Answer to Seizure Ratio-Based Routing

New SIP session agent constraints set a threshold for Answer to Seizure Ratio (ASR) has been implemented. ASR is considered when determining whether session agents are within their constraints to route calls (in addition to session and rate constraints).

The new session agent constraints indicate the minimum acceptable ASR value and computes the ASR while making routing decisions. ASR is calculated by taking the number of successfully answered calls and dividing by the total number of calls attempted (which are known as seizures).

If the ASR constraints are exceeded, the session agent goes out of service for a configurable period of time and all traffic is routed to a secondary route defined in the local policy (next hop with higher cost).

The two session agent constraints are:

minimum seizure: determines if the session agent is within its constraints. When the first call is made to the session agent or the if calls to the session agent are not answered, the minimum seizure value is checked.
For example, if 5 seizures have been made to the session agent and none of them have been answered, the sixth time, the session agent is marked as having exceeded its constraints and the calls will not be routed to it until the time-to-resume has elapsed.
minimum ASR: considered when make routing decisions. If some or all of the calls to the session agent have been answered, the minimum ASR value is considered to make the routing decisions.
For example, if the you set the minimum ASR at 50% and the session agent’s ASR for the current window falls below 50%, the session agent is marked as having exceeded its constraints and calls will not be routed to it until the time-to-resume has elapsed.

ASR Constraints Configuration

To configure ASR constraints:

In Superuser mode, type configure terminal and press Enter.
```
ORACLE# configure terminal
```
Type session-router and press Enter to access the system-level configuration elements.
```
ORACLE(configure)# session-router
```
Type session-agent and press Enter. The system prompt changes to let you know that you can begin configuring individual parameters.
```
ORACLE(session-router)# session-agent
ORACLE(session-agent)#
```
If configuring an existing session agent, enter the select command to select the session agent.
min-seizures—Enter the minimum number of seizures that when exceeded, cause the session agent to be marked as having exceeded its constraints. Calls will not be routed to the session agent until the time-to-resume has elapsed. The default value is 5. The valid range is:
- Minimum—1
- Maximum—999999999
min-asr—Enter the percentage you want as the minimum. If the session agent’s ASR for the current window falls below this percentage, the session agent is marked as having exceeded its constraints and calls will not be routed to it until the time-to-resume has elapsed. The default value is 0. The valid range is:
- Minimum—0
- Maximum—100

Save and activate your configuration.

The following example shows a session agent configuration.

session-agent
        hostname                       192.168.1.6
        ip-address
        port                           1720
        state                          enabled
        app-protocol                   H323
        app-type                       H323-GW
        transport-method
        realm-id                       external
        description
        carriers
        allow-next-hop-lp              enabled
        constraints                    enabled
        max-sessions                   0
max-inbound-sessions           4
        max-outbound-sessions          5
        max-burst-rate                 0
        max-inbound-burst-rate         10
        max-outbound-burst-rate        1
        max-sustain-rate               0
        max-inbound-sustain-rate       0
        max-outbound-sustain-rate      0
min-seizures                   5
        min-asr                        50
        time-to-resume                 30
        ttr-no-response                0
        in-service-period              0
        burst-rate-window              0
        sustain-rate-window            0
        req-uri-carrier-mode           None
        proxy-mode
        redirect-action
        loose-routing                  enabled
        send-media-session             enabled
        response-map
        ping-method
        ping-interval                  0
        media-profiles
        in-translationid
        out-translationid
        trust-me                       disabled
        request-uri-headers
        stop-recurse
        local-response-map
        ping-to-user-part
        ping-from-user-part
        li-trust-me                    disabled
        in-manipulationid
        out-manipulationid
        p-asserted-id
        trunk-group
        max-register-sustain-rate      0
        early-media-allow
        invalidate-registrations       disabled
        last-modified-date             2006-05-12 19:48:06