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WO1998013967A1 - Procede et dispositif permettant une synchronisation basee sur des messages - Google Patents

Procede et dispositif permettant une synchronisation basee sur des messages Download PDF

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Publication number
WO1998013967A1
WO1998013967A1 PCT/SE1997/001468 SE9701468W WO9813967A1 WO 1998013967 A1 WO1998013967 A1 WO 1998013967A1 SE 9701468 W SE9701468 W SE 9701468W WO 9813967 A1 WO9813967 A1 WO 9813967A1
Authority
WO
WIPO (PCT)
Prior art keywords
synchronisation
nodes
string
strings
node
Prior art date
Application number
PCT/SE1997/001468
Other languages
English (en)
Inventor
Tobias Adelgren
Original Assignee
Telefonaktiebolaget Lm Ericsson (Publ)
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Telefonaktiebolaget Lm Ericsson (Publ) filed Critical Telefonaktiebolaget Lm Ericsson (Publ)
Priority to AU41408/97A priority Critical patent/AU4140897A/en
Publication of WO1998013967A1 publication Critical patent/WO1998013967A1/fr

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Classifications

    • 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 present invention relates to a device in nodes in a network of interconnected, named nodes in which each node is associated with a value indicating with what priority it is to be used as synchronisation source for other nodes.
  • the nodes are adapted to each read the synchronisation messages which are written from adjacent nodes and from these synchronisation messages to determine which node is to act as synchronisation source.
  • the invention also relates to a telecommunications system which uses message-based synchronisation.
  • the invention furthermore relates to a process for establishing or re-establishing a synchronisation network in a network of interconnected named nodes.
  • synchronisation of the nodes is often achieved in that one of the nodes acts as master and other nodes are synchronised with the said master node. This is achieved by designating a node with highest priority. Should the master node be disconnected from the network for any reason, for example due to interruptions in one or more of the transmission lines, another node should act as master for other nodes. Ranking a plurality of nodes or all nodes in a network according to the priority in which they are to be used as master node for other nodes is therefore already known. The nodes then exchange the synchronisation messages with adjacent nodes, the synchronisation messages stating which node is master. From the synchronisation messages of adjacent nodes, the nodes are suitably adapted to select one message indicating a master node with highest priority.
  • a disadvantage with this known solution is that the nodes may first accept false information as the correct synchronisation signals and relay these a number of times before they are made to accept that the synchronisation messages are in reality false information originating from a synchronisation source no longer accessible.
  • Another disadvantage is that the said parameters cannot be used for an application more sophisticated than the representation of a distance.
  • a device in nodes in a network of named nodes interconnected by way of lines in which the nodes are associated with a value indicating with what priority they are to be used as synchronisation source for other nodes
  • the device in each of the nodes comprises means of reading in information in the form of synchronisation strings from adjacent nodes, the synchronisation strings comprising a sequence of node names representing the nodes which the synchronisation string has previously passed, including the synchronisation source.
  • the device in each of the nodes is adapted to select link to the synchronisation source by selecting either one of the synchronisation strings read in or none of them in a predetermined manner.
  • the device in a node select one of the synchronisation strings read in, this is adapted to form a new synchronisation string by adding its own node name to the sequence of node names in the selected synchronisation string Should none of the synchronisation strings be selected, the device is on the other hand adapted to form the new synchronisation string from its own node name.
  • the device in each of the nodes comprises means of writing in order to write information in the form of the new synchronisation string to adjacent nodes.
  • the said device is arranged in each node in a telecommunications system using message-based synchronisation.
  • a synchronisation network is established or re-established in a network of named nodes interconnected by way of lines.
  • the process assumes that the nodes are each associated with a value indicating in what priority they are to be used as synchronisation source for other nodes.
  • the nodes in the network are made to read in the synchronisation message in the form of synchronisation strings from adjacent nodes, the synchronisation strings comprising a sequence of node names, representing the nodes which the synchronisation message has passed previously, including the synchronisation source.
  • Each of the nodes is made to select a link to the synchronisation source. This is done in that either one of the synchronisation strings read in is selected or none at all, according to a predetermined pattern.
  • each of the nodes is made to form a new synchronisation string. Where one of the synchronisation strings read in was selected, this is done by adding its own node name to the sequence of node names in the selected synchronisation string. Where no synchronisation was selected this is done by forming the new synchronisation string from its own node name. Finally each of the nodes is made to write the new synchronisation string to adjacent nodes.
  • the advantage with the device according to the invention and the process according to the invention is that the entire sequence of nodes which the synchronisation string passes is included in the synchronisation strings which are exchanged between the nodes. If each of the nodes selects links by selecting one of those synchronisation strings present in which the sequence of node names does not include its own node name and in which the synchronisation source has a higher priority than the node itself, the false synchronisation messages are effectively prevented from circulating in the network.
  • Fig. 1 shows an example of a network in which the present invention is adapted to function
  • Fig. 2 shows a flow chart of the process in each node in the network in order to establish and re-establish a synchronisation network.
  • Fig. 1 shows a network comprising nodes (circles) and transmission lines (solid lines), the transmission lines (links) constituting connections between the nodes.
  • the network is preferably a telecommunications network.
  • Each of the nodes is named.
  • a priority is associated with each node name, either intrinsic to the node name or received by way of a data base in the node. The priority is common to the entire network. For implementation reasons it is a good idea to name the nodes in such a way that it is easy to determine from the node names the priority with which each node is to be used as synchronisation source for other nodes.
  • node A has the highest priority
  • node B the next highest priority etc. It may be advisable to rank ail nodes right down to those with the lowest priority, even though these nodes are rarely if ever used as synchronisation source for other nodes.
  • the flow chart in fig. 2 illustrates the various stages in the establishment according to the invention of a synchronisation network through which the equipment in the nodes learns by way of a decision taken locally which node is the synchronisation source (master) in the network.
  • stage 1 in fig. 2 all nodes are in an initiation condition in which they assume that they are their own synchronisation source.
  • each of the nodes reads the synchronisation strings which were written by their adjacent nodes, with which contact is achieved by way of the transmission lines.
  • the nodes store information on their own node name and further information I(n), which will be used on stages 3 and 4, and for that reason this information I(n) will be described in more detail in connection with these.
  • the nodes store the synchronisation strings read in, together with a string called the reference string, comprising its own node name and the information I(n).
  • node A stores the strings S(E), S(F) and R(A);
  • node B stores S(D), S(G) and R(B) etc.
  • each node n selects link to the synchronisation source by selecting any of the stored strings, either one of the synchronisation strings read in, or the reference string R(n), according to a predetermined pattern.
  • a new synchronisation string is created. This process varies according to whether the node n selected one of the synchronisation strings read in or the reference string. If one of the synchronisation strings read in was selected (denoted by S(selected) in fig. 2), the new synchronisation string is formed by adding its own node name from the reference string to the sequence of node names in the selected synchronisation string and adding a predetermined number x to the weighting factor w in the selected synchronisation string. The number x is obtained by using the stored information I(n) according to which synchronisation string was selected. This will be described in more detail later.
  • the synchronisation string consequently comprises a "list" containing the names of all nodes which the synchronisation message has passed previously.
  • stage 5 the new message S ne (n) is written to the adjacent nodes.
  • the entire procedure is then repeated starting from stage 2.
  • the synchronisation network is established when the node situated furthest from the synchronisation source (the master) learns which node is the synchronisation source. Since the nodes nearest the synchronisation source are first to learn which node is synchronisation source and this is then disseminated to one more node each time the procedure is repeated, the node furthest from the synchronisation source is informed when a number of cycles has elapsed which corresponds to the distance between the said node and the synchronisation source. Note that an established synchronisation network need not necessarily use all transmission lines, accessible in the network.
  • the synchronisation strings which are exchanged between the nodes will contain a long sequence of node names, representing nodes which have been passed previously.
  • the synchronisation source i.e. the master
  • the node which sent the synchronisation string to the said node is the synchronisation source (i.e. the master)
  • stage 3 the selection of link according to the above-mentioned predetermined pattern (stage 3) makes effective use of the information which is exchanged between the nodes.
  • the synchronisation strings which include the nodes own node name are first sorted out. This effectively prevents
  • strings (the reference string and/or synchronisation strings) in which the synchronisation source (the master) does not have highest priority are also sorted out. Either the reference string or one or more of the synchronisation strings now remain. Where it is the reference string that remains, this is selected, and where it is one of the synchronisation strings that remain, this is selected. Should more than one synchronisation string remain, the weighting factor decides which string is to be selected. If it is still not possible to select a synchronisation string, the string which is written by the neighbouring node having the highest priority may be selected, for example; in other words the priority of the last node name in the list of node names is what decides.
  • the synchronisation network can be optimised in various ways.
  • the network is optimised in respect of the number of nodes which the synchronisation string passes, the so-called "hop length".
  • the weighting factor may, however, be used in order to optimise the synchronisation network in many other ways.
  • the synchronisation network is optimised in respect of the length of the transmission lines (geographical distance) and in a further embodiment in respect of the probability of faults (in most instances referred to as accessibility).
  • the synchronisation network is optimised in respect of a combination of the above-mentioned.
  • X C E , and x C contain information on the transmission lines between the node C and the nodes D, E and F and where x C c contains information on its own node C.
  • the synchronisation string is selected so that the weighting factor + a predetermined number is minimised.
  • the synchronisation string with the lowest associated provisional weighting factor is thus selected as a link to the synchronisation source and in stage 4 in fig. 2 the predetermined number where i is the node from which the selected synchronisation string arrives, is added to the weighting factor for the selected synchronisation string.
  • the synchronisation network is optimised in respect of geographical distance.
  • the synchronisation network is optimised in respect of the both "hop length" and geographical distance. The ratio between ⁇ and ⁇ determines how the optimisation must be done.
  • the solution described in fig 2 functions not only in the establishing of a synchronisation network but also when a synchronisation network is to be reestablished, for example after interruptions on one or more transmission lines or after the equipment at one or more nodes has broken down Since stages 2 to 5 in the loop in fig 2 are performed continuously, in the event of an interruption or failure other ways are sought in order to obtain a stable synchronisation network again If, for example, there should be an interruption on the transmission line AE in fig.
  • the device according to the invention represented in the diagram in fig 2 seeks ways (via node F) of obtaining a stable synchronisation network again with node A as the synchronisation source Even if the synchronisation source should be entirely disconnected from the network, for example as a result of the transmission line AF also being affected by an interruption, a synchronisation network will be reestablished in which node B acts as synchronisation source

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

Abstract

L'invention concerne un dispositif en noeuds dans un réseau, et un procédé permettant d'établir ou de rétablir un réseau de synch ronisation dans ledit réseau. L'invention est caractérisée par le fait que des dispositifs de lecture sont ajustés de manière à lire des chaînes de synchronisation à partir de noeuds adjacents, les chaînes de synchronisation lues comprenant une séquence de noms de noeuds représentant les noeuds passés antérieurement par la chaîne de synchronisation, y compris la source de synchronisation. L'invention est également caractérisée par le fait que des dispositifs de sélection d'un lien avec la source de synchronisation sont ajustés de manière à sélectionner l'une des chaînes de synchronisation lues ou à n'en sélectionner aucune, en fonction d'un schéma prédéterminé; une autre caractéristique est que des dispositifs de fonctionnement sont ajustés de manière à former une nouvelle chaîne de synchronisation, et des dispositifs d'écriture sont ajustés de manière à écrire la nouvelle chaîne de synchronisation sur les noeuds adjacents.
PCT/SE1997/001468 1996-09-24 1997-09-03 Procede et dispositif permettant une synchronisation basee sur des messages WO1998013967A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU41408/97A AU4140897A (en) 1996-09-24 1997-09-03 Method and arrangement for message based synchronisation

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE9603479-8 1996-09-24
SE9603479A SE9603479L (sv) 1996-09-24 1996-09-24 Förfarande och anordning för meddelandebaserad synkronisering i ett nätverk

Publications (1)

Publication Number Publication Date
WO1998013967A1 true WO1998013967A1 (fr) 1998-04-02

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/SE1997/001468 WO1998013967A1 (fr) 1996-09-24 1997-09-03 Procede et dispositif permettant une synchronisation basee sur des messages

Country Status (3)

Country Link
AU (1) AU4140897A (fr)
SE (1) SE9603479L (fr)
WO (1) WO1998013967A1 (fr)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2986723A (en) * 1960-02-26 1961-05-30 Bell Telephone Labor Inc Synchronization in a system of interconnected units
US4142069A (en) * 1977-06-20 1979-02-27 The United States Of America As Represented By The Secretary Of The Army Time reference distribution technique
WO1995024772A2 (fr) * 1994-03-01 1995-09-14 Nokia Telecommunications Oy Procede de synchronisation hierarchisee

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2986723A (en) * 1960-02-26 1961-05-30 Bell Telephone Labor Inc Synchronization in a system of interconnected units
US4142069A (en) * 1977-06-20 1979-02-27 The United States Of America As Represented By The Secretary Of The Army Time reference distribution technique
WO1995024772A2 (fr) * 1994-03-01 1995-09-14 Nokia Telecommunications Oy Procede de synchronisation hierarchisee

Also Published As

Publication number Publication date
AU4140897A (en) 1998-04-17
SE506175C2 (sv) 1997-11-17
SE9603479L (sv) 1997-11-17
SE9603479D0 (sv) 1996-09-24

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