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Communication & Networking:An Overview

Prepared by :Swapan PurkaitDirectorNettech Private [email protected]+ 91 93315 90003

For Summer Training on Computer Networking visit www.nettech.in


Organization

• Communication Systems• Networking Fundamentals• The INTERNET• Network Security


Simple Communication Model

Source Destination

Transmission

media


Example

client program server

communicationschannel


Communication System

Source Modulator Demodulator Sink

Carrier

Noise

Transmissionmedia


Data Communication Model

Modem

DCE

Modem

DCE

Computer

DTE

Computer

DTE


Modes of Communication

Simplex

communications

Half-duplex (HDX)

communications

Full-duplex (FDX)

communications

or


Communication Ports

9-pin D-typemale connector (COM1:)

9-pin or 25-pin D-typemale connector (COM2:)


Transmission Media

• Wired– Twisted pair, Coaxial cable, FO

• Wireless– Short range

• Infrared– Long Range

• Microwave• Satellite


Transmission Media

Metal sheath Innerconductor

Insulating outer conductor

Coaxialcable

Twisted-paircable

Inner cladding(glass)Inner fibre

(glass)

Outer cladding(PVC)

Fibre opticcable


Telephone Network


Cable TV Network


Multiplexing

• Time-Division Multiplexing (TDM)• Frequency-Division Multiplexing (FDM)• Statistical Time-Division Multiplexing

(STDM)L1

L2

L3

R1

R2

R3Switch 1 Switch 2


Networks


Categories

• Communication Networks– PSTN

• Computer Networks– INTERNET

• Integrated Networks– Computer & Communication Networks


Building Blocks

• Nodes: PC, special-purpose hardware…– hosts– switches

• Links: coax cable, optical fiber…– point-to-point

– multiple access

…


Switched Networks

– two or more nodes connected by a link, or

– two or more networks connected by two or more nodes

• A network can be defined recursively as...


Switching Strategies

• Circuit switching: carry bit streams– original telephone network

• Packet switching: store-and-forward messages– Internet

• See the schematic diagram next


Ckt Vs. Pkt Switching

Circuit-switching

Packet-switching

possible routes

fixed routePSE


Addressing and Routing

• Address: byte-string that identifies a node– usually unique

• Routing: process of forwarding messages to the destination node based on its address

• Types of addresses– unicast: node-specific– broadcast: all nodes on the network– multicast: some subset of nodes on the

network


What Goes Wrong in the Network?

• Bit-level errors (electrical interference)• Packet-level errors (congestion)• Link and node failures

• Messages are delayed• Messages are deliver out-of-order• Third parties eavesdrop


Layering

• Use abstractions to hide complexity• Abstraction naturally lead to layering• Alternative abstractions at each layer

Request/replychannel

Message streamchannel

Application programs

Hardware

Host-to-host connectivity


Protocols

• Building blocks of a network architecture• Each protocol object has two different

interfaces– service interface: operations on this protocol– peer-to-peer interface: messages exchanged

with peer • Term “protocol” is overloaded

– specification of peer-to-peer interface– module that implements this interface


Host 1

Protocol

Host 2

Protocol

High-levelobject

High-levelobject

Serviceinterface

Peer-to-peerinterface

Interfaces


ISO-OSI 7 Layer Ref. Model

Application

Session

Transport

Network

Data Link

Physical

Presentation

Application

Session

Transport

Network

Data Link

Physical

Presentation

DATA

DATA

DATA

DATA

DATA

DATA

A

A

A

A

A

P

P

P

P

S

S

S

T

TN

DATAAPSTND D

DATA DATA

Actual Data Flow

Virtual Data Flow


Data Flow in Layered Model

DATA DATA

Actual Data Flow

Virtual Data Flow User application. processand management functionsData interpretation, formatand control transformationAdministration and controlof session between two nodesNetwork transparent data transferand transmission controlRouting, switching and flowcontrol over a networkMaintain and release data:link, error and flow controlElectrical and mechanicalcharacteristics

Application

Session

Transport

Network

Data Link

Physical

Presentation

Application

Session

Transport

Network

Data Link

Physical

Presentation


Logical View of Layers

N1

N7

Session

Transport

Network

Physical

Data Link

N2

N3

N4

N6

N8

N5

NETWORK A NETWORK B


Types of Networks

• LAN– Local area

• MAN– Metropolitan area

• WAN– Wide area


Ring, Star & Bus LAN

Ring network

Bus network

Star network

centralserver


IEEE LAN Standards

Physical

MAC

LLC

Physical

MAC

LLC

LAN

Physical

Data link

Logical link control (LLC) IEEE 802.2

Media accesscontrol (MAC)IEEE 802.5 IEEE 802.3

Token ring CSMA/CDOSI model

Media accesscontrol (MAC)


Campus Wide LAN

PRODUCTION_1

PRODUCTION_2

ADMIN_1

ADMIN_2

ELECT_1

INSTR_1MECH_1

Ethernet backbone

ELECT_1 can actas a stand-alonenetwork if required

Fan-outbox

Fan-outbox

Fan-outbox

Fan-outbox

Fan-outbox

Fan-outbox

Fan-outbox


Internetworking


Definition

• An internetwork is an interconnected collection of independent networks– Each independent network is often referred to

as an autonomous system (AS)• Internetwork is the generic name to any

kind of network interconnection • The INTERNET is a special internetwork

that uses TCP/IP protocol stack


Difference with network?

• A network is a collection of interconnected computers

• An internetwork is a collection of interconnected networks (or AS’s)

R2

R1

H4

H5

H3H2H1

Network 2 (Ethernet)

Network 1 (Ethernet)

H6

Network 3 (FDDI)

Network 4(point-to-point)

H7 R3 H8


Various Internetworking Cases

• LAN-LAN– EE LAN to CSE LAN in a campus network

• LAN-WAN– office LAN to the INTERNET

• WAN-WAN– ERNET to VSNL-net

• LAN-WAN-LAN– two offices connected via the INTERNET


Practical Internetworking Scenario

• LAN for small domains of computers• LAN-LAN interconnection for a campus• LAN-WAN interconnection for INTERNET

connectivity• LAN-WAN-LAN interconnection for

connectivity between distant computers


A common Example(LAN-LAN, LAN-WAN, LAN-WAN-LAN)

LAN A

LAN C

LAN D

Wide area

network

connection

Local network

backbone

Wide areanetwork

Gateway

or modem

LAN B

Bridge


Internetworking Devices

• Repeater (layer 1) bit-level• Bridge (layer 2) frame-level• Router (layer 3) packet-level• Gateway (layer 4-7)

message-level– Transport layer gateway TPDU-level– Application layer gateway APDU-level


The INTERNET


Early History

• 1969, Dec – ARPANET went on air:: US DoD

• 1974 – TCP/IP discovered :: Cerf & Kahn• 1983, Jan 01 – TCP/IP became the official

protocol• MILNET is isolated from ARPANET• 1990 – the Internet takes over, ARPANET

dies• NSFNET is merged with ARPANET• 1992 – the Internet Society was set up


The Internet Structure- Recent Past

NSFNET backboneStanford

BARRNET

regional

Berkeley

PARC

NCAR

UA

UNM

Westnet

regional

UNL KU

ISU

MidNet

regional


The Internet Structure- Today

Backbone service provider

Peering

pointPeering

point

Large corporation

Large corporation

Small

corporation

“Consumer ” ISP

“Consumer ”ISP

“ Consumer ” ISP


Traditional use of the Internet

• E-mail (SMTP)– Pine, outlook express, hotmail, yahoo, etc

• News (NNTP)– Usenet

• Remote login (Telnet)– Rlogin

• File transfer (FTP)– CuteFTP, download

• Browsing (HTTP)– WWW, Explorer, Netscape


How to be on the Internet?

• A machine is capable to be on the Internet, if it has – An IP address– TCP/IP support – Ability to send IP packets– Physical connectivity

• Today TCP/IP is built into most OS’s


Connecting from Home

• Windows/Linux has TCP/IP inbuilt• Configure TCP/IP for your ISP & modem• Configure dial-up connection• Connect modem to your PC (connectivity) • Dial ISP’s # using PPP• Login and get temporary IP• Start browser or e-mail client


Connecting to ISP via Modem

Modem

Modem

Modemstack

Modem

Modem33.6 Kbps

Modem56 Kbps

Public switchedtelecommunicationnetwork

ISP Server

INTERNET


TCP/IP Stack

• Unlike OSI, it is a 5 layer architecture– Session & presentation layers are merged into

application layer• Lower 2 layers are not specified

– Any LAN can fit into IP– This is a prime reason for its popularity

• Has its origin in UNIX OS


TCP/IP Architecture

Computer onnetwork A Physical medium

FTP/TELNETApplication

TCP

IP

Application

TCP

IP

Networkcontrollersoftware

Networkcontrollersoftware

Computer onnetwork B


Internet Routing

• Overview– Forwarding vs. routing

• 2-level routing– IGP and EGP

• Distance vector• Link state• Route calculation

– Dijkstra’s algorithm


INTERNET PROTOCOL(IP)


Versions

• Two versions are there:– Version 4 (IPv4)

• 32 bit address– Version 6 (IPv6)

• 128 bit address

• Mobility support– Mobile IP


Global IP Addresses

• Properties– globally unique– hierarchical: network + host– 32/128 bit

• Dotted Decimal Notation– 10.3.2.4– 128.96.33.81– 192.12.69.77


Subnetting

• Add another level to address/routing hierarchy: subnet

• Subnet masks define variable partition of host part• Subnets visible only within site

Network number Host number

Class B address

Subnet mask (255.255.255.0)

Subnetted address

111111111111111111111111 00000000

Network number Host IDSubnet ID


How are subnet masks specified?

Subnetid HostidNetwork ID = 128.138

16 bits 8 bits 8 bits

Subnetid (241) Hostid (78)Network ID = 128.138

16 bits 10 bits 6 bits

11111111 11111111 11111111 00000000 255.255.255.0

11111111 11111111 11111111 11 000000 255.255.255.192


IPv6

• Though CIDR has given IPv4 some breathing space, its days are numbered.

• In 1990, IETF started work on a new version of IP which will never run out of addresses

• In 19993, it is decided as IPv6 – Since IPv5 was already in use for an

experimental real-time streaming protocol


INTERNET Domain Names

edu gov com mil usa uk fr

ac

ed bath napier man

eece cs mmseeece.napier.ac.uk

intel sony nec

wwwwww.eece.napier.ac.uk


Examples

• Hostsnettech.in [domain name] 202.144.75.66 [IP address] --> 80:23:A8:33:5B:9F [ethernet MAC address]

• Files/usr/llp/tmp/foo (server, fileid)

• Users Swapan Purkait [email protected]


Network Security


Common Security Risks

Hacker To test out someone's security system; steal data

Businessman To discover a competitor's marketing strategy

Accountant To embezzle money from a company

Stockbroker To deny a promise made via e-mail

Con man To steal credit card numbers for sale

Student To have fun snooping on peoples' e-mail

Terrorist To destroy data (say by virus attack)


Security Measures

• Physical Layer: covert channel, spread-spectrum• Data Link Layer: link encryption• Network Layer: packet-filter• Application Layer: firewall, cryptography


Secret Key System

Alice Bob

D ES K ey DES K ey


SSL

• It is stream-based consisting of three phases

• In initial handshake phase, secure communications are established

• In intermediate data transfer phase, application-to-application dialog (with data encryption) occurs

• In closing handshake phase, connection is terminated


Looking Forward


The Power of “O”

YOUR BUSINESS

High data rate ~ Tbps

High reliability of fibre ~ 30 years

Low error rate < 10 (̂-6)

Un-repeatered over longer distances


The Power of “M”

YOUR BUSINESS

Handy devices Consumer oriented

Freedom for movement

Anywhere, anytime


Future = Optical + Mobile

• Wireless mobile communication has already attracted global attraction

• DWDM optical technology is maturing at a very high speed

• Future global trends show-Wide-spread adoption of wireless mobile

access to optical backbones


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