Application ISDN LAN's
File Transfer Various standards Internet or OSI standards
Information Services Proprietary or via World Any networkable information with multimedia content Wide Web (WWW) system or WWW technology
Multimedia Mail Based on H.320 video X.400 and MIME electronic conferencing mail with video content
Image Databases Proprietary systems File Server access
Information Kiosks Proprietary systems
Distance Learning Remote access to file server File Server Access
Existing file transfer protocols can be used. These may be XModem, and YModem in the case of asynchronous transfers or the Internet FTP as used over LANs and WANS. Either asynchronous communications software such as Crosstalk, Procomm or LAN TCP/IP applications such as FTP are needed.
Or file transfer protocols specifically written for ISDN can be used, using proprietary protocols or the emerging Eurofile standard. Data rates of about 1 Mbyte per minute are obtainable on an ISDN2 line.
The interesting feature of ISDN for World Wide Web users is that an ISDN channel offers at least 64 kbps which is dedicated to one user. ISDN in the narrow band form is the most widely available access and delivery medium available. Using remote LAN access products running TCP/IP, it is also relatively easy to implement.
ISDN is seen by many in the industry as the ramp through which multimedia networking will gain acceptance. The installed base of ISDN is growing rapidly (30,000 line per month in Germany). ISDN is able to provide connections throughout the world. In Europe there are 'Euro-ISDN' agreements between operators. In the USA the use of the Web is driving the growth of ISDN in some states.
Although ISDN could be cheaper, particularly in the UK, it is likely to be cheaper than ATM connections and more widespread in availability for a long time. ISDN will be the feeder network for broadband ISDN based on ATM standards. The idea that multimedia can only be delivered on broadband networks is erroneous as the assertion that only a Macintosh can deliver multimedia.
There are a number of issues in ISDN access to the World Wide Web. The relatively high cost of ISDN in the UK means that the user or organisation must carefully assess the cost effectiveness of their use of the Web over ISDN and participation with other organisations via LAN to LAN connections. The design of Web pages should make economic use of the ISDN call charging regime. This means that large images may need to be avoided, the size of a Web page in bytes can be dimensioned to fit within a call charging unit, and if your client can down load second level hyper-links response times would improve.
There are still major problems of software and hardware compatibility between different ISDN products. The cost of these products is still high but falling. ISDN access to World Wide Web servers on a LAN can be implemented in two ways, routing and bridging.
A Bridge is used to connect two different LAN's that use the same LAN protocol such as Novell IPX or TCP/IP. The bridge acts as an address filter, picking up packets from one LAN and passing on those packets intended for the other LAN. A bridge does not modify the packets or add anything to them. A bridge operates at the data link, Level 2 of the OSI model. A bridge uses the Media Access Control level addresses on LAN adapters to direct packets.
A Router is used to connect two networks that may not use the same LAN protocol. A router uses an inter-networking protocol which is understood by other routers and machines connected to each network. A router operates at the Network, Level 3 of the OSI model. A router uses an addressing scheme such as the Internet address scheme to direct packets.
ISDN connected LAN's can use either bridges or routers. Remote access to these LAN's is achieved by enabling the remote workstation to pretend that it is directly connected to the LAN.
Both routers and bridges need to provide basic functions to ensure reliability and security of data. The use of a bridge or router over ISDN also requires some additional mechanisms to reduce the cost of making unnecessary calls on the ISDN. At present this is implemented by 'spoofing' or fooling a LAN that wishes to send these packets to a remote LAN into thinking that these packets have actually been transmitted.
To connect LAN's which are closely coupled and within one organisation a bridge has some advantages and may give better performance. To connect LAN's operating between different organisations a router enables more effective management of addressing schemes and security.
The most efficient way to interconnect LAN's or remotely attach a workstation via a dial up connection such as ISDN is by use of the Point to Point Protocol.
At the end of 1994 about 27 suppliers had a bridge or routing product for ISDN. There are also a shareware PC based , and UNIX routers which may be able to be used over the ISDN. Some companies also provide a multiple serial line solution for access to a central host. The results of a survey by the Manchester ISDN Partnership [MIP95] indicate the following :-
Performance The use of ISDN to connect LANs and enable remote access to LANs and LAN based services is feasible and offers bit rates to users of up to 128 kbps, which is adequate for many sorts of computer based 'multimedia' sessions.
Costs The running cost of LAN to LAN and remote access connections would be considerably reduced if BT implemented a per second charging scheme. The cost to remote users, of hardware and software is still too high for widespread use of the equipment by small companies. Cheaper ISDN products are available on the German market, but are only just beginning to appear in the UK.
Standardisation The implementation of the de-facto ISDN channel bonding standard is necessary for remote users requiring high performance. Standardisation of asynchronous use of Terminal Adapters above the speed of 19.2 kbps would enable a greater degree of high speed inter-working with ISDN routers equipped with 115 kbps Terminal adapters.
Inter-operability The availability of remote workstation synchronous access via PC cards to a an ISDN LAN router using PPP software would enable some degree of inter-working for remote users of different routers.
The implementation of remote access using TCP/IP protocols by router manufacturers is often tied to on software companies TCP/IP 'stack'. Router manufactures need to provide more options for users to use their existing TCP/IP software, which may be different from that used by the manufacturers. An inter - operability test facility for ISDN routers using PPP and remote access solutions would be beneficial to users. There are already limited claims of inter-operability by AVM with other products.
The most promising products are, in alphabetical order :-
ACOTECH ISDN for Workgroups, AVM Multiple Protocol Router, with Netways remote access. EU-Systems Maxpro Multiple Protocol Router, Jaguar Nile ISDN Router, KNX ISIS Bridge and remote access, Sonix Arpegio Ethernet ISDN Bridge, Spider Networks Pico and Mezza with remote access using Spider Integrator, Telebit Netblazer.
Graphics Multimedia Virtual Environments Visualisation Contents