Snooping protocol

This technology is more commonly referred as the bus snooping protocol in the networking world as compared to the term snooping protocol. It is the protocol that is used in the networks for maintaining the cache coherency in the symmetric multiprocessing environments. In this system all the cache presents on the bus monitors the bus in order to determine that whether they have a copy of the block of the data that was requested by a networking device on the bus. This process is possible as every cache has the copy of the sharing status of every block of physical memory it has.

In a multiprocessing environment therefore all these multiple copies of shared documents can be accessed at once without any coherence problem. There are two different types of snooping protocols that are being implemented in the networking world. The following material gives a brief introduction of these two snooping protocols.

The first type of the snooping protocol is the Write Invalidate snooping protocol. In this type of snooping protocol the processor that is writing the data in the cache, causes the data from all the other cache of the other processors to be rendered invaluable and useless, before it changes its own local copy. This process is done with the help of the local machine that sends the invalidation signal over the bus, which in turn cause the cache to look for the invalidate file copy and once the cache copies have been invalidated then the processor can continue to send or upload the data until the other processor requests for it.

The second type of the snooping protocol is the write – update.  In this type of protocol, the processor that is writing or coding the new data, broadcasts it over the bus, hence, when this is done, then all the relevant cache copies are also updated.