WO1997036394A1

WO1997036394A1 - Process for switching from an interrupted working data circuit to a reserve data circuit for annular data networks

Info

Publication number: WO1997036394A1
Application number: PCT/DE1997/000602
Authority: WO
Inventors: Alfons Mittermaier; Nizar Zalila
Original assignee: Siemens Aktiengesellschaft
Priority date: 1996-03-25
Filing date: 1997-03-25
Publication date: 1997-10-02
Also published as: EP0890237A1; AU2691297A

Abstract

When a working data circuit (WCE2) is interrupted or disturbed, an optimised automatic protection switching system is used to switch to a protection data circuit (PCE1, .... PCE3; PCW2, ..., PCW4).

Description

description

Method for switching from a disturbed work data connection to a reserve data connection in the case of ring-shaped data networks

In order to increase the security of the long-distance data connections, in addition to the working data lines used for the regular handling of the data traffic, replacement data lines are also provided, via which the data transmission takes place in the event of disturbed or interrupted working data lines (or other transmission media) . Since both work and reserve lines belong to a cable or the transmission takes place in a single optical fiber, it can be assumed that a mechanical interruption between two neighboring terminals often includes all lines, a connection between them Stations are consequently only possible via the reserve lines on the “long path” of the ring-shaped data network.

The switchover takes place automatically in order to establish a new connection as soon as possible without major data loss. The reserve data line, which uses the "long way", is usually looped through further terminals to the neighboring station.

An equivalent circuit is particularly important for the transmission of high data rates, as is the case, for example, when transmitting STM-4 signals of the synchronous digital hierarchy, as defined in the CCITT recommendations. There are 2-fiber data networks with a ring structure. The transmission capacity of each optical fiber is divided into working channels and protection channels, over which a replacement data connection is established. In the synchronous digital hierarchy, useful data and additional information are transmitted in standardized data blocks. The additional information is inserted into an overhead according to CCITT G.708, General Aspects of Digital Transmission Systems, Geneve 1991, Figure 5-4.

A so-called APS protocol (Automatic Protection Switching) ensures that the spare switching devices of all terminals (nodes) of the ring are correctly synchronized taking into account multiple requests of different priorities, incorrect connections having to be avoided, and a connection via the reserve lines as quickly as possible should be produced and protocol errors must be recognized and correctable. The APS protocol provides two bytes for this, the bytes K1 and K2. In the case of systems that are not bound by standards, the necessary protocols can be designed as desired.

The terminals (network elements) of the ring are assigned three different states:

l. A terminal is in idle state if there is no equivalent switching request,

2. A terminal is in the switching state when there is an equivalent switching request for an adjacent connection and

3. A terminal is in pass-through state when there is an equivalent switching request for a more distant connection.

Depending on the respective state, the terminal responds to new requests by controlling its switching elements and sending APS protocols in the form of special information in special bytes, the K bytes, of the overhead. A known method according to ITU-T G.841 starts from scenarios that affect the entire ring. The individual states and state transitions of the network terminals of the entire ring determine the APS protocols.

The numerous state transitions require considerable effort and are difficult to test. Since the further behavior of the terminals depends on the existing state, every possibility must be checked in order to ensure perfect functioning.

The interruption of user data traffic is not minimized in all equivalent switching variants. If there is no protocol monitoring, a single protocol error can permanently block the ring. In addition, the startup behavior is not fully defined. Further details of the known method and the problems associated therewith will not be discussed further here.

The object of the invention is to provide a method for switching between a working data connection and a replacement data connection, which avoids the disadvantages indicated above and minimizes the switching time.

This object is achieved by the method specified in the independent claims.

In the method according to the invention, the complex information about the scenarios of the entire ring is dispensed with. The criteria transmitted between the terminals by APS protocols cause a rapid switchover to an alternative connection.

Further advantageous method steps are specified in the dependent claims. The invention is explained in more detail with reference to figures.

FIG. 1 shows a ring-shaped data network using 4-fiber technology and

FIG. 2 shows a 2-fiber data network planned for the synchronous digital hierarchy.

FIG. 1 shows a ring-shaped data network with four terminals TER1 to TER4. Each terminal TER1 is connected to its two neighboring terminals TER2, TER4 via a working data line WLW (working line west), WLE (working line east) and a replacement data line PLW (protection line west), PLE (working line east).

The network is constructed as a 4-fiber network; A useful signal or a substitute signal can be transmitted in one direction in each optical waveguide (or other data channel).

If the case occurs that the connection of the working data line WLW between the neighboring terminals TER1 and TER2 - the short path SW - is disturbed, the disturbed data exchange must now be made via a replacement data connection - here a replacement data line - be handled. As already mentioned in the introduction, it can be assumed that both the working data line and the replacement data line are frequently carried in one cable, so that, as a rule, a replacement connection can only be made over the long path LW using the replacement data line PLE can be created via the terminals TER4 and TER3. After the equivalent circuit has been carried out, the terminal TER1 consequently sends the useful information (DATA1) via the substitute data line PLE,..., PL2 and also receives via this connection (dashed lines with arrows) the data sent by the terminal TER2 and through the intermediate ones User information looped through terminals (DATA2). _O ther systems operate with spare circuits via the short route.

FIG. 2 shows a ring-shaped 2-fiber data network that is to be used in the synchronous digital hierarchy. The transmission of the useful information ÖATA1 and DATA2 in both directions between the first terminal TER1 and the neighboring terminal TER2 takes place in the case of trouble-free operation in working channels WCW1, WCE2 (working channels west / east) of two optical waveguides represented by double lines. In addition, the same transmission capacity _ symbolized by the double lines in replacement channels PCW1, PCW2, ...., PCW4, PCE1, PCE2,, ...., PCE3 (protection channels west / east) is provided in all optical fibers for equivalent circuit purposes. In this case, the working and replacement channels assigned to a direction of transmission are inserted into data blocks with a common overhead.

In the event of a malfunction - an interruption of the connection WCE2, PCE2 between the terminals TER1 and TER2 is again assumed - the replacement data connection takes place over the long path in the replacement channels PCE1,..., PCE4 in order to provide the information for the neighboring terminal TER2 to transmit certain useful information DATA1, and also to receive the useful information DATA2 from the neighboring terminal TER2 over the long path and the spare channels PCW2, ..., PCW4.

If an interruption of both fibers of the

Section (span) between terminal TER1 and terminal TER2 would take the initiative for an equivalent circuit from any terminal that receives no data. However, to explain the mode of operation, it is sufficient to only break the working data line WLW in FIG. 1 or a single optical waveguide with the working channels WCE2 and Consider replacement channels PCE2 (fiber break) in FIG. 2 or a corresponding fault.

The equivalent circuit procedure is used for both data networks:

1. The first terminal TER1 notices that there is a fault or interruption to the neighboring terminal TER2.

1.1 It checks whether there are no request priorities that prevent an replacement circuit and switches the replacement data lines PLE on the transmission side (it is also possible to switch from WLW to PLW over the short distance if these fibers are not affected by the fault; FIG. 1) or (FIG. 2) the substitute channels PCE1 (bridges - brigdes), while the user data continue to be transmitted over the short path via the user channels WCW1 (and the substitute channels are available for other purposes). Both the short path SW (WLW or WCWl) and the long path LW (PLE or PCEl), the user data DATA1 and a protocol with a request for the equivalent circuit are sent to terminal TER2.

2. The neighboring terminal TER2 initially receives the protocol over the short path SW and switches on the transmission side to the substitute line PL2 (FIG. 1) or the substitute channels PCW2 (FIG. 2) of the long path (bridges) and now transmits over the long path Path LW the user data DATA2 previously transmitted over the short path and a protocol with the confirmation that the transmitter side has been switched (bridged).

2.l If the protocol sent by Terminal TER1 is received by Terminal TER2 over the long path LW, Terminal TER2 also switches to receiving user data over the long path (selected). 2.2 The neighboring terminal TER2 sends a protocol that both the transmission and reception have been switched to the replacement data connection (bridged and selected).

3. The first terminal TER1 receives via a long path LW protocol from terminal TER2 that a switch has been made to the replacement data connection and switches over to reception of the user data DATA2 via the long path LW (selected).

3.1. Terminal 1 sends a protocol stating that it has switched (selected) to receive data over the replacement connection (and of course has also bridged).

Updated protocols are also transmitted in the state of the equivalent circuit. The terminals TER3 and TER4, which are switched on for the long way, loop through the data on the replacement line.

The procedure can be simplified even further by the terminal determining an interruption, in this example the terminal TER1, only sending a corresponding request for an emergency switch over the long path.

This procedure is necessary for 1-fiber networks that use wavelength division multiplexing.

With the known protocol previously provided, more protocol changes were required. The main differences lie in the fact that in the known method the first terminal TER1 must first be bridged and selected, a corresponding protocol must be sent to the neighboring terminal TER2 and evaluated by the latter before the latter is selected.

As already stated, the protocol is transmitted in the K bytes.

The request type (request type) is transmitted in bits 1 to 4 of the Kl byte: No request, east request, west request and remote request (no request, east request, west request and diet request) and the connection concerned, in the examples given WLW or WCE2, in bits 5 to 8.

The priorities of the requests transmitted in the K bytes (remote request) are compared with the priority of the local request (s) (local request), which the terminal itself determines by detecting a fault. If there are no higher priorities, the equivalent circuit is implemented immediately if a fault / interruption is detected.

The following criteria are to be observed for an equivalent circuit:. a) The end-related switchover (bridges) to the replacement data line or the replacement channels may only take place if a corresponding protocol has been received and no terminal receives or expects information about the replacement data connection (with higher priority). The corresponding information is transmitted in byte K2, bits 3 and 4. b) There is a selection request if the terminal contains a protocol with a request on the long route, c) it can then be switched over to receiving the data on the replacement connection (selected) if the expected traffic is already on the replacement data line (protection channel) is bridged. The corresponding information is transmitted in bits 1 and 2 of byte K2 (bridged traffic). It can be bridged: no traffic (00), "extra traffic" (01), "working traffic ^w , due to an earlier equivalent circuit (10); traffic that matches the equivalent circuit request (11).

There are the following generation rules for the protocol:

l. Generation rules for Kl *. Abut ₁ .1 If local (by the terminal itself detected) _A REQUIREMENTS highest priority of the adjacent terminals at both interfaces of a terminal, the request of the west side to the west and the requirement of the east side to the east is passed.

1.2 If there is a local request at an interface, it is passed on to the west and east.

1.3 Remote requests of the highest priority for two different connections (spanε) are looped through from east to west or from west to east.

1.3 A remote request of the highest priority for only one connection (span), if it is an adjacent connection, becomes in this direction as a local request detected for this connection and in the other direction as a highly prioritized request passed on.

1.4 If there is no adjacent connection (span), the requirements are passed on from one interface to the other (looped through).

The priority is transmitted in bits 1 to 4, information about the connection concerned (section and channel) is transmitted in bits 5 to 8.

2. Generation rules for K2:

2.1 The traffic that is bridged or selected is always specified in the protocol. A network element that only loops through information only indicates the direction east to west or vice versa.

If no equivalent circuit has been implemented, the replacement data lines are available for data exchange with low priority. It should also be added that the 5th bit of the K2 byte can be used to identify the connection sections so that data rings with 32 terminals can be implemented.

In principle, it is also possible to transmit separate data blocks in time-division multiplex operation, which contain the user channels or the replacement channels, in each case in an optical waveguide. When using the wavelength division multiplexing method, the working channels and the replacement channels of a transmission direction can also be combined.

The method according to the invention can be applied to all ring-shaped data networks.

Claims

Claims. Method for switching from a faulty working data connection (WLW, * WCE2) to a reserve data connection line (PLE, * PCEl, PCW4) in a ring-shaped data network containing several terminals (TER1 to TER4), characterized by the following equivalent switching procedure in an interruption between a first terminal (TER1) and an adjacent terminal (TER2):

1.1 The first terminal (TER1) determines that there is an interruption to the neighboring terminal (TER2).

1.2 If there are no other priorities that prevent an equivalent circuit, the terminal (TERl) sends (bridges) the substitute data connection (PLE; PCEl) on the transmitter side and sends both via the short path (SW: PLW; WCW1) , PCW1) also over the long path (LW: PLE, ..., PL2; PCE1, PCE3) user data and a protocol with a request for an equivalent circuit to the neighboring terminal (TER2),

1.3 The neighboring terminal (TER2) receives the protocol with the request via the short path (SW: WLW or PLW; WCWl) and switches to the replacement connection on the transmission side

(PL2, ..., PLE; PCW2,, PCW4) of the long path (LW)

(bridges) and sends the useful data (DATA2) and a protocol with the confirmation that the switchover (PL2, ..., PLE; PCW2, ..., PCW4) of the long path (LW) and a protocol bridged)

1.4 The neighboring terminal (TER2) receives the protocol sent by the first terminal (TERl) over the long path (LW) and thereby switches to receiving the long one via the replacement data connection (PLE, ..., PL2 or PCEl) User data (DATA1) transmitted via (selected) or switches if there was no request via the short path (KW) was received, on the transmission side to the replacement data connection (PL2 or PCW2) and the reception of user data (DATA1) over the long path (LW) (selected,

1.5 The neighboring terminal (TER2) sends a protocol that has been switched (bridged and selected) to the replacement data connection (PLE, ..., PL2, -. PCW2, PCE3) both on the sending and receiving side.

1.6. The first terminal (TER1) checks the protocol received from the neighboring terminal (TER2) over the long path (LW) and switches (εelected) to receive user data (DATA2) over the long path (LW).

2. Method for switching from a faulty working data line (WLW; WCE2) to a reserve data connection (PLE; PCE1, PCW4) in the case of ring-shaped data networks containing several terminals (TER1 to TER4), characterized by the following replacement circuit procedure in the event of an interruption between a first terminal (TERl) and an adjacent terminal (TER2):

2.1 The first terminal (TER1) determines that there is an interruption to the neighboring terminal (TER2).

2.2 If there are no other priorities that prevent an equivalent circuit, the first terminal (TERl) switches to the substitute data connection (PLE; PCEl) (bridged) and sends over a long path (LW; PLE, ... ., PL2;

PCE1, ..., PCE3) are user data (DATA1) and a protocol with a request for an equivalent circuit to the neighboring terminal (TER2),

2.3 The neighboring terminal (TER2) receives the protocol with the request over the long path (LW) and switches in terms of transmission and reception to the replacement data connection (PL2; PCEl) (bridges - bridges and selected).

2. ₄ The neighboring terminal (TER2) εendet a protocol that εowohl εende- as well as receiving primarily on the Replacement Datenver¬ _b indung switched (bridged and selects) was.

2.5 The first terminal (TER1) receives the protocol over the long path (LW) from the neighboring terminal (TER2) and switches over to receiving user data (DATA2) over the long path (LW) (selected).

3. The method according to claim l or 2, characterized in that the first terminal (TERl) after switching over to reception over the long path emits a protocol over the long path (LW) that eε εende and received on the replacement data connection (PLE , - PCEl, PCW4) has switched (bridged and selected).

4. The method as claimed in one of the preceding claims, namely that switching to receiving data via the substitute data connection is only carried out (selected) when the expected useful data (DATA1, DATA2) has already been transferred to the substitute data.

Data connection (PL2, PLE; PCW2, PCEl) are bridged.

5. The method according to any one of the preceding claims, characterized in that when local requirements of the highest priority of the neighboring terminals (TER2, TER4) are present at both interfaces of a terminal, the requirement of the west side is passed to the west and the requirement of the east side is passed to the east becomes.

6. The method according to any one of the preceding claims, characterized in that due to a received request of highest priority for only one connection, if it is an adjacent connection, in its direction as a local request detected for this connection and in the other direction as one highest priority requirement is passed on.