What is a network? What is a network? � Carrier of information between connected entities � What does a network consist of? Introduction Introduction – End hosts connected to the network – Routers/switches that move data through the network – Physical links that carry information • E.g. Ethernet, FDDI, ATM, Token Ring Srinidhi Varadarajan – Applications that communicate with each other to provide services • E-Mail, File Transfer, Web Browser Internet: Components Internet: Components What is an What is an internetwork internetwork? rout er � Network edge: workst at ion � A set of connected networks is called an – millions of connected server internetwork. computing devices running mobile network apps � The Internet is a specific example of an local I SP – pc’s workstations, servers internetwork. – PDA’s phones, toasters – The Internet is characterized by the use of a common network protocol (IP). regional I SP � Network core: � An internetwork need NOT be connected to the – routers: forward packets Internet (chunks) of data thru network � Media: – communication links: fiber, copper, radio, satellite company net wor k Internet: Components Internet: Components Internet: Services Internet: Services � protocols : control � communication infrastructure enables distributed rout er sending, receiving of workst at ion applications: msgs server mobile – WWW, email, games, e-commerce, database., voting, – e.g., TCP, IP, HTTP, FTP, local I SP – more? PPP � Internet: “network of � communication services provided: networks” regional I SP – connectionless – loosely hierarchical – connection-oriented – public Internet versus private intranet � Internet standards � cyberspace [Gibson]: “a consensual hallucination experienced daily by billions of operators, in – RFC: Request for comments every nation, ...." company – IETF: Internet Engineering net wor k Task Force Application Layer 1
What’s a protocol? What’s a protocol? A closer look at network structure A closer look at network structure human protocols: network protocols: � network edge: � “what’s the time?” � machines rather than applications and humans � “I have a question” hosts � all communication � introductions activity in Internet � network core: governed by protocols … specific msgs sent – routers … specific actions protocols define format, – network of networks taken when msgs order of msgs sent and received, or other received among network � access networks, events entities, and actions physical media: taken on msg communication links transmission, receipt The Network Edge The Network Edge Network edge: connection-oriented service Network edge: connection oriented service � end systems (hosts): Goal: data transfer TCP service [RFC 793] – run application programs between end sys. � reliable, in-order byte- – e.g., WWW, email � handshaking: setup stream data transfer – at “edge of network” (prepare for) data – loss: acknowledgements transfer ahead of time � client/server model and retransmissions – set up “state” in two – client host requests, receives communicating hosts � flow control: service from server � TCP - Transmission – sender won’t overwhelm – e.g., WWW client (browser)/ Control Protocol receiver server; email client/server – Internet’s connection- � congestion control: � peer-peer model: oriented service – senders “slow down – host interaction symmetric sending rate” when – e.g.: teleconferencing network congested Network edge: connectionless service Network edge: connectionless service The Network Core The Network Core Goal: data transfer App’s using TCP: � mesh of interconnected between end � HTTP (WWW), FTP (file routers systems transfer), Telnet � the fundamental – same as before! (remote login), SMTP question: how is data � UDP - User Datagram (email) transferred through net? Protocol [RFC 768]: – circuit switching: Internet’s dedicated circuit per connectionless service App’s using UDP: call: telephone net – unreliable data � streaming media, – packet-switching: transfer teleconferencing, data sent thru net in – no flow control Internet telephony discrete “chunks” – no congestion control Application Layer 2
Network Core: Circuit Switching Network Core: Circuit Switching Network Core: Circuit Switching Network Core: Circuit Switching � network resources (e.g., bandwidth) End-end resources divided into reserved for “call” “pieces” � pieces allocated to � link bandwidth, calls switch capacity � resource piece idle if � dedicated resources: not used by owning no sharing call (no sharing) � circuit-like � dividing link (guaranteed) bandwidth into performance “pieces” � call setup required – frequency division – time division Network Core: Packet Switching Network Core: Packet Switching Network Core: Packet Switching Network Core: Packet Switching each end-end data stream resource contention: divided into packets � aggregate resource � user A, B packets share demand can exceed 10 Mbs C network resources A Et hernet st at ist ical mult iplexing amount available � each packet uses full link � congestion: packets bandwidth 1.5 Mbs queue, wait for link B � resources used as use queue of packet s 45 Mbs needed , wait ing f or out put � store and forward: link packets move one hop Bandwidth division into at a time D “pieces” E – transmit over link Dedicated allocation – wait turn at next link Resource reservation Network Core: Packet Switching Network Core: Packet Switching Packet switching versus circuit switching Packet switching versus circuit switching Packet switching allows more users to use network! � 1 Mbitlink � each user: – 100Kbps when “active” – active 10% of time N users � circuit-switching: – 10 users 1 Mbps link � packet switching: Message Switching – with 35 users, probability > 10 active less that .004 Segmented Packet Switching Application Layer 3
Packet Packet-switched networks: routing switched networks: routing Packet switching versus circuit switching Packet switching versus circuit switching Is packet switching the “ultimate solution” � Goal: move packets among routers from source to � Great for bursty data destination – resource sharing � datagram network: – no call setup – destination address determines next hop – routes may change during session � Excessive congestion: packet delay and loss – analogy: driving, asking directions – protocols needed for reliable data transfer, � virtual circuit network: congestion control – each packet carries tag (virtual circuit ID), tag determines � Q: How to provide circuit-like behavior? next hop – bandwidth guarantees needed for audio/video – fixed path determined at call setup time , remains fixed apps thru call – routers maintain per-call state still an unsolved problem Access networks and physical media Access networks and physical media Residential access: point to point access Residential access: point to point access Q: How to end systems � Dialup via modem connect to an edge – up to 56Kbps direct access router? to router (conceptually) � residential access nets � ISDN: integrated services � institutional access digital network: 128Kbps all- networks (school, digital connect to router company) � ADSL:asymmetric digital � mobile access networks subscriber line – up to 1 Mbps home-to- Keep in mind: router � bandwidth (bits per – up to 8 Mbps router-to- second) of access home network? � shared or dedicated? Residential access: cable modems Residential access: cable modems Institutional access: local area networks Institutional access: local area networks � HFC: hybrid fiber coax � company/univ local area – asymmetric: up to 10Mbps network (LAN) connects upstream, 1 Mbps end system to edge router downstream � Ethernet: � network of cable and fiber attaches homes to ISP router – shared or dedicated – shared access to router cable connects end among home system and router – issues: congestion, dimensioning – 10 Mbs, 100Mbps, � deployment: available via Gigabit Ethernet cable companies, e.g., � deployment: institutions, MediaOne home LANs soon Application Layer 4
Recommend
More recommend
