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Overview

SBC supports a subset of the functionality required for a full-ICE agent:

• In controlling role, SBC initiates connectivity check with a STUN Binding Request. The connectivity check by SBC is sent in response to the first connectivity check, which is received from the peer. SBC selects the remote Ip address for media based on the address signaled in the first STUN Binding Request, which is received from the peer. To assert the selection of media, SBC sends STUN Binding Request with the USE-CANDIDATE attribute.
• In controlled role, SBC initiates a single connectivity check with a STUN Binding Request to the peer. This request is sent after receiving a Binding Request from the peer, which contains the USE-CANDIDATE attribute. This behavior is important to complete the full-ICE procedures when inter-operating with WRTC peers such as Google and Chrome.
• In controlling role, SBC protects against network loss of STUN message exchanges by introducing internal guard timers and sends STUN Keep-Alive messages at a configurable interval. This functionality is based on the procedures defined in RFC5245.

These functionalities allow SBC to inter-operate with other ICE peers, which require the connecting peer to act as a full-ICE agent.

When inter-operating with Lync endpoints, which require their own flavor of ICE, this feature extends the existing SBC implementation of ICE-Lync to support the following functionalities:

• Allows specification of IPv6 candidates at Signaling and in STUN messages.
• Validates the received STUN messages and attributes based on the MS-ICE2 standards.
• Protects against network loss of STUN message exchanges by introducing internal guard timers and sends STUN Keep-Alive messages at a configurable interval.

SBC supports the following functionalities to implement pseudo full-ICE and MS-Lync ICE:

• Timers
• Re-INVITE Generation

Anchor
Connectivity Check Timers Connectivity Check Timers

Timers

In pseudo full-ICE and MS-Lync ICE configuration, SBC determines the controlled or controlling role for a particular media stream. The role is determined based on the controlled attribute in the STUN Binding Request from the peer. SBC runs following new timers at different stages of the STUN processing:

• Connectivity Check Phase 1 Timer

• Connectivity Check phase 2 Timer

• USE-CANDIDATE Check Timer
• Keep-Alive Timer

Controlling Role

SBC assumes the controlling role when the controlled attribute is received in Binding Request for a media stream. In the controlling role, SBC retrieves the remote media IP or port based on the first Binding Request from the remote end. When the Binding Request with controlled attribute is received, SBC discontinues the phase 1 connectivity timer and sends initial Binding Request without USE-CANDIDATE. SBC starts the phase 2 connectivity timer of 5 seconds and wait for the STUN response. Once a successful response is received from the peer to the Binding Request without USE-CANDIDATE, SBC generates the Binding Request with USE-CANDIDATE and starts the USE-CANDIDATE check timer for 10 seconds. This timer is stopped after a successful binding response is received from the peer.

Controlled Role

SBC assumes the controlled role when the controlling attribute is received in Binding Request for a media stream.

When a STUN Binding Request with USE-CANDIDATE is received, SBC sends back the binding response and determines the remote address for media from the received Binding Request message. In the controlled role, SBC does not send STUN Keep-Alive. When configured as full-ICE, SBC generates Binding Request towards the peer even when assuming the controlled role. In a controlled role, SBC re-sends this Binding Request message (without use-candidate attribute) up to 10 times or until a successful response is received from the peer.

The following table describes the behavior of the timers:

A new parameter iceKeepaliveTimer is added to Network Address Translator (NAT) Traversal of SIP Trunk Group to enable Keep-Alive timer for ICE. This parameter is supported for Keep-Alive message on RTP port in Lync mode and RTP and RTCP ports in full-ICE mode.