CSE 123bCSE 123bCommunications SoftwareCommunications SoftwareSpring 2004Spring 2004Lecture 1: Introduction & ReviewLecture 1: Introduction & ReviewStefan SavageStefan SavageApril 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 2Class OverviewClass Overviewz Course Material◆ Class lectures, textbook readings, and handoutsz Course Assignments◆ Homework questions from book and handouts» Handed out on Tuesday due the following Tuesday◆ A small number of programming projectsz Exams◆ Midterm and Final◆ I will be explicit about what is covered in eachApril 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 3Some hintsSome hintsz Come to lecture◆ Yes, I will distribute the slides online, and yes the material is in the book◆ However, lecture materials are the basis for examsz Do the homework◆ You will have a hard time with the exams without doing the homework◆ Its 25% of your grade (easily the difference between an A and C)April 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 4Some hints (2)Some hints (2)z Ask questions◆ In class, via e-mail and at office hours ◆ Inevitably you won’t understand something… that’s my fault, but you need to helpz Start assignments early◆ There is a statistical relationship between when you start and what grade you get.z SleepApril 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 5Course materialCourse materialz The key aspects of modern computer networks and network services◆ Reliable communication◆ Congestion control◆ Routing (intradomain and interdomain)◆ Mobility, Naming◆ Address translation, Time synchronization◆ Web service, caching, load balancing, CDNs◆ Peer-to-peer networks◆ Security◆ ???April 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 6We will not coverWe will not coverz Queuing theoryz Signalsz Hardware designz Switching designz Physical/data link layersApril 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 7Overall goalsOverall goalsz Understand how to large scale, heterogeneousdistributed networks are built◆ Fundamental problems◆ Established design principles◆ Standard Internet protocols and implementationsApril 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 8Large scale?Large scale?April 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 9Large scale? (2)Large scale? (2)April 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 10Heterogeneous?Heterogeneous?z Homogenous network: the telephone system◆ Designed for making phone calls◆ Known call duration distribution, bandwidth, service constraints, service modelz Homogenous network: the Internet◆ Supports E-mail, web, e-commerce, audio, video, multi-player games…◆ Few underlying assumptions – a strength and a weakn essApril 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 11Distributed?Distributed?z Decentralized components ◆ Must update/manage changes in statez Long communication latency◆ Actions take timez Partial failures ◆ Must tolerate failures“A distributed system is a system in which I can’t do my work because some computer has filed that I’ve never even heard of” – Leslie LamportApril 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 12Some reviewSome reviewz Elementary componentsz Circuit switching vs packet switchingz Basic network model/metricsz Layering/protocols◆ Layering by example: fetching a Web pageApril 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 13Network componentsNetwork componentsz Hosts: endpoints that communicate◆ e.g. workstation, server, PDAz Links: transmission medium◆ e.g. Ethernet, 802.11b, FDDIz Routers/Switches: moves bits between links◆ Circuit switching: guaranteed channel for a session (Telephone system)◆ Packet switching: statistical multiplexing of independent pieces of data (Internet)April 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 14Circuit SwitchingCircuit Switchingz Three phases1. circuit establishment (dial)2. data transfer (talk) 3. circuit termination (hang up)z If circuit not available: “Busy signal”z Examples◆ Telephone networks◆ ISDN (Integrated Services Digital Networks)April 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 15Circuit SwitchingCircuit Switchingz A node (switch) in a circuit switching networkincoming links outgoing linksNodeSlide courtesy Ion StoicaApril 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 16Circuit switching: Circuit switching: time division multiplexingtime division multiplexingz Time divided in frames and frames divided in slotsz Relative slot position inside a frame determineswhich conversation the data belongs toz Needs synchronization between sender and receiverz In case of non-permanent conversations◆ Needs to dynamic bind a slot to a conservation◆ How to do this? Slide courtesy Ion StoicaApril 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 17Packet SwitchingPacket Switchingz Data is sent in a bundle of bit-sequences, called a packet.z Packets have the following structure:» Header and Trailer carry control information (e.g., destination address, check sum)z Each packet is passed through the network from node to node along some path (Routing)z At each node the entire packet is received, stored briefly, and then forwarded to the next node (Store-and-Forward Networks)z Typically no capacity is allocated for packetsHeader DataTrailerSlide courtesy Ion StoicaApril 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 18Packet SwitchingPacket Switchingz A node in a packet switching networkincoming links outgoing linksNodeMemorySlide courtesy Ion StoicaApril 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 19Packet Switching: Packet Switching: Statistical multiplexingStatistical multiplexingz Data from any conversation can be transmitted at any given timez How to tell them apart?◆ use header) to describe dataSlide courtesy Ion StoicaApril 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 20Pro/cons of packet switchingPro/cons of packet switchingz Efficiency◆ Can share network up to its capacity – no overhead for reserving bandwidth that is unused◆ Can support many different service typesz Low complexity◆ Don’t need to maintain state about each “call”z Harder to guarantee bandwidth/delayWe will focus on packet switching in this classApril 5, 2004 CSE 123b -- Lecture 1 – Introduction and Review 21Simple network