final chapt - 1 part - 1
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Data Communication Networks and
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Review Topics
, ,
Network Criteria, Network Models, Categories of
Connection Oriented Networks
Connectionless Networks, Wireless LAN, Gigabit
Interconnection of Networks: Internetwork Protocol Layering, OSI Model
TCP/IP Model
OSI vs TCP/IP
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Data Communications
, , ,television, means communication at a distance (teleis Greek word
forfar).
electronic equipment.
Datarefers to information presented in whatever form is agreed upon
by the parties creating and using the data.
Data Communications are the exchange of data between two
devices via some form of transmission medium such as a wire cable.
A communication system is made up of a combination of hardware
(physical equipment) and software (programs).
ec veness o a a a commun ca on sys em epen s on our fundamental characteristics delivery, accuracy, timeliness, and
jitter.
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Data Communications
Delivery:system must deliver data to the correct destination.
Accuracy:system must deliver data accurately.
Timeliness:system must deliver data in a timely manner.
Jitter:it refers to the variation in the packet arrival time or A
henomenon in real-time traffic caused b a s between
consecutive packets at the receiver.
Components of a data communication system ata commun cat on system as ve components.
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Data Communications
1. Message: is the information (data) to be communicated.
Information includes text, numbers, pictures, audio and
v eo.
2. Sender: is the device that sends the message. It can be a
computer, workstation, telephone handset, video camera etc.
3. Receiver:is the device that receives the message. It can be a
computer, workstation, telephone handset, video camera etc.
.
message travels from sender to receiver. It can be twistedpair
wire, coaxial cable, fiber optic cable and radio waves.
. ro oco : s a se o ru es a governs a a commun ca ons.It represents an agreement between communicating devices.
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Data Communications
Information can be represented in different forms such as text,
numbers, images or pictures, audio and video.
Text: text is represented as a bit pattern, different sets of bit
patterns have been designed to represent text symbols. Each set
is calledcode, and the process of representing symbols is called
coding. For example:32 bit Unicode,ASCIIcode, etc.
Numbers: numbers are represented by bit patterns, number is
directl converted to binar number. ASCII is not used to
represent numbers.
Images:images are also represented by bit patterns. An image is
,on the resolution.
For pure black white image: 1 bit is enough to represent a pixel
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:w e, : ac .
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Data Communications
Images:
If image is not pure black white image (gray scale): 2 bit patterns
are use to s ow our eve s o gray sca e : a ac p xe,
01: a dark gray pixel,10: a light gray pixel, 11: a white pixel.
For color images:RGB(red, green, blue) andYCM(yellow, cyan,
magenta met o s are use .
Audio:it refers to recording or broadcasting of sound or music.
It is continuous, not discrete. We can use microphone to changevoice or music to an electric signal (analog or digital).
Video:it refers recording or broadcasting of a picture or movie.
It can be either continuous entit b a TV camera or it can be
combination of images, each is a discrete entity, arranged to
convey the idea of motion. We can change video to a digital or
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Data Communications
Communication between two devices can be Simplex, Half
Duplex or Full Duplex.
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Data Communications
Simplex:communication is unidirectional, only one of the
two devices on a link can transmit; the other can only
receive. Keyboards and traditional monitors are
examples of Simplex devices.
,
not at the same time. When one device is sending, the
other can only receive, and vice versa.Walkie - talkiesan c zen an ra os are ot a up ex
systems.
Full - Du lex: both stations can transmit and receive
simultaneously, also called as Duplex. It is used when
communication in both directions is required all the time.
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Networks
A Network is a set of devices (often referred as nodes)connected by communication links. A node can be a computer,
printer or any other device capable of sending and / or
.
Networks allow users toshare resources, such as hardware,software, data and information.
Advantages of using a Network
Facilitates communications because people can communicate- , , ,
telephony, and videoconferencing.
Allow tight control over who has access to what data.
Reduce cost by sharing hardware (a printer) and software(using a network version or site license of a program).
Sharin data and information stored on other com uters on the
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network.
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Networks
The hardware, software, and expertise required to set up a
network can be expensive.
Networks are vulnerable to security problems.
If the server fails to work, the complete network may also fail
to work.
Distributed Processing:most of the networks use distributed
processing, in which task is divided among multiplecompu ers.
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Networks
number of criteria, most important criteria are performance,
reliability, and security.
Performance:performance is measured by transit time and
response time.
Transit time is the amount of time re uired for a
message to travel from one device to another.
Response Time is the elapsed time between an enquiry.
Performance of a network depends on a number of factors
such asnumber of users,type of transmission medium,
capabilities of connected hardware an efficiency ofsoftware.
Performance is often evaluated by two networkingmetrics:
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throughputanddelay.
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Networks
Reliability: in addition to accuracy of delivery, reliability is
measured by thefrequency of failure, the time it takes a link to
recover rom a ure.
Security:network security issues include protecting data from
unauthorized access, protecting data from damage and
development, and implementing polices and procedures for
recovery from breaches and data losses.
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Networks
Based on the size, distance covered and transmission
media used, networks are categorized into three types
namely: LAN, MAN, WAN.
LAN (Local Area Network):
small area such as a building, office or campus.
LANs are designed to allow resources to be shared betweenworkstations.
Covers distance up to 5 - 10 km.
- .
Today LANs have data rate/speed 100 or 1000 Mbps.
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Networks
LAN (Local Area Network)
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Networks
MAN (Metropolitan Area Network):
It covers the area inside a town or Metropolitan city.
It connects many LANs located at different offices orcampuses within a city.
.
Covers distance up to few hundred km.
It has data rate/speed in the range of 1.5 - 150 Mbps.
A good example of MAN is the part of the telephone
company network that can provide a high speedDSLline
to the customer.
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Networks
MAN (Metropolitan Area Network):
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Networks
WAN (Wide Area Network):
Used to interconnect computers over a very large
geographic area such as different cities within the country
or continent or even the whole world.
Covers distance u to few thousand km.
It has data rate/speed in the range of 1.5 Mbps to 2.4 Gbps.
An early example of Switched WAN is X.25 networkes gne to prov e connect v ty etween en users.
Today, a good example of switched WAN is ATM network.
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Networks
WAN (Wide Area Network):
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Networks
It is very rare to see a LAN, a MAN, or a WAN in isolation;
they are connected to one another.
When two or more networks are connected, they become an
Internetwork or internet.
The Internet has revolutionized man as ects of our dail lives.
It has affected the way we do business as well as the way we
spend our leisure time.
wealth of information to our fingertips and organized it for our
use.
: e wor ccess o n comp ex w c ng s a on. National ISP: National Internet Service Providers.
Re ional ISP andLocal ISP.
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Networks
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Network Models Layered Tasks:
We use the concept oflayersin our daily life. As an example, let us
consider two friends who communicate through postal mail.
Sender, Receiver, and Carrier that trans orts the letter.
There is hierarchy of tasks involved.
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Network Models: The OSI Model Established in 1947, the International Standards Organization (ISO) is a
mu t nat ona o y e cate to wor w e agreement on nternat onastandards.
AnISO standardthat covers all aspects of network communications is
t e pen ys ems n erconnec on mo e .
It was first introduced in the late 1970s.
An Open System is a set of protocols that allows any two different
systems to communicate regardless of their underlying architecture.
ISO is the organizationandOSI is the model.
An international standard that is referred by most network vendors for
their products and services.
Best tool for teaching people about sending and receiving data on a
network.
Consist of 7 layers: Physical (L1), Data Link (L2), Network (L3),Transport (L4), Session (L5), Presentation (L6) and Application (L7).
Each of the la er illustrates a articular network function.
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This separation of networking functions is called layering.
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Network Models: The OSI Model Advantages of multi layered model
Reduce complexity: simplified teaching and learning.
Standardize interface, accelerate evolution.
Prevent the chan e of one la er from affectin the other la ers.
Characteristics for the 7 layer model Peer to Peer process:layer Nof one computer can communicate
.
Alayer Ngets a service from thelayer N 1and provide a service to
thelayer N + 1. ApplicationLa er 7:
Presentation
Session
Layer 6:
Layer 5:
Network
Data link
Layer 3:
Layer 2:
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ayer :
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Network Models: The OSI Model The Interaction between layers in the OSI model.
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Network Models: The OSI Model Data Encapsulation: Wrapping of data with necessary protocol
information before network transit (adding header or trailer or
both).
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Network Models: The OSI Model Why Data Encapsulation?
To addcontrol information(in the form ofheader or trailer or
both) to the data being encapsulated in order to ensure accurate and
secure communication.
The data after encapsulated is calledProtocol Data Unit (PDU). Note:Headersare added to the data atlayers 7, 6, 5, 4, 3,and2.
ra ersare usua y a e on y a ayer .
The control information falls into the three categories:
Address:The address of the sender and / or receiver may beindicated.
Error-detecting code: some sort of frame check sequence.
implement the protocol functions such as priority,quality of
serviceandsecurity.
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Network Models: The OSI Model Functions of Physical Layer
Physical characteristics of interfaces and media:interface between the
devices and the transmission medium (e.g. NIC). It also defines the type of
transmission medium (e.g. Wire).
Representation of Bits:encoding the bits (0s and 1s ) into electrical or
optical signals. This layer also defines the type of encoding (e.g. ASK or
FSK).
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Network Models: The OSI Model Functions of Physical Layer
Data Rate: the transmission rate in terms of number of bit sent each
second (e.g. 56 Kb/s).
S nchronization of Bits: the sender and the receiver clocks must be
synchronized.
Line Configuration:the connection of devices to the medium (point
to ointormulti oint confi uration.
Physical Topology:the configuration for the devices to be connected to
form a network (mesh, star, ringorbus topology).
transmission between two devices: Simplex, Half-Duplex, or Full-
Duplex.
Exam le for the h sical la er rotocol: Point-to-Point Protocol PPP
Ethernet,FDDIetc.
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Network Models: The OSI Model Functions of Data Link Layer
The data link layer is responsible fornodetonode delivery, it makes the
physical layer appear error free to the upper layer (network layer). It also
take care of the following functions:
Framing:The data link layer divides the stream of bits received from the
network layer into manageable data units calledframes.
Ph sical Addressin :The data link la er adds a header to the frame to
define thephysical address (MAC)of thesender(source address) and/or
receiver(destination address) of the frame.
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Network Models: The OSI Model Functions of Data Link Layer
Flow control:If the rate at which the data are absorbed by the receiver is
less than the rate produced in the sender, the data link layer will impose a
flow control mechanism to prevent overwhelming the receiver.
Error control:Mechanism that can detect and retransmit damaged or lost
frames and also prevent duplication of frames. Error control is normallyachieved by the trailer at the end of the frame.
Access control:When one or more devices are connected to the same link,
data link layer protocols are necessary to determine which device has
control over the link at any given time.
Data 20 62DT
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Trailer Source address Destination address
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Network Models: The OSI Model Functions of Data Link Layer
The data link layer is responsible forNodetoNode orHoptoHop
delivery.
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Network Models: The OSI Model Functions of Network Layer
The network layer is responsible for thesourcetodestinationdelivery
of a packet possibly across multiple networks, if two systems are
connected to the same link, no need for a network layer.
Logical addressing:network layer adds a header to the incoming packet
from the upper layer with a logical address of the sender. If a packet passesthe network boundary, this universal (logical) address helps to distinguish
whether the packet belong to the source or destination systems.
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Network Models: The OSI Model Functions of Network Layer
Routing: Router (or gateways) connect independent networks together,
network layer routes the packet to their final destination by router
(gateway).
The figure shows the case for a computer"S" communicating with a
remote computer"D". SandDare thelogical addressesof the sourceand destination computers respectively, where 02 and79 are the local
physical addressesof the source and destination computers respectively.
S A
F
D
79DT Data S D 02 46
DT Data S D 23 09
DT Data S D 29 79
T
Router
X46
23 29
02 37
R
K
L
15
78Ring
Router
U 61
09
C
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OS
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Network Models: The OSI Model Functions of Network Layer
Network Layerresponsible forSourcetoDestinationdelivery.
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N k M d l Th OSI M d l
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Network Models: The OSI Model Functions of Transport Layer
Responsible for SourcetoDestination (EndtoEnd) delivery of the
entire message.
Se mentation occurs and this la er also ensures the whole messa e arrives
intact and in order.
A logical path can be set up (fixed pathway) between the Source and
Destination for all ackets in a messa e for additional securit .
This layer has more control oversequencing,flowanderror detection
andcorrection.
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N t k M d l Th OSI M d l
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Network Models: The OSI Model Functions of Transport Layer
Connection control:The transport layer can be eitherConnectionlessor
ConnectionOriented.
Flow control:It erform End to End flow control which differs from the
data link layer which is responsible for flow control in single link.
Error control:It performs End to End error control which make sure the
entire messa e arrives at the receivin trans ort la er without error
(damage, loss or duplication). Error correction is done by re-transmission.
Transport layer is responsible for the delivery of a message from one
process to another.
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N t k M d l Th OSI M d l
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Network Models: The OSI Model Functions of Session Layer
It is network dialog controlling layer. It establishes, maintains, and
synchronizes the interaction between communication systems.
Dialo control: It allows two s stems to enter into a dialo . The
communication between two processes can be controlled in either half-
duplex or full-duplex.
S nchronization:- It allows a rocess to addcheck ointsinto a stream
of data, when data loss during transmission occurred, more efficient re-
transmission can be performed.
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N t k M d l Th OSI M d l
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Network Models: The OSI Model Functions of Presentation Layer
The presentation layer is concerned with the syntax and semantics of the
information exchange between two systems.
Translation:It encodes the sender de endent format of the messa e into
a common format that can be readable by any receiving system.
Encryption:It can transform the original information into an encrypted
form to assure rivac .
Compression: Data compression can reduce the number of bits to be
transmitted, which is important for multimedia transmission.
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N t k M d l Th OSI M d l
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Network Models: The OSI Model Functions of Application Layer
This layer enable the user (human or software) to access the network by
user interfaces. Other services provided by this layer are:
Network virtual terminal:remote lo -in to other host in the internet.
File transfer, access, and management: store, retrieve or manage the
files from a remote computer. e.g. File Transfer Protocol (FTP).
. . .
Directory services:access for global information and services e.g.Hyper
Text Transfer Protocol (HTTP).
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Network Models: The OSI Model
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Network Models: The OSI Model Summary for the functions of OSI Layers
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Network Models: TCP/IP Protocol Suite
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Network Models: TCP/IP Protocol Suite TCP/IP vs OSI model:The layers in the TCP/IP protocol suite do not
exact y matc t ose n t e mo e . e or g na protoco su tewas defined as havingfour layers: host-to-network,internet,transport,
andapplication. However, whenTCP/IPis compared toOSI, we can say
, ,
network,transport, andapplication.
TCP/IP - Transmission Control Protocol / Internet Protocol.
s t e as c commun cat on anguage or protoco o t e nternet.
It can also be used as a communications protocol in the private networks
such as Intranets and Extranets. TCP/IP is a two layered program
TCP Manages the assembling of a message or file into smaller packets.
IP Handles the address part of each packet so that it gets to the right
destination.
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Network Models: TCP/IP Protocol Suite
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Network Models: TCP/IP Protocol Suite
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Network Models: TCP/IP Protocol Suite
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Network Models: TCP/IP Protocol Suite Application Layer: It contains all the higher level protocols such as
, , , , , , etc. Transport Layer: Designed to allow peer entities on the source and
destination hosts carry on a conversation. Contains protocols such as TCP,
an . an are en -to-en rotoco s.
TCP (Transmission Control Protocol):connection-oriented protocolthat manages the assembling of a message or file into smaller packets
t at are transm tte over t e nternet.
UDP (User Datagram Protocol): Connectionless protocol for
applications that do not want TCPs sequencing or flow controlpeec or eo .
SCTP (Stream Control Transmission Protocol):provides support
for newer applications such as Voice over Internet. It combines the
es ea ures o an .
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Network Models: TCP/IP Protocol Suite
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Network Models: TCP/IP Protocol Suite Internet Layer:defines an official packet format and protocol called as IP
nternet rotoco . nternet ayer e vers pac ets to w ere t ey aresupposed to go (packet routing). Contains protocols such as ARP, RARP,
ICMP, IGMP, RIP, OSPF etc.
ress eso u on ro oco : use to assoc ate t e og ca
address to physical address. RARP (Reverse Address Resolution Protocol):allows the host to
scover t s og ca a ress w en t nows on y t s p ys ca a ress.
ICMP (Internet Control Message Protocol):it is used by hosts and
gateways to send the notification of datagram problems back to sender. IGMP (Internet Group Message Protocol):it allows simultaneous
transmission of message to a group of recipients.
RIP (Routing Information Protocol):It is adistance vector route
discovery protocol. RIP broadcast their route table throughout the
network. The broadcasted information lists destination networks and
their distances from the broadcasting router in terms of hops, must be
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crosse . oes no wor we n arge an comp ca e n er-ne wor s.
Network Models: TCP/IP Protocol Suite
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Network Models: TCP/IP Protocol Suite Internet Layer: Contains protocols such as ARP, RARP, ICMP, IGMP,
, etc. OSPF (Open Shortest Path First):It was developed to address RIPs
weakness. It is a link state route discovery protocol that provides
t e a ty to scover t e networ s spec c topo ogy. t ex ts
better performance than RIP in large inter-network. Since it facilitatesClass-of-Servicebased onroutingandload balancing.
os o e wor ayer ys ca an a a n ayer : at
physical and data link layer, TCP/IP does not define any specific protocol.
Host connects to the network using relevant protocols so it can send IP
.
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Connection Oriented Networks / Service Connection-oriented services involves 5 phases:
1. Idle No Connection
2. Connection Establishment
3. Data transfer
4. Connection Release
5. Idle No Connection
Packet Switched Network
Idle No Connection
Connection Establishment
It provides substantial amount of care for the
user data.
Provides Acknowledgement, Flow Control and
Data Transfer
Connection Release
Error Recovery.
Involves more overheads because of many
support functions.
Idle No Connection
( ACK, Flow Control, Error Recovery )
e a e ut ower serv ce.
Example: TCPs service.
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Connectionless Networks / Service
Connectionless services involves 3 phases:
1. Idle No Connection
3. Idle No Connection
Also called as datagram networks.
Packet Switched Network
release phase.
Does not provide Acknowledgement, Flow
Control and Error Recovery.
Idle No Connection
It involves less overhead.
Faster service but unreliable Service.
Example: UDPs service.
Data Transfer
( No - ACK, Flow Control, Error Recovery )
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