LECTURE 1

Computer Networks BITS ZC481

Grading Policy

EC1 : 3 Quizes of 5% Weightage Each (Closed Book).

EC2: Mid Sem Test 35% on Sunday 08/09/2013 at

2 PM – 4 PM (Closed Book).

EC3: Compre Exam 50 % on Sunday 10/11/2013 at

2 PM – 5 PM (Open Book).

Required Textbook

Text Book: Computer Networking: A Top Down Approach Featuring the Internet, 3rd edition. Jim Kurose, Keith Ross Addison-Wesley, 2005.

R1: Andrew S. Tanenbaum, Computer Networks, Fourth Edition, Pearson Education, 2006.

R2: William Stallings, Computer Networking with Internet Protocols and Technology, Pearson Education, 2004

L. Peterson and B. Davie, Computer Networks: A Systems Approach, Fourth Edition, Elsevier, 2007 (Book From 24x7 Online Book)

Course Objectives

Learn how communication networks are put together mechanisms, algorithms, technology components

Understand fundamental challenges

Learn about existing solutions typically: no single dominant solution

What problems still need solving?

Today’s Agenda

Introduction to Internet/computer networks

Uses of Computer Networks

Network Hardware: The Network Edge, The Network Core, Access Networks

Internet :Nuts & Bolts View

Internet is hundreds of millions of connected computing devices (nodes). End Systems are the hosts.

Internet applications run on end system but don’t run in packet switches in network core.

All the nodes are connected via Communication links (fiber, copper, radio, satellite).

Transmission rate to transmit the data between the devices is measured in Bandwidth

Internet :Nuts & Bolts View(1)

Intermediate Nodes between two hosts forwards the packets (Packet Switching) from one node to other towards destination host can be routers or switches.

Home network

Institutional network

Mobile network

Global ISP

Regional ISP

PC

server

wirelesslaptopcellular handheld

wiredlinks

access points

router

Internet :Nuts & Bolts View(2)

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

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

Internet :Nuts & Bolts View(3)

End system attached to the Internet provides an API (Application programming interface).

API Specifies how a software piece running on one end system asks the internet infrastructure to deliver data to specific destination software piece running on other end system.

It is set of rules the sending software piece must follow.

Internet: a service view

Most people know about the Internet (a computer network) through applications like

World Wide Web Email Online Social Network Streaming Audio Video File Sharing Instant Messaging

Internet: a service view(1)

Communication infrastructure enables distributed applications: Web, VoIP, email, games, e-commerce, file sharing.

Different Communication services provided to apps: reliable data delivery from source to destination. “best effort” (unreliable) data delivery.

Protocol

All communication activity in Internet governed by protocols.

Define format, order of messages sent and received among network entities, and actions taken on messages transmission, receipt, or timeout.

eg: TCP, IP, HTTP, Skype, Ethernet

Protocol defines the interfaces between the layers in the same system and with the layers of peer system.

Protocol(1)

Each protocol object has two different interfaces: service interface: operations on this protocol peer-to-peer interface: messages exchanged with

peer

Protocol(2)

Except at the hardware level, where peers directly communicate with each other over a link, peer-to-peer communication is indirect—each protocol communicates with its peer by passing messages to some lower level protocol, which in turn delivers the message to its peer.

Network Structure

Network edge: applications and hosts.

Access networks, physical media: wired, wireless communication links

Network core: interconnected

routers network of networks

(Internet)

Network Edge

End systems (hosts): run application

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

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

Network Edge: connection-oriented service

Goal: data transfer between end systems

handshaking: setup (prepare for) data transfer ahead of time Hello, hello back human

protocol set up “state” in two

communicating hostsTCP - Transmission

Control Protocol Internet’s connection-

oriented service

TCP service [RFC 793]reliable, in-order byte-

stream data transfer loss: acknowledgements

and retransmissionsflow control:

sender won’t overwhelm receiver

congestion control: senders “slow down

sending rate” when network congested

Network Edge: connectionless service

Goal: data transfer between end systems

UDP - User Datagram Protocol [RFC 768]: connectionless unreliable data

transfer no flow control no congestion control

App’s using TCP: HTTP (Web), FTP

(file transfer), Telnet (remote login), SMTP (email)

App’s using UDP:streaming media,

teleconferencing, DNS, Internet telephony

Access networks

How to connect end systems to edge router?

residential access nets

institutional access networks (school, company)

mobile access networks

Access Network: Dial Up

User software actually dials a ISP Phone Number and makes a traditional phone connection with ISP.

Home Modem coverts digital output from PC to analog format and Modem in ISP converts back data from analog to digital format.

Access Network: Dial Up(1)

Drawback: up to 56Kbps direct access to router (often

less)Can’t surf and phone at same time: can’t be

“always on”

Access networks: DSL

Access networks: DSL(1)

Telephone lines carries both data and telephone signals encoded at different frequencies.

Splitter separates the data from telephone signals and transfers it to DSL Modem.

Upstream and downstream transmission rates are different (asymmetric).

Access Network: Cable

Cable head end broadcast the television channels through distribution networks of coaxial cable and amplifiers to residence.

Hybrid Fiber-coaxial (HFC) access network makes use of both coaxial and fiber cables.

Shared broadcast Medium

asymmetric: up to 30Mbps downstream, 2 Mbps upstream

Access Network: Cable(1)

Access Network: Ethernet

Access Network: Ethernet(1)

company/university local area network (LAN) connects end system to edge router.

Ethernet: 10 Mbps, 100Mbps, 1Gbps, 10Gbps Ethernet modern configuration: end systems connect into

Ethernet switch

Access Network: Wireless Access

In wireless LAN, Wireless users transmit/receive packets to/from access point. Eg: 802.11b/g (WiFi): 11 or 54 Mbps.

In wide area wireless access network, packets are transmitted to the base station over same wireless infrastructure used for cellular telephony.

Wimax(10’s Mbps over wide area).

Access Network: Wireless Access(1)

basestation

mobilehosts

router

Physical Media

Bit: propagates betweentransmitter/reciver 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

Physical Media: coax, fiber

Coaxial cable:two concentric copper

conductorsbidirectionalbaseband:

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

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) e.g. 3G: hundreds of kbps

satellite Kbps to 45Mbps channel

(or multiple smaller channels)

270 msec end-end delay geosynchronous versus

low altitude

Next Lecture

Network CoreISPDelay & loss in packet-switched networksProtocol layers, service modelsOSI and TCP/IP reference models

Thanks!!!Queries?