The present invention relates to a packet transmission equipment for a packet transmission system which implements communications through exchanges of packets as communication units. More particularly, the invention pertains to an IP packet transmission equipment for use in an IP communication network which carries out communications through exchanges of IP (Internet Protocol) packets as communication units.
With the recent explosive popularization of the Internet or the like, the data traffic volume in global area networks is now dramatically on the increase. In other words, the global area networks are evolving from the conventional voice traffic to a data traffic oriented network architecture. Various organizations predict that the IP backbone traffic will become increasingly denser. Against such a backdrop every IP router maker is pursuing the development of routers on the order of tera bits. A WDM (Wavelength Division Multiplexing) transmission system is considered as a near-term solution for the problem of supporting such high-capacity IP traffic, and each maker is also making strenuous efforts in the development of a WDM transmission equipment.
Conventionally, IP packets are transmitted over an ISDN system, but high-capacity transmission over a leased circuit utilizes an IP packet transmission equipment based on a technique called an IP over SDH (Synchronous Digital Hierarchy) which stores IP packets in an SDH path payload area. For particulars of this technique, see IETF Regulation RFC1619.
With the above-mentioned IP over SDH, as shown in FIG. 1, IP packets are accommodated in the SDH path payload for each destination, and IP routers at remote locations are interconnected over a SDH transmission network. For example, between an IP router 600-1 and IP routers 600-2 tp 600-4 there are set SDH paths. The SDH paths are multiplexed to construct an STM (Synchronous Transport Module) signal. The IP routers 600-1 to 600-4 are each connected to a local transmission liner of lower speed and lower capacity than a backbone transmission line BB, or to server equipment. The STM signal is transmitted over backbone transmission lines BB-1 to BB-7, and at SDH cross-connects 500-1 to 5004 on its way to destination, routing takes place for each SDH path signal so that the STM signal is sent to its desired destination.
As an IP packet transmission system suitable for use in an IP communication network which transfers information in units of IP packets, there is proposed an optical transmission system which performs routing at the optical level to build a higher-capacity IP communication network unlike the conventional SDH transmission system of FIG. 1 which involves routing at the electrical level in SDH cross-connects. In the optical transmission system, information is conveyed over the optical path transport network with IP packets accommodated in an optical path payload portion. In an optical path cross-connect which is a transit node in the optical path transport network, wavelength routing is performed which sets routes to respective destinations of transmission signals on a wavelength-wise basis. Such an optical communication network is disclosed in, for example, K. Sato, S. Okamoto and H. Hadama, xe2x80x9cOptical Path layer Technologies to Enhance B-ISDN Performance,xe2x80x9d ICC""93, May 23, 1993.
FIG. 2 depicts a WDM (Wavelength Division Multiplexing) type optical communication channel disclosed in, for instance, Japanese Patent Application Laid-Open Gazette No. 7-67153. It is considered that the illustrated structure can be used for each cross-connect 500 in FIG. 1 to handle an optical signal. In the WDM communication channel, wavelength-multiplexed signals WDMS provided to input optical backbone transmission lines OBB-11 to OBB-14 are demultiplexed for each wavelength in wavelength demultiplexing parts 51-1 to 51-3, then the optical signals of the individual wavelengths are regenerated by optical regenerators 52-1 to 52-16, respectively, then the regenerated optical signals are cross-connected by optical switches 53-1 to 53-4 to predetermined routes and are multiplexed in wavelength multiplexing parts 54-1 to 54-4, from which the wavelength-multiplexed optical signals are provided to output optical backbone transmission lines OBB-21 to OBB-24. The optical regenerators 52-1 to 52-16 each convert the optical path signal of one wavelength to an electrical signal, and applies it to a laser light source, thereby generating an amplified and shaped optical path signal.
Either literature mentioned above does not disclose how each of the IP routers 600-1 to 600-4 in the transmission system of FIG. 1 are constructed to convert signals of arbitrary formats to IP packets and how they are connected to the cross-connect 600-1. The most common-sense way is to connect, for instance, the output of the IP router 600-1 to one of the input optical highways in FIG. 2 and apply the wavelength-multiplexed signal from the IP router 600-1. To this end, it is necessary for the IP router 600-1 to convert respective input signals to IP packets, convert them to optical path signals by wavelength-multiplexing and provide the optical path signals to any one of the wavelength demultiplexing parts 51-1 to 51-4 of the cross-connect apparatus shown in FIG. 2. Such IP routers use laser light sources for the conversion of IP packets to optical path signals. The wavelengths of these laser light sources need to be always monitored and controlled together with the wavelengths of laser light sources used in the optical regenerators 52-1 to 52-16.
As described above, in the case of building the IP communication network by an optical path transmission network and connecting the IP routers to the optical cross-connects, laser light sources are provided in the IP routers. The optical signals generated by the laser light source in each IP router is regenerated by the laser light source of the optical regenerator in each optical cross-connect. Furthermore, it is necessary to monitor whether each laser light source operates at a predetermined wavelength, or effect control for wavelength stabilization. As the scale of the system becomes larger, the scale of monitoring also becomes larger accordingly.
It is therefore an object of the present invention to provide an IP packet transmission equipment which permits transmission and reception of IP packets and is small in the number of parts used and hence lightens the workload for control.
According to the present invention, there is provided an IP packet transmission equipment which is provided in a node of a transmission network containing backbone transmission lines and local transmission liners and transmits optical path signals between source and destination nodes via logically defined optical paths, said apparatus comprising:
wavelength demultiplexing means which receives from each of the backbone transmission lines a wavelength-multiplexed signal produced by wavelength-multiplexing optical path signals containing IP packets and demultiplexes the wavelength-multiplexed signal to optical path signals of individual wavelengths;
IP packet routing means for converting a transmission signal input from each of the local transmission liners to IP packets and for outputting the IP packets to routes corresponding to their destinations;
IP/optical path converting means provided in an output route of the IP packet routing means, for converting the IP packets to optical path signals;
optical path switching means which receives the optical path signals from the wavelength demultiplexing means and the optical path signals from the IP/optical path converting means and cross-connects the optical path signals to output routes corresponding to their destinations; and
optical path signal multiplexing means which wavelength multiplexes the optical path signals on predetermined output routes from the optical path switching means to generates an output wavelength-multiplexed signal and outputs the wavelength-multiplexed signal to each backbone transmission line.
With the above arrangement, the optical regenerators corresponding to OTM/optical path signal conversion parts connected directly to the IP packet transmission equipment in the prior art example becomes unnecessary, and hence it is possible to construct an IP packet transmission equipment with a smaller number of laser light sources than in the prior art.