- Overview
- Symptoms
- SCCP Version Identification
- SCCPv17 support in the Cisco portfolio
- Workarounds
- Definitions
Overview
Cisco UCM version 7.0 and Cisco UCME 8.0 (IOS 15.0(1)XA) introduce version 17 of the SCCP signaling protocol. SCCPv17 significantly changes message formats from previous versions. User functionality will be impacted if a network device that lacks SCCPv17 support attempts NAT fixup or inspection of the SCCP protocol.
Symptoms
Symptoms are more likely to be observed with:
- 3rd gen phones running phone load 8.4 or later
- UCM 7.0 or later
- UCME 8.0 or later ( IOS 15.0(1)XA or later )
Various symptoms may be observed based on devices, versions and topology. Some symptoms may include:
- One-way audio or no-way audio on calls - likely as openreceivechannel/openreceivechannelack messages are reformatted.
- Phones failing to register - likely as registration messages are reformatted.
- All phones unregistering - likely if a network device malfunctions or otherwise aborts all SCCP sessions upon encountering newly formatted messages
- Unexpected behavior in phone features that depend on messages that changed format in SCCPv17
- Going offhook on a phone results in "UCM Down" status message
- Phone displays "Temp Fail" status message when answering an inbound call
SCCP Version Identification
- Endpoint sends the desired protocol version to server via the StationRegister message.
- Server responds with StationRegisterAck. Endpoint should compare the protocol version returned in the StationRegisterAck message with the version that was sent in the StationRegister message.
- If the received version is lower than the sent version, the device should only expect the messages that are defined for the lower version, and ignore any other messages sent.
SCCP Protocol version can be identified in the SCCP StationRegister message. Most significant bytes indicate feature support and least significant bytes indicate protocol version. Here is an example of SCCPv17 StationRegister message from a 7970 model phone running 8.4 phone load registering to UCM7.0(1). Decimal 17 = Hex 0x11:
SCCPv17 support in the Cisco portfolio
Recommendations for complete Cisco solution are covered in Cisco Unified Communications System Documentation. Specifically Cisco UCM 7.0 is covered by the System Release Notes for IP Telephony: Cisco Unified Communications System, Release 7.0(1) . Information below supplements the System Release Notes.
Cisco Security Appliance Support
ASA and PIX support for SCCPv17 was added via CSCso36036 This fix is included in versions 8.0.3.22, 8.1.2, and 8.2.1 - and later.
Additionally, please be aware of the following defect which may trigger a crash when SCCPv17 messages are processed by the security appliance: CSCsz06748 This bug is resolved in the following versions: 8.0.4.33, 8.1.2.24, and 8.2.1.2
Cisco FWSM Support
FWSM support for SCCPv17 was added via CSCso38805 This fix is included in version 4.0.3 and later.
Cisco IOS Firewall Support
Support for SCCPv17 was added to IOS Zone-Based Firewall via
CSCso53203 Support IOS FW interopreability with CUCM 7.0 running SCCP v17
starting with versions 12.4(20)T1. Legacy IOS Firewall (CBAC) will not support SCCPv17
Cisco IOS NAT Support
Support for SCCPv17 in IOS NAT is not currently available, but is being considered with:
Please monitor CSCsy93500 for updates on IOS NAT support of SCCPv17.
Workarounds
SCCP phones initiate version negotiation. It is possible to downgrade phones to use and older version of SCCP. Downgrading phones will cause some loss of functionality. Older phone loads are not extensively tested with newer CM versions so long term production deployment is not recommended. See the Cisco Unified Communications Compatibility Tool for recommended versions.
- 2nd Gen Phones do not support SCCPv17 so will not be directly affected
- 3rd Gen Phone loads 8.3 and earlier use SCCPv15 and earlier so will not be directly affected
Phones using older SCCP versions may be peripherally affected when:
- Both 2nd gen SCCP traffic and 3rd gen SCCP traffic traverse the same transit network device that attempts inspection but does not support SCCPv17. This may cause unexpected behavior in the transit network device that affects all SCCP traffic.
- A 2nd gen SCCP phone calls a 3rd gen SCCPv17 phone and an affected transit network device is between CM and the 3rd gen phone. The transit network device will drop or corrupt new SCCPv17 format messages such as StationOpenReceiveChannelAckMessage between CM and the 3rd gen phone. This will in turn cause the 2nd gen phone to experience one way audio. This is not due to any issue with the 2nd gen phone but strictly related to the interrupted signaling of the 3rd gen phone.
Definitions
- 3rd Gen Phones - aka TNP Phones include models 7906, 7911, 7941, 7942, 7945, 7961, 7962, 7965, 7970, 7971, 7975
- 2nd Gen Phones - include models 7902, 7910, 7935, 7936, 7937, 7940, 7960
- Cisco UCM - Cisco Unfied Communications Manager. Product was originally called Cisco CallManager and abbreviated CM or CCM. UCM is a server based application.
- Cisco UCME - Cisco Unified Communicaitons Manager Express. Product was originally called Cisco CallManager Express and abbreviated CME or CCME. The Survivable Remote Site Telephony (SRST) feature is also affected.
- NAT - Network Address Translation
- SCCP - Selsius Client Control Protocol. Also known as Skinny. Session control protocol used over TCP to allow UCM and UCME to control endpoints such as phones, analog ports, and Unity voicemail ports. SCCP is also used for Media Termination Points(MTPs), Transcoders (XCODERs), and some conference bridges such as IOS hardware conferencing.
Questions? E-Mail Wes Sisk
