CHAPTER25 Routing SBC
Mediant 4000 SBC | User's Manual
● If any attempted proxy server sends a response code that you have not configured in the
Alternative Routing Reasons table, the routing of the SIP message fails and the device
does not make any further attempts to route the message.
● If the device has tried all the online proxy servers of the Proxy Set and no responses have
been received or responses have been received that you have also configured in the
Alternative Routing Reasons table, the device searches the IP-to-IP Routing table for a
matching alternative routing rule and sends the SIP message to the destination configured
for the rule (repeating steps 1 through 2 above, if needed).
You can also configure alternative routing for the following proprietary response codes (if configured
in the table) that are issued by the device itself:
■ 805 IP Profile Call Limit: The device generates the response code when Call Admission
Control (CAC) limits (e.g., maximum concurrent calls) are exceeded for an IP Group (or SRD).
The CAC rules are configured in the Admission Control table (see Configuring Admission
Control). When this occurs, the device sends a SIP 480 (Temporarily Unavailable) response to
the SIP entity. In such a scenario, an alternative route configured in the IP-to-IP Routing table
can be used.
■ 806 Media Limits Exceeded: The device generates the response code when the call is
terminated due to crossed user-defined thresholds of QoE metrics such as MOS, packet delay,
and packet loss (see Configuring Quality of Experience Profiles) and/or media bandwidth (see
Configuring Bandwidth Profiles). When this occurs, the device sends a SIP 480 (Temporarily
Unavailable) response to the SIP entity. This is configured by 1) assigning an IP Group a QoE
and/or Bandwidth profile that rejects calls if the threshold is crossed, 2) configuring 806 in the
Alternative Routing Reasons table and 3) configuring an alternative routing rule.
The device also generates the response code when it rejects a call based on Quality of Service
rules due to crossed Voice Quality and Bandwidth thresholds (see Configuring Quality of
Service Rules). If the response code is configured in the table and the device rejects a call due
to threshold crossing, it searches in the IP-to-IP Routing table for an alternative routing rule.
■ 818 Signalling Limits Exceeded: The device generates the response code when it rejects a
call based on Quality of Service rules due to crossed ASR, NER or ACD thresholds (see
Configuring Quality of Service Rules). If the response code is configured in the table and the
device rejects a call due to threshold crossing, it searches in the IP-to-IP Routing table for an
alternative routing rule.
● The device issues itself the SIP response code 408 when no response is received
from a sent SIP message.
● If the device receives a SIP 408 response, an ICMP message, or no response,
alternative routing is still performed even if the code is not configured in the
Alternative Routing Reasons table.
● SIP requests belonging to an SRD or IP Group that have reached the call limit
(maximum concurrent calls and/or call rate) as configured in the Call Admission
table are sent to an alternative route if configured in the IP-to-IP Routing table for
the SRD or IP Group. If no alternative routing rule is located, the device
automatically rejects the SIP request with a SIP 480 (Temporarily Unavailable)
response.
The following procedure describes how to configure the Alternative Routing Reasons table through
the Web interface. You can also configure it through ini file [SBCAlternativeRoutingReasons] or
CLI (configure voip > sbc routing sbc-alt-routing-reasons).
➢ To configure SIP reason codes for alternative IP routing:
1. Open the Alternative Routing Reasons table (Setup menu > Signaling & Media tab > SBC
folder > Routing > Alternative Reasons).
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