It appears to me that the question intends to make the point about the local
significance of the VPI/VCI values in ATM connections by only offering a one word
difference between the a) and b) answers.
While it is true that these values have local significance only, it is better to think
of these values as a connection identifier (again, much like FR). This is b/c there
are
in fact 'ATM addresses' involved w/ ATM connections that are different from the
VPI/VCI
fields in the cell header, and these are referred to as ATM End System Addresses
(AESA),
or more commonly as NSAP Addresses. The NSAP is analagous to the telephone numbers
involved in a telephone call and the VPI/VCI would be like the cable#/pair# that
carried
the call.
So, given that answer A) has the word "local" in it, I would agree that that is the
correct answer.
HTH,
______________________________________________________
Wayne Gustavus CCNP,FLCE,FLCI 703-582-9594
Consultant, Service Provider Engineering
Mentor Technologies, Inc. www.mentortech.com
****** Formerly Chesapeake Network Solutions ******
______________________________________________________
PGP Key: http://pgpkeys.mit.edu/
Tim Begley wrote:
> Hi Team,
> The below question is from the cert zone samples and it's confusing me
> slightly. They've given the answer as 'A' but I understand the VCI to be a
> local identifier only significant to the UNI but the VPI configuration must
> be the same at the local UNI at the remote node. Wouldn't that make it not a
> 'local' address by very definition?
> Answer 'B' seems more correct.
> Would any ATM guru/s like to clarify this for me?
> thanks
> Tim
> p.s. just realised I'm probably breaking all sorts of copyright/NDA stuff by
> copying this question and that I'll get flames from vigilantes everywhere -
> sorry won't do it again ;-)
> What is the purpose of VPI/VCI? How many bits are used for each?
>
> a) VPI/VCI is the ATM local addressing. The number of VCI bits is always 16,
> while the number of VPI bits is either 8 or 12.
> b) VPI/VCI is ATM addressing. The number of VCI bits is always 16, while the
> number of VPI bits is either 8 or 12.
> c) VPI/VCI is ATM addressing. The number of bits used is either 24 or 28.
> d) VPI/VCI is the ATM local addressing. The number of VPI/VCI bits is either
> 24 or 28.
>
> Answer
> a) VPI/VCI is the ATM local addressing. The number of VCI bits is always 16,
> while the number of VPI bits is either 8 or 12.
> Explanation
> VPI/VCI is the local ATM addressing, similar to the DLCI of the Frame Relay
> networks. The number of bits for VCI is always 16, while the VPI bits could
> be either 8 or 12. The VPI bit length of 8 bits is used in the UNI, while
> the VPI bit length of 12 is used in the NNI.
>
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