A Review of Multimedia Networking

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7.4. Iso-Ethernet

Architecturally, Iso-Ethernet, also known as IEEE 802.9 [Minoli94] is a multiplexing of four separate channels of information: a 10 Mbps packet channel (P) with the IEE 802.3 CSMA/CD media access protocol, 6.144 Mbps of isochronous information organised in 96 B channels of 64 kbps each, one 64 kbps D-channel for signalling, and a 96 kbps M-channel for maintenance. Additionally framing is added to allow for synchronisation with a wide area network. The complete data stream is modulated with 4B/5B coding. The total bandwidth is similar to that used in 10Base-T Ethernet so require similar cable technology and hardware to existing Ethernet systems. A typical network will consist of Iso-Ethernet terminals connected to LAN hubs. The hubs may be connected by a backbone network.

Iso-Ethernet combines the best properties of current IEE 802 LAN and ISDN networks. Multimedia applications requiring isochronous channels can use any combination of ISDN B channels for audio and video according to the desired quality requested. Wide area interfaces from synchronous data channels such as Megastream or SMDS can be connected to the Iso-Ethernet Hub. Narrow band basic rate ISDN and Primary rate ISDN can provide Wide Area connections using Q.931 signalling. ATM protocols can be added. The cost of Iso-Ethernet connections will be targeted to be competitive with existing high speed Ethernet cards.

At least one video conferencing application developer has an interface in development for this type of LAN.

7.5. Proprietary LANs

To enable video conferencing over existing LAN cabling some vendors have adopted proprietary solutions which replace the existing network hardware, but retain the cable infrastructure. On example is the C-Phone system [Griffin94] which uses additional modulation above the 10 Mbps Ethernet spectrum to carry video and audio channels. Another technique is the emulation of ISDN over Ethernet CSMA/CD employed by TELES [Schindler94]. This is satisfactory for the video component of video conferencing but the audio component must be carried over the telephone.

Such solutions are of limited applicability and have been superseded by the Iso-Ethernet LAN.

7.6. Local ATM

ATM is really a network protocol because it operates at layer 2 of the OSI model. The physical transport of ATM has been standardised for fibre optics at 155 Mbps, 100 Mbps and synchronous digital networks. Standards are recently been approved for 51 Mbps and IBM with about 20 other vendors has re-submitted a proposal for 25 Mbps ATM transport.

The implementation of an local ATM network requires an ATM switch connected to a high speed backbone. Initially users can remain on 10 Mbps Ethernet segments connected to the ATM switch. As requirements rise, direct higher speed native ATM connections can be provided. Use of existing applications that run well over Ethernet should be possible in the connection-less ATM class of service. effectively emulating an Ethernet LAN.

While some organisations will be able to provide optical fibre to the desk top for delivery of 155 Mbps, many have unshielded twisted pair (UTP) Ethernet LANs. The 25 Mbps specification may be worthwhile implementing in such situations if the cost of adapter cards and ATM switches is comparable with quality Ethernet cards. It is likely that the cost of implementing 51 Mbps over twisted pair cables will be considerably higher [CT95].

One such ATM adapter card for an ISA bus PC is able to operate over Category 3 UTP wiring. It provides NDIS-3 , ODI and native ATM socket type application programming interfaces. It is anticipated to cost around $400.

One pair of a cable is used for transmission, another for reception and token ring technology. ATM service classes are implemented in part by allowing different priority queues. Transmission is compatible with 16 Mbps Token ring physical components. A switch to support the adapters is available with 12 ports. Two port 155 Mbps modules are available for trunk connections. An Ethernet transparency module permits LAN emulation.

Obviously this type of low cost ATM implementation is very new and will require evaluation, but other vendors are certain to follow, so the option of low cost local ATM is a real possibility. At least one video conferencing application developer has an interface in development for this type of LAN.

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Graphics Multimedia Virtual Environments Visualisation Contents