Multiplex communications – Wide area network – Packet switching
Patent
1994-05-17
1997-10-21
Bowler, Alyssa H.
Multiplex communications
Wide area network
Packet switching
39518319, 370216, 359118, 359168, H04J 1400
Patent
active
056805462
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention concerns transmission systems using optical fibres and, in particular, optical networks of passive type structured in such a way as to be highly tolerant to faults affecting the transmission mean, that is, the fibre.
The passive optical fibre networks, that is, those containing no active inner components such as switches, bypasses, modems, and so on, provide very high information exchange speeds--up to a rate of around one terabit per second, using, for example, the WDM (Wavelength Division Multiplexing) technique.
The present application makes particular reference to passive optical networks for use in the so-called Metropolitan Area Networks (MAN). However, the invention is not limited to this type of application.
BACKGROUND ART
As we know, if we have to obtain total interconnectivity between stations linked by an optical network, the most frequently used mappings are based on star, bus and tree configurations or a suitable combination of these.
Star mapping is inconvenient from the point of view of the fibre installation costs, while the bus configuration is extremely limited with regard to the power budget that is the quantity of optical power that can be carried.
Tree mapping, whose limitations with regard to fibre installation costs and power budget are much less serious, does present the problem of being extremely fault-prone. If we take a metropolitan network as an example, we can see that a cut in one single fibre can completely disconnect an extensive part of a network with tree structure.
To overcome this problem, the use of redundant architecture and the insertion of suitable active elements in the network nodes have been suggested, to handle for example the signal routing or its amplification by alternative multiple routes contained in the network architecture. In this way, however, it is no longer possible to obtain the very high communication Bit rate (terabit/sec approx.) which can be obtained only by using optical networks realized with a completely passive physical mapping.
The document from the IEEE Military Communications Conference "Enhanced Network Survivability Through Balanced Resource Criticality"--M. A. Schroeder--vol, 1, October 1989, New York, US pages 682-687 discloses a tepological survivability for military networks in which all node and link resources are of equal importance. Additional four links are foreseen to assess how close a network design comes to being maximally survivable, without however to solve the problem of criticality of nodes whose destruction disconnects the network.
The aim of this invention is the creation of a passive optical network, designed in particular for the applications mentioned above, with high fault tolerance and complete user transparency, in the sense that the same network can be used for different types of service (requiring, for example, different transmission bit rates), rather than having to overlap a different network for each service.
Another aim of this invention is to obtain the characteristics described above without using active elements in the nodes, at least in the most frequent cases, where the network is constructed with a "monotype" tree structure--a completely binary structure, for example, or completely ternary--and so on.
The invention is also aimed at creating a passive optical network structure with low fibre installation costs, good signal losses and power budget.
DISCLOSURE OF INVENTION
These objectives have been obtained by means of a passive optical network structure with "tree configuration" comprising a number of nodes at different levels linked by connecting branches, in which a node at level is connected by m branches, with m>2, to m nodes of the level immediately below, wherein a supplementary connection is provided between each pair of nodes of the same level.
In line with this invention, the passive optical fibre network should preferably be structured in such a way that each node is connected to the same number of nodes at the level immediately below by two or possibly
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Chiaretti Guido
Gerla Mario
Bowler Alyssa H.
Davis Walter D.
Italtel Societa Italiana Telecomunicazioni S.p.A.
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