Handling Sip 3Xx Redirect Responses - AudioCodes Mediant 800 MSBG User Manual

SIP User's Manual
If there are no tokens, the request is dropped.
New tokens are added to the bucket at a user-defined rate (token rate).
If the bucket contains the maximum number of tokens, tokens to be added at that
moment are dropped.
A token bucket is configured using the following new parameters:
Rate = Rate at which tokens are added to the bucket (i.e., token rate). One token is
added to the bucket every 1000/Rate milliseconds. The rate of dialog setups per
second, or unlimited if set to 0 (default).
Max Burst = Maximum tokens that can fill the bucket. At any given time, the bucket
cannot contain more than this amount of tokens. The maximum burst size for the
dialog setup rate, unlimited if set to 0 (default).
Dropped requests are replied with the 486 "Busy Here" SIP response. Dropped requests
are not counted in the bucket.
The SIP dialog limits are defined in the Admission Control table (SBCAdmissionControl).
8.4.7

Handling SIP 3xx Redirect Responses

By default, the device's handling of SIP 3xx responses is to send the Contact header
unchanged. However, some network setups require that the new INVITE message sent as
a result of the 3xx traverse the device. This is enabled by the parameter SBC3xxBehavior.
Reasons for enforcing resultant INVITEs to traverse the SBC may vary:
The user that receives the 3xx can't route to the 3xx contact (i.e., the user is on the
LAN and the new contact is on the WAN). In such a scenario, the device helps the
user reach the WAN contact and overcome NAT problems.
Enforce certain SBC policies (e.g., call admission control, header manipulation, and
transcoding) on the resultant INVITE.
The device enforces this by modifying each Contact in the 3xx response as follows:
Changes the host part to the device's IP address – this change causes the remote
user agent to send the INVITE to the device.
Adds a special prefix ("T~&R_") to the Contact user part – to identify the new INVITE
as a 3xx resultant INVITE.
The SBC handling for the 3xx resultant INVITE is as follows:
1. The incoming INVITE is identified as a 3xx resultant INVITE according to the special
prefix.
2. The device automatically replaces the SBC host part (in the Request-URI) with the
host from the 3xx Contact.
3. The prefix ("T~&R_") remains in the user part for the classification, manipulation, and
routing mechanisms.
4. The classification, manipulation, and routing processes are done exactly like any other
INVITE handling. The special prefix can be used for specific routing rules for 3xx
resultant INVITEs.
Version 6.2 503
8. IP Telephony Capabilities
February 2011