Broadband Packet Switching Technologies: A Practical Guide to ATM Switches and IP Routers

APPENDIX

SONET AND ATM PROTOCOLS

The asynchronous transfer mode (ATM) was standardized by the International Consultative Committee for Telephone and Telegraphy (CCITT), currently called International Telecommunications Union—Telecommunication (ITU-T), as the multiplexing and switching principle for the Broadband Integrated Services Digital Network (B-ISDN). The ATM is a connection-oriented transfer mode based on statistical multiplexing techniques. It is asynchronous in the sense that the recurrence of cells containing information from an individual user is not necessarily periodic. It is capable of providing high-speed transmission with low cell loss, low delay, and low delay variation. It also provides flexibility in bandwidth allocation for heterogeneous services ranging from narrowband to wideband services (e.g., video on demand, video conferencing, video-phone, and video library).

ATM connections either are preestablished using management functions or are set up dynamically on demand using signaling, such as user-network interface (UNI) signaling and private network-network interface (PNNI) routing signaling. The former are referred to as permanent virtual connections (PVCs), while the latter are referred to as switched virtual connections (SVCs).

As shown in Figure A.1, two ATM end systems communicate through two ATM switches. The left end system sends messages generated at ...