From CLI:
asterisk*CLI> sip list peers
Name/username              Host            Dyn Nat ACL Port     Status               
peavey/peavey              87.49.92.235     D   N      55786    OK (128 ms)           
kok/kok                    83.94.174.23     D   N      5060     OK (19 ms)           
qdk/qdk                    83.94.174.23     D   N      1025     OK (30 ms)           
3 sip peers [Monitored: 3 online, 0 offline Unmonitored: 0 online, 0 offline]
  == Spawn extension (from-peavey-sip, 1, 2) exited non-zero on 'SIP/peavey-00d74000'
    -- Executing [1@from-peavey-sip:1] NoOp("SIP/peavey-00d77000", ""Peavey calling QDK -SIP2SIP-"") in ne           w stack
    -- Executing [1@from-peavey-sip:2] Dial("SIP/peavey-00d77000", "SIP/qdk") in new stack
    -- Called qdk
    -- SIP/qdk-00d84000 is ringing
    -- SIP/qdk-00d84000 answered SIP/peavey-00d77000
    -- Packet2Packet bridging SIP/peavey-00d77000 and SIP/qdk-00d84000
[Oct 16 00:46:17] WARNING[34996]: chan_sip.c:1848 retrans_pkt: Maximum retries exceeded on transmission Mm           FkMmY4M2QwMTUxMDFmMDgzYWExYzcxOTEwNzU1NGY. for seqno 2 (Critical Response)
[Oct 16 00:46:17] WARNING[34996]: chan_sip.c:1865 retrans_pkt: Hanging up call MmFkMmY4M2QwMTUxMDFmMDgzYWE           xYzcxOTEwNzU1NGY. - no reply to our critical packet.
  == Spawn extension (from-peavey-sip, 1, 2) exited non-zero on 'SIP/peavey-00d77000'
asterisk*CLI> 
Disconnected from Asterisk server
Executing last minute cleanups


From log/asterisk/messages:
[Oct 16 00:46:17] WARNING[34996] chan_sip.c: Maximum retries exceeded on transmission MmFkMmY4M2QwMTUxMDFmMDgzYWExYzcxOTEwNzU1NGY. for seqno 2 (Critical Response)
[Oct 16 00:46:17] WARNING[34996] chan_sip.c: Hanging up call MmFkMmY4M2QwMTUxMDFmMDgzYWExYzcxOTEwNzU1NGY. - no reply to our critical packet.
[Oct 16 00:46:17] ERROR[34996] rtp.c: RTP Transmission error to 55.68.0.0:13618: Address family not supported by protocol family