ADVANCED COMPUTER

NETWORKS
FALL 2011
1-1 Lec#1
Introduction

Tahira Mahboob
 SUGGESTED TEXT
Text :

Computer Networking, A top down approach featuring the Internet (5th Ed: 2009)
by James F Kurose & Keith W Ross

References :

1. Computer Networks: A Systems Approach, 4th Edition by Larry Peterson, Bruce

Davie, Morgan Kaufman Publishers.
2. Data Communications & networking by B A Forouzan

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 COURSE CONTENTS

• Introduction Overview of the Internet, client/server paradigm, circuit switching,

packet switching, physical media, queuing delay and packet loss, TCP/IP and OSI
reference models, Internet Protocol Stack

• Network Layer Addressing

NIC addressing, IP addressing, IPv4, IPv6, ICMP

• Application Layer
Service requirements, WWW, HTTP, Electronic Mail, Domain Name System,
Socket programming

• Transport Layer
Service models, Multiplexing/Demultiplexing, Connection-less transport (UDP),
Principles of reliable data transfer, Connection-oriented transport (TCP), TCP
congestion control, TCP Variants

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COURSE CONTENTS…….CON’T
• Network Layer Routing
Routing and forwarding, Routing algorithms, Routing in the Internet, Multicast
routing

• Link Layer and Local Area Networks

Link layer services, Error detection and correction, Multiple Access Protocols,
Link layer addressing, Ethernet, Hubs and switches, Point-to-Point Protocol

• Wireless and Mobile Networks

Wireless links and network characteristics, Wi-Fi: IEEE 802.11 Wireless LANs,
Cellular Internet Access, Mobility management and Mobile IP

• Multimedia Networking
Networked multimedia applications, best-effort service and multimedia delivery
requirements, Multimedia protocols (RTSP, RTP, RTCP, SIP), Content
Distribution Networks

• Security 1-4
introduction to Computer Network Security
ROADMAP
 What is a Computer Network?
 Applications of Networking
 Classification of Networks
 Layered Architecture
 Network Core
 Delay & loss in packet-switched networks
 Internet Structure
 Transmission Media (self study)
 History (self study)
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COMPUTER NETWORK?
 “interconnected collection of autonomous computers
connected with each other.
 What is the Internet?
 “network of networks”
 “collection of networks interconnected by routers”
 “a communication medium used by millions”
 Email, chat, Web “surfing”, streaming media

 Internet Web

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 What are basic Components of Computer Networks?

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THE “NUTS AND BOLTS” VIEW OF THE
INTERNET
 millions of connected router
workstation
computing devices: hosts, end-
systems server
mobile
 PCs workstations, servers local ISP
 PDAs phones, toasters

running network apps

 communication links regional ISP
 fiber, copper, radio, satellite
 Links have different bandwidth

 routers: forward packets

 Packet: a piece of messg.
company
network 1-8
ROADMAP
 What is a Computer Network?
 Applications of Networking
 Classification of Networks
 Layered Architecture
 Network Core
 Delay & loss in packet-switched networks
 Internet Structure
 Transmission Media (self study)
 History (self study)
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APPLICATIONS (1)
 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
 Client/server model is applicable
in an intranet.

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APPLICATIONS (2)
 peer-peer model:
 No fixed clients or servers
 Each host can act as both client & server

 Examples: Napster, Gnutella, KaZaA

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APPLICATIONS (3)
 WWW
 Instant Messaging

 Peer-to-Peer

 Internet Phone

 Video-on-demand

 Distributed Games

 Remote Login (SSH client, Telnet)

 File Transfer

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ROADMAP
 What is a Computer Network?
 Applications of Networking
 Classification of Networks
 Layered Architecture
 Network Core
 Delay & loss in packet-switched networks
 Internet Structure
 Transmission Media (self study)
 History (self study)
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A CLASSIFICATION OF NETWORKS
 Local Area Network (LAN)
 Metropolitan Area Network (MAN)

 Wide Area Network (WAN)

 Wireless LANs & WANs

 Home Networks

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LOCAL AREA NETWORK (LAN)
 company/univ local area
network (LAN) connects end
system to edge router
 Ethernet:
 shared or dedicated link connects
end system and router
 10 Mbs, 100Mbps, Gigabit
Ethernet
 deployment: institutions, home
LANs happening now
 LANs: chapter 5

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METROPOLITAN AREA NETWORK (MAN)
A Cable TV Network is an example of a MAN

Typically 500 to 5,000 homes

cable headend

home
cable distribution
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network (simplified)
CABLE NETWORK ARCHITECTURE: OVERVIEW

cable headend

home
cable distribution
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network (simplified)
WIDE AREA NETWORK (WAN)
 Spans a large geographic
area, e.g., a country or a
continent
 A WAN consists of
several transmission lines
and routers
 Internet is an example of
a WAN

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WIRELESS NETWORKS
 shared wireless access network To the wired network
connects end system to router
 via base station aka “access point” router
 wireless LANs:
 802.11b (WiFi): 11 Mbps base
 wider-area wireless access station
 provided by telco operator
 WAP/GPRS
 3G ~ 384 kbps

mobile
hosts
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HOME NETWORKS
Typical home network components:
 ADSL or cable modem

 router/firewall/NAT

 Ethernet

 wireless access

point
wireless
to/from laptops
cable router/
cable
modem firewall
headend
wireless
access
Ethernet point 1-20
(switched)
“INTERNETWORKING”?
 internetwork – interconnection of networks – also called
an “internet”
 Subnetwork – a constituent of an internet

 Intermediate system – a device used to connect two

networks allowing hosts of the networks to correspond
with each other
 Bridge
 Routers

 Internet is an example of an internetwork.

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ROADMAP
 What is a Computer Network?
 Applications of Networking
 Classification of Networks
 Layered Architecture
 Network Core
 Delay & loss in packet-switched networks
 Internet Structure
 Transmission Media (self study)
 History (self study)
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LAYERED ARCHITECTURE: WHY?
 Networks are complex with many pieces
Hosts, routers, links, applications, protocols,
hardware, software
 Can we organize it, somehow?
 Let’s consider a Web page request:
 Browser requests Web page from server
 Server should determine if access is privileged
 Reliable transfer page from server to client
 Physical transfer of “bits” from server to client

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MOTIVATION CONTINUED …

Application logic
Application Application
Services Services

Communication
Reliable delivery Communication
Service Service

Network
Transfer “bits” Network
Services Services

Web Server Web Client 1-24

MOTIVATION CONTINUED …
Dealing with complex systems:
 explicit structure allows identification, relationship of
complex system’s pieces
 layered reference model for discussion
 modularization eases maintenance, updating of system
 change of implementation of layer’s service transparent to rest
of system
 e.g., change in gate procedure doesn’t affect rest of system

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 LAYERS, PROTOCOLS, INTERFACES

Application Application logic Application

Services Services
protocol
Layer
Interface
Communication Reliable delivery Communication
Service protocol Service
Layer
Interface

Network Transfer “bits” Network

Services protocol Services

Web Server Web Client

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LAYERED ARCHITECTURE (REVIEW
1/2)
 Networks organized as a stack of layers?
 The purpose of a layer is to offer services to the layer above it
using an interface (programming language analogy: libraries
hide details while providing a service)
 Reduces design complexity
 Protocols: peer-to-peer layer-n conversations
 Data Transfer: each layer passes data & control
information to the layer below; eventually physical
medium is reached.

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REVIEW (2/2)
 A set of layers & protocols is called a Network
Architecture. These specifications enable
hardware/software developers to build systems
compliant with a particular architecture.
 E.g., TCP/IP, OSI

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LAYERING: DESIGN ISSUES
 Identify senders/receivers?
 Addressing

 Unreliable physical communication medium?

 Error detection
 Error control
 Message reordering

 Sender can swamp the receiver?

 Flow control
 Multiplexing/Demultiplexing

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REFERENCE MODELS
 Open Systems Interconnection (OSI) Model
 TCP/IP Model

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REFERENCE MODELS (2)

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TCP/IP MODEL
 Originally used in the ARPANET Application
 ARPANET required networks using leased
telephone lines & radio/satellite networks to Transport
interoperate
 Goals of the model are: Internet
 Seamless interoperability
 Wide-ranging applications Host-to-
 Fault-tolerant to some extent Network

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THE INTERNET LAYER
 End systems inject datagrams in the networks
 A transmission path is determined for each packet
(routing)
 A “best effort” service
 Datagrams might be lost
 Datagrams might be arrive out of order

 Analogy: Postal system

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THE TRANSPORT LAYER
 Concerned with end-to-end data transfer between end
systems (hosts)
 Transmission unit is called segment

 TCP/IP networks such as the Internet provides two types

of services to applications
 “connection-oriented” service – Transmission Control
Protocol (TCP)
 “connectionless” service - User Datagram Protocol (UDP)

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TCP: CONNECTION-ORIENTED
SERVICE
 Handshaking between client & server programs
 Parameters for ensuring exchange
 Maintain connection-state

 Packet switches do not maintain any connection-state;

 hence “connection-oriented”
 TCP is bundled with reliability, congestion control, and
flow control.

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UDP: CONNECTIONLESS SERVICE
 No handshaking
 Send whenever and however you want

 A “best effort” service

 No reliability
 No congestion & flow control services

 Why is it needed?

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THE APPLICATION LAYER
 Residence of network applications and their application
control logic
 Examples include:
 HTTP
 FTP
 Telnet
 SMTP
 DNS

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THE HOST-TO-NETWORK LAYER
 Somehow, host has to connect to the network and be able
to send IP Datagrams
 How?

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INTERNET PROTOCOL STACK
 application: supporting network applications
 FTP, SMTP, STTP
application
 transport: host-host data transfer
 TCP, UDP transport
 network: routing of datagrams from source
to destination network
 IP, routing protocols
 link: data transfer between neighboring link
network elements
 PPP, Ethernet physical
 physical: bits “on the wire”
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