Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L49/00—Packet switching elements
  • H04L49/60—Software-defined switches
  • H04L49/606—Hybrid ATM switches, e.g. ATM&STM, ATM&Frame Relay or ATM&IP
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04Q—SELECTING
  • H04Q11/00—Selecting arrangements for multiplex systems
  • H04Q11/04—Selecting arrangements for multiplex systems for time-division multiplexing
  • H04Q11/0428—Integrated services digital network, i.e. systems for transmission of different types of digitised signals, e.g. speech, data, telecentral, television signals
  • H04Q11/0478—Provisions for broadband connections
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J2203/00—Aspects of optical multiplex systems other than those covered by H04J14/05 and H04J14/07
  • H04J2203/0001—Provisions for broadband connections in integrated services digital network using frames of the Optical Transport Network [OTN] or using synchronous transfer mode [STM], e.g. SONET, SDH
  • H04J2203/0057—Operations, administration and maintenance [OAM]
  • H04J2203/006—Fault tolerance and recovery
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L12/00—Data switching networks
  • H04L12/54—Store-and-forward switching systems 
  • H04L12/56—Packet switching systems
  • H04L12/5601—Transfer mode dependent, e.g. ATM
  • H04L2012/5625—Operations, administration and maintenance [OAM]
  • H04L2012/5627—Fault tolerance and recovery

Definitions

• This invention relates in general to a telecommunications network and, more particularly, to protection techniques which facilitate continuity of service notwithstanding faults which may develop in the telecommunications network.
• synchronous transport mode STM
• ATM synchronous transport mode
• ATM asynchronous transport mode
• a given user of a communication path receives time slices which are not periodic, but instead occur at variable or random points in time .
• Faults occasionally develop in a telecommunications network, for example when an underground cable is broken by construction equipment.
• various protection techniques have been developed to facilitate automatic rerouting of data so as to ensure reliable and substantially uninterrupted service.
• One such technique is known as one-plus-one (1+1) line protection.
• each operational or working cable is associated with a corresponding protection or back-up cable.
• the working cable and protection cable both carry the same operational data streams, but the data streams on the protection cable are ignored until a fault is detected in association with the working cable.
• the system implements appropriate switching so as to stop using the data streams received through the working cable, and begin using the data streams received through the associated protection cable.
• a second protection technique is known as bidirectional line-switched ring (BLSR) protection.
• BLSR line-switched ring
• half of the communication paths in each cable are used for high priority data, and the other half are used for low priority data. If a fault is detected in association with the first cable, transmission of low priority data on both cables is terminated, and then the high priority information from the first cable is switched over to the low priority communication paths in the second cable, after which all of the communication paths in the second cable will be carrying high priority data until the fault can be repaired.
• a third protection technique is known as unidirectional path-switched ring (UPSR) protection.
• UPSR path-switched ring
• the detection of a fault does not necessarily result in the switching of data streams from an entire group of communication paths in one cable to a corresponding group of communication paths in a different cable. Instead, protection switching is carried out on a one-to-one basis among communication paths.
• switching circuits for STM communications usually include use of a protection technique, such as one of the techniques described above.
• switching circuits for ATM communications typically include little or no protection against interruption of service due to a fault. This is due in part to the fact that the amount of STM traffic was once much greater than the amount of ATM traffic.
• the amount of ATM traffic through telecommunication networks has been progressively increasing at a rapid rate. As one consequence, there has been a progressively increasing demand from network users for ATM traffic to enjoy the same level of protection and reliability that has traditionally been enjoyed by STM traffic.
• a need has arisen for a method and apparatus for effecting communication in a telecommunications network according to at least two different communication protocols, without providing completely separate and independent switching networks, but while providing reasonable protection for each protocol against interruptions in service due to network faults.
• a method and apparatus are provided to address this need, and involve selectively establishing a plurality of switching paths which each couple a respective one of plural first communication paths to a respective one of plural second communication paths, and which each facilitate communication according to a selected one of several different communication protocols, wherein each first communication path can be selectively coupled by the switching arrangement to any one of the second communication paths according to any one of the communication protocols.
• FIGURE 1 is a diagrammatic view of a portion of a telecommunications network, including a plurality of ingress and egress cables, and hybrid protection circuity which couples the ingress cables to the egress cables;
• FIGURE 2 is a further diagrammatic view of the circuitry of FIGURE 1, diagrammatically showing how it can be configured to implement a one-plus-one (1+1) line protection technique
• FIGURE 3 is yet another diagrammatic view of the circuitry of FIGURE 1, diagrammatical ly showing how it can be configured to implement a bidirectional line-switched ring (BLSR) protection technique
• FIGURE 4 is still another diagrammatic view of the circuitry of FIGURE 1, diagrammatically showing how it can be configured to implement a unidirectional path-switched ring (UPSR) protection technique.
• BLSR bidirectional line-switched ring
• UPSR unidirectional path-switched ring
• FIGURE 1 is a diagrammatic view of a hybrid protection circuit 10 which is operatively coupled to a plurality of ingress cables 12 and a plurality of egress cables 13.
• the hybrid protection circuit 10 and the cables 12 and 13 represent a portion of an overall telecommunications network.
• each of the cables 12 and 13 includes twelve communication paths. Each such communication path may, for example, be a respective fiber optic part. Data may be communicated through the communication paths in each cable according to various different protocols, which are standard in the industry.
• One standard protocol is the synchronous transport mode (STM) protocol
• another industry standard protocol is the asynchronous transport mode (ATM) protocol .
• a given user receives time slices which are at predetermined periodic intervals.
• a given user receives time slices at non-periodic times which may be variable or random.
• a further characteristic of the ATM protocol is that information is sent along communication paths in packets of 53 bytes, each such packet being referred to as a "cell". Since the ingress cables 12 include twenty four cables which each have twelve communication paths, the cables 12 include a total of 240 communication paths. Similarly, the twenty-four cables 13 include 240 communication paths.
• a purpose of the hybrid protection circuit 10 is to permit any one of the communication paths in the ingress cables 12 to be operatively coupled to any one of the communication paths in the egress cables 13, according to either the STM protocol or the ATM protocol, while providing protection against interruption of service due to a failure in the network.
• each communication path in the ingress cables 12 is coupled to a respective one of 240 inputs of an automatic protection switching (APS) line selector 31.
• the line selector 31 can be variously configured to carry out line protection switching in the form of various different configurations, in a manner which is described in more detail below.
• the line selector 31 has 240 outputs which are coupled to respective inputs up a squelch circuit 32, the purpose for which is described later.
• the squelch circuit 32 has 240 outputs, which are each coupled to a respective one of 240 inputs of an STM section 36, and also to a respective one of 240 inputs of an ATM section 37.
• the STM section 36 effects switching at the path level according to the STM protocol
• the ATM section 37 effects switching at the path level and at the cell level according to the ATM protocol.
• the circuits 31 and 32 each contain circuitry of a type which is known in the industry.
• arriving signals pass successively through a time slot interchange (TSI) circuit 41, a path select circuit 42, and a squelch circuit 43.
• TSI time slot interchange
• the TSI circuit 41 has 240 inputs and 240 outputs, and performs switching which can selectively couple each of its inputs to any of its outputs.
• the path select circuit 42 effects switching between communication paths within a cable.
• the squelch circuit 43 is provided for a purpose described later.
• the circuits 41, 42 and 43 each contain circuitry of a type which is known in the industry.
• each signal received at the inputs passes successively through a TSI circuit 46, a path select circuit 47, an ATM switch fabric circuit 48, a further TSI circuit 51, a further path select circuit 52, and a squelch circuit 53.
• the circuits 46-48 and 51-53 each contain circuitry of a type which is known in the industry.
• the TSI circuits 46 and 51 are each capable of switching operations that can selectively couple each of its 240 inputs to any respective one of 240 outputs.
• the TSI 51 has the specific function of routing ATM traffic from the ATM switching fabric 48 into appropriate egress time slots for the egress cables 13.
• the path select circuits 47 and 52 are each similar to the path select circuit 42, and effect switching among respective communication paths.
• the ATM switching fabric 48 effects ATM switching at a cell level. The purpose of the squelch circuit 53 is described later.
• the 240 outputs of the STM section 36 and the 240 outputs of the ATM section 37 are all coupled to respective inputs of an egress switching section 54. More specifically, the 240 outputs of the STM section 36 are coupled through an optional bridge circuit 56 to respective inputs of a 2:1 multiplexer 57. The 240 outputs of the ATM section 37 are coupled through an optional bridge circuit 58 to respective further inputs of the multiplexer 57.
• the multiplexer 57 may be viewed as 240 separate two-to-one multiplexers, which each select a respective output from either the STM section 36 or the ATM section 37 to be supplied to a respective one of the communication paths in the egress cables 13. Each of these 240 multiplexer circuits can be controlled independently of the others .
• the multiplexer 57 has 240 outputs which are each coupled to a respective input of an APS line bridge circuit 61, which has 240 outputs that are each coupled to a respective communication path in the egress cables 13.
• the bridge circuit 61 carries out line protection in a manner analogous to the line selector circuit 31.
• the bridge circuits 56 and 58 are effectively redundant to the bridge circuit 61, and thus only the bridge circuit 61 or the bridge circuits 56 and 58 would be present. In the disclosed embodiment, the bridge circuit 61 is present, and the bridge circuits 56 and 58 are omitted.
• the circuits 56 and 58 are nevertheless shown in FIGURE 1 in broken lines, for clarity and to facilitate an understanding of the present invention.
• circuits 56-58 and 61 each contain circuitry of a type which is known in the industry.
• the hybrid protection circuit 10 further includes a microprocessor control circuit 63, which produces at 64 a plurality of control signals for the rest of the hybrid protection circuit 10.
• Various control signals from 64 are supplied to respective portions of the circuit 10, including the line selector circuit 31, the TSI circuits 41, 46 and 51, the path select circuits 42, 47 and 52, the ATM switch fabric 48, the multiplexer 57, and the bridge circuit 61 (or bridge circuits 56 and 58) .
• the microprocessor control circuit 63 may be coupled at 68 to other circuitry disposed at remote locations in the telecommunications network.
• the hybrid protection circuit 10 of FIGURE 1 has the advantage that it can be configured to be compatible with any of several different protection techniques that are already used in the industry. As discussed in more detail below with reference to FIGURES 2-4, these techniques include bidirectional line-switched ring (BLSR) protection, unidirectional path-switched ring (UPSR) protection, and one-plus-one (1+1) protection.
• BLSR bidirectional line-switched ring
• UPSR unidirectional path-switched ring
• 1+1 one-plus-one
• FIGURE 2 is a further diagrammatic view of the hybrid protection circuit 10 of FIGURE 1, diagrammatically showing how this circuit can optionally be electrically configured to implement a one-plus-one (1+1) protection technique.
• the ingress cables 12 are organized in pairs, such that for each cable which is a working or operational cable, there is an associated protection or back-up cable.
• Egress cables 13 are paired in a similar manner. If any type of failure is detected with respect to the working cable or any of the twelve communication paths extending through it, then all traffic through the twelve communication paths of the working cable are switched over to the twelve communication paths of the corresponding protection cable.
• the selector circuit 31 is operationally configured in a manner so that it appears to be twelve two-to-one selectors, three of which are diagrammatically depicted for clarity at 71-73 in FIGURE 2.
• cable 16 in FIGURE 2 would be a working cable
• cable 17 would be the associated protection cable.
• the selector 71 would route the twelve communication paths of the working cable 16 to the outputs of selector 71, and ignore the cable 17.
• the selector 71 would be switched so as to select the cable 17 and ignore the cable 16.
• FIGURE 2 is not disclosing an alternative embodiment of FIGURE 1, but instead a diagrammatic view of one way in which the circuit of FIGURE 1 can be electrically configured.
• FIGURE 3 is a further diagrammatic view of the circuit 10 of FIGURE 1, showing diagrammatically how it would be operationally configured for operation according to the
• UPSR protection technique According to the standard UPSR protection technique, all protection switching is performed at the path level rather than at the cable level . In other words, all protection switching is carried out in circuits 42, 47 and 52. Consequently, the selector 31 is electrically configured to be effectively transparent, or in other words to couple each of its 240 inputs to a respective one of its 240 outputs. The selector 31 is therefore shown in broken lines in FIGURE 3, and FIGURE 3 diagrammatically shows that each of the inputs of selector 31 is passed directly therethrough to a respective output.
• FIGURE 4 is a further diagrammatic view of the circuit 10 of FIGURE 1, showing in a diagrammatic manner how it would be electrically configured for operation according to the BLSR protection technique.
• each cable has six communication paths that are used as working paths, and six communicating paths that are used as protection paths.
• the protection paths are not normally idle, but instead carry low priority data during normal operation of the network. If a fault is detected in association with a first cable, then transmission of the low priority data on the six protection paths of a second cable is terminated, and the information on the six working paths of the first cable is switched over to the protection paths of the second cable. The low priority data on the six working paths of the first cable is also terminated.
• FIGURE 4 shows diagrammatically that the selector 31 is electrically configured so as to functionally appear to be two selector stages 76 and 77.
• the selector stage 76 switches twelve communication paths, or in other words switches one cable for another cable.
• the selector stage 77 switches six communication paths, or in other words switches six working paths relative to six protection paths.
• AIS industry-standard alarm indication signal
• FIGURE 4 also shows that the bridge circuits 56 and 58 are provided in place of the bridge circuit 61. This variation is not specific to the BLSR protection technique.
• the present invention provides a number of technical advantages.
• One such technical advantage is that a single circuit is provided to handle two or more protocols such as STM and ATM, thereby avoiding the need to have an entirely separate switching system for each protocol .
• a single system is cheaper than two separate systems, and has lower maintenance costs. For example, there are fewer replacement parts to inventory, and maintenance personnel require training on only one system rather than two.
• a further advantage is that a cable can easily be switched from use according to one protocol to use according to a different protocol, without any need to manually effect a physical disconnection of a cable connector from one system and then a physical connection of that cable connector to another system.
• a further advantage is that the disclosed system implements protection for two protocols such as ATM and STM, whereas pre-existing systems usually implement protection for only a single protocol (such as STM) , or no protection at all. Further, in the disclosed embodiment, two protocols such as STM and ATM share a common protection mechanism. Yet another advantage is that the disclosed system makes it easy to vary the ratio of communication paths used for one protocol (such as STM) relative to another protocol (such as ATM) .
• the disclosed embodiment includes 240 communication paths organized as twenty-four cables each having twelve communication paths, but it will be recognized that the invention is compatible with a different number of communication paths or different configurations for cabling.
• the disclosed embodiment includes a particular configuration of circuit elements, including selector circuits, switching circuits and a multiplexer. However, it will be recognized that it is possible to vary the particular circuits used, or their particular configuration, while still realizing the present invention.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Data Exchanges In Wide-Area Networks (AREA)
• Small-Scale Networks (AREA)

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• 1999
  • 1999-06-03 US US09/325,499 patent/US6317426B1/en not_active Expired - Fee Related
• 2000
  • 2000-06-01 JP JP2001502310A patent/JP2003501954A/ja active Pending
  • 2000-06-01 AU AU53193/00A patent/AU5319300A/en not_active Abandoned
  • 2000-06-01 CA CA002375568A patent/CA2375568A1/en not_active Abandoned
  • 2000-06-01 WO PCT/US2000/015340 patent/WO2000076157A1/en not_active Ceased
  • 2000-06-01 EP EP00938107A patent/EP1183836A1/en not_active Withdrawn

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