Computer Network

Unit-I
Books To Be Referred :
1.Computer Network by Tanenbaum
2.Data Communication & Networking by Forouzan
OUTLINE
• Introduction to Computer Network
• Use of Computer Network
• Network Hardware
• Network Software
• Reference Model-OSI and TCP/IP
Introduction to Computer Network
• Computer Network is a large number of separate but interconnected
computers .
• Two computers are said to be interconnected if they are able to exchange
information.The connection need not be via a copper wire; fiber optics,
microwaves, infrared,and communication satellites can also be used.
• Network are usually connected together to make larger networks, with the
Internet(Internetwork) being the most well-known example of a network of
networks.
• A distributed system is a collection of independent computers appears to its
users as a single coherent system.For ex.- WWW
• Distributed System is implemented over a layer of software on top of the
operating system, called middleware. It runs on top of the Internet and
presents a model in which everything looks like a document (Web page).
Use of Computer Network
• Business Applications-resource sharing,servers,clients,client-server
model,Web application,communication medium,email,IP telephony
or Voice over IP (VoIP),Desktop sharing,e-commerce.
• Home Applications-connectivity,peer-to-peer communication,instant
messaging,Twitter,Facebook,wiki,IPTV,Ubiquitous Computing,power-
line networks,RFID (Radio Frequency IDentification).
• Mobile Users-Connectivity,hotspots,fixed wireless and mobile
wireless,texting or sms,smatphone,GPS,m-commerce,NFC,sensor
network,wearable computers.
• Social Issues-network neutrality,profiling users using
cookies,gmail,botnet,phishing,CAPTCHA.
Combinations of Wireless Networks and Mobile
Computing.
Some Forms of E-commerce.
Network Hardware
• Two dimensions stand out as
important:
• transmission technology
• broadcast
links(multicasting,broadcasting) and
and point-to-point links(unicasting).
• scale
• Classification of interconnected
processors by scale.
Classification Based on Scales
• Personal Area Networks-Wireless peripherals,bluetooth,RFID.
• Local Area Network-private networks,acces points,switch,port
• Wireless LANs called IEEE 802.11 mpopularly called Wifi(speed is 11 to 100
Mbps, 1 Mbps is 1,000,000 bits/sec,1 Gbps is 1,000,000,000 bits/sec),
• Wired LAN called IEEE 802.3, popularly called Ethernet( 100 Mbps to 1
Gbps)
• Virtual LAN
• Metropolitan Area Network-covers city-IEEE 802.16-WiMax
• WAN-spans a large geographical area-country ,continent.
• host,switches,router,Network service provider,Internet service
provider,routing algorithm(network),forwarding algorithm(router)
• InternetWorks or internet-Gateway
Network Software
• The first computer networks were designed with the hardware as the
main concern and the software as an afterthought. This strategy no
longer works. Network software is now highly structured.

• Protocol Hierarchies-layer/level,protocol,services,peers(can be software

processes, hardware devices, or even human beings),physical
medium,interface,network architecture,protocol stack.
• Design Issues for the Layers-error detection and error
correction,addressing/naming,scalable,router,protocol layering,statistical
multiplexing(sharing based on the statistics of demand),flow
control,congestion,Quality of Service,confidentiality,authentication,integrity.

• Connection-Oriented Versus Connectionless Service

Connection-Oriented Service
• Layers can offer two different types of service to the layers above them:
connection-oriented and connectionless.
• Connection-oriented service is modeled after the telephone system. To talk
to someone, you pick up the phone, dial the number, talk, and then hang up.
• Similarly, to use a connection-oriented network service, the service user first
establishes a connection, uses the connection, and then releases the
connection.
• The essential aspect of a connection is that it acts like a tube: the sender
pushes objects (bits) in at one end, and the receiver takes them out at the
other end. In most cases the order is preserved so that the bits arrive in the
order they were sent.
• Negotiation-about the parameters to be used, such as maximum message
size, quality of service required, and other issues.
• Circuit-is another name for a connection with associated resources,such as a
fixed bandwidth.
• example-file transfer.
Connectionless Service
• Connectionless service is modeled after the postal system. Each message
(letter) carries the full destination address,and each one is routed through the
intermediate nodes inside the system independent of all the subsequent
messages.
• There are different names for messages in different contexts:
• A packet is a message at the network layer. When the intermediate nodes
receive a message in full before sending it on to the next node, this is called
store-and-forward switching.
• The alternative, in which the onward transmission of a message at a node
starts before it is completely received by the node, is called cut-through
switching.
• For example-spammers send electronic junk-mail to many recipients.
• Connectionless service is often called datagram service, in analogy with
telegram service, which also does not return an acknowledgement to the
sender.
Service Primitives
• A service is formally specified by a set of primitives (operations)
available to user processes to access the service. These primitives tell
the service to perform some action or report on an action taken by a
peer entity.
• If the protocol stack is located in the operating system, as it often is,
the primitives are normally system calls. These calls cause a trap to
kernel mode, which then turns control of the machine over to the
operating system to send the necessary packets.
• The set of primitives available depends on the nature of the service
being provided. The primitives for connection-oriented service are
different from those of connectionless service.
• As a minimal example of the
service primitives that might
provide a reliable byte stream,
consider the primitives listed in
Fig.
• They will be familiar to fans of
the Berkeley socket interface, as
the primitives area simplified
version of that interface.
The Relationship of Services to Protocols
• Services and protocols are distinct concepts. This distinction is so important that we
emphasize it again here.
• A service is a set of primitives (operations) that a layer provides to the layer above it. The
service defines what operations the layer is prepared to perform on behalf of its users, but
it says nothing at all about how these operations are implemented.
• A service relates to an interface between two layers, with the lower layer being the service
provider and the upper layer being the service user.
• A protocol, in contrast, is a set of rules governing the format and meaning of the packets, or
messages that are exchanged by the peer entities within a layer.Entities use protocols to
implement their service definitions. They are free to change their protocols at will,
provided they do not change the service visible to their users.
• An analogy with programming languages is worth making. A service is like an abstract data
type or an object in an object-oriented language. It defines operations that can be
performed on an object but does not specify how these operations are implemented. In
contrast, a protocol relates to the implementation of the service and as such is not visible
to the user of the service.
REFERENCE MODELS
• The OSI Reference Model( ISO OSI (Open Systems Interconnection))
• The TCP/IP Reference Model
OSI Model
• This model is based on a proposal developed by the International
Standards Organization (ISO) as a first step toward international
standardization of the protocols used in the various layers.
• The model is called the ISO OSI (Open Systems Interconnection)
Reference Model because it deals with connecting open systems—
that is, systems that are open for communication with other systems.
• The OSI model has seven layers. The principles that were applied to
arrive at the seven layers can be briefly summarized as follows:
1. A layer should be created where a different abstraction is needed.
2. Each layer should perform a well-defined function.
3. The function of each layer should be chosen with an eye toward defining internationally
standardized protocols.
4. The layer boundaries should be chosen to minimize the information flow across the
interfaces.
5. The number of layers should be large enough that distinct functions need not be
thrown together in the same layer out of necessity and small enough that the architecture
does not become unwieldy.
Note- The OSI model itself is not a network architecture because it does not specify the
exact services and protocols to be used in each layer. It just tells what each layer should
do.
However, ISO has also produced standards for all the layers, although these are not part
of the reference model itself. Each one has been published as a separate international
standard.
The model (in part) is widely used although the associated protocols have been long
forgotten.
The Physical Layer
• The physical layer is concerned with transmitting raw bits over a
communication channel. The design issues have to do with making sure that
when one side sends a 1 bit it is received by the other side as a 1 bit, not as a 0
bit. Typical questions here are what electrical signals should be used to
represent a 1 and a 0,
• how many nanoseconds a bit lasts,
• whether transmission may proceed simultaneously in both directions,
• how the initial connection is established, how it is torn down when both sides
are finished,
• how many pins the network connector has, and
• what each pin is used for.
• These design issues largely deal with mechanical, electrical,and timing
interfaces, as well as the physical transmission medium, which lies below the
physical layer.
Physical Layer Summary
• Physical characteristics of interfaces
and medium
• Representation of bits-electrical or
optical
• Data rate-bit sent per sec
• Synchronization of bits-bit rate,bit
level
• Line configuration-point to point
,multipoint
• Physical topology-star,bus,mesh ..
• Transmission mode-simplex,half
duplex,full duplex.
 The Data Link Layer
• The main task of the data link layer is to transform a raw transmission facility into a line that
appears free of undetected transmission errors. It does so by masking the real errors so the
network layer does not see them.
• It accomplishes this task by having the sender break up the input data into data frames
(typically a few hundred or a few thousand bytes) and transmit the frames sequentially.
• If the service is reliable, the receiver confirms correct receipt of each frame by sending back
an acknowledgement frame.
• Another issue that arises in the data link layer (and most of the higher layers as well) is how
to keep a fast transmitter from drowning a slow receiver in data.
• Some traffic regulation mechanism may be needed to let the transmitter know when the
receiver can accept more data.
• Broadcast networks have an additional issue in the data link layer: how to control access to
the shared channel. A special sublayer of the data link layer, the medium access control
sublayer, deals with this problem.
Data Link Layer Summary
• Framing
• Physical addressing(same
network)
• Flow control(link to link)
• Error control(link to link)
• Access control
The Network Layer
• The network layer controls the operation of the subnet. A key design issue is
determining how packets are routed from source to destination. Routes can be
based on static tables that are ‘‘wired into’’ the network and rarely changed, or
more often they can be updated automatically to avoid failed components.
• They can also be determined at the start of each conversation, for example, a
terminal session, such as a login to a remote machine. Finally, they can be
highly dynamic, being determined a new for each packet to reflect the current
network load.
• If too many packets are present in the subnet at the same time, they will get in
one another’s way, forming bottlenecks.
• Handling congestion is also a responsibility of the network layer, in conjunction
with higher layers that adapt the load they place on the network. More
generally, the quality of service provided (delay,transit time, jitter(Is the
variation of delay time), etc.) is also a network layer issue.
• When a packet has to travel from one network to another to get to its
destination, many problems can arise. The addressing used by the
second network may be different from that used by the first one.
• The second one may not accept the packet at all because it is too
large. The protocols may differ, and so on.
• It is up to the network layer to overcome all these problems to allow
heterogeneous networks to be interconnected.
• In broadcast networks, the routing problem is simple, so the network
layer is often thin or even nonexistent.
Network Layer Summary
• Logical addressing(multiple
network)
• Routing
The Transport Layer
• The basic function of the transport layer is to accept data from above it, split it up
into smaller units if need be, pass these to the network layer, and ensure that the
pieces all arrive correctly at the other end. Furthermore, all this must be done
efficiently and in a way that isolates the upper layers from the inevitable changes in
the hardware technology over the course of time.
• The transport layer also determines what type of service to provide to the session
layer, and, ultimately, to the users of the network. The most popular type of
transport connection is an error-free point-to-point channel that delivers messages
or bytes in the order in which they were sent. However, other possible kinds of
transport service exist, such as the transporting of isolated messages with no
guarantee about the order of delivery, and the broadcasting of messages to multiple
destinations.
• The type of service is determined when the connection is established. (As an aside,
an error-free channel is completely impossible to achieve;what people really mean
by this term is that the error rate is low enough to ignore in practice.)
• The transport layer is a true end-to-end layer; it carries data all the
way from the source to the destination. In other words, a program on
the source machine carries on a conversation with a similar program
on the destination machine, using the message headers and control
messages.
• In the lower layers, each protocols is between a machine and its
immediate neighbors, and not between the ultimate source and
destination machines, which may be separated by many routers.
• The difference between layers 1 through 3, which are chained, and
layers 4 through 7,which are end-to-end, is illustrated in Fig. 1-20.
Transport Layer Summary
• Service-point addressing
• Segmentation and reassembly
• Connection control.
• Flow control(end to end)
• Error control(process-to-process)
The Session Layer
• The session layer allows users on different machines to establish
sessions between them. Sessions offer various services, including
dialog control (keeping track of whose turn it is to transmit), token
management (preventing two parties from attempting the same
critical operation simultaneously), and synchronization(check
pointing long transmissions to allow them to pick up from where they
left off in the event of a crash and subsequent recovery).
The Presentation Layer
• Unlike the lower layers, which are mostly concerned with moving bits
around,the presentation layer is concerned with the syntax and
semantics of the information transmitted.
• In order to make it possible for computers with different internal data
representations to communicate, the data structures to be exchanged
can be defined in an abstract way, along with a standard encoding to
be used ‘‘on the wire.’’
• The presentation layer manages these abstract data structures and
allows higher-level data structures (e.g., banking records) to be
defined and exchanged.
• Translation(interoperability)
• Encryption(for carrying sensitive info safely)
• Compression
The Application Layer
• The application layer contains a variety of protocols that are
commonly needed by users. One widely used application protocol is
HTTP (HyperText Transfer Protocol), which is the basis for the World
Wide Web.
• When a browser wants a Web page, it sends the name of the page it
wants to the server hosting the page using HTTP. The server then
sends the page back. Other application protocols are used for file
transfer, electronic mail, and network news.
• It Provides various services to the user.
• Network virtual terminal,File transfer, access, and
management,Mail services,Directory services.
The TCP/IP Reference Model
The Link Layer
• All these requirements led to the choice of a packet-switching
network based on a connectionless layer that runs across different
networks.
• The lowest layer in the model, the link layer describes what links such
as serial lines and classic Ethernet must do to meet the needs of this
connectionless internet layer.
• It is not really a layer at all, in the normal sense of the term, but
rather an interface between hosts and transmission links. Early
material on the TCP/IP model has little to say about it.
The Internet Layer

• The internet layer is the linchpin that holds the whole architecture together.
• It is shown in Fig. 1-21 as corresponding roughly to the OSI network layer.
• Its job is to permit hosts to inject packets into any network and have them
travel in dependently to the destination (potentially on a different network).
• They may even arrive in a completely different order than they were sent, in
which case it is the job of higher layers to rearrange them, if in-order delivery
is desired.
• Note that ‘‘internet’’ is used here in a generic sense, even though this layer is
present in the Internet.
• The analogy here is with the (snail) mail system. A person can drop a sequence
of international letters into a mailbox in one country, and with a little luck,most
of them will be delivered to the correct address in the destination country.
• The letters will probably travel through one or more international mail gateways
along the way, but this is transparent to the users. Furthermore, that each
country(i.e., each network) has its own stamps, preferred envelope sizes, and
delivery rules is hidden from the users.
• The internet layer defines an official packet format and protocol called
IP(Internet Protocol), plus a companion protocol called ICMP (Internet Control
Message Protocol) that helps it function. The job of the internet layer is to
deliver IP packets where they are supposed to go.
• Packet routing is clearly a major issue here, as is congestion (though IP has not
proven effective at avoiding congestion).
The Transport Layer
• The layer above the internet layer in the TCP/IP model is now usually called
the transport layer. It is designed to allow peer entities on the source and
destination hosts to carry on a conversation, just as in the OSI transport layer.
• Two end-to-end transport protocols have been defined here. The first one,
TCP (Transmission Control Protocol), is a reliable connection-oriented protocol
that allows a byte stream originating on one machine to be delivered without
error on any other machine in the internet.
• It segments the incoming byte stream into discrete messages and passes
each one on to the internet layer. At the destination, the receiving TCP process
reassembles the received messages into the output stream.
• TCP also handles flow control to make sure a fast sender cannot swamp a
slow receiver with more messages than it can handle.
• The second protocol in this layer, UDP (User Datagram Protocol), is
an unreliable, connectionless protocol for applications that do not
want TCP’s sequencing or flow control and wish to provide their own.
• It is also widely used for one-shot, client-server-type request-reply
queries and applications in which prompt delivery is more important
than accurate delivery, such as transmitting speech or video.
• The relation of IP, TCP, and UDP is shown in Fig. 1-22. Since the model
was developed, IP has been implemented on many other networks.
The Application Layer
• The TCP/IP model does not have session or presentation layers.
• No need for them was perceived. Instead, applications simply include any
session and presentation functions that they require.
• Experience with the OSI model has proven this view correct: these layers are
of little use to most applications.
• On top of the transport layer is the application layer. It contains all the higher-
level protocols. The early ones included virtual terminal (TELNET), file transfer
(FTP), and electronic mail (SMTP).
• Many other protocols have been added to these over the years. Some
important ones that we will study, shown in Fig. 1-22,include the Domain
Name System (DNS), for mapping host names onto their network addresses,
HTTP, the protocol for fetching pages on the World Wide Web,and RTP, the
protocol for delivering real-time media such as voice or movies.
XNS(Xerox Network System)
• Xerox Network Systems (XNS) is a set of protocols that were used by
Xerox Systems for data communication. Xerox used XNS for file
transfers, sharing network resources, packet transfers, sharing
routing information and remote procedure calls.
• Its basic working mechanism is almost the same as in the TCP/IP
protocol suit, but XNS contains 5 layer model . This differs from the
seven-layer Open Systems Interconnection (OSI) model, although the
functionality is basically the same.
• XNS was a public domain technology and therefore became one of
the most commonly used networking technologies through 1980s. It
was replaced by the Internet Protocol suite.
• As illustrated in Figure 33-1, Xerox provided a five-level model of
packet communications.
• Level 0 corresponds roughly to OSI Layers 1 and 2, handling link access
and bit-stream manipulation.
• Level 1 corresponds roughly to the portion of OSI Layer 3 that pertains
to network traffic.
• Level 2 corresponds to the portion of OSI Layer 3 that pertains to
internetwork routing, and to OSI Layer 4, which handles interprocess
communication.
• Levels 3 and 4 correspond roughly to the upper two layers of the OSI
model, handling data structuring, process-to-process interaction, and
applications.
• XNS has no protocol corresponding to OSI Layer 5 (the session layer).
Media Access

• Although XNS documentation mentions X.25, Ethernet, and High-

Level Data Link Control (HDLC),XNS does not expressly define what it
refers to as a Level 0 protocol.
• As with many other protocol suites,XNS leaves media access an open
issue, implicitly allowing any such protocol to host the transport of
XNS packets over a physical medium.
Network Layer
• The XNS network layer protocol is called the Internet Datagram
Protocol (IDP). IDP performs standard Layer 3 functions, including
logical addressing and end-to-end datagram delivery across an
internetwork.
• Figure 33-2 illustrates the format of an IDP packet.
• The following descriptions summarize the IDP packet fields illustrated
in Figure 33-2:
• • Checksum—A 16-bit field that helps gauge the integrity of the packet
after it traverses the internetwork.
• • Length—A 16-bit field that carries the complete length (including the
checksum) of the current datagram
• Transport control—An 8-bit field that contains the hop count and Maximum
Packet Lifetime (MPL) subfields. The Hop Count subfield is initialized to 0 by
the source and is incremented by 1 as the datagram passes through a router.
• When the Hop Count field reaches 16, the datagram is discarded on the
assumption that a routing loop is occurring. The MPL subfield provides the
maximum amount of time, in seconds, that a packet can remain on the
internetwork.
• Packet type—An 8-bit field that specifies the format of the data field.
• Destination network number—A 32-bit field that uniquely identifies the
destination network in an internetwork.
• Destination host number—A 48-bit field that uniquely identifies the
destination host.
• Destination socket number—A 16-bit field that uniquely identifies a socket
(process) within the destination host.
• Source network number—A 32-bit field that uniquely identifies the source
network in an internetwork.
• Source host number—A 48-bit field that uniquely identifies the source host.
• Source socket number—A 16-bit field that uniquely identifies a socket (process)
within the source host.
• Note:
• XNS supports unicast (point-to-point), multicast, and broadcast packets.
• Multicast and broadcast addresses are further divided into directed and global types.
• Directed multicasts deliver packets to members of the multicast group on the network
specified in the destination multicast network address.Directed broadcasts deliver
packets to all members of a specified network.
• Global multicasts deliver packets to all members of the group within the entire
internetwork, whereas global broadcasts deliver packets to all internetwork addresses.
• One bit in the host number indicates a single versus a multicast address. Conversely, all
ones in the host field indicate a broadcast address.
• To route packets in an internetwork, XNS uses the RIP dynamic routing scheme. Today,
RIP is the most commonly used Interior Gateway Protocol (IGP) in the Internet
community
Transport Layer
• OSI transport layer functions are implemented by several protocols. Each of the
following protocols is described in the XNS specification as a Level 2 protocol.
• The Sequenced Packet Protocol (SPP) provides reliable, connection-based, flow-
controlled packet transmission on behalf of client processes. It is similar in
function to the Internet Protocol suite’s Transmission Control Protocol (TCP) and
the OSI protocol suite’s Transport Protocol 4 (TP4).
• Each SPP packet includes a sequence number, which is used to order packets and
to determine whether any have been duplicated or missed. SPP packets also
contain two 16-bit connection identifiers.
• One connection identifier is specified by each end of the connection;together, the
two connection identifiers uniquely identify a logical connection between client
processes.
• SPP packets cannot be longer than 576 bytes. Client processes can negotiate use
of a different packet size during connection establishment, but SPP does not
define the nature of this negotiation.
• The Packet Exchange Protocol (PEP) is a request-response protocol
designed to have greater reliability than simple datagram service (as
provided by IDP, for example) but less reliability than SPP. PEP is
functionally similar to the Internet Protocol suite’s User Datagram
Protocol (UDP).
• PEP is single packet-based, providing retransmissions but no duplicate
packet detection. As such, it is useful in applications where request-
response transactions can be repeated without damaging data, or
where reliable transfer is executed at another layer.
• The Error Protocol (EP) can be used by any client process to notify
another client process that a network error has occurred. This
protocol is used, for example, in situations in which an SPP
implementation has identified a duplicate packet.
Upper-Layer Protocols
• XNS offers several upper-layer protocols. The Printing Protocol
provides print services, the Filing Protocol provides file access
services, and the Clearinghouse Protocol provides name services.
Each of these three protocols runs on top of the Courier Protocol,
which provides conventions for data structuring and process
interaction.
• XNS also defines Level 4 protocols, which are application protocols.
However, because they have little to do with actual communication
functions, the XNS specification does not include any pertinent
definitions.
• The Level 2 Echo Protocol is used to test the reachability of XNS
network nodes and to support functions such as that provided by the
ping command found in UNIX and other environments.
GUIDED TRANSMISSION MEDIA
• The purpose of the physical layer is to transport bits from one
machine to an_x0002_other. Various physical media can be used for
the actual transmission.
• Each one has its own niche in terms of bandwidth, delay, cost, and
ease of installation and maintenance.
• Media are roughly grouped into guided media, such as copper wire
and fiber optics, and unguided media, such as terrestrial wireless,
satellite, and lasers through the air.
Guided Media
• Magnetic Media
• Twisted pairs-unshield,shield
• Coaxial Cable
• Power Lines
• Fibre Optics
Twisted Pairs
• Twisted pair is a physical media made up of a
pair of cables twisted with each other. A
twisted pair cable is cheap as compared to
other transmission media. Installation of the
twisted pair cable is easy, and it is a
lightweight cable. The frequency range for
twisted pair cable is from 0 to 3.5KHz.

• A twisted pair consists of two insulated

copper wires arranged in a regular spiral
pattern.

• The degree of reduction in noise interference

is determined by the number of turns per
foot. Increasing the number of turns per foot
decreases noise interference.
 Types of Twisted pair:
An unshielded twisted pair is widely used in
telecommunication. Following are the categories of the
unshielded twisted pair cable:
• Category 1: Category 1 is used for telephone lines that have
low-speed data.
• Category 2: It can support upto 4Mbps.
• Category 3: It can support upto 16Mbps.
• Category 4: It can support upto 20Mbps. Therefore, it can be
used for long-distance communication.
• Category 5: It can support upto 200Mbps.
• Advantages Of Unshielded Twisted Pair:
• It is cheap.
• Installation of the unshielded twisted pair is easy.
• It can be used for high-speed LAN.
• Disadvantage:
• This cable can only be used for shorter distances
because of attenuation(the reduction of the amplitude
 Shielded Twisted Pair
• A shielded twisted pair is a cable that contains the mesh surrounding
the wire that allows the higher transmission rate.
• Characteristics Of Shielded Twisted Pair:
• The cost of the shielded twisted pair cable is not very high and not very low.
• An installation of STP is easy.
• It has higher capacity as compared to unshielded twisted pair cable.
• It has a higher attenuation.
• It is shielded that provides the higher data transmission rate.
• Disadvantages
• It is more expensive as compared to UTP and coaxial cable.
• It has a higher attenuation rate(quantity per unit length).
 Coaxial Cable
• Coaxial cable is very commonly used transmission
media, for example, TV wire is usually a coaxial
cable.
• The name of the cable is coaxial as it contains two
conductors parallel to each other.
• It has a higher frequency as compared to Twisted
pair cable.
• The inner conductor of the coaxial cable is made
up of copper, and the outer conductor is made up
of copper mesh. The middle core is made up of
non-conductive cover that separates the inner
conductor from the outer conductor.
• The middle core is responsible for the data
transferring whereas the copper mesh prevents
from the EMI(Electromagnetic interference).
Coaxial cable is of two types:
• Advantages Of Coaxial cable:
• The data can be transmitted at
• Baseband transmission: It is high speed.
defined as the process of • It has better shielding as
transmitting a single signal at compared to twisted pair cable.
high speed. • It provides higher bandwidth.

• Broadband transmission: It is • Disadvantages Of Coaxial cable:

defined as the process of • It is more expensive as compared
to twisted pair cable.
transmitting multiple signals
• If any fault occurs in the cable
simultaneously. causes the failure in the entire
network.
 Fibre Optic
• Fibre optic cable is a cable that uses
the concept of reflection of light
through a core made up of glass or
plastic.
• Fibre optic is a cable that holds the
optical fibres coated in plastic that are
used to send the data by pulses of light.
• The plastic coating protects the optical
fibres from heat, cold, electromagnetic
interference from other types of wiring.
• Fibre optics provide faster data
transmission than copper wires.
Basic elements of Fibre optic cable:

• Core: The optical fibre consists of a narrow strand of glass or plastic

known as a core. A core is a light transmission area of the fibre. The
more the area of the core, the more light will be transmitted into the
fibre.
• Cladding: The concentric layer of glass is known as cladding. The main
functionality of the cladding is to provide the lower refractive index at
the core interface as to cause the reflection within the core so that
the light waves are transmitted through the fibre.
• Jacket: The protective coating consisting of plastic is known as a
jacket. The main purpose of a jacket is to preserve the fibre strength,
absorb shock and extra fibre protection.
Following are the advantages of fibre optic cable
over copper:
• Greater Bandwidth: The fibre optic cable provides more bandwidth as
compared copper. Therefore, the fibre optic carries more data as
compared to copper cable.
• Faster speed: Fibre optic cable carries the data in the form of light. This
allows the fibre optic cable to carry the signals at a higher speed.
• Longer distances: The fibre optic cable carries the data at a longer
distance as compared to copper cable.
• Better reliability: The fibre optic cable is more reliable than the copper
cable as it is immune to any temperature changes while it can cause
obstruct in the connectivity of copper cable.
• Thinner and Sturdier: Fibre optic cable is thinner and lighter in weight so
it can withstand more pull pressure than copper cable.
UnGuided Transmission
• An unguided transmission
transmits the electromagnetic
waves without using any physical
medium. Therefore it is also
known as wireless transmission.
• In unguided media, air is the
media through which the
electromagnetic energy can flow
easily.
• Unguided transmission is
broadly classified into three
categories:
• Radio waves
• Infrared
• Microwaves
• Terrestrial microwave
• Satellite microwave communication.
Radio waves
• Radio waves are the electromagnetic
waves that are transmitted in all the
directions of free space.
• Radio waves are omnidirectional, i.e., the
signals are propagated in all the
directions.
• The range in frequencies of radio waves is
from 300 GHz to 3 kHz.
• In the case of radio waves, the sending
and receiving antenna are not aligned,
i.e., the wave sent by the sending
antenna can be received by any receiving
antenna.
• An example of the radio wave is FM
radio.
Applications Of Radio waves:
• A Radio wave is useful for multicasting when there is one sender and many
receivers.
• An FM radio, television, cordless phones are examples of a radio wave.

Advantages Of Radio transmission:

• Radio transmission is mainly used for wide area networks and mobile cellular
phones.
• Radio waves cover a large area, and they can penetrate the walls.
• Radio transmission provides a higher transmission rate.
Infrared • Characteristics Of Infrared:
• An infrared transmission is a wireless
technology used for communication • It supports high bandwidth, and
over short ranges. hence the data rate will be very
• The frequency of the infrared in the high.
range from 300 GHz to 400 THz. • Infrared waves cannot penetrate the
• It is used for short-range walls. Therefore, the infrared
communication such as data transfer communication in one room cannot
between two cell phones, TV remote be interrupted by the nearby rooms.
operation, data transfer between a • An infrared communication provides
computer and cell phone resides in better security with minimum
the same closed area. interference.
• Infrared communication is
unreliable outside the building
because the sun rays will interfere
with the infrared waves.
Microwaves Transmission media

• Microwaves are of two types:

• Terrestrial microwave
• Satellite microwave
communication.
Characteristics of Microwave:
• Frequency range: The frequency range of terrestrial
microwave is from 4-6 GHz to 21-23 GHz.
• Bandwidth: It supports the bandwidth from 1 to 10 Mbps.
• Short distance: It is inexpensive for short distance.
• Long distance: It is expensive as it requires a higher tower
for a longer distance.
• Attenuation: Attenuation means loss of signal. It is affected
by environmental conditions and antenna size.
• Advantages Of Microwave: • Disadvantages of Microwave
transmission:
• Eavesdropping: An eavesdropping
• Microwave transmission is cheaper creates insecure communication.
Any malicious user can catch the
than using cables. signal in the air by using its own
• It is free from land acquisition as it antenna.
does not require any land for the • Out of phase signal: A signal can
be moved out of phase by using
installation of cables. microwave transmission.
• Microwave transmission provides an • Susceptible to weather
easy communication in terrains as condition: A microwave
transmission is susceptible to
the installation of cable in terrain is weather condition. This means
quite a difficult task. that any environmental change
such as rain, wind can distort the
• Communication over oceans can be signal.
achieved by using microwave • Bandwidth limited: Allocation of
transmission. bandwidth is limited in the case of
microwave transmission.
Terrestrial Microwave Transmission(parabolic dish antenna)
• Terrestrial Microwave transmission is a technology that transmits the
focused beam of a radio signal from one ground-based microwave
transmission antenna to another.
• Microwaves are the electromagnetic waves having the frequency in
the range from 1GHz to 1000 GHz.
• Microwaves are unidirectional as the sending and receiving antenna
is to be aligned, i.e., the waves sent by the sending antenna are
narrowly focussed.
• In this case, antennas are mounted on the towers to send a beam to
another antenna which is km away.
• It works on the line of sight transmission, i.e., the antennas mounted
on the towers are the direct sight of each other.
Satellite Microwave Communication • How Does Satellite work?
• A satellite is a physical object
that revolves around the earth
at a known height. • The satellite accepts the signal
• Satellite communication is more that is transmitted from the
reliable nowadays as it offers earth station, and it amplifies
more flexibility than cable and the signal. The amplified signal
fibre optic systems. is retransmitted to another
• We can communicate with any earth station.
point on the globe by using
satellite communication.
• Advantages Of Satellite Microwave • Disadvantages Of Satellite
Communication: Microwave Communication:

• The coverage area of a satellite microwave is

more than the terrestrial microwave.
• Satellite designing and development
requires more time and higher cost.
• The transmission cost of the satellite is
independent of the distance from the centre • The Satellite needs to be monitored
of the coverage area. and controlled on regular periods so
• Satellite communication is used in mobile and that it remains in orbit.
wireless communication applications.
• The life of the satellite is about 12-
• It is easy to install.
15 years. Due to this reason,
• It is used in a wide variety of applications such another launch of the satellite has to
as weather forecasting, radio/TV signal
broadcasting, mobile communication, etc. be planned before it becomes non-
functional.
Transmission Modes
• The way in which data is transmitted • The Transmission mode is
from one device to another device
is known as transmission mode.
divided into three categories:
• The transmission mode is also
known as the communication mode. • Transmission modes
• Each communication channel has a • Simplex mode
direction associated with it, and • Half-duplex mode
transmission media provide the • Full-duplex mode
direction. Therefore, the
transmission mode is also known as
a directional mode.
• The transmission mode is defined in
the physical layer.
Simplex mode
In Simplex mode, the communication is unidirectional,
i.e., the data flow in one direction.
• A device can only send the data but cannot receive it
or it can receive the data but cannot send the data.
• This transmission mode is not very popular as mainly
communications require the two-way exchange of
data. The simplex mode is used in the business field
as in sales that do not require any corresponding
reply.
• The radio station is a simplex channel as it transmits
the signal to the listeners but never allows them to
transmit back.
• Keyboard and Monitor are the examples of the
simplex mode as a keyboard can only accept the data
from the user and monitor can only be used to display
the data on the screen.
• The main advantage of the simplex mode is that the
full capacity of the communication channel can be
utilized during transmission.
Half-Duplex mode
• In a Half-duplex channel, direction can be
reversed, i.e., the station can transmit and receive
the data as well.
• Messages flow in both the directions, but not at
the same time.
• The entire bandwidth of the communication
channel is utilized in one direction at a time.
• In half-duplex mode, it is possible to perform the
error detection, and if any error occurs, then the
receiver requests the sender to retransmit the
data.
• A Walkie-talkie is an example of the Half-duplex
mode. In Walkie-talkie, one party speaks, and
another party listens. After a pause, the other
speaks and first party listens. Speaking
simultaneously will create the distorted sound
which cannot be understood.
Full-duplex Mode
• In Full duplex mode, the communication is bi-
directional, i.e., the data flow in both the
directions.
• Both the stations can send and receive the
message simultaneously.
• Full-duplex mode has two simplex channels.
One channel has traffic moving in one
direction, and another channel has traffic
flowing in the opposite direction.
• The Full-duplex mode is the fastest mode of
communication between devices.
• The most common example of the full-duplex
mode is a telephone network. When two
people are communicating with each other by
a telephone line, both can talk and listen at
the same time.
Switching and Encoding
• When a user accesses the internet or another • Switches are used to forward the
computer network outside their immediate packets based on MAC
location, messages are sent through the addresses.
network of transmission media. This
technique of transferring the information • A Switch is used to transfer the
from one computer network to another data only to the device that has
network is known as switching. been addressed. It verifies the
• Switching in a computer network is achieved destination address to route the
by using switches. A switch is a small packet appropriately.
hardware device which is used to join • It is operated in full duplex
multiple computers together with one local mode.
area network (LAN).
• Network switches operate at layer 2 (Data
• Packet collision is minimum as it
link layer) in the OSI model.
directly communicates between
source and destination.
• Switching is transparent to the user and does
not require any configuration in the home • It does not broadcast the
network. message as it works with limited
bandwidth.
Switching Modes
• The layer 2 switches are used for
transmitting the data on the data link
layer, and it also performs error checking
on transmitted and received frames.
• The layer 2 switches forward the packets
with the help of MAC address.
• Different modes are used for forwarding
the packets known as Switching modes.
• In switching mode, Different parts of a
frame are recognized. The frame consists
of several parts such as preamble,
destination MAC address, source MAC
address, user's data, FCS.
Store-and-forward Switching
• Store-and-forward is a technique in which the intermediate
nodes store the received frame and then check for errors
before forwarding the packets to the next node.
• The layer 2 switch waits until the entire frame has received.
On receiving the entire frame, switch store the frame into
the switch buffer memory. This process is known as storing
the frame.
• When the frame is stored, then the frame is checked for the
errors. If any error found, the message is discarded
otherwise the message is forwarded to the next node. This
process is known as forwarding the frame.
• CRC (Cyclic Redundancy Check) technique is implemented
that uses a number of bits to check for the errors on the
received frame.
• The store-and-forward technique ensures a high level of
security as the destination network will not be affected by
the corrupted frames.
• Store-and-forward switches are highly reliable as it does not
forward the collided frames.
Cut-through Switching
• Cut-through switching is a technique in which the
switch forwards the packets after the destination
address has been identified without waiting for the
entire frame to be received.
• Once the frame is received, it checks the first six bytes
of the frame following the preamble, the switch
checks the destination in the switching table to
determine the outgoing interface port, and forwards
the frame to the destination.
• It has low latency rate(minimal delay) as the switch
does not wait for the entire frame to be received
before sending the packets to the destination.
• It has no error checking technique. Therefore, the
errors can be sent with or without errors to the
receiver.
• A Cut-through switching technique has low wait time
as it forwards the packets as soon as it identifies the
destination MAC address.
• In this technique, collision is not detected, if frames
have collided will also be forwarded.
Fragment-free Switching
• A Fragment-free switching is an advanced
technique of the Cut-through Switching.
• A Fragment-free switching is a technique that
reads atleast 64 bytes of a frame before
forwarding to the next node to provide the
error-free transmission.
• It combines the speed of Cut-through
Switching with the error checking
functionality.
• This technique checks the 64 bytes of the
ethernet frame where addressing information
is available.
• A collision is detected within 64 bytes of the
frame, the frames which are collided will not
be forwarded further.
Encoding
• The first step in turning nodes and links into usable building blocks is
to understand how to connect them in such a way that bits can be
transmitted from one node to the other.
• As we know signals propagate over physical links. The task, therefore,
is to encode the binary data that the source node wants to send into
the signals that the links are able to carry and then to decode the
signal back into the corresponding binary data at the receiving node.
• We ignore the details of modulation and assume we are working with
two discrete signals: high and low. In practice, these signals might
correspond to two different voltages on a copper-based link, two
different power levels on an optical link, or two different amplitudes
on a radio transmission.
• Most of the functions discussed in
this chapter are performed by a
network adaptor—a piece of
hardware that connects a node to
a link.
• The network adaptor contains a
signalling component that actually
encodes bits into signals at the
sending node and decodes signals
into bits at the receiving node.
• Thus, as illustrated in Figure ,
signals travel over a link between
two signalling components, and
bits flow between network
adaptors.
Digital Transmission
• Data can be represented either in
analog or digital form. The computers
used the digital form to store the
information. Therefore, the data needs
to be converted in digital form so that
it can be used by a computer.
• Digital-to-digital encoding is the
representation of digital information by
a digital signal. When binary 1s and 0s
generated by the computer are
translated into a sequence of voltage
pulses that can be propagated over a
wire, this process is known as digital-to-
digital encoding.
• Digital-to-digital encoding is
divided into three categories:

• Unipolar Encoding
• Polar Encoding
• Bipolar Encoding
Unipolar
• Digital transmission system sends the voltage pulses over
the medium link such as wire or cable.
• In most types of encoding, one voltage level represents
0, and another voltage level represents 1.
• The polarity of each pulse determines whether it is
positive or negative.
• This type of encoding is known as Unipolar encoding as it
uses only one polarity.
• In Unipolar encoding, the polarity is assigned to the 1
binary state.
• In this, 1s are represented as a positive value and 0s are
represented as a zero value.
• In Unipolar Encoding, '1' is considered as a high voltage
and '0' is considered as a zero voltage.
• Unipolar encoding is simpler and inexpensive to
implement.
Polar
• Polar encoding is an encoding
scheme that uses two voltage
levels: one is positive, and
another is negative.
• By using two voltage levels, an
average voltage level is reduced,
and the DC component problem
of unipolar encoding scheme is
alleviated.
Bipolar
• Bipolar encoding scheme represents
three voltage levels: positive,
negative, and zero.
• In Bipolar encoding scheme, zero
level represents binary 0, and
binary 1 is represented by
alternating positive and negative
voltages.
• If the first 1 bit is represented by
positive amplitude, then the second
1 bit is represented by negative
voltage, third 1 bit is represented by
the positive amplitude and so on.
This alternation can also occur even
when the 1bits are not consecutive.
Integrated Services Digital Network
• ISDN is a set of protocols that is based on high-speed fully digitized
telephone service. The main aim of ISDN is to provide a fully
integrated digital service to the users.
• In ISDN there are following three types of ISDN services:
• Bearer Services
• Tele Services
• Supplementary Services
• Bearer Services:This type of services is
used to transfer information such as
voice, data, and video between the users
without manipulating the content of the
network information. It belongs to the
first 3 layers of the OSI reference model.
• Tele Services:In these types of services,
the network may change the contents of
the data. It belongs to the last 4 layers of
the OSI reference model. It includes
telephony, tele box, fax, and
teleconferencing etc.
• Supplementary Services:It provides
additional functionality to the bearer
services and teleservices. Some of the
examples of supplementary services are
reverse charging, call waiting, and
message handling.
Principles of ISDN:
• Following are the principles of ISDN are:

• It supports both circuit switching & packet switching with the

connections at 64 kbps.
• In ISDN layered protocol architecture is used for specification.
• ISDN services provides maintenance.
• ISDN services includes some network management functions.
• In ISDN network several configurations are possible for
implementing.
 ISDN SERVICES:
• Following are the two types of services
associated with ISDN:
• Basic Rate Interface
• Primary Rate Interface
• In the Basic Rate Interface digital pipe consists
of 2 B channels and a 1 D channel. Therefore it
is denoted as "2B + 1 D". These two B channels
have a data rate of 64 kbps each, and the D
channel have a data rate of 16 kbps. It has also
a usable bandwidth of 144 kbps.
• Basic Rate Interface allows the concurrent use
of voice and various data applications such as
packet-switched access, a link to a central
alarm service, video, tax, etc. The signaling
information for the two channels is sent onto
the D channel. The two B channels can be used
for one 128 kbps connection or two
independent connections on the two channels.
• This service is used to meet the needs of most
individual users, including residential and small
offices. In this case, the two B channels and the D
channel are multiplexed with overhead bits in the
form of the frame structure. The overhead bits
include framing, DC balancing, and other bits.
• The 48 bit frame consists of
• 16 bits of B1 Channel
• 16 bits of B2 Channel
• 4 bits of D channel
• 12 overhead bits
• The frame is transmitted in 250 µsec, which results in
the following bit rates:
• In frame each B channel = 16 / 250 µsec = 64 kbps
• In frame D channel = 4 / 250 µsec = 16 kbps
• In frame Overhead Bits = 12 / 250 µsec = 48 kbps
• In frame Overall Bit rate = 48 / 250 µsec = 192 kbps
• Primary Rate Interface:
• Primary Rate Interface consists of
either 23 B channels or 30 B channels
and a one 64 Kbps D channel.
• In North America and the Japan, 23 B
channels and one D channel are used.
It is also denoted by '23 B + 1 D'.
• In addition, the Primary Rate Interface
service itself uses 8 kbps of overhead.
Therefore 23D + 1D requires a data
rate of 1.536 Mbps.
• In the case of 30 B channels and one D
channel(actually 2), the total bit rate is
2.048 Mbps.
ISDN CHANNELS:
• ISDN structure have a central
ISDN office in which all the users
are linked to this through a
digital pipe.
• This digital pipe have different
capacities and have a different
data transfer rates and these are
organized into multiple channels
of different sizes.
• B Channel:
• It stands for Bearer channel. It has a 64 kbps standard data rate. It is a basic user
channel and can carry any digital information in full-duplex mode. In this
transmission rate does not exceed 64 kbps. It can carry digital voice, digital data,
and any other low data rate information.
• D Channel:
• It stands for Data Channel. This channel carry control signal for bearer services.
This channel is required for signaling or packet-switched data and all-controlling
signals such as establishing calls, ringing, call interrupt, etc.
• H Channel:
• It stands for Hybrid Channel. It provides user information at higher bit rates.
• There are 3 types of Hybrid Channel depending on the data rates. Following are
the hybrid channels types:
• Hybrid Channel 0 with 384 kbps data rate.
• Hybrid Channel 11 with 1536 kbps data rate.
• Hybrid Channel 12 with 1920 kbps data rate.
 ISDN Devices:
• Following are the types of ISDN devices:
• TE1:Terminal equipment type (TE1) are specialized ISDN terminals. It includes digital
telephone instruments such as FAX, or data terminal equipment. All these devices have an
S-bus ISDN interface.
• TE2:Terminal equipment type (TE2) is Non-ISDN compatible is connected through a
Terminal Adapter. It includes analog phones and 3270 terminal Fax.
• TA:It stands for Terminal Adapter. This device acts as an intermediary device for non-ISDN
terminal devices. It converts the non-ISDN interface of these devices to the ISDN
interface. The ISDN terminal Adapter can be either a standalone device or a board inside
the Terminal equipment type 2. Some of the examples of Terminal adapter are EIA/TIA-
232-C, V.24 etc.
• NT1: It stands for Network Termination type 1. It provides a line termination at the
customer's premise. They can also provide line monitoring, power feeding, error
statistics, and proper timing.
• NT2:It stands for Network Termination type 2. It provides a switching, multiplexing,
concentrating, or distributing information for the customer's premises. Some examples of
Network termination type 2 are this could be a LAN server or Private Branch Exchange etc.
ISDN Reference Points:
• It specifies the
number of
reference points
that provide
interfaces between
the adjacent
devices.
• In the above figure it shows an ISDN configuration in which 3 devices attached to an ISDN
switch at the central office. In which 2 devices are ISDN compatible and they are attached
through the S reference point to Network termination type 2 devices. Out of these third device
is a standard non-ISDN telephone and is attached to a Terminal Adapter through an R reference
point.
• These reference points are R, S, T, and U.
• R:It stands for Rate Transfer point. It is an interface for non-ISDN devices and therefore is the
reference point between non-ISDN equipment and a Terminal Adapter. It can be RS-232-C, V, or
X series of ITU-T standard or ordinary telephone interface with two wires.
• S:It stands for System Transfer point. The interface between the user terminal and NT2. It is a
four-wire balanced to which upto eight ISDN terminals can be connected. The physical
connector for S - interface on terminals and NT1 is an 8-pin RJ-45 connector.
• T:It stands for Terminal Transfer point. It is the interface between Network termination type 1
and Network termination type 2
• U: It is the interface between Network Termination type 1 device and the line termination
equipment in the carrier network. The U interface is the local copper pair of the access
network. The same pair is used for full-duplex transmission of digital signals.
Narrowband
• N-ISDN was an attempt to replace the analog telephone system with a digital
one. Unfortunately, the standardization process was too long and regarding to
the technology progress in this area, once the standard was finally agreed, it
was obsolete.

• N-ISDN basic rate is too low so for home as for business today. N-ISDN may be
partly saved, but by an unexpected application: Internet access. Various
companies now sell ISDN adapters that combine the 2B + D channels into a
single 144 kbps digital channel.
• Many Internet providers also support these adapters. So the people can access
Internet over a 144 kbps digital link, instead of a 28.8 kbps analog modem link
and for affordable price that may be a niche for N-ISDN for the next few years.
ATM(ASYNCHRONOUS TRANSFER MODE)
• Why ATM networks?

• Driven by the integration of services and performance requirements of both telephony

and data networking: “broadband integrated service vision” (B-ISON).
• Telephone networks support a single quality of service and are expensive to boot.
• Internet supports no quality of service but is flexible and cheap.
• ATM networks were meant to support a range of service qualities at a reasonable cost-
intended to subsume both the telephone network and the Internet.
ATM
• It is an International Telecommunication Union- Telecommunications Standards
Section (ITU-T) efficient for call relay and it transmits all information including
multiple service types such as data, video, or voice which is conveyed in small
fixed-size packets called cells. Cells are transmitted asynchronously and the
network is connection-oriented.
• ATM is a technology that has some event in the development of broadband ISDN
in the 1970s and 1980s, which can be considered an evolution of packet
switching. Each cell is 53 bytes long – 5 bytes header and 48 bytes payload.
Making an ATM call requires first sending a message to set up a connection.
• Subsequently, all cells follow the same path to the destination. It can handle both
constant rate traffic and variable rate traffic. Thus it can carry multiple types of
traffic with end-to-end quality of service. ATM is independent of a transmission
medium, they may be sent on a wire or fiber by themselves or they may also be
packaged inside the payload of other carrier systems. ATM networks use “Packet”
or “cell” Switching with virtual circuits. Its design helps in the implementation of
high-performance multimedia networking.
ATM Cell Format –

• As information is transmitted in
ATM in the form of fixed-size
units called cells.
• As known already each cell is 53
bytes long which consists of a 5
bytes header and 48 bytes
payload.
 Asynchronous Transfer Mode can be of two format
types which are as follows:

• UNI Header: This is used within private

networks of ATMs for communication
between ATM endpoints and ATM
switches. It includes the Generic Flow
Control (GFC) field.

• NNI Header: is used for communication

between ATM switches, and it does not
include the Generic Flow Control(GFC)
instead it includes a Virtual Path Identifier
(VPI) which occupies the first 12 bits.
Working of ATM:
• ATM standard uses two types of connections. i.e., Virtual path connections (VPCs) which
consist of Virtual channel connections (VCCs) bundled together which is a basic unit
carrying a single stream of cells from user to user. A virtual path can be created end-to-
end across an ATM network, as it does not rout the cells to a particular virtual circuit. In
case of major failure, all cells belonging to a particular virtual path are routed the same
way through the ATM network, thus helping in faster recovery.

• Switches connected to subscribers use both VPIs(virtual path indicator) and VCIs(Virtual
Channel Identifier) to switch the cells which are Virtual Path and Virtual Connection
switches that can have different virtual channel connections between them, serving the
purpose of creating a virtual trunk between the switches which can be handled as a
single entity. Its basic operation is straightforward by looking up the connection value in
the local translation table determining the outgoing port of the connection and the new
VPI/VCI value of connection on that link.
ATM Layers:
• ATM Adaption Layer (AAL) –
• It is meant for isolating higher-layer protocols from details of ATM processes and prepares for
conversion of user data into cells and segments it into 48-byte cell payloads. AAL protocol excepts
transmission from upper-layer services and helps them in mapping applications, e.g., voice, data to
ATM cells.
• Physical Layer –
• It manages the medium-dependent transmission and is divided into two parts physical medium-
dependent sublayer and transmission convergence sublayer. The main functions are as follows:
• It converts cells into a bitstream.
• It controls the transmission and receipt of bits in the physical medium.
• It can track the ATM cell boundaries.
• Look for the packaging of cells into the appropriate type of frames.
• ATM Layer –
• It handles transmission, switching, congestion control, cell header processing, sequential delivery,
etc., and is responsible for simultaneously sharing the virtual circuits over the physical link known
as cell multiplexing and passing cells through an ATM network known as cell relay making use of
the VPI and VCI information in the cell header.
ATM Applications:
ATM WANs –
• It can be used as a WAN to send cells over long distances, a router serving as an end-point between ATM
network and other networks, which has two stacks of the protocol.
Multimedia virtual private networks and managed services –
• It helps in managing ATM, LAN, voice, and video services and is capable of full-service virtual private
networking, which includes integrated access to multimedia.
Frame relay backbone –
• Frame relay services are used as a networking infrastructure for a range of data services and enabling
frame-relay ATM service to Internetworking services.
Residential broadband networks –
• ATM is by choice provides the networking infrastructure for the establishment of residential broadband
services in the search of highly scalable solutions.
Carrier infrastructure for telephone and private line networks –
• To make more effective use of SONET/SDH fiber infrastructures by building the ATM infrastructure for
carrying the telephonic and private-line traffic.