Cisco CallManager Release 4.0 added support for video in both the SCCP and H.323 protocol. You can make calls between SCCP clients, between H.323 clients, and between SCCP and H.323 clients.
H.323 and SCCP endpoints have these characteristics:
- Computer telephony integration (CTI) applications (Telephony Application Programming Interface [TAPI] and Java TAPI [JTAPI])
- Media Gateway Control Protocol (MGCP)
Table 28-2 summarizes the key differences between H.323 and SCCP endpoints.
Register with Cisco CallManager
Register with H.323 gatekeeper
Send dialed number digit-by-digit
Send entire dialed number at once
Are configured in Cisco CallManager Administration
Are configured through user interface
Advertise their capabilities when registering
Advertise their capabilities on a call-by-call basis
Offer PBX-style features
Offer basic call capabilities in interaction with Cisco CallManager
SCCP Video Call Characteristics
If a call is placed from an SCCP phone that reported video capabilities to Cisco CallManager and the other end supports video as well (another SCCP phone with video capabilities or an H.323 device), Cisco CallManager automatically signals the call as a video call. The amount of bandwidth the call can consume is determined by your region configuration. The system does not ask users for bit rate.
In Cisco CallManager Release 4.1, H.264 support was added for SCCP video devices. H.264 contains a number of features that allow it to compress video much more effectively than older codecs. This capability allows H.264 to deliver better video call quality over less bandwidth. Cisco CallManager supports the H.261 and H.263+ codecs as well. In addition, Cisco CallManager Release 4.1 supports the audio codecs G.711, G.722, G.723.1, G.728, G.729, Cisco Wideband codec, and Global System for Mobile Communications (GSM). The wideband video codec of Cisco VT Camera reduces PC CPU utilization, unlike the resource-intensive H.263 and H.264 codecs. However, you will sacrifice a significant amount of bandwidth when using the wideband codec. For this reason, you will use this codec primarily in LANs, not over WAN links.
Cisco CallManager uses out-of-band H.245 alphanumeric dual-tone multifrequency (DTMF). DTMF might not work between SCCP and third-party H.323 devices because many H.323 devices pass DTMF in-band.
H.323 Video Call Characteristics
Call forwarding, dial plan, and other call routingrelated features work with H.323 endpoints. During all this, the Cisco CallManager remains the central call-routing intelligence. In Cisco CallManager, H.323 endpoints can be configured as H.323 terminals, H.323 gateways, or H.323 trunks. Many H.323 devices request a gatekeeper for registration.
Some vendors implement call setup such that they cannot increase the bandwidth of a call when the call is transferred or redirected. In such cases, if the initial call is audio, users might not receive video when they are transferred to a video endpoint.
Video H.323 clients that use trunks to other Cisco CallManager systems or other H.323 systems can use the same features as audio-only H.323 clients. Currently, neither video media termination points (MTPs) nor video transcoders exist. If an audio transcoder or MTP is required for a call, that call will be audio only. H.323 video endpoints cannot initiate hold, resume, transfer, park, or offer other similar features. Only if an H.323 endpoint supports ECS can the endpoint be held, parked, and so on.
Dynamic H.323 addressing within Cisco CallManager provides a facility to register H.323 video terminals on Cisco CallManager when the video terminal receives its IP address through a Dynamic Host Configuration Protocol (DHCP) server. Endpoints are tracked based on their E.164 address registration with an adjacent video gatekeeper. The E.164 address is a static identifier that remains constant from the perspective of both gatekeeper and Cisco CallManager. The feature became available with Cisco CallManager Release 4.1. To move to a converged voice and video dial plan, it is highly desirable that Cisco CallManager become the entity that manages call routing and digit manipulation for both the voice and video endpoints, regardless of call-signaling protocol. Earlier releases of Cisco CallManager required that an H.323 video terminal be configured on Cisco CallManager based on static IP address information. As a support and mobility issue, this design could not facilitate a scalable method for endpoint management because configuration information was accurate only as long as the DHCP lease did not expire with the endpoint in question.
Cisco CallManager Release 4.1 supports H.261 and H.263 when using H.323-based video endpoints; H.264 is supported only for SCCP endpoints. H.323 video clients support the voice codecs G.711, G.722, G.723.1, G.728, and G.729. H.323 endpoints can also support far-end camera control (FECC). FECC enables a user to control the camera of the far side during an active video call. For FECC, two separate, unidirectional RTP streams are set up. This feature was introduced in H.323 version 5 (H.323v5) as Annex Q.
Cisco CallManager uses out-of-band H.245 alphanumeric DTMF. DTMF might not work because many H.323 devices pass DTMF in-band. If an H.323 device uses in-band DTMF signaling, Cisco CallManager will not convert it to out-of-band signaling, and the DTMF signaling will fail. Both sides need to use a common scheme; either both devices need to use out-of-band signaling or the H.323 device needs to support both methods and autodetect the method it should use.
SCCP and H.323 in Cisco CallManager
The call-related features of the Cisco IP video telephony integration strongly depend on the protocol in use. FECC, for example, is an H.323 feature supported only by H.323 devices and is not available on SCCP devices. Videoconferencing with three or more parties on a call requires an MCU. The Cisco IP/VC 3540 MCU supports both protocol stacks: H.323 and SCCP. This can be configured in the MCU Administration window.
The Cisco IP/VC 3521 and 3526 videoconferencing gateways bridge the gap between the installed base of ISDN videoconferencing group and room systems and IP-based H.323 systems. The gateways connect H.320 video systems on ISDN to H.323 systems on IP by translating calls initiated from the PSTN to their equivalent on the packet network, and vice versa. To enable SCCP to call H.320 endpoints, an H.323-based video gateway is necessary as well.
Beginning in Cisco CallManager Release 4.1, mid-call video is supported. Mid-call video allows an active voice call to become a video call if the video capabilities are added during the active call (for instance, if the Cisco VT Advantage software is turned on). Cisco VT Advantage will then associate with the phone and try to set up a video stream. If both parties are SCCP video endpoints, the call immediately becomes a video call. If the other party is an H.323 endpoint, the SCCP endpoint tries to request a video channel. If the H.323 endpoint rejects the incoming channel or does not open a channel, the call becomes either one-way video or audio only.
Part I: Cisco CallManager Fundamentals
Introduction to Cisco Unified Communications and Cisco Unified CallManager
Cisco Unified CallManager Clustering and Deployment Options
Cisco Unified CallManager Installation and Upgrades
Part II: IPT Devices and Users
Cisco IP Phones and Other User Devices
Configuring Cisco Unified CallManager to Support IP Phones
Cisco IP Telephony Users
Cisco Bulk Administration Tool
Part III: IPT Network Integration and Route Plan
Cisco Catalyst Switches
Configuring Cisco Gateways and Trunks
Cisco Unified CallManager Route Plan Basics
Cisco Unified CallManager Advanced Route Plans
Configuring Hunt Groups and Call Coverage
Implementing Telephony Call Restrictions and Control
Implementing Multiple-Site Deployments
Part IV: VoIP Features
Configuring User Features, Part 1
Configuring User Features, Part 2
Configuring Cisco Unified CallManager Attendant Console
Configuring Cisco IP Manager Assistant
Part V: IPT Security
Securing the Windows Operating System
Securing Cisco Unified CallManager Administration
Preventing Toll Fraud
Hardening the IP Phone
Understanding Cryptographic Fundamentals
Understanding the Public Key Infrastructure
Understanding Cisco IP Telephony Authentication and Encryption Fundamentals
Configuring Cisco IP Telephony Authentication and Encryption
Part VI: IP Video
Introducing IP Video Telephony
Configuring Cisco VT Advantage
Part VII: IPT Management
Introducing Database Tools and Cisco Unified CallManager Serviceability
Configuring Alarms and Traces
Using Additional Management and Monitoring Tools
Part VIII: Appendix
Appendix A. Answers to Review Questions