Notes and Limitations

Notes and Limitations apply to SBC 1000/2000 and SBC SWe Lite, unless noted.

For functional differences between the SBC 1000/2000 and SBC SWe Lite, refer to Functional Differences Between SBC 1000/2000 and SBC SWe Lite.

IPv6 Requires Additional Configuration When Auto Is Configured

When Auto is set as the Signaling/Media Source IP field (in the SIP Signaling Group facing the Front End Server/Skype Mediation Server), call scenarios using IPv6 are not being transferred correctly. Most cases include a Skype Mediation Server or Front End Server which invokes call transfer (REFER SIP msg) incoming to the SBC Edge.

As a result, the following additional configuration is required for the calls to transfer correctly.

Step 1: Add Number/Name Transformation Entry

Add a Transformation Table (if the FQDN of the Skype Mediation Server/Front End Server is set as a pool), that includes a wildcard regex expression for the FQDN configured on the Transformation table (to match all Skype Mediation Server/Front End Servers within the pool).

For example:

If the Skype Mediation Server/Front End Server FQDN is "lync-rdc2.njsbclab.dev",  then ".*lync-rdc2.njsbclab.dev.*" regex expression must be configured as the Transformation entry.

If multiple Skype Mediation Server/Front End Server FQDNs, (i.e, sfbfe1.sfb.tst, sfbfe2.sfb.tst, ….) are configured within a pool, then “.*sfbfe..sfb.tst.*” regex expression must be configured as the Transformation Entry.

Example Transformation Entry

Step 2: Add Call Routing Table

Add a Call Routing Table which includes the following:

• The Number/Name Transformation Table entry created in Step 1 must be selected.
• The Destination Signaling Group must be facing the Skype Mediation Server/Front End Server.
• The Destination Signaling Group must be part of the routing list of Signaling Groups facing the Skype Mediation Server/Front End Server.

Add Call Routing Table

Lync E911 ELIN Support

Security desk conferencing with the emergency call in Unidirectional and Bidirectional mode is not supported.

ISDN - SBC Rejects Inbound BRI Calls if the First Channel is Blocked

The SBC Edge rejects inbound BRI calls if the first channel is blocked.

CAS Ringback Instead of Busy Tone

• Transferred calls to a Busy FXO line will receive Ringback instead of Busy Tone.
• Silence based disconnect only checks for audio in one direction. For this reason, a long timeout should be used.

SIP Features Not Supported

The following SIP features are not supported in the SBC Edge:

• Privacy and Screening on Diversion number.
• REGISTER messages with multiple contacts do not use multiple Registrar licenses. Multiple licenses will be supported in a future release.
• SBC Edge does not switch to the next server in the table if connection re-use is enabled per the configured value, it always waits 5 seconds.
• In DSP mode only multiple M-Lines works for Audio/FAX/Image combinations only. If the Multiple M-Lines have multiple audio or audio + video, only the first m=audio is recognized.

RTP Proxy Mode Does Note Use SBC Edge DSP Resources

RTP Proxy mode does not use SBC Edge DSP resources.  As a result, the following features are not supported in the SBC Edge when calls are operating in RTP Proxy mode:

• Ring-back generation
• Early 183
• Music on Hold
• QoE
• Call Transfers

Additionally, Ribbon recommends the SMM message translation with SDP manipulation not be used when operating in RTP Proxy mode, as it may introduce offer/answer issues. For details on using DSPs in calls, refer to SBC 1000-2000 System Performance and Capacity and SBC SWe Lite Performance and Capacity.

SNMP Process Restarts with Loss of SNMP Traps

In rare cases, the sym-snmp process restarts with a probable loss of SNMP traps sent during this interval of process restart during high volume periods of SNMP traps being sent from the SBC 1000/2000 to the management stations. This behavior is exhibited when the SBC 100/2000 is not licensed for Transcoding and is experiencing high call volumes (2-3 calls/sec). The node generates an alarm trap for failure to acquire a Transcoding license for attempted call.

Unsupported SNMP Counters

SIP/ISDN Counters

The following SNMP counters in the uxPortTable are unsupported:

• Blocked Calls (not supported for SIP)
• IngressBlockedCalls
• EgressBlockedCalls

Large MIB Table Retrievals

The retrieval of large MIB tables via SNMP during periods of heavy call volumes can result in call failures and failed SNMP requests. Tables in excess of 1000 rows when traffic exceeds 2 calls/second or tables in excess of 500 rows when traffic exceeds 4 calls/second are consider large.

Polling of these tables should be limited to a maximum frequency of once per 45 minute period. The SNMP timeout should be set between 60 and 120 seconds. Retries should be limited to a maximum of 5.

Transcoding between Tenor, SBC Edge, and Any SIP Phone That Sends a 180 Without SDP

No audio is transmitted between the end points when any SIP phone that sends a 180 without SDP employes a G.711 A-Law codec and the SBC Edge uses G.711 µ-Law codecs as the secondary codec in the Media List configuration in the following network topology:

Tenor-SBC Edge-SIP phone topology with G.711 A-law and µ-law codecs

 

Workarounds

There are two ways to work around this limitation:

Workaround 1

Configure the A-law codec such that it is specified as the first codec in the media list as shown below:

Configure A-law Codec

 

Workaround 2

Enable Early Media (183) in the corresponding signaling group as shown below:

Enable Early 183

 

Inter-digit Timer Begins Early

The inter-digit timer is designed to begin after the DTMF tone is generated, however it currently begins before. This may result in an early timeout and could result in a mis-dialed number. To compensate, increase the inter-digit timer by the time equal to the duration of incoming MF/DTMF tones.

This issue will be addressed in a future release

Log Reload Functionality Limitation

The Reload button appearing in the bottom left-hand corner of the Local Logs page of the WebUI becomes inactive when the logfile exceeds 10 Megabytes in size. This is done to prevent the log file from overloading the browser.

Internet Explorer: Browser Limitation
The previous description not withstanding, Internet Explorer has an additional browser dependent limitation of 3MB. When the log file exceeds 3MB, IE disables the Reload button.

Reload Button Disabled

 

FXO Conference Calls

In the following specific scenario, ringback is heard by all parties when adding another extension to a conference call.

Scenario:

• The Loop Start Type in the CAS FXO Signaling Group is set to either Basic or Forward Disconnect.
• One member of a conference call attempts to call another extension and add it to the conference. The attempt originates from an FXS port, through Lync and outbound over an FXO port to a corresponding FXS port.

When this scenario is encountered all parties to the conference call hear the ringback tones. No ringback tone should be heard when attempting to add another party to a conference call.

This issue will be addressed in a future release.

No Progress Tone in Transfer Scenario

When a call is transferred and the target extension is busy, a fast busy tone should be heard. In the following scenario, only a normal ringback signal is heard until the call times out:

• The call is transferred out over an FXO port.
• The Loop Start Type in the FXO Profile is set to Reverse Battery.

This issue will be addressed in a future release.

Lync Server 2013 Does Not Support Reason Headers

When a forked call to Lync is answered elsewhere, the RibbonSBC automatically generates a SIP CANCEL (including a Reason header) to suppress Lync's missed call notification. However, the Microsoft Lync Server 2013 does not support receiving the Reason header from gateways. Without Microsoft support, there is no mechanism to suppress the missed call notification sent from Lync to Exchange.

Lync SBA versions Require Different Operating Systems

Specific SBA versions require different Operating Systems:

• Windows Server 2012 R2 by default to run Windows Server 2008 R2
• Windows Server 2008 R2 by default to run Windows Server 2012 R2

The image that is based on a non-licensed Operating System will not be offered for re-initialization. If you are running a non-licensed OS, an alarm will be triggered. Ensure you are running a proper license for the ASM. For a list of licenses and instructions for deployment for a given SBA version, refer to Working with Licenses.

ASM Windows Server Support Specifications

An OS License is included at the time of shipment. To determine which OS was shipped, see below. If required, upgrade/downgrade packs for ASM images if needed are available for nodes that do not have the proper licensing for Windows 2008 R2 or Windows 2012 R2.

Downgrade Pack: Available for a node that needs Lync 2010 SBA but does not have a Windows Server 2008 R2 license (see Skype for Business - Best Practice Downgrade to Lync 2010 SBA). Ribbon will supply: 

• A Microsoft Windows Server 2008 R2 license (includes physical license label)
• A Ribbon license to use Windows Server 2008 R2 (includes a feature activation key)
• A Microsoft Lync 2010 SBA License (includes physical license label)

Upgrade Pack: Available for a node that needs Skype for Business 2015 SBA but does not have a Windows Server 2012 R2 license (Skype for Business - Best Practice Upgrade to Skype for Business 2015 SBA). Ribbon will supply:

• A Microsoft Windows Server 2012 R2 license (includes physical license label)
• A Ribbon license to use Windows Server 2012 R2 (includes a feature activation key)
• A Skype for Business 2015 SBA License (includes physical license label)

Perform the following to apply a downgrade/upgrade pack:

1. Obtain the upgrade/downgrade package from Ribbon.
2. Apply the license. See Installing Licenses. See Attach License Label for attaching the label on the unit.

Warning

Lync/Skype Ignores the Connected Name

Lync/Skype for Business ignores the connected name information in the SIP messages and does not render this to the user.

Single Cloud Connector Edition (Cloud Link) Goes Down and Existing Calls From the CCE Will Drop and Not Failover

For a deployment that uses multiple CCEs on a single site (High Availability), and a single CCE goes down, the existing calls from this CCE will drop and not failover to the additional CCE. New inbound and outbound calls are completed. The SBC follows this behavior for multiple SBCs on a single site.

Active calls are not preserved due to the behavior of the Cloud Connector Edition application.

Alert for SWe SIP Signaling Session License is Not Displayed

The SWe Lite does not display an alert on the WebUI when you attempt to install or add a SIP Signaling Session license with a total count of 250 or more licenses on a system that does not have a high capacity license present. This warning is displayed in the WebUI's alarm list. For details on viewing alarms, refer to Viewing Alarms and Events.

Skype for Business Call Parking Issue

A Skype for Business call parking issue occurs when the Music on Hold (MOH) feature has been activated on both the SWe Lite and Skype for Business server. A workaround to solve this issue is to activate MOH on either the Skype for Business server or the SWe Lite (not on both).

Microsoft Azure

• SBC SWe Lite performance in Microsoft Azure may differ from SWe Lite on-premises. For details, refer to SBC SWe Lite Performance and Capacity.
• SBC SWe Lite license for Microsoft Azure will not work for on-premises deployment and vice versa. Refer to Working with Licenses.

Too Many Subsystems in SBC SWe Lite May Cause Log Rotation to Fail

If too many subsystems are configured for verbose (debug/trace) local logging then log rotation may fail. If log rotation fails, new log entries are not written.

Proxy Mode/Access Mode

When Agent Type in SIP Signaling Group is configured for Access Mode or the Audio/Fax Stream Mode in Call Routing Table is set to Proxy, do not enable the Session Timer function in SIP Profile.