Page 161 - DCAP207_NETWORKS_DCAP406_COMPUTER_NETWORKS

Computer Networks/Networks

Notes

Task Differentiate between Class A, B, C, D and E type of IP addresses.

Self Assessment

Fill in the blanks:

1. ……………………………. is the collection of several independent networks, which are
interconnected with one another.
2. The ………………………. is basically network identifier or network address portion of an
IP unicast address.
3. ………………………… is reserved for IP unicast addresses.
4. CIDR stands for …………………………….

5. Technically, IP addresses are expressed using binary notation with ……… bit long string.
10.2 Congestion Control

Congestion causes chocking of the communication channel. When too many packets are present
in a part of the subnet, the performance of the subnet degrades. Hence, a communication channel
of a network is called congested if packets traversing the path experience delays largely in excess
of the paths propagation delay. It is called heavily congested when the packets never reach the
destination indicating that the delay approaches infinity. The reasons for congestion are not one
but many. When the input traffic rate exceeds the capacity of the output lines, the input part of
the subnet gets chocked and creates congestion. Congestion is also happened when the routers
are too slow to perform queuing buffers, updating tables, etc. Lack of capacity of the routers’
buffer is also one of many factors for congestion. However, enhancing memory of the router
may be helpful up to a certain point. Beyond a certain point of time, congestion gets worse
because of timeout retransmission will create more traffic load. Briefly, the apparent causes of
congestion are jamming by several input lines, slow processors, low bandwidth, finite number
of buffers, etc.

Did u know? Congestion control and flow control are two different phenomenons.
Congestion is a global phenomenon involving all hosts, all routers, the store-and-forward
processing within the routers, etc., whereas, flow control is concerned with point-to-point
traffic between a given source host and a given destination host. The example of congestion
control is a situation when a store-and-forward network with 1-Mbps lines and 1000 large
minicomputers, half of which were trying to transfer files at 100 kbps to the other half. An
example of flow control is when a fiber optic network with a capacity of 1000 gigabits/sec
on which a supercomputer was trying to transfer a file to a personal computer at 1Gbps.

10.2.1 General Principles of Congestion Control

According to control theory, the computer network, which is also a system, is divided into two
groups. They are open loop and closed loop solutions.
The open loop solutions: provide good design to ensure that the problem does not occur in the
first place. The designing tools include decision for accepting new traffic, discarding packets and
scheduling of the packets at various points in the network. The open loop solution’s decisions
are independent of the current state of the network.

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