Solution of computer network assignment
1. Describe the following terms:
a. Layered Architecture
Layered architecture is very useful and important term in computer network
which makes us to allow Complex problems to decompose in to small
manageable units. Implementation details of the layer are abstracted. Layered
architecture is needed for separation of implementation and specification. In
layered architecture, layers are work as one by sharing the services provided by
each other. Layering allows us in reuse functionality i.e., lower layers implement
common once. Provide framework to implement multiple specific protocols per
layer.
Fig: three layers architecture (fig. sources Google)
b. Internet Stack Layer
Internet stack layer is also known as internet protocol stack. The Internet protocol
stack provides a connection oriented reliable branch (TCP) and a connectionless
unreliable branch (UDP) both build on top of the Internet Protocol.
Internet stack layer is a group of internetworking methods, protocols, and specifications in
the Internet protocol suite that are used to transport datagram (packets) from the
originating host across network boundaries, if necessary, to the destination host specified by a
network addressor IP address which is defined for this purpose by the Internet Protocol (IP).
The internet layer derives its name from its function of forming an internet (uncapitalized), or
facilitating internetworking, which is the concept of connecting multiple networks with each
other through gateways.
(PDU: power distribution unit)
Fig: internet stack layer (sources: wikkipedia, google)
c. OSI Layer
- OSI refers to open system interconnection
- defines internetworking in terms of a vertical stack of seven layers
-mainly have two layers
-upper layer
-lower level
-beside these two layers they are further divided into seven sub-layers they are:
- Seven layers are:
- Upper layer
 Application
 Presentation
 Session
- Lower layer




Transport
Network
Data link
physical
Fig: OSI layers (sources: about tech)
2. Discuss about the history of the computer networks and internet.
Ans:
Computer network is the interconnection of two or more computer in different manner as
a telecommunication channels. The starting phase of computer network is on late 1950s later
on it has been developed in different phases till now they are listed below with their name:
year
1950
Name of network
Military radar system Semi-Automatic Ground
Environment (SAGE).
1960
1962
1964
1972
1973
1976
Commercial airline reservation system semiautomatic business research
environment (SABRE) went online with two
connected mainframes.
"Intergalactic Computer Network” a precursor to
the ARPANET
Used a computer to route and manage telephone
connections.
Commercial services using X.25 were deployed,
and later used as an underlying infrastructure for
expanding TCP/IP networks.
Describing Ethernet on the concept based on
ALOHA network developed in 1960s
Created ARCNET, a token-passing network first
used to share storage devices.
And later on 1995 the transmission speed of the Ethernet was increased from 10 Mbit/s
to 100 Mbit/s and also from 1998 it reaches up to gigabyte speed.
(Sources: Wikipedia)
Internet is the connection of computer all over the world in a same network by using certain
points known as server to the consumers known as users or client. The history of internet was just
started from the following date with some events:
- On October 4, 1957, the Soviet Union launched the world’s first manmade satellite
into
orbit which is consider as a first internet service
- In 1962, a scientist from M.I.T. and ARPA named J.C.R. Licklider proposed a solution to this
problem: a “galactic network” of computers that could talk to one another.
- In 1965, another M.I.T. scientist developed a way of sending information from one computer
to another that he called “packet switching.” Packet switching breaks data down into blocks, or
packets, before sending it to its destination. That way, each packet can take its own route from
place to place.
- In 1969, ARPANET delivered its first message: a “node-to-node” communication from one
computer to another.
- By the end of 1969, just four computers were connected to the ARPANET, but the network
grew steadily during the 1970s.
- In 1991 internet had changed in modern www (World Wide Web) computer programmer in
Switzerland named Tim Berners-Lee
(sources : the invention of internet)
Later on many changes has occurred in the field of internet.
3. Explain delay, loss and throughput in packet switched network.
ANS:
Delay is defined as the state of packets queue or wait for turn to access.
There are four sources of packet transfer delay. They are given below along with their function are
given below:
1. Nodal processing:
1. Check bits errors
2. Determine output link
2. Queuing:
1. Time waiting at output link for transmission
2. Depends on congestion level of router
3. Transmission delay:
1. R=Link bandwidth (bit/s)
2. L=Packet length (bits)
3. Time to send bits into link = L/R
4. Propagation delay:
1. d = Length of physical link
2. s = Propagation speed in medium
3. Propagation delay = d/s
Loss is the process of dropping a packet arriving to full queue. Lost packet
may be retransmitted by previous node, by source and system, or not all.
Fig: packet loss (sources: Google)
Throughput is the rate at which bit transfer between receiver and sender. Two types of
throughput on the basis of function. They are:
Instantaneous:
- Is the rate at given point
Average
-rate over long period of time
Throughput of a communication system may be affected by various factors, including the
limitations of underlying analog physical medium, available processing power of the system
components, and end-user behavior.
Fig: throughput in packet switching (sources from note downloaded)
4. Differentiate between packet switching and circuit switching and explain them in brief.
ANS:
Definitions:
PACKET-SWITCHING:
Packet-switched networks move data in separate, small blocks packets based on the
destination address in each packet. When received, packets are reassembled in the proper
sequence to make up the message. Circuit-switched networks require dedicated point-to-point
connections during calls.
CIRCUIT-SWITCHING:
Circuit-switched networks and packet switched networks have traditionally occupied different
spaces within corporations. Circuit-switched networks were used for phone calls and packetswitched networks handled data. But because of the reach of phone lines and the efficiency
and low cost of data networks, the two technologies have shared chores for years.
Packet-switched and circuit-switched networks use two different technologies for sending
messages and data from one point to another.
The following is the main difference between packet switching and circuit switching:
-It is easier and less expensive to double the capacity of a packet switched network whereas a
circuit network is heavily dependent on the number of channels available.
-Circuit-switched technologies, which take four times as long to double their performance/cost, force
ISPs to buy that many more boxes to keep up whereas packet switch does not.
-The battle between circuit and packet technologies has been around a long time, and it is starting to be
like the old story of the tortoise and the hare. In this case, the hare is circuit switching—fast, reliable and
smart. The hare starts out fast and keeps a steady pace, while the tortoise starts slow but manages to
double his speed every 100 meters. If the race is longer than 2 km (1.2 miles), the power of
compounding favours the tortoise (packet switching).(i.e.in this case packet switching is not reliable
then circuit switch)
-a packet switched network establishes a path from host to host over a shared medium
whereas A circuit switched network is greedier with its resources but ensures the availability of
those resources.