JPH0292124A - Transmission path switching system - Google Patents

Abstract

PURPOSE:To always attain a normal transmission line switching by superimposing a direct current onto a transmission line, superimposing the direct current to a reserve system transmission line at the active system abnormality time and after the closed loop setting is confirmed, executing the line switching, when 4-wire system transformer coupling active and reserve transmission lines are used. CONSTITUTION:When a direct current inversion detecting direct current supervising circuit 16 detects the direct current in a facing terminal equipment and an E system line fault detecting circuit 6 does not execute the abnormality detection, a line switching control circuit 14, while the closed loop of the direct current inversion detecting direct current supervising circuit 16 is closed as it is, executes the line switching at a line selecting circuit 8 after a prescribed time elapses, and executes the control to make it into 'open' at the time of being the abnormality detection. At the direct current superimposing side, after the prescribed time elapses, the loop is closed as it is, and then, it is judged that switching is 'completed (OK)', and at the line selecting circuit 8, the active and reserve switchings are executed. Thus, the transmission line switching is always and normally performed.

Description

【発明の詳細な説明】 〔産業上の利用分野〕 本発明は伝送路が２重化された通信回線によって端末装
置間の通信を行う際に用いられる伝送路切替方式に関す
る。DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a transmission line switching system used when communicating between terminal devices using a communication line in which transmission lines are duplicated.

〔従来の技術〕[Conventional technology]

まず、伝送路が２重化された通信回線を用いた端末間通
信の一例について第４図を参照して説明する。First, an example of communication between terminals using a communication line with duplicated transmission paths will be described with reference to FIG.

端末装置８は２系統の回線終端装置インタフェース回路
１及び２を備えており、同様にして端末装置８′も２系
統の回線終端装置インタフェース回路１′及び２′を備
えている。回線終端装置インタフェース回路１及び２は
夫々独立した加入者伝送路７を介して回線終端装置イン
タフェース回路１′及び２′に接続され、互いに独立し
た加入者系を構成している。The terminal device 8 includes two lines of line termination device interface circuits 1 and 2, and similarly, the terminal device 8' also includes two lines of line termination device interface circuits 1' and 2'. Line termination device interface circuits 1 and 2 are connected to line termination device interface circuits 1' and 2' via independent subscriber transmission lines 7, respectively, and constitute mutually independent subscriber systems.

このように２系統（２重化）の伝送路を備えることによ
り、一方の伝送路が障害により使用不能となった際に他
方の伝送路へう回することにより。By providing two transmission lines (duplicated) in this way, when one transmission line becomes unusable due to a failure, the data can be routed to the other transmission line.

端末装置間の通信を継続することが可能となる。It becomes possible to continue communication between terminal devices.

上記の伝送路２重化通信では、端末装置において、いず
れの伝送路を用いてデータの送受を行うかを選択する回
路、即ち、伝送路切替回路が必要と女る。In the above-mentioned transmission line duplex communication, a circuit for selecting which transmission line to use for transmitting and receiving data, ie, a transmission line switching circuit, is required in the terminal device.

従来の伝送路切替回路は第５図に示すように上述した回
線インタフェース回路１（１′）及び２（２’）　。Conventional transmission line switching circuits include the above-mentioned line interface circuits 1 (1') and 2 (2') as shown in FIG.

回線障害検出回路３及び４２回線切替制御回路５゜及び
回線選択回路６によって構成されている。It is composed of a line fault detection circuit 3 and 42, a line switching control circuit 5°, and a line selection circuit 6.

回線障害検出回路３または４によって現用回線の動作状
態を常時モニタし、障害を検出すると。When the line fault detection circuit 3 or 4 constantly monitors the operating state of the working line and detects a fault.

この障害検出結果によって１回線切替制御回路５が２回
線選択回路を制御して、現用回線と予備回線との切替を
行っている。Based on the failure detection result, the 1-line switching control circuit 5 controls the 2-line selection circuit to switch between the working line and the protection line.

このような２重化伝送路を用いた通信では常にデータの
送受が伝送路−つを用いて行なわれるので、予備系の伝
送路には、データは送出されない。In communications using such duplex transmission lines, data is always sent and received using one transmission line, so no data is sent to the backup transmission line.

次に第６図に伝送路系の他の例を示す。Next, FIG. 6 shows another example of a transmission line system.

第６図を参照して、端末装置８は２系統の回線終端装置
インタフェース回路１及び２を備えておシ、同様にして
端末装置８′も２系統の回線終端装置インタフェース回
路１′及び２′を備えている。回線終端装置インタフェ
ース回路１及び２はそれぞれ回線終端装置９及び１０．
加入者伝送路１１を介してサービスオフィス１２へ接続
されている。Referring to FIG. 6, the terminal device 8 includes two lines of line termination device interface circuits 1 and 2, and similarly, the terminal device 8' also includes two lines of line termination device interface circuits 1' and 2'. It is equipped with Line terminator interface circuits 1 and 2 are connected to line terminators 9 and 10, respectively.
It is connected to a service office 12 via a subscriber transmission line 11.

一方２回線終端インタフェース回路１′及び２′はそれ
ぞれ回線終端装置９′及び１０′、加入者伝送路１１′
を介してサービスオフィス１２′へ接続されている。そ
して、これらサービスオフィス１２及び１２′は中継伝
送路１３に含まれる。On the other hand, the two line termination interface circuits 1' and 2' are line termination devices 9' and 10', respectively, and subscriber transmission line 11'.
It is connected to the service office 12' via. These service offices 12 and 12' are included in the relay transmission path 13.

このようにして、互いに独立した加入者系が構成されて
いる。In this way, mutually independent subscriber systems are constructed.

前述のように伝送路２重化通信では、端末装置において
、いずれの伝送路を用いてデータの送受を行うかを選択
する回路、即ち、伝送路切替回路が必要となる。As described above, in transmission line duplex communication, a terminal device requires a circuit for selecting which transmission line to use for transmitting and receiving data, that is, a transmission line switching circuit.

従来の伝送路切替回路は前述した第５図に示す構成とな
っている。A conventional transmission line switching circuit has the configuration shown in FIG. 5 mentioned above.

〔発明が解決しようとする問題点〕[Problem that the invention seeks to solve]

上述した従来の２重化伝送路通信では、データの送受は
必ず伝送路の一方のみを用いて行なわれるので、予備系
には、データが送出されない。In the conventional duplex transmission line communication described above, data transmission and reception is always performed using only one of the transmission lines, so no data is sent to the backup system.

このため、予備系の伝送路障害を監視することができず
、現用、予備両系障害時に、伝送路切替が連続して発生
するという問題点がある。Therefore, it is not possible to monitor transmission path failures in the protection system, and there is a problem in that transmission path switching occurs continuously when both the active and protection systems fail.

また、中継伝送路の障害によっては、その障害が、対向
する端末装置へ同時に伝達されるとは限らないため１片
側の端末装置でのみ障害が検出されることがある。この
場合、障害検出を行った端末装置でのみ伝送路切替が行
なわれるので、端末装置間で使用する伝送路が異なり正
常な通信が行えないという問題点がある。さらに、第２
図及び第４図において、端末装置の回線終端装置インタ
フェース回路と回線終端装置との間で障害が発生した場
合２回線終端装置は端末装置からの受信信号フレーム同
期はずれを検出する。ところが２回線終端装置によって
は、サービスオフィスに向かって送出する信号のフレー
ムを正常につけかえて送出するので、その結果、対向す
る端末装置では障害を検出できず、対向する端末装置で
は障害検出が行なわれず、端末装置間で使用する伝送路
が異なシ企常な通信が行えないという問題点がある。Further, depending on a fault in a relay transmission path, the fault may not be transmitted to opposing terminal devices at the same time, so the fault may be detected only in one terminal device. In this case, since the transmission path is switched only in the terminal device that has detected the failure, there is a problem that the transmission paths used between the terminal devices are different and normal communication cannot be performed. Furthermore, the second
In FIG. 4 and FIG. 4, when a failure occurs between the line terminating device interface circuit of the terminal device and the line terminating device, the two line terminating devices detect a loss of frame synchronization of the received signal from the terminal device. However, depending on the two-line termination device, the frame of the signal sent to the service office is correctly changed and sent, so that the opposing terminal device cannot detect the fault, and the opposing terminal device cannot detect the fault. However, there is a problem in that unintended communication cannot be performed between terminal devices if the transmission paths used are different.

〔問題点を解決するだめの手段〕[Failure to solve the problem]

本発明によれば、４線式トランス結合の現用及び予備の
伝送路を備える通信回線を用いて互いに通信を行う端末
装置に用いられ、該現用又は予備の伝送路障害の際、前
記伝送路の切替を行う伝送路切替方式において、前記端
末装置には前記現用及び予備の伝送路の障害を検出する
伝送路障害検出回路と、該伝送路に直流重畳を行う直流
重畳回路と、前記伝送路に重畳された直流を検出する直
流検出回路と、前記現用及び予備の伝送路の切替を行う
切替スイッチと・、該切替スイッチを制御する切替制御
回路とを有する伝送路切替回路が備えられ、前記現用の
伝送路の障害が検出されると。According to the present invention, the present invention is used in a terminal device that communicates with each other using a communication line having a four-wire transformer-coupled working and standby transmission line, and when a fault occurs in the working or standby transmission line. In a transmission line switching method that performs switching, the terminal device includes a transmission line fault detection circuit that detects a fault in the working and backup transmission lines, a DC superimposition circuit that superimposes a DC on the transmission line, and a DC superposition circuit that superposes a DC on the transmission line. A transmission line switching circuit is provided, which includes a direct current detection circuit that detects superimposed direct current, a changeover switch that switches between the working and standby transmission lines, and a switching control circuit that controls the changeover switch. When a fault in the transmission path is detected.

前記端末装置の一方が前記直流重畳回路によって前記予
備の伝送路に直流を重畳し、前記端末装置の他方は前記
重畳電流を検出した際、前記予備の伝送路に切替可であ
れば、前記直流重畳回路を閉としたままで伝送路切替を
行い、前記予備の伝送路に切替不可であれば、前記直流
重畳回路を開とし、前記端末装置の一方は前記直流重畳
の後、所定時間経過後、閉ループが形成されていること
が検出されると、伝送路切替を行うことを特徴とする伝
送路切替方式が得られる。When one of the terminal devices superimposes a direct current on the backup transmission line by the DC superimposition circuit, and the other terminal device detects the superimposed current, if it is possible to switch to the backup transmission line, the DC Transmission path switching is performed with the superimposition circuit closed, and if switching to the spare transmission path is not possible, the DC superimposition circuit is opened, and one of the terminal devices is connected after a predetermined period of time has passed after the DC superimposition. , a transmission path switching method is obtained in which transmission path switching is performed when it is detected that a closed loop is formed.

さらに本発明によれば、中継伝送路を含み、現用及び予
備の伝送路を備える通信回線を用いて互いに通信を行う
端末装置に用いられ、該現用の伝送路障害の際、前記伝
送路の切替を行う伝送路切替方式において、前記端末装
置間の伝送信号フォーマットがフレーム同期ビットと情
報伝送ビットとによって構成されておシ、該端末装置は
前記フレーム同期ビット内に伝送路切替制御ビットを伝
送する手段と、前記伝送路障害が検出された際。Further, according to the present invention, the present invention is used in terminal devices that communicate with each other using a communication line that includes a relay transmission line and has a working transmission line and a backup transmission line, and when the working transmission line fails, the switching of the transmission line is performed. In the transmission path switching method, the transmission signal format between the terminal devices is composed of a frame synchronization bit and an information transmission bit, and the terminal device transmits a transmission path switching control bit in the frame synchronization bit. means and when said transmission path failure is detected.

前記伝送切替制御ビット位置に伝送路切替可否信号を送
出する手段と、該伝送路切替可否信号の受信及び伝送路
切替可否返送を行う手段と、前記伝送路の現用、予備を
切替える切替スイッチと、該切替スイッチを制御する切
替制御手段とを有し。means for sending a transmission line switchability signal to the transmission switching control bit position; means for receiving the transmission line switchability signal and returning the transmission line switchability signal; a changeover switch for switching the transmission line between active and standby; and a changeover control means for controlling the changeover switch.

前記端末装置の一方で前記伝送路障害が検出されると、
前記端末装置の他方に前記伝送路切替制御ビット位置で
伝送路切替可否信号を送出するようにしたことを特徴と
する伝送路切替方式が得られる。When the transmission path failure is detected on one of the terminal devices,
A transmission path switching system is obtained, characterized in that a transmission path switching permission/inhibition signal is sent to the other terminal device at the transmission path switching control bit position.

〔実施例〕〔Example〕

次に本発明について実施例によって説明する。 Next, the present invention will be explained with reference to examples.

第１図は本発明が適用された端末装置の一実施例を示す
ブロック図である。第１図を参照して。FIG. 1 is a block diagram showing an embodiment of a terminal device to which the present invention is applied. Referring to FIG.

１はＮ系回線終端装置インタフェース回路、２はＥ糸回
線終端装置インタフェース回路、５はＮ系回線障害検出
回路、６はＥ系回線障害検出回路。1 is an N-system line termination device interface circuit, 2 is an E-thread line termination device interface circuit, 5 is an N-system line failure detection circuit, and 6 is an E-system line failure detection circuit.

１４は回線切替制御回路、８は回線選択回路、１５及び
１６はそれぞれＮ、］１１ｍの直流重畳検出・直流重畳
回路である。14 is a line switching control circuit, 8 is a line selection circuit, and 15 and 16 are each a DC superposition detection/DC superposition circuit of N, ]11 m.

今、現用系をＮ系、予備系をＥ系とする。端末装置の送
受信信号はＮ系の回線終端装置より端子Ａを介して入出
力され、Ｎ系回線終端装置インタフェース回路１で装置
内信号レベルとの整合をとる。Ｎ系回線障害検出回路５
及びＥ系回線障害検出回路６はそれぞれＮ系及びＥ不伝
送路の障害検出を行い１通信不能をもたらす伝送路障害
２例えば、フレーム同期はずれ、及び、入力信号断を検
出する。Ｎ系及びＥ系回線障害検出回路３及び４の検出
出力は回線切替制御回路１４に入力される。Now, assume that the active system is the N system and the backup system is the E system. Transmission/reception signals from the terminal device are input/output from the N-system line termination device via terminal A, and matched with the internal signal level in the N-system line termination device interface circuit 1. N system line failure detection circuit 5
and E-system line fault detection circuit 6 detect faults in the N-system and E-non-transmission paths, respectively, and detect (1) transmission path faults that cause communication failure (2), for example, frame synchronization loss and input signal disconnection. The detection outputs of the N-system and E-system line fault detection circuits 3 and 4 are input to the line switching control circuit 14.

対向端末装置間の加入者回路は４線式トランス結合によ
シ構成されておシ、直流反転検出・直流重畳回路１５及
び１６は通常閉ループを形成しているが、直流重畳は行
なわ々い。The subscriber circuit between opposing terminal devices is constructed by a four-wire transformer coupling, and the DC reversal detection/DC superposition circuits 15 and 16 normally form a closed loop, but DC superposition is rarely performed.

Ｎ系伝送路に前述した障害が発生すると、Ｎ系回線障害
検出回路５が障害発生を回線切替制御回路１４に通知す
る。回線切替制御回路１４は直流反転検出、直流重畳回
路１６に直流重畳をオンとする指示をする。When the aforementioned fault occurs in the N-system transmission line, the N-system line fault detection circuit 5 notifies the line switching control circuit 14 of the occurrence of the fault. The line switching control circuit 14 detects DC reversal and instructs the DC superposition circuit 16 to turn on DC superposition.

一方、対向端末装置において直流反転検出・直流重畳回
路１６が直流検出をすると、Ｅ系回線障害検出回路６が
異常検出を行っていない場合２回線切替制御回路１４は
直流反転検出・直流重畳回路１６の閉ループを閉のまま
として、所定時間の後９回線選択回路８にて回線切替を
行い、異常検出時開とする制御を行う。On the other hand, when the DC reversal detection/DC superposition circuit 16 detects DC in the opposite terminal device, if the E system line failure detection circuit 6 does not detect an abnormality, the two-line switching control circuit 14 detects the DC reversal detection/DC superposition circuit 16 The closed loop remains closed, and after a predetermined period of time, the nine line selection circuits 8 perform line switching, and control is performed to open the line when an abnormality is detected.

また、直流重畳側では、所定時間後、ループが閉のまま
であれば、切替了（ＯＫ）”と判断して。Furthermore, on the DC superimposition side, if the loop remains closed after a predetermined period of time, it is determined that the switching is complete (OK).

回線選択回路８にて現用、予備の切替を実行する。The line selection circuit 8 executes switching between active and standby lines.

閉ループが開となった場合、切替不可信号受信と判断し
、切替を行なわない。If the closed loop becomes open, it is determined that a signal indicating that switching is not possible has been received, and switching is not performed.

次に２本発明の他の実施例について説明する。Next, two other embodiments of the present invention will be described.

第２図を参照して、■はＮ系回線終端装置インタフェー
ス回路、２はＥ糸回線終端装置インタフェース回路、５
はＮ系回線障害検出回路、６はＥ系回線障害検出回路、
１７は回線切替制御回路。Referring to FIG. 2, ■ is an N-line line termination device interface circuit, 2 is an E-line line termination device interface circuit, and 5 is an E-line line termination device interface circuit.
is an N-system line failure detection circuit, 6 is an E-system line failure detection circuit,
17 is a line switching control circuit.

８は回線選択回路、１８及び１９はそれぞれＮ。8 is a line selection circuit, 18 and 19 are each N.

Ｅ系の伝送路切替可否信号送受信回路を有するフレーム
同期回路である。This is a frame synchronization circuit having an E-system transmission line switching permission/inhibition signal transmission/reception circuit.

今現用系をＮ系、予備系をＥ系とする。端末装置の送受
信信号はＮ系の回線終端装置より端子Ａを介して入出力
され、Ｎ系回線終端装置インタフェース回路１で装置内
信号レベルとの整合をとる。Let us now assume that the current system is the N system and the backup system is the E system. Transmission/reception signals from the terminal device are input/output from the N-system line termination device via terminal A, and matched with the internal signal level in the N-system line termination device interface circuit 1.

Ｎ系回線障害検出回路５及びＥ系回線障害検出回路６は
それぞれＮ系及びＥ光伝送路の障害検出を行い２通信不
能をもたらす伝送路障害１例えば。The N-system line fault detection circuit 5 and the E-system line fault detection circuit 6 detect faults in the N-system and E-optical transmission lines, respectively, and detect a transmission line fault 1 that causes communication failure, for example.

フレーム同期はずれ及び、入力信号断を検出する。Detects frame synchronization loss and input signal disconnection.

Ｎ系及びＥ系回線障害検出回路５及び６の検出出力は回
線切替制御回路１７に入力される。The detection outputs of the N-system and E-system line failure detection circuits 5 and 6 are input to the line switching control circuit 17.

ここで、第３図にこの実施例で用いられる信号のフレー
ムフォーマットを示す。Here, FIG. 3 shows the frame format of the signal used in this embodiment.

第３図において、Ｆはフレーム同期をとるだめのフレー
ム同期用ビットであり２本実施例では６７／ｌ／−Ｆ−
フレームによ’）　Ｆｏ−Ｆ５によシフレーム同期がと
られる。フレーム同期用ビットの第６マルチフレームの
位置には、伝送路切替制御ビットが多重化される。端末
装置間の通信信号はＨピットにより伝送される。In FIG. 3, F is a frame synchronization bit for frame synchronization, and in this embodiment there are two bits, 67/l/-F-
Frame synchronization is performed by Fo-F5. A transmission path switching control bit is multiplexed at the position of the sixth multiframe of the frame synchronization bit. Communication signals between terminal devices are transmitted by H pits.

Ｎ系伝送路に前述の障害が発生すると、Ｎ系回線障害検
出回路５がこの障害を検出し回線切替制御回路１７に通
知する。回線切替制御回路１７はＥ系フレーム同期回路
１９にてＳビットをオンとして対向端末装置へ通知する
指示をする。対向装置にて、予備未了（ＯＫ）と判断で
きれば、Ｓビ。When the aforementioned fault occurs in the N-system transmission line, the N-system line fault detection circuit 5 detects this fault and notifies the line switching control circuit 17. The line switching control circuit 17 instructs the E-system frame synchronization circuit 19 to turn on the S bit and notify the opposite terminal device. If the opposing device determines that the preliminary preparation has not been completed (OK), the S-vi.

トオンとして返送する。この後、対向端末装置では２回
線選択回路８にて予備系切替を行う。一方。Return it as a toon. Thereafter, in the opposite terminal device, the two-line selection circuit 8 performs backup system switching. on the other hand.

送信側端末装置では、対向端末装置からの切替ＯＫ倍信
号受信すると、現用、予備切替を行う。対向端末装置よ
りＳビットオンが返送されない時切替を実行しない。When the transmitting terminal device receives the switching OK double signal from the opposing terminal device, it performs switching between working and backup. Switching is not executed when the S bit ON is not returned from the opposite terminal device.

〔発明の効果〕〔Effect of the invention〕

以上説明したように２本発明では、４線式トランス結合
の現用及び予備の伝送路を用いる場合。As explained above, in the present invention, there are two cases in which four-wire transformer-coupled working and backup transmission lines are used.

伝送路上に直流重畳を行い、現用系異常時に予備系の伝
送路に直流重畳し、閉ループ設定を確認後回線切替を行
うことにより、常に正常に伝送路切替を行うことができ
るという効果がある。By superimposing DC on the transmission line, superimposing DC on the protection transmission line when an abnormality occurs in the working system, and switching the line after confirming the closed loop setting, the effect is that the transmission line can always be switched normally.

また、中継伝送路を含む通信回路の場合、伝送路上に伝
送路切替制御ビットを設け、現用系異常時に、予備系の
制御ビットにより切替可否を間合わせ、切替再受信時に
のみ回線切替を行うようにしたから、常に正常に伝送路
切替を行うことができるという効果がある。In addition, in the case of a communication circuit that includes a relay transmission line, a transmission line switching control bit is installed on the transmission line, and when an abnormality occurs in the active system, the control bit of the standby system is used to determine whether switching is possible or not, and line switching is performed only when switching is received again. This has the advantage that transmission path switching can always be performed normally.

【図面の簡単な説明】[Brief explanation of the drawing]

第１図は本発明の一実施例を示す端末装置のブロック図
、第２図は本発明の他の実施例を示す端末装置のブロッ
ク図、第３図は本発明の他の実施例に用いられる信号の
フレームフォーマットを示す図、第４図は伝送路２重化
構成の一例を示す図。 第５図は従来の伝送路切替回路を示すブロック図。 第６図は伝送路２重化構成の他の例を示す図である。 ■・・・Ｎ系回線インタフェース回路、２・・・Ｅ糸回
線インタフェース回路、３．３’・・端末装置、　４　
、４’・・・加入者伝送路、５・・・Ｎ系回線障害検出
回路、６・・・Ｅ系回線障害検出回路、７・・・回線切
替制御回路。 ８・・回線選択回路、１１・・・回線切替制御回路、１
２・・Ｎ系直流反転検出 直流重畳回路 直流反転検出 直流重畳回路。 Ｅ系 第３図FIG. 1 is a block diagram of a terminal device showing one embodiment of the invention, FIG. 2 is a block diagram of a terminal device showing another embodiment of the invention, and FIG. 3 is a block diagram of a terminal device showing another embodiment of the invention. FIG. 4 is a diagram showing an example of a duplex transmission line configuration. FIG. 5 is a block diagram showing a conventional transmission line switching circuit. FIG. 6 is a diagram showing another example of a duplex transmission line configuration. ■...N system line interface circuit, 2...E thread line interface circuit, 3.3'...Terminal device, 4
, 4'...Subscriber transmission line, 5...N system line failure detection circuit, 6...E system line failure detection circuit, 7... Line switching control circuit. 8... Line selection circuit, 11... Line switching control circuit, 1
2...N system DC reversal detection DC superposition circuit DC reversal detection DC superposition circuit. E series diagram 3

Claims (1)

【特許請求の範囲】 １、４線式トランス結合の現用及び予備の伝送路を備え
る通信回路を用いて互いに通信を行う端末装置に用いら
れ、該現用の伝送路障害の際、前記伝送路の切替を行う
伝送路切替方式において、前記端末装置には前記現用及
び予備の伝送路の障害を検出する伝送路障害検出回路と
、該伝送路に直流重畳を行う直流重畳回路と、前記伝送
路に重畳された直流を検出する直流検出回路と、前記現
用及び予備の伝送路の切替を行う切替スイッチと、該切
替スイッチを制御する切替制御回路とを有する伝送路切
替回路が備えられ、前記現用の伝送路の障害が検出され
ると、前記端末装置の一方が前記直流重量回路によって
前記予備の伝送路に直流を重畳し、前記端末装置の他方
は前記重畳電流を検出した際、前記予備の伝送路に切替
可であれば、前記直流重畳回路を閉としたままで伝送路
切替を行い、前記予備の伝送路に切替不可であれば、前
記直流重畳回路を開とし、前記端末装置の一方は前記直
流重畳の後、所定時間経過後、閉ループが形成されてい
ることが検出されると、伝送路切替を行うことを特徴と
する伝送路切替方式。 ２、中継伝送路を含み、現用及び予備の伝送路を備える
通信回線を用いて互いに通信を行う端末装置に用いられ
、該現用の伝送路障害の際、前記伝送路の切替を行う伝
送路切替方式において、前記端末装置間の伝送信号フォ
ーマットがフレーム同期ビットと情報伝送ビットとによ
って構成されており、該端末装置は前記フレーム同期ビ
ット内に伝送路切替制御ビットを伝送する手段と、前記
伝送路障害が検出された際、前記伝送切替制御ビット位
置に伝送路切替可否信号を送出する手段と、該伝送路切
替可否信号の受信及び伝送路切替可否返送を行う手段と
、前記伝送路の現用、予備を切替える切替スイッチと、
該切替スイッチを制御する切替制御手段とを有し、前記
端末装置の一方で前記伝送路障害が検出されると、前記
端末装置の他方に前記伝送路切替制御ビット位置で伝送
路切替可否信号を送出するようにしたことを特徴とする
伝送路切替方式。[Scope of Claims] Used in terminal devices that communicate with each other using communication circuits that are equipped with 1 and 4-wire transformer-coupled working and standby transmission lines, and in the event of a fault in the working transmission line, the In a transmission line switching method that performs switching, the terminal device includes a transmission line fault detection circuit that detects a fault in the working and backup transmission lines, a DC superimposition circuit that superimposes a DC on the transmission line, and a DC superposition circuit that superposes a DC on the transmission line. A transmission line switching circuit is provided, which includes a direct current detection circuit that detects superimposed direct current, a changeover switch that switches between the working and standby transmission lines, and a switching control circuit that controls the changeover switch. When a fault in the transmission path is detected, one of the terminal devices superimposes DC on the backup transmission path using the DC weight circuit, and when the other terminal device detects the superimposed current, it superimposes DC on the backup transmission path. If it is possible to switch to the transmission line, the transmission line is switched with the DC superimposition circuit closed; if it is not possible to switch to the spare transmission line, the DC superposition circuit is opened, and one of the terminal devices A transmission line switching method characterized in that the transmission line is switched when it is detected that a closed loop is formed after a predetermined period of time has elapsed after the DC superimposition. 2. Transmission line switching used in terminal devices that communicate with each other using a communication line that includes a relay transmission line and has a working transmission line and a backup transmission line, and that switches the transmission line in the event of a failure of the working transmission line. In this method, the transmission signal format between the terminal devices is configured by a frame synchronization bit and an information transmission bit, and the terminal device includes means for transmitting a transmission path switching control bit within the frame synchronization bit, and a means for transmitting a transmission path switching control bit in the frame synchronization bit, means for sending a transmission line switchability signal to the transmission switching control bit position when a failure is detected; means for receiving the transmission line switchability signal and returning the transmission line switchability signal; and a current use of the transmission line; A selector switch to switch the spare,
and a switching control means for controlling the changeover switch, and when one of the terminal devices detects the transmission path failure, transmits a transmission path switching enable/disable signal to the other terminal device at the transmission path switching control bit position. A transmission path switching method characterized by transmitting a signal.