Support For Tdm Using Third Party Units; Flow Control - Alvarion BreezeACCESS LB System Manual

Appendix D - Support for TDM using Third Party Units
Support For TDM Using Third Party
Units
802.1p
The BreezeACCESS LB uses IEEE 802.1p to ensure QoS to TDM based
applications such as mobility backhaul and enterprise PBX traffic. IEEE
802.1p allows the wireless transmit queue to be split into two (high and
low priority) queues. Ethernet packets are queried to determine if they
are priority tagged. Packets tagged with a priority value greater than or
equal to four are automatically placed in the high priority queue. All
other packets go into a default queue. The LB always services the traffic
in its high priority queue before the default, low priority queue. A low
priority packet will only be transmitted once the high priority queue is
empty.

Flow Control

For improved traffic handling the BreezeACCESS LB supports standard
IEEE 802.3x flow control.
Upon reception of a pause control frame, the Ethernet port will not
transmit the next normal frame until the timer specified in the pause
control frame expires, or another pause control frame is received.
During the flow controlled period, only flow control packets will be
transmitted between the LB and its interfacing device (i.e. Switch/
Router or Third Party T1/E1 Unit).
The LB will also transmit pause control frames based on the availability
of its own internal resources, including buffers, transmit queues and
receive queues.
Ethernet traffic can easily exceed the total capacity of a wireless link
and thereby trigger indiscriminate packet discarding on all traffic
streams. To avoid this condition the LB also provides a dynamic traffic
shaping capability that continually adjusts itself to the current wireless
throughput conditions. With adaptive modulation enabled, wireless
throughput can automatically decrease, in order to maintain acceptable
Packet Error Rates. In response to such a decrease, the LB will also
automatically throttle-back (traffic shape) the lower priority traffic
streams by first discarding the packets in its default Tx queue.
D-2
BreezeACCESS LB System Manual