JPH11191779A - Atm switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a logical path VCC confluent system where a resource amount of virtual path identifier(VPI)/virtual channel identifier(VCI) in a trunk system network is especially reduced by integrating pluralities of logical parts (VCCs) into one and no hindrance is caused to transfer of packets. SOLUTION: In the case of retrieving a routing table 15 based on header information of a cell received from an incoming channel 13, a mask bit pattern specific to each VPI/VCI is used to mask part of header information of the received cell and the cell is retrieved. Thus, outgoing exchange information of each cell received through each incoming channel 13 is made in common to attain a network where pluralities of VCCs are integrated into one.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ATM (Asynchro
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ATM switch used for communication, and more particularly to an ATM switch having a feature in a cell exchange information search method.

[0002]

2. Description of the Related Art In recent years, ATM communication for transmitting and receiving data in fixed-length packets of 53 bytes, that is, cells, has attracted attention as a basic technology of multimedia communication. In ATM communication, since data is communicated in fixed-length packets, it can be exchanged at a hardware level, and can be readily applied to not only data communication but also communication of voice, image, and the like.

[0003] In the ATM communication, each cell is provided with 5-byte header information, to which an identifier called VPI / VCI is assigned. Here, VPI / VCI will be briefly described.

[0004] In the ATM network, several virtual paths (VP) are set, and further, several virtual channels (VC) for actually transmitting data are set for each virtual path. Therefore, first, in order to identify which VP is used, the VPI (Vi
rtual Path Identifier (virtual path identifier). Further, a VCI (Virtual Channel Identifier) is provided in the header of the cell to identify which VC in the VP should be used to send data to the other party. This VPI / VCI is
Since it is a part which determines which VC and which VC should be selected to communicate with the other party, it is called a routing bit (bit for selecting a communication path). The cell is 53
5 bytes are used as a header, and the remaining 48 bytes are used as user information.

[0005] In the 5-byte header, the VPI field is reserved for 8 bits at the UNI (User-Network Interface) and 12 bits at the NNI (Network Node Interface), and the VPI field is reserved at 16 bits each. .

The identifier of such VCI / VPI is En
In starting the communication between d-End (between terminals), allocation is performed in units of physical lines, and after the allocation is completed, the cell header is sequentially rewritten from the start point of communication to the header value of the next physical link, and the allocation identifier is traced. Cells are sent.

On the other hand, in an IP network used in the Internet and the like, an IP between End and End is an IP network.
Communication is performed using numbers called addresses that identify each place. How to assign this IP address
The same network address is assigned to each large network, and one network is further divided into a certain number of groups, grouped as subnets, and each terminal is assigned to be located in this subnet. As a result, the entire network can be easily managed, and the network exchange between End and End can be performed efficiently.

[0008] IP networks and subnets are divided by dividing the IP address by a number of bits from the upper bits. In particular, subnets are clearly identified by assigning a bit, which filters an address called a subnet mask, to each subnet. To

[0009]

SUMMARY OF THE INVENTION
In a data network using the P protocol or the like, when data transmission / reception is started, End-E
A plurality of VPI / VCIs obtained between nd and nd are acquired by some means, and data communication is performed using these VPI / VCIs.

In this case, since the IP communication does not clearly indicate the end point of the communication, the VPI / VCI is held for a while, for example, a procedure such that the VPI / VCI is released when there is no communication for a certain time is adopted. Was. For this reason, there is a problem that VPI / VCI resources are wasted.

This will be described with reference to a network configuration example shown in FIG. In FIG. 6, reference numeral 21 denotes a public line.
e, for example, a public line such as NTT Net.
Reference numerals 22 and 23 denote GWs (gateways) for interconnecting systems / networks of different protocols. In the example of FIG. 6, two GWs 24 and 25 are installed, and a Backbone net (backbone network)
24, 25 and IP-Subnets (subnets) 26 to 29 connected to them constitute one network. In this case, the GWs 24 and 25 correspond to gateways of this network, and the networks are connected by a dedicated line service of a carrier.

When such a network is constructed by ATM, a configuration as shown in FIG. 7 has conventionally been adopted. A VCC (Virtual Channel Connection) in the figure is a communication path formed by a VCI conversion rule, and a number of such VCCs are provided for each terminal using the network.

Note that, for simplicity of explanation, VP
The logical path (VCC) characterized by I / VCI is shown only as an example. Also, actually, the VPI /
Although one VCI is usually allocated between physical links, it is not essential in the present description and is simplified in the figure.

Normally, the dedicated line service is provided by VP exchange, so that one VP (virtual path) is provided between the GWs 22 and 23.
Is allocated. In the network, allocation is performed by VCC, because it is desired to allocate VPI / VCI every time an event of data transmission / reception occurs.

However, even in this case, as shown in FIG. 7, the VCC used in each of the IP-Subnets 26 to 29 is used.
Are also assigned to the Backbone nets 24 and 25 at the same time. Actually, IP-Subnet2
Since the number of terminals is allocated by the number of terminals within 6 to 29, Back
A very large number of VCCs will be concentrated on the bone nets 24 and 25 and the GWs 22 and 23.

As the network scale increases and the number of terminals increases, this problem becomes more serious, exceeding the number of VCCs that can be handled by the GWs 22 and 23, and causing a problem that communication cannot be performed even though there are line resources. That is, VPI
/ VCI resources are wasted.

In order to solve such a problem, conventionally, a method of merging a plurality of VCCs into one VCC has been proposed. However, in order to avoid that different data packet flows are mixed at the ATM cell level, for example, when two flows are merged, the first packet is passed first and the next packet is passed. When the data of one packet is long, or when the interval between cells constituting the packet is wide, it takes time to pass the first packet. There was a problem that the second packet could not be easily transferred.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and combines a plurality of VCCs into one to reduce the amount of VPI / VCI resources particularly in a backbone network.
It is another object of the present invention to provide an ATM switch that realizes a VCC merging system that does not hinder packet transfer.

[0019]

An ATM switch according to the present invention searches a routing table based on header information of a cell input from an incoming line and rewrites the header information of the input cell to information of an outgoing side. In an ATM switch for switching to a predetermined output line, a mask means for masking a part of the header information of the input cell, a table search means for searching the routing table based on the header information masked by the mask means, Information rewriting means for rewriting header information of the input cell to outgoing information specified in the routing table based on a search result by the table search means.

According to such a configuration, when searching the routing table based on the header information of the input cell, a part of the header information is masked and searched to be input through each incoming line. It is possible to realize a network in which a plurality of VCCs are integrated into one by sharing outgoing exchange information of each cell.

[0021]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
The TM switch will be described. (First Embodiment) FIG. 1 is a diagram showing a schematic configuration of an ATM switch according to a first embodiment of the present invention. In this drawing, those not directly related to the present invention are omitted.

As shown in FIG. 1, an ATM switch 11 of the present invention comprises an ATM switch module 12 and a plurality of incoming lines 13 and outgoing lines 14 to / from which cells exchanged by the module 12 are input / output. And it is composed of a routing table 15. In the example of FIG. 1, only one incoming line 13 is shown for simplification of the description. Although the routing table 15 is shown as being located on each incoming line 13, the arrangement of the routing table 15 only depends on the contents of the cell exchange information, which is not directly related to the present invention. This is shown as one example.

In the ATM, information to be sent from a terminal on the transmitting side to a terminal on the receiving side is divided into 48 bytes, and header information of 5 bytes is added thereto, and the information is transmitted in units of a fixed-length cell having a total of 53 bytes. I do. The cells sent to the ATM network are switched (exchanged) at high speed by hardware based on the header information. The ATM switch 11 shown in FIG. 1 is used as an exchange for performing the switching at this time, and is installed in a relay device of the ATM network.

When the ATM switch 11 receives a cell input from the incoming line 13, it reads the value of VPI / VCI described in the header of the cell and outputs the cell with reference to the routing table 15. Outgoing line 1
4 is determined.

Here, the routing table 15 includes:
VPI / VCI information of the input cell, outgoing header information to be converted when output to the outgoing line 14,
In this embodiment, the output exchange information, which is information as to whether or not to exchange, and a mask bit pattern unique to each VPI / VCI are stored.

That is, in the ATM cell switching method according to the present invention, the VPI / VIP described in the header of the input cell is used.
The routing table 15 is searched based on the value of the VCI. At this time, the header information of the input cell is masked by a mask bit pattern defined in the routing table 15 (AND calculation of the VPI / VCI field bits of the header). Then, the VPI / VCI field of the routing table 15 is searched.

The input cells are exchanged by the ATM switch module 12 in accordance with the output exchange information of the column hit at this time, and output to a predetermined outgoing line 14. In this cell exchange, the cell header value is rewritten in the outgoing header information of the routing table 15.
In the PI / VCI field, only the bits masked by the mask bits are rewritten.

The algorithm at this time will be described with reference to the flowchart of FIG. FIG. 2 is a flowchart showing a cell exchange algorithm in the first embodiment.
When a cell is input from the incoming line 13 (step A1)
1), the ATM switch 11 determines the VP from the header of the input cell.
The I / VCI value is extracted and checked for each entry defined in the routing table 15 (step A).
12).

As an inspection, the routing table 15
Bit pattern and VPI / V of input cell header
The value of CI is ANDed, and this is added to the routing table 1
5 matches the value of the VPI / VCI field.

As a result, when both match completely (when the search hits), that is, when the value of VPI / VCI masked by the mask bit pattern exists in the routing table 15 (step A).
13 (Yes), the ATM switch 11 rewrites the header information of the corresponding cell based on the output header information defined in the routing table 15 (step A14).
Note that information rewriting at this time will be described later with reference to FIG.
This will be described with reference to FIG.

After rewriting the header information, the cell is switched (switched) through the ATM switch module 12 in accordance with the output switching information (output line) defined in the routing table 15 (step A15). It is sent (step A16).

On the other hand, if they do not match (the search does not hit), that is, if the value of VPI / VCI masked by the mask bit pattern does not exist in the routing table 15 (Yes in step A13), The ATM switch 11 determines that the cell is an unnecessary cell and discards it (step A17).

As described above, for each of the entries in the routing table 15, the header information (VPI) of the input cell is determined using the predetermined mask bit pattern.
/ VCI), the header information is rewritten into output header information, and the cell is exchanged according to the output exchange information. Thus, the outgoing exchange information of each cell input through each incoming line 13 can be shared, and a plurality of VCCs can be integrated into one.

Here, a cell multiplexing method according to the present invention will be described. FIG. 3 is a diagram for explaining a cell multiplexing method according to the first embodiment. Now, as shown in FIG. 3, the VPI is “0” and the VCI is “64” to “6”.
It is assumed that four groups of cells having header information “7” are input from a plurality of incoming lines 13. That is, four VCCs are provided on the input side of the ATM switch 11.
Assume that (communication route) is drawn.

The physical outgoing line 14 is the same, and here, 1 indicated by VPI = 0 and VCI = 128
It is assumed that the VCC of the book and the mask bit value “18” are set in the routing table 15. The mask bit value "18" means that 18 bits from the beginning of the VPI / VCI field of the input cell are masked with all ones.

In such a configuration, each incoming line 13
When each cell is input through VP, the VP of the header of each cell is
The routing table 15 is searched after the I / VCI value is masked by the mask bit value “18”, and the header information of the cell is rewritten according to the search result. In this case, specifically, the following logical calculation is performed.

$ (ALL "1" * MASK) & VPI / V
CI @ or output side header information, where MASK: mask bit pattern *: exclusive OR &: logical product or: logical sum That is, first, all data of VPI / VCI are all 1
The EXOR is performed on the set value and the mask bit pattern (a bit example in which 18 bits are 1), and the VPI / VCI value of the input cell is ANDed with the value. In this case, 5
In the header of the byte, the VPI field has 8 bits for UNI and 12 bits for NNI, and the VPI field has 16 bits for each. Therefore, this 24 bits (UNI) or 28 bits (NNI)
EXOR of the value obtained by setting the VPI / VCI value of the minute to all 1s and the mask bit pattern of 18 bits to 1 is ANDed with the actual VPI / VCI value. And
The value obtained in this way is ORed with the outgoing header information.

As a result, in the example of FIG.
The input VCI values of the header of each cell are rewritten to “128”, “129”, “130”, and “131”, respectively.

In this way, the input four VCCs
Are masked by mask bit values “18”, respectively, and L
It is multiplexed into one VCC such as VPI = 0 and VCI = 128 of INE1. Thereafter, in an ATM switch that is exchanged while being multiplexed, a plurality of VCCs are exchanged by one VCI by setting the same mask pattern. In the case of separation at the final stage, the mask bit pattern is a full bit of 24 bits (UNI)
Alternatively, they can be easily separated by setting them to 28 bits (NNI).

In the above embodiment, the mask bit value is described as "18", but the setting of the mask bit value is arbitrary. For example, if the mask bit value is set to a large value, the number of input VCCs can be reduced. The range to be masked is not based on the distinction between VPI and VCI. In short, a pattern that can mask the VPI / VCI value of an input cell may be applied so that a plurality of VCCs can be combined into one.

(Second Embodiment) Next, a second embodiment of the present invention will be described. In the first embodiment,
Although a unique mask bit pattern is set for each VPI / VCI, the mask bit pattern does not need to be so large compared to the number of VCCs. Therefore, in the second embodiment, only the mask bit pattern is prepared as a separate table, and the mask processing of the cell header is sequentially performed for each predetermined mask bit pattern, but the routing table search uses the conventional method as it is. I do.

FIG. 4 shows a table configuration according to the second embodiment of the present invention. The difference from the first embodiment is that
The only difference is that only the mask bit pattern is a separate table. That is, in the second embodiment, the routing table 15a and the mask pattern table 15b are separately provided in the ATM switch 11.

As shown in FIG. 4A, the routing table 15a contains VPI / VCI information of an input cell, outgoing header information to be converted when output to the outgoing line 14, and which outgoing line 14 Output exchange information, which is information on whether or not to exchange, is stored. Also, as shown in FIG. 3B, a plurality of different mask bits for masking the VPI / VCI value of the input cell, such as pattern 1, pattern 2, pattern 3,. The pattern is stored.

FIG. 5 shows a cell exchange algorithm according to the second embodiment. In this case, the inspection termination condition is not the last entry in the routing table 15a but the last entry in the mask pattern table 15b.

That is, when a cell is input from the incoming line 13 (step B11), the ATM switch 11 extracts the value of VPI / VCI from the header of the input cell, thereby obtaining each mask bit pattern from the mask pattern table 15b. Are obtained one by one, and the VPI /
The routing table 15b is searched while masking the VCI field (step B12).

If the search hits, that is, if a VPI / VCI value masked by a certain mask bit pattern exists in the routing table 15a (Yes in step B13), the ATM switch 11 sends the header information of the corresponding cell to the routing table 15a. The cell is rewritten based on the output header information specified in 15a (step B14), and the cell is switched (switched) through the ATM switch module 12 in accordance with the output switching information (output line) specified in the table 15a (step B15). Is transmitted to a predetermined outgoing line 14 (step B16).

On the other hand, if the search does not hit, that is,
VPI / VCI masked by a certain mask bit pattern
If the value does not exist in the routing table 15a (No in step B13), the ATM switch 11 extracts the next mask bit pattern from the mask pattern table 15b and performs the same search as above (No in step B17). As a result, if the search does not hit even if the last mask bit pattern in the mask pattern table 15 is used (Yes in step B17), the ATM switch 1
1 judges that the cell is an unnecessary cell and discards it (step B18).

In the case of such an algorithm, since the routing table search can be realized by the associative memory, the degree of freedom of the mask bit pattern is slightly limited as compared with the first embodiment, but the search logic can be simplified. There is an advantage that can be realized with simple hardware. However, in such a method, a plurality of mask bit patterns must be extracted one by one at the time of routing table search and applied to an input cell. Therefore, as in the first embodiment, a unique determination is made for a cell group. It is preferable to use the set mask pattern in starting the network.

FIG. 8 shows an example in which the method of the present invention is applied to an actual network. As shown in FIG. 8, for example, two GWs 24 and 25 are installed in a public line (public line) 21 such as an NTT net, and
ackbone net (backbone network) 24,
25, in the case where one network is composed of IP-Subnets (subnets) 26 to 29 connected thereto, as described above, by using the method of searching after exchanging the cell exchange information after masking the header information. , A plurality of VCCs can be combined into one. This allows VPI / VC especially in backbone networks
The resource amount of I can be reduced, and even if different data packets flow together, those packets can be efficiently transmitted without waiting for another packet transfer.

[0050]

As described above, according to the present invention, when the routing table is searched based on the header information of the input cell, a part of the header information is masked and searched, so that each incoming line can be searched. , The outgoing exchange information of each cell, which is input through the network, can be shared to realize a network in which a plurality of VCCs are integrated into one. As a result, it is possible to reduce the amount of VPI / VCI resources in the backbone network, and realize a VCC merging system that does not hinder packet transfer.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an ATM switch according to a first embodiment of the present invention.

FIG. 2 is a flowchart illustrating a cell exchange algorithm according to the first embodiment.

FIG. 3 is a diagram for explaining a cell multiplexing method according to the first embodiment.

4A and 4B are diagrams illustrating a table configuration according to a second embodiment of the present invention. FIG. 4A illustrates a configuration of a routing table, and FIG. 4B illustrates a configuration of a mask pattern table.

FIG. 5 is a flowchart illustrating a cell exchange algorithm according to the second embodiment.

FIG. 6 is a diagram showing a configuration example of an IP network.

FIG. 7 is a diagram showing a configuration example of an ATM network according to a conventional method.

FIG. 8 is a diagram showing a configuration example of an ATM network to which the method of the present invention is applied.

[Explanation of symbols]

 11 ATM switch 12 ATM switch module 13 Incoming line 14 Outgoing line 15 Routing table 15a Routing table 15b Mask pattern table

Claims (4)

[Claims] An ATM switch for retrieving a routing table based on header information of a cell input from an incoming line, rewriting the header information of the input cell to information of an outgoing side, and exchanging the header information for a predetermined output line, Mask means for masking a part of the header information of the input cell; table search means for searching the routing table based on the header information masked by the mask means; and An ATM switch comprising: information rewriting means for rewriting header information of an input cell to information on an outgoing side defined in the routing table. 2. A routing table is searched on the basis of VPI / VCI described in header information of a cell input from an incoming line, and the header information of the input cell is rewritten into information on an outgoing line to output a predetermined output line. A mask pattern storing means for storing a mask bit pattern, and a VPI / VCI bit example described in the header information of the input cell using the mask bit pattern stored in the mask pattern storing means. Mask means for masking a part of the input cell; table search means for searching the routing table based on the VPI / VCI masked by the mask means; header information of the input cell based on a search result by the table search means To the outgoing side information specified in the above routing table ATM switch being characterized in that comprising a that information rewriting means. 3. The mask pattern storage means stores a mask bit pattern unique to each VPI / VCI defined in the routing table, and the mask means selects one of the mask pattern storage means from the mask pattern storage means. 3. The AT according to claim 2, wherein the mask processing is performed using a mask bit pattern corresponding to the input cell.
M switch. 4. The mask pattern storage means is provided separately from the routing table and stores a plurality of different mask bit patterns. The mask means stores each mask bit stored in the mask pattern storage means. 3. The ATM switch according to claim 2, wherein mask processing is performed using each of the patterns.