dfgdfg

1. Assignment No#(۱)
Submitted by: Ahmad iqbal
Rool ۶۸no:
Assignment: data communication
Submitted to: Izaz Ahmad
Semester: ۵th
bs(cs)
Section:"B"

2. List the layers of the internet model?
Physical
data link
network
transport
application.
Which Layers of the Internet model are the network support layers?
The network support layers are the physical, data link, and network layers.
which is the user support layer
User support layers:
The user support layers are: Session layer, Presentation layer, Application layer. These
allow interoperability among unrelated software system.
What is peer-to-peer process?
A layer appears to be communicating directly with the same layer at the other end of the link (i.e.
its peer). What is actually happening is that the data is being passed down to lower layers for
transmission and is passed up again at the other end.
How does information get passed from one layer to the next in the
internet model?
Each layer in the sending device adds its own information to the message it receives from the
above layer and sends it to the layer below it. At layer ١ the entire package is converted to a form
to be transmitted to the receiving device.
On the receiving device side, the package is unwrapped layer to layer. Each layer removes data
meaningful to it and sends the rest to the above layer and so on.
what are headers and trailers and how do they get added and removed?
Headers and trailers are the concepts of OSI model.
Headers are information structures which identifies the information that follows, such as a block of
bytes in communication.
Trailer is the information which occupies several bytes at the end of the block of the data being
transmitted.They contain error-checking data which is useful for confirming the accuracy and status of
the transmission.
During communication of data the sender appends the header and passes it to the lower layer while
the receiver removes header and passes it to upper layer. Headers are added at layer ۶ ۵ ۴ ٣ & ٢
while Trailer is
What is port address
Port address is transport layer ID (simillar to IP in Network Layer) which identify the
application on the host.
What are the responsibilities of data link layer?
The data link layer is responsible for moving frames from one hop or node to the next.
Other responsibilities of the data link layer include the foollowing...
١. Framing -
The DLL dividdes the stream of bits received from the network layer into manageable data units called
frames...
٢. Physical addressing -
If the frames are to be distributed to different systems on the network, the DLL adds a header to the
frame to define sender or receiver of the frame...
٣. Flow control -
Flow control is one of the important design for DLL...Flow control, that controls the flow of data
between sender and receiver...

3. ۴. Error control -
DLL is responsible to detect and retransmit damaged or lost frames...It also user a mechanism to
recognize duplicate frames...
۵. Access control -
When two or more devices are connected to the same link, DLL protocols are determine, which
device has control over the link at any given time...
What are the responsibilities of the network layer?
Hey network layer is the most essential layer of osi model as it deals with the data transferring from
on to another place...
The network layer is the third layer out of seven in the OSI model and the third layer out of five in the
TCP/IP model. In the TCP/IP reference model it is called the Internet layer. In all of the models, the
network layer responds to service requests from the transport layer and issues service requests to the
data link layer.
What are the transport layer responsibilities?
Keeping track of the individual conversations taking place between applications on the source
and destinations on the source and destination hosts.
٢. Segmenting data and adding a header to identify and manage each segment.
٣. Using the header information to reassemble the segments into applications data.
۴. Passing the assembled data to the correct applications.
What is the difference between port address, logical address and
physical address?
logical Address: An IP address of the system is called logical address. This address is the
combnation of Net ID and Host ID. This address is used by network layer to identify a particular
network (source to destination) among the networks. This address can be changed by changing the
host position on the network. So it is called logical address.
Physical address: Each system having a NIC(Network Interface Card) through which two
systems physically connected with each other with cables. The address of the NIC is called Physical
address or mac address. This is specified by the manficture company of the card. This address is
used by data link layer.
Port Address: There are many application running on the computer. Each application run with a port
no.(logically) on the computer. This port no. for application is decided by the Karnal of the OS. This
port no. is called port address.
How do the layers of the Internet model correlate to the layers of the
OSI?
The OSI, or Open System Interconnection, model defines a networking framework for
implementing protocols in seven layers. Control is passed from one layer to the next, starting at
the application layer in one station, proceeding to the bottom layer, over the channel to the next
station and back up the hierarchy.
Name some services provided by the application layer in the internet
model?

4. the Services provided by the application layer in the internet model is
١) Network virtual terminal
٢) File transfer, access, and management,
٣) Mail services,
۴) Directory services
What are the concerns of the physical layer in the internet model?
The physical layer is responsible for transmitting a bit stream over a physical medium. It is
concerned with a. physical characteristics of the media b. representation of bits c. type of
encoding d. synchronization of bits e. transmission rate and mode f. the way devices are
connected with each other and to the links"
How are the OSI and ISO related to each other?
The ISO is the International Standards Organization. It is a volunteer organization
dedicated to the worldwide agreement on standards. The OSI is the Open Systems
Interconnection model, which is the standard for networking communications. The ISO
is the organization that developed the OSI model.
Match the following to one or more layers of the OSI model
a. Route determination-> network layer
b. Flow control -> data link layer & transport layer
c. Interface to transmission media ->physical layer
d. Provides access for the end user->application layer
Match the following to one or more layers of the OSI model
a. Reliable process-to-process message delivery –>transport layer
b. Route selection-> network layer
c. Defines frames-> data link layer
d. Provides user services such as email and file transfer->application layer
e. Transmission of bit stream across physical medium-> physical layer
Match the following to one or more layers of the OSI model
a. Communicates directly with user’s application program ->application layer
b. Error correction and retransmission -> transport layer

5. c. Mechanical, electrical, and functional interface – >physical layer
d. Responsibility for carrying frames between adjacent nodes->data link layer
Match the following to one or more layers of the OSI model
a. Format and code conversion services->presentationlayer
b. Establishes, manages, and terminates sessions-> session layer
c. Ensures reliable transmission of data->transport layer
d. Log-in and log-out procedures->application layer
e. Provides independence from differences in data representation->presentation layer
If the data link layer can detect errors between hops why do you think we need
another checking mechanism at the transport layer?
The errors between the nodes can be detected by the data link layer control, but the error at
the node (between input port and output port) of the node cannot be detected by the data
link layer.