Computer Network | Delays in Networks


Data transmission from one point to another point, is a combination of different movements of data over multiple stages. Each of these movements takes its own time depending of the location of data, capacity of transmission medium, signal velocity and various other factors. The following are some basic time aspects which can be used to asses a transmission network or a protocol.

Transmission Delay(Tt)

Time taken to schedule a data packet from a host system to its outgoing link is known as transmission delay. It depends on mainly two parameters- band width and size of data packets.

Band width is the amount of data which can send in unit time.

If Band Width= 1 bps [bit per second] and Data packet/unit is of 10 bits, then Transmission Delay
Tt= 10 bits /(1 bit/ second) = 10 seconds
which implies, If Band Width is B bps and Data is of length L bits the Transmission Delay Tt=(L/B)

Which means the transmission delay will becomes too big for a larger data packet size on narrow band width. So to boost transmission transmission speed, it requires a much wider band width.

Representation of Kilo(K) for data will be interpreted as 1024 and for band width it is the usual notation of standard '1000' (Kilogram=1000gram), which means Band width given as 1 Kbps is equal to 1000 bps and length of data packet given as 1 Kb is equal to 1024 bits



Propagation Delay(Tp)
Assume a data packet is sending form source and receiver. As explained above time taken for the source to set the data into a link which connects receiver and sender is called transmission delay, then the time to propagate from source to receiver is called propagation delay(Tp).
Propagation delay depends on distance between source and receiver and how faster the signal can move in its propagation medium or simply velocity of the signal.
Tp= d/v
d: distance between source and receiver
v: velocity of the signal in its propagation medium

Now a days propagation mediums are mainly optical fibers, in which signal travel with a speed, about 70% of actual speed of light(210,000,000 m/s).

Example:
Let d = 42 Km & v= 2.1 * 108 m/s
Tp = d/ v = (42 * 103) / (2.1 * 108) = 2* 10-4 = 0.2 ms

So total time required to send a packet of data form source to destination is the sum of transmission time Tt and propagation time Tp.



Queuing Delay

The packets of data reached at receiver end will be aligned in a buffer queue, the amount of time a packet spend in this queue before being processed by receiver is called queuing delay.



Processing Delay
The time for fetching and processing of data packets by the receiver is called processing delay.

Queuing delay and processing delays are solely depend on processing capacity of the receiving system.

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