W.4 Negotiation of End-to-End and Uplink/Downlink PLR
26.1143GPPIP Multimedia Subsystem (IMS)Media handling and interactionMultimedia telephonyRelease 18TS
W.4.1 General
In addition to the negotiated codecs and codec modes, the end-to-end quality and robustness to packet loss of a service can depend on the MTSI client implementation of functions such as packet loss concealment (PLC) and de-jitter buffer management (JBM).
A set of end-to-end and link-by-link PLR parameters is specified to provide the following:
– enable MTSI clients to indicate for each RTP payload type the effective maximum tolerable PLR resulting from the codec, codec mode, packet loss concealment, de-jitter buffer management and other implementation considerations.
– enable MTSI clients to negotiate with each other and suggest to the PCRF/PCFs how the maximum tolerable end-to-end PLR budget can be distributed across the uplink and downlink in a media transport path. In the absence of any additional negotation or information from the terminals, the PCRF/PCFs may default to distributing the maximum tolerable end-to-end PLR equally (50-50) across the uplink and downlink. The link-specific PLR parameters enable the terminals to suggest to the PCRF/PCFs an unequal distribution, e.g. 60% of the maximum end-to-end PLR allowed on the uplink and 40% allowed on the downlink before the terminals are handed off.
– indicate to the PCRFs/PCFs what PLR values may be used on the local uplink and downlink to the MTSI clients.
W.4.2 Offering MTSI Client
SDP PLR attributes and parameters are defined for use with each payload type. For each RTP payload type, an offering MTSI client supporting the CHEM feature may include the following SDP attribute in its SDP offer:
Name: MAXimum-e2e-PLR(maximum end-to-end PLR of the media decoder in the MTSI client)
Value: MAX-e2e-PLR-value
Usage Level: media
Charset Dependent: no
Syntax:
MAX-e2e-PLR-value = payload-type SP maxe2e-PLR [“:”maxDL-PLR] [“/”maxUL-PLR]
payload-type = zero-based-integer
maxe2e-PLR = plr-value
maxDL-PLR = plr-value
maxUL-PLR = plr-value
plr-value = integer
: integer taken from IETF RFC 4566
The IANA registration information for the MAXimum-e2e-PLR SDP attribute is provided in Annex M.10.
The maxe2e-PLR represents the maximum end-to-end packet loss rate that can be properly received by the media decoder in the offering MTSI client (including effects of codec mode, packet loss concealment, de-jitter buffering, etc…) indicated by the RTP payload type number payload-type (as used in an “m=” line).
The maxDL-PLR parameter indicates the maximum packet loss rate that the offering MTSI client is able to handle on its local downlink and shall not exceed the maxe2e-PLR value in the SDP offer. If the parameter is not included then the default value from the offering MTSI client is set to ½ of the maxe2e-PLR value included in the SDP offer.
The maxUL-PLR parameter indicates the maximum packet loss rate that the offering MTSI client is able to handle on its local uplink. If the parameter is not included then the default value from the offering MTSI client is set to ½ of maxe2e-PLR value the answering MTSI client will include in its corresponding SDP answer.
If maxe2e-PLR is not included in the SDP answer then its value is set to a recommended value for the codec and mode (e.g., obtain value from Annex Y if available).
The plr-value represents 1/100th of a percent (i.e. 10E-4) of packet loss as an integer.
The following table W.4.2-1 summarizes the SDP offer parameters.
Table W.4.2-1 SDP offer attributes and parameters
|
Parameter |
Requirement |
Default Value if not included in SDP offer |
Limit |
Limit Condition |
|
maxe2e-PLR |
Included when attribute is supported |
A recommended value for the codec and mode (e.g., obtain value from Annex X if available) |
||
|
maxDL-PLR |
Optional |
½ maxe2e-PLR value in SDP offer |
No greater than maxe2e-PLR value in SDP offer |
Always |
|
maxUL-PLR |
Optional |
½ maxe2e-PLR value in SDP answer |
Clause X.2.4 provides examples of how the MAXimum-e2e-PLR attribute is used in the SDP offer.
W.4.3 Answering MTSI Client
For each RTP payload type, an answering MTSI client supporting the CHEM feature may include the SDP attribute from sub-clause W.4.2 in its SDP answer with the following semantics of the parameters.
The maxe2e-PLR represents the maximum end-to-end packet loss rate that can be properly received by the media decoder in the answering MTSI client (including effects of codec mode, packet loss concealment, de-jitter buffering, etc…) indicated by the RTP payload type number payload-type (as used in an “m=” line).
If maxe2e-PLR is not included in the SDP offer then its value is set to a recommended value for the codec and mode (e.g., obtain value from Annex Y if available).
The maxDL-PLR parameter included in the SDP answer indicates the maximum packet loss rate that the answering MTSI client is able to handle on its local downlink and shall not exceed the maxe2e-PLR value in the SDP answer.
If the maxUL-PLR value included in the SDP offer is no greater than ½ the maxe2e-PLR value included by the answering MTSI client in the SDP answer, then maxDL-PLR in the SDP answer shall be set to no greater than (maxe2e-PLR value included in the SDP answer minus maxUL-PLR value included in the SDP offer). Otherwise (the maxUL-PLR value included in the SDP offer is greater than ½ the maxe2e-PLR value included in the SDP answer) the maxDL-PLR in the SDP answer should be set to no greater than (maxe2e-PLR value included in the SDP answer minus maxUL-PLR value included in the SDP offer). If the answerer sets the maxDL-PLR in the SDP answer to be greater than (maxe2e-PLR value included in the SDP answer minus maxUL-PLR value included in the SDP offer), the answerer shall not set maxDL-PLR greater than ½ maxe2e-PLR value included in the SDP answer.
If the maxDL-PLR parameter is not included in the SDP answer then the default value from the answering MTSI client is set to ½ of the maxe2e-PLR value included in the SDP answer.
The maxUL-PLR parameter included in the SDP answer indicates the maximum packet loss rate that the answering MTSI client is able to handle on its local uplink and shall not exceed the maxe2e-PLR value in the SDP offer.
If the maxDL-PLR value included in the SDP offer is no greater than ½ the maxe2e-PLR value included by the offering MTSI client in the SDP offer, then maxUL-PLR in the SDP answer shall be set to no greater than (maxe2e-PLR value included in the SDP offer minus maxDL-PLR value included in the SDP offer). Otherwise (if the maxDL-PLR value included in the SDP offer is greater than ½ the maxe2e-PLR value included in the SDP offer), ten maxUL-PLR in the SDP answer should be set to no greater than (maxe2e-PLR value included in the SDP offer minus maxDL-PLR value included in the SDP offer). If the answerer sets the maxUL-PLR in the SDP answer to be greater than (maxe2e-PLR value included in the SDP offer minus maxDL-PLR value included in the SDP offer), the answerer shall not set maxUL-PLR greater than ½ maxe2e-PLR value included in the SDP offer.
If the maxUL-PLR parameter is not included then the default value from the answering MTSI client is set to ½ of the maxe2e-PLR value included in the SDP offer.
The plr-value represents 1/100th of a percent (i.e. 10E-4) of packet loss as an integer.
The table W.4.3-1 below summarizes the usage of the SDP answer attributes and parameters.
Table W.4.3-1 Usage of the SDP answer attributes and parameters
|
Attribute/ |
Requirement |
Default Value if not included in SDP Answer |
Limit Condition |
Limit |
|
maxe2e-PLR |
Included when attribute is supported |
A recommended value for the codec and mode (e.g., obtain value from Annex X if available) |
||
|
maxDL-PLR |
Optional |
maxe2e-PLR value included in the SDP answer minus maxUL-PLR value included in the SDP offer. If maxUL-PLR is not included in the SDP offer then the default value is ½ maxe2e-PLR value in the SDP answer. |
maxUL-PLR value included in the SDP offer is no greater than ½ maxe2e-PLR value included in the SDP answer |
maxe2e-PLR value included in the SDP answer minus maxUL-PLR value included in the SDP offer |
|
maxUL-PLR value included in the SDP offer is greater than ½ maxe2e-PLR value included in the SDP answer |
½ maxe2e-PLR value in the SDP answer |
|||
|
maxUL-PLR |
Optional |
maxe2e-PLR value included in the SDP offer minus maxDL-PLR value included in the SDP offer. If maxDL-PLR is not included in the SDP offer then the default value is ½ maxe2e-PLR value in the SDP offer. |
maxDL-PLR value included in the SDP offer is no greater than ½ maxe2e-PLR value included in the SDP offer |
maxe2e-PLR value included in the SDP offer minus maxDL-PLR value included in the SDP offer |
|
maxDL-PLR value included in the SDP offer is greater than ½ maxe2e-PLR value included in the SDP offer |
½ maxe2e-PLR value in the SDP offer |
Clause X.2.4 provides examples of how the MAXimum-e2e-PLR attribute is used in the SDP answer.
Annex X (Informative):
Example Maximum Packet Loss Rate (Max. PLR) Values for Setting CHEM Handover Thresholds