Lec01 02 Introduction

8/8/2019 Lec01 02 Introduction

1/43

Computer Networks-FallComputer Networks-Fall

0909Lec-IntroductionLec-Introduction

Prepared byPrepared by

Zia QureshiZia Qureshi

Fatima Jinnah Women UniversityFatima Jinnah Women University


2/43

A non technical look at networksA non technical look at networks Let us look at a few examples of networks from

our day to day lives and try to learn a fewconcepts.

What are examples of networks we use in life?

Power distribution network

Water distribution network

Network of city roadsThe good old surface mail network


3/43

IssuesIssuesHow is the content delivered?

Are the links between source and receiver one-way or both-ways?

Do we need identifiers (or addresses) for

delivering the service?Is the content provided by the network to each

receiver the same?

Is the content given to the network by each sourcethe same?

Can we keep adding sinks indefinitely?

Can we keep adding sources indefinitely?


4/43

Motivation for NetworksMotivation for Networks Information Access

Sharing of Resources

Facilitate Communications


5/43

What a Network IncludesWhat a Network Includes Hardware: Talk just a bit about how you can configure

a bunch of computers into a network:

Local Area Networks (LAN)

Metropolitan Area Networks (MAN)

Wide Area Networks (WAN)

Software: This is what actually makes computernetworks not the hardware!

Protocols: describe howtwo communicating partiesexchange information.

encodes and formats data

detects and corrects problems

Reference models: Describe how the OSI andInternet networks are organized.


6/43

What a Network DoesWhat a Network Does Provides communication that is

Reliable

Fair

Efficient

From one application to another


7/43

What a Network DoesWhat a Network Does Automatically detects and corrects

Data corruption

Data loss

Duplication

Out-of-order delivery

Automatically finds optimal path from source to

destination


8/43

Data Communication versus NetworkingData Communication versus Networking

With only two nodes, mostly EE issues.

With more than two nodes, lot more issues!


9/43

Direction of TransmissionDirection of Transmission

Broadcast Point to Point


10/43

Broadcast NetworksBroadcast Networks Single Communication channel shared by all

the machines on the network.

Any machine can send short messages(packets).

Each packet contains the address of intendedrecipient.

All machines receive the messages, only theaddressed machine processes the message.


11/43

Broadcast NetworksBroadcast Networks Example of a person shouting in a corridor

Calling name of some other person

What is one key issue with Broadcast

Networks? Packet Collisions.


12/43

Point-to-point NetworksPoint-to-point Networks Individual pairs of machines are physically

connected.

To go from a source to a destination a packettypically goes through intermediate nodes.

What is a key issue in point-to-point networks?

How do you optimally connect pairs of

machines?


13/43

Network ScopeNetwork Scope Local Area Network (LAN)

Wide Area Network (WAN)

Metropolitan Area Network (MAN)


14/43

Local Area Networks (LANs)Local Area Networks (LANs) Mostly used to connect PCs, shared resources

like printers, file servers etc. in a building. LANs are broadcast networks

Their size is limited:

Maximum distance between two nodes.

Number of nodes connected.


15/43

Local Area Networks (LANs)Local Area Networks (LANs) Traditionally the common media was a cable

that all nodes were attached to.

We will study bridges etc. later.

Wireless LANs are available now.


16/43

Local Area Networks (LANs)Local Area Networks (LANs)


17/43

Local Area Networks (LANs)Local Area Networks (LANs)LANs generally dont have any switching

elements

The wire does all the work.

This makes them extremely efficient

But harder to scale.


18/43

Wide Area Network (WAN)Wide Area Network (WAN) WANs cover large geographic areas (country or

continent). Two key components of a WAN are:

Transmission lines

also called channels, circuits, trunks etc.

Move bits from one node to the other

Switching elements

also called packet switching nodes, routers etc.

select outgoing transmission lines for data coming onincoming lines.


19/43

Wide Area Networks (WANs)Wide Area Networks (WANs)

In a WAN, hosts are connected to a subnet

Subnet Consists of routers and transmissionlines

Routers are switching elements


20/43

Wide Area Networks (WANs)Wide Area Networks (WANs)Routers generally adhere to a store-and-

forward principle

Each router first receives a complete packetover some link

Stores the packet in its internal memory

Forwards the packet across the selected output

line.


21/43

MANMANMetropolitan area Network covers a city.

Examples include Cable TV Network.

Cable modem for internet access.


22/43

Wireless NetworksWireless NetworksDivided into 3 Main Catagories

System Interconnection Interconnecting components of a computer using short

range radio. E.g. Bluetooth to connect KB,Mouse,Printer.

Wireless LANs

Every Computer has a radio modem and antenna withwhich it can communicate with other systems (IEEE 802.11)

Wireless WANs

Radio Network for cellular phones. Operate below 1Mpbs over many KM.

High bandwidth WANs are being developed for highspeed wireless internet access. Standard developed for it iscalled IEEE802.16


23/43

Bigger NetworksBigger Networks

Or, two or morenetworksconnected by two

or more nodes

A network can be defined recursively

as...two or morenodes connectedby a link


24/43

Switched NetworksSwitched NetworksSwitching nodes:

Sole purpose is store and forward

Host nodes:

Use the networkRun application programs

SwitchSwitch

HostHost


25/43

Interconnection of NetworksInterconnection of NetworksIndependent networks are interconnected to

form an internetworkor internetfor shortNode connected to two or more networks is

called a Router or Gateway

RouterRouter


26/43

Network ComponentsNetwork Components

Network Core Network Edge


27/43

The Network Core: StrategiesThe Network Core: Strategies Mesh of interconnected routers

Fundamental question: how is datatransferred through net?

Circuit switching:

dedicated circuit per call

telephone net

Packet-switching:data sent through net in discrete chunks


28/43

Network Core: Circuit SwitchingNetwork Core: Circuit Switching

End-to-End resources

reserved for call link bandwidth, switch

capacity

dedicated resources: nosharing

circuit-like (guaranteed)performance

call setup required


29/43

Network Core: Circuit SwitchingNetwork Core: Circuit Switching

Network resources (e.g., bandwidth)

divided into pieces Pieces allocated to calls

Resource piece idleif not used by owning call

(no sharing)

Dividing link bandwidth into pieces

Frequency division

Time division


30/43

Circuit Switching: FDMA and TDMACircuit Switching: FDMA and TDMA

FDMA

frequency

time

TDMA

frequency

time

4 usersExample:


31/43

Network Core: Packet SwitchingNetwork Core: Packet Switching Instead of having a continuous stream of data, divide it into

chunks; Packet

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

Bandwidth division intopieces

Dedicated allocation

Resource reservation

N t k Ed


32/43

Network Edge:Network Edge:

End systems (hosts):

Run application programs

e.g. Web, email

at edge of network

Client/Server modelClient host requests, receives

service from always-on server

e.g. Web browser/server; emailclient/server

How do end systemscommunicate?

Through Protocols

?Wh t t l?


33/43

Whats a protocol?Whats a protocol?Human protocols:

whats the time? I have a question

Introductions

specific msgs sent

specific actions takenwhen msgs received,or other events

Network protocols:

Machines rather thanhumans

All communicationactivity in Internet

governed by protocolsProtocols define:

Msg format

Order of msgs sent andreceived among networkentities

Actions taken on msgtransmission, receipt

Wh l?Wh t t l?


34/43

Whats a protocol?Whats a protocol?

A human protocol

Hi

Hi

Got thetime?

2:00

Connection

requiredConnectionresponsed

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

time

A computer network protocol:

P t l L P t l L


35/43

Protocol LayersProtocol Layers

Networks are complex! Many pieces:

hosts

routers

links of variousmedia

applications

protocols

hardware, software

Question:

Is there any hope of

organizingstructure ofnetwork?

O i i f i lO i ti f i t l


36/43

Organization of air travelOrganization of air travel

a series of steps

ticket (purchase)

baggage (check)

gates (load)

runway takeoff

airplane routing

ticket (complain)

baggage (claim)

gates (unload)

runway landing

airplane routing

airplane routing

A Diff t ViA Diff t Vi


37/43

Layers: each layer implements a service

via its own internal-layer actions

relying on services provided by layer below

ticket (purchase)

baggage (check)

gates (load)

runway takeoff

airplane routing

ticket (complain)

baggage (claim)

gates (unload)

runway landing

airplane routing

airplane routing

A Different ViewA Different View

L d i t l iL d i t l i


38/43

Layered air travel: servicesLayered air travel: services

Counter-to-counter delivery of person+bags

baggage-checkin-to-baggage-claim delivery

people transfer: loading gate to arrival gate

runway-to-runway delivery of plane

airplane routing from source to destination

Di ib dDi t ib t d i l i f l f i lii l t ti f l f ti lit


39/43

DistributedDistributed implementation of layer functionalityimplementation of layer functionality

ticket (purchase)

baggage (check)

gates (load)

runway takeoff

airplane routing

ticket (complain)

baggage (claim)

gates (unload)

runway landing

airplane routing

airplane routing

Departing

air

port

arrivinga

irport

intermediate air traffic sites

airplane routing airplane routing

Wh l i ?Wh l i ?


40/43

Why layering?Why layering?

Modularization eases maintenance, updating

of system

Change of implementation of layers servicetransparent to rest of system

e.g., change in gate procedure doesntaffect rest of system

I t t t l t kI t t t l t k


41/43

Internet protocol stackInternet protocol stack Application: supporting network applications

FTP, SMTP, STTP

Transport: host-host data transfer

TCP, UDP

Network: routing of datagrams from source todestination

IP, routing protocols

Link: data transfer between neighboringnetwork elements

PPP, Ethernet

Physical: bits on the wire

application

transport

network

link

physical

I t t P t l l i d d tI t t P t l l i d d t


42/43

Internet Protocol layering and dataInternet Protocol layering and data

Each layer takes data from above

Adds header information to create new data unit

Passes new data unit to layer below

applicationtransportnetwork

linkphysical


linkphysical

source destination

M

M

M

M

Ht

HtHn

HtHnHl

M

M

M

M

Ht

HtHn

HtHnHl

message

segment

datagram

frame

Physical View

I t t P t l l i d d tI t t P t l l i d d t


43/43

Internet Protocol layering and dataInternet Protocol layering and data


linkphysical


linkphysical

source destination

M

M

M

M

Ht

HtHn

HtHnHl

M

M

M

M

Ht

HtHn

HtHnHl

message

segment

datagram

frame

Each layer takes data from above

Adds header information to create new dataunit

Passes new data unit to layer below

Layer 4 ProtocolLayer 4 Protocol




Documents

Lec01 02 Introduction