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What's a Protocol? Chapter 1: Roadmap Last Course Review What’s the Internet What is a protocol? communication infrastructure enables distributed applications: Web, email, games, e- protocols define format, commerce, file sharing order of msgs sent and communication services received among network provided to apps: entities, and actions Connectionless unreliable taken on msg connection-oriented transmission, receipt reliable Introduction 1-1 Introduction 1-2 What’s a protocol? Chapter 1: roadmap a human protocol and a computer network protocol: 1.1 What is the Internet? 1.2 Network edge Hi TCP connection 1.3 Network core req Hi 141.4 Network access and physical media TCP connection Got the response 1.5 Internet structure and ISPs time? Get http://www.awl.com/kurose-ross 2:00 1.6 Delay & loss in packet-switched networks <file> 1.7 Protocol layers, service models time 1.8 History Q: Other human protocols? Introduction 1-3 Introduction 1-4 Network edge: connection-oriented service Network edge: connectionless service Goal: data transfer TCP service [RFC 793] Goal: data transfer App’s using TCP: between end systems reliable, in-order byte- between end systems HTTP (Web), FTP (file handshaking: setup stream data transfer same as before! transfer), Telnet (prepare for) data loss: acknowledgements UDP -User Datagram (remote login), SMTP transfer ahead of time and retransmissions Protocol [RFC 768]: (email) Hello, hello back human flow control: connectionless protocol sender won’t overwhelm unreliable data set up “state” in two receiver App’s using UDP: transfer communicating hosts congestion control: streaming media, no flow control TCP - Transmission senders “slow down sending teleconferencing, DNS, Control Protocol rate” when network no congestion control Internet telephony Internet’s connection- congested oriented service Introduction 1-5 Introduction 1-6 1 The Network Core Network Core: Circuit Switching mesh of interconnected End-end resources routers reserved for “call” the fundamental link bandwidth, switch question: how is data capacity transferred through net? dedicated resources: circuit switching: no sharing dedicated circuit per circuit-like call: telephone net (guaranteed) packet-switching: data performance sent thru net in call setup required discrete “chunks” Introduction 1-7 Introduction 1-8 Network Core: Circuit Switching Circuit Switching: FDM and TDM Example: network resources dividing link bandwidth FDM (e.g., bandwidth) into “pieces” 4 users divided into “pieces” frequency division pieces allocated to calls time division frequency resource piece idle if not used by owning call time (no sharing) TDM frequency time Introduction 1-9 Introduction 1-10 Network Core: Packet Switching Packet switching versus circuit switching each end-end data stream resource contention: Packet switching allows more users to use network! divided into packets aggregate resource 1 Mb/s link user A, B packets share demand can exceed network resources amount available each user: 100 kb/s when “active” each packet uses full link congestion: packets active 10% of time bandwidth queue, wait for link use N users resources used as needed store and forward: circuit-switching: packets move one hop 1 Mbps link 10 users at a time Bandwidth division into “pieces” Node receives complete packet switching: Dedicated allocation packet before forwarding with 35 users, Resource reservation probability > 10 active less than .0004 Introduction 1-11 Introduction 1-12 2 Packet switching versus circuit switching Packet-switching: store-and-forward Is packet switching a “slam dunk winner?” L R R R Great for bursty data resource sharing Takes L/R seconds to Example: transmit (push out) simpler, no call setup L = 7.5 Mbits packet of L bits on to R = 1.5 Mbps EiExcessive congestion: packet dldelay and loss link or R bps delay = 15 sec protocols needed for reliable data transfer, Entire packet must congestion control arrive at router before Q: How to provide circuit-like behavior? it can be transmitted bandwidth guarantees needed for audio/video on next link: store and apps forward still an unsolved problem (chapter 6) delay = 3L/R Introduction 1-13 Introduction 1-14 Network Taxonomy Packet-switched networks: forwarding Telecommunication Goal: move packets through routers from source to networks destination we’ll study several path selection (i.e. routing) algorithms (chapter 4) Circuit-switched Packet-switched datagram network: networks networks destination address in packet determines next hop routes may change during session Networks Datagram analogy: driving, asking directions FDM TDM with VCs Networks virtual circuit network: each packet carries tag (virtual circuit ID), tag determines next hop • Datagram network is not either connection-oriented or connectionless. fixed path determined at call setup time, remains fixed • Internet provides both connection-oriented (TCP) and thru call connectionless services (UDP) to apps. routers maintain per-call state Introduction 1-15 Introduction 1-16 Chapter 1: roadmap Access networks and physical media Q: How to connect end 1.1 What is the Internet? systems to edge router? 1.2 Network edge residential access nets 1.3 Network core institutional access networks (school, 1. 4 Network access and physical media company) 1.5 Internet structure and ISPs mobile access networks 1.6 Delay & loss in packet-switched networks Keep in mind: 1.7 Protocol layers, service models bandwidth (bits per 1.8 History second) of access network? shared or dedicated? Introduction 1-17 Introduction 1-18 3 Residential access: point to point access Residential access: cable modems Dialup via modem HFC: hybrid fiber coax up to 56Kbps direct access to asymmetric: up to 30Mbps downstream, 2 router (often less) Mbps upstream Can’t surf and phone at same network of cable and fiber attaches homes to time: can’t be “always on” ISP router ADSL: asymmetric digital subscriber line homes share access to router up to 1 Mbps upstream (today typically < 256 kbps) deployment: available via cable TV companies up to 8 Mbps downstream (today typically < 1 Mbps) FDM: 50 kHz - 1 MHz for downstream 4 kHz - 50 kHz for upstream 0 kHz - 4 kHz for ordinary telephone Introduction 1-19 Introduction 1-20 Residential access: cable modems Cable Network Architecture: Overview Typically 500 to 5, 000 homes cable headend home cable distribution network (simplified) Diagram: http://www.cabledatacomnews.com/cmic/diagram.html Introduction 1-21 Introduction 1-22 Cable Network Architecture: Overview Cable Network Architecture: Overview server(s) cable headend cable headend home home cable distribution cable distribution network (simplified) network Introduction 1-23 Introduction 1-24 4 Cable Network Architecture: Overview Company access: local area networks FDM: company/univ local area C network (LAN) connects O V V V V V V N I I I I I I D D T end system to edge router D D D D D D A A R E E E E E E T T O Ethernet: O O O O O O A A L 12 34 56789 shared or dedicated link Channels connects end system and router 10 Mbs, 100Mbps, Gigabit Ethernet cable headend LANs: chapter 5 home cable distribution network Introduction 1-25 Introduction 1-26 Wireless access networks Home networks shared wireless access Typical home network components: network connects end system ADSL or cable modem to router router router/firewall/NAT via base station aka “access Ethernet point” base wireless access wireless LANs: station 802.11b (WiFi): 11 Mbps point wider-area wireless access wireless to/from laptops provided by telco operator cable router/ cable 3G ~ 384 kbps modem firewall mobile headend • Will it happen?? hosts wireless WAP/GPRS in Europe access Ethernet point Introduction 1-27 Introduction 1-28 Physical Media Physical Media: coax, fiber Twisted Pair (TP) Coaxial cable: Fiber optic cable: Bit: propagates between two insulated copper glass fiber carrying light two concentric copper transmitter/rcvr pairs wires pulses, each pulse a bit conductors physical link: what lies Category 3: traditional high-speed operation: phone wires, 10 Mbps bidirectional between transmitter & high-speed point-to-point receiver Ethernet baseband: transmission (e. g., 5 Gps) Category 5: guided media: single channel on cable 100Mbps Ethernet low error rate: repeaters signals propagate in solid legacy Ethernet spaced far apart ; immune media: copper, fiber, coax broadband: to electromagnetic noise unguided media: multiple channel on cable signals propagate freely, HFC e.g., radio Introduction 1-29 Introduction 1-30 5 Physical media: radio Chapter 1: roadmap signal carried in Radio link types: electromagnetic terrestrial microwave 1.1 What is the Internet? spectrum e.g. up to 45 Mbps channels 1.2 Network edge no physical “wire” LAN (e.g., Wifi) 1.3 Network core bidirectional 2Mbps, 11Mbps 141.4 Network access and physical media propagation wide-area (e.g., cellular) environment effects: e.g. 3G: hundreds of kbps 1.5 Internet structure and ISPs reflection satellite 1.6 Delay & loss in packet-switched networks obstruction by objects up to 50Mbps channel (or 1.7 Protocol layers, service models interference multiple smaller channels) 270 msec end-end delay 1.8 History geosynchronous versus low altitude Introduction 1-31 Introduction 1-32 Internet structure: network of networks Tier-1 ISP: e.g., Sprint roughly hierarchical Sprint US backbone network at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity, Sprint, AT&T), national/international
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