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CPSC 826Internetworking

A Whirlwind Introduction to the Internet(“Networking Nouns and Verbs”)

Michele WeigleDepartment of Computer Science

Clemson Universitymweigle@cs.clemson.edu

August 20, 2004

http://www.cs.clemson.edu/~mweigle/courses/cpsc826

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A Whirlwind Introduction to the InternetOverview

What’s the Internet What’s a protocol? Network edge Network core Access nets, physical media Performance: loss, delay Protocol layers, service models Backbones, NAPs, ISPs

Introduce themajor nouns and

verbs ofnetworking!local ISP*

companynetwork

regional ISP

*Internet Service Provider

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Just What is the Internet?The “nuts and bolts” view

Millions of connected computingdevices: hosts, end-systems» PCs, workstations, servers» PDAs, phones, toasters running

“network applications”

Communication links» Different media (fiber, copper wire,

radio, satellite)» Different transmission rates – bits

per second (bps) 103 (Kbps) to 106 (Mbps) to 109 (Gbps)

Routers: forward “packets” ofdata though the network

router workstation

server mobile

local ISP

companynetwork

regional ISP

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Protocols: control sending,receiving of messages» E.g., TCP, IP, HTTP, SMTP,

…. Internet: “network of

networks”» Loosely hierarchical» Public Internet versus private

intranet Internet standards

» RFC: Request for comments» IETF: Internet Engineering

Task Force

Just What is the Internet?The “nuts and bolts” view

local ISP

companynetwork

regional ISP

router workstation

server mobile

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A communicationinfrastructure enablingdistributed applications:» WWW, email, games, e-

commerce, database, voting, ...

Communication servicesprovided:» Connectionless: No guarantees» Connection-oriented: Guarantees

order and completeness

Just What is the Internet?The “services” view

local ISP

companynetwork

regional ISP

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The Nuts & Bolts ViewWhat is a protocol?

Main Entry: pro-to-col1: An original draft, minute, or record of a document

or transaction2a: A preliminary memorandum often formulated and signed by

diplomatic negotiators as a basis for a final convention or treaty b: The records or minutes of a diplomatic conference or congress that

show officially the agreements arrived at by the negotiators3a: A code prescribing strict adherence to correct etiquette and

precedence (as in diplomatic exchange and in the military services) b: A set of conventions governing the treatment and especially the

formatting of data in an electronic communications system4: A detailed plan of a scientific or medical experiment, treatment, or

procedure

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The Nuts & Bolts ViewWhat is a protocol?

Human protocols:» “Do you have the time?”» “I have a question”» Introductions

Network protocols:» Machines rather than

humans» All communication

activity in Internetgoverned by protocols

Protocols define format, orderof messages sent and receivedamong network entities, and

actions taken on messagetransmission, receipt

Both:» Specific messages sent» Specific actions taken

when messages (or otherevents) received

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What is a protocol?A specification for a set of message exchanges

Example:

Hi

Hi

Do you havethe time?

Yes!It’s 2:00

TCP connection request

Get http://www.cs.clemson.edu/~mweigle/courses/cpsc826

<web page>Time

» Human protocols: Get thetime from a stranger

» Computer protocols: Get theclass time from a web server

TCP connectionreply

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What is a Protocol?The Internet protocol food-chain (some examples)

Network interface-to-transmissionmedia» Media access protocols

Router-to-router» Routing protocols

Operating system-to-server» Name resolution protocols

Transport protocol-to-transportprotocol» Reliable transmission» Congestion and flow control

Application-level protocols» File transfer, email, ...

local ISP

companynetwork

regional ISP

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A Whirlwind Introduction to the InternetOverview

What’s the Internet What’s a protocol? Network edge Network core Access nets, physical media Performance: loss, delay Protocol layers, service models Backbones, NAPs, ISPs

local ISP

companynetwork

regional ISP

11

The Structure of the InternetThe physical makeup of the Internet

Network edge:» Applications running on hosts

“host” = “end system”

Network core:» Routers» Network of networks

In between: Access networks» Physical media: communication

links

local ISP

companynetwork

regional ISP

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Network StructureThe network edge

End systems (hosts)» Live at the “edge of network”» Run applications

Interaction paradigms:» Client/server model

Client requests, receives servicefrom server

WWW browser/server; emailclient/server

» Peer-to-peer model: Host interactions symmetric File sharing (Napster, MusicCity,

Gnutella,…)

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The Network EdgeConnection-oriented service

Goal: Transfer databetween end systems» handshaking: setup data

transfer ahead of time “Hello, hello-back” human

protocol Set up “state” in two

communicating hosts» Transmit data

Connection-orientedservice on the Internet:» TCP - Transmission

Control Protocol [RFC 793]

TCP service model» reliable, in-order byte-stream

Losses handled byacknowledgements andretransmissions

» flow control: Sender won’t overwhelm

receiver» congestion control:

Senders “slow down sendingrate” when network congested

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The Network EdgeConnectionless service

Goal: Transfer databetween end systems» Same as before!

Connectionless service onthe Internet:» UDP - User Datagram

Protocol [RFC 768] Unreliable data transfer No flow control No congestion control

Applications using TCP:» HTTP (WWW), FTP (file

transfer), Telnet (remotelogin), SMTP (email)

Applications using UDP:» DNS (name to address

mapping), streamingmedia, teleconferencing,Internet telephony

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Network StructureThe network core

A mesh of interconnected routers

The fundamental question:How is data routed through thenetwork?» Circuit switching: dedicated

circuit (path) per call used by alldata (e.g., telephone)

» Packet switching: data sent indiscrete “chunks” (packets); eachhas a path chosen for it

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Network Map

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Network StructureThe network core

A mesh of interconnected routers

The fundamental question:How is data routed through thenetwork?» Circuit switching: dedicated

circuit (path) per call used by alldata (e.g., telephone)

» Packet switching: data sent indiscrete “chunks” (packets); eachhas a path chosen for it

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The Network CoreCircuit Switching

Resources reserved end-to-endfor the connection (“call”)» Resources: Link bandwidth,

switch capacity» Reservation: Dedicated fraction

of available bandwidth, buffers,etc.

Circuit-like (guaranteed)performance» Call setup required» Call rejection (“busy signal”)

possible

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Circuit SwitchingAllocating fractions of bandwidth — Multiplexing

Network bandwidth dividedinto transmission “slots”» Slots allocated to calls» Slots are unused (“idle”) if

not used by owning call» No sharing of slots!

How to divide linkbandwidth into slots?» Frequency division

multiplexing (FDM)» Time division multiplexing

(TDM)

Time

TransmissionFrequency 4 KHz

Call 1Call 2

Call 4Call 3

Linkcapacity

4 4 41 1 12 3 2 3 2 3

FrameSlot

Call data

TDM

FDM

frames/sec X bits/slot = TDM per-call transmission rate

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The Network CorePacket Switching Each sender divides its

messages into packets(sequence of bits)» Senders’ packets share (compete

for) network resources» Each packet uses full link

capacity until transmissioncompleted

» Resources allocated & used asneeded

But now we haveresource contention!» Aggregate resource

demand can exceedamount available

» Congestion: packetsqueue, wait for linkavailability

» Store and forward: packetsmove one hop at a time

Transmit over link Wait turn at next link Bandwidth division

into slots Dedicated allocation Resource reservation

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Packet SwitchingStatistical multiplexing

Packet-switching versus circuit switching:» Restaurant seating analogy» Other familiar analogies?

A

B

C10 MbpsEthernet

1.5 Mbps

45 Mbps

D E

statistical multiplexing

queue of packetswaiting for output

link

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The Network CorePacket switching v. Circuit switching

Assume that on a 1 Mbps link:» Each user consumes 100Kbps when “active”» Each user active 10% of time

Circuit-switching can support 10 users Packet switching can support 35 users

» With 35 users the probability of more than 10 users activesimultaneously is approximately 0.0004.

Packet switchingallows more usersto use the network!N users

1 Mbps link

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Packet Switching v. Circuit SwitchingIs packet switching a “no brainer”?

Great for bursty data» Resource sharing» No call setup

Excessive congestion: packet delay and loss» Protocols needed for reliable data transfer, congestion

control

How to provide circuit-like behavior?» Bandwidth guarantees needed for audio/video applications?» Still an unsolved problem (that’s why we do research!)

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5 seconds5 seconds

Packet SwitchingWhy switch packets instead of entire messages?

“Message switching” example» Transmit a 7.5 Mb message over a network with 1.5 Mbps

links» What is the total elapsed time?

1.5 Mbps

5 seconds

7.5 MbMessage

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Packet-switching: store and forward behavior» 1,500 bit packets, 1 packet forwarded every 1 ms

Packet SwitchingWhy switch packets instead of entire messages?

1.5 Mbps

7.5 MbMessage

5,000Packets

Time0.0000.0010.0020.0030.004

12345

12 1

2 12...

49964997499849995000

...

3...

4997499849995000

34...

499849995000

49995000

4.9984.9995.0005.0015.002

...

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Packet SwitchingRouting

The process of moving packetsamong routers from source todestination» Lots of path selection algorithms

Datagram network:» Each packet carries a destination

address» Destination address used to look up

next hop» Route (next hop) may change at any time

local ISP

companynetwork

regional ISP

Virtual circuit (path) network:» Packets carry a “tag” (virtual circuit ID) that determines the next

hop» Path determined at call setup time & remains fixed throughout call» Routers maintain per-call path state

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Routing in Packet Switched NetworksVirtual circuit routing

A (static) route is computedbefore any data is sent

Packets contain a VC identifier» Identifier replaced at every hop

a b

c

aab

InboundInterface

...

bbc...

OutboundInterface

VCNumber

1273284...

New VCNumber

19863...

Routers maintain per-connection state andperform set-up/tear-down operations

(Why not choose asingle VC identifierfor the entire path andavoid replacing it ateach hop?)

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Routing in Packet Switched NetworksDatagram routing

Packets contain a destination address» Address specifies both a network and a host

Each router examines the destination address andforwards packet towards the next router closest to thedestination network» Routers maintain a table of “next hops” to all networks

Routers maintain no per-connection state

a b

c

xxx.yyy.uuu.vvv.sss.ttt.

bbc

NetworkID

NextHop

... ...

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The Structure of the InternetThe physical makeup of the Internet

Network edge:» Applications and hosts

Network core:» Routers» Network of networks

In between: Access networks» Physical media: communication

links

local ISP

companynetwork

regional ISP

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Network StructureAccess networks and physical media

How to connect end-systemsto edge router?» Residential access nets» Institutional/enterprise access

networks» Mobile access networks

Issues:» Transmission speed (bits per

second) of access network» Shared or dedicated?

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Access Networks and Physical MediaPhysical Media

Transmission is the prop-agation of an electro-magnetic wave (or opticalpulse) through a physicalmedium

Media types» Guided media — signals

propagate in solid media(copper, fiber)

» Unguided media — signalspropagate freely (radio,infrared)

What do you use?» Twisted Pair (UTP) — Two

insulated copper wires

Category 3 UTP:» Traditional phone wires,

10 Mbps Ethernet Category 5 UTP:

» 100Mbps Ethernet» Gigabit possible» Distance limited (100 m)

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Physical MediaCoaxial and fiber optic cable

Coaxial cable» Wire (signal carrier) within a wire (shield)

Baseband: single channel on cable Broadband: multiple channel on cable

» Bi-directional transmission» Largely used for cable TV

Fiber optic cable» Glass fiber carrying light pulses» Higher-speed operation:

100-1,000 Mbps Ethernet High-speed point-to-point transmission (e.g., 10

Gbps)» Low signal attenuation – long distances» Low error rate

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Physical MediaRadio

Signal carried in electro-magnetic spectrum» No physical “wire”

Bi-directional Physical environment

effects propagation» Reflection» Obstruction by objects» Interference

Radio link types:» Microwave

Up to 45 Mbps channels» LAN (e.g., 802.11)

2 Mbps, 11, 56 Mbps» Wide-area (e.g., cellular)

CDPD, 10’s Kbps» Satellite

Up to 50Mbps channel (ormultiple smaller channels)

270 msec end-end delay Geosynchronous versus

LEOS

basestation

uplink

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Access Networks and Physical MediaResidential access: point-to-point access Dialup via modem

» Modem (modulator-demodulator) does digitalanalog signal conversions

» Up to 56Kbps direct access to router ISDN: Integrated Services Digital

Network» 128Kbps all-digital connection to

router DSL: Digital Subscriber Line

» Asymmetric speeds Up to 8 Mbps to the home Up to 1 Mbps from the home Distance-dependent, typical is 1-2 Mbps to home

» Dedicated access

...

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Access Networks and Physical MediaResidential access: cable modems

20,000 – 40,000homes

500 – 1,000homes

200,000 – 400,000homes

2 Mbps to home0.5 Mbps from home

HFC (Hybrid Fiber-Coax)» Asymmetric

speeds» Shared access

Issues:» Congestion» Provisioning

Providers:» Time Warner» AT&T» Cox» Comcast» …..

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Residential Broadband Deployment

North America Residental Broadband

0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

7,000,000

8,000,000

Q3 2000 Q4 2000 Q1 2001 Q2 2001 Q3 2001

Cable

DSL

(Kinetic Strategies, 12/2001)US Cable Internet Share

22%

26%

13%

8%

13%

18%

AT&T

Time Warner

Comcast

Charter

Cox

Other

*

**pending merger of AT&T Broadband and Comcast

US DSL Internet Share

34%

29%

12%

13%

2%

10%

SBC

Verizon

Qwest

BellSouth

Broadwing

Covad

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Access Networks and Physical MediaInstitutional access: local area networks

Local area network (LAN)connects end system to edgerouter

Ethernet is the dominanttechnology» Shared or dedicated cable

connects end system and router» 10 Mbps, 100Mbps, 1Gbps

Ethernet

Deployment: institutions, homeLANs

...

...

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Access Networks and Physical MediaWireless access networks

Shared wireless access networkconnects end-system to router

Wireless LANs:» Radio spectrum replaces wire.

e.g., Lucent Wavelan (2-12 Mbps)

Wider-area wireless access» CDPD: wireless access to ISP

router via cellular network

basestation

mobile hosts

router