Data Communication & Computer Networks

CS 1652

The slides are adapted from the publisher’s material All material copyright 1996-2009

J.F Kurose and K.W. Ross, All Rights Reserved

Jack LangeUniversity of Pittsburgh

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Course Objectives

Understand modern data communication systems and computer networks Understand the key concepts How they are designed & implemented How they are operated How they are likely to evolve in the future

Course Approach Top-down : from what’s familiar to nuts and

bolts The Internet as the main focus Hands-on experience on networked systems 1-2

Administrativia

Instructor: Jack Lange Email: jacklange@cs.pitt.edu Office: Sennott Square #5407 Office Hours: Weds. 2-4PM

Teaching Assistant: TBD

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Communication

Course homepage http://www.cs.pitt.edu/~jacklange/teaching/cs1652-f13/ Announcements, clarifications, corrections Additional resources for projects

Google Group http://groups.google.com/group/pitt-cs1652-

f13 pitt-cs1652-f13@googlegroups.com Private discussion group

• Open venue for class discussions and questions

Based on email (Pitt addresses)• Email me if you want to use a different one

TextBooks

Computer Networking: A Top-Down Approach James Kurose and Keith Ross Fifth/Sixth Edition, Addison Wesley, 2010

TCP/IP Illustrated, Volume I: The Protocols Richard Stevens Addison Wesley, 1994

Class meeting times

Lecture Tues/Thurs: 4:00-5:15PM Sennott Square, Rm. 6110

Lab Sessions Sennott Square, Rm. 5506 Periodically replace lectures Hands on exercises Answer project question Hopefully guest lectures

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Networking Lab

Sennott Square, Rm. 5506 16 Linux machines (Fedore Core 13) Login: Hopefully will be your Pitt login Available for projects

• Can use other machines, but…• Must work on lab equipment

Dual NICS 1 internal network interface to be used for projects 1 external network interface for external access

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Homework

Reading assignments Expected to read before each class

Homework 4 problem sets spaced over semester

Projects Web server (20%) TCP (50%) Routing (30%)

Check Syllabus!

Grading

GradingMidterm (20%)Final (20%)4 Homework (10%) 3 Projects (50%)

Late policySubmit by midnight of the due date10% penalty for every day late

Projects

Work in groups of 2 C/C++ is required

Lot of work, but will be worth it Build a TCP stack and a Web server that runs on it IP routing

Highly Recommended: OS or having some familiarity with Unix systems programming, preferably in C or C++ Minet is in C++ BUILDING software is 50% of the grade of this class

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Today’s topic Computer Networks Overview

What’s the Internet?• Nuts and bolts vs. service view

What’s a protocol?• A set of rules between communicating entities

Network edge/core• Hosts, access networks, physical media• Packet switching/circuit switching, Internet structure

Goal Get “feel” and terminology More depth, detail later in course

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What is the internet?

Flows, packets, and bits

Optical light, electricity, and radio waves

Servers, clients, and peers

Hosts, switches, and routers

What’s the Internet: Hardware view millions of

connected computing devices: hosts = end systems

Home network

Institutional network

Mobile network

Global ISP

Regional ISP

router

PC

server

wirelesslaptop

cellular smartphone

wiredlinks

access points

communication links

fiber, copper, radio, satellite

transmission rate = bandwidth

routers: forward packets (chunks of data)

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What’s a protocol?human protocols: “what’s the time?” “I have a question” introductions

… specific msgs sent

… specific actions taken when msgs received, or other events

network protocols: machines rather than

humans all communication activity

in Internet governed by protocols

protocols define format, order of msgs sent and received among network entities,

and actions taken on msg transmission, receipt

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

protocol:

Hi

Hi

Got thetime?

2:00

TCP connectionresponse

Get http://www.awl.com/kurose-ross

<file>

time

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TCP connection request

Where are we?

What’s the Internet? Nuts and bolts vs. service view

What’s the protocol? Network edge/core

Hosts, access networks, physical media Packet switching/circuit switching, Internet

structure

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A closer look at network structure:

network edge: applications and hosts

access networks, physical media: wired, wireless communication links

network core: interconnected routers network of networks Edge routers “uplink” to

core routers 1-20

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/server

peer-peer model: minimal (or no) use of dedicated

servers e.g. Skype, BitTorrent

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Traditionally where the action is

Internet structure: network of networks

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

NTT, Quest, Level3, Global Crossing, Tata, Savvis, TeliaSonera), 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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Internet structure: network of networks

“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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Internet structure: network of networks

“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 ISPTier-2 ISP

Tier-2 ISP Tier-2 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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Internet structure: network of networks

a packet passes through many networks!

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP

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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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What’s the Internet: Software-ish view

protocols control sending, receiving of msgs

e.g., TCP, IP, HTTP, Skype, Ethernet

Provides meaning

Internet standards RFC: Request for comments IETF: Internet Engineering Task

Force

Internet: “network of networks”

loosely hierarchical public Internet versus private

intranet

Home network

Institutional network

Mobile network

Global ISP

Regional ISP

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What’s the Internet: Service view communication

infrastructure enables distributed applications: Web, VoIP, email,

games, e-commerce, file sharing

communication services provided to apps: reliable data delivery

from source to destination

“best effort” (unreliable) data delivery

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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

Keep in mind: bandwidth (bits per

second) of access network?

shared or dedicated?1-22

100 Mbps

100 Mbps

100 Mbps1 Gbps

server

Ethernetswitch

Institutionalrouter

To Institution’sISP

Ethernet Internet access

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

Ethernet switch1-32

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 802.11n: ~450Mbps

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

(EVDO, HSDPA, 3G) next up: WiMAX (10’s Mbps)

over wide area

basestation

mobilehosts

router

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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 up to 8 Mbps downstream dedicated physical line to telephone central office

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Residential access: cable modems

Diagram: http://www.cabledatacomnews.com/cmic/diagram.html 1-26

Cable Network Architecture: Overview

home

cable headend

cable distributionnetwork (simplified)

Typically 500 to 5,000 homes

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Cable Network Architecture: Overview

home

cable headend

cable distributionnetwork

server(s)

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Cable Network Architecture: Overview

home

cable headend

cable distributionnetwork (simplified)

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Cable Network Architecture: Overview

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 (next class):

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ONT

OLT

central office

opticalsplitter

ONT

ONT

opticalfiber

opticalfibers

Internet

Fiber to the Home (FTTH)

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

Passive Optical Network (PON) – e.g. Verizon FIOS Active Optical Network (AON) – Switched Ethernet

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

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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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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

• Digital signal legacy Ethernet

broadband: multiple channels on

cable

• Analog Signal 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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Physical media: radio

signal carried in electromagnetic spectrum

no physical “wire” bidirectional propagation environment

effects: reflection obstruction by objects interference

Radio link types: terrestrial microwave e.g. up to 45 Mbps channels LAN (e.g., Wifi) 11Mbps, 54 Mbps wide-area (e.g., cellular) 3G cellular: ~ 1 Mbps satellite Kbps to 45Mbps channel (or

multiple smaller channels) 270 msec end-end delay geosynchronous versus low

altitude

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Summary

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The Internet can be defined as A set of hosts running distributed applications

communicating via routers Infrastructure providing popular services

Protocols define the message formats, orders, actions on transmission and reception

Access networks: at the network edge Residential (dial-up, DSL, Cable, FTTH) Institutional (Ethernet) Wireless (Wi-fi, WiMAX)

Cable modems

Does not use telephone infrastructure Instead uses cable TV infrastructure

HFC: hybrid fiber coax asymmetric: up to 30Mbps downstream,

2 Mbps upstream network of cable and fiber attaches homes

to ISP router homes share access to router unlike DSL, which has dedicated access

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