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BreezeMAX Modular Base Station System Manual 227
needs of the connection. QoS Profile parameters include Committed
Information Rate (CIR) and Committed Time (CT).
Non-Real-Time (NRT) service is very similar to the Real-Time polling service
except that connections may utilize random access transmit opportunities for
sending bandwidth requests. These Non Real Time Variable Bit Rate services,
such as file transfer and Internet access with a minimum guaranteed rate, are
characterized by requirement for a guaranteed rate, but can tolerate longer
delays and are rather insensitive to jitter. QoS Profile parameters include
Committed Information Rate (CIR), Committed Time (CT) and Maximum
Information Rate (MIR) that limits the rate so that bandwidth intensive
services will not expand to occupy the full bandwidth.
Best Effort (BE) service is for services where neither throughput nor delay
guarantees are provided. The Subscriber Unit sends requests for bandwidth in
either random access slots or dedicated transmission opportunities. The
occurrence of dedicated opportunities is subject to network load, and the
Subscriber Unit cannot rely on their presence. Service parameters include
Maximum Information Rate (MIR). Committed Time (CT) is set to a fixed value
(Short) and cannot be configured.
Continuous Grant (CG) service is tailored for carrying constant bit rate (CBR)
real-time services characterized by fixed size data packets on a periodic basis
such as VoIP or E1/T1. The Base Station schedules regularly, in a preemptive
manner, grants of the size defined at connection setup, without an explicit
request from the Subscriber Unit. This eliminates the overhead and latency of
bandwidth requests in order to meet the delay and jitter requirements of the
underlying service. Service parameters include Packet Size (unsolicited grant
size) and Sampling Rate (grant interval).
The priorities of allocating bandwidth to connections are in accordance with the
QoS Type of the connections, in the following order:
1 CG
2 RT
3 NRT
4 BE
For each of the RT, NRT and BE connection, there is a second level of priorities
according to the Committed Time (CT), where connections with CT=Short gets the
highest priority and connections with CT=Long gets the lowest priority.