Looking at my handy World of Protocols book from Radcom, the ATM header format is quite clear For UNI, there is a four bit GFC field, followed by 8 bits VPI and 16 bits VCI fields For NNI, there is no GFC field, and the extra four bits goes to the VPI field, making it 12 bits. the VCI field remains 16 bits. Looking at it from that point of view ( header format ) the answers below do make sense. Also, the VPI has only local significance, much like the frame relay DLCI. As you know, CertZone tends to prod one into looking at the full field of vision. The question ( and answer ) is a bit indirect. Chuck -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Tim Begley Sent: Tuesday, October 31, 2000 5:24 PM To: '[EMAIL PROTECTED]' Subject: Clarification on ATM VPI/VCI question from Cert Zone please 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. _________________________________ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _________________________________ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
