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Interface Message Processor ( IMP )


Interface Message Processor ( IMP ) is a special purpose Computer. The Processor plays a vital role in Host-to-Host communication. IMP is placed between Host Computers.  IMP helps Hosts to exchange information.

IMPs ( Interface Message Processors ) form a group. The group dedicates itself towards reliable transmission of Packets.

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Note: An Interface Message Processor can be supposed to have a face. Firstly this supposed face of IMP is in the direction of the first Host, which sends the  message. Secondly, this face is turned towards the other Host.  Now, the IMP,  with its face turned around, communicates with this other Host.  Transformed message from IMP is communicated to this Host.

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Message ( a piece of information ) sent from the Host ( source of information  ) is transformed into Packets. Transformation of the message into Packets is performed by an IMP. These Packets are forwarded to the receiver Host.

We should note the word 'Interface'. It means the qualified processor ( Interface Message Processor - IMP ) is placed between two objects ( here the two objects are the two Host Computers ). The processor interfaced between two Hosts ( actually IMP ) is an important element of Network Structure. 

As we learnt, IMP divides messages into Packets. Someone can say that IMP performs the act of segmentation of messages. When a message is segmented, a number of Packets are formed. 

Yes, a message is bigger than Packet. In other words, a Packet is smaller than message.


IMPs play an important role in Packet Switching. The Packets are formed by an IMP from the Host's message. After formation these Packets are transmitted to the target Host Computer. Other IMPs help in this  transmission of Packets. The other IMPs are there to ensure reliable Packet Switching. Thus, Packet Switching is not allowed to fail. 

Presence of some extra IMPs serves to safeguard Packet Switching against failure of a Packet route. So, if one route fails, there is no problem. Packets are driven through the other route. We can say that extra IMPs serve to backup transmission of Packets. Some of  extra IMPs also forward the Packets. Forwarding of Packets is required.

So, we can see that IMPs carry out the communication between two Host Computers. 

It is important to note that there are two Host Computers that communicate successfully. These Hosts do not know the actual internal working of IMPs. IMPs just do their job and provide service to the Hosts. 

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Special purpose IMPs:

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1 ) Terminal IMP: Terminal IMP  is placed in front of Small Computers. Here the message from the Small Computers is transformed into Packets. Besides, the Terminal IMP serves as a small Host Computer. This IMP provides  Small Computers with information.

2 ) Satellite IMP: Satellite IMP comes with extra memory. Satellite Links are slow.  This  IMP stores the directed messages. Extra memory is helpful here and more space is available with IMP for receiving the messages.  The messages are transformed into packets by the Satellite IMP. These packets are placed on Satellite Links. 

Now, slow Satellite Links are not a problem. It is because the problem due to slow speed of the Links does not turn more painful.  Armed with  extra memory, Satellite IMP is always ready with Packets. These packets are communicated to the other end. Thus, Satellite IMP serves well.




3 ) Encryption IMP: This IMP also gives out Packets. The Packets  are additionally encrypted by the Encryption IMP. Packet Encryption is important for secure communication. Encrypted Packets are naturally protected from unauthorized access. Encryption IMP helps to make Packet Switching secure. 

Such IMP performs encryption with the help of hardware. Encryption IMP has built-in Message Encryption Hardware. Message Encryption Hardware encrypts the Packets that originate from the messages.


4 ) Control Program IMP: Control Program IMP run special Control Programs. The Packets formed by the IMP are special. Speciality is achieved by the use of Control Programs. Control Programs impact the resulting Packets in a specific way.  Packet content is suitably altered. Actually the content of each Packet is encoded. The Packets so encoded  can be communicated easily. So, Packet Switching is helped.

These Packets make the most of communication facilities. Such packets can be easily carried across a Network. These Packets  cannot be distorted while they are on the way.  The  Packets so enabled help Packet Switching. 

One point more. The noise that is a Network problem also fails to harm the Packets. Yes, these Packets are on their way to the target Host. Thanks to the Control Program that was applied on these Packets. This Control Program thus made these Packets resistant to noise.


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