User Manual

Chapter 2 - MAIN FEATURES, PROTOCOL AND QoS
1QDF10134AAP-SYD-FCC Issue 03
4Mbit - Draft 05
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 Allowed packet loss rate that applications can sustain.
 Bandwidth for the application - video requires constant signal flow:
 Packets are generated usually every 30ms. (depending on the Residential
Access Gateway (RAG) and sampling rate)
 Requires minimal delay.

Silence suppression – no packets
2.2. PPMA Protocol
This section describes the Pre-emptive Polling Multiple Access (PPMA) protocol. It
discusses the environment in which this protocol operates, its task and description of
the PPMA protocol as used by WipLL.
To support the above environment the main task of the PPMA protocol is to
combine all these requirements in the most efficient manner.
2.2.1. What is PPMA?
2.2.1.1. Concept
PPMA is a centrally coordinated protocol. The BSR performs the task of
coordination over the air. It constantly gathers information from the Subscriber
Premises Radio (SPR) regarding their requirements for resources. These are rated
according to the combination of parameters such as the number of packets in the
SPR queues and the maximum allowed delay for the first packet in the queue.
Once the BSR has determined the requirements of resources for the next few
milliseconds it starts to poll the SPRs accordingly. SPRs that receive the highest
score are polled first and the others follow in order.
2.2.1.2. Slotted Aloha Process
The constant gathering of information regarding the required resources from the
SPRs is performed by using a mechanism called "Slotted Aloha".