1: Introduction 1

Internet History

1961: Kleinrock - queueing theory shows effectiveness of packet-switching

1964: Baran - packet-switching in military nets

1967: ARPAnet conceived by Advanced Reearch Projects Agency

1969: first ARPAnet node operational

1972: ARPAnet

demonstrated publicly NCP (Network Control

Protocol) first host-host protocol

first e-mail program ARPAnet has 15 nodes

1961-1972: Early packet-switching principles

1: Introduction 2

Internet History

1970: ALOHAnet satellite network in Hawaii

1973: Metcalfe’s PhD thesis proposes Ethernet

1974: Cerf and Kahn - architecture for interconnecting networks

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

1972-1980: Internetworking, new and proprietary nets

1: Introduction 3

Internet History

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

1980-1990: new protocols, a proliferation of networks

1: Introduction 4

Internet History

Early 1990’s: ARPAnet decomissioned

1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)

early 1990s: WWW hypertext [Bush 1945,

Nelson 1960’s] HTML, http: Berners-Lee 1994: Mosaic, later

Netscape late 1990’s:

commercialization of the WWW

Late 1990’s: est. 50 million

computers on Internet est. 100 million+

users backbone links

runnning at 1 Gbps

1990’s: commercialization, the WWW

1: Introduction 5

ATM: Asynchronous Transfer Mode nets

Internet: today’s de facto

standard for global data networking

1980’s: telco’s develop ATM:

competing network standard for carrying high-speed voice/data

standards bodies: ATM Forum ITU

ATM principles: small (48 byte payload, 5

byte header) fixed length cells (like packets) fast switching small size good for voice

virtual-circuit network: switches maintain state for each “call”

well-defined interface between “network” and “user” (think of telephone company)

1: Introduction 6

ATM layers

ATM Adaptation Layer (AAL): interface to upper layers end-system segmentation/

reassembly ATM Layer: cell

switching Physical

AALATM

physical

AALATM

physical

AALATM

physical

AALATM

physical

ATMphysical

Where’s the application? ATM: lower layer functionality only IP-over ATM: later

applicationTCP/UDP

IP

applicationTCP/UDP

IP

applicationTCP/UDP

IP

applicationTCP/UDP

IP

1: Introduction 7

Summary on IntroductionCovered a “ton” of

material! Internet overview what’s a protocol? network edge, core,

access network performance: loss,

delay layering and service

models backbones, NAPs, ISPs history ATM network

You now hopefully have:

context, overview, “feel” of networking

more depth, detail later in course

1: Introduction 8

Application LayerGoals: conceptual +

implementation aspects of network application protocols client server

paradigm service models

learn about protocols by examining popular application-level protocols

More goals specific protocols:

http ftp smtp pop dns

programming network applications socket programming

1: Introduction 9

Applications and application-layer protocols

Application: communicating, distributed processes running in network hosts

in “user space” exchange messages to

implement app e.g., email, file transfer,

the WebApplication-layer protocols

one “piece” of an app define messages

exchanged by apps and actions taken

user services provided by lower layer protocols

application

transportnetworkdata linkphysical

application

transportnetworkdata linkphysical

application

transportnetworkdata linkphysical

1: Introduction 10

Client-server paradigm

Typical network app has two pieces: client and server

application

transportnetworkdata linkphysical

application

transportnetworkdata linkphysical

Client: initiates contact with server

(“speaks first”) typically requests service

from server, e.g.: request WWW page,

send emailServer: provides requested service

to client e.g., sends requested WWW

page, receives/stores received email

request

reply

1: Introduction 11

Application-layer protocols (cont).

API: application programming interface

defines interface between application and transport layer

socket: Internet API 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? 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 12

What transport service does an app need?Data loss some apps (e.g., audio) can

tolerate some loss other apps (e.g., file

transfer, telnet) require 100% reliable data transfer Timing

some apps (e.g., Internet telephony, interactive games) require low delay to be “effective”

Bandwidth some apps (e.g., multimedia)

require minimum amount of bandwidth to be “effective”

other apps (“elastic apps”) make use of whatever bandwidth they get

1: Introduction 13

Transport service requirements of common apps

Application

file transfere-mail

Web documentsreal-time audio/video

stored audio/videointeractive games

financial apps

Data loss

no lossno lossno lossloss-tolerant

loss-tolerantloss-tolerantno loss

Bandwidth

elasticelasticelasticaudio: 5Kb-1Mbvideo:10Kb-5Mbsame as above few Kbps upelastic

Time Sensitive

nononoyes, 100’s msec

yes, few secsyes, 100’s msecyes and no

1: Introduction 14

Internet apps: their protocols and transport protocols

Application

e-mailremote terminal access

Web file transfer

streaming multimedia

remote file serverInternet telephony

Applicationlayer protocol

smtp [RFC 821]telnet [RFC 854]http [RFC 2068]ftp [RFC 959]proprietary(e.g. RealNetworks)NSFproprietary(e.g., Vocaltec)

Underlyingtransport protocol

TCPTCPTCPTCPTCP or UDP

TCP or UDPtypically UDP