1: Introduction1 Protocol “Layers” Networks are complex! r many “pieces”: m hosts m routers m links of various media m applications m protocols m hardware, software Layering: r The network is organized in layers, with each layer providing services to the layers above r Each layer is distributed across many nodes r If the layering is not done properly, the result is inefficiency

1: Introduction2 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

1: Introduction3 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

1: Introduction4 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

1: Introduction5 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

1: Introduction6 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

1: Introduction7 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

1: Introduction8 National Backbone Provider e.g. BBN/GTE US backbone network

1: Introduction9 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 program m ARPAnet has 15 nodes : Early packet-switching principles

1: Introduction10 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 : Internetworking, new and proprietary nets

1: Introduction11 Internet History r 1983: deployment of TCP/IP r 1982: smtp 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 : new protocols, a proliferation of networks

1: Introduction12 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

1: Introduction13 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)

1: Introduction14 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

1: Introduction15 Chapter 1: 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