JPS62236222A - Switching system for faulty end line - Google Patents

Switching system for faulty end line

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Publication number
JPS62236222A
JPS62236222A JP8064286A JP8064286A JPS62236222A JP S62236222 A JPS62236222 A JP S62236222A JP 8064286 A JP8064286 A JP 8064286A JP 8064286 A JP8064286 A JP 8064286A JP S62236222 A JPS62236222 A JP S62236222A
Authority
JP
Japan
Prior art keywords
line
fault
satellite
relay
lines
Prior art date
Legal status (The legal status 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 status listed.)
Pending
Application number
JP8064286A
Other languages
Japanese (ja)
Inventor
Kozo Kamata
鎌田 幸藏
Koji Tawara
田原 宏二
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Japan Radio Co Ltd
Original Assignee
Japan Radio Co Ltd
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 Japan Radio Co Ltd filed Critical Japan Radio Co Ltd
Priority to JP8064286A priority Critical patent/JPS62236222A/en
Publication of JPS62236222A publication Critical patent/JPS62236222A/en
Pending legal-status Critical Current

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Abstract

PURPOSE:To economically build a faulty end switching network at a short period by allowing relay stations at both ends of a faulty section to use a satellite line set in common for fault relief of a section being a part of a line network in advance. CONSTITUTION:Standby lines are constituted via a satellite S, doted lines show standby satellite lines capable of being set at a fault and one-dashed chain lines indicate satellite lines in use for a detour of a fault section. Further, standby satellite lines are used between low-order relay stations such as a0',a0, and between relay stations between the low-order relay station and a relay station such as a0-a3. For example, if a fault takes place between relay sections, e.g., a2 and a3, the relay stations a2,a3 detect the fault and the line is switched into the satellite standby line shown in one-dashed chain lines. The fault is detected normally by the hardware processing' and in order to detect a fault not detected by the said processing, a fault supervisory function is provided in the relay stations such as a0 a3 and communication is applied periodically between opposite relay stations opposed to each other while clipping a relay line.

Description

【発明の詳細な説明】 (産業上の利用分野〉 本発明は通信網を構成する障害端回線切替方式%式% (従来の技術) 通信網を構成する回線の信頼度を向上させる手段として
予備回線を設置して、該回線を二重化する方法や、障害
地点を迂回する方法などがあるが、基本的な回線切替方
式は回線端切替方式と障害端切替刃式とに大別される。
DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention is directed to a failed end line switching system that constitutes a communication network. There are methods such as installing a line and duplicating the line, and bypassing a point of failure, but basic line switching methods are broadly divided into line end switching methods and fault end switching methods.

(イ)障害端切替刃式 第3図は障害端切替刃式を説明するための伝送ルート図
で、a □ ” a 3及びす。−b2はそれぞれA及
びB地方の大都市に配置された有線または無線中継局を
示す。[a□’、 a□“・・・・・・]、[ab”、
・・・・・弓、[b2’、 b2“、・・・・・・]は
それぞれa □ −83及びbo−b2中継局管内の下
位中継局で、前記各無線または有線中継局は回線の集束
、配分機能を有し、図示していない単数または複数の交
換局に回線を巣、配分する。また太線で示すルートは多
重度の大きい回線を示す。
(B) Faulty end switching blade type Figure 3 is a transmission route diagram to explain the faulty end switching blade type, in which a □ ” a 3 and - b2 are located in large cities in regions A and B, respectively. Indicates a wired or wireless relay station. [a□', a□“・・・・・・], [ab”,
... Bow, [b2', b2", ......] are lower relay stations within the jurisdiction of a □ -83 and bo-b2 relay stations, respectively, and each of the wireless or wired relay stations is connected to the line. It has convergence and distribution functions and distributes lines to one or more exchanges (not shown).Routes shown in bold lines indicate lines with high multiplicity.

障害端切替刃式を完全に実施J゛るには、各中継局間対
応に点線で示す予備回線を設け、二重化し、もし障害が
発生し例えばX印で示ツa2  a3中継局間であると
すると両端の82 、a3中継局は該障害を検知して、
点線で示す予備回線に切替える。
In order to fully implement the failure end switching blade method, a backup line is provided between each relay station as shown by the dotted line, and if a failure occurs, for example between A2 and A3 relay stations, as shown by the X mark. Then, the 82 and A3 relay stations at both ends detect the failure,
Switch to the protection line indicated by the dotted line.

このように単純な完全救済を行うのには、予備回線容量
を現用と同一とした予備ルートを合めた二重化網を構成
する枝対応(区間対応)に設けることになる。
In order to carry out such simple complete relief, it is necessary to provide each branch (corresponding to a section) of a redundant network including backup routes with the same backup line capacity as the current line.

(ロ)回線端切替方式 第4図は回線端切替方式を説明するための伝送ルート図
で、第3図に示す障害端切替方式と比較して中継局間の
点線で示す予備回線が無いことが相違している。しかし
現実的には、簡単な有線方式、無線方式による2ルー1
へ化が行われている。
(b) Line end switching method Figure 4 is a transmission route diagram to explain the line end switching method.Compared to the failed end switching method shown in Figure 3, there is no backup line shown by dotted lines between relay stations. are different. However, in reality, it is possible to use simple wired or wireless methods.
conversion is being carried out.

障害区間が第3図と同様にX印で示すa2、a3中継局
区間で発生したとすると、両端のa2、a3中継局は△
地方の網管理中継局であるa。局に障害発生を図示して
いない共通線を用いて通知する。a□局はへ地方内の各
a。、al、a2.83間ルート、必要に応じa2  
a2’・・・・・・a1′−a1’  alまたは a
l  a1’  81′・・・・・・a3″−a3ノー
83などのルートを経由して、 a2 83間の回線を
救済する。
Assuming that the failure section occurs in the a2 and a3 relay station sections indicated by the X marks as in Fig. 3, the a2 and a3 relay stations at both ends
A, which is a local network management relay station. The station is notified of the occurrence of a failure using a common line (not shown). a □ station is each a in the region. , al, a2.83 route, a2 as necessary
a2'...a1'-a1' al or a
The line between a2 and 83 is rescued via a route such as l a1'81'...a3''-a3 no 83.

このため、86局はa2 83間にはどの中継局向けに
、例えばFDM方式の場合は、MG(マスターグループ
電話300 CI−1相当)単位の切替網構成で、何M
G必要か、またTDM方式の場合はどのようにタイムス
ロットが割当てられているか管理しており、△地方内容
中継局の図示していない切替スイッチ装置に指示し、あ
たかもa2−83間が正常であるかのように伝送ルート
の回線を再編成する。この場合、網を構成する中継区間
(回線網の枝)の回線容量は20〜30%増しとしてあ
くことにより可能とされる。ざらに回線効率をめげるた
めに、A地方、B地方の網管理中継W4ao 、 bo
を更に上位の図示していない網管理局によるグランドフ
ァザーコントロールも一部では導入されている。
Therefore, between A2 and 83, 86 stations have a switching network configuration in units of MG (master group telephone 300 CI-1 equivalent), and how many M
G is necessary, and in the case of the TDM system, how time slots are allocated. △ Instructs the changeover switch device (not shown) at the local content relay station to make it appear as if the area between a2 and 83 is normal. Reorganize the lines of the transmission route as if there were. In this case, the line capacity of the relay sections (branches of the line network) constituting the network can be increased by 20 to 30%. In order to roughly reduce the line efficiency, network management relays W4ao, bo of A region and B region
Grandfather control by a higher-level network management station (not shown) has also been introduced in some cases.

(発明が解決しようとする問題点) 上述した2つの切替方式において、前者の障害端切替方
式では暴風雨、洪水などの災害、停電事故を想定すると
予備回線のルート選定は単なる打線、無線の二重化程度
では対処ができず、現実的には現用回線と予備回線は地
理的に数十Kmiillすれたルート選定の必要が生じ
極めて多額の費用と長年月の網構築期間を要し、全国規
模の公衆通信網の切替方式としては、現実性の乏しい方
式で必る。
(Problems to be Solved by the Invention) In the above-mentioned two switching methods, in the former faulty end switching method, assuming disasters such as storms and floods, and power outage accidents, the route selection of the backup line is only a simple line or duplication of radio. In reality, it is necessary to select routes for the working line and the backup line that are geographically separated by several tens of kilometres, which requires an extremely large amount of money and many months of network construction time, and it is necessary to select a route for the working line and the backup line, which is geographically separated by several tens of kilometers. As a network switching method, this is necessary because it is a method with little practicality.

また、後者の回線端切替方式では、網管理中継局は膨大
なデータベースを必要とし、ざらにこれに加えて各中継
局切替装置を連動させるだめの複雑なソフトウェアが必
要であるなどの欠点を有する。
In addition, the latter line-end switching method requires a huge database for the network management relay station, and in addition, it requires complicated software to link each relay station switching device. .

また我が国における公衆通信w4(アナログ方式)はす
でに巨額な経費と長年月をかけ、本方式によるMG切替
網が既に構築されており、一方、通信網のデジタル化に
対処するためにデジタル切替網が部分的に構築されつつ
ある。このような事情からビジネス通信などの企業網に
これらの回線切替方式をそのまま利用することは、経済
的に不利であり、適応した切替方式の導入が望まれてい
た。
In addition, public communication W4 (analog system) in Japan has already been constructed with MG switching networks based on this system at a huge cost and many years.On the other hand, digital switching networks have been developed to cope with the digitalization of communication networks. It is being partially constructed. Under these circumstances, it is economically disadvantageous to use these line switching systems as they are in corporate networks such as business communications, and it has been desired to introduce an adapted switching system.

(問題点を解決するための手段) 本発明はこのような点に鑑み、衛星回線の特長であるす
べての地上局が、該衛星回線を共同で使用することがで
きること、及び任意の地上局間の地点間で通信回線を構
成することができる利点を活用し、本発明は障害端回線
切替方式の予備回線として該衛星回線を共用しようとす
るものである。
(Means for Solving the Problems) In view of these points, the present invention is characterized by the fact that all the ground stations can jointly use the satellite link, which is a feature of the satellite link, and that the satellite link can be shared between any ground stations. By taking advantage of the advantage of being able to construct a communication line between two points, the present invention attempts to share the satellite line as a backup line in a failed line switching system.

以下、実施例図面により本発明の詳細な説明する。Hereinafter, the present invention will be explained in detail with reference to the drawings.

(実施例) 第1図は本発明を説明するための伝送ルート図で、第3
図で図示した予備回線(点線)は、本発明方式において
は、衛星S経由で回線が構成されている点が相違し、特
長とするものである。ここで、点線は障害時に設定可能
な衛星回線の予備回線を、また、一点鎖線は、障害区間
の迂回用として使用中の衛星回線を示す。
(Example) Figure 1 is a transmission route diagram for explaining the present invention.
The protection line (dotted line) shown in the figure is different in that the line is configured via the satellite S in the system of the present invention, which is a feature. Here, the dotted line indicates a backup satellite line that can be set up in the event of a failure, and the dashed line indicates a satellite line that is being used as a detour for the failed section.

また、[a□’、 ao’、・・・・・・コ等の下位中
継局間及び該下位中継局と[aO〜a3・・・・・・コ
等との中継局間は、衛星回線による予備回線を共通に使
用することができる。
In addition, between the lower relay stations such as [a□', ao', ..., etc., and between the lower relay stations and the relay stations [aO to a3..., etc.], satellite lines are used. A protection line can be used in common.

例えば中継局区間a2 、a3で障害が発生(X印)し
たときは、a2 、a3中継局は障害を検知して、一点
鎖線で示す衛星予備回線に切替る。この障害の検知は、
通常ハードウェア的な処理により行なわれるが、当該処
理により検知不能な障害を検知するために、[a□−a
3・・・・・・]等の中継局内に障害監視機能を設け、
中継線をはさんで対向する相手中継局間で定期的に通信
を行う場合がおる。
For example, when a failure occurs (X mark) in relay station sections a2 and a3, relay stations a2 and a3 detect the failure and switch to the satellite protection line shown by the dashed line. Detection of this failure is
This is usually done by hardware processing, but in order to detect failures that cannot be detected by this processing, [a□-a
3...] etc., a fault monitoring function is installed in the relay station,
There are cases where communication is performed periodically between relay stations facing each other across a relay line.

本発明によるlti星回線への切替は、障害端の中i局
[a□ ”a3・・・・・・]等が独自に行う場合と、
図示せざる網管理局に対し共通線信号により衛星予備回
線の割当てを要求し、割当てられた衛星回線に切替える
場合とがある。
The switching to the lti star line according to the present invention is carried out independently by the central i station [a□ ``a3...] etc. at the faulty end;
In some cases, a network management station (not shown) is requested to allocate a satellite protection line using a common line signal, and the communication is switched to the assigned satellite line.

曲名の場合は、各中継局に網内で独立な識別信号を付与
して、障害区間の相手中継局との優先順位関係に基づき
予め割当てられた共通の衛星予備回線の適切なものを選
択し切替える。この切替え1       時に該衛星
予備回線が他の中継局間において使用されていないこと
を予め確認する必要がおるが、これは該予備回線を監視
することによって容易に確認できる。これは網管理局と
障害区間の中継局との間での通信が必要とされないため
、網管理局の障害時にも予備回線への切替えが可能であ
るため、網管理局を必要とせず、小規模網の障害端切替
方式として有用である。
In the case of song titles, each relay station is given an independent identification signal within the network, and an appropriate one is selected from the pre-assigned common satellite protection line based on the priority relationship with the partner relay station in the faulty section. Switch. At the time of this switching, it is necessary to confirm in advance that the satellite protection line is not being used between other relay stations, but this can be easily confirmed by monitoring the protection line. This eliminates the need for communication between the network management station and the relay station in the failed section, so it is possible to switch to a protection line even in the event of a failure at the network management station. It is useful as a failed end switching method for large-scale networks.

一方、後者の場合は、障害区間に割当てる回線容旧を網
管理局で集中的に制御できるため回線責源の効率的な分
配が可能であり、大規模網の障害端切替方式として有用
である。
On the other hand, in the latter case, the network management station can centrally control the line capacity allocated to the faulty section, which enables efficient distribution of line liability, and is useful as a faulty end switching method for large-scale networks. .

第2図は本発明障害端回線切替方式の一実施例にかかる
パケット伝遂中継局の機能構成例を示し、第一図で示す
a3中継局に設置した場合を示す。
FIG. 2 shows an example of the functional configuration of a packet transmission relay station according to an embodiment of the failed end line switching system of the present invention, and shows a case where the packet transmission relay station is installed in the A3 relay station shown in FIG.

図中100〜102は現用回線に接続するための地上回
線端局装首部、103は予備耐星回線に接続するための
衛星回線端極装置部、110〜112は現用中継回線群
、113は予備衛星回線群、200〜202はパケット
のルーティング及び中継区間へのバケツ1−の流聞を制
御するためのトランクアクセス機能部、203は予備衛
星回線に接続するトランクアクセス澹縫部、300はト
ランクアクセス機能間のインターフェイス部であり、通
常コンピュータのシステムバスとして実現されている。
In the figure, 100 to 102 are terrestrial line terminal equipment units for connecting to the working line, 103 is a satellite line terminal equipment unit for connecting to the backup star-resistant line, 110 to 112 are the working relay line group, and 113 is the backup line. Satellite line group, 200-202 is a trunk access function unit for controlling packet routing and dissemination of bucket 1 to the relay section, 203 is a trunk access sewing unit that connects to the backup satellite line, 300 is a trunk access function It is an interface between computers and is usually implemented as a computer system bus.

400は情報の転送径路を登録するためのルーティング
テーブル、401は各トランクアクセスは能部が読み出
すルーティング情報、402は網の障害状況に基づきル
ーティングテーブルの更新を行なうための更新情報、5
00は障害監視機能部であり、501に示すハードウェ
ア的な障害検出信号、または中継区間により対向してい
る中Ii!局内の障害監視機能部との通信により障害を
検知し、更新信号402によりルーティングテーブルの
更新を行うものでおる。
400 is a routing table for registering information transfer routes; 401 is routing information read out by Nobu for each trunk access; 402 is update information for updating the routing table based on network failure status; 5
00 is a failure monitoring function unit, which outputs a hardware failure detection signal shown in 501 or an intermediate Ii! A failure is detected through communication with a failure monitoring function section within the station, and the routing table is updated using an update signal 402.

次に本方式の動作について述べると、非障害時にはルー
ティングテーブル400には転送径路としてトランクア
クセス機能部200〜202が登録してあり、各トラン
クアクセスは縫部はトランクラインから受信したパケッ
ト内に含まれるルーテング情報とルーティングテーブル
の内容に基づいて宛先トランクアクセス機能部200〜
203を選択し、共通インターフイス部300を経由し
て該トランクアクセス機能部にパケットを送出する。非
障害時には予備衛星回線に接続する1〜クランククセス
機能部203にパケットルーティングされることはない
。障害監視機能部500は常時障害検出信号501を監
視し、並行して対向中継局内の障害監視機能との間で一
定聞隔で情報の送受を行っている。障害検出信号501
または、該対向中継局内の障害監視機能の一定時間無応
答により障害を検知し、ルーティングテーブル4. O
O内の障害区間トランクアクセスは能を予備衛星回線ト
ランクアクセス機能のに更新登録を行う。この更新は該
障害区間を経由して通信中の呼を全て切断して行う方法
と、呼を保持したままで行う方法がある。網内端末間プ
ロトコルにおいてこのような現用・予備回線切替に伴っ
て発生するパケットの紛失、重複順序誤り、及び無通信
時間に対しての対応策がとられていれば後者の方法が適
用できる。
Next, to describe the operation of this system, when there is no failure, the trunk access function sections 200 to 202 are registered as transfer routes in the routing table 400, and the stitching section of each trunk access is included in the packet received from the trunk line. Based on the routing information and the contents of the routing table, the destination trunk access function unit 200~
203 and sends the packet to the trunk access function section via the common interface section 300. When there is no failure, packets are not routed to the 1 to crank access function units 203 connected to the backup satellite line. The fault monitoring function unit 500 constantly monitors the fault detection signal 501, and in parallel, sends and receives information at regular intervals to and from the fault monitoring function in the opposing relay station. Failure detection signal 501
Alternatively, a failure is detected by the failure monitoring function in the opposite relay station not responding for a certain period of time, and the routing table 4. O
The failed section trunk access function within O is updated and registered to the backup satellite line trunk access function. There are two methods for performing this update: one method is to disconnect all calls in progress via the faulty section, and the other method is to perform this update while holding the calls. The latter method can be applied if measures are taken in the intra-network terminal-to-terminal protocol to deal with packet loss, duplication order errors, and non-communication time that occur due to switching between working and protection lines.

障害時においてもトランクアクレス機能部200〜20
3の動作は非障害時と差異はないが、ルーティングテー
ブル400の内容が障害区間のトランクアクセス機能部
の代りに予備衛星回線用トランクアクセス機能部に登録
変更されているため、障害区間へ向けてのパケットは予
備衛星回線用トランクアクセス機能へルーティングされ
る。障害監視機能は、障害中においても障害検出信号5
01の監視と、障害中継区間をはさんで対抗する中継局
内の障害監視機能への発呼を継続して行っており障害の
回復を検知すると、上述したのと同様の手順により非障
害時の状態のルーティングテーブルに復旧する。
Even in the event of a failure, the trunk access function section 200 to 20
The operation in step 3 is the same as when there is no failure, but the contents of the routing table 400 have been changed to the backup satellite line trunk access function section instead of the trunk access function section for the failed section. packets are routed to the backup satellite line trunk access function. The fault monitoring function detects the fault detection signal 5 even during a fault.
01 monitoring and calling to the fault monitoring function in the relay station that opposes the fault relay section, and when the fault recovery is detected, the same procedure as described above is used to restart the non-fault situation. restore the state's routing table.

(発明の効果) 本発明は、従来経済的でないとされていた障害端回線切
首方式において、予備回線として網を構成する多数の回
線区問(回線網の枝)に共通に設定した衛星回線を用い
ることにより、上記欠点を改善したものであり、経済的
にかつ短期間に障害端切替網が構築できる大ぎな効果が
jqられ、信頼度の高い企業網が容易に実現できる。な
お小規模企業網については、複数の企業網に共用の予備
y111回線を設定することににり更に経済化がばから
れる。
(Effects of the Invention) The present invention utilizes a satellite line that is commonly set up in a large number of line sections (branches of a line network) constituting a network as a protection line in the failed line disconnection method, which has been conventionally considered to be uneconomical. By using this method, the above-mentioned drawbacks are improved, and a great effect is achieved in that a failed end switching network can be constructed economically and in a short period of time, and a highly reliable corporate network can be easily realized. As for small business networks, further economicalization can be achieved by setting up shared backup Y111 lines for multiple business networks.

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

第1図は本発明に係わる衛星回線を利用する障害端回線
切替方式を説明するための伝送ルー1〜図、第2図は本
発明に係わる一実施例であるパケット伝送中継局におけ
る障害端切替機能構成引回、第3図は障害端切替方式を
説明するための伝送ルー1〜図、第4図は回線端切替方
式を説明するだめの伝送ルート図である。 a □ ” a 3・・・・・・A地方の中継局、ao
′、ao″・・・・・・。 a 11. a 1//、 、、、、、、、 a 31
. a 34/、、、、、、 a、 〜a3中継局の下
位中継局、bo〜b2・・・・・・B地方の中継局、 
bo’、 bo’、 、−−−−−b、’、 b1″、
 −・・・−b2’。 b2′・・・・・・b0〜b2中継局の下位中I!!局
、S・・・・・・通信衛星、100〜102・・・・・
・地上回線端局装置部、103・・・・・・衛星回線端
局装置部、110〜112・・・・・・現用中継回線群
、113・・・・・・予備衛星回線群、200〜203
・・・・・・トランクアクセスは縫部、=100・・・
・・・ルーティングテーブル、500・・・・・・障害
監視機能部。
Fig. 1 is a transmission route 1 to diagram for explaining a failed end line switching method using a satellite line according to the present invention, and Fig. 2 is a diagram showing failed end switching at a packet transmission relay station which is an embodiment of the present invention. FIG. 3 is a diagram showing transmission routes 1 to 1 for explaining the failed end switching method, and FIG. 4 is a transmission route diagram for explaining the line end switching method. a □ ” a 3...A relay station, ao
', ao''... a 11. a 1//, ,,,,,,, a 31
.. a34/,,,,,,,,,,,,,,,,,,,,,,,,,,, lower relay station of ~a3 relay station, bo~b2......B local relay station,
bo', bo', ,----b,', b1'',
-...-b2'. b2'...lower middle I of b0 to b2 relay stations! ! Station, S...Communication satellite, 100-102...
・Terrestrial line terminal equipment unit, 103... Satellite line terminal equipment unit, 110-112... Working relay line group, 113... Reserve satellite line group, 200- 203
...Trunk access is at the sewing part, =100...
. . . Routing table, 500 . . . Fault monitoring function unit.

Claims (1)

【特許請求の範囲】[Claims] 通信網を形成する複数の回線区問において、該区間の障
害発生に際し障害区間の両端の中継局は、予め回線網を
構成する区間の障害救済用として共通に設定した衛星回
線に情報を迂回させることを特徴とする障害端回線切替
方式。
When a fault occurs in multiple line sections that form a communication network, relay stations at both ends of the faulty section divert information to a satellite line that has been set up in advance for fault relief in the sections that make up the line network. A fault line switching method is characterized by the following.
JP8064286A 1986-04-07 1986-04-07 Switching system for faulty end line Pending JPS62236222A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP8064286A JPS62236222A (en) 1986-04-07 1986-04-07 Switching system for faulty end line

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP8064286A JPS62236222A (en) 1986-04-07 1986-04-07 Switching system for faulty end line

Publications (1)

Publication Number Publication Date
JPS62236222A true JPS62236222A (en) 1987-10-16

Family

ID=13724017

Family Applications (1)

Application Number Title Priority Date Filing Date
JP8064286A Pending JPS62236222A (en) 1986-04-07 1986-04-07 Switching system for faulty end line

Country Status (1)

Country Link
JP (1) JPS62236222A (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000261361A (en) * 1999-03-08 2000-09-22 Fujitsu Denso Ltd Radio relay system and radio relaying method
JP2004064314A (en) * 2002-07-26 2004-02-26 Nec Mobiling Ltd Outdoor public address device, emergency administration radio system, and its outdoor public address method

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000261361A (en) * 1999-03-08 2000-09-22 Fujitsu Denso Ltd Radio relay system and radio relaying method
JP2004064314A (en) * 2002-07-26 2004-02-26 Nec Mobiling Ltd Outdoor public address device, emergency administration radio system, and its outdoor public address method

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