Re: Clock Rate

Agreed ..
wahtever you told is correct ! thats what a clocking and a DCE end means .

Whatever I told was from Cisco point of view and how things work in cisco
routers environment . Hence what i meant was that cisco routers only act as
DCE .(providing clock)

As far as your last point is concerned ; Cisco does sell the cables with one
end as DCE and other end as DTE . In fact all the SS (smart serial) cables
have a Male part and a female part (connector in middle) and hence have a
DCE end and a DTE end .

Thnx
Gaurav Madan
CCIE

On Mon, Jul 18, 2011 at 3:35 PM, Carlos G Mendioroz <tron_at_huapi.ba.ar>wrote:

> Gaurav,
> I would like to share my understanding of what clock is.
> I guess it should be clear that clock rate is of no use in
> dynamips and its clients (dynagen/GNS3), as no phy layer
> emulation takes place there, and data is transferred using
> UDP between interfaces.
>
> When you have an asynchronous link, the bits timing is recognized
> on each byte boundary in an independent way. Each byte is independent of
> the previous, and there is no out of band reference between Tx and Rx.
> This is expensive in terms of time, because you need start bits and
> stop bits.
>
> So in synchronous links, a reference timing is kept at the endpoints
> to be reused for all bits/bytes. DCE's do that (recover the clock)
> and share it via an out of band signal with the DTE. Each side of
> a serial link is supposed to have a DCE and a DTE.
>
> So routers (DTEs) should actually use clock info from its associated DCE.
> Routers has no business in clocking.
>
> But we sometimes use routers connected back to back, and we don't want
> to set up DCEs, so we use sort of null modems, thanks to the ability
> of routers to fake being a DCE to the linked router. This faking implies
> the provision of a clock reference, hence the clock rate command, and
> a specially wired cable that connects a clock source pin on the smart
> connector to the pin used by DCEs to provide the clock. What we call
> a DCE cable. Routers recognize the presence of such cable (that's why
> we call them smart cables I guess :) and enable the clocking.
>
> Last, some actually use cables that combine a DTE cable and a DCE
> cable, becoming real "null modems". Those cables do have a DCE end
> and a DTE end indeed. AFAIK, cisco does not sell such cables, but
> they are handly in labs.
>
> HTH,
> -Carlos
>
>
> GAURAV MADAN @ 17/07/2011 11:35 -0300 dixit:
>
>> :)))))
>>
>> DTE , DCE are devices (routers in your case) each having defined purpose .
>>
>> But you need to plug in right cable to right device .
>> Physically a serial WIC / HWIC card plugged in a router can assume a role
>> of a DTE as well as DCE.
>> It depends on the cable that is connected to serial interface that the end
>> takes a role of DCE or a DTE .
>>
>> Each serial cable type (RS 232 , V.35 , 449 , 530 etc etc) have a DTE end
>> and a DCE end ; so depending on what is plugged in where .. the end is
>> defined .
>>
>> Hope some clarity this time ,
>>
>> Gaurav Madan
>> CCIE .
>>
>> On Sun, Jul 17, 2011 at 7:05 PM, Carlos G Mendioroz <tron_at_huapi.ba.ar<mailto:
>> tron_at_huapi.ba.ar>> wrote:
>>
>> This is getting so distant from reality ... as a lab can get.
>> What exactly is DCE and DTE ? Is a router a DTE or a DCE ?
>> Is the cable a DCE or a DTE ? :)
>> -Carlos
>>
>> Radioactive Frog @ 17/07/2011 01:57 -0300 dixit:
>>
>> Great explaination Gaurav.
>> Just would add on top of gaurav's statement - You need a very
>> SPECIFIC
>> cables that has one end DTE and other end DCE to get it working.
>>
>> On Sun, Jul 17, 2011 at 2:12 AM, GAURAV MADAN
>> <gauravmadan1177_at_gmail.com
>> <mailto:gauravmadan1177_at_gmail.**com <gauravmadan1177_at_gmail.com>
>> >>__wrote:
>>
>>
>> Things to consider here are :
>>
>> 1) Clock rate is applicable to DCE devices and not on DTE
>> devices
>> 2) Devices can be categorized as DCE or DTE depending the
>> cable connected
>> to
>> serial interface.
>> 3) Generally DCE devices are FR switch etc.
>> 4) If you are configuring the back to back connection ;
>> configure "clock
>> rate <> " CLI on DCE end only
>> 5) I think latest IOS on serial HWIC will take clock rate
>> command only on
>> DCE end and not on DTE end . However older IOS used to take
>> it on any
>> device
>> 6) Any rate is good ... as long as it is working .. default
>> 9600 bps should
>> be OK .
>>
>>
>> HTH
>> Gaurav Madan
>> CCIE
>>
>> On Sat, Jul 16, 2011 at 9:36 PM, <jhnrose401_at_gmail.com
>> <mailto:jhnrose401_at_gmail.com>> wrote:
>>
>> Dear
>>
>> I want to know what clock rate i will use when i am in
>> the lab or when i
>>
>> am
>>
>> using
>> dynamips what is the method or way i will configure
>> the correct clock
>> rate to
>> my routers
>>
>> Eg
>>
>> For DCE i ll configure the clock rate not for DTE correct
>>
>> if both devices are DCE i will define CR on both or in a
>> single devices.
>>
>> R1 --ser1/0 -------------------s1/0 R2
>>
>> I am facing problem my ospf adj flap after few minutes
>> is CR are the
>>
>> reason
>>
>> R1 = s1/0 ip add 10.1.1.1/24 <http://10.1.1.1/24> and
>> loop back 1.1.1.1/24 <http://1.1.1.1/24>
>> R2 = s1/0 ip add 10.1.1.2/24 <http://10.1.1.2/24> and
>> loop back 2.1.1.1/24 <http://2.1.1.1/24>
>>
>> clock rate 64000 on both sides
>> R1 and R2
>>
>> router ospf 1
>> net 0.0.0.0 255.255.255.255 are 0
>>
>> thks
>>
>>
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>>
>> -- Carlos G Mendioroz <tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar
>> >>
>> LW7 EQI Argentina
>>
>>
>>
> --
> Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina

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Received on Mon Jul 18 2011 - 20:22:02 ART