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control word


1)I heard that control word is not mandatory in ethernet attached circuits in a VPWS ? Can anyone let me know the reason ?

2) Is there any equivalent concept of control word in IP pseudowire ( the case of Kompella circuits , ATM on one side and FR on the other)

Thanks in advance,


Cisco Employee

Re: control word

1) According to draft Martini encapsulation, the control word is optional for both type ethernet and ethernet vlan. For a better explanation of why the CW is optional for these types, please refer to the CW definition and functions in section 4.1 of the Martini encapsulation draft:

2) For L2VPN Interworking, the control word is also optional.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
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Community Member

Re: control word

Thank Harold for your reply.

But in (2) I just wonder why the need of Martini control word is there.Because , if one end of the attached circuit is FR , the L2 header will be chopped off at the P.E , and there is no meaning if I carry B ,F ,Discard eligible flags in martini encapsulation towards the other end P.E in which an ATM attachment circuit is attached.This is because for ATM signals there is no meaning for FR related control word bits.

Also ,is martini encapsulation is used in L2VPN interworking ,since this is just an IP pseudowire

and martini encapsulation is in Layer 2. Please correct me if I am wrong.

Thanks in advance,


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