You need to keep a few considerations in mind when selecting and implementing a compression
method:
Modem compression Modems can compress data up to four times smaller than its original size.
There are different types of modem compression techniques, so make sure you understand that
modem compression and router software compression are not compatible. However, the modems
at both ends of the connection will try to negotiate the best compression method to use. If compression
is being done at the modem, do not configure the router to also run compression.
Encrypted data Compression happens at the Data Link layer (layer 2), and encryption
functions at the Network layer (layer 3), although the payload is also encrypted, which
includes layer 7. After the application encrypts the data, the data is then sent to the router,
which provides compression. The problem is that encrypted data typically does not have
repetitive patterns, so the data will not compress. The router will spend a lot a processor
time to determine the traffic is not compressible. So, if data is encrypted, do not attempt to
compress it by using a layer 2 compression algorithm.
CPU cycles versus memory The amount of memory that a router must have varies according
to the protocol being compressed, the compression algorithm, and the number of configured
interfaces on the router. Memory requirements will be higher for Predictor than for Stac, but
Stac is typically more processor intensive.