Access network frequency plan

Written on 4:13 PM by ooe

LLU will often be used in conjunction with DSL technology to provide data services. BT has, for many years, been a leader in research into DSL crosstalk interference and in the formulation of deployment rules to control it [4,5]. Before LLU was introduced to the UK, BT was solely responsible for ensuring that its transmission systems were used in a way that avoided excessive crosstalk on its network. With the introduction of LLU, it was no longer appropriate nor possible for BT alone to control system deployments. A new set of rules was required that all operators could follow. The new rules had to be clear, easy to implement, fair and had to take account of likely future developments in the access network.

The NICC DSL Task Group [7] was the cross-industry technical forum that was tasked by Oftel to design an access network frequency plan to meet these requirements. The task group was chaired by BT and was open to all interested parties. A wide range of telecommunications operators and equipment vendors actively participated with BT and Oftel. The access network frequency plan (ANFP) for the BT network is described in detail in Chapter 4.

The ANFP for the BT network controls crosstalk by defining limits on the power, frequency and location of DSL systems. The ANFP works by placing limits on the worst-case crosstalk noise in the network. By ensuring that new developments in the access network are no more harmful to their neighbours than current systems, the ANFP provides the stability that allows all operators to plan for the future with confidence. The ANFP places the onus on individual operators to ensure that their DSL deployments are compliant and remain so. The DSL task group designed a code of practice to be used when investigating allegations of interference.

When the ANFP was first mooted, line sharing and sub-loop LLU were not required so the first issue of the ANFP made no specific provision for them. Similarly, international standards for VDSL technology were at that time not agreed and the first plan excluded VDSL. At the time of writing the DSL task group is extending the plan to accommodate VDSL and sub loop unbundling.