Basics of COMPUTER NETWORKS

Basics of COMPUTER NETWORKS

Book in glance

Computer EngineeringFaculty of EngineeringKurdistan University

( Email : [email protected])

سرفصل هاي درس

Contact information

: مفاهيم اوليه1فصل •: اليه فيزيكي 2فصل •: اليه پيوند داده3فصل •: اليه شبكه4فصل •: اليه انتقال5فصل •: اليه كاربرد6فصل • : كابل كشي ساخت يافته7فصل •

What’s a Computer Network?

• Connecting two or more computers or other devices via a Communication media( Physical or wireless)

• Categorizing networks according to size:

– LAN (Local Area Network)– MAN (Metropolitan Area Network)– WAN (Wide Area Network)– Internet

3Kurdistan UniversityComputer Network

Kurdistan UniversityComputer Network 4

Types of Links

Point-to-Point Multiple Access

…

5Kurdistan UniversityComputer Network



Protocol Demultiplexing

FTP HTTP TFTPNV

TCP UDP

IP

NET1 NET2 NETn…

TCP/UDPIP

IPX

Port Number

Network

Protocol Field

Type Field

• Multiple choices at each layer


OSI Layers and Locations

Switch RouterHost Host

Application

Transport

Network

Data Link

Presentation

Session

Physical

Hub


Network Interface Card (NIC)


Hub (layer 1 device)Just knows bits


Switch (layer 2 device)Knows MAC addresses


Router (layer 3 device)Knows Logical addresses (IP and IPX)



Connector

Twisted Pair

UTP

STP


Bad Good


Connectors


Connectors

Fiber Optic



A Fiber Optic Ring with Active repeaters


Electromagnetic Spectrum


Types of Propagation


Basic Modulation Types


Compression:

Huffman Coding

Run-length Coding

Ziv Lempel compression



FDM (Frequency Division Multiplexing)


WDM (Wavelength Division Multiplexing)


TDM (Time Division Multiplexing)



Circuit Switching



Time Division Switch


Packet Switching


Message Switching


Framing Methods

Character Count

Byte Stuffing

Bit Stuffing


Handling Errors


Single bit Error

Multiple bit Error


0110100

1011010

0010110

1110101

1001011

1

0

1

1

0

1000110 1

Parity bit

One Dimensional Parity

Two Dimensional Parity


Cyclic Redundancy Check (CRC)

• Represent a (n+1)-bit message as an n-degree polynomial M(x)–E.g., 10101101 M(x) = x7 + x5 + x3 + x2 + x0

• Choose a divisor k-degree polynomial G(x)• Compute reminder R(x) of M(x)*xk / C(x), i.e., compute

A(x) such thatM(x)*xk = A(x)*G(x) + R(x), where degree(R(x)) < k

• Let T(x) = M(x)*xk – R(x) = A(x)*G(x)

• Then–T(x) is divisible by G(x)


Hamming Code


Categories of Flow Control


Stop-and-Wait


ReceiverReceiverSenderSender

Sliding WindowSender/Receiver State

… …

Sent & Acked Sent Not Acked

OK to Send Not Usable

… …

Max acceptable

Receiver window

Max ACK received Next seqnum

Received & Acked Acceptable Packet

Not Usable

Sender window

Next expected


Example of Sliding Window


Sliding WindowGo-Back-n, Damaged Frame


Sliding windowSelective-Repeat, Damaged Frame


Evolution of Contention Protocols

Developed in the 1970s for a packet radio network

Aloha

SlottedAloha

Improvement: Start transmission only at fixed times (slots)

CSMA

CSMA = Carrier Sense Multiple AccessImprovement: Start transmission only if no transmission is ongoing

CD = Collision Detection

Improvement: Stop ongoing transmission if a collision is detected (e.g. Ethernet)

CSMA/CD

Media Access Control


The Aloha Protocol

•simple: if you have pkt to send, "just do it" •if pkt suffers collision, will try resending later


Slotted Aloha

•synchronous system: time divided into slots •slot siz equals fixed packet transmission time •when pkt ready for transmission, wait until start of next slot •packets overlap completely or not at all


Carrier Sensing Protocols

•Aloha is inefficient (and rude!): doesn't listen before talking! •Carrier Sense Multiple Access: CSMA

non-persistent CSMA: 1.sense (listen to) channel 2.if {channel sensed busy}

then wait random time; go to 1 else transmit packet

p-persistent CSMA: 1.sense (listen to) channel 2.when {channel sensed idle}

transmit with probability p else wait random time, go to 1


CSMA/CD

•CSMA with collision detection(CD): •listen while talking! •stop transmitting when another pkt has collided with your pkt

•wait random time before attempting to resend •worst case time to detect a collision? •performance depends (as in CSMA) on channel length


Collision free protocolsReservation

No collisions reservation is made before sending

average waiting time before transmission is N low load utilization: d/(d+N) – not good if N is large high-load utilization d/(d+1)

d bits

N bits

t


Collision free protocols



IEEE 802 Standards



802.3 Frame structure


10Base5


10Base2


10BaseT


10BaseF


IEEE 802.4Token Bus Network


Token Ring IEEE 802.5

Data Token/Data

l1

l3 l2

l4

min/ TRTclPROPi i

TRT=Token Rotation Time

Listen:

Talk:


Token Ring IEEE 802.5


IEEE 802.11 Wireless LAN (WLAN)

802.11b

802.11 802.11a 802.11g


ISM Bands(Unlicensed )

802.11b (11Mbps)

802.11g(54 Mbps)

802.11a(54 Mbps)


Wireless Access PointWireless Network Interface Card


Spread Spectrum Methods

FHSS DSSS


FHSS


DSSS

Original Data

Transmitted Data


ESSExtended Service Set

BSS: Basic Service Set

Overlapped Area for roaming


CSMA/CA





Internetworking

Hop-by-hop

Network Layer


Need of Network Layer

Host-to-host (End-to-end)


Packet delivery in Network layer

Internet


Routing Algorithms

• Calculate the shortest path (lowest cost)

• Two common methods– Distance vector routing (RIP , IGRP , … )– Link state routing (OSPF , IS-IS)


The concept of distance vector routing


Concept of link state routing


Hierarchical Routing

Routing in Autonomous Systems (IGP)

EGP

IGP

Routing between Autonomous Systems (EGP)

Basics of COMPUTER NETWORKS

Documents

router layer

hub layer

switch layer

types of linkspoint

osi layers

fiber optic ring

wirelesscategorizing

communication media