Computer Networks

Running Head: COMPUTER NETWORKS 0 | P a g e
Computer Networks
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Computer Networks 1 | P a g e
1.a Open Systems Interconnect (OSI) model is having seven layers, which are application,
session, presentation, transport, network, data link and physical layer. Host A is sending a
request to the Hub-B for accessing a webpage form the Server F. Host A and Hub B are
connected with physical layer technology, which is Ethernet. Hub-B accepts the request at
physical layer, and forwards it to the Router-C. therefore, these devices are at different layers of
the OSI model, such as Hub-B is at data link layer, Router-C is ate Network Layer, Router-D at
Network Layer, Switch-E at data link layer.
1.b Message size is 2000 bytes. Header size is 200 bytes for each layer. Therefore, total header
size is 1200 bytes. Total size of header and message is 3200 bytes.
So, (1200/3200)*100 = 37.5 %

Computer Networks 2 | P a g e
1.c Encapsulation is process in which message is added some bytes for information about the
data and protocols for the understanding the control and data flow. Each layer is having
separated work, such as network layer is used for the node-to-node delivery of the packet.
Therefore, each layer is adding the header in the main message for understand about the packet.
It is like postal services.
1.d client-server model is having a centralized computer, which manage all the other systems.
Client-server model is stable, as it is responding clients for their request. Client-server model is
more scalable, as new client is easily added in the system. Security is high in the Client server
model as it is having access controls for each client separated. Performance of client-server
model is high, as server is dedicated for all the clients. Backup feature is so important for the
safety of the data. It is better in the client-server network model.
1. e a network is required proper addressing of the computer systems. Computer systems are
connected than they are required IP addresses for each system. So, according to choose address
for networking, such as 192.168.10.1 for group of 254 computer systems with a subnet mask,
which is 255.255.255.0. It is also possible by the DHCP.

Computer Networks 3 | P a g e
Source: (study-ccna.com, 2018)
TCP is having 3-way handshake in which host send a request to the server. Than server send a
response with acknowledgement. In the end, host send the acknowledgement of the connection
establishment to the server as shown in below figure.
Source: (study-ccna.com, 2018)
For closing the connection host send a request as FIN as shown in the below figure.
Source: (study-ccna.com, 2018)

Computer Networks 4 | P a g e
2.b TCP is reliable protocol as it is taking acknowledgement of the packet. Few features make it
more reliable. TCP is providing reliable data transfer. It uses sequence number for the segments.
It provides flow control and error control, which makes it more reliable. It is having connection-
oriented service. TCP is more flexible than other protocols. It is sending data in the ordered way.
It retransmits the lost packets. It is also discarding duplicate packets.
1. TCP is reliable protocol and UDP is unreliable protocol
2. TCP is having sequencing of segments and acknowledgements but UDP is not having it.
2.d i Data in the first segment is 1910-1010 = 900
2.d ii Acknowledgement number is 1010
2.d.iii The value of rwnd = 3500-1000 = 2500.
Host B can receive only 2500 bytes of data before overflowing its buffer. Host B advertises this
value in its next segment to A.

Computer Networks 5 | P a g e
Routing protocols are needed for the transfer data from a dedicated route with a proper security.
It is specifies about the communication between the routers for distributing data and selecting
routes for data transfer (FS.COM, 2018). Routing Information Protocol (RIP) is follows the
distance vector routing protocol and Open Shortest Path First is follows link state routing
protocol. RIP is having slow convergence and OSPF is having fast convergence. RIP uses
Bellman-ford algorithm for routing and OSPF uses Dijkstra’s algorithm for routing
(techdifferences.com, 2017).