background image
Compression Overview 313
In compression, CPU utilization of the router increases considerably. However, the WAN link
utilization drops considerably. It's a trade-off because all that has been accomplished is the
displacement of utilization from the WAN to the router. Obviously, the effects of compression
vary based on the algorithm implemented, but, hopefully, the point is made.
As technology advances, compression will move from a software function to a hardware
function. This is already a reality in some router models with the addition of newly available
modules specifically geared toward performing data compression in hardware. Not only is this
much faster than software compression, it is less costly for the CPU (generally).
The effects of compression must be taken into account prior to any implementation. If your
routers are already at 80 percent or more CPU utilization, it's not a good idea to implement
compression. Doing so can result in a catastrophic outage.
Data compression makes efficient use of bandwidth and increases WAN throughput by reducing
the size of the frame being transported. Compression is best utilized on slower WAN links.
There will come a point when the router can send the data faster than the router can compress,
send, and then decompress the data.
Cisco supports a number of compression types:
·
Link
·
Payload
·
TCP Header
·
Microsoft Point-to-Point
Microsoft's Point-to-Point compression, which is an algorithm, is out of scope for our purposes
and is not discussed further in this book.
Figure 10-7 illustrates where various types of compression make transmission more efficient.
Figure 10-7
Compression Methods
WAN
technology-
specific
header
Network layer
Protocol
header
Data Payload
Header
compression
Payload
compression
Link
compression