CS 5565 Network Architecture and Protocols

1. CS 5565Network Architecture and Protocols Godmar Back Lecture 2

2. High-level Objectives • Gain theoretical & practical understandings of the basics of networking • Be equipped to start research in communication networks CS 5565 Spring 2006

3. Outline for today • Internet: • “nuts and bolts” view • Service view • Network edge view • Network core view • Types of switching • Assignment: • Do Ethereal Lab 1 (pg 69 in book) • Don’t need to hand it in. CS 5565 Spring 2006

4. millions of connected computing devices: hosts = end systems running network apps communication links fiber, copper, radio, satellite transmission rate = bandwidth routers: forward packets router workstation server mobile local ISP regional ISP company network The Internet: “nuts and bolts” view CS 5565 Spring 2006

5. protocolscontrol sending, receiving of msgs e.g., TCP, IP, HTTP, FTP, PPP Internet: “network of networks” loosely hierarchical public Internet versus private intranets Internet vs internet Internet standards RFC: Request for comments IETF: Internet Engineering Task Force The Internet: “nuts and bolts” view router workstation server mobile local ISP regional ISP company network CS 5565 Spring 2006

6. ESnet vBNS Internet2 Example:Net.Work.Virginia Architecture Backbone / Internet Gateway Source: www.networkvirginia.net Internet SprintLink Router DS3 OC3 Sprint WTN OC3 OC3 Sprint RIC OC3 Sprint ROA

7. communication infrastructure enables distributed applications: Web, email, games, e-commerce, file sharing communication services provided to apps: Connectionless unreliable Connection-oriented reliable The Internet: a service view CS 5565 Spring 2006

8. a human protocol and a computer network protocol: TCP connection response Get http://www.awl.com/kurose-ross Got the time? 2:00 <file> time What’s a protocol? Hi TCP connection req Hi CS 5565 Spring 2006

9. human protocols: “what’s the time?” “I have a question” introductions … 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 What’s a protocol? protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt CS 5565 Spring 2006

10. network edge: applications and hosts network core: routers network of networks access networks, physical media: communication links A closer look at network structure: CS 5565 Spring 2006

11. end systems (hosts): run application programs e.g. Web, email at “edge of network” client/server model 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 The network edge: CS 5565 Spring 2006

12. Goal: data transfer between end systems handshaking: setup (prepare for) data transfer ahead of time Hello, hello back human protocol set up “state” in two communicating hosts TCP - Transmission Control Protocol Internet’s connection-oriented service TCP service[RFC 793] reliable, in-order byte-stream data transfer loss: acknowledgements and retransmissions flow control: sender won’t overwhelm receiver congestion control: senders “slow down sending rate” when network congested Connection-oriented service CS 5565 Spring 2006

13. 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 Connectionless service CS 5565 Spring 2006

14. 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? The Network Core CS 5565 Spring 2006

15. End-end resources reserved for “call” (or session) link bandwidth, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup required Network Core: Circuit Switching CS 5565 Spring 2006

16. network resources (e.g., link bandwidth) divided into “pieces” pieces allocated to calls resource piece idle if not used by owning call (no sharing) Network Core: Circuit Switching • multiplex different calls • frequency division multiplexing (FDM) • time division multiplexing (TDM) • synchronous vs. asynchronous (aka statistical) TDM CS 5565 Spring 2006

17. Example: 4 users FDM frequency time TDM frequency time Circuit Switching: FDM and TDM CS 5565 Spring 2006

18. S(ynchronous) TDM Suppose m slots Total bandwidth 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 bandwidth is R Per channel bandwidth is R/m L bit packet takes Lm/R seconds Computing transmission delay CS 5565 Spring 2006

19. Packet Packet Packet Message vs. Packets vs. Cells • Message • Entity with some application/protocol defined meaning • Packets • 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) Message CS 5565 Spring 2006

20. each end-end data stream divided into packets user A, B packets share network resources each packet uses full link bandwidth resources used as needed no dedicated allocation no resource reservation Network Core: Packet Switching 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 time • Node receives complete packet before forwarding CS 5565 Spring 2006