VoIP Traffic on Managed APN

All traffic on the Managed APN service is managed the same (i.e. no shaping or prioritising ), unless there are specific custom firewalling rules that have been requested by a customer.

The Managed APN uses network address translation (NAT). Quality of Service also depends on what protocol the voice is run over. If the VoIP connection is using SIP (Session Initiation Protocol), there are additional overheads in the transport and termination of these data packets.

SIP ALG (Application Layer Gateway) is an application within many routers. It inspects any VoIP traffic to prevent problems caused by firewalls and if necessary modifies the VoIP packets. Routers will often have SIP ALG activated by default.

Signs that SIP ALG is affecting VoIP calls

There are a few categories of symptoms SIP ALG could affect VoIP traffic (Note: It's not always apparent, especially since these issues often happen silently without users knowing.)

• One-way audio (only one person can hear the other)
• Phones do not ring when called
• Calls drop after being connected
• Calls going straight to voicemail for no known reason

The cause of these symptoms is that some VoIP traffic is lost between the phone and the VoIP service provider. This interruption could be because of router firewalls. This traffic is essential to maintaining the phone's availability and selecting the proper audio codecs.

Although we have many customers successfully using our Managed APN for VoIP applications, VoIP Quality of Service can not be guaranteed on mobile data in general because of the way different codecs are managed by routers and firewalls, as well as as last mile issues. There are many variables between SIM, tower and VoIP server that can affect quality.

To ensure acceptable Quality of Service for your specific VoIP service we suggest doing thorough field testing on the hardware & codec combination before deploying.

If the Managed APN service is not suitable for your specific VoIP application please enquire about public or unrestricted APN options.