Avaya IP Line User Manual download pdf (Page 193)

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Codecs Page 193 of 770

IP Line Description, Installation, and Operation

Known issues include:

• After an on-hold and off-hold scenario (that triggers Master/Slave

negotiation), the codec used for the restored call can be different than the

codec used before the call was placed on hold. The Master/Slave

information could have been changed when the call was on hold.

• Since the terminating end of a call is always the Master, a call from

Telephone1 (Node1) to Telephone2 (Node2) can use a different codec

than a call from Telephone2 (Node2) to Telephone1 (Node1).

• For tandem calls, the Master/Slave information is not relevant. That is,

the Master/Slave information is designed to be used only between two

nodes, not among three or more nodes. The Master/Slave algorithm

makes the codec selection for tandem calls more complex and inefficient.

To solve the issues, another codec selection algorithm was needed. This

algorithm is called the Best Bandwidth codec Selection algorithm and is not

based on the unpredictable Master/Slave information.

The Best Bandwidth codec Selection algorithm is used for virtual trunk calls

between Nortel Networks equipment, since any change to the Master/Slave

algorithm implies a change to the H.323 standard. The H.323’s Master/Slave

algorithm is used when there is a virtual trunk call between Nortel Networks

equipment and third-party equipment.

Best Bandwidth Codec Selection algorithm

The Best Bandwidth Codec Selection algorithm was implemented to solve

the issues caused by the H.323 Master/Slave algorithm. The Best Bandwidth

Codec Selection algorithm selects one common codec based on two codec

lists. With this algorithm, every time the selection is done using the same two

lists, the selected codec is always the same.

The “Best Bandwidth” codec selection is based on the codec type only; it does

not take into account the fact that some codecs, while generally using less

bandwidth, consume more bandwidth than others at certain payload sizes.

• The Best Bandwidth Codec Selection algorithm finds the first codec in

the near-end list that is also in far-end list (codec is the same type and has

the same payload size). Call the selected codec C1.

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