Serial port => Clock Rate and Bandwidth

[Kuldeep singh]

Hi experts,

Anyone please confirm that in the Router serial interface,

when we specify the signal clock rate 64000 and bandwidth

to 64, Does it mean that the connected WAN link provided

by ISP is of 64 kbps ?

Router# conf t

Router(config)# interface serial 1/0

Router(config-if)# clock rate 64000 (represented in BITS per second)

Router(config-if)# bandwidth 64 (represented in kilobits per second)

Suppose if i use connection of different bandwidth like 128k, 256k

or even 2 Mpbs, then what should be the clock rate and Bandwidth

for respective links ? you can take example of 2 mbps and tell

me what should i assign to Clock-rate and Bandwidth ??

Plz explain this thing in both cases:

1. Internet access link terminate over single router serial port

2. Router to Router connectivity

[JohnTylerPearce]

With a serial connection you typically have two ends, which are DTE and DCE. DTE would be Data Terminal Equipment and DCE would be Data Communications Equipment. The DCE end will provide the clocking. So if on the other end is a 64kbps link you would enter your 'clock rate' command to specify this in bps. The Bandwidth command is basically a logical command that is really only used in QoS and Routing Protocols to put information into the metric calculations.

[Kuldeep singh]

Any other expert out there..........

[paolo bevilacqua]

You do not specify any clock rate on circuits provided by ISP. You can check teh received clcok rate with "show controllers serial x/y"

[Kuldeep singh]

Then in which scenerio i can put "clock-rate" and "bandwidth"

command over serial port.

[paolo bevilacqua]

In the scenario where you have a DCE cable going to some kind of DTE device, that can be a router as well.

About bandwisth command, that has been answered above.

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[Kuldeep singh]

Hi Paolo,

I want to know something about DCE/DTE:

1) What is maximum distance between

    DCE  and  DTE  devices/cable.

2) Suppose I have E1 lease line of 2.05 mbps which

    connects two sites and distance between sites is 100 Kms.

    Both end of router having serial handoff.

    Is there any concept of DCE/DTE ?

[paolo bevilacqua]

1, depends on speed and specific serial interface, however assume few meters.

2. for E1 circuits is it better to use E1 interfaces, not serial. However if using serial (not recommended), both routers will be DTE, and the interface converters (sometime called E1 modem), are DCE providing clock.

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[Kuldeep singh]

Suppose i have 512 kbps lease line between sites.

and i want to assign Clock rate to DCE router.

what will be the value of Clock Rate  64000

or 512000 ??

[paolo bevilacqua]

As answered above already:on leased lines, router is DTE, hence can not set any clock rate.

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[mikelucasis]

I hope to add to this conversation a little bit as I am just learning this material as well.

In the case of Router to Router connectivity (assuming you control both) the scenario would be one side is DCE (Provides clocking - 'Master of the link') and the other side with be DTE (Terminal receives clocking - 'Timing Slave')

In the case you don't control both sides then the ISP or other controlling entity will set/provide the clock rate.  

In the case your router is connected to another source via Serial such as a modem the modem will provide the clocking, the only case you need to worry about setting the clock is if you control both routers (or if you are the ISP I suppose.)  But in either case you will need to set the bandwidth to match.

So on the DCE side (if you don't control it this will be set by the ISP or other controlling entity so you will not set anything) the settings will look like this

interface s0/0
 bandwidth 8000000
 ip address 10.1.1.2 255.255.252
 clock rate 800000

And on the DTE side (only the bandwidth needs to be set as the DCE is the master of the link and provides 'slave' timing for the other router) the settings will look like this

interface s0/0
 bandwidth 8000000
 ip address 10.1.1.1 255.255.255.252

As I have stated I am just learning this material myself so if I got anything wrong or left anything out feel obliged to correct, teach, instruct me. :)

I know my bandwidth is high but in the examples I saw they set these very low which didn't make sense to me.  This is actually my first time setting up a serial to serial connection between my cisco routers so I'm a bit excited no real traffic and I'm not even sure what the actual bandwidth limitations between them on that link are yet.  I might put them under load with some TFTP traffic later.

- Mike