Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Patent
1996-01-26
1998-06-02
Negash, Kinfe-Michael
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
359117, 359119, 359168, 370404, H04J 400, H04J 1400
Patent
active
057609357
DESCRIPTION:
BRIEF SUMMARY
This invention relates to communications networks and in particular to optical communications networks.
BACKGROUND OF THE INVENTION
Optical fibre transmission is a widely used technique in the communications field. The technique has the major advantages of low attenuation and high bandwidth in comparison with electronic transmission techniques. However, in communications network applications, the use of fibre has not extended significantly beyond trunk transmission. Thus, local transmission and switching are performed electrically. This requirement for both electrical and optical communications introduces two significant limitations. Firstly there is the need to provide electronic/optical and optical/electronic interfaces between the two transmission media. Secondly, the bandwidth restrictions of the electrical part of the network present the full potential bandwidth available in the optical spectrum from being utilised. For example, the complete radio and microwave spectrum has a bandwidth of about 300 GHz, whereas the potential bandwidth available in the optical spectrum in the typical transmission wavelength range of 1500 to 1600 nm is of the order of 4000 to 6700 GHz.
Furthermore, in a communications network, it is necessary to provide a number of levels of multiplexing, the highest level being used for trunk transmission. This necessitates the provision of multiplexing and demultiplexing equipment. Although the recent introduce of synchronous systems (SDH) to replace the present plesiochronous systems (PDH) has resulted in a reduction of the volume of multiplexing/demultiplexing equipment required, this equipment still represents a significant proportion of the overall system cost.
It is an object of the invention to minimise or to overcome those disadvantages.
SUMMARY OF THE INVENTION
According to the invention there is provided an optical communications network, including an inner core network having a plurality of nodes, outer networks coupled to at least some of said nodes, and local distribution networks each coupled to a said outer network and each providing access to a plurality of terminals, wherein information transported via the network between terminals is carried in elements of a two dimensional discrete communications space, each said element being defined by respective time and wavelength co-ordinates.
The communications space extends throughout the network
The network architecture is designed to be integrated with, and eventually replace, the current network in incremental steps from the top down using a common set of components throughout. In general this will ensure that maximum benefit can be derived by spreading costs amongst users at the higher network levels, and reductions in component costs, due to mass production of standardised modules at the subsequent lower levels.
In the first stage of evolution we envisage existing transmission links within an inner core network being upgraded to use Dense WDM transmission but with each carrier operating within the Synchronous Digital Hierarchy (SDH) to standard interfaces. Later these interfaces would be replaced by transparent wavelength switches and thereby facilitate transmission between rings entirely in the optical domain. Ultimately, individual customers could be serviced directly through passive optical networks (PONs) optically connected to the rings.
In a high capacity network carrying traffic multiplexed from many users, one would not expect the mean traffic flow along routes to fluctuate by large amounts in short times. Accordingly, we propose that the traffic carrying ability in the inner and outer core networks (mesh and rings) should be allocated on a slowly time varying basis (.about.hours), initially in blocks of one optical carrier e.g. at the synchronous transport module standard STM-4. The choice of STM-4 may seem low, at a time when much interest centres on transmitting at STM-16 or higher rates, however, we have two reasons for proposing it. Firstly, a nation-wide transparent optical network with transmission at
REFERENCES:
patent: 3731002 (1973-05-01), Pierce
patent: 5351146 (1994-09-01), Chan et al.
Sabry et al., "A Modular and Scalable Transparent Optical Network", ECOC '93, Sep. 12-16, 1993, Proceedings, vol. 3. pp. 97-100.
Midwinter John
Sabry Martin
Negash Kinfe-Michael
Northern Telecom Limited
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