5.3 Wire-Line Backhaul Technology
5.3.1 DSL Technologies
Digital Subscriber Line (DSL) technologies utilize the existing copper lines originally installed for Plain Old Telephone Service (POTS) for data transmission. DSL is used for access transmission to provide IP services for home computer users, but it is very common backhauling technology, too. The DSL subscriber line is called loop and it is typically a cable pair, but most DSL-variants can also combine (bundle) several pairs. The reach and maximum capacity of different xDSL technologies varies according to the loop rate, noise conditions and complexity of modulation and coding, see Table 5.5.
The most common technology is Asymmetric Digital Subscriber Line (ADSL). It has different standards for Europe and North America, while the newest ADSL+ is more harmonized. It uses the same line as POTS but a DSL filter allows the same copper line to be used for both voice and data transmission. Capacity is asymmetric; downlink direction to the BTS or customer premises is greater than uplink capacity. The configurations are star-like. The customer premises equipment (CPE) is small and cheap while the network end, called Digital Subscriber Line Access Multiplexer (DSLAM), usually terminates several tens or hundreds of access lines and connects to the data network by ATM/IP/SDH interface. With G.bond extension capacity can be doubled to 48/6 Mbit/s.
Single-Pair High-speed Digital Subscriber Line (SHDSL) is a symmetric DSL technology. ...