Introduction1-1 Chapter 1 Computer Networks and the Internet Computer Networking: A Top Down Approach Featuring the Internet, 2 nd edition. Jim Kurose, Keith Ross Addison-Wesley, July A note on the use of these ppt slides: We’re making these slides freely available to all (faculty, students, readers). They’re in powerpoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following:  If you use these slides (e.g., in a class) in substantially unaltered form, that you mention their source (after all, we’d like people to use our book!)  If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material.  This slide show has been modified by Merrie Bergmann 1/26/03 Thanks and enjoy! JFK/KWR All material copyright J.F Kurose and K.W. Ross, All Rights Reserved

Introduction1-2 What’s the Internet: “nuts and bolts” view  millions of connected computing devices: hosts, end-systems m PCs, workstations, servers m PDAs, phones, toasters running network apps  communication links m fiber, copper, radio, satellite m transmission rate = bandwidth  routers: forward packets (chunks of data) local ISP company network regional ISP router workstation server mobile

Introduction1-3

Introduction1-4 “Cool” internet appliances Web-enabled toaster+weather forecaster

Introduction1-5 What’s the Internet: “nuts and bolts” view  protocols control sending, receiving of msgs m e.g., TCP, IP, HTTP, FTP, PPP  Internet: “network of networks” m loosely hierarchical  Internet standards m RFC: Request for comments m IETF: Internet Engineering Task Force ( local ISP company network regional ISP router workstation server mobile

Introduction1-6 What’s a protocol? a human protocol and a computer network protocol: Hi Got the time? 2:00 TCP connection req TCP connection response Get time

Introduction1-7 What’s the Internet: a service view  communication infrastructure enables distributed applications: m Web, , games, e- commerce, database, voting, file (MP3) sharing  communication services provided to apps: m connectionless m connection-oriented m “Loosely speaking, the connection-oriented service guarantees that data transmitted from a sender to a receiver will eventually be delivered to the receiver in order and in its entirety.” (p.5) m Currently, no time delay guarantees!

Introduction1-8 A closer look at network structure:  network edge: applications and hosts  network core: m routers m network of networks  access networks, physical media: communication links

Introduction1-9 The network edge:End systems, clients, and servers  end systems (hosts): m run (distributed) application programs m e.g. Web, m at “edge of network”  client/server model m client host requests, receives service from always-on server m e.g. Web browser/server; client/server  peer-peer model: m minimal (or no) use of dedicated servers m e.g. Napster, Gnutella, KaZaA

Introduction1-10 Network edge: connection-oriented service Goal: data transfer between end systems  handshaking: setup (prepare for) data transfer ahead of time m Hello, hello back human protocol m set up “state” in two communicating hosts  TCP - Transmission Control Protocol m Internet’s connection- oriented service TCP service [RFC 793]  reliable, in-order byte- stream data transfer m loss: acknowledgements and retransmissions  flow control: m sender won’t overwhelm receiver  congestion control: m senders “slow down sending rate” when network congested

Introduction1-11 Network edge: connectionless service Goal: data transfer between end systems m same as before!  UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service m unreliable data transfer m no flow control m no congestion control App’s using TCP:  HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP ( ) App’s using UDP:  streaming media, teleconferencing, DNS, Internet telephony

Introduction1-12 The Network Core  mesh of interconnected routers  the fundamental question: how is data transferred through net? m circuit switching: dedicated circuit per call: telephone net m packet-switching: data sent thru net in discrete “chunks”

Introduction1-13 Network Core: Circuit Switching End-end resources reserved for “call”  link bandwidth  dedicated resources: no sharing  circuit-like (guaranteed) performance  call setup required

Introduction1-14 Network Core: Circuit Switching network resources (e.g., bandwidth) divided into “pieces”  pieces allocated to calls  resource piece idle if not used by owning call (no sharing)  dividing link bandwidth into “pieces” m frequency division m time division

Introduction1-15 Circuit Switching: FDM and TDM FDM frequency time TDM frequency time 4 users Example: