Lecture 1. Introduction. Computer Networking: A Top Down Approach Featuring the Internet,

Lecture 1

Introduction

Computer Networking: A Top Down Approach Featuring the Internet, 3rd edition.

Jim Kurose, Keith Ross Addison-Wesley, July 2004.

All material copyright 1996-2005

J.F Kurose and K.W. Ross, All Rights Reserved Various other sources on the net,

Introduction 1-2

Course Outline

Instructor: Ghulam Murtaza

([email protected])

Room: S-214 Office Hours: Mon 2:00-4:00, Thu 2:00-4:00 (other times, by email appt)

TA: TBD

Course Web: http://cscs311.wordpress.com

Reading Material



REQUIRED TEXTS:

 Computer Networking: A Top Down approach

featuring the Internet (3rd Edition) by James F. Kurose and Keith W. Ross 



References:

 Data and Computer Communications, 6th Edition by

William Stallings

 Computer Networks by Andrew Tanenbaum



Other material will be posted on the web or

Reading Material

 HOMEWORKS, QUIZZES, PROGRAMMING: 40%

MIDTERM EXAMINATION: 25% FINAL EXAMINATION: 35%

 REGRADING CAN BE REQUESTED WITHIN FOLLOWING

TIME LIMITS:

QUIZZES AND HOMEWORKS: 2DAYS, EXAMS: 3DAYS

 Exams: Open book, open notes

 Three flex days, can either be used as a three day extension on one project, or 3, 1 day extensions on three projects. Afterwards, 25% of the grade will be lost per day.

Outline

Introduction and Overview

Basic Concepts of Networking Circuit switching

Packet switching

Multiplexing (TDM, FDM) Throughput and delay Internet Architecture Protocol Layering

Application Layer

Network application architectures HTTP, FTP, Email, DNS

P2P applications

Writing network applications The C socket API

Transport Layer

Multiplexing in UDP and TCP Connectionless Transport: UDP Reliable data transfer and TCP Congestion avoidance and control

Network Layer

The Internet Protocol

- IPv4 Datagram

- Internet Address Classes - Special IP Addresses - ARP: I need your address! - IPv6

- ICMP: Tracing a route

- Network Address Translation (NAT)

Internet Routing Protocols and Algorithms

- RIP - OSPF - BGP

X.25, Frame relay and ATM MPLS

Outline continued

Physical & Link Layer Functionalities

Error Detection & Control, ARQ Link layer addressing

LAN Technologies Bridges and Hubs Multiple Access

Special topics

Security

Overlay networks, naming Content distribution networks Peer to peer systems, DHTs

Academic honesty:

Freedom of information rule:

Collaboration is acceptable

To assure that all collaboration is on the

level, you must always write the name(s) of

your collaborators on your assignment.

Failure to adequately acknowledge your contributors is at best a lapse of

professional etiquette, and at worst it is plagiarism. Plagiarism is a form of cheating.

Course

Introduction 1-8

Networking is easy

Memory, acronyms, definitions

Strong sense of logic

Algorithms

Chapter 1: Introduction

Our goal:

 get “feel” and

terminology

 more depth, detail

later in course

 approach:

 use Internet as

example

Overview:

 what’s the Internet  what’s a protocol?  network edge

 network core

 access net, physical media  Internet/ISP structure  performance: loss, delay

 protocol layers, service models  network modeling

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

 Over a billion of connected

computing devices: hosts =

end systems

 running network apps

 communication links

 fiber, copper, radio, satellite  transmission rate = bandwidth  routers: forward packets

(chunks of data)

 Anyone speaking IP can join

local ISP

company

regional ISP

router _workstation

server

Introduction 1-12

Some internet appliances

World’s smallest web server

http://www-ccs.cs.umass.edu/~shri/iPic.html IP picture frame

http://www.ceiva.com/

Web-enabled toaster + weather forecaster

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

 protocols control sending,

receiving of msgs

 e.g., TCP, IP, HTTP, FTP, PPP

 Internet: “network of

networks”

 loosely hierarchical

 public Internet versus

private intranet

 Internet standards

 RFC: Request for comments

 IETF: Internet Engineering

Task Force local ISP company regional ISP router _workstation server mobile

Introduction 1-14

What’s the Internet: a service view

 communication

infrastructure enables distributed applications:

 Web, email, games,

e-commerce, file sharing

 communication services

provided to apps:

 Connectionless unreliable

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

Introduction 1-16

What’s a protocol?

a human protocol and a computer network protocol:

Q: Other human protocols?

Hi Hi

Got the time?

2:00

TCP connection request

TCP connection response

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

<file>

A closer look at network structure:

and hosts

 network core:

 routers

 network of networks

 access networks, physical

Introduction 1-18

End system



Typically a computing device

 PC, workstation, server, laptop….toaster



End-systems connected by some medium

 Copper wire, optical fiber, coaxial cable etc

 Communication link



Different transmission rates or bandwidths

of communication links

continued



What do you do if you want to connect>2

end-systems to each other

Introduction 1-20

continued



What do you do if you want to connect>2

end-systems to each other

 Multiplie access link

 switches or routers

 a switch has several interfaces or ports

Client-Server Applications

Networks: Introduction

Networks: Introduction 22

Client-Server Model

Clients request and receive service from a

server machine

Peer-to-Peer Applications

In a peer-to-peer system there are no fixed

clients and servers.

Introduction 1-24

The network edge:

 end systems (hosts):

 run application programs  e.g. Web, email

 at “edge of network”

 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. Gnutella, KaZaA, Skype

 The internet generally provides two

Network edge: connection-oriented service

Goal:

 handshaking: setup

(prepare for) data

transfer ahead of time

 Hello, hello back human protocol

 set up “state” in two communicating hosts

 TCP - Transmission

Control Protocol

 Internet’s connection-oriented service

TCP service

 reliable, in-order

byte-stream data transfer

 loss: acknowledgements

and retransmissions

 flow control:

 sender won’t overwhelm

receiver

 congestion control:

 senders “slow down sending

Introduction 1-26

Network edge: connectionless service

Goal:

between end systems

 same as before!

 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

The Network Core

routers

 the fundamental question:

how is data transferred through net?

 Two approaches

 circuit switching:

dedicated circuit per call: telephone net

 packet-switching: data

Lecture 1: Introduction 28

Multiplexing



Need to share network resources



How? Switched network

 Party “A” gets resources sometimes

 Party “B” gets them sometimes

Lecture 1: Introduction 30

Circuit Switching

 Source first establishes a connection (circuit) to the

destination

 Each switch along the way stores info about connection (and

possibly allocates resources)

 Source sends the data over the circuit

 No need to include the destination address with the data since

the switches know the path

 The connection is explicitly torn down

Network Core: Circuit Switching

End-end resources

reserved for “call”

 link bandwidth, switch

capacity

 dedicated resources:

no sharing

 circuit-like

(guaranteed) performance

Introduction 1-32

Circuit Switching: FDM and TDM

frequency

time TDM

frequency

time

4 users Example:

Circuit Switching Discussion

 Fast and simple data transfer, once the circuit has been

established

 Predictable performance since the circuit provides

isolation from other users

• E.g. guaranteed bandwidth

 Negatives

 How about bursty traffic

• Circuit will be idle for significant periods of time • Circuit establishment takes time

 How about users with different bandwidth needs

Lecture 1: Introduction 34

Packet Switching

 Source sends information as self-contained packets

that have an address.

 Source may have to break up single message in multiple

 Each packet travels independently to the destination

host.

 Switches use the address in the packet to determine how to forward the packets

 Store and forward

Network Core: Packet Switching

each end-end data stream divided into packets

 user A, B packets share

network resources

 each packet uses full link

bandwidth

 resources used as needed

resource contention:

 aggregate resource

demand can exceed amount available

 congestion: packets

queue, wait for link use

 store and forward:

packets move one hop at a time

 Node receives complete

packet before forwarding Bandwidth division into “pieces”

Dedicated allocation Resource reservation

Lecture 1: Introduction 36

Packet Switching –

Statistical Multiplexing

Packet Switching Discussion



Efficient

 Can send from any input that is ready



General

 Multiple types of applications



Accommodates bursty traffic

 Addition of queues



Store and forward

 Packets are self contained units

 Can use alternate paths – reordering



Contention (i.e. no isolation)