[asterisk-bugs] [JIRA] (ASTERISK-26005) res_pjsip: Multiple SIP messages are combined into 1 TCP packet

[Ross Beer (JIRA)]

Ross Beer created ASTERISK-26005:
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             Summary: res_pjsip: Multiple SIP messages are combined into 1 TCP packet
                 Key: ASTERISK-26005
                 URL: https://issues.asterisk.org/jira/browse/ASTERISK-26005
             Project: Asterisk
          Issue Type: Bug
      Security Level: None
          Components: Channels/chan_pjsip
    Affects Versions: 13.9.0, 13.8.2
         Environment: CentOS 7
            Reporter: Ross Beer
            Severity: Critical


When using chan_pjsip with TCP transport multiple packets are concatenated into one TCP packet causing the packet to exceed the MTU size.

Setting the standard kernel options has no effect:

net.ipv4.ip_no_pmtu_disc = 1
net.ipv4.tcp_low_latency = 1
net.ipv4.tcp_autocorking = 0

The above options should stop the kernel concatenating the packets, however this is still occurring.

This causes an issue for a lot of handsets, this is most noticeable on handsets that have multiple BLF keys. For example Snom D715 or Cisco SAP504G + Sidecarts. This causes the phones to misbehave and to be come unusable. Switching to UDP or TLS resolves the issue and the phones function correctly. 



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