 Office Service Repeater Provisioning Repeaters every 3,000 ft (900 m) to 6,000 ft (1,800 m); no bridge taps allowed Local Exchange Remote Terminal 784-1.168Mbps Customer T-1/E-1 Service HTU-C HTU-R Provisioning Up to 12,000 ft (3.6 km) of 24 AWG (.5mm) twisted-pair wire; bridge taps allowed Figure 12.1 Traditional T-1/E-1 versus HDSL provisioning Chapter 12 Broadband Access Alternatives E-1 capacities; in the T-1 environment, it offers 784Kbps on each pair, and in the E-1 environment, it offers 1.168Mbps on each pair. With HDSL, you need a repeater only every 2.2 miles (3.6 km) or SO. In addition, bridge taps are allowed with HDSL. These factors reduce the cost of provisioning services to customers and allow more customers who are outside the range of the traditional T-1/E-1 environ- ment to enjoy the privileges of this high-bandwidth option. Because taps can be used with HDSL, provisioning can occur rather quickly. Also, HDSL is a good solu- tion for increasing the number of access lines via the digital loop carrier transport because it is compatible with the existing loop carriers. Key applications of HDSL include replacement of local repeatered T-1/E-1 trunks, use as a local Frame Relay option, use in PBX interconnection, and use in general traffic aggregation. HDSL is largely used to provision digital services to business premises. It is standardized under ITU G.991.1 and ANSI T1E1.4, Tech Report 28. The HDSL2 (two-wire) and HDSL4 (four-wire) specifications were developed in order to provide the capacities and symmetry of HDSL to residences. HDSL2 involves the use of a single twisted copper pair for distances up to 2.2 miles 3.6km). HDSL2 is a symmetrical, full-duplex service that offers up to 1.5Mbps in each direction. HDSL2 does not support voice telephone service on the same wire pair. The main difference between HDSL2 and HDSL is that HDSL2 uses one pair of wires, whereas HDSL uses two pairs. HDSL4 makes use of two pairs and also sup- ports 1.5Mbps in each direction. HDSL4 is the same as HDSL2 except tha