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Seven years ago 90 percent of all data that was stored was being stored to be moved from processor to processor. Today 90 percent of all data is being stored to be viewed: Its goal is not to be processed but to be seen. All the Web data is there to be viewed. So we've moved from where the center of gravity for computing was data processing to where it is data delivery. As a result, the center of the computer farm is the backplane of the switch, even though that has not been widely recognized.

1N5824

Seven years ago 90 percent of all data that was stored was being stored to be moved from processor to processor. Today 90 percent of all data is being stored to be viewed: Its goal is not to be processed but to be seen. All the Web data is there to be viewed. So we've moved from where the center of gravity for computing was data processing to where it is data delivery. As a result, the center of the computer farm is the backplane of the switch, even though that has not been widely recognized.

The L3 power mode is a total sleep mode where no traffic can be communicated over the ADSL connection when the user is not on-line. When the user returns to go on-line the ADSL transceiver require approximately three seconds to re-initialize and enter into steady state communication mode.

Rate Adaptation Telephone wires are bundled together in multi-pair binders containing 25 or more twisted wire pairs. As a result, electrical signals from one pair can electromagnetically couple onto other adjacent pairs in the binder (Figure 3) . This phenomenon is known as crosstalk” and can impede ADSL data rate performance. As a result, changes in the crosstalk levels in the binder can cause an ADSL system to drop the connection.

1N5824

Crosstalk is just one reason that ADSL lines drop connections. Others include changes in the narrowband, AM radio disturbers; temperature changes, and water in the binder.

ADSL2 addresses this problem by including the ability to seamlessly adapt the data rate on-line. This new innovation, called seamless rate adaptation (SRA), enables the ADSL2 system to change the data rate of the connection while in operation without any service interruption or bit errors. ADSL2 simply detects changes in the channel conditions — for example, a local AM radio station turning off its transmitter for the evening — and adapts the data rate to the new channel condition transparently to the user.

1N5824

SRA is based on the decoupling of the modulation layer and the framing layer in ADSL2 systems. This decoupling enables the modulation layer to change the transmission data rate parameters without modifying parameters in the framing layer which would cause the modems to loose frame synchronization resulting in uncorrectable bit errors or system restart. SRA uses the sophisticated online reconfiguration (OLR) procedures of ADSL2 systems to seamlessly change the data rate of the connection. The protocol used for SRA works as follows:

Bonding For higher Data Rates One of the big requests by today's carriers is the ability to provide different service level agreements (SLAs) to different customers. For example, carriers want to deliver a standard bandwidth requirement to the majority of home users while providing higher bandwidth offerings for corporations.

1N5824

The original ADSL standard did not support bonding, so designers did not have the ability to deliver these advanced SLA capabilities in equipment designs. However, through the support for bonding, ADSL2 is addressing these requests.

Bonding multiple phone lines together is a relatively simple way to significantly increase data rates to homes and businesses. To provide bonding, the ADSL2 spec taps into the inverse multiplexing for ATM (IMA) standard developed for traditional ATM architectures. Through IMA, equipment designs can bind copper pairs in an ADSL link (Figure 4) . The result is a far greater deal of flexibility with downstream data rates:

Figure 5 shows the required number of parallel capacitor arms for a filter with a 30 Hz cut-off frequency and maintaining continuous current in the filter inductor until 20% of full load. The increase in capacitor volume at high output power is apparent. In fact, we additionally need approximately 1 arm per kW for N=1 and 2 arms per kW for N=5 compared to an undamped filter.

Sudden Load Steps

Figure 6:  Output voltage excursion due to a sudden change in load

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