System information

Adjusting Buffers
Book Title
15-332
Inverting the Transmit Clock
If you are attempting serial connections at speeds greater than 64 kbps with a CSU/DSU that does
not support SCTE, you might have to invert the transmit clock on the router. Inverting the transmit
clock compensates for phase shifts between the data and clock signals.
The specific command used to invert the transmit clock varies between platforms. On a Cisco 7000
series router, enter the invert-transmit-clock interface configuration command. For Cisco 4000
series routers, use the dte-invert-txc interface configuration command.
To ensure that you are using the correct command syntax for your router, refer to the user guide for
your router or access server and to the Cisco IOS configuration guides and command references.
Note On older platforms, inverting the transmit clock might require that you move a physical
jumper.
Adjusting Buffers
Excessively high bandwidth utilization over 70% results in reduced overall performance and can
cause intermittent failures. For example, DECnet file transmissions might be failing due to packets
being dropped somewhere in the network.
If the situation is bad enough, you must increase the bandwidth of the link. However, increasing the
bandwidth might not be necessary or immediately practical. One way to resolve marginal serial line
overutilization problems is to control how the router uses data buffers.
Note In general, do not adjust system buffers unless you are working closely with a Cisco technical
support representative. You can severely affect the performance of your hardware and your network
if you incorrectly adjust the system buffers on your router.
Use one of the following three options to control how buffers are used:
• Adjust parameters associated with system buffers
• Specify the number of packets held in input or output queues (hold queues)
• Prioritize how traffic is queued for transmission (priority output queuing)
The configuration commands associated with these options are described in the Cisco IOS
configuration guides and command references.
The following section focuses on identifying situations in which these options are likely to apply and
defining how you can use these options to help resolve connectivity and performance problems in
serial/WAN interconnections.