Question

Broadband services over copper wire include a variety of technologies with distinct advantages and limitations. Answer the four parts below about broadband services over copper wire.
Part 1: What are some limitations of digital subscriber line (DSL) technology?
Part 2: What are some examples of improvements of asymmetric digital subscriber line 2 (ADSL2) beyond regular DSL?
Part 3: What are some of the methods that very high speed DSL 2 (VDSL2) uses that represent an improvement over DSL?
Part 4: What is the purpose of Bonded DSL?

Answer 1

Part1:

No current standardization: A person moving from one area to another might find that their DSL modem is just another paperweight. Customers may have to buy new equipment to simply change ISPs. Expect standardization within 1-2 years. Currently in U.S. West territory the version of DSL being implemented is RADSL or Rate Adaptive DSL.

Expensive: Most customers are not willing to spend more than $20 to $25 per month for Internet access. Current installation costs, including the modem, can be as high as $750. Prices should come down within 1-3 years. As with all computer technology, being first usually means an emptier wallet.

Distance dependence: The farther you live from the DSLAM (DSL Access Multiplexer), the lower the data rate. The longest run lengths are 18,000 feet, or a little over 3 miles.

Access: Once again, rural areas get shorted. These markets are not as profitable for the Telco.

Asymmetry. Downstream/Upstream ratios may be unacceptably high (3 or more). There is nothing new here, as X.90 (56kbs) and cable modems also suffer in this area. Expect this to improve within 2-3 years.

Limited availability

Very new technology

Low or no CIR (Committed Information Rate). This means that as traffic across the telco switch increases your data could in effect, be locked out, until call volumes and other traffic subsides.

Downtime after line failure could be weeks compared with days for ISDN and hours for data circuits such as Frame Relay and Point to Point circuits.

U S West DSL service is tarrifed as a "consumer grade" product. "Commercial grade" DSL is being planned, but is not yet defined or available.

Reliability and potential down time issues makes DSL a very risky choice for mission critical systems unless backup / fail over links are put in place.

Part 2:

Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines rather than a conventional voiceband modem can provide. ADSL differs from the less common symmetric digital subscriber line (SDSL). In ADSL, Bandwidth and bit rate are said to be asymmetric, meaning greater toward the customer premises (downstream) than the reverse (upstream). Providers usually market ADSL as a service for consumers for Internet access for primarily downloading content from the Internet, but not serving content accessed by others.

Currently, most ADSL communication is full-duplex. Full-duplex ADSL communication is usually achieved on a wire pair by either frequency-division duplex (FDD), echo-cancelling duplex (ECD), or time-division duplex (TDD). FDD uses two separate frequency bands, referred to as the upstream and downstream bands. The upstream band is used for communication from the end user to the telephone central office. The downstream band is used for communicating from the central office to the end user.

Part 4:

True bonded ADSL is where multiple ADSL lines are effectively combined into a single aggregated connection to deliver greater download and upload speeds. ADSL bonding involves the aggregation of two or more ADSL or ADSL2+ connections.

While the concept of ADSL bonding is deceptively simple (i.e. combining multiple ADSL connections together), the practical implementation of bonded ADSL is relatively involved and requires significant processing in the splitting and recombination of datastreams.

Consider a video stream (e.g. BBC iPlayer or YouTube) being viewed on a PC. With bonding, the original streamed video datastream has to be split up into multiple streams, each of which is sent down an individual ADSL or ADSL2+ connection. The process of splitting datastreams is performed at a special datacentre operated by the bonding provider. At the customer’s premises, the separate datastreams are recombined to form a single data stream.