[c-nsp] HDLC or PPP for layer 2 encapsulation?

[Roy]

Dave Lim wrote:
> Bear with me guys. I am more of a PIX and switching guy and have not
> really done such implementation before.
>
> I am configuring 2 Cisco routers for a point to point connection.
> Circuit will be provided by the telco. Am wondering about the layer2
> encapsulation between the 2 Cisco 1841 router with WIC-1T module using
> V.35 cables.
>
>  I am wondering should I use HDLC or PPP for the layer 2
> encapsulation. HDLC is the default encapsulation used by Cisco Routers
> right? I understand that HDLC encapsulation doesnt support
> asynchronous lines which goes to say that if both circuits are
> operating on different timing, the line connection will be down.
>
>  With PPP, it supports both synchronous and asynchronous connection.
> So which means that if the timing are different, the line will still
> be up. And PPP supports PAP and CHAP for authentication.
>   

You assumptions about timing are false.  PPP and HDLC say nothing about 
timing.  Asynchronous and synchronous are line format issues.  Since you 
are using a WIC-1T card then this is a synchronous circuit. 

The routers have to be "clocked" correctly for their environments.  The 
V.35 cable will most likely be connected to a CSU/DSU that will provide 
timing to the router.  You need to talk to the telco to make sure you 
are on the right page on the CSU/DSU issue.  In the US, the telco does 
not provide one and you have to do that.  That's why most of us in the 
US would use a WIC-1DSU-T1 card which has the integral CSU/DSU.


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