Stateful SIP Transfer Settings

This page allows the system administrator to enable and configure the Stateful SIP Transfer system.

Stateful SIP Transfer

Stateful SIP Transfer (SST) is a WAN failover enhancement for SIP voice services.

Data Collection Interval

The SST process does not run continuously. It runs in intervals. This setting tells the process of how often data should be collected and analyzed. In between runs, the process listens for events from the WAN interfaces. This pause when the process listens for events is known as the 'tick' time.

Calculation Time(s)

Calculation time is the total time period for which the SST process holds calculation data. This data is for Packet Monitoring and UDP Loop Monitoring.

EdgeView Reporting Interval

EdgeView Reporting Interval is the time interval after which Operational Measurements (OM) reports are sent to the database. The provided intervals are 1 minute, 15 minutes, 1 hour, and 1 day. Once a time interval is selected, all OM reports of greater time intervals are also sent on the shorter time interval.

Event Notifications

Enable to generate and send link switching event notifications to EdgeView.

Summary Reports

Enable to generate and send report data to the EdgeView. Report summaries is a report based on the data used to determine when a link switching event occurs. The summary report is useful for historical references when troubleshooting issues or visualizing the metrics for quality or WAN health information. There are three settings for this option, Off, On-Normal and On-Debug.

Off: Turns reporting off.
On-Normal: This setting generates reports during link switch events with details of the switch.
On-Debug: This setting reports internal state information. The option generates large amounts of reports, and should only be activated when directed by customer support.

Enable Link Monitoring

This lets the SST process react to changes in link status of the physical Ethernet interface. If one WAN link is physically down, the SST process detects this. Although the process constantly listens for such events, it triggers a WAN link switch only if this option is enabled.

Recovery Wait Time(s)

Recovery Wait Time specifies the time gap to be maintained before a switch to the primary WAN link is made, following a physical failure. Although the switchover is made only after the failed link returns to service, this setting is necessary to protect the device from multiple rapid switches if a link is rapidly going into and out of service.

Enable Packet Monitoring

Enable Packet Monitoring enables the SST process to detect possible packet losses. When this is enabled, the process looks at the total packet counts of each link on each tick. If the received packet count is not incrementing in line with the transmitted packet count, the process detects a possible problem. It then looks at the ping data coming from the WAN failover process. If the WAN failover process has ping issues, the process initiates a link switch.

Recovery Wait Time(s)

Recovery Wait Time specifies the time gap to be maintained before a switch to the primary WAN link is made, following a WAN failover. It is also the time period for which the SST process remains in contact with the WAN failover process for ping statistics, on problem detection.

Look Back Tick

The number of time slices (ticks) in the data history that is compared to the current received packet count.

Enable UDP LOOP Monitoring

Enabling this setting starts a 2-way UDP loop between the primary and secondary WAN links. 19 byte UDP packets are sent out to each link. The frequency of packet deployment is one packet per tick. If a late or lost packet is detected, the process then looks at the ping data coming from the WAN failover process. If the WAN failover process is observed to have ping issues, a link switch is initiated.

Recovery Wait Time(s)

Recovery Wait Time specifies the time gap to be maintained before a switch to the primary WAN link is made, following a WAN failover. It is also the time period for which the SST process remains in contact with the WAN failover process for ping statistics, on problem detection.

UDP Port 1

This is the port used for the primary WAN link. The default port is set to 7798, but any available port between 1025-65535 can be used. This port cannot be the same as UDP Port 2.

UDP Port 2

This is the port used for the secondary WAN link. The default port is set to 7799, but any available port between 1025-65535 can be used. This port cannot be the same as UDP Port 1.

Lost Packet Threshold

The percentage number of lost packets in the Calculation Time period that causes an alarm.

Late Packet Threshold

The percentage number of late packets in the Calculation Time period that causes an alarm.

Late Packet Time (ms)

The time period (in milliseconds) after which an expected UDP test loop packet is considered late. This time period is different for each installation depending on the path length between the two WAN networks.

Enable SIP Impairment Monitor

Enables SIP to monitor several impairments that indicate possible WAN link problems.

Data Collection interval

This setting selects how often the SIP process examines impairments on the system.

SIP Server Availability Monitor

SIP Server Availability Monitor enables SIP to request a WAN link switch if no SIP server is available on the active WAN link. SIP tries this only once and does not switch back and forth between links repeatedly.

SIP Individual Call Switch

This setting enables SIP to switch individual calls between the primary and secondary WAN interface if there is any issue in the call media. This issue is detected either by Call RTP Loss Monitor or Call MOS Impairment Monitor. Individual call switch is initiated only if the secondary WAN interface is found available by the system.

Enable Call RTP Loss Monitor

This parameter enables SIP to check for RTP Loss Events on each call.

Number of active calls to trigger event

This is the minimum required number of active calls in order to trigger a switch. This prevents a small number of calls with RTP problems from triggering a link switch.

RTP Loss Threshold

RTP Loss Threshold specifies the minimum percentage of calls with RTP loss events that trigger a WAN link switch. 

RTP Loss Event Time (ms)

This is the minimum amount of time that has to pass since a call receives an RTP packet to be considered an RTP loss.

Enable Call MOS Impairment Monitor

This setting enables SIP to check for MOS Score events. These events are generated every 10 seconds for a call if the call encounters a MOS score of 2.5 or less.

Number of active calls to trigger event

This is the minimum required number of active calls on the system to initiate this check. If the number of calls is below this number, MOS Impairment triggers a WAN link switch. This setting prevents a small number of calls with MOS problems from triggering a link switch.

MOS Indication Threshold

MOS Indication Threshold specifies the minimum percentage of calls with MOS score events that trigger a WAN link switch.

Number of MOS BTC Events

This is the number of MOS BTC reports in the MOS History Period that flags a call as having MOS problems.

MOS History Period(s)

This is the time period for which MOS BTC events are collected.

Enable SIP Expires Override

This setting modifies the Expires value in the SIP 200OK REGISTER response message.

Default Expires Override(s)

Default expires override sets the Expires value in the SIP 200OK REGISTER response message for non-vendor specific SIP devices.

Cisco Expires Override(s)

Cisco expires override sets the Expires value in the SIP 200OK REGISTER response message for Cisco specific SIP devices.

Polycom Expires Override(s)

Polycom expires override sets the Expires value in the SIP 200OK REGISTER response message for Polycom specific SIP devices.

Yealink Expires Override(s)

Yealink expires override sets the Expires value in the SIP 200OK REGISTER response message for Yealink specific SIP devices.

Enable SIP Registration Hold

SIP Registration Hold provides a feature to increase the availability of LAN side devices registering to a host voice SIP provider.

Default SIP Registration Hold(s)

The time delay (in seconds) before sending the SIP 200OK register response message for non-vendor specific SIP devices.

Cisco SIP Registration Hold(s)

The time delay (in seconds) before sending the SIP 200OK register response message for Cisco specific SIP devices.

Polycom SIP Registration Hold(s)

The time delay (in seconds) before sending the SIP 200OK register response message for Polycom specific SIP devices.

Yealink SIP Registration Hold(s)

The time delay (in seconds) before sending the SIP 200OK register response message for Yealink specific SIP devices.

Enable Soft-Switch Expires Override

When enabled, this value replaces the Expires value given by the phone in the SIP REGISTER message. This value should be higher than the rate-pacing value, otherwise, the SIP server may consider the phones’ registration to have expired.

Softswitch/IP PBX Expires Override(s)

The number of seconds for which the SIP server should consider the registration valid.

Rate-Pacing behavior

This field controls the rate-pacing mode being used. This setting impacts the throttling rate at which SIP registrations are forwarded through the system to the configured SIP server. SIP client registrations during this interval are responded to by the system with a 200OK response. After the interval has expired the SIP client’s next REGISTER message is forwarded to the SIP server.

The drop-down menu offers three options to choose from.

• None: Choosing this disables rate pacing. SIP REGISTER messages are forwarded to the SIP server at the client frequency.
• Soft-Switch/IP PBX provided value: The rate is calculated from the expires value provided by the SIP server. This value is calculated by subtracting 2 times the configured Phone Expires Override value from the
  SIP Server Expires value.
• Configured value: This is the configured rate at which the SIP registrations are forwarded through the system to the configured SIP Server.

Rate-Pacing interval(s)

This is the configured rate at which SIP registrations are forwarded through the system to the configured SIP server.