WO2004109979A1

WO2004109979A1 - A method for carrying out service-transmitting in a synchronous digital hierarchy network

Info

Publication number: WO2004109979A1
Application number: PCT/CN2004/000525
Authority: WO
Inventors: Jingling Liao; Yue Liu
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2003-06-09
Filing date: 2004-05-24
Publication date: 2004-12-16
Also published as: WO2004109979A8; CN1567867A; CN100490404C

Abstract

The invention discloses a method for carrying out service transmitting in a synchronous digital hierarchy (SDH) network. First, it determines the number of the demanded virtual containers (VC) according to the current service to be transmitted. Secondly, the VCs are mapped a virtual concatenation VC frame by adopting virtual concatenation mapping method, and the VC frame is transmitted to the receiver unit by the same route. The receiver unit unmaps the received VC frame by the adjacent concatenation unmapping method. The method can avoid the question about bandwidth wasting in the SDH networks transmitting service, and the higher demand to each net ware in the SDH transmitting network, and the long time delay under the virtual concatenation. And the method also makes the SDH network has the strongpoint of the adjacent concatenation and the virtual concatenation in the transmitting service.

Description

Method for realizing service transmission in synchronous digital transmission network

Technical field

The present invention relates to service transmission technology, and more particularly, to a method for implementing synchronous digital

(SDH) A method for service transmission in a transmission network. Background of the invention

In the SDH transmission network, adjacent concatenation can be used to transmit services, or virtual concatenation can be used to transmit services.

Adjacent concatenation in SDH optical transmission technology refers to: when a container (C) -n cannot meet the requirements of transmission services, concatenate adjacent Cn in the same synchronous transmission module (STM) -N into a whole The Cn-XC structure transmits services. Taking C-4 as an example, the European Telecommunications Standards Institute (ETSI) standard currently defines VC-4-4C and VC-4-16C for 4 and 16 virtual containers (VC) -4 concatenated adjacently, respectively. cascade. When STM-N is mapped to VC-4-XC in cascade, the structure of VC-4-XC is shown in Figure 1. There is only one channel overhead (POH) in this VC-4-XC, and not every frame Can have its own separate pointer, only one pointer in the first frame is used as the pointer of all consecutive frames in the payload of the adjacent cascade, and the remaining pointers are set as cascade indicators, so the VC after cascade -4-XC can only be locked together for transmission.

According to the above description of adjacent cascades, it is learned that during adjacent cascades, the network needs to save a group of frames of adjacent cascades for transmission together. This transmission method prevents services from transmitting between frames. The problem of mutual delay, so in the case of cascading, you can directly demap VC-4-XC, and generally do not need to set a cache. However, it is necessary for the network to maintain continuous bandwidth during the entire process of transmitting the group of frames, that is, all network elements that the group passes must support this continuous bandwidth transmission method. In fact, most current devices cannot reach This requirement. and, When cascading, only a specified number of Cn can be cascaded together, but not cascading arbitrarily. This cascading method will result in the fact that when only one Cn is needed to realize the transmission service, multiple must be added. Taking C-4 as an example, the cascaded mode needs to use VC-4-4C's bandwidth to transmit services at least, so the waste of bandwidth is bound to be great. According to the cascade method, a virtual large-structure VC-n-XV is formed for transmission. Unlike the cascade, each VC-n in the VC-n-XV can be transmitted in the same route, or it can be Transmission in different routes is mainly due to the virtual concatenated mapping mode, so that each VC-n in VC-n-XV has its own independent POH and pointer. Taking VC-4-XV as an example, the structure of VC-4-XV obtained during virtual concatenation mapping is shown in Figure 2. Each VC-4 in VC-4-XV has its own POH. Therefore, when an SDH network adopting the virtual concatenation technology transmits services, it can first transmit the continuous bandwidth of VC-n-XV through each of these VC-n independently in different routes, and then transfer these VC- n is merged together to obtain continuous bandwidth, that is, these VC-n virtual cascades into VC-n-XV at the end of the transmission, so from the implementation point of view, the virtual cascade only requires the terminal device to have the function of virtual cascade.

The use of virtual concatenation can compensate for the delay, can correct the out-of-order, and can also increase or decrease the member channels of the virtual concatenation group losslessly through the Link Capability Adjustment Plan (LCAS) technology to meet the needs of bandwidth changes. However, the virtual concatenation technology also has some disadvantages. Specifically, because each VC-n transmission route may be different, the pointers of each VC-n may be different, so the pointer needs to be adjusted, in order to avoid When the pointer is adjusted incorrectly, the terminal device generally buffers at least one frame. In this way, even if there is no delay between the two VC-n, the demapping of the virtual concatenation processing will have a frame length, that is, a processing delay of 125us, and For services that require low-latency transmission, such a large delay will cause a sharp reduction in bandwidth. Taking the enterprise system connection (ESCON) service as an example, the ESCON service requires one transmission and one transmission to establish a link. The receiving end first receives the link establishment frame sent by the sending end, and then the receiving end sends the sending end to the sending end. Send a response frame to establish the link. In the process of establishing a link, the receiving end will have a delay of 125us when receiving a link establishment frame, and there will be a delay of 125us when sending a response frame to the transmitting end, that is, there will be two 125us when the link is established. Frame delay. If the transmission speed of the service in the optical fiber is 2 x 10E5Km / s, the transmission time is 25Km at 125 μs, that is, the unidirectional transmission distance is 25Km. According to the relationship between ESCON service transmission distance and bandwidth in Figure 3, ESCON is at 25Km The service bandwidth is about 9MB / sec, which is only half of the normal bandwidth.

In summary, when using the adjacent concatenation method to transmit services in an SDH transmission network, the network needs to maintain continuous bandwidth during the entire service transmission process. The bandwidth requirements of network elements are relatively high, and this cascade method cannot be based on The actual service needs to determine the cascading situation, and can only be cascaded to the set VC-n-XC, so it will often cause a relatively large waste of bandwidth; and when using the virtual cascading method to transfer services, in order to avoid pointer jitter, The impact of service transmission requires a long time delay, and this delay will cause the bandwidth of some specific services to decrease sharply during the transmission process. Summary of the Invention

In view of this, the main object of the present invention is to provide a method for implementing service transmission in an SDH transmission network, so that the service transmission of the SDH transmission network has the advantages of transmission in the case of adjacent concatenation and virtual concatenation at the same time. The business situation arbitrarily determines the number of virtual containers for transmitting the service, and the problem of delay does not occur to avoid affecting the network bandwidth.

To achieve the above objective, the technical solution of the present invention is implemented as follows: A method for implementing synchronous service transmission in a digital transmission network, the method includes the following steps:

a. Determine the number of virtual container VCs required to transmit the service according to the service to be transmitted;

b. Perform mapping processing on all the VCs determined in step a through a virtual concatenated mapping method to obtain a virtual concatenated VC structure, and pass the obtained VC nodes through the same route. Output to receiver equipment;

c. The receiving end device uses the adjacent cascade demapping method to demapping the received VC structure.

In step b, the mapping processing for all VCs in a virtual concatenated mapping mode is: setting an independent channel overhead POH for each VC.

The step c further includes: setting a cache for adjusting the VC pointer in the obtained VC structure, and adjusting each VC pointer in the obtained VC structure through the cache.

In step c, each VC pointer in the VC structure is adjusted by using a virtual cascading pointer adjustment method.

The buffer set in step c is greater than or equal to 6 bytes.

The buffer is set to a size smaller than one frame.

The buffer is set to the size of one line in one frame.

The VC is VC-3, VC-4 or VC-12.

The present invention adopts a mapping and demapping scheme combining a combination of adjacent cascades and virtual cascades, that is, mapping m VCs required by the current service to virtual cascaded VC structures in a virtual cascade manner, and using the same route For transmission, the receiver device uses adjacent concatenation to demap the received VC structure, so that the service transmission of the SDH transmission network can have the advantages of using adjacent concatenation and virtual concatenation to transmit services at the same time. In other words, when transmitting services in an SDH transmission network, there will be no waste of bandwidth in the case of adjacent concatenation, high bandwidth requirements of each network element in the SDH transmission network, and no virtual concatenation. A long delay causes a sharp decrease in bandwidth. Brief description of the drawings

FIG. 1 is a structural diagram of VC-4-XC obtained during mapping in the case of cascading in the prior art; FIG. 2 is a structural diagram of VC-4-XV obtained during mapping in case of cascading in the prior art; Figure 3 is the relationship between ESCOM service transmission distance and bandwidth;

Fig. 4 is a flowchart for realizing the scheme of the present invention. Mode of Carrying Out the Invention

The scheme of the present invention will be described in further detail below with reference to the drawings and specific embodiments. Referring to FIG. 4, the solution of the present invention processes the sending end and the receiving end of a transmission service, which is specifically implemented through the following steps:

Step 401: Determine the required number of VCs according to the needs of the service.

The required number is the ratio of the service rate to the transmission rate. For example, the ESCON service rate is 200Mbit / s. For services without flow control and cannot compress bandwidth, the VC-4 rate is 155Mbit / s, so two VC-4 (2 x 155) must be used.

Step 402: The identified VCs are mapped at the sending end in the same mapping manner as the virtual concatenation, so that each VC has its own independent POH overhead, and these VC channels are bundled together to form a virtual-like channel. These VCs are transmitted to the receiving end device through the same route.

Different from virtual concatenation, this type of virtual channel takes the same route when transmitting in the network. Step 403: The receiving end device performs demapping by using a demapping manner of adjacent concatenation. This solution is applicable to VC-3, VC-4, and VC-12. The following uses VC4 as an example.

If a certain service requires three VC-4s for transmission, the three VC-4s are first mapped using the virtual cascade mapping method to form a virtual large structure VC-4-3V. The difference from the virtual cascade is In this embodiment, the VC-4-3Vs are bundled together and transmitted through the same route to ensure that the transmission paths of the services are consistent. In this way, it can not only have the advantage that there is almost no delay in the arrival of a service when the adjacent technology is concatenated in the prior art, but also have the advantage that the existing technology can determine the VC-4 to be used according to the service when virtual concatenation.

The same route transmission method can be used to make each VC-4 corresponding to the service reach the receiver. The time of the end device remains the same. Therefore, the management unit (AU) pointer of each VC-4 is also the same, that is, the same as the case of reaching the terminal in the case of cascading. Therefore, the demapping method in the case of adjacent cascading can be used, There is no need to cache like virtual concatenation.

However, there are some differences from the adjacent cascade when demapping. In the case of cascading, since the adjacent cascaded VC-4-XC has only one separate pointer, when adjusting the pointer, only this one pointer needs to be adjusted, and for this one pointer, it will not A difference in the pointer adjustment value appears. The pointer adjustment is caused by the difference between the data recovery clock and the system clock. Adjustment is to increase or decrease the pointer by one. Each unit adjustment indicates that the payload is partially filled or reduced by 3 bytes.

However, in the solution of the present invention, each VC-4 after virtual concatenation has its own independent pointer. Therefore, the pointer in each VC-4 needs to be adjusted. After testing, it was found that although the transmission of each VC-4 by the same route makes the adjustment of the pointers of each VC-4 not macroscopically the problem of inconsistent pointers in each VC-4, but microscopically there may still be various VCs. The adjustment difference between the pointers in -4 is different from each other. Because the pointer is adjusted once, the payload is filled or reduced by three bytes, so the biggest difference between the two VC-4s is 6 bytes. For the possible difference between pointers, you can borrow the method of virtual concatenation, that is, use the cache to resolve the difference in pointer adjustment. Because the maximum possible difference in the solution of the present invention is only 6 bytes, and the buffer of one frame during virtual concatenation corresponds to 9 * 270 bytes, so the buffer of one frame during virtual concatenation is not needed at all, and can be greater than or equal to The 6-byte buffer can realize pointer adjustment. In actual operation, for convenience, a line size in a frame, that is, a 270-byte buffer can be used, so that when the adjustment between the VC-4s in the solution of the present invention is implemented, the virtual concatenation can be borrowed. Caching approach.

'The above description is only a preferred embodiment for implementing the solution of the present invention, and is not used to limit the protection scope of the present invention.

Claims

Claim

1. A method for implementing service transmission in a synchronous digital transmission network, characterized in that the method includes the following steps:

b. Perform mapping processing on all the VCs determined in step a through a virtual concatenation mapping method to obtain a virtual concatenated VC structure, and transmit the obtained VC structure to the receiving end device through the same route;

c The receiving end device uses the adjacent cascading demapping method to demapping the received VC structure. ·

2. The method according to claim 1, characterized in that in step b, the mapping processing for all VCs by means of virtual concatenation mapping is: setting an independent channel overhead POH for each VC.

3. The method according to claim 1, wherein the step c further comprises: setting a cache for adjusting a VC pointer in the obtained VC structure, and performing each VC pointer in the obtained VC structure through the cache. Adjustment.

4. The method according to claim 3, wherein in step c, each VC pointer in the VC structure is adjusted by using a virtual concatenated pointer adjustment method.

5. The method according to claim 3, wherein the buffer set in step c is greater than or equal to 6 bytes.

6. The method according to claim 5, wherein the buffer is set to a size smaller than one frame.

7. The method according to claim 6, wherein the buffer is set to a size of one line in one frame.

8. The method according to claim 1, wherein the VC is VC-3, VC-4, or VC-12.