Classifications

• • 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
  • H04J3/00—Time-division multiplex systems
  • H04J3/02—Details
  • H04J3/08—Intermediate station arrangements, e.g. for branching, for tapping-off
  • H04J3/085—Intermediate station arrangements, e.g. for branching, for tapping-off for ring networks, e.g. SDH/SONET rings, self-healing rings, meashed SDH/SONET networks
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/22—Arrangements for detecting or preventing errors in the information received using redundant apparatus to increase reliability
• • 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
  • H04Q11/06—Time-space-time switching
• • 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
  • H04J2203/0003—Switching fabrics, e.g. transport network, control network
  • H04J2203/0019—Multicast/broadcast capabilities
• • 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
  • H04J2203/0028—Local loop
  • H04J2203/0039—Topology
  • H04J2203/0041—Star, e.g. cross-connect, concentrator, subscriber group equipment, remote electronics
• • 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

Definitions

• This invention relates to a method, according to the preamble of claim 1, for implementing path protection in a digital TST cross connect.
• the invention also relates to a method of implementing broadcasting in a digital cross connect (DXC) .
• DXC digital cross connect
• the recommendations CCITT G.707 define the Synchronous Transport Module (STM-1) signals of the first level of SDH signals. Other defined levels are STM-4 and STM-16.
• the STM-1 frame enables the transmission of 63 subsystem containers (e.g., TU-12, Tributary Unit, which can contain a two Mbps signal of an ordinary 30- channel PCM system) .
• the STM-N frames are assembled from several STM-1 signals, for example, the STM-4 signal is composed of four STM-1 signals.
• a digital SDH cross connect is a cross connect device having two or more interfaces at SDH rates (G.707) and being at least able to terminate a transmission section and to controllably, transparently connect and reconnect virtual containers (VC) between the interface ports.
• An SDH DXC can transmit traffic between different SDH levels and connect traffic between different signals.
• the use of the cross connect also includes a possibility for remote control of routing, path protection, initialization of reserve routes, connection from one signal to several signals (broadcasting) , and so on.
• the connections are usually bidirectional.
• Cross connects can be implemented with a number of architectures.
• the TST cross connect is also adapted to very large cross connects, though in this case certain problems arise when expanding the system. It has been attempted to eliminate these problems, among other things, through a double capacity TST architecture.
• the starting point in this invention is a digital cross connect that is known per se, i.e. a DXC unit in which TST architecture is used. It is known that blocking can occur in a cross connect when the traffic need exceeds the routing possibilities of the switch. In an ordinary TST architecture, blocking can occur, for example, in cases in which broadcasting and/or path protection are needed.
• the problem could be solved with a different kind of architecture. For example, by means of the n(TS)T architecture presented in our parallel patent application , non-blocking broadcasting can be accomplished through simple measures and at a moderate cost because one path protection possibility that exists in a TST node is to connect the parallel T switch next to the real T switch of the input side. In this case, the incoming signal is copied to both T switches.
• the task of the present invention is thus to propose a solution by means of which non-blocking routing and path protection can be provided for an existing DXC node.
• path protection the problem presented is solved by means of the invention by virtue of the characteristic features set forth in claim 1.
• Embodiments of the invention are presented in the dependent claims. Briefly, the invention can be described in such a way that the number of signals accessing a time switch is selected to be smaller than half of the capacity and that the signal to be path-protected is duplicated, through the software, i.e. the signal is not multiplied by connecting it to parallel time switches, whereby the signals that are duplicated according to the invention are routed with an ordinary routing algorithm for discrete signals.
• the signals to be path-protected are advantageously 2 Mbps signals.
• the method in accordance with the invention can advantageously be applied in a node of a mesh network, in an interconnecting access node and especially in an access node that is located in a protected SDH ring, in a so-called self-healing ring, SHR.
• the method in accordance with the invention can also be used for broadcasting.
• the advantage of the solution by way of this invention is that no hardware changes or other software changes need be made to the existing TST architecture because with the new routing algorithm alone, both path protection and broadcasting can be handled, in which case, of course, the numbers of signals accessing the time switches must be adjusted to the capacity of the switch.
• Figure 1 shows the typical interfaces of the node of an STM-4 ring
• Figure 2 shows the configuration of a non-blocking node in which there are 63 path-protected containers TU-12;
• Figure 3 shows an example of an SHR node in which the path- protected configuration is used;
• Figure 4 shows an example of an access node between networks
• Figure 5 shows an example of an access node of a mesh network
• Figure 6 is a schematic representation of the card slots of a DXC subrack that is known per se and the equipping alternatives for the card slots.
• the DXC node that we have taken as an example in Figure 6 can comprise the subrack in accordance with a Synfonet system that is known per se, which subrack has slots for 19 circuit board units.
• the Synfonet system is manufactured by Nokia Telecommunications, Finland.
• the slots in the subrack can be equipped in a manner specified separately and in a specified order, of which certain of the most common alternatives are shown in Figure 6.
• the subrack is shown schematically as a rectangle in which the card slots are marked 1...19 in the bottommost row. On the left-hand side of the rack are shown alternative cards, or circuit boards, that can be installed in this subrack of the system.
• the S switch can offer spare capacity.
• the spare capacity is used in accordance with the invention to guarantee non-blocking operation.
• the source and target of the path protection are a 2 Mbps interface. This can also be expressed in such a way that in broadcasting, the 1 -> 2 source is a 2 Mbps port and in the selection situation 2 -> 1 the target is also a 2 Mbps port.
• the solution to the problem stated is handled by means of the software, whereby without hardware modifications nearly the same effect can be achieved as with the above-mentioned n(TS)T solution.
• the duplication can be implemented in the first, i.e. the real, T stage.
• the duplication, or multiplication is then done through the software, i.e. by means of the program, and not by duplicating interfaces, as was done in the n(TS)T example.
• the fundamental routing problem remains: now two identical signals must be routed from the same input port through TS instead of these two signals being routed from two parallel input ports.
• n(TS)T is implemented by means of software in the 2 Mbps part of the TST.
• Figure 2 shows an STM-4 ring access node in which 63 (31 + 31 + 1) TTJ-12 signals access the T switches at any given time.
• the abbreviation TTJ-12 (tributary unit) in Figure 2 refers to the 2 Mbps signal according to the standard.
• the node in the figure is non-blocking in accordance with the invention and there are 63 path-protected links.
• the abbreviation W for the signals means working and the abbreviation P means protecting; practically speaking, it makes no difference which of the signals is selected as the "working" one.
• the parallel W and P signals are created in the transmission direction in the time switch (T) that is the source by means of duplication. Thereafter these signals are routed through the TST in the manner of normal point-to-point signals and thus a conventional TST routing problem arises.
• the W and P signals are routed to the same target T switch of the output side, in which the final selection is made (W or P is selected) . This means that the same number of TU-12 signals as in the original case calls for more S switch capacity in order to form path-protected links.
• the configuration specification is for one 2MTA per 63 Mbps channel, in which case 3 2M cards use the same time switch that is on the 2MTA card. Since the time switch has three ports, they can be utilized by replacing part of the 2M cards with 2MTA cards, whereby, for example, only 31 2 Mbps signals are connected to one time switch on a 2MTA card, and now non- blocking path protection can be guaranteed for these signals.
• a different number of 2 Mbps signals can be provided with non- blocking protection by selecting a suitable number of 2MTA cards to be put into use. If 4 2MTA cards are selected, a maximum of 124 2 Mbps signals can be protected.
• the original configuration specifies 2 2MTA cards, in which case a maximum of 62 signals can be protected.
• the number of 2MTA units can be doubled, there is nothing preventing an even greater increase in this amount. If in the subrack in the example, the number of 2MTA units selected is the number of available card slots, then the maximum 2MTA number is 8. With this amount, the number of connected path-protected 2 Mbps signals can be raised to the maximum value of 126. It should be noted that the maximum amount (126) of 2 Mbps signals can be achieved already with six 2MTAs. The advantage obtained from using eight 2MTA units does not show up until some degree of broadcast (1 -> n) has to be implemented. The differences are summed up in Table
• path protection 1 the number of ports in other use than for 2 Mbps interfaces decreases by 2 compared with the normal configuration.
• the path-protected DXC node according to the invention thus offers two STM-1 interfaces less than in the normal case. Usually this loss is of no significance, as is explained below in more detail.
• SHR SHR ring access node
• the signals to be protected in the access node have two Mbps interfaces as sources and targets, whereas the other signals, which have other nodes as sources and targets, travel through the given node in the point-to-point mode.
• Figure 3 gives a schematic representation of the SHR access node in the path protection configuration.
• Figure 2 shows the largest numbers of interfaces in conformity with the system in the example. It should be noted that non-blocking cannot be guaranteed for a protected TU-12 signal (TU, Tributary Unit) which resides in the STM-N interface signal.
• Table 2 Configuration alternatives for the access node
• the table shows the maximum configuration values at any given time.
• simple STM-4 or STM-1 SHR rings will be used, in which case eight or two ports of the STM-1 level will be made available from the S switch. In these cases, utilization of the S switch will still be low.
• the fundamental idea of the invention can also be used in an interconnecting access node.
• the task of the node is then to deliver the traffic gathered in the SHR to the upper level network and vice versa. This is illustrated schematically in Figure 4.
• the task is now to implement path-protected routing between the source and the target. This can be done in a non- blocking way for the path-protected VC12 when the same principle is applied as in the previous example. In other words, less than half of the interconnecting line capacity can be used. The reason for this is that half of the T switch capacity is needed to realize the duplication and for the selection of the path-protected VC12 signals. From the standpoint of the configuration, this means that the interconnecting capacity of the S switch must be more than twice the amount of the ring capacity. An STM-1-SHR ring thus requires 3 STM-1 interconnecting lines to the other network.
• the path protection In a mesh network it is not always possible to guarantee non- blocking connection of path-protected VC12 signals to STM-N signals. In this case, the path protection must be realized with a separate TST path protection algorithm in which the protection is implemented with a space switch and which involves some degree of blocking.
• the signals of a 2 Mbps interface can be path protected in a non-blocking manner.
• a change is made in the existing system to provide path protection through the software.
• the path protection somewhat limits the utilization of the capacity of the S switch of the TST node, but to a very moderate degree, which can be expressed as follows:
• Table 3 Maximum configuration of the S switch (With the example in Figure 6, cf. Table 1) :
• the problems of the protection algorithm can be minimized by "removing" a portion of the path protections, i.e., the protection algorithm is used to process a number of different signals (W or P) of protected links as separate signals, which also enhances the performance of the protection algorithm.

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

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Cited By (2)

Citations (3)

• 1994
  • 1994-05-26 FI FI942466A patent/FI96469C/sv active
• 1995
  • 1995-05-26 AU AU25681/95A patent/AU2568195A/en not_active Abandoned
  • 1995-05-26 WO PCT/FI1995/000294 patent/WO1995033321A1/en active Application Filing

Patent Citations (3)

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