When the field service development personnel develop the N2150, they cannot briefly and clearly tell the differences between DSMs of different levels, especially the difference between the DSMs of level 2 and level 3.
Level 0: The DSL modem does not provide the information required by the SMC. The SMC performs the spectrum management according to the recommendations, the standard, and certain assigned solutions. This is static spectrum management. Level 1: The DSM of this level is what we called DLM. The DSM collects information such as the line rate, transmit power, and noise margin through the DSM-D. The DSM adjusts parameters such as the line rate, noise margin (maximum, minimum, and the target noise margin), flat gain of the PSD, and total transmit power through the DSM-C. Both the functions, however, are simple spectrum management including the power control.
Level 2: In addition to the parameters mentioned in level 1, the SMC obtains more specific parameters, including the data of the DELT test from the DSM. In addition, the SMC can better control the spectrum of the transmit power on the ports. Because the DSM of level 2 can obtain more information and support comprehensive control methods to control the spectrum more precisely, the SMC can optimize the power spectrum density and related parameters of all the pairs in the whole cables through the DSM. The applications of the DSM of level 2 are still under research. The applications do not involve modifications to the lower layer software and hardware.
Level 3: Level 3 is also called "Crosstalk Cancellation" technology. That is, the DSM cancels the crosstalk interference on the line by using a series of methods. In this level, the SMC and the DSL-LT are in the same location. The SMC can obtain and control some or all the sent messages in the uplink and downlink of the DSL-LT, and can coordinate the transmit signals of some or all the ports in the LT. In this way, the SMC realizes joint transmitting and receiving.
From level 0 to level 2, the DSM avoids or reduces the crosstalk interference when the crosstalk interference exists on the line. In this way, the DSM cannot cancel the crosstalk interference but reduces the line rate. The DSM of level 3, however, avoids the crosstalk on the line by canceling the crosstalk. Thus, the whole line has no crosstalk interference.
The DSM manages the signals of many pairs in the same bundled cables in a centralized manner to obtain the transmit signals of the neighboring pairs and the crosstalk transfer function through the crosstalk cancellation technology (DSM of level 3). On this basis, each pair transmits its own signals and also the signals of the neighboring pairs. In this way, each pair can cancel the interference of the neighboring pairs on the receive end and decode its own signals.