Specifications

Chapter 6 TR-08 Option
6-1
TR-08 OPTION
TR- 08 DESCRIPTION
Bellcore’s Technical Reference TR-TSY-000008, titled “Digital Interface Between the SLC96
Digital Loop Carrier System and a Local Digital Switch,” describes a Subscriber Loop Carrier
(SLC) system. It provides for up to 96 telephone connections to be deployed over 3 to 5 T1 lines
running from a Local Digital Switch (LDS) to a Remote Terminal (RT). RTs can be connected to
the serving LDS by repeatered T1 carrier, HDSL, microwave links, or optical fibers (typically
SONET). Initially, SLC systems were substituted for coarse grade feeder cables for serving low
density areas. As the economics of SLC systems improved, they were employed for pair gain
over crowded telecommunications rights-of-way.
Advantages of TR-08 implementation include:
• Direct LDS monitoring of T1 and RT alarms,
• A higher port density supported from the LDS,
• A decreased deployment cost on a per subscriber basis,
• Reduced equipment and power requirements,
• No necessity for A/D and D/A conversions at the switch interface,
• Use of existing T1 equipment and facilities, and
• Increased test and maintenance access.
There are three forms of TR-08: Mode I, Mode II, and Mode III.
• Mode I is a non-concentrated, non-blocking implementation where each
telephone connection is physically tied to a specific DS-0 channel.
• Mode II is a 2:1 concentrated implementation that permits blocking where 48
telephone connections are dynamically assigned to 24 DS-0 channels, on a
demand basis, and only for the duration of the call.
• Mode III is a special non-concentrated form of TR-08 used with pay phones and
true D4 channel units.
Although TR-08 employs 7 5/6 bit µ 255 companded PCM coding identical to that used by D4 or
ESF channel banks, there are differences in T1 framing, channel counting, and signalling
between the two systems. These differences will be addressed later in this chapter.
TR-08 ACCESS BANK I PRODUCT DESCRIPTION
The Access Bank I Voice Multiplexer with the TR-08 option provides low-cost, compact, wiring
closet deployment of subscriber line services from Nortel DMS™, Lucent 5ESS™, or other local
exchange switches. It allows inexpensive carrier provisioning of physically separate single shelf
groups for 12 or 24 fully-managed analog lines served by a single T1. The TR-08 Access Bank I