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Telepresence Communications Links

Some form of data communications network is needed between the User of a Telepresence system and the Remote Site to transmit video, audio and control signals. We have experimented with many different communications systems, each with their own advantages and disadvantages. In addition, if broadband cable/broadcast is not available, some form of Video Compression and Audio Compression is needed.

Communications systems we have experimented with include:

ISDN
9.6K GSM Mobile Telephones
19.2K Multi-Link GSM Mobile Telephones
14.4, 28.8 and 33.6K Modems
10M Ethernet
The Internet

 

ISDN

Original long distance telepresence experiments were conducted using an ISDN line. A British Telecom VC7000 video conferencing terminal was used to compress video at the Remote Site which was transmitted via ISDN. At the Users Site, another VC7000 decompressed the video for display on a VR Headset. The VC7000 also allowed control signals sent via a pseudo RS232 link over the ISDN link. ISDN offers high bandwidth (64Kbits) but requires special installation of telephone lines and ties you to a fixed location.

vc7000_comms.jpg (7164 bytes)
VC7000 Videophone


GSM Mobile Telephone

In order to allow free roaming telepresence, the group teamed up with Orange, a UK mobile telephone company. Using Orange's GSM phones, we are now able to demonstrate telepresence from anywhere in the world with GSM coverage. The mobile phone acts as a 9.6Kbits modem and can connect to another mobile phone or a standard telephone modem. Using mobile phones on both remote and local telepresence sites allows untethered operation at both ends of the communications link.

The Computer Science Department at Strathclyde University have developed a unique Video Compression CODEC suited to low bandwidth links, such as the mobile phones. Video and control signals are sent via the phones and users have been able to be telepresent in our Glasgow lab from numerous locations in the UK, as well as Boston in the US by using an Orange mobile phone with roaming capability.

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Toshiba Libretto and
Orange Mobile phone


19.2K Multi-Link GSM Mobile Telephones

[Comment: Picture of serious laptop with two mobiles]

A single Mobile Phone link restricts us to 9.6KBits of data per second. In order to increase this, thus improving the video quality, we have developed a system using two mobile phones running in parallel. The data transmitted is shared between the two phones, giving a 19.2K bits channel. This also acts as a safety feature. If one phone drops its line, the connection from User to Remote Site is not lost. The other mobile phone keeps going, leaving us a single 9.6Kbits channel. The failed phone can redial and reconnect, restoring the 19.2Kbits link.


14.4, 28.8 and 33.6K Modems

[Comment: Picture of Desktop PC running contoller software]

Where the User and the Remote Site are near telephone lines, we can swap the 9.6K Mobile phones, for 33.6K modems, raising the bandwidth, allowing for better quality compressed video. It also lowers the latency through the communications system.


Standard Ethernet

Within our laboratory, we are able to connect our Remote Site equipment and user's equipment to a 10Mbits ethernet. This allows very high bandwidth situations to be tested. We can also restrict the bandwidth to simulate the effects of the other communications systems.


The Internet

[Comment: picture of some aspect of the WWW - globe or whatever]

By making the Remote Site a server connected to the Internet, we have been able to link up from anywhere in the world via the Internet. In the US, we connected a desktop PC to the Internet via an AOL account. We were able to connect to the Remote Site server on Glasgow and send the video and control signals via the Internet. By using Mobile Phones at the Remote Site to dial into an Internet Service Providor, anyone who can connect to the Internet can communiate with the remote site. There are problems of varying delays, latencies and bandwidths, but by selecting a low bandwidth, these usual internet bottlenecks can be minimised.


Protocols

We are experimenting with various protocols over the mobile phones. Our current configutation uses a TCP/IP link between the Users Site and the Remote Site. The PPP protocol is used on standard modem links; mobile phone users have the choice of using PPP or a custom protocol of our own design which minimizes overheads and maximises throughput over the GSM network.

Using TCP/IP allows us to rapidly switch from lab based ethernet setups, to Internet Connections, to dial-up model and mobile phone connections at ease. These protocols have their overheads and we are researching ways to reduce and remove overheads, increasing the bandwidth of the link. This is especially important at mobile phone bandwidths.


Video Compression

All the experiments (except ISDN) have used the University's own Video Compression CODEC which easily scales from very low (9.6K) to high (150K) bandwidths. By using our own CODEC, we can easily adapt to new situations.


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