The present invention relates to a packet routing apparatus and a method of communicating a packet, and in particular to a packet routing apparatus and a method of communicating a packet which performs protection switching (line) at a time of failure occurrence in a network layer or a lower layer in a packet routing apparatus employing a redundancy or protection switching.
In recent years, communication apparatuses provided with not only a system required for a normal operation but also a backup system to allow backup of various communications, so-called “redundancy (for example, doubled configuration)”, are spreading widely for failure measure in various communication systems. In the communication system provided with the redundancy, for example, a plurality of processors, file devices or the like (which respectively serve as workings and protections) are provided, thereby allowing switching in 1+1 or 1:n manner at a time of failure occurrence.
In an IP network constituted with a plurality of IP packet routing apparatuses, a route failure is detected using a routing protocol for exchanging route information pieces. As the routing protocol used in this IP network, for example, there are ROUTING INFORMATION PROTOCOL (RIP), OPEN SHORTEST PATH FIRST (OSPF) or the like. In a failure detection according to OSPE, for example, communications are periodically performed between IP packet routing apparatuses using a Hello packet for confirming connection of the IP packet routing apparatuses. A reliability of a route is verified by a communication or conduction test between the IP packet routing apparatuses. Incidentally, information about connection between the IP packet routing apparatuses is stored, for example, in a routing table in a processor.
Also, the routing protocol used in the IP network performs, for example, route selection, communication between IP packet routing apparatuses, update of a routing table, when a route failure is detected. Incidentally, a switching time from a working route to a protection route for failure recovery requires several tens seconds to several minutes.
On the other hand, in a public network, a failure detection is carried out by a SYNCHRONOUS DIGITAL HERARCHY (SDH: SONET in northern America) system prescribed in INTERNATIONAL TELECOMMUNICATION UNION TELECOMMUNICATION STANDARDIZATION SECTOR (ITU-T) RECOMMENDATION G.707 (refer to 9.2.2 SOH BYTES DESCRIPTION OF RECOMMENDATION G.707). This SDH system is constituted with, for example, SDH transport systems. A packet where a frame multiplexed with a user signal, called VIRTUAL CONTAINER (VC), is attached with a header, so-called a section overhead, is used for transmission between respective SDH transport systems.
Mapped on the section overhead is information for performing switching at a time of failure. In the SDH system, switching between the working line and the protection line is performed at a time of failure on the basis of the mapped information. This switching system is called “AUTOMTIC RPOTECTION SWITCHING (APS) system and prescribed in BELLCORE GR-253-CORE, ITU-T G.782.
According to the APS system, a transmission network with a high reliability and a high maintenance can be configured so that a high reliability required for a public network can be achieved. Also, in the APS system, a switching sequence including an external device is defined, and a switching time from a working line to a protection line for failure recovery is within 50 ms.
Also, recently, a high speed IP packet routing apparatus has been introduced even in the public network. This is because data system traffic flowing on a network is rapidly increasing due to a rapid spreading of computers and shifting from a network configuration mainly comprising audio or sound system traffics through conventional public switches to a network configuration mainly comprising data system traffic through high speed IP packet routing apparatuses becomes significant.
In a network where the IP packet routing apparatus has been introduced into the public network, the IP packet routing apparatus and the above-mentioned SDH transport system are ordinarily used in a mixed manner. Also, there is an approach which realizes the SDH system with an IP packet routing apparatus provided with a SDH interface without using a SDH transport system. Such a network obtained by the combination of the IP packet routing apparatus and the SDH system is called “IP OVER SDH (SONET) system (refer to IEEE COMMUNICATION MAGAZINE, MAY 1998, P136–142).
In a failure detection performed by this IP OVER SDH system, switching from a working line to a protection line can rapidly be performed by the APS switching system at a time of failure occurrence in a physical layer such as a line failure, a failure of a physical layer processing section in the IP packet routing apparatus or the like. Incidentally, at this time, since a high speed switching at the physical layer is not detected at an ordinary network layer, a routing protocol operating in a network layer is not actuated.
Also, at a time of failure occurrence in the network layer due to a failure of a network layer processing section in the IP packet routing apparatus or the like, since it is impossible to recover the failure by such a switching in the physical layer, the routing protocol is activated to perform switching in the network layer. That is, the failure recovery in the network of the IP OVER SDH (SONET) system comprises a recovery performed by the APS of the physical layer and a recovery performed by the routing protocol of the network layer.
In a network in which a high reliability is required, such as a public network, it is desirable that all failures including a line failure, a node failure, and the like can be recovered rapidly with a high reliability. For this reason, when such a failure as a failure in the network layer can not be recovered by only the recovery of the APS, a high speed and high reliable switching approach is inevitable in a case that a switching is performed in the network layer.
There have been proposed several approaches where a switching in the network layer is realized in a network where a high reliability is required, such as a public network or the like. As one of these approaches, for example, there is a technique described in Japanese Patent Application Laid-Open (JP-A) No. 10-13449 publication.
In JP-A 10-13449, such a technique is employed that the status change of K1, K2 bytes serving as the APS byte are monitored and, when a status change of the APS byte occurs due to a failure, a routing protocol of a network layer is actuated to update a routing table and perform a line switching.
Also, as another approach, for example, there is an approach where a switching from a working line to a protection line is performed without actuating a routing protocol and without updating a routing table. For example, there are an approach where a working configuration and a protection configuration serving as configurations for transmission/reception of a packet are prepared in each communication or routing apparatus, and a packet is copied by a software processing and packets are transmitted in a multicast manner from both the working configuration and the protection configuration so that a configuration for receiving a packet in only an apparatus on a reception side is switched from the working configuration to the protection configuration at a time of failure occurrence, and another approach where a transmission destination (address) for performing transmission by a working configuration and a transmission destination for performing transmission by a protection configuration are stored in a routing table, and packets are transmitted from both the working and protection configurations according to an address retrieval so that only an apparatus on a reception side is switched from the working configuration to the protection configuration at a time of failure occurrence like the former approach.