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Fax transmission made easy.

In the past, small network designers worked at a disadvantage since they could not effectively use a broadband strategy in their network designs. Unlike larger T1 networks with multiple link strategies, small network designers were limited to multiple dedicated lines, an expensive network strategy.

Further, networking equipment that provided economies of scale in larger networks could not be cost justified for a small one.

While T1 local loop costs have remained relatively the same, competition among major carriers has brought the cost of a fractional T1 strategy within the budgetary limits of small network planners.

Applications such as videoconferencing, CAD/CAM, or imaging, which use 384 or 512 kb/s, are now within the reach of the small network planner.

Competitive F-T1 service and inexpensive multiplexing equipment can now be combined into cost effective deployment strategies. A network strategy deploying F-T1 IXC links with digital access at the local level now provides a far more cost effective solution for small networks than ever before.

Most offerings are in the form of single DSO (64 kb/s) or multiple DSO channels (128 kb/s to 768 kb/s). While local carriers presently require full T1 local loops to provision F-T1 service, this requirement is expected to change as analog voice grade lines and DDS service migrate to F-T1 links.

AT&T offers an array of enhanced services through their spectrum of intelligent network services. Their ASDS service, provisioned through a digital inter-office channel, allows users to tailor F-T1 service to specific needs and pay only for bandwidth actually used.

F-T1 service can be ordered as contiguous time slotted groups of DSO channels for some applications (video, imaging) or in multiples of 2, 4, 6, 8 or 12 channels.

For some applications, contiguous DSO channels may not be required. These would be routed separately via DACS grooming and assigned to separate DSI channels for transportation over inter-office channels.

The AT&T network supports either 56 kb/s or 64 kb/s through their Clear Channel Capability which provides much better throughput. However, customer premise equipment must support either B8ZS or Alternate Channel Alternate Mark Inversion (ACAMI) line coding.

Connecting remote locations

Typically a small network will link remote locations using dedicated point to point circuits between their host and the remote locations. A typical configuration deploys F-T1 service on the IXC portion of the network.

However, with this network arrangement, the planner can define four DSO channels on the IXC F=T1 link instead of deploying dedicated point to point circuits. In this situation, the user had a requirement for a total of 256 kb/s of non-contiguous bandwidth which could be fanned out at the remote end using M24 multiplexing.

Consequently, the user was able to contain costs for transporting data between remote locations providing 128 kb/s of bandwidth for the minicomputer link, and 64 kb/s links between a remote PBX and a terminal controller.

Developing fax relay network

In this example, multiple DDS and VGPL circuits are used between locations.

However, by deploying a single ASDS F-T1 link on the IXC portion of the network, the planner is able to reduce recurring IXC network costs by as much as 25% on end to end service. In addition, deployment of multiplexing equipment enabled the network planner to increase the number of tie lines and provide other improved services.

The planner first installed a local T1 loop into the CO linked to an AT&T Paradyne 740 multiplexer. This allowed the planner to interface directly with AT&T's ASDS service and four 64 kb/s IXC links provisioned via a F-T1 link.

These four non-contiguous 64 kb/s links were used to interface the host and PBX at the headquarters end with the public network and three remote plants in a city some 500 miles distant.

Next the planner added Advanced Compression Technology's SDM-T mux which utilizes advanced bit compression technology to pack both voice and data over a single digital channel.

In this application the planner configured two 64 kb/s channels through the ACT SDM-T multiplexer, which provided the equivalent of four voice channels at 16 kb/s plus four data at 9.6 b/s and two at 2.4 b/s.

In addition fax relay cards were added which allow transmission of Group III fax at 9600 b/s.

The cards provided a unique "on net/off net" switching capability, allowing remote locations to be dialed through the SDM-T's card at the distant end.

This fax relay feature permitted customers and vendors at the distant city end to send on-net fax transmissions to headquarters by dialing the listed number for the fax machine at the other location. This allows transmission of fax traffic between headquarters, remote plants, and customers in the same area code as the remote plants.

The SDM-T mux also allowed the network planner to increase the effective number of E&M tie lines by four, add six additional subrate data channels and incorporate a fax relay network on only two 64 kb/s channels.

Through effective deployment of network compatible equipment, the planner was able to pack on to 256 kb/s of bandwidth the equivalent of more than 768 kb/s of bandwidth.
COPYRIGHT 1992 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1992 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Modems & Muxes
Author:Llana, Andres
Publication:Communications News
Date:Feb 1, 1992
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