Chapter 1 Introduction Computer Networks and the Internet.

Chapter 1 Introduction

Computer Networks and the Internet

Home network

Institutional network

Mobile network

Global ISP

Regional ISP

What is networking? A network? Hardware? Software

04/21/23 Introduction: copyright J.F Kurose and K.W. Ross 1-2

History: 60’s

Mainframes with terminals Not much more than keyboard and display Character based (display and comms) ASCII and EBCDIC

Is this networking?


Remote offices

Modem access Telephone company acted as a “cable” Modulator-Demodulator


Telco

Telco

Actually a series of offices When dialed a connection formed a

physical link

Each connection a switch so switched connection, or circuit-switched


telephonenetwork

central office

Bandwidth Audio frequencies limited bandwidth Local connections: 9600 or 19.2 bps Early modems 400 baud


telephonenetwork

central office

10 Million bps!!70’s and Ethernet

Ethernet was developed at Xerox Palo Alto Research Center Incorporated (PARC)


Coax

Frame basedFrame based

Bridged

Only so many could share the same media

Collisions (CSMA/CD)


Bridge Bridge

Telco

Connecting offices

Telco began providing high speed connections


T11.54Mbps

DS0 - 64 k ilobits per secondISDN - Two DS0 lines plus signaling (16 kilobytes per second), or 128 kilobits per secondT1 - 1.544 megabits per second (24 DS0 lines)T3 - 43.232 megabits per second (28 T1s)

80’s UTP and PCs

Unshielded Twisted Pair (UTP) Early 1Mbs but quickly 10Mbps

(now 100 and above) Still shared (hubs)

PCs


Meanwhile As early as the 60s began investigating

packet switching (vs. physically switched)

First packet switching network The Advanced Research Projects Agency

Network (ARPANET) Funded by the Defense Advanced Research

Projects Agency (DARPA) 1969 contract awarded to

BBN Technologies (originally Bolt, Beranek and Newman)


Took a decade

Various packet switching protocols vied for dominance

1981 NSF funded creation of a “backbone” 1982 the Internet Protocol Suite (TCP/IP)

was accepted as standard


Finally the internet

Late 80’s early 90’s ARPANET and

NSFNET decommissioned (commercialized)

ISPs began emerging


1974: Term Internet first used as shorthand for internetworking

• RFC 675 – Specification of Internet Transmission Control Program, by Vinton Cerf, Yogen Dalal, and Carl Sunshine

1974: Term Internet first used as shorthand for internetworking

• RFC 675 – Specification of Internet Transmission Control Program, by Vinton Cerf, Yogen Dalal, and Carl Sunshine

telephonenetwork Internet

homedial-upmodem

ISPmodem(e.g., AOL)

homePC

central office

Home PCs and Dial-up Modems

You’ve got mail You’ve got mail


Switched, analog network to the internet service provider

Then packet switched

00’s

Remember hubs and bridges


Hubs

Bridge

Bridges/Also known as switches

What’s the advantageWhat’s the advantage

Is it really circuit-switch?Is it really circuit-switch?

Introduction: copyright J.F Kurose and K.W. Ross 1-16

What is the internet?

World Wide Web? The hardware? The protocols?

Home network


Mobile network

Global ISP

Regional ISP

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What’s the Internet: “nuts and bolts” view

millions of connected computing devices: hosts = end systems running network apps

Home network


Mobile network

Global ISP

Regional ISP

router

PC

server

wirelesslaptop

cellular handheld

wiredlinks

access points

communication links fiber, copper,

radio, satellite transmission

rate = bandwidth

routers: forward packets (chunks of data)

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Backbone Optical Fiber and bandwidth

OC3 - 155 megabits per second (84 T1s) OC12 - 622 megabits per second (4 OC3s) OC24 - 1.25 gigabits per seconds (2

OC12s) OC48 - 2.5 gigabits per seconds (4 OC12s) OC192 - 9.6 gigabits per second (4 OC48s) OC768 - 9.6 gigabits per second (4

OC192s)


Institutional networkGlobal ISP

Regional ISP


What’s the Internet: “nuts and bolts” view Protocols control

sending, receiving of msgs e.g., TCP, IP, HTTP, Skype,

Ethernet

Internet: “network of networks” loosely hierarchical public Internet versus

private intranet

Home network


Mobile network

Global ISP

Regional ISP

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What’s a protocol?a human protocol and a computer network protocol:

Q: Other human protocols?

Hi

Hi

Got thetime?

2:00

TCP connection request

TCP connectionresponseGet http://www.awl.com/kurose-ross

<file>time

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protocols define format, order of msgs sent and

received among network entities, and actions taken on msg transmission, receipt


Already talked about one protocol

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Shared media


With packet switched

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Packet comes into a router Which outward bound link should it take?

packetWhich path? Which path?


A closer look at network structure:

Hosts (and applications): network edge

Access networks, LAN, physical media: wired, wireless communication links

Network core: interconnected

routers network of

networks04/21/23


The network edge: end systems (hosts):

run application programs e.g. Web, email at “edge of network”

client/server

peer-peer

client/server model client host requests,

receives service from always-on server

e.g. Web browser/server; email client/serverpeer-peer model:

minimal (or no) use of dedicated servers

e.g. Skype, BitTorrent

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Access networks and physical media

Q: How to connect end systems to edge router?

residential access nets institutional access

networks (school, company)

mobile access networks

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telephonenetwork

DSLmodem

homePC

homephone

Internet

DSLAM

Existing phone line:0-4KHz phone; 4-50KHz upstream data; 50KHz-1MHz downstream data

splitter

centraloffice

Digital Subscriber Line (DSL)

Also uses existing telephone infrastruture up to 1 Mbps upstream (today typically < 256

kbps) up to 8 Mbps downstream (today typically < 1

Mbps) dedicated physical line to telephone central office



Residential access: cable modems Does not use telephone infrastructure

Instead uses cable TV infrastructure Homes share access unlike DSL (dedicated)

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Cable Network Architecture: Overview

home

cable headend

cable distributionnetwork (simplified)

Typically 500 to 5,000 homes

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home

cable headend

cable distributionnetwork

server(s)

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home

cable headend

cable distributionnetwork (simplified)

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home

cable headend

cable distributionnetwork

Channels

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

DATA

DATA

CONTROL

1 2 3 4 5 6 7 8 9

FDM (more shortly):

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ONT

OLT

central office

opticalsplitter

ONT

ONT

opticalfiber

opticalfibers

Internet

Fiber to the Home

Optical links from central office to the home Two competing optical technologies:

Passive Optical network (PON) Active Optical Network (AON)

Much higher Internet rates; fiber also carries television and phone services


100 Mbps

100 Mbps

100 Mbps1 Gbps

server

Ethernetswitch

Institutionalrouter

To Institution’sISP

Ethernet Internet access

Typically used in companies, universities, etc 10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet Today, end systems typically connect into

Ethernet switch04/21/23 Introduction: copyright J.F Kurose and K.W. Ross 1-33


Wireless access networks

shared wireless access network connects end system to router via base station aka “access

point”

wireless LANs: 802.11b/g (WiFi): 11 or 54

Mbps

wider-area wireless access provided by telco operator ~1Mbps over cellular system

(EVDO, HSDPA) next up (?): WiMAX (10’s Mbps)

over wide area

basestation

mobilehosts

router

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Home networks

Typical home network components: DSL or cable modem router/firewall/NAT Ethernet wireless access point

wirelessaccess point

wirelesslaptops

router/firewall

cablemodem

to/fromcable

headend

Ethernet

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Wireless is shared medium. As such uses a contention based protocol (CSMA/CD)

Wireless is shared medium. As such uses a contention based protocol (CSMA/CD)


Physical Media

Bit: propagates betweentransmitter/rcvr pairs

physical link: what lies between transmitter & receiver

guided media: signals propagate in solid

media: copper, fiber, coax

unguided media: signals propagate freely,

e.g., radio

Twisted Pair (TP) two insulated copper

wires Category 3: traditional

phone wires, 10 Mbps Ethernet

Category 5: 100Mbps Ethernet

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Physical Media: coax, fiber

Coaxial cable: two concentric copper

conductors bidirectional baseband:

single channel on cable legacy Ethernet

broadband: multiple channels on

cable HFC

Fiber optic cable: glass fiber carrying

light pulses, each pulse a bit

high-speed operation: high-speed point-to-point

transmission (e.g., 10’s-100’s Gps)

low error rate: repeaters spaced far apart ; immune to electromagnetic noise

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The Network Core

How data moves through the network

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The Network Core

mesh of interconnected routers

Packet switched or circuit switched? circuit switching:

dedicated circuit per call: telephone net

packet-switching: data sent thru net in discrete “chunks”

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Circuit Switching: FDM and TDM

FDM

frequency

time

TDM

frequency

time

4 users

Example:

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Circuit switched wasteful?

When not transmitting over circuit? TDM: Empty time slots FDM: Unused channels

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Network Core: Packet Switching

Packetize data Put in Queue If link available, go

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A

B

C100 Mb/sEthernet

1.5 Mb/s

D E

statistical multiplexing

queue of packetswaiting for output

link



each packet uses full link bandwidth

resources used as needed

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A

B

C100 Mb/sEthernet

1.5 Mb/s

D E



link



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If one path through network crowded can follow another

But how?

A

B

C100 Mb/sEthernet

1.5 Mb/s

D E



link

Routing

How do packets find their way through the network?


Data Header

Source/Destination Address

Packet Packet


Speed

Will a packet arrive instantly at the ultimate destination?

R R RL

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Packet-switching: store-and-forward

takes L/R seconds to transmit (push out) packet of L bits on to link at R bps

store and forward: entire packet must arrive at router before it can be transmitted on next link

delay = 3L/R (assuming zero propagation delay)

Example: L = 7.5 Mbits R = 1.5 Mbps transmission delay =

15 sec

R R RL

more on delay shortly …

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Packet switching versus circuit switching

great for bursty data resource sharing simpler, no call setup

excessive congestion: packet delay and loss protocols needed for reliable data transfer,

congestion control Q: How to provide circuit-like behavior?

bandwidth guarantees needed for audio/video apps

still an unsolved problem (chapter 7)

Is packet switching a “slam dunk winner?”

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Internet structure: network of networks

roughly hierarchical at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T,

Cable and Wireless), national/international coverage treat each other as equals

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-1 providers interconnect (peer) privately

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Tier-1 ISP: e.g., Sprint

…

to/from customers

peering

to/from backbone

….

………

POP: point-of-presence

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“Tier-2” ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet tier-2 ISP is customer oftier-1 provider

Tier-2 ISPs also peer privately with each other.

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“Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems)

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP



Tier-2 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP

Local and tier- 3 ISPs are customers ofhigher tier ISPsconnecting them to rest of Internet

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a packet passes through many networks!

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP



Tier-2 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP

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Delay, loss, and throughput

Do all packets make it?At what delay?

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A

B


How do loss and delay occur?packets queue in router buffers packet arrival rate to link exceeds output link

capacity packets queue, wait for turn

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A

B

packet being transmitted (delay)

packets queueing (delay)

free (available) buffers: arriving packets dropped (loss) if no free buffers


Four sources of packet delay

1. nodal processing: check bit errors determine output link

A

B

propagation

transmission

nodalprocessing queueing

2. queueing time waiting at output

link for transmission depends on

congestion level of router

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Delay in packet-switched networks3. Transmission delay: R=link bandwidth

(bps) L=packet length (bits) time to send bits into

link = L/R

4. Propagation delay: d = length of physical

link s = propagation speed in

medium (~2x108 m/sec) propagation delay = d/s

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A

B

propagation

transmission

nodalprocessing queueing


Nodal delay

dproc = processing delay typically a few microsecs or less

dqueue = queuing delay depends on congestion

dtrans = transmission delay = L/R, significant for low-speed links

dprop = propagation delay a few microsecs to hundreds of msecs

proptransqueueprocnodal ddddd

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“Real” Internet delays and routes

1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms17 * * *18 * * *19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms

traceroute: gaia.cs.umass.edu to www.eurecom.frThree delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu

* means no response (probe lost, router not replying)

trans-oceaniclink

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Throughput

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

data at rate

Rs bits/sec)

pipe that can carrydata at rate

Rc bits/sec)

server sends bits

(fluid) into pipe

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Throughput: if push 1 frame1 frame per delayTrans: L/RS + prop Proc+Queue

L/RC + prop


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 scenario

6 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/6)

in practice: Rc or Rs is often bottleneck

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Layered architecture Software stack

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API

ApplicationApplication

TranslationTranslation

DriverDriver

API

ApplicationApplication

TranslationTranslation

DriverDriver

Physical cables/switches/routersPhysical cables/switches/routers


Internet protocol stack application: supporting network

applications FTP, SMTP, HTTP

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”

application

transport

network

link

physical

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ISO/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 needed?

application

presentation

session

transport

network

link

physical

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sourceapplicatio

ntransportnetwork

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/bridge

Encapsulationmessage M

Ht M

Hn

frame

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Think of it as Network layers talking to other network layers, transport layers talking to other transport layers, application layers…

Think of it as Network layers talking to other network layers, transport layers talking to other transport layers, application layers…


applic

ati

on

transp

ort

netw

ork

link

physi

cal

Ht Hn HlM

Encapsulation

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Remember book organization


application

presentation

session

transport

network

link

physical

Chapter 2

Chapter 3Chapter 4

Chapter 5

Routing

Bridging/Switching

Routing

Bridging/Switching

TCPIP

Transmission Control Protocol / Internet Protocol.

04/21/23 Course Overhead: copyright J.F Kurose and K.W. Ross 72

Chapter 1 Introduction Computer Networks and the Internet.

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Transcript of Chapter 1 Introduction Computer Networks and the Internet.