LLU variants

Written on 4:11 PM by ooe

The two major variants of LLU are full unbundling and sub-loop unbundling. Each of these variants may be offered exclusively or with shared use. Full unbundling involves leasing the use of a complete access pair from a local exchange site to the end-user premises. The LLU operator may choose to make exclusive use of the line or may choose to share it with the incumbent operator. In shared access, the incumbent uses the lower frequency part of the line to provide conventional telephony service, while the LLU operator uses ADSL technology to provide a data service.

In sub-loop unbundling the LLU operator is given access to the line at a sub-loop access point which will usually be located at a flexibility point between an exchange building and the end user premises. This may be attractive to operators who wish to use very-high-speed DSL or VDSL technology. If the sub-loop access is shared, the incumbent will use the lower-frequency part of the loop to provide a conventional telephone or basic rate ISDN service.

LLU operators will usually require certain ancillary services to allow them to make use of unbundled loops. A key service is space for the operator to place its network equipment. In the case of full unbundling, the LLU operator may be able to lease some space within the exchange building; this is called collocation. Alternatively, the operator may be able to place its equipment in a nearby building or street cabinet. This is called distant location.

The LLU operator does not need physical access to the main distribution frame. Tie cables are used to connect a handover distribution frame (HDF) in the LLU operator accommodation to the MDF. If distant location is used, the tie cable may be provided by either incumbent or by the LLU operator in conjunction with the incumbent.

Close co-operation between the LLU operators and network owner is particularly necessary during the ordering and maintenance stages. Much of this interaction is being automated using operational support systems that can be connected to the LLU operator's systems. The approach to systems is described later in the chapter.

LLU operators also need core network transmission links to connect the unbundled loops to the rest of their network. These links may be leased from any suitable operator or may be built by the LLU operator themselves. The LLU product variants are described in more detail below.