HPS ATM Switch Prefix Decoder Every ATM switch has a prefix which uniquely identifies that switch on the network. The prefix is a series of thirteen eight-bit bytes (or octets). If fully utilized this one hundred and four bit prefix would allow you to build a network of 20,000,000,000,000,000,000,000,000,000,000 switches. Even with the way we divide up the ATM prefix we have room for 33,554,432 switches! The table below depits how HPS divvies up the ATM prefix in HELPnet: First nine octets: does not change PNNI Peer Group No. Site No. Closet No. Switch No. Fabric Side 39.00.00.00.00.00.00.00.00.00 .11 .01 .02 .2 A The first nine octets of the prefix are unchanging. Every ATM switch prefix in HELPnet starts with 39.00.00.00.00.00.00.00.00. The in information in the last four octets makes each switch unique and provides physical location information. The tenth byte indicates which PNNI peer group the switch belongs to (in the initial build of HELPnet, this byte indicated which physical ring the switch was on - this changed with planning for hierarchical PNNI routing). The eleventh byte is a unique site identifier; in this example (01) is the Oxford Center. The twelfth octet is a network closet ID. Closet 01 is the Main Distribution Frame (MDF) in each building -- the location where the fiber optic cable coming in from the street is terminated. For buildings with Intermediate Distribution Frames (IDFs) the closet number is incremented for each additional DF. The example (02) is the first IDF in the building. The thirteenth octet is divided into two parts. The first four bits (or "nybble") of the byte indicate the switch chassis number within the DF. Most DFs only have one switch chassis, to the number is usually 1. The last four bits indicate which fabric within the switch chassis you are dealing with. The Nortel Networks 5000BH ATM switch chassis has two switching fabrics; left and right. The last nybble of the thirteenth byte is either A or B to indicate left or right fabrics. The Nortel 5005BH only has one fabric; in a 5005BH the second nybble is always A. An exception to this rule comes with the Nortel Networks C1000 switches in the network. Their thirteenth octect is in the form of Cx where C indicates a C1000 switch and the x indicates switch number within the closet. For example the Bulkeley High School C1600's prefix is: 39.00.00.00.00.00.00.00.00.11.04.01.C1. This deviation is designed to make the C1000s stand out when looking at a number of switch prefixes (or complete End Sation Identifiers {ESIs}). Hartford Public Schools Information Technology Department | Updated 4-16-00