle most of the time Dynamic Channel Allocation Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.18 Dynamic Channel Allocation ● Assumptions on dynamic channel allocation ● Station Model: ● There are N independent stations (computers) that generate frames for transmission. ● Single channel ● A si ngl le ch annel i s avail abl e f or communi cati on and all st ati ons can t ransmit and recei ve on it. ● Collisions ● If two frames are transmitted simultaneously, they overlap and the signals are garbled. ● Time ● Continuous time: No master clock,,gy transmission of frames can begin at anytime. ● Slotted time: Time is divided into discrete intervals called slots. Frame transmissions begin always at the start of a slot. ● Sensing
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