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Introduction to local loop unbundling

The part of the telephone line arriving at the subscriber is called the "local loop". In order to use high speed internet (ADSL), Internet Service Providers (ISP) must install connection hardware to their server at the telephone exchange of the historical operator, i.e. the subscriber hubs (NRA) where the subscribers' telephone lines end. Generally there are several subscriber hubs per town, distributed throughout France.

The aim of unbundling is to give ISPs access to the local loop (full or partial). In the event of partial unbundling, line maintenance is conducted by the historical operator and only the frequencies used for transporting things other than voice are leased (< 4 KHz). In the event of full unbundling, it is the ISP who takes care of line maintenance and passes on the main subscription cost through the ADSL subscription cost. However, full unbundling is not frequently practiced by operators.

The historical operator must open his subscriber hubs to other Internet Service Providers so that they can install their own hardware in a particular room. Legally, France Telecom, the historical French operator has a time frame of three months in which to give an Internet Service Provider the requested access. During these three months, the historical operator must create two rooms in the subscriber hub:

• a room dedicated to the dispatcher,
• and a room called the "unbundling" or colocalisation room.

The hardware installed by ISPs in the unbundling room is called DSLam (for Digital Subscriber Line Access Multiplexer). DSLams are connected directly to the ISP's servers by fibre optic cables. These DSLams make it possible to multiplex several types of data (in particular voice over IP, television and Internet).

Let us summarise the path taken by your data using an unbundled ADSL connection:

• The subscriber's telephone socket is connected to an historical operator's distribution frame (connection point for the whole district) located in a subscriber hub;
• This distribution frame is itself connected to a mirror head, which is the distribution point between the dispatcher room and the unbundling room, the place where the ISP takes over;
• The mirror heads are connected to the DSLAMs of the various ISPs in the unbundling room;
• These DSLAM are in turn connected to the ISP's servers using specialist connections (generally in fibre optic).

Webography

Sources:

• http://www.art-telecom.com,
• http://www.aduf.org,
• and various forums and site about ADSL in general.

Article written by Kalamit