EEC-484/584 Computer Networks

1. EEC-484/584Computer Networks Lecture 3 Wenbing Zhao wenbing@ieee.org (Part of the slides are based on Drs. Kurose & Ross’s slides for their Computer Networking book)

2. Outline • Delay, loss and throughput in packet-switched networks • Protocol layers, reference models • Network standards • Internet history EEC-484/584: Computer Networks

3. pipe that can carry fluid at rate Rsbits/sec) pipe that can carry fluid at rate Rcbits/sec) Throughput • Throughput:rate (bits/time unit) at which bits transferred between sender/receiver • Instantaneous: rate at given point in time • Average: rate over longer period of time link capacity Rcbits/sec link capacity Rsbits/sec server, with file of F bits to send to client server sends bits (fluid) into pipe EEC-484/584: Computer Networks

4. Rs > RcWhat is average end-end throughput? Rsbits/sec Rcbits/sec Rcbits/sec bottleneck link link on end-end path that constrains end-end throughput Throughput (more) • Rs < RcWhat is average end-end throughput? Rsbits/sec EEC-484/584: Computer Networks

5. Throughput: Internet Scenario • Per-connection end-end throughput: min(Rc,Rs,R/10) • In practice: Rc or Rs is often bottleneck Rs Rs Rs R Rc Rc Rc 10 connections (fairly) share backbone bottleneck link Rbits/sec EEC-484/584: Computer Networks

6. Networks are complex! many “pieces”: hosts routers links of various media applications protocols hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks? Protocol “Layers” EEC-484/584: Computer Networks

7. ticket (complain) baggage (claim) gates (unload) runway landing airplane routing ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing airplane routing Organization of Air Travel • A series of steps EEC-484/584: Computer Networks

8. ticket ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing baggage gate airplane routing airplane routing takeoff/landing airplane routing departure airport intermediate air-traffic control centers arrival airport Layering of Airline Functionality Layers: each layer implements a service • Via its own internal-layer actions • Relying on services provided by layer below EEC-484/584: Computer Networks

9. Why Layering? Dealing with complex systems: • Explicit structure allows identification, relationship of complex system’s pieces • Layered reference model for discussion • Modularization eases maintenance, updating of system • Change of implementation of layer’s service transparent to rest of system • E.g., change in gate procedure doesn’t affect rest of system EEC-484/584: Computer Networks

10. Application: supporting network applications HTTP, DNS, SMTP Transport: process-process data transfer TCP, UDP Network: routing of datagrams from source to destination IP, routing protocols Link: data transfer between neighboring network elements PPP, Ethernet Physical: bits “on the wire” Application Transport Network Link Physical Internet Protocol Stack EEC-484/584: Computer Networks

11. Presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions Session:synchronization, checkpointing, recovery of data exchange Internet stack “missing” these layers! these services, if needed, must be implemented in application Application Presentation Session Transport Network Link Physical ISO/OSI Reference Model EEC-484/584: Computer Networks

12. network link physical link physical M M M Ht M Hn Hn Hn Hn Ht Ht Ht Ht M M M M Ht Ht Hn Hl Hl Hl Hn Hn Hn Ht Ht Ht M M M source Encapsulation message application transport network link physical segment datagram frame switch destination application transport network link physical router EEC-484/584: Computer Networks

13. Network Standardization • Why standard? • Only way to achieve interoperability • Standards also increase the market for products adhering to them • Two kinds of standards • De facto – from the fact (standards that just happened) • De jure – by law (formal, legal standards adopted by authorized organization) EEC-484/584: Computer Networks

14. United Nations ITU - International Telecommunications Union CCITT/ITU-T – telephone and data communications Treaty Organization between Nations EEC-484/584: Computer Networks

15. ISO (International Standards Organization) issues standards on wide range of topics 200 TC (Technical Committees) TC97 – computers and info processing SC (Subcommittees) WG (Working Groups) ANSI (American National Standards Institute) Voluntary, Nontreaty Organization EEC-484/584: Computer Networks

16. IEEE 802 Standards EEC-484/584: Computer Networks

17. Internet Standard Body • Internet Society (used to be Internet Architecture Board) • Internet Research Task Force (IRTF) • Concentrate on long term research • Internet Engineering Task Force (IETF) • Deal with short term engineering issues • Standardization process • Proposed standard: request for comments (RFCs) • Draft standard: after >= 4 month test by >= 2 sites • Internet standard: if convinced the idea is sound EEC-484/584: Computer Networks

18. 1961: Kleinrock - queueing theory shows effectiveness of packet-switching 1964: Baran - packet-switching in military nets 1967: ARPAnet conceived by Advanced Research Projects Agency 1969: first ARPAnet node operational 1972: ARPAnet public demonstration NCP (Network Control Protocol) first host-host protocol first e-mail program ARPAnet has 15 nodes Internet History 1961-1972: Early packet-switching principles EEC-484/584: Computer Networks

19. 1970: ALOHAnet satellite network in Hawaii 1974: Cerf and Kahn - architecture for interconnecting networks 1976: Ethernet at Xerox PARC late70’s: proprietary architectures: DECnet, SNA, XNA late 70’s: switching fixed length packets (ATM precursor) 1979: ARPAnet has 200 nodes Cerf and Kahn’s internetworking principles: Minimalism, autonomy - no internal changes required to interconnect networks Best effort service model Stateless routers Decentralized control Define today’s internet architecture Internet History 1972-1980: Internetworking, new and proprietary nets EEC-484/584: Computer Networks

20. 1983: deployment of TCP/IP 1982: SMTP e-mail protocol defined 1983: DNS defined for name-to-IP-address translation 1985: FTP protocol defined 1988: TCP congestion control New national networks: Csnet, BITnet, NSFnet, Minitel 100,000 hosts connected to confederation of networks Internet History 1980-1990: new protocols, a proliferation of networks EEC-484/584: Computer Networks

21. Early 1990’s: ARPAnet decommissioned 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) Early 1990s: Web Hypertext [Bush 1945, Nelson 1960’s] HTML, HTTP: Berners-Lee 1994: Mosaic, later Netscape Late 1990’s: commercialization of the Web Late 1990’s – 2000’s: More killer apps: instant messaging, P2P file sharing Network security to forefront Est. 50 million host, 100 million+ users Backbone links running at Gbps Internet History 1990, 2000’s: commercialization, the Web, new apps EEC-484/584: Computer Networks

22. 2007: ~500 million hosts Voice, Video over IP P2P applications: BitTorrent (file sharing) Skype (VoIP), PPLive (video) More applications: youtube, gaming Wireless, mobility Internet History EEC-484/584: Computer Networks

23. Covered a “ton” of material! Internet overview What’s a protocol? Network edge, core, access network Packet-switching versus circuit-switching Internet structure Performance: loss, delay, throughput Layering, reference models Networking standards History You now have: Context, overview, “feel” of networking More depth, detail to follow! Introduction: Summary EEC-484/584: Computer Networks

24. Exercise • A system has an n-layer protocol hierarchy. Applications generate messages of length M bytes. At each of the layers, an h-byte header is added. What fraction of the network bandwidth is filled with headers? EEC-484/584: Computer Networks