Description: This is a ( 4 + n*134 ) byte octet string where n => 1. The first and second byte is the interface/slot id of the link/IOP going down or link goes up. The third byte is the reason why circuits go down: 1 is a user link goes down, 2 is a trunk link goes down, 3 is an IOP goes down and 4 is an user link goes up The fourth byte is the count of entries in the following circuit bit map array. Each circuit bit map entry is 134 bytes. The first 2 bytes is the IOP slot on which dlci's are defined. The second 2 bytes is the Physical port ID on which dlci's are defined. The third 2 bytes is the interface id on which dlci's are defined. The following 128 bytes (1024 bits) is a bit map for dlci's defined on the interface. The left-most bit of the first byte represent dlci 0 and the right-most bit of the 128th byte represent dlci 1023. If a bit is set, it means the corresponding dlci on that interface is up/down.