6.1 Applications of SHDSL

   


The definition of SHDSL was driven to support high capacity network access applications to business and small-medium enterprise customers. Such applications include T1 or E1 extension, fractional T1 or E1 access, wireless base station access to the central office, provisioning of multiple voice channels via a high-access channel (also referred to as a "pair-gain" access), work at home applications supporting data and digitized voice, campus applications, and others. The support of SHDSL for each of these applications is described below.

6.1.1 T1 or E1 Extension Application

A fundamental application of SHDSL is the equivalent to that of HDSL2. In North America, HDSL2 transports a DS1 (1.544 Mb/s) payload on a single twisted wire pair on loops that fall within the carrier serving area (CSA) limits of 9 kft of 26-gauge wire or 12 kft of 24-gauge wire. The block diagram in Figure 6.1 shows the use of SHDSL in the provisioning of a T1 access circuit, as is done using HDSL2. In the central office (CO), the T1 circuit is connected to the SHDSL unit via a DSX-1 interface. The T1 AMI interface circuit within the SHDSL central office unit converts the AMI signal into a 1.544 Mb/s bit-stream. At the customer premises, the SHDSL unit provides a T1 AMI interface to the end customer per the T1.403 DS1 standard. For this application, the SHDSL transceiver is configured to the parameters defined by the HDSL2 standard, which is included in Annex A (North American annex) of the SHDSL Recommendation G.991.2.

Figure 6.1. T1 extension application.

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SHDSL may also be used to provision an E1 (2.048 Mb/s) access circuit. In this case, the T1 AMI interface circuits shown in Figure 6.1 would be replaced by a G.703/G.704 interface circuit, and the SHDSL transceiver would need to be configured to support the payload bit rate of 2.048 kb/s (or 2.304 kb/s if the extra four 64 kb/s time slots are to be supported) [1, 2, 7] and the corresponding PSD in Annex B of G.991.2.

Fractional T1 access may be supported in the following manner. The DS1 circuit would contain predetermined time slots with active data, which the service operator provisions prior to service activation. The SHDSL transceiver takes only those active time slots from the DS1 circuit and transports them on the subscriber line at a bit rate that is less than the T1 rate of 1.544 Mb/s. The lower line bit rate allows for operation on longer loops than would be feasible with SHDSL transporting the full 1.544 Mb/s rate.

6.1.2 Connection of Wireless Base Station to Central Office

The application in Figure 6.2 shows SHDSL providing a transport of the voice channels in a wireless base station and feeding them to the nearby central office for switching or routing. Proper interface circuits would need to be defined for connecting the multiple voice channels into an SHDSL frame.

Figure 6.2. Transport application from wireless base station to central office.

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6.1.3 Campus Applications

SHDSL transceivers may also be applied to limited distance modem applications in a campus environment. In this case, the public network is not utilized. An example of campus application is shown in Figure 6.3. SHDSL modems may be configured with proper interfaces to interconnect local area networks and PBXs located within different buildings on a campus. The distance between buildings would determine the maximum bit rate configurable for the SHDSL transceivers.

Figure 6.3. Campus private network application.

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6.1.4 Provisioning of Multiple Voice Circuits

In situations where there may be a shortage of wire pairs, SHDSL transceivers may be used to transport multiple digitized voice channels on a single wire pair, as shown in Figure 6.4. At the remote location, the individual digitized voice channels would be converted back to analog voice signals and provisioned on individual wire pairs to the end subscriber. An example would be that one wire pair feeds a building that is a two-family residence. An SHDSL access line could be provisioned to transport four digitized voice channels where two voice channels could be made available to each unit in the two-family residence. Note that in such an application, to provide lifeline service the remote unit would need to be powered from the central office or have a battery backup capability at the remote location. Lifeline service provides operation of the analog voice service in the event of a local power failure.

Figure 6.4. Provisioning of voice service using pair gain configuration.

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6.1.5 Work-at-Home Application

Figure 6.5 shows a possible work-at-home scenario where an access circuit is used to deliver one or more pulse code modulation (PCM) voice circuits together with a high-speed data channel. In this configuration, the SHDSL transceiver would be used to transport the multiplexed data and voice channels on a single high-speed access between the residence location and the CO. The distance between CO and customer location would determine the maximum bit rate that could be supported in the access line.

Figure 6.5. Work-at-home application ”data plus PCM voice.

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DSL Advances
DSL Advances
ISBN: 0130938106
EAN: 2147483647
Year: 2002
Pages: 154

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