To view information about the status of compression on the router, use the show compress
command. The following is a sample of the output from this command:
Router2#show compress
Serial1
uncompressed bytes xmt/rcv 82951/85400
1 min avg ratio xmt/rcv 0.798/0.827
5 min avg ratio xmt/rcv 0.789/0.834
10 min avg ratio xmt/rcv 0.779/0.847
no bufs xmt 0 no bufs rcv 0
restarts 0
Additional Stacker Stats:
Transmit bytes: Uncompressed = 27044 Compressed = 66749
Received bytes: Compressed = 76758 Uncompressed = 0
938 Chapter 30 Queuing and Compression
This command shows the uncompressed byte count of compressed data transmitted and
received as well as the ratio of data throughput gained or lost in the compression routine in the
last 1, 5, and 10 minutes. If the restarts are more than 0, the compression routine detected that
the dictionaries were out of sync and restarted building the compression dictionary. Using this
command, you will be able to see if compression is making a difference for the type of traffic
being compressed.
Summary
Queuing is an important technology when using WAN links. As the speed of LAN interfaces
increases more and more, data will be expected to traverse WAN links. Congestion is inevitable,
so to ensure that important data gets through, a queuing mechanism is necessary. There are
many queuing options available when using Cisco IOS.
Weighted fair queuing (WFQ) is the default technique when using interfaces of 2.048Mbps
or slower. WFQ will track conversations and enable lower bandwidth conversations to take
priority over higher bandwidth conversations. This feature can be tuned to allow tracking of
more conversations.
Priority queuing is used to classify traffic into four queues of high, medium, normal, and low.
Each queue is serviced sequentially, and the traffic is forwarded from the higher level queues
before the router services the lower level queues. The lower level queues might not be serviced
for quite some time if there is a large amount of higher priority traffic.
Custom queuing can allocate a certain percentage of the total bandwidth available on the
interface. There are 16 queues available, which can hold a certain type of traffic, and each
queue can be allocated a specific amount of bandwidth. Custom queuing does not suffer
from queue starvation as priority queuing can.
To alleviate congestion on WAN links, compression can be configured on the interface. The
types of compression algorithms are Stac, Predictor, and MPPC. MPPC is used primarily for Windows
clients, whereas Stac and Predictor can be used on many types of WAN technologies. TCP
header compression is the simplest compression technique. Payload compression compresses the
payload portion of the packet and does not alter the layer 2 or layer 3 header information. The
link compression algorithm uses Stac or Predictor to compress the traffic and then encapsulates
the compressed traffic in another link layer such as PPP or LAPB to ensure error correction and
packet sequencing.
Various techniques can ensure that the queuing and compression technologies are working
correctly. The show queue command is used to see queuing on the interface, and the show
queueing [priority | custom | fair] command is used to display the queuing technique
configured on the router. For compression, the show compress command is used to see how
well the compression process is compressing traffic and whether problems might occur with the
compression process.