SIP & H.323 protocol search sequence

When placing a call to or from the Pexip Service, there is a search prioritization that dictates the order that the destination address is searched on both the Pexip network and external networks.

The searching includes the interworking of protocols from the native SIP of registered standards-based endpoints.

URI search sequence

  1. Check Pexip's internal database to see if the domain is registered in the service network. If so, attempt to connect the call internally first and stop the search.
  2. If the domain is not registered internally, perform a DNS SRV lookup on SIP and try to connect the call. While SIP calls are attempted, the service waits for a response before proceeding.

    Any _SIPS SRV records are tried first, before moving on to _SIP.

  3. If SIP fails to connect or has no records, search for Skype for Business or Lync destinations with a _sipfederationtls lookup and attempt to connect if there is a result. TLS has a higher priority than TCP.
  4. Look up any _h323cs DNS SRV records. If successful, attempt to interwork to H.323 through Pexip as a gateway call.
  5. If all the above steps fail, check DNS for an A record for the domain and attempt to connect on SIP to the result of that A record.

IP address search sequence

  1. Attempt to connect the call using SIP TLS.
  2. Attempt to connect using SIP TCP.
  3. Attempt to interwork to H.323 through Pexip as a gateway call.