The invention is based on a priority application EP01440195.4 which is hereby incorporated by reference. 
The invention relates to an internal liner for fastening cables, and also to a method of laying an internal liner. 
The use of waste-water, rainwater or mixed-water conduits or other discharge or supply lines for laying communication cables is one possible way, which has already been used, of reducing underground construction costs for the connection of subscribers (access).  In addition, it makes possible to expand such connection of subscribers in a demandorientated and rapid manner; something which has become increasingly important of late because of the large number of operators.  In what follows, the term xe2x80x9cwaste-water conduitxe2x80x9d (waste-water pipe) is also intended to cover rainwater conduits, mixed-water conduits and discharge and supply lines.  Whereas it is possible, in case of accessible conduits, to employ the existing standard techniques for laying communication cables, the problems in case of inaccessible conduits are still unresolved to a very great extent. 
When laying cables in inaccessible waste-water conduits, care has to be taken to ensure that
the hydraulically usable cross-sectional area is only slightly reduced;
as far as possible, no objects must be laid transversely to the direction of flow;
no points of attachment are produced which can lead to the formation of snags (for example, the accumulation of sewage materials) and consequently to obstruction; and
that cleaning of the waste-water conduit is not prevented. 
A fastening element, with the aid of which telecommunication cables can be held in waste-water conduits, is known from EP 953 162.  This known fastening element consists of a resiliently pretensioned, closed stainless-steel ring which presses against the internal wall of the waste-water conduit.  By using already existing, inaccessible conduit or pipe systems, such as the waste-water system or gas-pipe installations for example, the light wave guide cables can be laid right into the individual buildings in a simple manner.  Laying is carried out with the aid of a remotely controllable conduit robot which takes the cables into the conduit and pipe systems and fastens them to the internal walls, taking the known fastening elements out of a magazine which is conveyed with it.  Fastening elements of this kind, such as are described in EP 953 162, can only be laid with the aid of remotely controllable conduit robots.  They therefore cannot be adapted for waste-water conduits which have such a small diameter (smaller than 20 cm) that no robot can be introduced.  Yet it is precisely in the so-called xe2x80x9clast milexe2x80x9d, that is to say the lateral stretch which ends at a final consumer""s building, that the demand for laying telecommunications cables is very high. 
The object underlying the invention is to develop internal liners which permit the fastening of cables to the internal wall of a pipe, and also satisfactory renovation of the latter, without impairing the free space of the waste-water pipe too much in the process. 
The object is achieved, according to the invention, by means of
an internal liner for fastening cables to the internal wall of a pipe, preferably an inaccessible waste-water pipe, wherein the internal liner is constructed from at least two layers: the first layer, resting against the internal wall of the pipe when in the laid condition and having a profile or empty spaces for receiving cables, and the second layer, of envelope-like type, which carries the first layer; and
a method of laying an internal liner against the internal wall of a pipe, preferably an inaccessible waste-water pipe, wherein an internal liner for fastening cables to the internal wall of the pipe, which is constructed from at leas two layers, the first layer, resting against the internal wall of the pipe when in the laid condition and having a profile or empty spaces for receiving cables, and the second layer, of envelope-like type, which carries the first layer, is introduced, closed at one end in a hose-like manner, into the pipe in the desired position, and is brought into the inflated condition with the aid of an element such as hot water, steam or infrared irradiation, until the internal liner is pressed against the internal wall of the pipe. 
The construction of internal liners from two layers, a first layer which is provided with a profile for laying cables, preferably telecommunication cables, and a second, envelope-like layer, simultaneously permits the renovation of lateral waste-water pipes having a typically small diameter and also the laying of cables, preferably telecommunication cables, against the internal wall of such pipes.  The formation of profiles for holding telecommunication cables inside this first layer prevents points of disturbance from being formed on the renovated internal wall, through the fact that the internal periphery of the internal liner remains uniform. 
Advantageous refinements of the invention emerge from the dependent claims, the following description and the drawings.