Abstract:
Methods and apparatus for assigning and/or storing routing metric values for routing traffic in a network having line terminating equipment connected by an line data communications channel (LDCC), so that routing traffic is sent across the LDCC. These methods and systems include a node and network that use the LDCC for transmitting routing information, such as Intermediate System to Intermediate System Level 2 routing traffic.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to the transmission of data in a synchronous optical network, and more particularly, to transmitting routing traffic in a synchronous optical network. 
     As shown in FIG. 1, there are three layers in a Synchronous Optical Network (SONET) architecture. These layers include a section, a line, and a path. A section concerns communications between two adjacent network elements, referred to as a section terminating equipment (STE)  110 - 1  through  110 - 6 . Regenerators  140 - 1  and  140 - 2  and add-drop multiplexers (ADM)  150 - 1  and  150 - 2  are examples of STE. 
     A line concerns communications between line terminating equipment (LTE)  120 - 1  through  120 - 4 , such as ADMs  150 - 1  and  150 - 2 . As shown in FIG. 1, a line includes one or more sections. LTEs  120 - 1  through  120 - 4  perform line performance monitoring and automatic protection switching. Regenerators generally are not LTEs, although add-drop multiplexers typically include both an STE and an LTE. 
     An end-to-end connection is called a path and the equipment on either end that sends or receives a signal is called path-terminating equipment (PTE)  130 . As shown in FIG. 1, a path includes one or more lines, each of which includes one or more sections. 
     SONET includes a section data communications channel (SDCC) providing a 192 kbps channel and a Line Data Communications Channel (LDCC) providing a 576 kbps channel. 
     SONET presently uses the Intermediate System to Intermediate System (IS-IS) level 2 routing protocol for exchanging routing traffic between Intermediate Systems in different areas within the same routing domain. An Intermediate System is typically defined as a router. 
     Presently, IS-IS level 2 traffic is sent over the SDCC. As stated above, the SDCC provides only a 192 kbps channel, which at present is heavily used. As currently defined, the SDCC does not have a priority mechanism for determining which information can be discarded when the SDCC channel is overloaded. Therefore, in the event the capacity of the SDCC channel is exceeded, the stack discards information without any intelligent discrimination. This can result in the loss of vital messages and lead to network failures. 
     Because the IS-IS level 2 protocol requires a contiguous backbone of IS Level 2 capable network elements, using the SDCC for IS-IS level 2 traffic, increases the costs of STE only equipment, such as regenerators. Because STE-only network elements are low end, cost sensitive devices, this can greatly increase network costs. 
     Thus, it is desirable to have a method and system for intermediate system level 2 transparency that overcomes the above and other disadvantages of the prior art. 
     SUMMARY OF THE INVENTION 
     Methods and systems consistent with the invention, as embodied and broadly described herein, comprise the step of assigning routing metric values for sending routing traffic in a network having line terminating equipment connected by an LDCC, such that routing traffic is sent across the LDCC. 
     In another embodiment, such methods and systems comprise a node that includes means for storing routing metric values for an LDCC and an SDCC, and means for placing routing traffic on the LDCC. 
     In another embodiment, such methods and systems comprise a network that includes means for assigning routing metric values to LDCC links, means for assigning routing metric values to SDCC links, means for computing a routing metric from the assigned routing metric values, and means for determining from the computed routing metrics whether to place routing traffic on the LDCC or SDCC, wherein the routing metric values are assigned such that the routing traffic is placed on the LDCC. 
    
    
     The summary of the invention and the following detailed description should not restrict the scope of the claimed invention. Both provide examples and explanations to enable others to practice the invention. The accompanying drawings, which form part of the description for carrying out the best mode of the invention, show several embodiments of the invention, and together with the description, explain the principles of the invention. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the Figures: 
     FIG. 1 is an illustration of a SONET network; 
     FIG. 2 is an illustration of a SONET network connected to an OSS for network management, in accordance with methods and systems consistent with the invention; 
     FIG. 3 is a block diagram of a prior art add drop multiplexer configured to send routing traffic over the SDCC; and 
     FIG. 4 is a block diagram of an add drop multiplexer configured to send routing traffic over the LDCC, in accordance with methods and systems consistent with the invention. 
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     As shown in FIG. 1, there are three types of equipment within a SONET network element: path terminating equipment (PTE)  130 - 1  and  130 - 2 , line terminating equipment (LTE)  120 - 1  through  120 - 4 , and section terminating equipment (STE)  110 - 1  through  110 - 6 . In addition, FIG. 1 shows a section data communications channel (SDCC)  160  connecting STE  110 - 1  thru STE  10 - 6  and a line data communications channel (LDCC)  170  connecting LTE  120 - 1  thru LTE  120 - 4 . 
     Although the detailed description is directed to the invention&#39;s use with SONET, the invention is equally applicable to synchronous digital hierarchy (SDH). 
     In a preferred embodiment, the LDCC is used to carry IS-IS Level 2 traffic. This is preferably accomplished by setting routing metric values for the links between LTEs to a value that is less than the sum of the routing metrics for the SDCC links between the LTEs. 
     As shown in FIG. 1, two LTEs, for example LTE  120 - 2  and LTE  120 - 3 , are linked by a single LDCC  170  and through STEs  110  by three SDCC links  160 - 1 ,  160 - 2 , and  160 - 3 . In a preferred embodiment, routing metric values are assigned to the LDCC  170  and the three SDCC links  160 - 1 ,  160 - 2 , and  160 - 3  in such a manner that the system sends IS-IS Level 2 routing traffic over the LDCC  170 . 
     The system sends routing traffic over the channel with the lowest computed routing metric, where the computer routing metric is the sum of the routing metric values for each link of the connection between the nodes of interest. For example, if the routing metric value for the LDCC is set to 10, and the three SDCC links are each assigned a routing metric of 5, then the sum of the three SDCC links routing metric values is 15. As such, the IS-IS Level 2 traffic is sent across the LDCC because the sum of the routing metric values over the LDCC is less than the sum of the routing metric values for the three SDCC links. If, however, the routing metric value for the LDCC link is set to 20, then the IS-IS Level 2 traffic is sent across the three SDCC links. 
     FIG. 2 provides a block diagram of a SONET network  100 , which is connected via a Gateway Network Element (GNE)  230  to an Operations Support System (OSS)  220  connected to a computer  210  in accordance with an embodiment of the invention. From computer  210 , a network administer manages the SONET network  100 . 
     FIG. 3 provides a more detailed block diagram of an Add Drop Multiplexer (ADM)  310 , in accordance with an embodiment of the invention. As shown, ADM  310  includes STE  312 , LTE  314 , a TSI  316 , a processor  318 , memory  320 , and a craft port  322 . The processor  318 , preferably, includes a Connectionless Network Protocol (CLNP) machine  330 , a IS-IS protocol machine  332 , a management application  334 , and a management interface  336 , an OSI stack layers  4 - 7  machine  342 , and a Link Access Protocol-D (LAP-D) machine  344 . The memory  320 , preferably, includes an IS-IS routing table  338 . 
     In a preferred embodiment, when a network administrator wishes to change the routing metric values in ADM  310 &#39;s routing table, the administrator enters appropriate instructions through the computer  210  connected to OSS  220 . These instructions are then routed from the OSS  220  to the appropriate GNE  230 , after which, they are routed through the SONET network  100  to the proper ADM  310  over either the LDCC or SDCC, depending on the current routing metric values. The instructions are then routed by the LTE  312  or STE  314 , respectively, to the TSI  316  where they are routed through the Link Access Protocol-D (LAP-D) machine  344  to the CLNP protocol machine  330  of the processor  318 . The CLNP protocol machine  330  then sends the instructions up through the OSI stack layers  4 - 7  machine  342  to the management application  334 , which makes the appropriate changes to the IS-IS routing table  338  in memory  320 . 
     In another embodiment, a network administrator makes changes to the IS-IS routing table  338  though a computer  340 , also referred to as a craft interface, connected to the ADM  310  via a craft port  322 . The network administrator sends instructions from the computer  340  to the ADM  310  through craft port  322 , which sends the instruction to the management interface  336  of the processor  318 . The management interface  336  then sends the instructions to the management application  334 , which makes the appropriate changes to the routing table  338  in memory  320 . 
     In addition, to receiving IS-IS routing traffic from a network administrator, network elements, such as ADM  310 , may also exchange IS-IS routing traffic amongst themselves. In a preferred embodiment, this information is received by ADM  310  and routed to the CLNP Protocol Machine  330 , which sends the information to the IS-IS protocol machine  332 . The IS-IS protocol machine  332  then examines the information and makes the appropriate changes in the routing table  338  in memory  320 . 
     In a preferred embodiment, through any of the methods and systems described above, the routing tables of the various LTEs in a SONET network can be set such that all IS-IS Level 2 traffic is sent over the LDCC rather than the SDCC. For example, as shown in FIG. 3, the routing table is set such that the computed routing metric for sending IS-IS Level 2 traffic results in the traffic being sent across the SDCC. This is because there is one LDCC link between LTEs with a routing metric value of 50, and three SDCC links, each with a routing metric value of 10. As such, the computed routing metric for sending traffic across the LDCC is 50, and the computed routing metric for the SDCC is 30, or 10+10+10. Because the computed routing metric for sending the IS-IS Level 2 traffic over the SDCC is less than the computed metric for sending the traffic over the LDCC, the routing traffic is sent over the SDCC. Thus, as previously discussed, STE-only equipment, such as regenerators, must be an IS Level 2 capable network element. 
     In an embodiment, a processor, such as processor  318 , computes the sums of routing metric values, and determines on which link to place the IS-IS Level 2 traffic. Further, in an embodiment, a processor running the OSI stack protocols, which, for example, may also be processor  318 , places the IS-IS Level 2 traffic on the determined link. Also, as will be obvious to one skilled in the art, separate processors can be used to implement these various functions. 
     FIG. 4 provides a block diagram of ADM  310 , after the routing table has been adjusted so that IS-IS level 2 traffic is sent across the LDCC, in accordance with an embodiment of the invention. As shown, the assigned routing metric value for the LDCC is 50, while the assigned routing metric value for each SDCC link is now 20. As such, the computed metric value for sending the traffic over the SDCC is 60, while for the LDCC it is still 50. As such, the IS-IS Level 2 traffic is now sent across the LDCC. Accordingly, the intervening STE-only equipment need not be IS Level 2 capable. 
     While it has been illustrated and described what is at present considered to be the preferred embodiment and methods of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made, and equivalents may be substituted for elements thereof without departing from the true scope of the invention. 
     In addition, many modifications may be made to adapt a particular element, technique or, implementation to the teachings of the present invention without departing from the central scope of the invention. Therefore, it is intended that this invention not be limited to the particular embodiment and methods disclosed herein, but that the invention includes all embodiments falling within the scope of the appended claims.