AudioCodes Mediant 3000, User Manual

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User's Manual 280 Document #: LTRT-89729
Mediant 3000

UPDATE: terminated at each leg independently and may cause only changes in the
RTP flow - Hold\Retrieve are the only exceptions that traverse the two legs.

Re-INVITE: terminated at each leg independently and may cause only changes in the
RTP flow - Hold\Retrieve are the only exceptions that traverse the two legs.

PRACK: terminated at each leg independently.

REFER (within a dialog): terminated at each leg independently.

3xx Responses: terminated at each leg independently.

401\407 responses to initial INVITE: in case the back-to-back session is associated
with an Account, the responses is terminated at the receiving leg; in other cases, the
responses are passed transparently.

REGISTER: handled only in cases associated with a User-type IP Group - Contact,
To, From specific parameters are omitted.
20.1 Theory of Operation
The device's IP-to-IP SIP session is performed by implementing Back-to-Back User Agent
(B2BUA). The device acts as a user agent for both ends (
legs ) of the SIP call (from call
establishment to termination). The session negotiation is performed independently for each
call leg, using global parameters such as coders or using IP Profiles associated with each
call leg to assign different configuration behaviors for these two IP-to-IP call legs.
If transcoding is required, the RTP streams for IP-to-IP calls traverse the device and two
DSP channels are allocated per IP-to-IP session. Therefore, the maximum number of IP-to-
IP sessions is 1008 (corresponding to a maximum of 2016 media channels that can be
designated for IP-to-IP call routing is).
If transcoding is not needed, the device also supports up to 1008 IP-to-IP sessions.
The device also supports NAT traversal for SIP clients behind NAT, where the device is
defined with a global IP address.
The figure below provides a simplified illustration of the device's handling of IP-to-IP call
routing:
Figure 20-1: Basic Schema of the Device's IP-to-IP Call Handling
The basic IP-to-IP call handling process can be summarized as follows:
1. Incoming IP calls are identified as belonging to a specific logical entity in the network
referred to as a
Source IP Group , according to Inbound IP Routing rules.
2. The Source IP Group is sent to a specific IP Group referred to as a Destination IP
Group; the IP destination address being as configured by the Proxy Set associated
with the Destination IP Group.
3. Number manipulation can be done on inbound and outbound legs.
The following subsections discuss the main terms associated with the IP-to-IP call routing
application.