of compression is to reduce the number of bytes sent across the link. However, there is a price
to pay for compression--CPU cycles and possibly increased latency for the packets. The
following list summarizes the trade-offs when considering whether to use compression:
compression.
the output queue due to link congestion. With the compressed frames, however, the queue
is shorter.
compression can be desirable. However, care must be taken to avoid excessive CPU utilization.
Cisco recommends avoiding sustained CPU utilization exceeding between 40 and 65 percent,
depending on the platform.
HDLC, and PPP link compression in software; when software compression is used, CPU
utilization is impacted. For hardware compression, either a VIP2 card or a Compression Service
Adapter (CSA) on a 72xx or 75xx series router is required. When hardware compression is
performed, the CPU is not affected.
STAC, Predictor, and Microsoft Point-to-Point Compression algorithm (MPPC). The details of
the algorithms are beyond the scope of the CCNA exam. However, the MPPC algorithm and
protocols can be used between a router and a PC on a dial connection when compression is
desired.
Predictor algorithms. Only PPP supports the MPPC algorithm. Table 8-7 summarizes the
support for each type.