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Network ProtocolsNetwork Protocols
Network Protocols
Network Protocols are a set of rules governing exchange of information in an easy, reliable and
are a set of rules governing exchange of information in an easy, reliable and
secure way. Before we discuss the most common protocols used to transmit and receive data over a
secure way. Before we discuss the most common protocols used to transmit and receive data over a
network, we need to understand how a network is logically organized or designed. The most popular
network, we need to understand how a network is logically organized or designed. The most popular
model used to establish open communication between two systems is themodel used to establish open communication between two systems is the Open Systems InterfaceOpen Systems Interface
(OSI) model
(OSI) model proposed by ISO.
proposed by ISO.
OSI Model OSI Model
OSI model is not aOSI model is not a network architecturenetwork architecture because it does not specify the exact services and protocolsbecause it does not specify the exact services and protocols
for each layer. It simply tells what each layer should do by defining its input and output data. It is up to
for each layer. It simply tells what each layer should do by defining its input and output data. It is up to
network architects to implement the layers according to their needs and resources available.
network architects to implement the layers according to their needs and resources available.
These are the seven layers of the OSI model −These are the seven layers of the OSI model −
Physical layer
Physical layer −It is the first layer that physically connects the two systems that need to
−It is the first layer that physically connects the two systems that need to
communicate. It transmits data in bits and manages simplex or duplex transmission by
communicate. It transmits data in bits and manages simplex or duplex transmission by
modem. It also manages Network Interface Card’s hardware interface to the network, like modem. It also manages Network Interface Card’s hardware interface to the network, like
cabling, cable terminators, topography, voltage levels, etc.
cabling, cable terminators, topography, voltage levels, etc.
Data link layer
Data link layer − It is the firmware layer of Network Interface Card. It assembles datagrams
− It is the firmware layer of Network Interface Card. It assembles datagrams
into frames and adds start and stop flags to each frame. It also resolves problems caused by
into frames and adds start and stop flags to each frame. It also resolves problems caused by
damaged, lost or duplicate frames. damaged, lost or duplicate frames.
Network layer
Network layer − It is concerned with routing, switching and controlling flow of information
− It is concerned with routing, switching and controlling flow of information
between the workstations. It also breaks down transport layer datagrams into smaller
between the workstations. It also breaks down transport layer datagrams into smaller
datagrams. datagrams.
Transport layer
Transport layer − Till the session layer, file is in its own form. Transport layer breaks it down
− Till the session layer, file is in its own form. Transport layer breaks it down
into data frames, provides error checking at network segment level and prevents a fast host
into data frames, provides error checking at network segment level and prevents a fast host
from overrunning a slower one. Transport layer isolates the upper layers from network from overrunning a slower one. Transport layer isolates the upper layers from network
hardware.
hardware.
Session layer
Session layer − This layer is responsible for establishing a session between two
− This layer is responsible for establishing a session between two
workstations that want to exchange data. workstations that want to exchange data.
Presentation layer
Presentation layer − This layer is concerned with correct representation of data, i.e. syntax
− This layer is concerned with correct representation of data, i.e. syntax
and semantics of information. It controls file level security and is also responsible for
and semantics of information. It controls file level security and is also responsible for
converting data to network standards. converting data to network standards.
Application layer
Application layer − It is the topmost layer of the network that is responsible for sending
− It is the topmost layer of the network that is responsible for sending
application requests by the user to the lower levels. Typical applications include file transfer,
application requests by the user to the lower levels. Typical applications include file transfer,
E-mail, remote logon, data entry, etc. E-mail, remote logon, data entry, etc.
It is not necessary for every network to have all the layers. For example, network layer is not there in
It is not necessary for every network to have all the layers. For example, network layer is not there in
broadcast networks.
broadcast networks.
When a system wants to share data with another workstation or send a request over the network, it is
When a system wants to share data with another workstation or send a request over the network, it is
received by the application layer. Data then proceeds to lower layers after processing till it reaches the
received by the application layer. Data then proceeds to lower layers after processing till it reaches the
physical layer.
physical layer.
At the physical layer, the data is actually transferred and received by the physical layer of the
At the physical layer, the data is actually transferred and received by the physical layer of the
destination workstation. There, the data proceeds to upper layers after processing till it reaches
destination workstation. There, the data proceeds to upper layers after processing till it reaches
application layer.
application layer.
At the application layer, data or request is shared with the workstation. So each layer has opposite
At the application layer, data or request is shared with the workstation. So each layer has opposite
functions for source and destination workstations. For example, data link layer of the source
functions for source and destination workstations. For example, data link layer of the source
workstation adds start and stop flags to the frames but the same layer of the destination workstation
workstation adds start and stop flags to the frames but the same layer of the destination workstation
will remove the start and stop flags from the frames.will remove the start and stop flags from the frames.
Let us now see some of the protocols used by different layers to accomplish user requests.
Let us now see some of the protocols used by different layers to accomplish user requests.
TCP/IP
TCP/IP
TCP/IP stands for
TCP/IP stands for Transmission Control Protocol/Internet Protocol
Transmission Control Protocol/Internet Protocol
. TCP/IP is a set of layered . TCP/IP is a set of layered
protocols used for communication over the Internet. The communication model of this suite is client-
protocols used for communication over the Internet. The communication model of this suite is client-
server model. A computer that sends a request is the client and a computer to which the request is
server model. A computer that sends a request is the client and a computer to which the request is
sent is the server.sent is the server.
Network layer
Network layer − Network layer connection is established using Internet Protocol (IP) at the
− Network layer connection is established using Internet Protocol (IP) at the
network layer. Every machine connected to the Internet is assigned an address called IP
network layer. Every machine connected to the Internet is assigned an address called IP
address by the protocol to easily identify source and destination machines. address by the protocol to easily identify source and destination machines.
Data link layer
Data link layer − Actual data transmission in bits occurs at the data link layer using the
− Actual data transmission in bits occurs at the data link layer using the
destination address provided by network layer.
destination address provided by network layer.
TCP/IP is widely used in many communication networks other than the Internet.
TCP/IP is widely used in many communication networks other than the Internet.
FTP
FTP
As we have seen, the need for network came up primarily to facilitate sharing of files between
As we have seen, the need for network came up primarily to facilitate sharing of files between
researchers. And to this day, file transfer remains one of the most used facilities.The protocol that
researchers. And to this day, file transfer remains one of the most used facilities.The protocol that
handles these requests is
handles these requests is File Transfer Protocol
File Transfer Protocol or
or FTP
FTP
Using FTP to transfer files is helpful in these ways −
Using FTP to transfer files is helpful in these ways −
Easily transfers files between two different networks Easily transfers files between two different networks
Can resume file transfer sessions even if connection is dropped, if protocol is configure
Can resume file transfer sessions even if connection is dropped, if protocol is configure
appropriately
appropriately
Enables collaboration between geographically separated teams
Enables collaboration between geographically separated teams
PPP PPP
Point to Point Protocol or PPP is a data link layer protocol that enables transmission of TCP/IP trafficPoint to Point Protocol or PPP is a data link layer protocol that enables transmission of TCP/IP traffic
over serial connection, like telephone line.
over serial connection, like telephone line.
To do this, PPP defines these three things −
To do this, PPP defines these three things −
A framing method to clearly define end of one frame and start of another, incorporating errors
A framing method to clearly define end of one frame and start of another, incorporating errors
detection as well. detection as well.
Link control protocol (LCP) for bringing communication lines up, authenticating and bringing
Link control protocol (LCP) for bringing communication lines up, authenticating and bringing
them down when no longer needed.
them down when no longer needed.
Network control protocol (NCP) for each network layer protocol supported by other networks.
Network control protocol (NCP) for each network layer protocol supported by other networks.
Using PPP, home users can avail Internet connection over telephone lines.
Using PPP, home users can avail Internet connection over telephone lines.
