CN1567867A - A method for implementing service transmission in synchronous digital transmission network - Google Patents

Abstract

The invention discloses a method for realizing service transmission in a synchronous digital (SDH) transmission network. The method firstly determines the number of virtual containers (VCs) required to transmit the service according to the current service to be transmitted, and then uses these VCs to The virtual concatenation mapping method is mapped to a virtual concatenation VC structure, and the VC structure is transmitted to the receiving end device through the same route, and the receiving end device performs the demapping method on the received VC structure through the adjacent concatenation Unmapping processing. This method solves the problems of wasting bandwidth in the case of cascading when transmitting services in the SDH transport network, and has high requirements on the bandwidth of each network element in the SDH transport network, and the problem of long time delay in the case of virtual cascading. The SDH transport network can simultaneously have the advantages of using adjacent cascades and virtual concatenations to transmit services when transmitting services.

Description

A Method for Realizing Service Transmission in Synchronous Digital Transmission Network

technical field

The present invention relates to service transmission technology, more specifically to a method for realizing service transmission in a synchronous digital (SDH) transmission network.

Background technique

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

Adjacent cascading in SDH optical transmission technology refers to: when a container (C)-n cannot meet the requirements of transmission services, cascading adjacent C-n in the same Synchronous Transport Module (STM)-N into a whole The C-n-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 adjacent cascaded virtual containers (VC)-4 respectively. cascade. When mapping STM-N to VC-4-XC in cascading, see Figure 1 for the structure of VC-4-XC. There is only one path overhead (POH) in this VC-4-XC, and not every frame Can have its own separate pointers, only one pointer in the first frame is used as the pointer of all consecutive frames in the adjacent concatenated payload, and the rest of the pointers are set as cascading instructions, so the concatenated VC -4-XC can only be locked together to teleport.

From the above description of adjacent cascading, it is known that during adjacent cascading, the network needs to store a group of adjacent cascading frames together for transmission. The problem of mutual delay, so in the case of cascading, the VC-4-XC can be directly demapped, and generally there is no need to set a cache. However, the network needs to maintain continuous bandwidth during the entire process of transmitting the frame, that is, all network elements that the frame passes through must support this continuous bandwidth transmission method. In fact, most of the current equipment cannot achieve this. Require. Moreover, when cascading, only a specified number of C-n can be cascaded together, but not arbitrarily cascaded. This cascading method will lead to the fact that only one C-n needs to be added to realize the transmission service, but it must be increased. One, taking C-4 as an example, the bandwidth of VC-4-4C needs to be used to transmit services at least in the cascade mode, which inevitably wastes a lot of bandwidth.

The virtual concatenation technology in the SDH optical transmission technology is to form a virtual large structure VC-n-XV for transmission by cascading the VC-n distributed in different STM-Ns. Each VC-n in VC-n-XV can be transmitted in the same route or in different routes. This is mainly because the mapping method of virtual concatenation makes each VC-n-XV VC-n 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, and each VC-4 in VC-4-XV has its own POH. Therefore, when the SDH network using virtual concatenation technology transmits services, it can first transmit the continuous bandwidth of VC-n-XV through each VC-n in different routes independently, and then transfer these VC-n at the end of the transmission. n are combined to obtain continuous bandwidth, that is, virtual concatenation of these VC-n into VC-n-XV at the end of the transmission, so from the perspective of implementation, virtual concatenation only requires the terminal equipment to have the function of virtual concatenation.

The use of virtual concatenation can compensate for delay, correct out-of-sequence, and increase or decrease member channels of the virtual concatenation group losslessly through Link Capability Adjustment Scheme (LCAS) technology to meet the needs of bandwidth changes. However, the virtual concatenation technology also has some disadvantages. Specifically, because the routes passed by each VC-n transmission may be different, the pointers between each VC-n may be different, so the pointers need to be adjusted to avoid If there is an error in pointer adjustment, the terminal equipment will usually buffer at least one frame. In this way, even if there is no delay between the two VC-n, the demapping of the virtual concatenation process will be one frame long, that is, the processing delay of 125us, while 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, if the transmission speed of the service in the optical fiber is 2×10E5km/s, it takes 125us to transmit 50km. Since the establishment of the service requires sending and receiving, the one-way transmission distance is 25Km , according to the relationship between ESCON transmission distance and bandwidth in Figure 3, at 25Km, the ESCON bandwidth is 9MB/sec, which is only half of the normal bandwidth.

To sum up, when using the adjacent cascading method to transmit services in the SDH transport network, the network needs to maintain continuous bandwidth during the entire service transmission process, and the bandwidth requirements for network elements are relatively high, and this cascading method cannot be based on The actual needs of the service determine the cascading situation, but it can only be cascaded to the set VC-n-XC, so it often causes a relatively large waste of bandwidth; when using the virtual concatenation method to transmit services, in order to avoid pointer jitter on the The impact of service transmission requires a long time delay, which will lead to a sharp reduction in bandwidth of some specific services during the transmission process.

Contents of the invention

In view of this, the main purpose of the present invention is to provide a method for realizing service transmission in the SDH transport network, so that the service transmission of the SDH transport network has the transmission advantages of adjacent concatenation and virtual concatenation at the same time. The business situation arbitrarily determines the number of virtual containers for the transmission of the business, and there will be no delay problem, avoiding the impact on the network bandwidth.

In order to achieve the above object, the technical solution of the present invention is achieved in this way: a method for realizing service transmission in a synchronous digital transmission network, the method comprising the following steps:

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

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

c. The device at the receiving end performs demapping processing on the received VC structure by using an adjacent cascading demapping method.

Said step c may further include:

Set up a cache for adjusting the VC pointers in the received VC structure, and adjust each VC pointer in the received VC structure.

Each VC pointer in the VC structure can be adjusted by using a pointer adjustment method of virtual concatenation.

The cache can be set to be greater than or equal to 6 bytes.

The cache can be set to a size smaller than one frame.

The cache can be further set to the size of one line in one frame.

The VC can be VC-3, VC-4 or VC-12.

In step b, the mapping process of all the determined VCs by means of virtual concatenation mapping is as follows: each VC is given its own independent path overhead (POH).

The present invention adopts the mapping and demapping scheme combining adjacent concatenation and virtual concatenation, that is, the m VCs required by the current service are mapped to the VC structure of virtual concatenation in the form of virtual concatenation, and the same routing For transmission, the receiver device uses the method of adjacent concatenation to demap the received VC structure, so that the service transmission of the SDH transport network can have the advantages of using adjacent concatenation and virtual concatenation to transmit services at the same time. That is to say, when transmitting services in the SDH transport network, there will be no waste of bandwidth in the case of adjacent cascading, and there will be no problem of high bandwidth requirements for each network element in the SDH transport network, and there will be no virtual cascading The problem of a sharp decrease in bandwidth due to a long delay.

Description of drawings

Fig. 1 is the structural diagram of the VC-4-XC obtained when mapping under the cascading situation in the prior art;

Fig. 2 is the structural diagram of VC-4-XV obtained when mapping under the situation of virtual concatenation in the prior art;

Figure 3 is a relationship diagram between ESCOM service transmission distance and bandwidth;

Fig. 4 is a flowchart for realizing the solution of the present invention.

Detailed ways

The scheme of the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

The scheme of the present invention processes the sending end and the receiving end of the transmission service, and specifically determines the number of VCs required according to the needs of the business. The required number is the ratio of the service rate to the transmission rate. For example, the ESCON service rate is 200Mbit/s, which is For services without flow control and bandwidth compression, the rate of VC-4 is 155Mbit/s, so two VC-4s (2×155) must be used. At the originating end, the determined VCs are mapped using the same mapping method as the virtual concatenation, so that each VC has its own independent POH overhead, and these VC channels are bundled together to form a quasi-virtual channel, which is different from the virtual concatenation The most important thing is that this type of virtual channel takes the same route when it is transmitted in the network; when the receiving end performs demapping, the receiving end device adopts the adjacent cascading demapping method.

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 by virtual concatenation to form a virtual large-structure VC-4-3V at the originating end. The difference from virtual concatenation is that In this embodiment, the VC-4-3Vs are bundled together and transmitted through the same route, so as to ensure that the transmission paths of the services are consistent. In this way, it can not only have the advantage of the prior art that there is almost no delay in the arrival of a service at the end point during adjacent concatenation, but also have the advantage of the prior art that the VC-4 used can be determined according to the service during virtual concatenation.

The method of using the same route transmission can make the time when each VC-4 corresponding to the service arrives at the receiving end device to be consistent. Therefore, the management unit (AU) pointer of each VC-4 is also consistent, that is, it is the same as the AU pointer of the terminal in the case of cascading. The situation is the same, so the demapping method in the case of adjacent concatenation can be adopted, and caching is not required like virtual concatenation.

However, there is also a difference between the demapping and the adjacent cascading situation. In the cascading situation, since the adjacent cascaded VC-4-XC has only one separate pointer, when performing pointer adjustments, only the pointer needs to be adjusted. This one pointer is adjusted, and for this one pointer, no difference in pointer adjustment value occurs. The pointer adjustment is caused by the difference between the data recovery clock and the system clock. The adjustment means that the pointer is increased or decreased by one. Each adjustment unit means that the payload part is filled or reduced by 3 bytes. And each VC-4 after the virtual concatenation in the scheme of the present invention has its own independent pointer, therefore, need to adjust the pointer in each VC-4, find through testing, although each VC-4 is transmitted by the same route So that the adjustment of each VC-4 pointer will not cause inconsistent pointers in each VC-4 on a macro level, but on a micro level, there may still be adjustment differences between the pointers in each VC-4. The pointer is adjusted once, and the payload is padded or reduced by three bytes, so the maximum difference between two VC-4s is 6 bytes. For this difference that may exist between pointers, the method of virtual concatenation can be borrowed, that is, cache is used to solve the difference in pointer adjustment. Since the maximum difference that may exist in the solution of the present invention is only 6 bytes, and the cache memory of one frame corresponds to 9*270 bytes during virtual concatenation, therefore the cache memory of one frame during virtual concatenation is not needed at all, and can be greater than or equal to A 6-byte buffer is sufficient for pointer adjustments. In actual operation, for the sake of convenience, the size of one line in a frame can be adopted, i.e. a buffer of 270 bytes, so that when realizing the adjustment between each VC-4 in the scheme of the present invention, the virtual concatenation time can be borrowed. cache handling method.

The above descriptions are only preferred embodiments for realizing the solutions of the present invention, and are not intended to limit the scope of protection of the present invention.

Claims (8)

1. A method for realizing service transmission in a synchronous digital transmission network, characterized in that the method comprises the following steps: a. Determine the number of virtual containers (VC) required to transmit the service according to the current service to be transmitted; b. Mapping all VCs determined in step a through a virtual concatenation mapping method to obtain a virtual concatenation VC structure, and transmitting the obtained VC structure to the receiving end device through the same route; c. The device at the receiving end performs demapping processing on the received VC structure by using an adjacent cascading demapping method. 2. The method according to claim 1, characterized in that said step c further comprises: Set up a cache for adjusting the VC pointers in the received VC structure, and adjust each VC pointer in the received VC structure. 3. The method according to claim 2, characterized in that the pointer adjustment method of virtual concatenation is used to adjust each VC pointer in the VC structure. 4. The method according to claim 2, characterized in that the buffer is set to be greater than or equal to 6 bytes. 5. The method according to claim 4, wherein the buffer is set to a size smaller than one frame. 6. The method according to claim 5, wherein the buffer is set to a size of one line in one frame. 7. The method according to claim 1, wherein the VC is VC-3, VC-4 or VC-12. 8. The method according to claim 1, characterized in that, in step b, performing mapping processing on all the determined VCs through a virtual concatenation mapping method is: giving each VC its own independent channel overhead (POH).

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