Queues Vcs And Packet Memory - Avaya P550R User Manual

Appendix A

Queues VCs and Packet Memory

A-2
Avaya P550R/P580/P880/P882 Multiservice Switch ATM Uplink Module User Guide, Version 2.0
Constant Bit Rate (CBR) - traffic which reserves a specified
portion of the available bandwidth and guarantees delivery
of all packets offered to that connection within that
bandwidth limit.
Variable Bit Rate (VBR) - traffic which reserves a portion of
bandwidth and guarantees delivery of all packets offered to
that connection at an average rate and does not exceed a
specified maximum burst size and duration. Both "Real
Time" and "Non-Real Time" VBR are supported.
CBR and VBR traffic are scheduled for transmission using the
Generic Cell Rate Algorithm (GCRA). Traffic scheduled for
transmission through the GCRA is "shaped" to smooth out the
burstiness of the offered load, and to ensure compliance with the
traffic contract. The frames offered to shaped connections are
queued while their cells are transmitted onto the network.
The ATM Uplink Module supports queues, maintained as linked
lists, for each shaped Virtual Connection (VC), and it is to these
queues that RED may be applied. Although the ATM Uplink Module
supports per/VC queues, it partitions packet memory (the queue
entries) by traffic class. Hence all connections with a common traffic
class compete for the same packet resource. This fact has
implications on the application of RED as outlined below (Figure 0-
1).