ASSIGNMENT #3
SOLUTION
BRIDGES
A Bridge is a combination of hardware and software. It has its own operating system. It
helps to conserve the bandwidth of a network. Bandwidth is the speed of a network. It
indicates how many bits can be transmitted across a network in a given time. In case of a
bridge, the larger network is physically chopped into smaller segments. A bridge can read the
MAC (Media Access Control) or physical address of a computer on data packets. MAC
address is printed on the Network Interface Card. A bridge matches this MAC address with
the one stored in its table and judges that which particular segment does a data packet
belong to and accordingly sends that packet to such a segment. It does not allow other
packets belonging to other segments to spread to a particular segment and hence conserves
the bandwidth.
SWITCHES
A switch is also a combination of hardware and software having its own operating system.
Like bridges, the switches are also used to increase the bandwidth of a network. However, in
case of a switch, a network is virtually divided into small segments called Virtual LANs or
VLANs. Similar type of users can be grouped into a VLAN despite that they have no
physical proximity or closeness. A switch would read the MAC address on a data packet and
match it with the list of MAC addresses of the user machines contained in it. It then sends
data packets only to that machine on a VLAN to which these packets relate. Packets
belonging to other VLANs are not allowed to enter into a particular VLAN, hence
bandwidth increases.
ROUTERS
Routers use a combination of hardware and software to forward data packets to their
destination on the internet. They are more efficient and sophisticated than bridges and
switches. They can divide large networks into logical segments called Subnets on the basis of
IP addressing scheme. A router can communicate with another router on the internet with
the help of Routing Information Protocol, and thus it can build a routing table. This routing
table contains information about different network addresses and different routes for
delivery of data packets to a host machine on a network. A router is a decision making
device. When a data packet arrives at a router it reads the network addresses from the IP
address on the data packet and determines the shortest possible path through which this
packet can be delivered to its destination.
Following diagram (Fig. 5) explains how routers on the internet backbone forward data
packets by determining the shortest possible path for the destination. In this example a client
machine ‘A’ sitting on network no. 140.57 sends data to a web server ‘B’ hosted at network
no. 100. ‘R1’ is the router attached to network no. 140.57. After consulting its routing table it
can find that the shortest possible path for sending data to machine ‘B’ is to forward data
packets to ‘R2’, the router attached to network no. 100. In case there is a blockade then‘R1’
can look for the alternative shortest path. Here, the alternative shortest
path for the delivery of data packets to ‘B’ can be R1-R3-R4-R2.
100
R1
140.57
R2
AA
R3
R4
R5
R6
Fig. 5
B
B