This invention relates to data networks, and, in particular, to an improved technique of routing data in a data network utilizing optical transport means.
Optical fiber networks, such as SONET, are in widespread use due to their ability to support high bandwidth connections. The bandwidth of optical fibers runs into gigabits and even terabits. Optical links can thus carry hundreds of thousands of communications channels multiplexed together. Optical fiber networks are subject to outages if and when breaks in the fibers occur. A cut in a single fiber between two network nodes could conceivably render communications along certain nodes of the system impossible. Moreover, because each fiber carries so many independent voice and/or data channels, a large number of communications sessions would be interrupted.
In a conventional packet switched data network, packets are multiplexed onto high speed connections between packet data switches. These switches are, at the data level, routers, such as the CISCO family of routers well known in the art. The routers output the data packets to a physical transport level constructed out of optical fibers and equipment to propagate the optical signals along them. Such optical transport equipment is commonly known, as, for example, that manufactured and sold by Lucent Technologies and Nortel Networks. A portion of such a network is shown in FIG. 1, which includes four exemplary routers (R), 101, 102, 120 and 121, and a network of transport equipment nodes (TE) 103-106. Each router feeds into the transport network. Although the data layer and the physical layer exchange the data packets through each other, these layers are not integrated, and are each operated as discrete and autonomous entities. Each packet switch reads the address header in packets to be routed through the network, and interprets the required information for transmission from one switch to the next. It then hands the packet to the physical layer for transportxe2x80x94according to the then prevailing xe2x80x9cassumptionsxe2x80x9d the router makes about the transport layer""s topology.
The connections between the packet switches are often extremely high speed, and carry a relatively large number of multiplexed packets. If a fiber is cut or a communications channel damaged in some other way, then a large volume of data would be cut off. Since the router, or data, layer of the network does not recognize a xe2x80x9cfiber cutxe2x80x9d, and only deduces its existence from the failure of a number of packets to acknowledge having arrived at the intermediate node, this information is not available to the router for some minutes. Accordingly, it is required, in order to insure reliability, that such networks have some way of recovering from cut fibers and/or other loss of data channel capability.
In one conventional method, a redundancy route (i.e. a backup route) and a primary route are provided. When an interruption occurs on the primary route somewhere between a source node and a destination node, the packet data is routed from the source node to the destination node over the backup route. Such recovery techniques usually do not provide for the isolation of the problem along a particular portion of the route. Rather, if communications between two switches fail, a new route is used.
Even though the interruption may only occur along a length of the primary route between two adjacent nodes, the whole primary route is replaced by the backup route for transmitting the packet data from the source node to the destination node. This is not optimal because the operable portions of the route are not used during the fault. Thus, the network effectively operates at 50% capacity in order to ensure backup capability.
Other conventional methods attempt to provide for backup communications links without duplicating each and every link, by distributing the diverted data packets along various other routes. While allowing operation at greater than 50% capacity, this approach inevitably increases packet latency, as more packets are required to be carried along the distributed backup links than is optimal.
FIG. 2 illustrates the occurrence of such a fiber cut along link 212. This link connects routers R1201 and R2202. Illustrating the first option described above, there is a backup link 220 running between the same transport network nodes as link 212, TE 203 and TE 205. As described above, since this link 220 is only used if link 212 has failed, it is essentially wasted most of the time.
FIG. 2 also depicts the implementation of the second option offered by the prior art. Links 221 and 222 depict the distributed rerouting of packets formerly sent along link 212. Link 222 has a pathway over link 214, through TE 206, and over link 215, to destination transport node TE 205. Similarly, link 221 runs along link 210 to intermediate TE node 204, then along link 211 to the destination transport node TE 205. In the situation illustrated in FIG. 2, there are no routers connected to transport network nodes 204 and 206, just transport network switches, such as optical cross connects. Thus, packets cannot be switched at these nodes by intelligent switches, so the backup routes 221 and 222 to router R2202 must be pre-provisioned at router R1201. To do this requires running (a) additional links from R1201 to TE 203, shown in FIG. 2 as dotted links 231 and 232, as well as (b) additional links from R2202 to TE 205, shown in FIG. 2 as dotted links 241 and 242. Ports associated with these additional links must be created, and dedicated, to these links as well. Further, these additional links must be provided with backup or protection themselves, further increasing cost and complexity.
It should be noted that links 221 and 222 do not physically exist, as they are mere depictions of the traffic that used to run along link 212 now running along the described two hop pathways within the transport network. As described above, this method does not waste as much bandwidth as a fully redundant backup link, but it can cause latency, and in times of heavy loading even loss of packets, if traffic along the two hop pathways is already at or near full capacity.
Besides the wasting of valuable bandwidth, the increase of packet latency and required links between routers and the transport network, or some compromise of the two, the conventional method introduces needless complexity. The calculation of the primary and the backup data paths, being divorced from the real time changes to the actual transport network is always, at best, an approximation of the optimal routing of packets through the network. This approximation is then mapped onto the actual transmission equipment. When a communications link in the physical transport network fails, as described above, the optics senses the fiber cut relatively immediately. However, since the routers cannot be apprised of this fact, the calculated backup path or paths are used. The mapping of these paths onto the physical transport layer of the network requires administrative overhead.
In view of the above, there exists a need in the art for a more efficient technique for dealing with communication link failures in the physical layer of data networks. Such a method would reduce the wasted bandwidth, increased latency, and administrative overhead which is ubiquitous in the various solutions used in the current art. Such a method would integrate the near immediate detection of a fiber cut available in the transport layer with the decision making routing processes operative in the data layer.
An object of the present invention is to provide a technique for immediately detecting the failure of a communications link in a data network, and communicating said communications link failure in substantially real time to the routers utilized in the network.
Another object is to provide a technique that immediately communicates, in substantially real time, after such a communications link failure, the revised transport network topology to the routers.
Another object of the invention is to provide a more efficient technique of backing up faulty communications channels in a multiple node packet data network by immediately rerouting the data packets.
According the present invention, packet data is transmitted from a source node to a destination node over a plurality of intermediate nodes. Each internodal hop occurs via a communications link. When a communications link fails (e.g. a cut in the optical fiber occurs) between a first and second nodes, this fact, and the resultant revised network topology, is immediately communicated to the routers for the appropriate rerouting of network data.
In a preferred embodiment, each network node is comprised of an edge switch. The edge switch comprises a packet engine connected to a packet switched data network, and an optical engine connected to an optical transport network, where the packet engine and the optical engine are under common hardware or software control, and where the optical engine continually communicates the topology of the optical transport network to the packet engine substantially in real time.