Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L41/00—Arrangements for maintenance, administration or management of data switching networks, e.g. of packet switching networks
  • H04L41/24—Arrangements for maintenance, administration or management of data switching networks, e.g. of packet switching networks using dedicated network management hardware
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J3/00—Time-division multiplex systems
  • H04J3/02—Details
  • H04J3/06—Synchronising arrangements
  • H04J3/0635—Clock or time synchronisation in a network
  • H04J3/0679—Clock or time synchronisation in a network by determining clock distribution path in a network

Definitions

• the invention relates to a method as claimed in the preamble of the attached claim 1 and an arrangement as claimed in the preamble of the attached claim 3 for implementing in a telecommunications network a secured bus for management purposes etc.
• a management bus refers to such a data transmission connection which is used for transmitting network management information, that is, information whose purpose is e.g. to collect fault information or to direct functional units of the network into a specific state.
• network management information that is, information whose purpose is e.g. to collect fault information or to direct functional units of the network into a specific state.
• the method of the invention is suited for implementing any kind of bus, although in practice, transmission of management information is by far the most important thinkable implementation of the bus.
• the primary object of the present invention is to carry out a secured management connection in a loop network or a so-called mesh network which consists of loops (in a mesh network, there are more than one route between any two nodes), but the invention is generally suited for implementing a secured bus if the form of the bus is suitable for the structure of synchronization hierarchy used in the network.
• Nodes that are connected to the bus may transmit their messages to the bus, and they will thus spread along the bus to all the nodes connected to it.
• the bus may not contain a loop, because in that case the transmitted message would remain passing round in the loop (the crossing points of the data connections of a telecommunications network are herein referred to as nodes.
• Node devices include e.g.
• Signals between the nodes of the network may be e.g. 2048 kbit/s signals in accordance with ITU-T (former CCITT) recommendations G.703/G.704, a frame of said signal containing 32 time-slots (TS0...TS31) and the multiframe containing 16 frames.
• the management information may be transmitted in the frame structure of such a signal e.g. so that a service channel reserves e.g. three bits of the bits of time-slot TSO from the frame structure. In every other frame, time- slot TSO contains a frame alignment signal, but in every other time-slot bits 4 to 8 are free for domestic use, in which case they may be used for transmitting network management information.
• a secured management bus is typically implemented by making use of conditional methods especially implemented for this purpose, in other words, the state of the signal to be transmitted and some specific status flags are monitored in a node of the network. When they meet specific predetermined conditions, a securing connection is switched on. This will be described in more detail in the following.
• Figure la illustrates the principle according to which the management bus is typically implemented within a nodal device of the network.
• the node has a summer 11 to which all the connections of the management bus are applied. These connections may include:
• a local management interface 12 located in the device, to which interface e.g. the network management system may be directly connected. There may be more than just one of these local management interfaces.
• EOC_l...EOC_N EOC, Embedded Operation Channel or ECC, Embedded Control Channel
• Messages may arrive from all the directions shown in the figure, and all these directions receive messages (in other words, the traffic from the summer is bidirectional in all the directions shown in the figure) .
• a summing point 11 channels coming from the different directions are combined. Data coming from a certain direction is switched (transmitted) further to all the other directions. Only one transmitter at a time may transmit data (in case more transmitters transmit data to the bus simultaneously, the signals will be summed with each other and the data will be corrupted) .
• the summer is a very simple device; a single logical AND operation is carried out in it for the management or service channels connected to it. If at least one of the signals is in a "zero" state, the result is zero. This means in practice that the idle mode of the line is one. In other words, if the device is not transmitting anything, it remains in state 1. (The line coming from the control block 13 to the summer is in state 1 when the node has nothing to transmit, whereby it does not have any effect on the other lines) .
• the traffic is serial from the point of view of the summer 11 and communication blocks of the devices connected to the service channel. At some stage, the data may be in the parallel form, but when applying it to the summer, it must be converted into the serial form.
• the desired EOC channels When securing is carried out in the solution disclosed above, the desired EOC channels must be able to be switched on or off when need be (depending on the states of the signal and the monitored bits) .
• This may be carried out e.g. in accordance with Figure lb so that there is a separate switch SW for each EOC channel, said switch being controlled on the basis of the states of the signal and of the monitored bits.
• a signal entering the node is first directed to a multiplexing block MUX/DEMUX, in which the signal of the EOC channel is separated from the rest of the signal and applied to the switch SW.
• the other time ⁇ slots of the arriving signal are switched to a cross- connection block XC, from which they are switched further.
• the control block CTR of the switch receives the information on the state of the signal from the multiplexing block, and it also reads the condition bits from the cross-connection block. On the basis of this information, it switches the securing connection on by commanding the corresponding switch SW on. (For the sake of simplicity, only one signal is shown in the figure, but in the case of more signals, the operation is carried out logically in the same way.
• the network management system On the network level, the above appears in such a way that the network management system has been connected to the management bus in one node via which it has an access to the other nodes of the network along the management bus. This is illustrated in Figure 2, in which the network shown comprises a master node M and eight nodes 1...8, and the network management system NM is connected to node 2.
• Normal data connections between the nodes are marked with broken lines and the management bus MB with a thicker, solid line.
• the management bus thus consists of normal data connections (i.e. it passes within normal data connections), but in the logical sense, however, it is a network that is separate from the normal data transmission connections (as shown in Figure 2) .
• conditional connections for the management bus (similar to those in Figure lb) for switching on the securing management connection.
• conditional connections which are marked with a reference symbol E, are located in nodes M, 3 and 4, whereby node M is able to switch on a secured connection in the direction of node 1, node 3 to the direction of node 7, and node 4 in the direction of node 6, when need be.
• the management bus is constructed in the network as separate switchings. It is determined separately in each node where the management connections (that must be connected to the summer) come from. The determinations are made by the user and they are permanent. The switchings are always valid when the signal containing the management channel is valid. In case it is detected the signal is faulty (it has a fault that causes e.g. an alarm at the far end, or an alarm is received from the far end) , connecting the management channel to the summer is prevented so that the interferences possibly coming from the connection would not interfere with the traffic on the service channel via the summer.
• one or more switching points of the management connection are conditional, that is, a connecting is carried out to the summer only if a specific predetermined condition (e.g. a predetermined state of a monitored bit) is fulfilled. Depending on the device, the condition may be linked to different factors.
• the secured management bus implemented in the manner described above is attended by the drawback that the user (operator) has had to create a separate system for securing, in which system a condition bit is transferred.
• the condition bit remains in a certain state in a normal situation and changes its state at that point of the network at which an unusual situation, such as a fault situation arises.
• the object of the present invention is to relieve the drawback mentioned above and achieve a new, simpler solution than heretofore for implementing a management bus or the like. This is achieved with a method of the invention, which is characterized in what will be set forth in the characterizing part of the attached claim 1.
• the arrangement according to the invention is characterized in what will be set forth in the characterizing part of the attached claim 3.
• the idea of the invention is to make use of a Synchronization Status Message SSM specified in ITU-T standard G.704 so that the criterion used at the conditional switching point of a secured service channel is linked to the state of this message.
• information intended for the use of synchronization of the network and already existing in the network is thus utilized for a new purpose in the invention.
• the criterion information is thus already in the network, and there is thus no need to create any kind of arrangements for transmitting the criterion bit in the network.
• Figure la illustrates the principle of implementation of the management bus inside a nodal device of the network
• Figure lb illustrates the principle of implementation of securing the management bus inside a nodal device of the network
• FIG. 2 illustrates implementation of the management bus on the network level
• Figures 3a and 3b illustrate the operation of the method of the invention in a ring network
• FIG. 4 illustrates those elements of the network node by means of which the method of the invention is implemented
• FIGS. 5a...5d illustrate the operation of the method of the invention in a so-called mesh network
• FIGS 6a...6d show alternative switching devices for the node shown in Figure 4.
• ITU-T standard G.704 specifies the frame structure of a digital transmission system operating at the rate of 2048 kbit/s.
• bits 4 - 8 in every other frame are free (spare bits), and they may be used e.g. for transmitting synchronization status messages mentioned above. Only one of the bits 4 - 8 in the frame may be used for this purpose, and a four-bit synchronization status message thus consists of the selected bit (4-8) in the frames 1, 3, 5, 7 and 9, 11, 13 and 15 of the multiframe.
• the latter quality level (15) is used in implementing a secured management bus or the like in such a manner that upon the status message changing from status "XXXX" ("XXXX" being unequal to "1111") into status "1111", the management bus is switched on at the conditional switching point of the network.
• Figures 3a and 3b illustrate the operation of the method according to an embodiment of the invention in a ring network comprising a total of five nodes, which are marked with reference symbols N1...N5.
• the management bus MB has been constructed so that it goes through the entire ring and is cut off beside the master node (Nl) in the direction of node N5.
• a criterion (reference symbol E) is set to this break point (i.e. to the output port of node Nl in the direction of node N5) .
• it is monitored at the normal switching point whether the incoming connection has such a fault due to which the use of the connection for synchronizing must be forbidden. In case such a fault arises, the bus is cut off at this point.
• the quality level (QL:XXXX) of the internal clock of the node is marked on top.
• the quality level (QL:XXXX) of the internal clock of the node is marked on top.
• the quality level there is the synchronization list of the node, the selected timing source being marked in italics on said list.
• the synchronization method used is of such a type that each node selects as the timing source the signal that contains the synchronization message with the highest quality level. In case several signals have the same quality level, the one highest on the priority list will be selected.
• the synchronization status message transmitted by the node is marked with reference symbol "QL:XXXX".
• FIG. 3a shows the network in its normal state (no faults) .
• the master node thus transmits this synchronization status message in both directions.
• Figure 3b shows a situation in which a fault has arisen on the connection between nodes Nl and N2.
• node N2 detects this fault, it selects a new timing source.
• FIG. 4 illustrates those units of a single network node that are essential for the invention.
• a node N comprises a plurality of parallel interface units IUl...IUn, by means of which the node is connected to the network (the interface may be e.g. a 2 Mbit/s PCM interface according to the above recommendations, as shown in the figure) , and a control unit CU common to several interface units.
• Each interface unit comprises at its input a multiplexing/demultiplexing block 81, which is connected via a switch SW to an internal bus IBUS of the node.
• the EOC management channel is thus separated from the rest of the signal in multiplexing blocks 81, and the control block commands the switch on when the synchronization status message shifts from state "XXXX" into state "1111" ("XXXX” being unequal to "1111") .
• the value of the synchronization status message is provided to the control block from the multiplexing block 81, which forms the value from the bits that have been selected for this purpose. It is assumed in Figure 4 that a criterion has been set only to the port corresponding to interface unit IUl, and the value of the synchronization status message is thus transmitted to the management bus switching control only in this port (in the other ports said value is transmitted to be used by synchronization only) .
• the control unit CU comprises a summer 83 for connecting the management channel coming from a control block 13 of the node and from the network management system NM in a corresponding manner by means of the switch SW to summer 11 (cf. Figure 1) .
• the network management system is connected by means of a data connection (typically a serial connection, such as V.ll) to a serial port SP at the input of the control unit, said serial port in turn being connected to summer 83.
• Figures 5a...5d show the operation of the method of the invention in a network in accordance with Figure 2.
• the network is shown in the normal state, in which all the switches of the conditional switching points are in off-position.
• a fault occurs in the master loop A between nodes M and 2.
• nodes M and 2 cut the bus off from the faulty connection.
• the nodes of the master loop are synchronized in the opposite direction.
• a fault also occurs in the slave loop C, whereby nodes (6 and 8) on both sides of the fault cut off the connection.
• a fault occurs in the other subloop (B) , as well.
• the nodes (5 and 6) at the ends of the faulty connection again cut the bus off from the faulty connection.
• Figures 6a...6d show various examples for implementing a single interface unit provided with a conditional switching.
• Figure 6a shows a solution corresponding to that in Figure 4 in which solution the fault and status information are obtained directly from the multiplexing block and in which separate switches SW are used, via which the signal of the management channel is switched to the summer 11 when need be.
• the signal is switched to the cross-connection block 91 (not shown in Figure 8), from which it is switched further.
• Figure 6b shows a second alternative in which the entire signal (all the time ⁇ slots) are applied from the multiplexing block to the cross-connection block 92, from which the EOC channel is connected (when need be) to the summer 11 and the other channels are connected to the other desired points.
• FIGS. 6c and 6d show such alternatives in which the control block 82 controlling the switch SW obtains the fault information and the QL value from a separate fault database 93, not directly from the multiplexing block.
• the implementation of Figure 6c thus corresponds to that shown in Figure 6a
• the implementation in Figure 6d corresponds to that in Figure 6b.

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• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Small-Scale Networks (AREA)

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• 1995
  • 1995-06-28 FI FI953205A patent/FI98582C/fi active
• 1996
  • 1996-06-26 WO PCT/FI1996/000372 patent/WO1997001905A1/en not_active Application Discontinuation
  • 1996-06-26 EP EP96920853A patent/EP0840968A1/de not_active Withdrawn
  • 1996-06-26 AU AU62263/96A patent/AU6226396A/en not_active Abandoned

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