Abstract:
A method and system provides the capability to provision Dual Working mode service in a SONET network, while maintaining compatibility with existing SONET provisioning systems. In one embodiment of the present invention, a method for provisioning dual working mode in a Synchronous Optical Network/Synchronous Digital Hierarchy network comprises the steps of generating provisioning commands to provision a non-dual working mode of operation in the Synchronous Optical Network/Synchronous Digital Hierarchy network, modifying the generated commands to indicate to a first network element that dual working mode is being provisioned, and transmitting the modified commands to provision the Synchronous Optical Network/Synchronous Digital Hierarchy network.

Description:
FIELD OF THE INVENTION 
   The present invention relates to provisioning dual working mode in a SONET or SDH network. 
   BACKGROUND OF THE INVENTION 
   In order to provision Dual Working mode service in a SONET network, it is necessary to establish different information on the working and protecting paths. The normal SONET provisioning models don&#39;t support this. A need arises for a technique that provides the capability to provision Dual Working mode service in a SONET network, while maintaining compatibility with existing SONET provisioning systems. 
   SUMMARY OF THE INVENTION 
   The present invention provides the capability to provision Dual Working mode service in a SONET network, while maintaining compatibility with existing SONET provisioning systems. The present invention “overloads” the current Unidirectional Path Switched Ring (UPSR) provisioning of the SONET network in order to provide the paths needed for Dual Working. Since it is important to do this under the Operations Systems Modification of Intelligent Network Elements (OSMINE) (Tl1 based management) process this must also be considered. 
   For Operations Systems Modification of Intelligent Network Elements (OSMINE) the Dual Working mode looks much like Unidirectional Path Switched Ring (UPSR) and can be treated as such at all but the “endpoint” network elements (NEs). These are the network elements (NEs) that host the Ethernet interfaces. Those network elements (NEs) must send different information on the working and protecting paths and also know to receive same in the opposite direction. Changing keywords is the simplest approach under Operations Systems Modification of Intelligent Network Elements (OSMINE). For that reason a new keyword in the EPORT command would be added. This keyword when specified as dual informs the Ethernet interface to send a Virtually Concatenated Ethernet stream split between both line interfaces. In the case that cross connect provisioning is also needed (all 4000 network elements (NEs) except 4020) then the cross connects are provisioned as if they were Unidirectional Path Switched Ring (UPSR). However, the system knows due to the earlier entry of the key word under EPORT that the cross connects are actually Dual Working and knows to bypass the path selector and send both the working and protecting traffic to the Ethernet service. 
   In one embodiment of the present invention, a method for provisioning dual working mode in a Synchronous Optical Network/Synchronous Digital Hierarchy network comprises the steps of generating provisioning commands to provision a non-dual working mode of operation in the Synchronous Optical Network/Synchronous Digital Hierarchy network, modifying the generated commands to indicate to a first network element that dual working mode is being provisioned, and transmitting the modified commands to provision the Synchronous Optical Network/Synchronous Digital Hierarchy network. 
   In one aspect of the present invention, dual working mode comprises communicating different data on each of a plurality of Synchronous Optical Network/Synchronous Digital Hierarchy network paths to the first network element. The different data may be generated at a second network element using virtual concatentation. The different data may be generated from a data stream communicated with a local area network coupled to the second network element. The different data may be reassembled at the first network element using virtual concatentation. The reassembled different data may be communicated with a local area network connected to the first network element. 
   In one aspect of the present invention, the first network element comprises a first local area network service unit and a first plurality of logical units, a second network element comprises a second local area network service unit and a second plurality of logical units, the second local area network service unit communicates with a second local area network and the different data is generated from a data stream communicated with the second local area network, and each of the second plurality of logical units communicates different data with a different one of the first plurality of logical units over a different Synchronous Optical Network/Synchronous Digital Hierarchy network path. The different data may be generated at the second network element using virtual concatentation. The first local area network service unit may communicate with a first local area network. The different data may be reassembled at the first network element using virtual concatenation. The reassembled different data may be communicated with the first local area network. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The details of the present invention, both as to its structure and operation, can best be understood by referring to the accompanying drawings, in which like reference numbers and designations refer to like elements. 
       FIG. 1  is an exemplary block diagram of a SONET network  100  operated in Dual Working mode. 
       FIG. 2   a  is an exemplary diagram of dual working mode operation from a perspective external to a network element. 
       FIG. 2   b  is an exemplary diagram of “0:2” mode of operation from a perspective external to a network element. 
       FIG. 2   c  is an exemplary diagram of “Unidirectional Path Switched Ring (UPSR)” mode of operation from a perspective external to a network element. 
       FIG. 3   a  is an exemplary diagram of processing control for “0:2” and “Unidirectional Path Switched Ring (UPSR)” modes of operation from a perspective internal to a network element. 
       FIG. 3   b  is an exemplary diagram of processing control for dual working mode of operation from a perspective internal to a network element. 
       FIG. 4  is an exemplary block diagram of a provisioning scenario for Unidirectional Path Switched Ring (UPSR) mode in a SONET network. 
       FIG. 5  is an exemplary block diagram of a provisioning scenario for dual working mode in a SONET network. 
       FIG. 6  is an exemplary block diagram of a full SONET ring view of dual working mode connections in a SONET network. 
       FIG. 7  is an exemplary block diagram of a full SONET ring view of dual working mode connections in a SONET network, which is a non-Telcordia example, in which an internal fully protected ring with peripheral Dual Working Mode (DWM) is running. 
       FIG. 8  is an exemplary block diagram of a full SONET ring view of a transmit example of dual working mode connections in a SONET network, which is a non-Telcordia example and which includes an interface between a Dual Working Mode (DWM) network element and a Non-Dual Working Mode (DWM) network element (Transmit). 
       FIG. 9  is an exemplary block diagram of a full SONET ring view of a transmit example of dual working mode connections in a SONET network, which is a non-Telcordia example and which includes an interface between a Dual Working Mode (DWM) network element and a Non-Dual Working Mode (DWM) network element (Receive). 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Dual working mode is a mode of operation of a SONET network in which each of the OCn side interfaces is used independently by the data service side interfaces. Dual working mode effectively doubles service unit backplane bandwidth and SONET ring bandwidth. For example, Dual Working mode allows a full Gigabit per second (Gbps) rate on OC12 when used with Virtual Concatenation (VCAT) and allows three times a 100 Megabit per second (Mbps) rate on OC3 when used with Virtual Concatenation (VCAT). 
   An example of a SONET network  100  operated in Dual Working mode is shown in  FIG. 1 . Exemplary network  100  includes Local Area Network Service Units (LANSUs)  102 A-B, Line Units (LUs)  104 A-D, and SONET ring  106 , which includes Working path  108  and Protecting path  110 . LANSUs  102 A-B provide the interface between the other networks  112 A-B connected to LANSUs  102 A-B and the working  108  and protection  110  paths of SONET network  100 . For example, LANSUs  102 A-B may connect the working  108  and protection  110  paths of SONET network  100  to Local Area Networks such as Ethernet networks, Token Ring networks, etc. Each LANSU is connected to two LUs. For example, LANSU  102 A is connected to LU  104 A and LU  104 B and LANSU  102 B is connected to LU  104 C and LU  104 D. Each line unit provides the interface from the LANSU to the SONET network path, as well as providing timing control to access precision network clock and SONET frame pulse reference. 
   In Dual Working mode, different data is communicated over each path of SONET ring  106 , rather than the conventional SONET operation in which the same data is communicated over both paths. For example, data  114 A is communicated over working path  108 , while data  114 B is communicated over protecting path  110 . Data to/from LAN  112 A-B is split between working path  108  and protecting path  110  using the well-known Virtual Concatenation (VCAT) standard. Each path may carry data at the full path bandwidth, thus providing twice the network bandwidth of the conventional SONET operation in which the same data is communicated over both paths. 
   If a fault occurs in one of the paths of SONET network  106  (either a path failure or an electronics failure) when operated in Dual Working mode, the fact is noted at the receiving end, which signals using Link Capacity Adjustment Scheme (LCAS) back to the data source that the Synchronous Transport Signal (STS) (or block of Synchronous Transport Signals (STSs) in case of path failure) is down. Link Capacity Adjustment Scheme (LCAS) drops the “broken” Synchronous Transport Signals (STSs) from the active members of the Virtual Concatenation (VCAT) group. In a typical scenario in which a path fails, half the Synchronous Transport Signals (STSs) are down and the data rate is cut in half. 
   A comparison of several modes of operation of a SONET network from a perspective external to a network element is shown in  FIGS. 2   a - c . Dual working mode operation is shown in  FIG. 2   a . Network element  201 A communicates data i with a LAN  202 A. Network element  201 A communicates data over a SONET network including working path  203 A and protecting path  204 A. The data on working path  203  is data o and the data on protecting path  204 A is data p. In Dual Working mode, the data o+p=data i, thus the sum of the data communicated on the SONET interfaces  203 A and  204 A is equal to the information communicated with the LAN  202 A. 
   The conventional “0:2” mode of operation is shown in  FIG. 2   b . In 0:2 mode, the same data, which is the data communicated by network element  201 B with LAN  202 B, is fed to both SONET interfaces  203 B and  204 B, but only appears on one output. For example, the data on working path  203 B, o, equals the data on LAN  202 B, i (o=i), while there is no data on protecting path  204 B (p=0). Dual working mode looks similar to 0:2 mode when a non-Virtual Concatenation (VCAT) data stream is fed to one of the interfaces. Dual working mode looks different from 0:2 when Virtual Concatenation (VCAT) is used to “spread” a single data stream between the two interfaces. 
   The conventional “Unidirectional Path Switched Ring (UPSR)” mode of operation is shown in  FIG. 2   c . In Unidirectional Path Switched Ring (UPSR) mode, the data communicated by network element  201 C with LAN  202 C, is fed to both SONET interfaces  203 C and  204 C, and appears on both outputs. For example, the data on working path  203 C, o, equals the data on LAN  202 C, (o=i), and the data on protecting path  204 C, p, equals the data on LAN  202 C (p=0), thus, o=p=i. 
   A comparison of several modes of operation of a SONET network from a perspective internal to the network element is shown in  FIGS. 3   a - b . In  FIG. 3   a , the processing control for 0:2 and Unidirectional Path Switched Ring (UPSR) modes is shown. These are modes where the input process  302  simply transfers the data to the output processes  304 A-B, and the output processes  304 A-B determines which information from the input facility  306  is allocated to which output facility  308 A-B. 
   In  FIG. 3   b , the processing control for Dual Working mode is shown. In Dual Working mode the input process  302  determines which information from the input facility  306  is allocated to which output facility  308 A-B, while the output processes  304 A-B simply transfer the data. 
   In order to operate a SONET network in Dual Working mode, the SONET network must be configured, or provisioned, to operate that way. Conventional SONET provisioning models do not support provisioning of a SONET network in Dual Working mode. The present invention “overloads” the standard Unidirectional Path Switched Ring (UPSR) provisioning of the SONET network in order to provide the paths needed for Dual Working mode. 
   A standard service that is used to provision a SONET network is known as Operations Systems Modification of Intelligent Network Elements (OSMINE). Most domestic telecommunications networks depend on operations support systems (OSS) software developed and maintained by TELCORDIA™. The major local exchange carriers manage their networks using these systems. The Telcordia Operations Systems Modification of Intelligent Network Elements (OSMINE) Services process helps enable network equipment compatibility and interoperability with Telcordia OSSs. This helps to ensure operations systems automation, a requirement to provide Operation, Administration, Maintenance and Provisioning (OAM&amp;P) of services in a timely fashion and on a volume basis. Since it is important to provision Dual Working mode under the Operations Systems Modification of Intelligent Network Elements (OSMINE) process, this must also be considered. 
   For Operations Systems Modification of Intelligent Network Elements (OSMINE) the Dual Working mode looks much like Unidirectional Path Switched Ring (UPSR) and can be treated as such at all but the “endpoint” network elements (NEs). These are the network elements (NEs) that host the Ethernet interfaces. Those network elements (NEs) must send different information on the working and protecting paths and also know to receive same in the opposite direction. Changing keywords is the simplest approach under Operations Systems Modification of Intelligent Network Elements (OSMINE). For that reason a new keyword in the EPORT command would be added. This MODE keyword when specified as dual informs the Ethernet interface to send a Virtually Concatenated Ethernet stream split between both line interfaces. In the case that cross connect provisioning is also needed (all 4000 network elements (NEs) except 4020) then the cross connects are provisioned as if they were Unidirectional Path Switched Ring (UPSR). However, the system knows due to the earlier entry of the MODE under EPORT that the cross connects are actually Dual Working and knows to bypass the path selector and send both the working and protecting traffic to the Ethernet service. 
   An exemplary provisioning scenario for Unidirectional Path Switched Ring (UPSR) mode in a SONET network is shown in  FIG. 4 . In the example shown in  FIG. 4 , the Ethernet unit is present in the same network element as the switch that normally does Unidirectional Path Switched Ring (UPSR). It is assumed that this is the case at both ends of the SONET network, although, for clarity, only one direction of SONET communication is shown. However, one of skill in the art would recognize that the other direction of SONET communication is similar to the example shown. As shown, a transmitting network element (NE-TX)  402  transmits the same data over two separate paths, working path  404  and protecting path  406 , to receiving network element (NE-RCV)  408 . Each network element, NE-TX  402  and NE-RCV  408 , includes a LANSU and two LUs. For example, NE-TX  402  includes LAN SU  410  and LUs  412 A-B, and NE-RCV  408  includes LANSU  414  and LUs  416 A-B. LANSUs  410  and  414  provide the interface between the other networks connected to LANSUs  410  and  414  and the working  404  and protection  406  paths of the SONET network. Each line unit provides the interface from the LANSU to the SONET network path, as well as providing timing control to access precision network clock and SONET frame pulse reference. 
   In the Unidirectional Path Switched Ring (UPSR) mode of operation, the same data traffic is transmitted from LANSU  410  to each LU  412 A-B. This data traffic is transmitted over both working path  404  and protecting path  406  to LUs  416 A-B. At NE-RCV  408 , typically within one of the LUs, such as LU  416 A, the data traffic from the best path, selected by best path selector  418  between working path  404  and protecting path  406 , is sent to LAN SU  414 . For example, if LANSU  410  receives Ethernet data at 50 Mbps, then the same Ethernet data is transmitted over working path  404  at 50 Mbps and over protecting path  406  at 50 Mbps. Best path selector  418  selects the data traffic from the best path and LANSU  414  outputs the Ethernet data at 50 Mbps. 
   An example of provisioning commands that may be used to provision NE-TX  402  and NE-RCV  408  for Unidirectional Path Switched Ring (UPSR) mode is as follows: 
   On NE-TX:
         ENT-EPORT:&lt;LAN1-P1&gt;:WANLINK=STS1   ENT-CRS-STS1:&lt;LAN  1 -P1&gt;,&lt;LU1-STS1&gt;   ENT-CRS-STS1:&lt;LAN1-P1&gt;,&lt;LU2-STS1&gt;       

   On NE-RCV:
         ENT-EPORT:&lt;LAN2-P1&gt;:WANLINK=STS1   ENT-CRS-STS1:&lt;LAN2-P1&gt;,&lt;LU1-STS1&gt;   ENT-CRS-STS1:&lt;LAN2-P1&gt;,&lt;LU2-STS1&gt;       

   In order to provision dual working mode, the present invention tricks the Operations Systems Modification of Intelligent Network Elements (OSMINE) service into thinking it is setting up a standard Unidirectional Path Switched Ring (UPSR) so that only a keyword change informs the system that this is not the case. The reason this works is that the middle of the network does not know the difference between dual working and Unidirectional Path Switched Ring (UPSR) virtual ring. 
   An example of dual working mode physical connections in a SONET network is shown in  FIG. 5 . In the example shown in  FIG. 5 , the Ethernet unit is present in the same network element as the switch that normally does Unidirectional Path Switched Ring (UPSR). It is assumed that this is the case at both ends of the SONET network, although, for clarity, only one direction of SONET communication is shown. However, one of skill in the art would recognize that the other direction of SONET communication is similar to the example shown. As shown, a transmitting network element (NE-TX)  502  transmits different data over two separate paths, working path  504  and protecting path  506 , to receiving network element (NE-RCV)  508 . Each network element, NE-TX  502  and NE-RCV  508 , includes a LANSU and two LUs. For example, NE-TX  502  includes LANSU  510  and LUs  512 A-B, and NE-RCV  508  includes LANSU  514  and LUs  516 A-B. LANSUs  510  and  514  provide the interface between the other networks connected to LANSUs  510  and  514  and the working  504  and protection  506  paths of the SONET network. Each line unit provides the interface from the LANSU to the SONET network path, as well as providing timing control to access precision network clock and SONET frame pulse reference. 
   In the dual working mode of operation, the different data traffic is transmitted from LANSU  510  to each LU  512 A-B. The data traffic received by LANSU  510  is divided into two data streams of alternating bytes using Virtual Concatenation (VCAT). Each data stream is transmitted over a different path. Thus, one data stream is transmitted over working path  504  and the other data stream is transmitted over protecting path  506  to LUs  516 A-B. At NE-RCV  508 , the path selectors  518 A-B are fixed as selecting the incoming path to each LU. Thus, path selector  518 A is fixed as selecting working path  504  and path selector  518 B is fixed as selecting protecting path  506 . Data from both paths is recombined using Virtual Concatenation (VCAT) and is sent to LAN SU  514 . For example, if LANSU  510  receives Ethernet data at 100 Mbps, then a portion of the Ethernet data is transmitted over working path  504  at 50 Mbps and a portion of the Ethernet data is transmitted over protecting path  506  at 50 Mbps. Data from both paths is recombined using Virtual Concatenation (VCAT) and sent to LAN SU  514 , which outputs the Ethernet data at 100 Mbps. 
   An example of provisioning commands that may be used to provision NE-TX  502  and NE-RCV  508  for Dual Working mode is as follows: 
   On NE-TX  502 
         ED-EQPT:&lt;LAN1&gt;:PATHPROT=DUAL   ENT-EPORT:&lt;LAN1-P1&gt;:WANLINK=STS1   ENT-CRS-STS1:&lt;LAN1-P1&gt;,&lt;LU1-STS1&gt;   ENT-CRS-STS1:&lt;LAN1-P1&gt;,&lt;LU2-STS1&gt;       

   On NE-RCV  508 
         ED-EQPT:&lt;LAN2&gt;:PATHPROT=DUAL   ENT-EPORT:&lt;LAN2-P1&gt;:WANLINK=STS1:   ENT-CRS-STS1:&lt;LAN2-P1&gt;,&lt;LU1-STS1&gt;   ENT-CRS-STS1:&lt;LAN2-P1&gt;,&lt;LU2-STS1&gt;       

   It is to be noted that the PATHPROT parameter is set to a new value, “DUAL”, rather than the default value of “Unidirectional Path Switched Ring (UPSR)”. By adding a new keyword to the ED-EQPT command the present invention uses the same command structure at both end-points. All other nodes and TL1 for end point nodes have exactly the same provisioning as Unidirectional Path Switched Ring (UPSR). Additional keywords should have negligible impact on Operations Systems Modification of Intelligent Network Elements (OSMINE) (this may be a CLIE controlled default so that Operations Systems Modification of Intelligent Network Elements (OSMINE) does not need to set it). 
   A full SONET ring view example of dual working mode connections in a SONET network is shown in  FIG. 6 . In the example shown in  FIG. 6 , NE-TX  502  and NE-RCV  508  are shown along with intermediate network elements  602 ,  604 ,  606 , and  608 . 
   Dual working mode may also be provisioned as a modification of 0:n service. This 0:n like provisioning may be accomplished, for example, if only a single STS1 is used (Virtual Concatenation (VCAT) is not used) as follows: 
   On NE-TX  502 
         ED-EQPT:&lt;LAN1&gt;:PATHPROT=DUAL   ENT-EPORT:&lt;LAN1-P1&gt;:WANLINK=STS1   ENT-CRS-STS1:&lt;LAN1-P1&gt;,&lt;LU1-STS1&gt;       

   On NE-RCV  508 
         ED-EQPT:&lt;LAN2&gt;:PATHPROT=DUAL   ENT-EPORT:&lt;LAN2-P1&gt;:WANLINK=STS1   ENT-CRS-STS1:&lt;LAN2-P1&gt;,&lt;LU1-STS1&gt;       

   The only difference is that only a single cross connect is made. This is the same distinction as between 0:n and Unidirectional Path Switched Ring (UPSR). 
   A general model of provisioning dual working mode, which is a superset of the Telcordia provisioning model, may be defined using the WANLINK parameter. WANLINK defines the amount of Synchronous Transport Signals (STSs) allocated to each direction of the SONET paths, which, for convenience, may be termed the East and West paths. For example, WANLINK=STS1-2V means that there are allocated at most 2 STS1&#39;s on the East path and at most 2 STS1&#39;s on the West path. Cross connects may be similar to Unidirectional Path Switched Ring (UPSR) or to a single path. Service is present when the first cross connect is made. If Link Capacity Adjustment Scheme (LCAS) is used there is no “hit” for additional cross connects up to the maximum. 
   An example of dual working mode connections in a SONET network, which is a non-Telcordia example, in which an internal fully protected ring with peripheral Dual Working Mode (DWM) is running, is shown in  FIG. 7 . In the example shown in  FIG. 7 , NE-TX  702  transmits different data over both legs of two separate paths, working path legs  704 A-B and protecting path legs  706 A-B, to NE-RCV  708 . NE-TX  702  and NE-RCV  708  each include a LANSU and two LUs. For example, NE-TX  702  includes LANSU  710  and LUs  712 A-B, and NE-RCV  708  includes LANSU  714  and LUs  716 A-B. LANSUs  710  and  714  provide the interface between the other networks connected to LANSUs  710  and  714  and the working path legs  704 A-B and protecting path legs  706 A-B of the SONET network. Each line unit provides the interface from the LANSU to the SONET network path, as well as providing timing control to access precision network clock and SONET frame pulse reference. 
   In the dual working mode of operation, the different data traffic is transmitted from LANSU  710  to each LU  712 A-B. The data traffic received by LANSU  710  is divided into two data streams of alternating bytes using Virtual Concatenation. Each data stream is transmitted via additional network elements, such as NE-B  720 , over both legs of a different path. Thus, one data stream is transmitted by LU 1   722 A of NE-B  720  onto both leg  704 A and leg  704 B of the working path and the other data stream is transmitted by LU 2   722 B of NE-B  720  onto both leg  706 A and leg  706 B of the protecting path. Both data streams are transmitted to NE-RCV  708  via intermediate network elements, such as NE-D  724 . At NE-D  724 , best path selectors  726 A-B select the best path from between the two legs of each path. Thus, best path selector  726 A, included in LU 1   728 A of NE-D  724 , selects the best path from between leg  706 A of the protecting path and leg  706 B of the protecting path. Likewise, best path selector  726 B, included in LU 2   728 B of NE-D  724 , selects the best path from between leg  704 A of the working path and leg  704 B of the working path. At NE-RCV  708 , the path selectors  718 A-B are fixed as selecting the incoming path to each LU. Thus, path selector  718 A is fixed as selecting working path  704  and path selector  718 B is fixed as selecting protecting path  706 . Data from both paths is recombined using Virtual Concatenation (VCAT) and sent to LAN SU  714 . For example, if LANSU  710  receives Ethernet-data at 100 Mbps, then a portion of the Ethernet data is transmitted over working path  704  at 70 Mbps and a portion of the Ethernet data is transmitted over protecting path  706  at 70 Mbps. Data from both paths is recombined using Virtual Concatenation (VCAT) and sent to LAN SU  714 , which outputs the Ethernet data at 100 Mbps. 
   A transmit example of dual working mode connections in a SONET network, which is a non-Telcordia example and which includes an interface between a Dual Working Mode (DWM) network element and a Non-Dual Working Mode (DWM) network element (Transmit), is shown in  FIG. 8 . In the example shown in  FIG. 8 , NE-TX  802  transmits different data over both legs of two separate paths, working path legs  804 A-B and protecting path legs  806 A-B, to NE-RCV  808 . NE-TX  802  and NE-RCV  808  each include a LANSU and two LUs. For example, NE-TX  802  includes LANSU  810  and LUs  812 A-B, and NE-RCV  808  includes LANSU  814  and LUs  816 A-B. LANSUs  810  and  814  provide the interface between the other networks connected to LANSUs  810  and  814  and the working path legs  804 A-B and protecting path legs  806 A-B of the SONET network. Each line unit provides the interface from the LANSU to the SONET network path, as well as providing timing control to access precision network clock and SONET frame pulse reference. 
   In the dual working mode of operation, the different data traffic is transmitted from LANSU  810  to each LU  812 A-B. The data traffic received by LANSU  810  is divided into two data streams of alternating bytes using Virtual Concatenation. Each data stream is transmitted via additional network elements, such as NE-B  820 , over both legs of a different path. Thus, one data stream is transmitted by LU 1   822 A of NE-B  820  onto both leg  804 A and leg  804 B of the working path and the other data stream is transmitted by LU 2   822 B of NE-B  820  onto both leg  806 A and leg  806 B of the protecting path. Both data streams are transmitted to NE-RCV  808  via intermediate network elements. At NE-RCV  808 , best path selectors  826 A-B select the best path from between the two legs of each path. Thus, best path selector  826 A, included in LU 1   816 A of NE-RCV  808 , selects the best path from between leg  806 A of the protecting path and leg  806 B of the protecting path. Likewise, best path selector  826 B, also included in LU 1   816 A of NE-RCV  808 , selects the best path from between leg  804 A of the working path and leg  804 B of the working path. The data streams from both paths are sent to LAN SU  814 , where they are recombined using Virtual Concatenation (VCAT). 
   A receive example of dual working mode connections in a SONET network, which is a non-Telcordia example and which includes an interface between a Dual Working Mode (DWM) network element and a Non-Dual Working Mode (DWM) network element (Receive), is shown in  FIG. 9 . In the example shown in  FIG. 9 , NE-TX  902  transmits different data over one leg of each path to NE-RCV  908 . Thus, NE-TX  902  transmits one data stream over working path leg  904 A and protecting path leg  906 A and a different data stream over working path leg  904 B and protecting path leg  906 B. NE-TX  902  and NE-RCV  908  each include a LANSU and two LUs. For example, NE-TX  902  includes LANSU  910  and LUs  912 A-B, and NE-RCV  908  includes LANSU  914  and LUs  916 A-B. LANSUs  910  and  914  provide the interface between the other networks connected to LANSUs  910  and  914  and the working path legs  904 A-B and protecting path legs  906 A-B of the SONET network. Each line unit provides the interface from the LANSU to the SONET network path, as well as providing timing control to access precision network clock and SONET frame pulse reference. 
   In the dual working mode of operation, the different data traffic is transmitted from LANSU  910  to each LU  912 A-B. The data traffic received by LANSU  910  is divided into two data streams of alternating bytes using Virtual Concatenation. Each data stream is transmitted via additional network elements, such as NE-TX  902 , over one leg of both paths. Thus, one data stream is transmitted by LU 1   912 A of NE-TX  902  onto both leg  904 A of the working path and leg  906 A of the protecting path and the other data stream is transmitted by LU 2   912 B of NE-TX  902  onto both leg  904 A of the working path and leg  906 B of the protecting path. Both data streams are transmitted to NE-RCV  908  via intermediate network elements. At NE-RCV  908 , the path selectors  926 A-B are fixed as selecting the incoming paths. The data streams from both paths are sent to LAN SU  914 , where they are recombined using Virtual Concatenation (VCAT). 
   It is important to note that while the present invention has been described in the context of a fully functioning data processing system, those of ordinary skill in the art will appreciate that the processes of the present invention are capable of being distributed in the form of a computer readable medium of instructions and a variety of forms and that the present invention applies equally regardless of the particular type of signal bearing media actually used to carry out the distribution. Examples of computer readable media include recordable-type media such as floppy disc, a hard disk drive, RAM, and CD-ROM&#39;s, as well as transmission-type media, such as digital and analog communications links. 
   Although specific embodiments of the present invention have been described, it will be understood by those of skill in the art that there are other embodiments that are equivalent to the described embodiments. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiments, but only by the scope of the appended claims.