Internet History 1961 -1972 Early packet-switching principles r

Internet History 1961 -1972: Early packet-switching principles r 1961: Kleinrock - queueing theory shows effectiveness of packetswitching r 1964: Baran - packetswitching in military nets r 1967: ARPAnet conceived by Advanced Reearch Projects Agency r 1969: first ARPAnet node operational r 1972: m m ARPAnet demonstrated publicly NCP (Network Control Protocol) first host protocol first e-mail program ARPAnet has 15 nodes 1: Introduction 1

Internet History 1972 -1980: Internetworking, new and proprietary nets r 1970: ALOHAnet satellite r r r network in Hawaii 1973: Metcalfe’s Ph. D thesis proposes Ethernet 1974: Cerf and Kahn architecture for interconnecting networks late 70’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: 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 1: Introduction 2

Internet History 1980 -1990: new protocols, a proliferation of networks r 1983: deployment of r r 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 r new national networks: Csnet, BITnet, NSFnet, Minitel r 100, 000 hosts connected to confederation of networks 1: Introduction 3

Internet History 1990’s: commercialization, the WWW r Early 1990’s: ARPAnet decomissioned r 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) r early 1990 s: 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 1: Introduction 4

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 m ATM Forum ITU ATM principles: r small (48 byte payload, 5 byte header) fixed length cells (like packets) m m fast switching 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: Introduction 5

ATM layers r ATM Adaptation Layer (AAL): interface to upper layers m m end-system segmentation/rea ssembly r ATM Layer: cell switching r Physical application TCP/UDP IP AAL ATM physical Where’s the application? r ATM: lower layer r functionality only r IP-over ATM: later ATM physical application TCP/UDP IP AAL ATM physical 1: Introduction 6

Summary on Introduction Covered a “ton” of material! r Internet overview r what’s a protocol? r network edge, core, r r r access network performance: loss, delay layering and service models backbones, NAPs, ISPs history ATM network You now hopefully have: r context, overview, “feel” of networking r more depth, detail later in course 1: Introduction 7

Application Layer Goals: r conceptual + More goals r specific protocols: implementation aspects of network application protocols m client server paradigm m service models r learn about protocols by examining popular r application-level protocols m m m http ftp smtp pop dns programming network applications m socket programming 1: Introduction 8

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. , email, 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 1: Introduction 9

Client-server paradigm Typical network app has two pieces: client and server Client: r initiates contact with server (“speaks first”) r typically requests service from server, r e. g. : request WWW page, send email Server: r provides requested service to client r e. g. , sends requested WWW page, receives/stores received email application transport network data link physical request reply application transport network data link physical 1: Introduction 10

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 m IP address of host running other process “port number” - allows receiving host to determine to which local process the message should be delivered … lots more on this later. 1: Introduction 11

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 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 Timing r some apps (e. g. , Internet telephony, interactive games) require low delay to be “effective” 1: Introduction 12

Transport service requirements of common apps Data loss Bandwidth Time Sensitive file transfer e-mail Web documents real-time audio/video no loss-tolerant no no no yes, 100’s msec stored audio/video interactive games financial apps loss-tolerant no loss elastic audio: 5 Kb-1 Mb video: 10 Kb-5 Mb same as above few Kbps up elastic Application yes, few secs yes, 100’s msec yes and no 1: Introduction 13

Internet apps: their protocols and transport protocols Application e-mail remote terminal access Web file transfer streaming multimedia remote file server Internet telephony Application layer protocol Underlying transport protocol smtp [RFC 821] telnet [RFC 854] http [RFC 2068] ftp [RFC 959] proprietary (e. g. Real. Networks) NSF proprietary (e. g. , Vocaltec) TCP TCP TCP or UDP typically UDP 1: Introduction 14