EEC-484/584 Computer Networks

EEC-484/584EEC-484/584Computer NetworksComputer Networks

Lecture 3Lecture 3

Wenbing ZhaoWenbing Zhao

[email protected](Part of the slides are based on Drs. Kurose & (Part of the slides are based on Drs. Kurose &

RossRoss’’s slides for their s slides for their Computer Networking Computer Networking book)book)

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04/20/2304/20/23 EEC-484/584: Computer NetworksEEC-484/584: Computer Networks

OutlineOutline

• Delay, loss and throughput in packet-switched networks

• Protocol layers, reference models

• Network standards

• Internet history

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EEC-484/584: Computer NetworksEEC-484/584: Computer Networks

ThroughputThroughput

• Throughput: rate (bits/time unit) at which bits transferred between sender/receiver– Instantaneous: rate at given point in time– Average: rate over longer period of time

server, withfile of F bits

to send to client

link capacity

Rs bits/sec

link capacity

Rc bits/sec pipe that can carry

fluid at rate

Rs bits/sec)

pipe that can carryfluid at rate

Rc bits/sec)

server sends bits

(fluid) into pipe

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Throughput (more)Throughput (more)

• Rs < Rc What is average end-end throughput?

Rs bits/sec Rc bits/sec

• Rs > Rc What is average end-end throughput?

Rs bits/sec Rc bits/sec

link on end-end path that constrains end-end throughput

bottleneck link

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Throughput: Internet ScenarioThroughput: Internet Scenario

10 connections (fairly) share backbone bottleneck link R

bits/sec

Rs

Rs

Rs

Rc

Rc

Rc

R

• Per-connection end-end throughput: min(Rc,Rs,R/10)

• In practice: Rc or Rs is often bottleneck

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Protocol “Layers”Protocol “Layers”Networks are complex! • many “pieces”:

– hosts– routers– links of various media– applications– protocols– hardware, software

Question: Is there any hope of organizing structure of

network?

Or at least our discussion of networks?

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Organization of Air TravelOrganization of Air Travel

• A series of steps

ticket (purchase)

baggage (check)

gates (load)

runway takeoff

airplane routing

ticket (complain)

baggage (claim)

gates (unload)

runway landing

airplane routing

airplane routing

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ticket (purchase)

baggage (check)

gates (load)

runway (takeoff)

airplane routing

departureairport

arrivalairport

intermediate air-trafficcontrol centers

airplane routing airplane routing

ticket (complain)

baggage (claim

gates (unload)

runway (land)

airplane routing

ticket

baggage

gate

takeoff/landing

airplane routing

Layering of Airline FunctionalityLayering of Airline Functionality

Layers: each layer implements a service

– Via its own internal-layer actions– Relying on services provided by layer below

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Why Layering?Why Layering?Dealing with complex systems:• Explicit structure allows identification,

relationship of complex system’s pieces– Layered reference model for discussion

• Modularization eases maintenance, updating of system– Change of implementation of layer’s service

transparent to rest of system– E.g., change in gate procedure doesn’t affect rest

of system

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1010


Internet Protocol StackInternet Protocol Stack• Application: supporting network applications

– HTTP, DNS, SMTP

• Transport: process-process data transfer– TCP, UDP

• Network: routing of datagrams from source to destination– IP, routing protocols

• Link: data transfer between neighboring network elements– PPP, Ethernet

• Physical: bits “on the wire”

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ISO/OSI Reference ModelISO/OSI Reference Model• Presentation: allow applications to

interpret meaning of data, e.g., encryption, compression, machine-specific conventions

• Session: synchronization, checkpointing, recovery of data exchange

• Internet stack “missing” these layers!– these services, if needed, must be

implemented in application

Application

Presentation

Session

Transport

Network

Link

Physical

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source

application

transportnetwork

linkphysical

HtHn M

segment Ht

datagram

destination

application

transportnetwork

linkphysical

HtHnHl M

HtHn M

Ht M

M

networklink

physical

linkphysical

HtHnHl M

HtHn M

HtHn M

HtHnHl M

router

switch

EncapsulationEncapsulationmessage M

Ht M

Hn

frame

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Network StandardizationNetwork Standardization

• Why standard?– Only way to achieve interoperability– Standards also increase the market for

products adhering to them– Two kinds of standards

• De facto – from the fact (standards that just happened)

• De jure – by law (formal, legal standards adopted by authorized organization)


1414

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Treaty Organization between Treaty Organization between NationsNations

United Nations

ITU - International Telecommunications Union

CCITT/ITU-T – telephone and data communications


1515

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Voluntary, Nontreaty OrganizationVoluntary, Nontreaty Organization

ISO (International Standards Organization)issues standards on wide range of topics

200 TC (Technical Committees)

TC97 – computers and info processing

SC (Subcommittees)

WG (Working Groups)

ANSI (American National Standards Institute)


1616

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IEEE 802 StandardsIEEE 802 Standards


1717

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Internet Standard BodyInternet Standard Body• Internet Society (used to be Internet Architecture

Board)– Internet Research Task Force (IRTF)

• Concentrate on long term research

– Internet Engineering Task Force (IETF)• Deal with short term engineering issues

• Standardization process– Proposed standard: request for comments (RFCs)– Draft standard: after >= 4 month test by >= 2 sites– Internet standard: if convinced the idea is sound


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Internet HistoryInternet History

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

• 1964: Baran - packet-switching in military nets

• 1967: ARPAnet conceived by Advanced Research Projects Agency

• 1969: first ARPAnet node operational

• 1972: – ARPAnet public demonstration– NCP (Network Control Protocol)

first host-host protocol – first e-mail program– ARPAnet has 15 nodes

1961-1972: Early packet-switching principles

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• 1970: ALOHAnet satellite network in Hawaii

• 1974: Cerf and Kahn - architecture for interconnecting networks

• 1976: Ethernet at Xerox PARC• 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

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2020



• 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

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• Early 1990’s: ARPAnet decommissioned

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

• Early 1990s: Web– Hypertext [Bush 1945, Nelson

1960’s]– HTML, HTTP: Berners-Lee– 1994: Mosaic, later Netscape– Late 1990’s: commercialization

of the Web

Late 1990’s – 2000’s:• More killer apps: instant

messaging, P2P file sharing• Network security to forefront• Est. 50 million host, 100

million+ users• Backbone links running at

Gbps

1990, 2000’s: commercialization, the Web, new apps

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2007:• ~500 million hosts• Voice, Video over IP• P2P applications: BitTorrent (file sharing) Skype

(VoIP), PPLive (video)• More applications: youtube, gaming• Wireless, mobility

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Introduction: SummaryIntroduction: SummaryCovered a “ton” of material!• Internet overview• What’s a protocol?• Network edge, core, access

network– Packet-switching versus

circuit-switching– Internet structure

• Performance: loss, delay, throughput

• Layering, reference models• Networking standards• History

You now have: • Context, overview,

“feel” of networking• More depth, detail to

follow!

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04/20/2304/20/23 EEC-484/584: Computer NetworksEEC-484/584: Computer Networks

ExerciseExercise

• A system has an n-layer protocol hierarchy. Applications generate messages of length M bytes. At each of the layers, an h-byte header is added. What fraction of the network bandwidth is filled with headers?

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EEC-484/584 Computer Networks

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