Computer Networks-3

Question 1

Ethernet

Answer 1

– Ethernet is a widely deployed LAN technology.
– This technology was invented by Bob Metcalfe and D.R. Boggs in the
year 1970.
– It was standardized in IEEE 802.3 in 1980.
– Ethernet shares media. Network which uses shared media has high
probability of data collision.
– Ethernet uses Carrier Sense Multi Access/Collision Detection
(CSMA/CD) technology to detect collisions.
– On the occurrence of collision in Ethernet, all its hosts roll back, wait
for some random amount of time, and then re-transmit the data.
– Ethernet connector is network interface card equipped with 48-bits
MAC address.
(* This helps other Ethernet devices to identify and communicate with remote
devices in Ethernet.)

Question 2

Computer Network Topology (based
on inter-connectivity)

Answer 2

• A Network Topology is the arrangement with which
  computer systems or network devices are connected to
  each other.
• Topologies may define both physical and logical aspect of
  the network.

Question 3

Network topology includes:

Answer 3

– Point-to-point
– Bus topology
– Star topology
– Ring topology
– Mesh topology
– Tree topology
– Hybrid topology

Question 4

Point-to-Point

Answer 4

– Point-to-point network contains exactly two hosts
such as computer, switches, routers, or servers
connected back to back using a single piece of cable.
– If the hosts are connected point-to-point logically,
then may have multiple intermediate devices.
– But the end hosts are unaware of underlying
network and see each other as if they are connected
directly.

Question 5

Bus Topology

Answer 5

– All devices share single communication line or cable.
– There is a problem while multiple hosts sending data at the
same time.
– Therefore, Bus topology either uses CSMA/CD technology or
recognizes one host as Bus Master to solve the issue.
– It is one of the simple forms of networking where a failure of a
device does not affect the other devices.
– But failure of the shared communication line can make all
other devices stop functioning.

Question 6

Star Topology

Answer 6

– All hosts in Star topology are connected to a
central device, known as hub device, using a
point-to-point connection.
– There exists a point to point connection between
hosts and hub.
– The hub device can be any of the following:
* Layer-1 device such as hub or repeater
* Layer-2 device such as switch or bridge
* Layer-3 device such as router or gateway
– hub acts as single point of failure. If hub fails, connectivity of all hosts to all
other hosts fails.
– Every communication between hosts takes place through only the hub.

Question 7

Ring Topology

Answer 7

– Each host machine connects to exactly two other
machines, creating a circular network structure.
– When one host tries to communicate or send
message to a host which is not adjacent to it, the
data travels through all intermediate hosts.
– To connect one more host in the existing
structure, the administrator may need only one
more extra cable.
– Failure of any host results in failure of the whole
ring.
– Thus, every connection in the ring is a point of
failure.

Question 8

Mesh Topology

Answer 8

– A host is connected to one or multiple hosts.
– This topology has hosts in point-to-point connection
with every other host or may also have hosts which
are in point-to-point connection with few hosts only.
– Hosts in Mesh topology also work as relay for other
hosts which do not have direct point-to-point links.
– Mesh technology comes into two types:
* Full Mesh
* Partially Mesh

Question 9

Tree Topology

Answer 9

– Also known as Hierarchical Topology, this is the most
common form of network topology in use presently.
– This topology imitates as extended Star topology and
inherits properties of Bus topology.
– This topology divides the network into multiple
levels/layers of network.
– Mainly in LANs, a network is bifurcated into three layes.
* The lowermost is access-layer where computers are attached.
* The middle layer is known as distribution layer, which works as
mediator between upper layer and lower layer.
* The highest layer is known as core layer, and is central point of
the network, i.e. root of the tree from which all nodes fork.
* All neighboring hosts have point-to-point connection
between them.
* If the root goes down, then the entire network suffers
even though it is not the single point of failure.
* Every connection serves as point of failure, failing of
which divides the network into unreachable segment.

Question 10

Hybrid Topology

Answer 10

– A network structure whose design contains more
than one topology is said to be hybrid topology.
– Hybrid topology inherits merits and demerits of all
the incorporating topologies.