Re: Clock Rate

GAURAV MADAN @ 18/07/2011 11:52 -0300 dixit:
> 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)

I don't think this is right. Routers (including cisco's) are DTEs.
Their ability to provide clock do not make them DCEs, even if we
call them so. But this is semantic.

> 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 .

This is confusing. There's only one gender for SS cables, and I would
say they are "male". If that is the case, a DTE cable has two males,
and a DCE cable has one of each. Note that a "DTE" cable is one that
signals the router to behave as a DTE.

The cables I was referring to have two SS connectors.

-Carlos

>
> 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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-- 
Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
Blogs and organic groups at http://www.ccie.net