Telephonic communications – Diagnostic testing – malfunction indication – or electrical... – Testing of subscriber loop or terminal
Reexamination Certificate
1999-11-12
2003-03-11
Kuntz, Curtis (Department: 2643)
Telephonic communications
Diagnostic testing, malfunction indication, or electrical...
Testing of subscriber loop or terminal
C379S001040, C379S024000, C379S027030, C379S027080, C379S001030
Reexamination Certificate
active
06532277
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for controlling transmission power from a customer premise equipment device over a local loop of a digital subscriber line.
BACKGROUND ART
xDSL is a generic term for digital subscriber line equipment and services, including packet-based architectures, such as ADSL, HDSL, SDSL, VDSL, and RADSL. That is, x is the generic. xDSL technologies provide extremely high bandwidth over embedded twisted pair, copper cable plant. xDSL technologies offer great potential for bandwidth-intensive applications, such as Internet access, remote LAN access, video conferencing, and video-on-demand.
ADSL or asymmetric digital subscriber line services generally use existing unshielded twisted pair (UTP) copper wires from the telephone company's central office to the subscriber's premise, utilize electronic equipment in the form of ADSL modems at both the central office and the subscriber's premise, send high-speed digital signals up and down those copper wires, and send more information one way than the other. The ADSL flavor of xDSL services is capable of providing a downstream bandwidth of about 1.5 Mbps-8 Mbps, and an upstream bandwidth of about 16 Kbps-64 Kbps with loop distances ranging from about 3.7 km-5.5 km. HDSL or high bit rate digital subscriber line services provide a symmetric, high-performance connection over a shorter loop, and typically require two or three copper twisted pairs. HDSL is capable of providing both upstream and downstream bandwidth of about 1.5 Mbps, over loop distances of up to about 3.7 km. SDSL or single line digital subscriber line services provide a symmetric connection that matches HDSL performance using a single twisted pair, but operating over a shorter loop of up to about 3.0 km. VDSL or very high bit rate digital subscriber line services are typically implemented in asymmetric form, as a very high speed variation on the ADSL theme over a very short loop. Specifically, target downstream performance is typically about 52 Mbps over UTP local loops of 300 m, 26 Mbps at 1,000 m, and 13 Mbps at 1,500 m. Upstream data rates in asymmetric implementations tend to range from about 1.6 Mbps to about 2.3 Mbps. Additionally, there is RADSL or rate adaptive digital subscriber line services. RADSL provides a dynamic connection that adapts to the length and quality of the line.
In the xDSL family of services, many xDSL themes, including ADSL, HDSL, SDSL, VDSL, and RADSL, utilize a packet-based approach that does away with the line-grabbing practice of circuit switched networks, such as ISDN (although ISDN service is a form of digital subscriber line). This packet-based approach is very advantageous in a variety of situations, such as high-speed data services, including high definition television or HDTV transmissions.
Of course, xDSL services, also commonly referred to as simply DSL or digital subscriber line services, are much more dependent on line conditions than traditional telephone services. Traditional telephone services typically use a bandwidth including frequencies up to about 3 kilohertz, while the DSL services utilize a bandwidth including frequencies up into the hundreds of kilohertz. While some local loops are in great condition for implementing DSL services, that is, the local loops have short to moderate lengths with minimal bridged taps and splices, many local loops are not as clean. For example, local loop length vary widely, for example, from as short as a few hundred meters to as long as several kilometers.
Further, sometimes the wire gauge for a local loop is not continuous over the length of the loop. That is, a portion of the local loop may be one wire gauge, while an adjacent portion of the local loop has a different wire gauge, with the two portions being spliced together. Still further, many existing local loops have one or more bridged taps. A bridged tap is a length of wire pair that is connected to a loop at one end and is unterminated at the other end. Sometimes, an existing local loop will have several bridged taps so that the telephone company may connect a customer to any one of the taps (while leaving the other taps unterminated). Tapped lines may allow the telephone company to better utilize its copper cable plant distribution. For example, a particular service area may include 25 residences. Because not all residences require multiple phone lines, there may be a total of about 30 or 35 local loops, with some of the loops having multiple bridged taps. As such, it may be possible for any one of the residences to order multiple line service, so long as only a few of the residences do so.
However, because DSL services have a strong dependence on line condition, splices and bridged taps may affect DSL services. If the line conditions are not excessively poor (loop length is not excessively long, while splices and taps are relatively minimal) increasing power for the DSL transmissions may be sufficient to provide adequate DSL services over the loop. It is to be appreciated that, however, simply increased transmission power alone does not always produce successful results.
In addition to loop lengths, number of splices, and number of bridged taps, there are other factors that are involved in providing a successful DSL solution. In addition to the conditions of the local loop itself affecting DSL implementation, crosstalk between local loops may also impair DSL service. For example, the central office side of a local loop is usually bundled into a binder group with other local loops. A binder group typically includes from as few as twenty-five pairs to as many as several hundred pairs. That is, a large number of pairs (loops) are bundled together into a binder group at the central office (or at a digital subscriber line access multiplexer or DSLAM, or at any other distribution point). As the binder group is routed away from the central distribution point, such as the central office, the loops branch out, with loops and small groups of loops departing from the binder group, until eventually, all of the loops are separated, similar to the way that a tree trunk branches out into smaller and smaller branches. On the customer end of the loop, DSL transmissions are sent from the end of the loop toward the central office (or DSLAM, or other distribution point). As the transmission travels toward the distribution end of the loop, the loop becomes bundled together with other loops. When the loops are bundled together, there is potential for crosstalk between different services of the same bundle or binder group. Accordingly, although increasing transmission power may sometimes reduce the effect the splices and bridged taps have on transmissions from the customer premise, the increased transmission power results in increased potential for crosstalk that may affect other loops when the transmission reaches the bundled loops.
Because a power control scheme is needed to assure that DSL transmissions are not underpowered and incapable of overcoming splices and bridged taps, an existing customer premise equipment device is capable of stepping up transmission power in the presence of excessive background noise (or back off when noise decreases). However, in an environment where each DSL service is introduced to a binder group one service at a time, the conventional scheme of measuring wideband frequency response and adjusting transmission power accordingly tends to create a so called race condition. In a race condition, the background noise causes each DSL service in a binder group to constantly boost transmission power a little bit at time. Eventually, all pairs will transmit at a fixed maximum power level. With all loop transmissions being fixed at the maximum power level, the effectiveness of the transmission power back-off functions are nullified. Further, because loop length and conditions vary widely, the race condition results in crosstalk from the better quality loops excessively interfering with the poorer quality loops.
For the foregoing reasons, there is a need for an improved DSL
Kung Darwei
Ulanskas A. John
Kuntz Curtis
Qwest Communications International Inc.
Townsend and Townsend / and Crew LLP
Tran Quoc
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