А может у них порт для приема Invite на Прокси сервере нестандартный порт?
Допустим 5061, а 5060 стоит unreachable. Посмотрите трэйс, если есть ICMP - port unreachable пакеты, то похоже на то.
OfficeServ can send a request message to the register port only.
It is impossible to change the destination port of a request message dynamically.
So soft switch port needs to be fixed and please inform this specification to ITSP manager.
(Сие означает, что динамически OfficeServ менять порт на Invite не умеет)
Собственно RFC4566 рекоммендует следующее
http://tools.ietf.org/html/rfc4566#section-3.2 o The transport port for media
This address and port are the destination address and destination
port of the multicast stream, whether being sent, received, or both.
For unicast IP sessions, the following are conveyed:
o The remote address for media
o The remote transport port for media
The semantics of this address and port depend on the media and
transport protocol defined. By default, this SHOULD be the remote
address and remote port to which data is sent. Some media types may
redefine this behaviour, but this is NOT RECOMMENDED since it
complicates implementations (including middleboxes that must parse
the addresses to open Network Address Translation (NAT) or firewall
pinholes).Ну и собственно, надо зафиксировать этот нестандартный порт по регистрации Registra Port (если регистрация прошла, то все в порядке) и по обмену сообщениями вызовов Outbound Proxy Port:
In case of using "Carrier", you should change <Outbound Proxy Port (or Registra Port)> in DM 5.2.13 SIP Carrier Options.
So Outbound Proxy port should be set "5061" in this case.In summary, the destination port of SIP message is as below.
-. Carrier : DM 5.2.13 SIP Carrier Options -> Outbound Proxy Port (or Registra Port)
-. Peering : DM 5.2.16 VoIP Peering -> Remote Port