Video on Frame Relay Tandberg D11624 rev 01
Tandberg Video on Frame Relay Table of Contents 1. Introduction ...............................................................................................................................................3 2. Background on transmission of video over frame relay.............................................................................4 3. Technical issues .........................................................................................................................................5 4.
Tandberg Video on Frame Relay 1. Introduction This document is designed as an 'eye-opener' to video over frame relay and the idea is to show a solution that works. The equipment described in this document is the VFX-250S, a framer unit from Science Dynamics Corporation. Tandberg video conferencing codecs are being used over frame relay together with this equipment and according to the setup described here. The setup has been tested and found reliable and it works well.
Tandberg Video on Frame Relay 2. Background on transmission of video over frame relay The successful transmission of digitised voice over public frame relay data services the past few years has drawn attention to the question of whether video services can be transmitted over the same link. Voice, data & video over frame relay Digitised Video is not new. It has been used for several years by a myriad of users on ISDN or leased line connections.
Tandberg Video on Frame Relay 3. Technical issues There are two potential technical issues, which may affect the quality of packetised, digitised video. One is delay, or more properly jitter. Jitter is the variation in delay from one frame to the next. This is critical for video, as video requires a constant bit stream in order to maintain an image. The second is dropped frames. If a video frame is lost, it may cause a click or pop in the audio and some pixelation on the video.
Tandberg Video on Frame Relay Cell based systems cut packet into fixed sizes Dropped frames are potentially a more serious problem. The frame relay standard allows the network service provider to control congestion by simply disposing of any frames which exceed the users CIR. In other words, if you contract for a CIR of 128 kbps but send a burst at 192 kbps, frames which exceed the 128 kbps CIR will have a DE (Discard Eligible) bit set.
Tandberg Video on Frame Relay 2. The second method is to establish a traffic prioritisation scheme for any channels carrying video through a FRAD (Frame Relay Access Devices) on a defined DLCI. This ensures that video frames are first out. Therefore, intelligent buffer management ensures video frames, which are less tolerant of delay, have priority over data frames which can usually tolerate some delay. 4. Equipment for Video over Frame Relay There are many H.
Tandberg Video on Frame Relay framer both at the ACT-recommended setting of 256 bytes and at 1.500 bytes (which is in line with the recommendations of other framer users) without any difference in the overall performance. You can connect either the VFX-250S or the ABL VT2C directly to a DSU/CSU on a frame relay network.
Tandberg Video on Frame Relay 6. Application Overview The diagram below shows the use of the VFX-250S in a video-conferencing over frame relay application. In this application the VFX-250S takes the H.320 datastream from the end point video-conferencing equipment and packetises it into a frame relay format for transmission over the network. This application also includes a MCU (Multi-point Conferencing Unit) which can interface with multiple VFX-250S units. D11624 rev.
Tandberg Video on Frame Relay 7. Technical Specification of VFX-250S 7.1 Network & User Interface Connector: Female 37-pin D type to user equipment (Video codec) Male 37-pin D type to network equipment (FRAD) Interface: RS449 (X.21, V.35 and others with adapter cables) RS422 balanced drivers and receivers and RS423 receivers 7.
Tandberg Video on Frame Relay • 4 configuration entries, each of which contains TX and RX DLCI settings, User Clock Speed, Packet Length, and AVB • LMI type control selection & parameter entry (ITU Annex A, ANSI Annex D, Frame Relay Forum, or Off) • Master, Slave, or Auto-assign settings for Enhanced Buffer Management • Local/Remote loopback facilities Memory: 4 configuration entries are maintained within the memory of the VFX-250S.
Tandberg Video on Frame Relay 8. Approvals FCC Class A Digital Devices and Peripherals This equipment has been tested and found to comply with the limits for a Class A digital device, pursuant to Part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment.
Tandberg Video on Frame Relay 10. Economics of Video over Frame Relay The economics of video over frame relay are similar to those driving the use of voice over frame relay. Voice over frame relay is fairly well accepted as being economical when used in international applications. With international ISDN call prices frequently exceeding $1 per minute per line, the payback period for voice or video over frame relay, even with the higher international rates for frame relay, are dramatic.
Tandberg Video on Frame Relay 11. Appendix A: Cables and Pinouts 11.1 Standard Console Cable The console port on the VFX-250S conforms to EIA-232/V.24 electrical specifications. D11624 rev.
Tandberg Video on Frame Relay 11.2 Standard EIA-449/RS449 Cables 11.2.1 Network Cable 11.2.2 User Cable A note about RTS signalling: Some manufacturers state that their network interface is RS449 (which uses RS422 signalling levels) but actually use RS423 signals for the control leads. If this is the case, then check the position of the RTS straps on page 11. D11624 rev.
Tandberg Video on Frame Relay 11.3 Standard EIA-530/RS530 Cables 11.3.1 Network Cable 11.3.2 User Cable D11624 rev.
Tandberg Video on Frame Relay 11.4 Standard V.35 Cables 11.4.1 Network Cable 11.4.2 User Cable D11624 rev.
Tandberg Video on Frame Relay 12. Appendix C: Glossary and abbreviations AVB - Automatic Variable Buffer. Buffering - This is a term used to describe a method where data is held in a queue to allow equalisation of speeds on either side. CIR - Committed Information Rate Codec - A device, which takes an analogue or digital video signal and converts it into a serial data bit-stream compatible with a standard data-communications infrastructure.
Tandberg Video on Frame Relay - This is a Videoconferencing term, which is used to identify picture break-up. Digital video pictures are made up of 1000’s of pixels, each representing a colour on the image. In videoconferencing, pixels are grouped into blocks (the number of which is determined by the speed of the link). Pixelation is a term often used to describe an image, which has errors in the colours of these blocks, creating obvious squares of wrong colour on the screen. QoS - Quality of Service.
