PRACTICAL-1

Aim:- Study about the OSI reference model.

OSI Layer Architecture

□ OSI 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.
□ It was revised in 1995.
□ The model is called the 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.
1. Physical Layer
2. Data Link Layer
3. Network Layer
4. Transport Layer
5. Session Layer
6. Presentation Layer
7. Application Layer

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Figure : OSI Reference Model

Physical Layer
□ The physical layer, the lowest layer of the OSI model, is concerned with the transmission and
reception of the unstructured raw bit stream over a physical medium.
□ It describes the electrical/optical, mechanical, and functional interfaces to the physical
medium, and carries the signals for all of the higher layers. It provides:
□ Data encoding: modifies the simple digital signal pattern (1s and 0s) used by the PC to better
accommodate the characteristics of the physical medium, and to aid in bit and frame
synchronization.
□ Transmission technique: determines whether the encoded bits will be transmitted by
baseband (digital) or broadband (analog) signalling.
□ Physical medium transmission: transmits bits as electrical or optical signals appropriate for
the physical medium.

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 Data link Layer
□ The data link layer provides error-free transfer of data frames from one node to another over
the physical layer, allowing layers above it to assume virtually error-free transmission over
the link.
□ To do this, the data link layer provides:
□ Link establishment and termination: establishes and terminates the logical link between
two nodes.
□ Frame traffic control: tells the transmitting node to "back-off" (stop) when no frame
buffers are available.
□ Frame sequencing: transmits/receives frames sequentially.
□ Frame acknowledgment: provides/expects frame acknowledgments. Detects and recovers
from errors that occur in the physical layer by retransmitting non-acknowledged frames and
handling duplicate frame receipt.
□ Frame delimiting: creates and recognizes frame boundaries.
□ Frame error checking: checks received frames for integrity.
□ Media access management: determines when the node "has the right" to use the physical
medium.
Network Layer
□ The network layer controls the operation of the subnet, deciding which physical path the data
should take based on network conditions, priority of service, and other factors.
□ To do this, the data link layer provides:
□ Routing: routes frames among networks.
□ Subnet traffic control: routers (network layer intermediate systems) can instruct a sending
station to "throttle back" its frame transmission when the router's buffer fills up.
□ Frame fragmentation: if it determines that a downstream router's maximum transmission
unit (MTU) size is less than the frame size, a router can fragment a frame for transmission
and re- assembly at the destination station.
□ Logical-physical address mapping: translates logical addresses or names, into physical
addresses.
□ Subnet usage accounting: has accounting functions to keep track of frames forwarded by
subnet intermediate systems, to produce billing information.
Transport Layer
□ The transport layer ensures that messages are delivered error-free, in sequence, and with no
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 losses or duplications. It relieves (release) the higher layer protocols from any concern with
the transfer of data between them and their peers.
□ The size and complexity of a transport protocol depends on the type of service it can get from
the network layer. For a reliable network layer with virtual circuit capability, a minimal
transport layer is required. If the network layer is unreliable and/or only supports datagrams,
the transport protocol should include extensive error detection and recovery.
□ The transport layer provides:
□ Message segmentation: accepts a message from the (session) layer above it, splits the
message into smaller units (if not already small enough), and passes the smaller units down
to the network layer. The transport layer at the destination station reassembles the message.
□ Message acknowledgment: provides reliable end-to-end message delivery with
acknowledgments.
□ Message traffic control: tells the transmitting station to "back-off" when no message buffers
are available.
□ Typically, the transport layer can accept relatively large messages, but there are strict message
size limits imposed by the network (or lower) layer. Consequently, the transport layer must
break up the messages into smaller units, or frames, prepending a header to each frame.
□ The transport layer header information must then include control information, such as
message start and message end flags, to enable the transport layer on the other end to
recognize message boundaries.
□ In addition, if the lower layers do not maintain sequence, the transport header must contain
sequence information to enable the transport layer on the receiving end to get the pieces back
together in the right order before handing the received message up to the layer above.
Session Layer
□ The session layer allows session establishment between processes running on different
stations. It provides:
□ Session establishment, maintenance and termination: allows two application processes
on different machines to establish, use and terminate a connection, called a session.
□ Session support: performs the functions that allow these processes to communicate over
the network, performing security, name recognition, logging, and so on.
Presentation Layer
□ The presentation layer formats the data to be presented to the application layer. It can be

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 viewed as the translator for the network. This layer may translate data from a format used
by the application layer into a common format at the sending station, then translate the
common format to a format known to the application layer at the receiving station.
□ The presentation layer provides:
□ Character code translation: for example, ASCII to EBCDIC.
□ Data conversion: bit order, CR-CR/LF, integer-floating point, and so on.
□ Data compression: reduces the number of bits that need to be transmitted on the network.
□ Data encryption: encrypt data for security purposes. For example, password encryption.
Application Layer
□ The application layer serves as the window for users and application processes to access
network services.
□ This layer contains a variety of commonly needed functions:
1. Resource sharing and device redirection
2. Remote file access
3. Remote printer access
4. Inter-process communication
5. Network management
6. Directory services
7. Electronic messaging (such as mail)
8. Network virtual terminals
 PRACTICAL-2

Aim:- Study about the various network devices..

• 1. Bridge

• 2. Repeater

• 3. Hub and Switch

• 4. Router

• 5. Gateway

Repeater

•Repeater is an electronic device, which operates, only in physical layer of OSI model as shown in fig

•Signal that carry information within a network can travel a fixed distance before noise can affect
integrity of data.
•Repeater installed on a link receives the signal before it becomes too weak or corrupted.
• It regenerates the original bit pattern and puts the new refreshed copy back onto the link.``

•A repeater is a regenerator, not an amplifier. When it receives a noise signal or corrupted signal, it
creates a copy bit for bit at the original strength
• A repeater allows us to extend only the physical length of a network.

• It connects two segments of the same network, overcoming the distance limitations of the transmission
media.
• A repeater forwards every frame; it has no filtering capability.

Bridge

• Bridges operate in both the physical and data link layer of the OSI model
• It has one input and one output.
• A bridge connects two or more LANs
• Bridge can divide a large network into smallersegments.
• Used to isolate network traffic andcomputers
  Repeaters retransmit frames to the entire connected device. Bridges transmit frames only to the
separate segment. Like this way bridges Handle Traffic.

• Bridges can also provide security through this partitioning of traffic (Means preventing unauthorized
access).

• Bridges operates at the data link layer, As a bridge found frame, it reads the address contained in the frame
& compares that address with a table of all the stations on both segments. When the bridge finds corrects
match,it find to which segment the station belongs and send the frame only to that segment.

• Bridge must have a look up table that contains the physical addresses of every station connected to it.
• Selective Forwarding

• Types of Bridges

1) Simple Bridge:
• A simple Bridge is the most primitive and least expensive types of bridge.
• It links two LAN.
• It contains a table that lists thephysical
• addresses of all the stations connected with the bridge.
• Physical addresses must be entered manually

• Whenever a new station is added, the table must be modified If a station is removed then also
address must be deleted from the table. So, installation and maintenance of simple bridges are
timeconsuming.

2) Multiport Bridge:
• It can be used to connect more than two LANs
• In this bridge three tables are created, each one holding the physical
address of stations reachable through the correspondingport.

3) Transparent Bridge:

 Transport Bridge builds its table of physical station addresses on its own as it performs its bridge
 functions.

• Table is automatically built by frame movements in the network.

• When Transparent Bridge is first installed, its table is empty.

• When it receives packet it looks at source & destination address.

• Destination address is used for forwarding decision to the particular segments. Source address is
used for adding entries to the table and for updating table.

• It checks destination address to decide where to send packet. If it is not inside table, it sends the
packet to all of the station on both segments excepting sender (source) station.

• Bridge is constantly checking source address of received. So, it updates entry for devices
according to the change if two devices exchanging theirplace.

Hub

• Hub is used to create connections between stations. Hub is a central network device that connects
network nodes as shownin fig.

• It can have multiple inputs & outputs all active at onetime.

 • It Permits large numbers of computer to be connected on a single or multiple LANs.

• It enables high speedcommunication

Types of Hub

1) Active Hub: Most hubs are active in that they regenerate and retransmit the signals the same way
a repeater does.
• In fact, because hubs usually have eight to twelve ports for computers to
connect to, they are often called multiport repeaters.
• Active hubs need electrical power to run

2) Passive Hub: It provides physical connectionbetween the attached device.

• Passive hubs act as connection points and do not amplify or regenerate the
signal.
Passive hubs do not require electricity to run.

3) Intelligent Hub: Intelligent hubs are increased functionality of active hubs.

A hub -based network can be expanded by connecting more than onehub.

It also has functions which can add intelligence to a hub like Hub management (control the hub)
and switching hub (which includes circuitry that very quickly routes signals between port s or'

Switches

• Switch provides bridging functionality with greater efficiency. It acts as multiport bridge to
connect devices or segments in a LAN as shown in fig
 • Switch has a buffer for each link to which it isconnected.
• Switch operates In Data Link Layer of the OSI model.
• When it receives a frame, It - stores the frame in the buffer of receiving link & checks
address to find outgoinglink.

• If the outgoing link is free the switch sends the frameto that particular link.

Two different Strategies of Switch:

1. Store and Forward switch:

• This switch stores the frame in the input buffer untilthe whole packet has arrived.

2. Cut -through switch :

It forwards the frame to the output buffer as soon as the destination address isreceived

Routers

• Routers operate in the physical, data link and network layers of the
OSI model as shown in fig

• It is most active in network layer.

• Routers are able to access network layer address (logical address)of the device.

• It contains software that enables them to determine which of several paths between those
addresses is the best for aparticular transmission.
 • function of routers is to receive packets from one connected network and [pass them to a
second connectednetwork

Types of Router

1. Static Router
Routing Table information's are entered manually. Means the administrator enters the route for each
destination into the table

2. Dynamic Router
Routing table is created automatically
Geteway

• Gateways operate in all seven layers of OSI model as shown in fig

• A Gateway is also called as protocol converter.

• Gateway is used to connect two different network

• A Router is used to transfers, accepts and relays packets only across and networks
using similar protocols.

• A Gateway can accept a packet formatted for one protocol and converts in to a packet
formatted for another protocol before forwarding it.

• Gateway must adjust data rate, size and format. It converts the protocol from one
network to another.
 PRACTICAL-3

Aim:-Create topology to connect two pc and configure them.

PROCEDURE:-

- Take two pc from end devices option.

- Now connect this 2 pc.
- Then set IP configuration for pc 1 in static configuration.
- Then set IP address and default gateway.
- In similar way set IP configuration for pc 2 in DHCP in IPV6 configuration.
- Similarly set IP address and default gateway for pc 2.
- Now send message from pc 0 to pc 1 with help of send message box.
- At last we get last status as successful.

PC 0:- PC 1:-
IP Address:-172.168.0.1 IP Address:-172.168.0.2
Gateway:-172.168.0.1 Gateway:-172.168.0.1
Subnet mask:-255.255.0.0 Subnet mask:-255.255.0.0
 PRACTICAL-4

Aim:- Create topology to connect LAN using hub.

PROCEDURE:-
- Take four pc from end devices.
- Then take one hub.
- Join four PC with hub.
- Then after set IP address for all PCs.
- Now send message from PC0 to PC1 with help of send message box.
- Then see simulation process of PCs and hub from simulation pannel.

PC 0:- PC 1:-
IP Address:-172.168.0.2 IP Address:-172.168.0.3
Gateway:-172.168.0.1 Gateway:-172.168.0.1
Subnet mask:-255.255.0.0 Subnet mask:-255.255.0.0

PC 2:- PC 3:-
IP Address:-172.168.0.4 IP Address:-172.168.0.5
Gateway:-172.168.0.1 Gateway:-172.168.0.1
Subnet mask:-255.255.0.0 Subnet mask:-255.255.0.0
 PRACTICAL-5

AIM:-Create a topology to connect LAN using switch.

PROCEDURE:-
-Take four PCs from end devices option.
-Then after take one switch.
-Join four PCs to switch.
-Then after set IP address of all PCs.
- Now send message from PC0 to PC1 with help of send message box.
-Then see simulation process of PCs and hub from simulation pannel.

PC 0:- PC 1:-
IP Address:-172.168.0.2 IP Address:-172.168.0.3
Gateway:-172.168.0.1 Gateway:-172.168.0.1
Subnet mask:-255.255.0.0 Subnet mask:-255.255.0.0

PC 2:- PC 3:-
IP Address:-172.168.0.4 IP Address:-172.168.0.5
Gateway:-172.168.0.1 Gateway:-172.168.0.1
Subnet mask:-255.255.0.0 Subnet mask:-255.255.0.0

25 | 2 1 4 0 7 0 9 - C o m p u t e r N e t w o r k
 PRACTICAL-6

AIM:-Create a topology to connect LAN using switch and hub.

PROCEDURE:-
-Take six PCs from end devices option.
-Then after take one switch and one hub.
-Join three PCs to switch and join three PC with hub.
-Then after set IP address of all PCs.
- Now send message from PC2 to PC3 with help of send message box.
-Then see simulation process of PCs and hub from simulation pannel.
-Message passing from PC2 to PC3 then after hub with joint PC message pass.
-But in switch message pass from PC3.

PC 0:- PC 1:-
IP Address:-172.168.0.7 IP Address:-172.168.0.2
Gateway:-172.168.0.1 Gateway:-172.168.0.1
Subnet mask:-255.255.0.0 Subnet mask:-255.255.0.0

PC 2:- PC 3:-
IP Address:-172.168.0.3 IP Address:-172.168.0.4
Gateway:-172.168.0.1 Gateway:-172.168.0.1
Subnet mask:-255.255.0.0 Subnet mask:-255.255.0.0

PC 4:- PC 5:-
IP Address:-172.168.0.5 IP Address:-172.168.0.6
Gateway:-172.168.0.1 Gateway:-172.168.0.1
Subnet mask:-255.255.0.0 Subnet mask:-255.255.0.0

P Prof. Firdos Sheikh

P Prof. Firdos Sheikh
 PRACTICAL-7

AIM:-Create a topology to connect LAN using router.

PROCEDURE:-
-Take router and two PCs from end devices option.
-Then assign different gateway and IP address of all PCs.
-Connect router and PCs.
-In router IP address use PCs gateway
- Now send message from PC0 to PC1 with help of send message box.

PC 0:- PC 1:-
IP Address:-172.168.0.2 IP Address:-165.168.0.2
Gateway:-172.168.0.1 Gateway:-165.168.0.1
Subnet mask:-255.255.0.0 Subnet mask:-255.255.0.0

Router:-
Fastethernet0/0:-172.168.0.1
`Fastethernet0/1:-165.168.0.1

P Prof. Firdos Sheikh

P Prof. Firdos Sheikh
 PRACTICAL-9

AIM:-Create a topology to connect LAN using two switch and router.

PROCEDURE:-
-Take one router and two switches six PCs from end devices option.
-Connect two PCs to each switch and switch with router.
-Assign a common gateway to each two PCs.
-No configuration is required in switch.
-In router IP address use gateway of each PCs group.
- Now send message from PC0 to PC3 with help of send message box.

PC 0:- PC 1:-
IP Address:-172.168.0.1 IP Address:-172.168.0.3
Gateway:-172.168.0.2 Gateway:-172.168.0.2
Subnet mask:-255.255.0.0 Subnet mask:-255.255.0.0

PC 2:- PC 3:-
IP Address:-172.168.0.4 IP Address:-165.168.0.1
Gateway:-172.168.0.2 Gateway:-165.168.0.2
Subnet mask:-255.255.0.0 Subnet mask:-255.255.0.0

PC 4:- PC 5:-
IP Address:-165.168.0.3 IP Address:-165.168.0.4
Gateway:-165.168.0.2 Gateway:-165.168.0.2
Subnet mask:-255.255.0.0 Subnet mask:-255.255.0.0

Router:-

Fastethernet0/0:-172.168.0.2
Fastethernet0/1:-165.168.0.2

P Prof. Firdos Sheikh

P Prof. Firdos Sheikh