ISDN Videoconferencing
- Understanding ISDN
- Call Charges
- Equipment Requirement
- ISDN Multipoint Videoconferencing
- Gatewayed Conferences
- Registration Details
- The JVCS Booking Service
- Using Videoconferencing
- Problem Resolution
- Further Information
ISDN is a service offered by telephone companies over the circuit switched network to support Voice, Telephone and Data Applications. This document will give an overview of H.320 protocols and outline the procedures for using JVCS-ISDN.
Background
The JANET Videoconferencing Service (JVCS) is currently operated by the JVCS Management Centre, which is located at the University of Edinburgh Computing Services. The service is operated under contract to JANET(UK) and is funded by the Joint Information Systems Committee (JISC). The JVCS came into service in September 1997 and allows any JANET organisation, school or content provider with suitable equipment to participate in a videoconference.
This service is for academic use, and is subject to the normal JANET Acceptable Use Guidelines. Further Education, and Research communities who have a JANET link. The service is also available to JANET linked schools and content providers for the duration of the Videoconferencing Services Project.
The JVCS currently provides videoconferencing over JANET, an IP network, using the International Telecommunications Union (ITU) Standard, ITU H.323 standard or via the Integrated Services Digital Network (ISDN), using the ITU H.320 standard.
The original local loop network provided only analogue connections via the Circuit Switched Telephone Network (CSTN) which limited the bandwidth to 3000 Hz. ISDN technology overcome bandwidth limitation and allowed network traffic to be transferred over the local loop by upgrading of switches. A Packet Switched Telephone Network over a Circuit Switched System proves to be very reliable and is still used today by many organisations for both networking and videconferencing.
There are two types of ISDN interface: Primary Rate ISDN (PRI) Interface and Basic Rate ISDN (BRI) interface.
A BRI is an ISDN interface that provides two 64Kbps B-channels and one D-channel. B-Channels carries the voice, video and data traffic over 64 Kbit/s bandwidth whilst D-Channels control the call set-up and termination and control of Data through the B Channels.
The B-Channels can be obtained at different rates of bandwidth: i.e. from the basic level consisting of two at 64 Kbit/s (128 Kbit/s in total) complete with a 16 Kbit/s D-Channel up to multiple known as the Basic Rate Interface (BRI); Up to multiple combinations which generally requires the use of an Inverse Multiplexer (IMUX). The bandwidth level required to experience the quality expected in industry would consist of three 128 Kbit/s BRI lines (384 Kbit/s). For an even greater quality experience 6 BRI lines (768 Kbit/s) can be used, however it should be noted the more lines used the greater the cost will be both in terms of line rental and call charges.
A PRI is an ISDN interface that provides either 23 B-channels also known as T1 (USA) or 30 B-channels also known as E1 (Europe) and one D-channel.
Most connections via JVCS are generally between a minimum of 2 lines and a maximum 6 lines. Organisations with multiple videoconferencing suites can divide up and allocate channels to each of the studios as appropriate.
JVCS-ISDN enables:
- Access to multipoint videoconferencing at ISDN 2, ISDN4 or ISDN 6.
- Dial-in to a core MCU
- A dial-in number, which will be like a phone number will be issued, by email to the organisation on a per conference basis. The uses should ensure that they have a copy of this number prior to the start of the videoconference, so that they can dial the number to join the conference.
- JVCS-ISDN makes use of 0870, national dial rate numbers for videoconferencing.
- The core service is free of charge. However, ISDN charges will be payable locally by the user to their ISDN service provider. ISDN call charges vary, depending on the service provider, the local user should check with their local administration department or service provider to ascertain the exact tariff for ISDN call charges.
- Some service providers charge 0870 numbers at a premium rate, therefore it may be more cost effective for the local users to dial an area code. Information about 0870 number mapping can be found here.
- JVCS can, in some circumstances, dial-out to ISDN endpoints and invoice an organisation within the UK for the call charges. Details of the JVCS-ISDN dial-out facility can be seen here.
- Institutions may use gateway services e.g. IP to ISDN dial-out or ISDN to ISDN dial-out to connect with organisations outside of the academic community.
To gain access to JVCS-ISDN you will need:
- Connection to the public ISDN network at ISDN 2, ISDN 4 or ISDN 6;
- A compatible COder DECoder (CODEC) with ISDN connectivity at ISDN 2, ISDN 4 or ISDN 6. A CODEC is a piece of equipment which converts the audio and video signals, from the microphones and camera, into a signal which can be transmitted over the ISDN transmission lines. The CODEC also converts the received H.320 ISDN signal into a recognised signal for distribution to the loudspeakers and monitor;
- Suitable video camera(s) to provide the video feed to the CODEC;
- Suitable microphone(s) to provide the audio feed to the CODEC;
- An echo canceller to stop distracting echo being heard during a videoconference. These are built into the latest generation of CODEC;
- Suitable display unit to view sent video;
- Suitable audio system to distribute sent audio.
In order to co-ordinate the JVCS facilities, the JVCS Management Centre runs the JVCS Booking Service, which logs all videoconference bookings. Videoconferences are booked on a first come, first served basis.
ISDN Multipoint Videoconferencing
A videoconference which involves several CODECs is called a multipoint videoconference. Multipoint videoconferencing is made possible by utilising a Multipoint Control Unit (MCU) which is, in its simplest form, a switch which distributes audio and video appropriately to all venues who participate in a single videoconference. The MCU switches between venues in two ways depending upon the mode it has been configured to operate in (either Voice Activated Video Switching or continuous presence).
In Voice Activated mode the view switches, so that all other venues see and hear the current speaker and the current speaker sees the person that last spoke.
In Continuous Presence mode a screen can be split into various layouts, so each site will see all other sites on the monitor. In this mode up to ten sites can be seen on the monitor at any single time, in the screen layout that was chosen at the time that the conference was booked. Where more than ten venues are involved in a videoconference, the view changes, so the most recent nine speakers can be seen.
To provide order in a meeting there are available two control mechanisms known as Chair Control and Lecture Style. Chair Control is a mechanism for passing control from site to site and a variation of this is Lecture Style where a designated site takes control and can enable and disable control access.
Fig. 2: A multipoint ISDN videoconference, with all the CODECs dialing into the MCU
A point-to-point conference between two ISDN CODECs can be established without the use of the MCU (as can a point-to-point conference between IP CODECS), all other configurations of conference will require the use of an MCU. The MCU can interconnect up to 68 CODECs participating in a single conference.
As well as videoconferencing with other venues using ISDN technology, it is also possible to communicate with venues which use other videoconferencing technologies on other networks, such as IP. To do this requires a gateway, which is a link from one videoconferencing technology to another.
The JVCS-ISDN provides multipoint videoconferencing over ISDN. This service also allows users to participate in multipoint videoconferences with other users who are making use of JVCS-IP and the H.323 protocol. Such videoconferences make use of a gateway, which provides a bridge between the two technologies. The gateways are integrated into the MCUs and are also managed by the JVCS Management Centre.
Gateways are automatically booked when venues on different networks are booked in the same videoconference. No additional booking is required.
Multipoint videoconferences can involve participants using H.320 and H.323 videoconferencing technologies which are interconnected as shown on the technology topology diagram below.
Fig. 3: Videoconferencing between ISDN (H.320) and IP (H.323) CODECs
All venues must register to connect to this service.
To ensure that there is an acceptable standard of conferencing on the JVCS all HE and FE venues have to pass a Quality Assurance (QA) test. For those in the schools sector there is a Quality Assurance Assessment (QAA). These are short tests carried out by the JVCS Management Centre which checks the audio and video quality of the venue's facilities. Once the QA test or QAA has been completed the venue will be able to take part in all JVCS booked conferences.
Videoconferencing resources are limited, you must pre-book your conference. Bookings are made on a first-come, first-served basis so it is advisable to book your conference as soon as is possible. A booking specifies a set of resources to be allocated at a certain time for a certain period. These periods of time, and the resources required, are presented to an on-line booking system via a WWW based form.
All bookings are recorded within an on-line JVCS Booking Service. Note that only registered users can make and alter bookings. For further information on the Booking System see PDFs below for User Guides and factsheets.
Booking Service User Guide (pdf)
Booking Service Factsheet (pdf)
A videoconference meeting requires more organisation than a face-to-face meeting and different skills. If you have never taken part in a videoconference before it is useful to sit in on a meeting and have someone show you how things work before you arrange your own videoconference.
In the event that a booked videoconference has problems relating to the non-establishment of a link or poor audio-visual quality, the local venue contact should be the initial contact. The local venue contact should investigate to determine if the fault is hardware or network related. If the fault appears to be network related, check the booking summary to ensure that the venue actually appears in the booked time. If there are any queries or if the fault cannot be rectified then the Management Centre should be contacted.
For help contact JVCS:
Telephone: 0131 650 4933
E-mail: vidconf@jvcs.video.ja.net
After any problem resolution the JVCS may request an unscheduled QA test.
- Further information about videoconferencing and videoconferencing service developments is available on the JANET Video Services page.