why do we need clock rate?

I have been playing with switches for several months, I have never experienced the need to set clock rate (maybe i should, just that I am not aware).

Now I have moved into router and the first thing i am taught is to set the clock rate. Why do we need clock rate for routers, but not switch?

thanks

Reply to
zibin
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Because the hardware interfaces for some kinds of WAN links are not able to determine what the actual clock rate is.

The clock rate is only used for a very small number of things; primarily it is used so that if you are using an SNMP based monitoring program (such as MRTG or WhatsUp) then the monitoring program can read off the link rate you have set, and use that to compute what percent of the link capacity you are using. Setting the clock rate does NOT make any difference in how quickly data is transfered on the link.

I've read that there is one other use for it: something along the lines that if you are using OSPF, then it uses the clock rate you have set in order to determine the proper "cost" to associate with the link. I probably have the details a bit wrong. It wasn't something I'd ever had to do myself.

Other than the uses above... well, it's handy documentation. But it does NOT control how fast anything gets transmitted.

Reply to
Walter Roberson

Clock is (almost) always there when you are talking about a communication link, simply because sender and receiver needs to synchronize in order to understand each other flows, it's not a matter of switch or router. Several technologies are based on an external clock source, some of them lets you choose the speed of that source, such as synchrounous serial. Other technologies doesn't have a specific clock source, instead they make use of some "tricks"; ethernet, for example, uses the first 64 bits (the preamble) of each frame in order to synchronize the clock of the receiver from the one of the sender. Hope this helps. Bye, Tosh.

Reply to
Tosh

thanks walter and tosh. Appreciate the guidance

Reply to
zibin

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