Is it
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required to use operator APN?
Enterprise Voice Security Suite uses two separate communication channels:
- SIGNALING
- protocol: used to initiate and receive a call. It uses SIP protocol, transported over TCP in a TLS secured tunnel
- MEDIA SESSION: it is the actual audio flow. It uses RTP protocol, transported over UDP, encrypted using SRTP. UDP is the same protocol used to transport video streaming
Over mobile network, a PDP context is required to open an IP tunnel to public internet (see GPRS Core Network)
Blackberry devices use an overlay network from RIM (both with MDS or BIS-B transport): your device has an active PDP context to this 'sort of' VPN to RIM infrastructure and, from there, exit to public internet.
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