1: Introduction1 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: Introduction2 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: Introduction3 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: Introduction4 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: Introduction5 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: Introduction6 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: Introduction7 Summary on Introduction 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

1: Introduction8 Application Layer Goals: r conceptual + implementation aspects of network application protocols m client server paradigm m service models r learn about protocols by examining popular application-level protocols More goals r specific protocols: m http m ftp m smtp m pop m dns r programming network applications m socket programming

1: Introduction9 Applications and application-layer protocols Application: communicating, distributed processes m running in network hosts in “user space” m exchange messages to implement app m e.g., , file transfer, the Web Application-layer protocols m one “piece” of an app m define messages exchanged by apps and actions taken m user services provided by lower layer protocols application transport network data link physical application transport network data link physical application transport network data link physical

1: Introduction10 Client-server paradigm Typical network app has two pieces: client and server application transport network data link physical application transport network data link physical Client: r initiates contact with server (“speaks first”) r typically requests service from server, r e.g.: request WWW page, send Server: r provides requested service to client r e.g., sends requested WWW page, receives/stores received request reply

1: Introduction11 Application-layer protocols (cont). API: application programming interface r defines interface between application and transport layer r socket: Internet API m two processes communicate by sending data into socket, reading data out of socket Q: how does a process “identify” the other process with which it wants to communicate? m IP address of host running other process m “port number” - allows receiving host to determine to which local process the message should be delivered … lots more on this later.

1: Introduction12 What transport service does an app need? Data loss r some apps (e.g., audio) can tolerate some loss r other apps (e.g., file transfer, telnet) require 100% reliable data transfer Timing r some apps (e.g., Internet telephony, interactive games) require low delay to be “effective” Bandwidth r some apps (e.g., multimedia) require minimum amount of bandwidth to be “effective” r other apps (“elastic apps”) make use of whatever bandwidth they get

1: Introduction13 Transport service requirements of common apps Application file transfer Web documents real-time audio/video stored audio/video interactive games financial apps Data loss no loss loss-tolerant no loss Bandwidth elastic audio: 5Kb-1Mb video:10Kb-5Mb same as above few Kbps up elastic Time Sensitive no yes, 100’s msec yes, few secs yes, 100’s msec yes and no

1: Introduction14 Internet apps: their protocols and transport protocols Application remote terminal access Web file transfer streaming multimedia remote file server Internet telephony Application layer protocol smtp [RFC 821] telnet [RFC 854] http [RFC 2068] ftp [RFC 959] proprietary (e.g. RealNetworks) NSF proprietary (e.g., Vocaltec) Underlying transport protocol TCP TCP or UDP typically UDP