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528 Chapter 8: WAN Protocols and Design
traffic being sent has been compressed already, then the compression ratios probably will be
low; Cisco recommends not using compression if this is the case.
The show process output, which is abbreviated, shows the CPU utilization. The numbers seem
to be in a reasonable range; for perspective, however, I simply let a ping command run on the
Seville router for a few minutes to create the output. No true user traffic was generated for
Example 8-2. Watching for compression driving the CPU utilization too high will be important.
WAN Cabling Standards
Cisco expects CCNAs to have an understanding of the cabling options for LAN and WAN
interfaces. For any of the point-to-point serial links or Frame Relay links in this chapter, all that
is needed on the router is a synchronous serial interface. Traditionally, this interface is a 60-pin
D-shell connector. This interface must then be cabled to a DSU/CSU, which in turn is connected
to the cable supplied by the service provider. Figure 8-3 shows a typical connection, with the
serial cabling options listed.
Figure 8-3
Serial Cable Options
Table 8-8 summarizes the variety of standards that define the types of connectors and physical
signaling protocols used on WAN interfaces.
Service
Provider
End User
Device
DTE
DCE
Router Connections
EIA/TIA-232 EIA/TIA-449 V.35
X.21 EIA-530
Network Connections at the CSU/DSU
CSU/
DSU
ch08.fm Page 528 Monday, March 20, 2000 5:17 PM