Announcements CS 5565 Network Architecture and Protocols Lecture 2 Godmar Back Created Lectures Page Created CS5565 Forum Use this to find a project partner All projects will be done in groups of up to 2. Do Wireshark Lab 1/Intro Either follow old link to Ethereal lab, or, if you have a textbook website subscription, download from website 2 Outline for today Internet: nuts and bolts view Service view Network edge view Network core view Types of switching Sources of Delay 3 The Internet: nuts and bolts view millions of connected computing devices: hosts = end systems running network apps communication links fiber, copper, radio, satellite transmission rate = routers: forward packets router server local ISP company network workstation mobile regional ISP 4 The Internet: nuts and bolts view Network Virginia protocols control sending, receiving of msgs e.g., TCP, IP, HTTP, FTP, PPP Internet: network of loosely hierarchical public Internet versus private intranets Internet vs internet Internet standards RFC: Request for comments IETF: Internet Engineering Task Force router server local ISP company network workstation mobile regional ISP 5 Source: Sean Gillespie CS 5565 Spring 2009 1/26/2009 6 1
The Internet: a service view communication infrastructure enables distributed applications: Web, email, games, e- commerce, file sharing communication services provided to apps: Connectionless unreliable Connection-oriented reliable What s a protocol? a human protocol and a computer network protocol: Hi Hi Got the? 2:00 TCP connection req TCP connection response Get http://www.awl.com/kurose-ross <file> 7 8 human protocols: what s the? I have a question introductions What s a protocol? specific msgs sent specific actions taken when msgs received, or other events network protocols: machines rather than humans all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt 9 A closer look at network structure: network edge: applications and hosts network core: routers network of access, physical media: communication links 10 end systems (hosts): run application programs e.g. Web, email at edge of network client/server model The network edge: client host requests, receives service from always-on server e.g. Web browser/server; email client/server peer-peer model: minimal (or no) use of dedicated servers e.g. Gnutella, KaZaA 11 Connection-oriented service Goal: data transfer TCP service [RFC 793] between end systems reliable, in-order bytestream data transfer handshaking: setup (prepare for) data transfer ahead of Hello, hello back human protocol set up state in two communicating hosts TCP - Transmission Control Protocol Internet s connectionoriented service loss: acknowledgements and retransmissions flow control: sender won t overwhelm receiver congestion control: senders slow down sending rate when network congested 12 2
Connectionless service Goal: data transfer between end systems same as before! UDP - User Datagram Protocol [RFC 768]: connectionless unreliable data transfer no flow control no congestion control TCP-friendliness App s using TCP: HTTP (Web), ssh (remote login), SMTP (email), Bittorrent (file-sharing), XMPP (instant messenging) App s using UDP: streaming media, teleconferencing, DNS, Internet telephony 13 The Network Core the fundamental question: how is data transferred through net? circuit switching: dedicated circuit per call: telephone net packet-switching: data sent thru net in discrete chunks How are the network s resources shared? 14 Network Core: Circuit Switching End-end resources reserved for call (or session) link, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup required Network Core: Circuit Switching network resources (e.g., link ) divided into pieces pieces allocated to calls resource piece idle if not used by owning call (no sharing) multiplex different calls frequency division multiplexing (FDM) division multiplexing (TDM) synchronous vs. asynchronous (aka statistical) TDM 15 16 Circuit Switching: FDM and TDM Example: FDM 4 users frequency TDM frequency Computing transmission delay S(ynchronous) TDM Suppose m slots Total is R L bit packet takes Lm/R seconds L/R seconds if packet fits into slot (but next packet must wait m-1 slots) FDM Suppose m channels Total is R Per channel is R/m L bit packet takes Lm/R seconds 17 18 3
Network Core: Switching each end-end data stream divided into packets user A, B packets share network resources each packet uses full link resources used as needed no dedicated allocation no resource reservation resource contention: aggregate resource demand can exceed amount available congestion: packets queue, wait for link use store and forward: packets move one hop at a Node receives complete packet before forwarding Switching: Statistical Multiplexing A B 10 Mb/s Ethernet queue of packets waiting for output link statistical multiplexing 1.5 Mb/s D C Note: transmission i delay is L/R Sequence of A & B packets does not have fixed pattern statistical multiplexing. E 19 20 switching versus circuit switching switching allows more users to use network! 1 Mb/s link each user: 100 kb/s when active active 10% of circuit-switching: N users 10 users packet switching: with 35 users, probability > 10 active less than.0004 1 Mbps link switching versus circuit switching Is packet switching a slam dunk winner? Great for bursty data resource sharing simpler, no call setup Excessive congestion: packet delay and loss protocols needed for reliable data transfer, congestion control Challenge: How to provide circuit-like behavior where needed? guarantees needed for audio/video apps 21 22 Circuit vs. Switching (1) Circuit Switching Dedicated link Dedicated switch capacity Low link utilization Low overall utilization Switching Better link utilization Better overall utilization Need for congestion control Need to identify to which call a packet belongs 23 -switched : forwarding Goal: move packets through routers from source to destination we ll study several path selection (i.e. routing) algorithms Note distinction between routing & forwarding datagram network: (aka dynamic routing) destination address in packet determines next hop routes may change during session analogy: driving, asking directions virtual circuit network: (aka virtual circuit routing) each packet carries tag (virtual circuit ID), tag determines next hop fixed path determined at call setup, remains fixed thru call routers maintain per-call state 24 4
Message vs. s vs. Cells Message Message Entity with some application/protocol defined meaning s Chunks of data into which messages are split Can be further decomposed, e.g., into smaller packets or cells (small packets, ATM-cell: 53 bytes) 25 FDM Network Taxonomy Circuit-switched Telecommunication TDM -switched Networks with VCs Datagram Networks 26 Summary Terminology: hosts (end systems), communication links, routers, transmission rates, packets, internet vs. intranet vs. the Internet Protocols: protocols define format, order of messages sent and received among network entities, and actions taken on msg transmission, receipt View from network edge: Client/server, peer2peer, other models Service view Communication infrastructure provide connection-oriented + connectionless service View from network core: Circuit-switching vs packet-switching Datagram network vs. virtual-circuit 27 5