1. 1 Protocol “Layers” Networks are complex! r many “pieces”: m hosts m routers m links of various media m applications m protocols m hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks?

2. 2 Organization of air travel r a series of steps ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing

3. 3 Organization of air travel : a different view Layers: each layer implements a service m via its own internal-layer actions m relying on services provided by layer below ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing

4. 4 Layered air travel: services Counter-to-counter delivery of person+bags baggage-claim-to-baggage-claim delivery people transfer: loading gate to arrival gate runway-to-runway delivery of plane airplane routing from source to destination

5. 5 Distributed implementation of layer functionality ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing Departing airport arriving airport intermediate air traffic sites airplane routing

6. 6 Why layering? Dealing with complex systems: r explicit structure allows identification, relationship of complex system’s pieces m layered reference model for discussion r modularization eases maintenance, updating of system m change of implementation of layer’s service transparent to rest of system m e.g., change in gate procedure doesn’t affect rest of system r layering considered harmful?

7. 7 Internet protocol stack r application: supporting network applications m ftp, smtp, http r transport: host-host data transfer m tcp, udp r network: routing of datagrams from source to destination m ip, routing protocols r link: data transfer between neighboring network elements m ppp, ethernet r physical: bits “on the wire” application transport network link physical

8. 8 Layering: logical communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical Each layer: r distributed r “entities” implement layer functions at each node r entities perform actions, exchange messages with peers

9. 9 Layering: logical communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical data E.g.: transport r take data from app r add addressing, reliability check info to form “datagram” r send datagram to peer r wait for peer to ack receipt r analogy: post office data transport ack

10. 10 Layering: physical communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical data

11. 11 Protocol layering and data Each layer takes data from above r adds header information to create new data unit r passes new data unit to layer below application transport network link physical application transport network link physical source destination M M M M H t H t H n H t H n H l M M M M H t H t H n H t H n H l message segment datagram frame

12. 12 Protocol Data Units r The combination of data from the next higher layer and control information is referred to as PDU. m Control Information in the Transport Layer may include: Destination Service Access Point (DSAP) Sequence number Error-detection code

13. 13 Internet structure: network of networks r roughly hierarchical r national/international backbone providers (NBPs) m e.g. BBN/GTE, Sprint, AT&T, IBM, UUNet m interconnect (peer) with each other privately, or at public Network Access Point (NAPs) r regional ISPs m connect into NBPs r local ISP, company m connect into regional ISPs NBP A NBP B NAP regional ISP local ISP local ISP

14. 14 National Backbone Provider e.g. BBN/GTE US backbone network

15. 15 Internet History r 1961: Kleinrock - queueing theory shows effectiveness of packet- switching r 1964: Baran - packet- switching in military nets r 1967: ARPAnet conceived by Advanced Reearch Projects Agency r 1969: first ARPAnet node operational r 1972: m ARPAnet demonstrated publicly m NCP (Network Control Protocol) first host- host protocol m first e-mail program m ARPAnet has 15 nodes 1961-1972: Early packet-switching principles

16. 16 Internet History r 1970: ALOHAnet satellite network in Hawaii r 1973: Metcalfe’s PhD thesis proposes Ethernet r 1974: Cerf and Kahn - architecture for interconnecting networks r late70’s: proprietary architectures: DECnet, SNA, XNA r late 70’s: switching fixed length packets (ATM precursor) r 1979: ARPAnet has 200 nodes Cerf and Kahn’s internetworking principles: m minimalism, autonomy - no internal changes required to interconnect networks m best effort service model m stateless routers m decentralized control define today’s Internet architecture 1972-1980: Internetworking, new and proprietary nets

17. 17 Internet History r 1983: deployment of TCP/IP r 1982: smtp e-mail protocol defined r 1983: DNS defined for name-to-IP- address translation r 1985: ftp protocol defined r 1988: TCP congestion control r new national networks: Csnet, BITnet, NSFnet, Minitel r 100,000 hosts connected to confederation of networks 1980-1990: new protocols, a proliferation of networks

18. 18 Internet History r Early 1990’s: ARPAnet decomissioned r 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) r early 1990s: WWW m hypertext [Bush 1945, Nelson 1960’s] m HTML, http: Berners-Lee m 1994: Mosaic, later Netscape m late 1990’s: commercialization of the WWW Late 1990’s: r est. 50 million computers on Internet r est. 100 million+ users r backbone links runnning at 1 Gbps 1990’s: commercialization, the WWW

19. 19 ATM: Asynchronous Transfer Mode nets Internet: r today’s de facto standard for global data networking 1980’s: r telco’s develop ATM: competing network standard for carrying high-speed voice/data r standards bodies: m ATM Forum m ITU ATM principles: r small (48 byte payload, 5 byte header) fixed length cells (like packets) m fast switching m small size good for voice r virtual-circuit network: switches maintain state for each “call” r well-defined interface between “network” and “user” (think of telephone company)

20. 20 ATM layers r ATM Adaptation Layer (AAL): interface to upper layers m end-system m segmentation/rea ssembly r ATM Layer: cell switching r Physical AAL ATM physical AAL ATM physical AAL ATM physical AAL ATM physical ATM physical Where’s the application? r ATM: lower layer r functionality only r IP-over ATM: later application TCP/UDP IP application TCP/UDP IP application TCP/UDP IP application TCP/UDP IP

21. 21 Summary Covered a “ton” of material! r Internet overview r what’s a protocol? r network edge, core, access network r performance: loss, delay r layering and service models r backbones, NAPs, ISPs r history r ATM network You now hopefully have: r context, overview, “feel” of networking r more depth, detail later in course