Performance Considerations of Signaling Networks in an ISDN Environment
01 January 1986
An essential component of ISDN is the out-of-band signaling capability. On ISDN access facilities this signaling capability is provided on a D-channel (16 kb/s for the basic access and 64 kb/s for the primary rate access) employing the Q.921 (LAPD) protocol at layer 2 and Q.931 at layer 3. At layer 3 the D-channel conveys user-to-network information for B-channel call-associated signaling and user-to-user information (UU) for end-to-end information transfer between users.