Subject: [PWE3] How to choose Interface MTU for PW heterogeneous transport

From: "Yijun Xiong" <[email-masked]>
Date: Mon, 4 Apr 2005 10:12:42 -0700

Hi,
 
In draft-ietf-pwe3-control-protocol-16.txt "Pseudowire Setup and
Maintenance using LDP", Interface MTU parameter is used when setting up
PWs. It is stated that if this parameter does not match in both
directions of a specific PW, that PW MUST NOT be enabled.
 
I have the following questions while implementing the heterogeneous
transport, e.g., when one AC (between CE1 and PE1) is ATM, another AC
(between PE2 and CE2) is FR.
 
(1) Suppose PW1 is for ATM to FR direction, PW2 for FR to ATM direction,
how to select PW type, ATM PW or FR PW for PW1 and PW2? Can PW1 be ATM
type and PW2 be FR type?
 
(2) For FR AC, I would assume that one can use FR UNI MTU as interface
MTU for PW, How to choose interface MTU for ATM AC, as ATM UNI has no
such parameter like MTU?

Thanks.
 
Yijun Xiong 
Hammerhead Systems Inc.
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From: Luca Martini <[email-masked]>
Date: Wed, 13 Apr 2005 10:56:01 -0600

Yijun Xiong wrote:

> Hi,   In draft-ietf-pwe3-control-protocol-16.txt "Pseudowire Setup and 
> Maintenance using LDP", Interface MTU parameter is used when setting 
> up PWs. It is stated that if this parameter does not match in both 
> directions of a specific PW, that PW MUST NOT be enabled.   I have the 
> following questions while implementing the heterogeneous transport, 
> e.g., when one AC (between CE1 and PE1) is ATM, another AC (between 
> PE2 and CE2) is FR.   (1) Suppose PW1 is for ATM to FR direction, PW2 
> for FR to ATM direction, how to select PW type, ATM PW or FR PW for 
> PW1 and PW2? Can PW1 be ATM type and PW2 be FR type?   (2) For FR AC, 
> I would assume that one can use FR UNI MTU as interface MTU for PW, 
> How to choose interface MTU for ATM AC, as ATM UNI has no such 
> parameter like MTU?     Thanks.   Yijun Xiong Hammerhead Systems Inc.
>
>  
>
Interworking of frame-relay - ATM is not part of the PWE3 specification. 
The PW has to be of the same type on both ends , just pick one.
Then implement the interworking function at one end to convert the ATM 
to F/R.
The interface MTU is determined by the interworking function. So if you 
are converting ATM AAL5 , presumably you'll have a maximum AAL5 fame 
size. you can use that as the MTU of the F/R PW.

Luca

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