K.3 Handling T.38 SDP attributes at the I-MGCF

29.1633GPPInterworking between the IP Multimedia (IM) Core Network (CN) subsystem and Circuit Switched (CS) networksTS

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Table K.3.1: Action at I-MGCF depending on SDP T.38 attribute values in SDP offer

	Handling of received SDP offer	Value provided in sent SDP answer
T38FaxVersion	Accept any value. Provide to the IM-MGW the received value or the maximum supported value at the IM-MGW (whatever is lower).	If I-MGCF supports received version, reply with that version. Otherwise reply with highest supported version. Provide value sent in the answer also to the IM-MGW.
T38MaxBitRate	Accept any value in the offer. Provide to the IM-MGW the received value or the maximum supported value at the IM-MGW (whatever is lower).	Supply value according to IM-MGW capabilities in the answer.
T38FaxFillBitRemoval	Accept offer with or without this attribute.	Do not include parameter in the answer. (NOTE 2).
T38FaxTranscodingMMR	Accept offer with or without this attribute.	Do not include parameter in the answer. (NOTE 2)
T38FaxTranscodingJBIG	Accept offer with or without this attribute.	Do not include parameter in the answer. (NOTE 2)
T38FaxRateManagement	Only accept calls with "transferredTCF" in the offer for T38FaxVersion 2 or higher. Otherwise reject offer (NOTE 3).	Supply "transferredTCF" value in the answer
T38FaxMaxBuffer	Accept any value in the offer. Provide to the IM-MGW the received value or the maximum supported value at the IM-MGW (whatever is lower).	Supply value according to IM-MGW capabilities in the answer.
T38FaxMaxDatagram	Accept any value in the offer. Provide to the IM-MGW the received value or the maximum supported value at the IM-MGW (whatever is lower).	Supply value according to IM-MGW capabilities in the answer.
T38FaxMaxIFP	Accept any value in the offer. If T.38 version 4 is supported by the MGW, provide to the IM-MGW the received value or the maximum supported value at the IM-MGW (whatever is lower).	If T.38 version 4 is indicated in the answer, supply value according to IM-MGW capabilities in the answer. Otherwise omit the SDP attribute from the answer.
T38FaxUdpEC	Accept value in the offer according to IM-MGW capabilities and provide it to the IM-MGW. Otherwise reject offer (NOTE 3).	Supply value according to IM-MGW capabilities in the answer.
T38FaxUdpECDepth	Accept any value in the offer. If T.38 version 4 is supported by the IM-MGW, provide to the IM-MGW the received value.	If T.38 version 4 is indicated in the answer, supply value according to IM-MGW capabilities in the answer. Otherwise omit the SDP attribute.
T38FaxUdpFECMaxSpan	Accept any value in the offer. If T.38 version 4 is supported by the IM-MGW, provide to the IM-MGW the received value.	If T.38 version 4 is indicated in the answer, supply value according to IM-MGW capabilities in the answer. Otherwise omit the SDP attribute.
T38ModemType	Accept any value in the offer. If T.38 version 4 is supported by the IM-MGW, provide to the IM-MGW the received value.	Do not include parameter in the answer. (NOTE 2)
T38VendorInfo	Accept any value in the offer.	Do not include parameter in the answer.
NOTE 1: With Version 4, default values for the SDP attributes apply if the attributes are omitted. NOTE 2: In the Mn H.248 profile the IM-MGW does not modify the T.30 bit stream encapsulated within T.38 when passing it to or from the CS network. NOTE 3: If other offered media lines are acceptable, set port in media line to zero. Otherwise reject offer in INVITE request by sending the SIP status code 488 "Not Acceptable Here". NOTE 4: "Any value" means any valid value that conforms to ITU-T Recommendation T.38 [72].