## 2 Broadband System
### Fixed-Line Broadband System
#### 2.1.3 Digital Subscriber Line
In addition, as presented in Table 2, neither asymmetric DSL (ADSL) nor symmetric DSL (SDSL) is capable of meeting the required bandwidth for HDTV as listed in Table 3. Besides, it might be challenging for the schemes to effectively offer the fundamental video services and/or VoD services over the network. Nevertheless, very-high-bitrate DSL  
\begin{table}
\begin{tabular}{l l l l l l l} \hline \hline
**DSL Type** & **Acronym** & **Downstream Capacity** & **Upstream Capacity** & **Range (m)** & **Standard** & **Reference** \\ \hline Asymmetric & ADSL & 1.5–9 Mbps & 16–640 kbps & 5500 & ITU G.992.1, ANSI & [133; 134; 135; 136] \\  & & & & & & T1.413, ITU-T G.992.3 & \\  & & & & & (ADS12) & \\ \hline ADSL Version 2 & ADSL2 & Up to \(\sim\)10 Mbps & Up to \(\sim\)1 Mbps & 5500 & ITU G.992.3 & [135; 137] \\ \hline ADSL Version 2 & ADSL2+ & Up to \(\sim\)20 Mbps & Up to \(\sim\)2 Mbps & 5500 & ANSI T1.413, ITU & [135; 137] \\ Extended bandwidth & & & & & G.992.5 & \\ \hline Splitterless & G.lite & 1.5–6 Mbps & 16–640 kbps & 5500 & ITU G.992.2 & [133; 134] \\ \hline High-bit-rate & HDSL & 1.544 or 2.048 Mbps & 1.544 or 2.048 Mbps & 4000 & ITU G.991.1, ETS TS 101 & [133; 134] \\  & & & & & 135, ANSI T1.TR28 & \\ \hline High-bit-rate 2 nd & HDSL2 & 1.544 Mbps & 1.544 Mbps & 4000 & ANSI T1.418, ITU-T & [133; 134; 135] \\ generation & & & & G.991.2 & \\ \hline ISDN & IDSL & 144 kbps & 144 kbps & 5500 & T1.601 & [133; 134] \\ \hline Single-pair & SDSL & 1.544 or 2.048 Mbps & 1.544 or 2.048 Mbps & 4000 & Proprietary & [133; 134] \\ \hline Very-high-bit-rate & VDSL & 13–53 Mbps & 1.5–2.3 Mbps & 330–1500 & ANSI T1.424, ITU-T & [133; 134; 136; 137] \\  & & & & G.993.1, ETS I501.270 & [138; 139; 140; 141; 142; 143; 144; 145; 146; 147; 148; 149; 150; 151; 152; 153; 154; 155; 156; 157; 158; 159; 160; 161; 162; 163; 164; 165; 166; 167; 168; 169; 170; 171; 172; 173; 174; 175; 176; 177; 178; 179; 180; 181; 18(VDSL) and an extended version of ADSL broadband technology, ADSL2+, can provide bandwidths that are sufficient for supporting video services over a relatively short distance. Note that xDSL is distance-sensitive, and its performance depends significantly on the distance between the exchange and the respective home/office. Furthermore, the sensitivity to distance varies from one variant of DSL to the others. Therefore, the subscribers that are in close proximity to the exchange can enjoy significantly higher DL connection speeds, when they are supported by ADSL2 or ADSL2+ compared with ADSL technology. However, with an increase in the distance, there is no significant difference in their performance. Similarly, broadband signals are susceptible to attenuation during propagation from the exchange to the user's modem. This brings about a considerable reduction in the actual speed that could be delivered to the user. Furthermore, the line attenuation/line loss is a function of the total cable length and distance; for instance, with up to 50 dB line loss, ADSL2/2+ offers some performance gains compared with the ADSL technology [142]. Furthermore, as xDSL is a distance-sensitive technology, for VDSL to deliver services to a substantial amount of the populace, the DSL access modules (DSLAMs) have to be in close proximity to the subscriber. For instance, it can be relocated to street cabinets, and the fiber feeds have to be deployed up to the street cabinets. Moreover, ADSL is a more attractive option for homes that are considerably farther from the DSLAM compared with VDSL. In addition, note that, although ADSL is more widely deployed and less susceptible to attenuation, it offers significantly slower connection than VDSL. However, the associated expenses for the system upgrade and fiber deployment make VDSL to be expensive compared with ADSL technology [16].