v=0
o=MxSIP 363557643167144492 47645779394347481 IN IP4 10.250.253.3
s=-
c=IN IP4 10.250.253.3
t=0 0
a=partnerfsm:738512736_4_98_3_1
m=image 27598 RTP/AVP t38
a=T38MaxBitRate:14400
a=T38FaxRateManagement:transferredTCF
a=T38FaxFillBitRemoval:0
a=T38FaxTranscodingMMR:0
a=T38FaxTranscodingJBIG:0
a=T38FaxVersion:0
a=T38FaxUdpEC:t38UDPRedundancy
a=sendrecv
m=image 34380 RTP/SAVP t38
a=T38MaxBitRate:14400
a=T38FaxRateManagement:transferredTCF
a=T38FaxFillBitRemoval:0
a=T38FaxTranscodingMMR:0
a=T38FaxTranscodingJBIG:0
a=T38FaxVersion:0
a=T38FaxUdpEC:t38UDPRedundancy
a=sendrecv
a=key-mgmt:mikey AQAVgPwtOloCAAAAAAAAAAAAAABZ+s2kAAAAAAUBAAVtaWtleQsA1kMaMwAAAAAKFPhiiuMYI6Rr/kmTTbCu0sR43a/HAQAA
ADYCAQEDBAAAAKAEBAAAAHALBAAAAFAAAQEBBAAAAIAJAQAGAQAFAQAIAQEKAQEHAQEMBAAAAAAAAAAkABAAENR6NqV530allXc23CkfQucADmG1yYfFo
+6Tw3+ofqCTAA==
a=crypto:1 AES_CM_128_HMAC_SHA1_80 inline:qa7LFKEFmfQF4exgJl2q78jJnxTGgsJGVjZqqg3u
m=image 34740 udptl t38
a=T38MaxBitRate:14400
a=T38FaxRateManagement:transferredTCF
a=T38FaxFillBitRemoval:0
a=T38FaxTranscodingMMR:0
a=T38FaxTranscodingJBIG:0
a=T38FaxVersion:0
a=T38FaxUdpEC:t38UDPRedundancy
a=sendrecv
[Nov 29 14:50:43] VERBOSE[32504] chan_sip.c: — (19 headers 35 lines) —
[Nov 29 14:50:43] DEBUG[32504][C-000000d3] sip/reqresp_parser.c: Begin: parsing SIP "Supported: timer"
[Nov 29 14:50:43] DEBUG[32504][C-000000d3] sip/reqresp_parser.c: Found SIP option: timer
[Nov 29 14:50:43] DEBUG[32504][C-000000d3] sip/reqresp_parser.c: Matched SIP option: timer
[Nov 29 14:50:43] VERBOSE[32504][C-000000d3] chan_sip.c: Sending to 10.250.253.3:5060 (no NAT)
[Nov 29 14:50:43] DEBUG[32504][C-000000d3] chan_sip.c: Initializing initreq for method INVITE - callid 518c51512a0a75
e77ab794d2353881fb@10.250.253.59:5060
[Nov 29 14:50:43] DEBUG[32504][C-000000d3] chan_sip.c: Processing session-level SDP v=0... UNSUPPORTED OR FAILED.
[Nov 29 14:50:43] DEBUG[32504][C-000000d3] chan_sip.c: Processing session-level SDP o=MxSIP 363557643167144492 47645779394347481 IN IP4 10.250.253.3... OK.
[Nov 29 14:50:43] DEBUG[32504][C-000000d3] chan_sip.c: Processing session-level SDP s=-... UNSUPPORTED OR FAILED.
[Nov 29 14:50:43] DEBUG[32504][C-000000d3] chan_sip.c: Processing session-level SDP c=IN IP4 10.250.253.3... OK.
[Nov 29 14:50:43] DEBUG[32504][C-000000d3] chan_sip.c: Processing session-level SDP t=0 0... UNSUPPORTED OR FAILED.
[Nov 29 14:50:43] VERBOSE[32504][C-000000d3] netsock2.c: == Using UDPTL CoS mark 5
[Nov 29 14:50:43] DEBUG[32504][C-000000d3] chan_sip.c: Setting NAT on UDPTL to Off
[Nov 29 14:50:43] DEBUG[32504][C-000000d3] chan_sip.c: Processing session-level SDP a=partnerfsm:738512736_4_98_3_1... UNSUPPORTED OR FAILED.
[Nov 29 14:50:43] WARNING[32504][C-000000d3] chan_sip.c: Rejecting image media offer due to invalid or unsupported syntax: image 27598 RTP/AVP t38
[Nov 29 14:50:43] VERBOSE[32504][C-000000d3] chan_sip.c:
<--- Reliably Transmitting (no NAT) to 10.250.253.3:5060 --->
SIP/2.0 488 Not acceptable here

the problem is the RTP/AVP and RTP/SAVP, asterisk should decline it from sdp. I couldn't test my patch today I will, next days.