User Manual

Chapter 2 - MAIN FEATURES, PROTOCOL AND QoS
1QDF10134AAP-SYD-FCC Issue 03
4Mbit - Draft 05
2-9 of 2-14
Polling of SPRs can happen according to the information gathered during the Slotted
Aloha process or in a periodic manner – every few milliseconds – regardless of the
Slotted Aloha process depending on the application transmitting data at the time.
The polling sequence of data applications is managed by the BSR based on the
information gathered during the Slotted Aloha process. Data applications can sustain
relatively long delays before expecting a response and therefore their packets can be
delayed within the SPRs before being sent to the BSR and on to the network. Other
applications which require a smaller delay for their packets are polled first.
Some applications are configured to transmit a burst of several packets in a row
before expecting any response from the other party. In such a case the polling
mechanism is able to support several polls of an SPR one after the other.
This mode is called "PPMA" (Preemptive Polling Multiple Access).
Real-time applications such as video often sends a constant flow of packets. In this
case the BSR polls the SPR that is related to such an application in accordance with
the flow of the packets. IP Telephony systems send packets about every 30ms and
require a very small delay. Therefore, an SPR that was recognized as sending
packets is polled usually every 30ms (see 2.1.14) without having to go through the
Slotted Aloha process to inform the BSR about each packet.
This mode is called "Adaptive TDMA" (Time Division Multiple Access).
2.3. Security
Being a centrally coordinated protocol gives PPMA several options of security that
are independent of other layers.
2.3.1. Login Mechanism
In order to be served by a BSR an SPR must be registered to it. This registration
process is based on the SPR's MAC address and the BSR address that is configured
by the network management.
When a new SPR tries to register to the BSR it sends a "Request to Send" message
during the "Slotted Aloha" time. The BSR then checks if the SPR MAC address is
listed as an "Allowed SPR" list. This list is maintained by the network management
system. If it is listed as such then an "Association" message is sent to the SPR that
includes information about the cell such as the public key for the encoding, number