WO1998004064A1 - Synchronisation maitre-esclave - Google Patents

Synchronisation maitre-esclave Download PDF

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Publication number
WO1998004064A1
WO1998004064A1 PCT/FI1997/000432 FI9700432W WO9804064A1 WO 1998004064 A1 WO1998004064 A1 WO 1998004064A1 FI 9700432 W FI9700432 W FI 9700432W WO 9804064 A1 WO9804064 A1 WO 9804064A1
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WO
WIPO (PCT)
Prior art keywords
network
master
network element
base station
signal
Prior art date
Application number
PCT/FI1997/000432
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English (en)
Inventor
Jouko Juhani Kapanen
Original Assignee
Nokia Telecommunications Oy
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 Nokia Telecommunications Oy filed Critical Nokia Telecommunications Oy
Priority to AU33467/97A priority Critical patent/AU3346797A/en
Priority to EP97929329A priority patent/EP0917779A1/fr
Publication of WO1998004064A1 publication Critical patent/WO1998004064A1/fr
Priority to US09/233,650 priority patent/US6134234A/en

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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
    • H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
    • H04J3/0641—Change of the master or reference, e.g. take-over or failure of the master
    • 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
    • H04J2203/0042—Ring
    • 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
    • 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
    • H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
    • H04J3/0647—Synchronisation among TDM nodes

Definitions

  • This invention relates to the maintenance of the mutual synchroniza- tion between network elements of a telecommunications network that uses master-slave synchronization.
  • a telecommunications network typically consists of several network elements and the trunk lines that connect these elements to one another.
  • the network can be synchronous, such as a Synchronous Digital Hierarchy (SDH) network, or plesiochronous such as a Plesiochronous Digital Hierarchy (PDH) network.
  • SDH Synchronous Digital Hierarchy
  • PDH Plesiochronous Digital Hierarchy
  • the PDH networks include, among others, the digital mobile commu- nications network which is used as an example to illustrate the application network of the invention. References are made to Figure 1 which shows a simplified diagram of the GSM network (Groupe Speciale Mobile) from the point of view of transmission.
  • the network subsystem NSS consists of the mobile switching center MSC through whose system interface the mobile communica- tions network connects to other networks, such as the public switched telephone network PSTN.
  • the network subsystem NSS is connected via the interface A to the base station subsystem BSS which consists of base station controllers BSC, each of which controls the base transceiver stations BTS connected to these controllers.
  • the interface between the base station controller and the base stations connected to it is an A bis interface.
  • the RF parts of the base stations are completely controlled by the base station controller BSC, mostly consisting of transceivers TRX which implement the radio interface to the mobile station.
  • the network formed by the base stations controlled by the base station controllers can be star-shaped as the system on the left in the Figure, in which case each base station is directly connected to the base station control- ler, or a loop which consists of base stations chained to one another and which terminates either in one of the base stations as in the system shown in the middle of the Figure, or in the base station controller.
  • the network can also be a chain, in which case a trunk line leads from the base station controller to one of the base stations, from that to another base station, etc., as shown in the base station system on the right in Figure 1.
  • a mobile communications network any of the above base station network types or a combination of them can be used as necessary.
  • the network elements should operate in synchronization with one another to avoid frame slips. Additionally, the base stations require an exact synchroniza- tion to form the correct kind of signal for the air interface and to keep it with sufficient precision in the frequency band reserved for it.
  • a separate clock signal can be input into the network element from an accurate clock source which can be shared by the entire network.
  • Each network element can have a separate accurate clock source, or they can receive synchronization, for example, through the GPS satellite system.
  • master-slave synchronization the higher element of the network hierarchy provides the synchronization to a lower element as part of the transmitted signal, in which case an accurate timing source is only needed in the topmost network element of the hierarchy.
  • the master clock is in the mobile switching center MSC which provides the clock signal to base station controllers which further transmit the clock signal to the base stations controlled by them.
  • the network elements receive the clock frequency and phase directly from the bit speed of the trunk line at 2 Mbit/s.
  • the clock signal thereby travels via the route MSC ⁇ BSC ⁇ BTS1->BTS2 ⁇ etc.
  • a network element must not receive a synchronization signal simultaneously from several directions. Even if the base station network were a loop, as far as the master clock signal is concerned, it is not a loop, but the loop has been interrupted at a point so that the base stations only receive their clock signal from one direction. However, as far as voice and data transfer are concerned, the loop is not interrupted, in which case a fault in one of the links does not affect the speech transfer, although the synchronization with the master clock is lost.
  • the drawback in the master-slave synchronization in a mobile communications network is that in network fault situations, for example, when the fault is in the connection MSC ⁇ -» BSC, the isolated part of the network, for example, from the BSC down, synchronizes itself according to the clock formed by some network element and because of this the base stations drift outside their frequency band.
  • the base station can maintain its synchronization and frequencies even through long interruptions in the synchronization chain.
  • a harmful situation is created when a base station corrects its own frequency by thinking that the synchronization comes from a high-quality clock source (of nominal frequency), while this is not actually the case.
  • the drifting of a base station frequency outside of the frequency band may cause, among other things, the operator's network and that of a competing operator to go to an unusable state for several hours.
  • the unusable state causes economic losses for the operator through lost charges, possible compensations paid to the other network operator, and new subscribers lost because of the loss of repute.
  • the base station deduces that syn- chronization is allowed if the base station has a communications connection with the base station controller.
  • the synchronization occurs repeatedly in 20 minute intervals so that the phase of the base station clock is compared n times with the phase of the clock received from the network (MSC ⁇ BSC ⁇ BTS), and the average is calculated for these phase differences. If the phase difference according to the final average were to require too large a correction, the result is discarded.
  • the requirement for the activation of the synchronization event and for its continuation is thereby that the communications connection is held throughout the entire synchronization phase.
  • the weakness of this known method is that in certain network fault situations or in a combination situation of several simultaneous errors the signals are connected through and the communications connection in the interval BSC -> BTS operates but some of the base stations have lost their synchronization.
  • the situation described above may be generated, for example, in a loop network when two one-way faults are simultaneously in effect and if the signal which contains the alert for the far end is not allowed as a clock source. Simi- larly during network modification operations and especially after them one of the intervening nodes might be left on its internal clock without anybody noticing it.
  • the reliability of master-slave synchronization can be improved by adding a special control bit MCB (Master Clock Bit) in the clock signal.
  • MCB Master Clock Bit
  • the control bit MCB is added to the clock signal at the base station BTSO of the loop network which is connected to the base station controller BSC and from which the loop thereby starts and in which the loop terminates.
  • This control bit is in the agreed logical state, for example, 0.
  • base station BTS1 receives the MCB control bit whose value is 0, the base station knows that the clock signal comes from the true master clock.
  • the transmission unit TRU of the base station synchronizes itself with the master clock and transmits the clock signal as a reference signal further via the internal bus B of the base station to the clock oscillators implemented, for example, by using the PLL connection located in the other functional parts of the base station. Additionally, the base station transmits the clock signal with its MCB bit set to "0" to the next base station BTS2.
  • the transmission unit TRU of the next base station detects from the MCB bit that the received clock signal is the true signal, and it transmits the clock signal and the MCB bit further to the next base station BTS3, etc.
  • each base station input directions have been assigned to the clock inputs of the transmission unit, two of which are indicated in the figure by numbers 1 and 2. If there are more directions, they are numbered consecutively.
  • the directions are prioritized so that direction 1 is the direction, from which the clock signal comes, to which the system primarily synchronizes, and direction 2 is the direction to which the clock signal is transmitted and to which the system synchronizes secondarily.
  • One of the clock inputs in the priority list is the internal clock of the transmission unit.
  • the units are connected via their clock inputs in the loop in the manner shown in Figure 2.
  • the first base station BTS2 lo- cated after the interruption does not receive the clock signal.
  • the transmission unit TRU of the base station starts using its internal clock and transmits it further as the clock signal, but changes the MCB bit to "1".
  • the addition of the MCB bit to the clock signal in the mobile communications network is sufficient, if the base station network is chained.
  • the network automatically divides at one of the links into two parts, and all network elements located after the fault lock to the internal clock of the base station located nearest to the fault.
  • a looped network in the case of one fault, it is possible to bring the master clock signal to the base stations from the other direction, in other words, from direction 2; see Figure 2.
  • the base stations must be told in one way or another that the clock signal that arrives from this direction is, after all, the master clock and the base stations must synchronize to it.
  • This can be implemented by adding another special monitoring bit LCB (Loop Clock Bit) in addition to the MCB bit to the clock signal that leaves from the base station BTSO which operates as the main station; see Figure 2.
  • LCB Loop Clock Bit
  • Both monitoring bits are, as the signal leaves the main station, in 0 state.
  • the value 0 of the LCB bit indicates to the receiving base station BTS1 ,...,BTS3 that the clock signal is not a returned looped clock signal.
  • each base station of the loop transmits the clock signal further and keeps both the MCB bit and the LCB bit in 0 state.
  • the base station also transmits the clock signal back in the direction from which it arrived, and keeps the MCB bit in state 0 as a signal that the base station is locked to the original master clock signal.
  • the LCB bit is changed to 1 which indicates that the clock signal is a returned master clock signal in which case the preceding base station does not lock to this signal. If the value of the LCB bit is 0 and the value of the MCB bit is 0, it means that the base station must synchronize itself to this clock signal that arrives from direction 2, as it arrives from the master clock.
  • the implementation according to the prior art described above does not solve the problem of how to maintain synchronization when the base station network is a looped network and two simultaneous faults occur in the loop.
  • the first fault between BTSO and BTS1 prevents the clock signal from getting from direction 1 to the transmission unit of the base station BTS1 and the second fault between the BTS3 and BTSO causes the transmitting of the far end alarm bit FEA from BTSO in the direction of BTS3, because of which BTS3 is not allowed to lock to the signal arriving from the direction in question.
  • the difficulty is caused by the fact that as far as voice/data traffic is concerned, the loop is a true loop and in the case of an interruption, the connection to the base station controller is automatically formed via the other branch.
  • the loop is not a true loop, but it is formed by the chain BTS0,... ,BTS3. During an interruption the traffic can, therefore, continue without interruption but the base stations BTS1 to BTS3 do not receive the master clock signal.
  • the base station BTS1 reverts to using the internal clock and transmits both the MCB bit and the LCB bit in state 1 to direction 2, in other words, to the base station BTS2.
  • BTS2 also reverts to using the internal clock and transmits the aforementioned bits without changes further in direction 2 to base station BTS3.
  • This signal arrives to the base station BTS2 from the direction which is second in the priority list so the base station locks itself to this clock signal and transmits the signal further back to the base station BTS1.
  • the values of the monitoring bits are 1/0 so BTS1 also locks to this clock signal.
  • the final result conforms to Figure 3 where the base stations BTS1 to BTS3 are synchronized to the inter- nal clock signal of the base station BTS3.
  • the issue described above can also be seen so that as a result of the first fault the network is already synchronized as a chain.
  • BTS3 the device of the chain that is closest to the fault, BTS3, reverts to using the internal clock and transmits MCB as 1 to the other devices of the chain which keep their synchronization in the direction in question.
  • the network administrator receives no notification of the fact that a part of the network is no longer in synchronization.
  • the situation may continue for weeks, or even for months, until the part of the network in question has drifted badly away from its frequency band.
  • the objective of this invention is a method by which the synchronization of a chained and looped base station network reverts quickly to use of the master clock in different fault situations and which ensures that the base station receives reliable information about the quality of the synchronization signal in use. In this manner it is ensured that the fault situation of a master-slave syn- chronized base station network described above does not cause the base station to drift away from its frequency band.
  • the slave network element selects the clock signal from the group of candidate synchronization signals which includes the master synchronization signal, the internal clock signal of the slave network element, and the synchronization signals of the other network elements that arrive from different directions in the network.
  • the system adds information as to whether the signal is the master synchronization signal or the internal clock signal selected by another slave unit for use, and additional information on whether it is allowed to select the clock signal as the synchronization signal. If some signal other than the master synchronization signal is selected as the synchronization signal, the slave network element generates an alarm signal.
  • the method according to the invention uses the known looped network monitoring bit MCB (Master Clock Bit).
  • the use of the MCB bit is extended so that it is transmitted from the master network element, for example from the mobile switching center (MSC), and if one of the network elements located between the mobile switching center and a specific slave network element, for example a base station, does not accept the received signal as the synchronization source because of its quality, the network element in question forces the MCB bit placed in the signal to state 1 when the base station transmits it further.
  • the transmission unit of a specific base station is locked to a signal which contains the MCB in state 1 , or if the base station is forced to revert to using the internal clock because of a fault situation in the received signal, the transmission unit activates the alarm (FEr, Frequency Error).
  • the alarm is transmitted to other units of the base station in question from which the fault monitoring unit further transmits it via a separate operation and mainte- nance network to the operations center of the network operator.
  • the base station reads the error status of the transmission unit and prevents or interrupts the synchronization, if the alarm is on.
  • Figure 1 shows a mobile communications network
  • Figure 2 shows the base station network from the point of view of the known synchronization method
  • Figure 3 shows the synchronization situation in the case of two concurrent faults
  • Figure 4 shows the situation immediately after the fault
  • Figure 5 shows the situation when the notice about the interruption has reached the last base station
  • Figure 6 shows the situation when the network has been resynchronized
  • Figure 7 shows a fault in a chained network
  • Figure 8 shows the situation when the network has been resynchronized.
  • the network used in the example is a mobile communications network.
  • the base station receives and further transmits the MCB and LCB bits in state 0, but returns the MCB bit in state 0 and LCB bit in state 1.
  • Figure 4 shows the situation after the fault.
  • the base station BTS1 loses the master clock signal that arrives in the input 1 of the transmission unit, and with it, the monitoring bits.
  • the base station detects the loss, it reverts to use of the internal clock and transmits the internal clock signal to the next base station converting the MCB signal from state 0 to state 1 as an indication of the fact that the clock signal is not the master clock signal.
  • the transmission unit TRU of the base station BTS1 gives the alarm signal FEr to the monitoring unit of the base station. All this takes about 200 ms of time.
  • the values of the monitoring bits that have changed compared to the normal situation ( Figure 2) are underlined for clarity. As can be seen, the base stations BTS2 and BTS3 have not yet reacted to the fault but they transmit the information "OK" to their monitoring units.
  • Figure 5 shows a situation in which the information about the interrup- tion in the monitoring bit MCB has reached the base station BTS3.
  • BTS2 has received the clock signal transmitted by BTS1 and the information about the fact that the signal comes from the internal clock and it has transmitted back this clock signal and the MCB bit in state 1.
  • the base station BTS2 is synchronized to the clock of the base station BTS1 and the transmission unit has given the alert signal FEr to the monitoring unit of the base station.
  • the last base station of the chain BTS3 has received the MCB bit in state 1 transmitted by BTS2 from direction 1.
  • the priority of the clock inputs of the base station BTS3 is such that direction 2 can be accepted as the input, if the master clock signal is not received from direction 1 , but it is received from direction 2.
  • the base station connects its synchronization to the master clock signal received from direction 2, and it transmits the LCB bit in state 1 to this direction. Simultaneously it transmits the master clock signal received from direction 2 to direction 1 in the feedback branch and with it the MCB bit in state 0 (indication of the fact that the signal is the master clock signal) and the LCB bit in state 0 as an indication of the fact that the clock signal is not looped and BTS2 is thereby allowed to lock on to this clock signal.
  • the transmission unit of the base station BTS3 has for the whole time given the OK" signal to the monitoring unit as a sign that the synchronization with the master clock signal has been maintained.
  • the base stations BTS1 and BTS2 are synchronized to the internal clock of the BTS1 and the transmission units give the fault signal FEr.
  • the events continue from the situation of Figure 5 so that the base station BTS2 connects to the master clock signal transmitted by BTS3 and the transmission unit gives the "OK" signal to the monitoring unit as an indication of the fact that the base station has been synchronized.
  • the base station also transmits the master clock signal in the feedback branch to the base station BTS1 and includes in the signal the MCB bit in state 0 as an indication of the fact that the signal in question is the true master clock signal, and the LCB bit in state 0 as an indication of the fact that the base station is allowed to synchronize to this clock signal. In this manner the synchronization to the master clock has started from the base station BTS3, reached the base station BTS2, and is now approaching the base station BTS1.
  • Figure 6 shows a situation after the base station BTS1 has synchronized itself to the master clock signal as the last base station.
  • the transmission unit of the base station also synchronizes to the master clock signal received from direction 2 and transmits the "OK" signal to the monitoring unit.
  • the base station transmits the master clock signal and the MCB bit in state 0 (an indication of the fact that the clock signal in question is the master clock signal) and the LCB bit in state 0 (an indication of the fact that the clock signal is not an immediately returned clock signal) to the main base station BTSO.
  • the synchronization starts in the last base station BTS3 and progresses from one base station to another as each base station transmits the monitoring bits backwards towards the base station located nearest to the fault.
  • All base stations are now synchronized to the master clock signal despite the fact that the interruption still exists.
  • all base stations of the loop synchronize to the clock signal that arrives from direction 1 instead of that arriving from direction 2.
  • the synchronization starts from the base station next to the fault, in the above example from the base station BTS1 , and progresses towards the last base station as the monitoring bits MCB and LCB progress from one base station to another.
  • the mechanism is the same as described above and there is no need to describe it in more detail. In this manner the base stations maintain their synchronization in spite of changing the input direction of the master clock signal.
  • Figure 7 shows the base station network in which the stations are chained.
  • the figure shows a situation in which the interruption has occurred between base stations BTS1 and BTS2 and the synchronization changes have taken place.
  • the LCB bit is not used because the network in question is not a looped network.
  • the master clock signal progresses from one base station to another as described earlier.
  • Each base station also transmits the unchanged clock signal and its MCB bit backwards.
  • the clock in direction 2 of the base station is not allowed to be used for synchronization.
  • the base station BTS located immediately after the fault reverts to using the internal clock and the transmission unit gives the alarm signal FEr to the monitoring unit.
  • the information about the fault has not yet progressed to BTS3 so at this point its transmission unit gives the "OK" signal to the monitoring unit.
  • BTS3 gives the alert signal FEr and returns the MCB bit in state 1.
  • Figure 7 The situation at this point is shown in Figure 7 in which a part of the network, i.e. base stations BTS2 and BTS3, are synchronized to a different clock signal from the rest of the network.
  • the base station BTS2 again receives the master clock signal in the direction 1 input. Its transmission unit con- nects to the direction 1 input and gives the "OK" signal to its monitoring unit. This takes approximately 200 ms. At this point the base station BTS2 is synchronized to the master clock, but the base station BTS3 is not and the alarm is still in effect in it. The base station BTS2 gives the MCB bit in state 0 as the feedback data. The situation at this point is shown in Figure 8. Right after the base station BTS2 has transmitted to the base station
  • BTS3 the master clock signal and MCB bit whose value it has changed from 1 to 0, the latter base station synchronizes to the received master clock signal and removes the alarm by giving the "OK" signal instead. BTS3 still returns the MCB bit in state 0 as feedback data, at which point the synchronization has completely returned to the master clock signal.
  • the method according to the invention can also be used to improve the readability of the synchronization in network fault situations.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

La présente invention concerne la synchronisation d'éléments de réseaux d'un réseau fonctionnant en synchronisation maître-esclave. Le procédé consiste à étendre le bit de surveillance 'MCB' (Master Clock Bit = bit de synchronisation maître) déjà connu de façon qu'il soit retransmis en permanence depuis l'élément de réseau maître, par exemple, le centre de commutation de téléphonie mobile ou 'MSC' (Mobile Switching Centre). Si l'un des éléments de réseau situé entre l'élément de réseau maître et un élément de réseau esclave spécifique, par exemple une station de base, ne prend pas en compte le signal reçu comme source de synchronisation en raison de sa qualité, l'élément de réseau considéré force le bit MCB situé dans le signal de façon que l'élément le retransmette à l'état 1. Si l'unité de transmission d'un élément de réseau esclave spécifique est verrouillé sur le signal qui inclut le bit MCB à l'état 1, ou si l'élément est forcé à 0 de façon à utiliser la synchronisation interne en raison d'un état d'incident du signal, l'unité de transmission instaure l'état d'alerte. Avant le début et pendant la synchronisation de l'horloge de la station de base, il y a lecture de l'état d'incident à partir de l'unité de transmission, ce qui fait que la synchronisation ne peut avoir lieu ou qu'elle est interrompue si l'alerte est instaurée. L'état d'alerte est communiqué aux autres unités de la station de base considérée, de sorte que l'unité de détection des incidents communique cet état d'alerte au centre d'exploitation de l'opérateur de réseau par un réseau séparé d'exploitation et de maintenance.
PCT/FI1997/000432 1996-07-19 1997-07-03 Synchronisation maitre-esclave WO1998004064A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
AU33467/97A AU3346797A (en) 1996-07-19 1997-07-03 Master-slave synchronisation
EP97929329A EP0917779A1 (fr) 1996-07-19 1997-07-03 Synchronisation maitre-esclave
US09/233,650 US6134234A (en) 1996-07-19 1999-01-19 Master-slave synchronization

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI962910A FI104592B (fi) 1996-07-19 1996-07-19 Synkronoinnin ylläpito tietoliikenneverkossa
FI962910 1996-07-19

Related Child Applications (1)

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US09/233,650 Continuation US6134234A (en) 1996-07-19 1999-01-19 Master-slave synchronization

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WO1998004064A1 true WO1998004064A1 (fr) 1998-01-29

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EP (1) EP0917779A1 (fr)
CN (1) CN1228894A (fr)
AU (1) AU3346797A (fr)
FI (1) FI104592B (fr)
WO (1) WO1998004064A1 (fr)

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EP0975114A2 (fr) * 1998-07-18 2000-01-26 Alcatel Méthode de synchronisation, générateur primaire d'horloge de référence et élément pour un réseau de transmission de données digital synchrone
GB2341041A (en) * 1998-08-26 2000-03-01 Fujitsu Ltd Clock synchronisation
WO2000022763A1 (fr) * 1998-10-13 2000-04-20 Nokia Networks Oy Unite de commande de noeud d'un noeud d'acces dans un systeme de telecommunication synchrone, et procede de commande du basculement d'une unite fournissant des signaux d'horloge dans un systeme de telecommunication
WO2000051366A2 (fr) * 1999-02-26 2000-08-31 Telefonaktiebolaget Lm Ericsson (Publ) Signaux horodateurs utilisant les canaux communs de signalisation dans un reseau cellulaire de telecommunications
US7408916B2 (en) 2000-05-30 2008-08-05 Nokia Corporation Synchronisation of frame transmissions in a telecommunications network

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US7483448B2 (en) * 2004-03-10 2009-01-27 Alcatel-Lucent Usa Inc. Method and system for the clock synchronization of network terminals
CN1870492B (zh) * 2005-05-25 2016-04-20 游天童 无线局域网或自由网中实现时间框架精细同步的方法
CN100450230C (zh) * 2005-12-02 2009-01-07 华为技术有限公司 一种射频远端模块中时钟恢复方法和装置
CN101330374B (zh) * 2007-06-18 2012-11-14 大唐移动通信设备有限公司 传输网中的时钟同步方法、系统和从时钟侧实体
CN101631013B (zh) * 2008-07-17 2013-03-06 大唐移动通信设备有限公司 接入网时钟同步的方法、设备及系统
KR20150030737A (ko) * 2012-06-20 2015-03-20 노키아 솔루션스 앤드 네트웍스 오와이 컴퓨터 네트워크에서의 동기화

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WO1994022251A1 (fr) * 1993-03-16 1994-09-29 Nokia Telecommunications Oy Procede de synchronisation de reseaux interconnectes de telecommunication a hierarchie numerique plesiochrone et a hierarchie numerique synchrone
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US6618455B1 (en) 1998-08-26 2003-09-09 Fujitsu Limited Clock management method and transmission apparatus for synchronous network system
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WO2000051366A2 (fr) * 1999-02-26 2000-08-31 Telefonaktiebolaget Lm Ericsson (Publ) Signaux horodateurs utilisant les canaux communs de signalisation dans un reseau cellulaire de telecommunications
WO2000051366A3 (fr) * 1999-02-26 2000-12-07 Ericsson Telefon Ab L M Signaux horodateurs utilisant les canaux communs de signalisation dans un reseau cellulaire de telecommunications
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CN1228894A (zh) 1999-09-15
FI962910A (fi) 1998-01-20
FI104592B (fi) 2000-02-29
FI962910A0 (fi) 1996-07-19
AU3346797A (en) 1998-02-10
EP0917779A1 (fr) 1999-05-26

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