Table Of Contents
Audio and Video RTCP Passthrough on ISR Gateways for MTP, TRP, and RSVP Agent Services
Revised: November 11, 2011, OL-20468-01First Published: November 11, 2011Last Updated: November 11, 2011
This feature describes Audio Real-time Transport Protocol (RTP) Control Protocol (RTCP) enhancements and Video RTCP support for both IPv4 and IPv6 on Integrated Services Router (ISR) gateways for Resource Reservation Protocol (RSVP), Media Termination Point (MTP), and Trusted Relay Point (TRP) services.
The following are the features added in this module:
•RTCP passthrough for MTP, RSVP, and TRP agents
•RTCP passthrough for IPv6 and video calls
•RTP/RTCP port multiplexing
The following enhancements are aslo added to this module:
•RTCP Socket Bypass
RTCP provides statistics, feedback, keep alives, and collects metrics. It provides mechanism to convey Quality of Service (QoS) data about participants in an audio or video session.
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Information About Audio and Video RTCP Passthrough on ISR Gateways for MTP, TRP, and RSVP Agent Services" section.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Prerequisites for Audio and Video RTCP Passthrough on ISR Gateways for MTP, TRP, and RSVP Agent Services
•Cisco Unified Communications Manager (CUCM) Version 9.0
Restrictions for Audio and Video RTCP Passthrough on ISR Gateways for MTP, TRP, and RSVP Agent Services
•CME call-flows are not supported for RTCP passthrough.
•RTCP for transcoding call-flows is not supported.
•RTCP is not supported for conference calls.
•RTP/RTCP port multiplexing is not supported for SIP/H323.
•Any CUCM scenario that does not handle media is not supported. This includes the RSVP calls with IPv6.
•IPv6 for RSVP agent call-flows is not supported.
Information About Audio and Video RTCP Passthrough on ISR Gateways for MTP, TRP, and RSVP Agent Services
RTCP Passthrough for MTP, RSVP, TRP Services
RTCP passthrough will be supported for SWMTP, TRP, and RSVP call flows. HWMTP in passthrough mode (codec passthrough) will be supported for RTCP passthrough.
Media Termination Point (MTP) is a media device controlled by CUCM/CUCME using Skinny Client Control Protocol (SCCP), and provides services such as transcoding, adhoc conference, and software MTP to CallManager. It bridges RTP streams between two or more endpoints, and allows setup and teardown of the connections independently by CallManager.
A Trusted Relay Point (TRP) is a software function that runs on Cisco network devices and is dynamically inserted in the call flow by CallManager when requested. The function is similar to an MTP, but a new name is used to distinguish the way it is being utilized that will extend the behavior beyond the MTP.
The following are the main functions of the TRP agent:
•UC Trusted QoS Enforcement
•UC Trusted VLAN Traversal
•UC Trusted Firewall Traversal
The RSVP agent enables CUCM to provide resource reservation for voice and video media to ensure QoS and call admission control (CAC). CUCM controls the RSVP agent through SCCP. This signaling is independent of the signaling protocol used for the call so SCCP, SIP, H.323, and MGCP calls can all use the RSVP agent.
There would be no extra bandwidth support for the RTCP channel that is enabled because of RTCP passthrough. RTCP traffic is very minimal (5% of RTP traffic) and is generally not counted for the bandwidth calculation.
RTCP Passthrough for IPv6 and Video Calls
RTCP passthrough support will be added for video calls for both IPv4 and IPv6. Support is also extended to IPv6 call flows involving MTP and TRP agents. However, IPv6 for RSVP agent call flows is not supported.
RTP/RTCP Port Multiplexing
An RTP session comprises data packets (RTP) and periodic control packets (RTCP) as described in RFC3550. This RFC does not specify any mechanism for multiplexing the RTP and RTCP packets for the RTP session, and this is deferred to the underlying transport protocol. This was done to keep the implementation simple and efficient and to avoid privacy issues in a multicast session. At the transport layer, the multiplexing was carried out using separate ports (UDP) for RTP and RTCP packets.
One drawback in using separate UDP ports for the RTP/RTCP is that it requires opening of multiple pinholes (for NAT and firewall), and requires complex signaling. RFC5761 proposes a mechanism to multiplex the RTP/RTCP by using the RTCP packet type field occupying the same position as combination of the RTP marker (M) bit (bit 8) and the payload type (PT) field (bits 9 to 15).
Because RTCP packet types 200 to 207 are supported, this means there would be a direct conflict with RTP payload type 72 to 79 with the marker bit set to 1.
VOIP RTP functionality will be restructured and broken down in to different modules. This will remove duplicated functionalities and improve compile-time and run-time performance. Restructuring also helps merge the port management functionality.
RTCP Socket Bypass
Processing the RTCP packets in the fast path or process path eliminates the need for a socket which helps improve processing performance and save system resource. It minimizes processing overhead because the packet is already received at the fast path or process path.
This feature has been tested on the following platforms:
How to Display RTP/RTCP Packet Count
The show voip rtp connections [detail] command is modified to display the RTP and RTCP packet counts per VOIP RTP stream.
Verifying RTP/RTCP Packet Count
To display the RTP and RTCP packet counts per VOIP RTP stream, perform the following steps:
2. show voip rtp connections [detail]
The following example displays the RTP and RTCP packet counts per VOIP RTP stream:Router> enableRouter# show voip rtp connection detailVoIP RTP active connections :No. CallId dstCallId LocalRTP RmtRTP LocalIP RemoteIP1 282 284 18100 16474 126.96.36.199 188.8.131.52callId 282 (dir=2): called= calling= redirect= loopback=NO RTP(tx:386/rx:14011) RTCP(tx:44/rx:196)peer callId 284: called= calling= redirect=1 context 11B xmitFunc 611046D02 283 284 17074 18540 184.108.40.206 220.127.116.11callId 283 (dir=2): called= calling= redirect= loopback=NO RTP(tx:14011/rx:386) RTCP(tx:196/rx:44)peer callId 284: called= calling= redirect=
Configuration Examples for Audio and Video RTCP Passthrough on ISR Gateways for MTP, TRP, and RSVP Agent Services
There are no new configuration commands required to enable the RTCP passthrough.
Where to Go Next
Related configurations are done in the CUCM 9.0 Release. For the updated CUCM documentation, see http://www.cisco.com/en/US/products/sw/voicesw/ps556/prod_maintenance_guides_list.html. For more information about the show voip rtp connections command, see http://www.cisco.com/en/US/docs/ios/ipv6/command/reference/ipv6_16.html#wp2683095.
Related Topic Document Title
Cisco IOS commands
No new or modified standards are supported and support for existing standards has not been modified.
MIB MIBs Link
No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.
RTP: A Transport Protocol for Real-Time Applications
Extended RTP Profile for Real-time Transport Control
Feature Information for Audio and Video RTCP Passthrough on ISR Gateways for MTP, TRP, and RSVP Agent Services
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Note Table 1 lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
CUCM—Cisco Unified Call Manager
MTP—Media Termination Point
NAT—Network Address Translation
RSVP—Resource Reservation Protocol
SCCP—Skinny Call Control Protocol
TRP—Trusted Relay Point
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