[asterisk-bugs] [JIRA] (ASTERISK-29433) Frequently no audio and/or video due to Asterisk sending dat to the wrong port

[Chris (JIRA)]

Chris created ASTERISK-29433:
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             Summary: Frequently no audio and/or video due to Asterisk sending dat to the wrong port
                 Key: ASTERISK-29433
                 URL: https://issues.asterisk.org/jira/browse/ASTERISK-29433
             Project: Asterisk
          Issue Type: Bug
      Security Level: None
          Components: pjproject/pjsip
    Affects Versions: 16.17.0
            Reporter: Chris
            Severity: Major


Frequently our field-testers are complaining about missing audio and video.

After troubleshooting with the developer of our client SIP stack (AmSip/OSip2) we came to the conclusion that the root-cause is in Asterisk.

In the cases where no audio (or video) is received, it seems that Asterisk is sending the media packets to the wrong port.

See our engineer's detailed network analysis below.
_________________________________
FIRST OBSERVATION
_________________________________
>From asterisk_tcpdump.cap
packet 1243: asterisk (192.168.1.2) makes a STUN BINDING REQUEST from port 14429
packet 1251: asterisk receive an answer MAPPED-ADDRESS: 78.22.132.194:14429

This means the packet was received by stun server from the NAT IP 78.22.132.194 AND NAT PORT 14429
This means the NAT has forwarded the packet **without** changing the PORT. (NAT are often changing port)

This means the candidate should be:
a=candidate:S4e1684c2 2 UDP 1694498814 78.22.132.194 14429 typ srflx raddr 192.168.1.2 rport 14429\r\n

But it appears in SDP as:
a=candidate:S4e1684c2 2 UDP 1694498814 78.22.132.194 14429 typ srflx raddr 192.168.1.2 rport 14428\r\n

CONCLUSION: THIS IS AN ERROR FROM ASTERISK

_________________________________
SECOND OBSERVATION
_________________________________
Let's look at iphone_tcpdump.pcap  "with filter (udp.port == 12600) && (ip.addr == 192.168.1.2)"

We can see many packets being sent to 192.168.1.2:14428, but nothing received. I guess
this is expected.


Let's look at asterisk_tcpdump.pcap  "with filter udp.port == 14428 && ip.addr == 192.168.0.201"

packet 1529: We can see a a bind request being sent  + a retransmission
The request is sent FROM 192.168.1.2 from port 14428 to 192.168.0.201on port 12601
The request TID is :Message Transaction ID: 0e5c00008d4ca0783b1a7b48

Then, asterisk receive a response:
packet 1538 is the symmetric response. It contains a XOR-MAPPED-ADDRESS: 192.168.0.145:14428
This response has been built from amsip.
This response is coming from 192.168.0.201from PORT 12601

Let's look  iphone_tcpdump.pcap if we can find this request + answer:
Let's use the filter "(udp.port == 12601) && (ip.addr == 192.168.0.145 && udp.port == 14428)"

The packet 721 is matching the request. It's coming on RTCP port (12601) but comes from the RTP port (14428)
The packet 723 is correct and match the response

amsip has correct processing: amsip understand this is coming to the RTCP port and establish the RTCP connection.

Unfortunately, asterisk has sent the packet from port 14428 instead and this is NOT CORRECT.


____________________
FINAL CONCLUSION
______________________
Asterisk has sent packet 1529 from the wrong port.

The fact that asterisk is using the wrong port (14428) in the RTCP candidate has no impact, but still it's WRONG.

There was no NAT issue.




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