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Non-INVITE Transaction Issues

Non-INVITE Transaction Issues. Robert Sparks dynamicsoft. The Race Condition. UAS. UAC. Request. 64*T1. 64*T1. Response. Timeout. The Race Condition. UAS. UAC. Request. UAS believes it responded in time UAC and UAS have different ideas of the result of the transaction

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Non-INVITE Transaction Issues

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  1. Non-INVITE Transaction Issues Robert Sparks dynamicsoft

  2. The Race Condition UAS UAC Request 64*T1 64*T1 Response Timeout

  3. The Race Condition UAS UAC Request • UAS believes it responded in time • UAC and UAS have different ideas of the result of the transaction • UAS has no way to know how much its transaction has been offset from the UAC • Each proxy makes the race easier to lose 64*T1 64*T1 Response Timeout RESULT: UAS Non-INVITE transactions must complete immediately!

  4. 408 is Not Useful UAS UAC Request 64*T1 64*T1 Timeout 408 Request Timeout

  5. 408 is Not Useful Proxy Proxy Proxy UAS UAC Request Request Request Request 64*T1 64*T1 408 408 408 408 408 408 408 408 408 408

  6. 408 is Not Useful Proxy Proxy Proxy UAS UAC Request Request Request Request 64*T1 64*T1 200 408 408 200 408 200 200

  7. Non-INVITE Timeouts Doom Forking Proxies Proxy Proxy UAS1 UAS2 UAC Request 415 64*T1 408 415 415 UAS2’s failure to respond forces both proxies to lose the race

  8. Failure to Respond Gets You Blacklisted • RFC 3263 discusses moving to next SRV on a no-response timeout (or explicit transport failure) • Non-INVITE can’t use next SRV on this request – transaction is already over • If failure isn’t cached (address temporarily blacklisted), next request is doomed to the same failure.

  9. Non-INVITE Provisional Responses • Arguments for Banning • Wasteful since transaction must complete immediately • (Early) provisionals harm recovery from lost final responses • Arguments Against • No response causes blacklisting • Losing the race is the same as not responding at all Should they be banned?

  10. Proposals • Proposal A • Make minor changes to use of current Non-INVITE transaction • Proposal B • Reform the Non-INVITE transaction to allow it to pend indefinitely

  11. Proposal A • Disallow non-100 provisionals • Disallow 100 Trying before Timer E reaches T2 • Encourage 100 Trying if no final response after Timer E reaches T2 • Disallow 408 to non-INVITE requests • Absorb late non-INVITE responses

  12. Proposal A • Disallow non-100 provisionals • Disallow 100 Trying before Timer E reaches T2 • Encourage 100 Trying if no final response after Timer E reaches T2 • Prevents blacklisting • Doesn’t harm lost final response recovery • Doesn’t allow reliable provisional responses

  13. Proposal A • Disallow 408 to non-INVITE requests • Currently they waste network • Absorb late non-INVITE responses • Don’t statelessly forward after the transaction times out

  14. Proposal B • Allow Non-INVITEs to pend (no timer F) • Allow CANCEL • ACK is not needed • Backwards safe

  15. Contrast • Proposal A • Removes waste from the network • Improves recovery from a failed node • UAS NI transactions still have to complete immediately or risk losing the race • Does not address proxy doom • Proposal B • 408s become useful again • Relieves proxies from timeout doom • Still need to address harmful provisionals for UDP • Either deprecate UDP or take Proposal A 1-3

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