JP4298930B2 - PPP frame multiplexer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a system for accommodating IP (Internet Protocol) traffic in a digital exchange (hereinafter simply referred to as an exchange) constituting a public communication network. In particular, the present invention relates to a method of multiplexing and transmitting a PPP (Point-to-Point Protocol) frame in which IP packet data is stored in a data portion.
[0002]
[Prior art]
In recent years, a new subscriber exchange called a multi-location type described in, for example, “NTT Technology Journal September 1996, Special Feature: New Node System NS8000 Series” has been introduced and has started providing services. In this technology, as shown in FIG. 10, the function of the subscriber exchange is divided into a subscriber accommodation function (subscriber accommodation / concentration / multiplexing) and a service processing function (service processing / distribution / relay). Instead of giving these two functions to the exchange, the necessary functions are optimally arranged. In such a multi-location type subscriber exchange 13 shown in FIG. 10, a line processing unit (ASM) 13b having a function that can be aggregated in one place such as a service processing function is arranged in a wide area, and a large number of subscriber accommodating units. (SBM) 13a is controlled. A standardized transmission line interface called SDH (Synchronous Transfer Mode) is used between the line processing unit (ASM) 13b and the subscriber accommodation unit (SBM) 13a.
[0003]
FIG. 11 shows functional configurations of the subscriber accommodation unit (SBM) 13a and the line processing unit (ASM) 13b. The subscriber accommodation unit (SBM) 13a includes an ISDN subscriber circuit (OCU) 20a, a demultiplexing unit (MDX) 20d, and a concentrator switch unit 20b. The line processing unit (ASM) 13b includes a distribution switch unit 21b, a frame handler (FH) 21j, an I subscriber line signal processing unit (ISIG) 21d, and a processor 21g for controlling the line processing module.
[0004]
Here, a dial-up IP network connection via a general public communication network using this exchange will be described. When the ISDN network is used as an access line for ISP (Internet Service Provider) connection, the ISDN communication mode is generally a dial-up connection method using the same circuit switching as that for voice calls. Further, PPP is used as the layer 2 protocol at this time, and as shown in the protocol stack of FIG. 12, the protocol configuration is such that the IP packet is stored in the data portion of the PPP frame.
[0005]
FIG. 10 shows an example in the case where an access point to the IP network exists in the same city as the subscriber. When the subscriber issues a call setup instruction from the terminal device to the access point, the Dch already set is shown. A connection control is performed by transmitting and receiving call control packets between the terminal adapter (TA) 11-I subscriber signal processing unit (ISIG) 21d using a link, and the processor 21g is a concentrator switch unit of the subscriber accommodation unit (SBM) 13a. 20b and a distribution switch unit 21b of the line processing unit (ASM) 13b, a Bch path is set, and a layer 1 path is established between the terminal 10 and the PPP terminating device 14. In this case, the path setting of the distribution switch unit 21b is in the local station loopback state. At this stage, the PPP frame can be transmitted. First, a layer 2 link is established by LCP (Link Control Protocol) in the PPP, and a communication path for passing an upper layer protocol such as IP is set. At this time, user authentication and header compression can also be executed. Thereafter, an IP address assignment to the terminal is executed by NCP (Network Control Protocol), and the state where the network layer protocol can communicate is prepared, and the PPP data communication state is set. The PPP terminator 14 terminates the PPP frame used for communication between the terminal 10 and connects to the IP network.
[0006]
[Problems to be solved by the invention]
The IP network connection via the ISDN exchange described above uses ISDN line exchange. For this reason, for example, when the Bch1 channel is used, a band of 64 kbit / s per subscriber is occupied in the exchange. Also, a PPP termination device, which is an access point to the IP network, is installed on the user / network interface (UNI) side. Therefore, in order to connect to the PPP termination device, it is necessary to secure a bandwidth corresponding to the number of subscribers. As a result, packet transmission having bursty traffic characteristics is inefficient, and it is difficult to reduce network costs.
[0007]
On the other hand, since it is necessary for a PPP termination device to prepare ports for 64 kbit / s × n subscribers, there is a problem that the amount of hardware increases as the number of subscribers increases.
[0008]
Japanese Patent Laid-Open No. 5-183469 has been proposed as a method for accommodating IP traffic in a public communication network. In this method, Bch 64 kbit / s data used for IP network connection is framed as it is, multiple subscriber frames are multiplexed, and connected to the IP network through a dedicated line interface. Since Bch data is framed regardless of the presence or absence of IP packets on Bch, a bandwidth of 64 kbit / s or more per subscriber is required, and there is nothing regarding efficient accommodation of IP packets in the switching network. Not considered.
[0009]
An object of the present invention is to improve line efficiency when connecting to an IP network using an ISDN network.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention performs the following processing. That is, a PPP (Point-to-Point Protocol) frame , a LAPD (Link Access Procedure on the D-channel) frame, or a LAPB (Link Access Procedure Balanced) transmitted via any one of a plurality of subscriber lines. Mode) information including a frame is received . By identifying the subscriber line through which the received information has been transmitted, the subscriber who transmitted the information is identified. The received LAPD frame or the LAPB frame is converted into a LAPF (Link Access Procedure for Frame Mode Bearer Service) frame by adding identification information to the PPP frame included in the information, and the PPP frame is multiplexed. The PPP frame is converted into PPPoE (Point-to-Point Protocol over Ethernet) for each subscriber with reference to the identification information and output.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, an existing ISDN Dch packet service is used as an IP network connection route. This is an example in which PPP frames are stored in 25 packets and packet processing hardware in a subscriber exchange is used for multiplexing of PPP frames. Therefore, the subscriber exchange in the present embodiment simultaneously accommodates subscribers who receive the conventional packet service and subscribers who receive the IP network connection service. In the present embodiment, it is assumed that DchPVC (Permanent Virtual Circuit) connection is used.
[0012]
FIG. 1 is a diagram showing a network configuration when a subscriber exchange according to the first embodiment of the present invention is used. That is, in this embodiment, the subscriber exchange 13 accommodates each subscriber line and is connected to the PPP termination device 14. The PPP termination device 14 is connected to the IP network.
[0013]
A subscriber terminal device (hereinafter referred to as a terminal) 10, a terminal adapter (TA) 11, and a network termination device (DSU) 12 are installed in each subscriber home 1.
[0014]
The terminal 10 performs PPP frame processing, TCP / IP processing, and the like using software. That is, the terminal 10 generates PPP frame data 720 including the IP packet 710 (see FIG. 6). Furthermore, the terminal 10 asynchronously transmits and receives PPP frame data to and from the terminal adapter (TA) 11 using RS-232C or the like (see FIG. 5).
[0015]
The terminal adapter (TA) 11 is an X. 25 (OSI reference model layer 3) and LAPD (Link Access Procedure on the D-channel) protocol (OSI reference model layer 2). For example, the terminal adapter 11 divides the PPP frame data 720, Processing to encapsulate 25 packets 730 is performed (see FIGS. 5 and 7).
[0016]
The network termination unit (DSU) 12 terminates the subscriber line of the exchange.
[0017]
The subscriber exchange 13 includes a plurality of subscriber accommodation units (SBM) 13a and a line processing unit (ASM) 13b. Each subscriber accommodation unit 13a accommodates a plurality of subscriber lines. The line processing unit 13 b is connected to the PPP termination device 14. The line processing unit 13 b multiplexes the PPP frame data and outputs it to the PPP terminating device 14.
[0018]
Here, the format of input data and output data of the subscriber exchange 13 will be described. FIG. 6A shows a format of data input from each subscriber home 1 to the subscriber exchange 13. That is, the input data is IP in layer 5 of the OSI reference model, PPP in layer 4, and X. 25, Layer 2 indicates that LAPD is used. FIG. 6B shows a format of data output from the subscriber exchange 13 to the PPP termination device 14. That is, the output data uses a frame for PPPoE (Point-to-Point Protocol over Ethernet) in layer 5 and Ethernet (registered trademark of Fuji Xerox Co., Ltd.) in layer 2.
[0019]
FIG. 2 shows a detailed block configuration of the subscriber exchange 13. A subscriber accommodation unit (SBM) 13a includes an ISDN subscriber circuit (OCU) 20a for terminating a subscriber line, a demultiplexing unit (MDX) 20d for time-division multiplexing and demultiplexing of subscriber data, and an ISDN subscriber line. It has a line collecting switch unit 20b for collecting lines and a transmission interface (SDH) 20c.
[0020]
A Dch path is set in the line collecting switch unit 20b. The PPP data from the subscriber is X. 25 packets 730 are stored. The X. The 25 packets are further stored in the LAPD frame 740. Details of the LAPD file format are shown in FIG. This LAPD frame 740 passes through the ISDN subscriber circuit (OCU) 20a, the demultiplexing unit (MDX) 20d, the concentrator switch unit 20b, and the transmission interface (SDH) 20c in the subscriber accommodation unit (SBM) 13a, and the line processing unit. (ASM) 13b. In the demultiplexing unit (MDX) 20d, a plurality of subscriber data is time-division multiplexed.
[0021]
The subscriber can be identified by identifying the subscriber line. That is, if it is known from which subscriber line the data is transmitted, the subscriber can be specified. Further, when time division multiplexing is performed by the demultiplexing unit (MDX) 20d, it is determined in advance to which time slot number the data transmitted from each subscriber line is set. Therefore, when time division multiplexing is performed, the sender subscriber can be specified by the time slot number.
[0022]
The line processing unit (ASM) 13b includes transmission interfaces 21a and 21h, a distribution switch unit 21b, an I subscriber line signal processing unit (ISIG) 21d that performs layer 2 protocol processing of ISDN subscriber control signals, and a line processing unit 13 A processor 21g that controls each module, a frame handler (FH) 21c that performs multiplexing / demultiplexing processing in layer 2 of Dch / Bch packets and call control signals, and a plurality of IP network interfaces 21f having an interface function with the IP network side, The frame distribution unit 21e outputs a frame to any one of the plurality of IP network interfaces 21f.
[0023]
The distribution switch unit 21b takes out one B channel or D channel arbitrarily defined from the channel structure of the ISDN basic interface or primary group interface multiplexed in the subscriber terminal unit. In addition, the distribution switch unit 21b separates and edits information of each time slot according to the time division multiplexed time slot number. In addition, a path for Dch is set in the distribution switch unit 21b.
[0024]
The frame handler 21 (FH) c distributes the control packet and the Dch packet and performs a process of multiplexing the D channel packet in the PPP frame. Hereinafter, the processing of the frame handler 21 (FH) c will be described with reference to FIG. FIG. 3 shows how the frame handler 21 (FH) c receives an input from the distribution switch 21b and distributes a frame output to the ISIG 21d and a frame output to the distribution switch 21b again.
[0025]
Time-division multiplexed subscriber data is input to the frame handler (FH) 21c. Each subscriber data accepts each time slot as an independent 16 kbit / s input channel. A subscriber can be uniquely identified by the time slot number (input channel number) assigned to each time slot which is an input channel.
[0026]
In the present embodiment, an example of accommodating 8000 subscribers is shown. The frame handler (FH) 21c confirms the SAPI field 801 (see FIG. 7A) of the received LAPD frame 800 for each input channel. If “0” or “63” indicating that the frame is a control signal is set in the SAPI field 801, the frame handler 21c outputs the frame to the ISIG 21d. When “16” indicating that the frame is a packet is set in the SAPI field 801, the service form of the subscriber corresponding to the input channel is further confirmed. The service form is confirmed with reference to a table (not shown) storing service contract information for each subscriber. The following multiplexing is performed on the packet frame.
[0027]
The frame handler 21c converts the packet frame from LAPD to LAPF (Link Access Procedure for Frame Mode Bearer Service). Specifically, the LAPD frame format 800 shown in FIG. 7A is converted into the LAPF frame format 810 shown in FIG. 7B. To convert from LAPD to LAPF, a header is added. Among the headers to be added, an address capable of uniquely identifying a subscriber is assigned to DLCI 813. The LAPD information field 802 becomes the LAPF information field 812 without being converted.
[0028]
For example, when the SAPI of the received LAPD frame is “16”, the input channel number is converted into a LAPF frame as DLCI 811 of LAPF. Further, depending on whether the subscriber is a conventional packet subscriber or an IP connection subscriber, the output channel is assigned to channel # 1 for the packet switch or channel # 2 for the IP network. The channel for the IP network of channel # 2 is connected to the frame distribution unit via the distribution switch unit 12. The output channel has a bandwidth of 1.5 Mbit / s, and a plurality of subscriber data is multiplexed within this 1.5 Mbit / s bandwidth. With this frame multiplexing function, when all 8000 subscribers are IP network subscribers, a maximum of about 80: 1 multiplexing can be realized (16 kbit / s × 8000 subscribers / 1.5 Mbit / s≈80).
[0029]
The multiplexed data is input to the frame distribution unit 21e via the distribution switch unit 21b.
[0030]
The frame distribution unit 21e receives the LAPF frame and performs a process of distributing it to one of the plurality of IP network interfaces 21f. This process will be described with reference to FIG.
[0031]
FIG. 4 illustrates a case where the frame handler (FH) 21c includes five devices (# 0 to # 4) and the IP network interface 21f includes ten devices (# 0 to # 9). Five 1.5 Mbit / s channels into which PPP frame data of a maximum of 8000 subscribers are multiplexed are input to the frame distribution unit 21e. On the output side, a 3 Mbit / s channel is set for each IP network interface 21f. The frame distribution unit 21e divides the input DLCI into 10 for each input channel, and distributes the frames so that they are output to the channels # 0 to # 9 of the IP network interface 21f in ascending order of DLCI.
[0032]
The frame distribution unit 21e converts the DLCI 811 of the LAPF frame. That is, address conversion is performed in each IP network interface 21f so that DLCI does not overlap. By providing the frame distribution unit 21e, the hardware amount of the IP network interface 21f can be minimized when the number of IP network connection subscribers accommodated by each frame handler (FH) 21c is small.
[0033]
The IP network interface 21f performs protocol conversion so that the multiplexed frame matches the line protocol on the IP network side, and interfaces with the outside. In the present embodiment, the multiplexed LAPF frame is converted into an Ethernet frame (LAN data). Here, PPPoE defined by RFC2516 is used as the protocol on the IP network side.
[0034]
Hereinafter, a specific conversion procedure will be described with reference to FIGS. 6 and 7. With reference to DLCI 811 of LAPF frame 810, PPP frame 720 is extracted for data from the same subscriber. The retrieval of the PPP frame 720 includes LAPF, LAPD, X. 25 is terminated. The extracted PPP frame 720 is stored in a PPPoE frame 760. The PPPoE frame 760 generated here is further stored in an Ethernet frame 770.
[0035]
Further, the PPPoE frame 760 generated here is assigned a session ID based on the correspondence table 90 shown in FIG. The table 90 shown in FIG. 8 correlates the DLCI address 91 of the LAPF frame, the session ID 92 for identifying the subscriber in the PPPoE frame, and the MAC address 93 of the PPP terminating device 14. Therefore, the PPP terminating device 14 can identify each subscriber's link by the session ID. As a result, the subscriber exchange 13 and the PPP terminator 14 can be connected by a multiplexed line.
[0036]
FIG. 5 summarizes the protocol conversion described above. That is, based on the PPP frame generated by the terminal 10, X. A LAPD frame containing 25 frames is generated. This LAPD frame is converted into a LAPF frame by a frame handler (FH) 21c. Further, the LAPF frame is converted into a PPPoE frame in the IP network interface 21f. The PPP terminator 14 that has received this PPPoE frame terminates the PPP and takes out the IP frame.
[0037]
In the above embodiment, DchPVC connection is taken as an example, and the case where LAPD is used as a communication protocol between the subscriber exchange 13 and the subscriber's home has been described. However, when the B channel communication is multiplexed, LAPB (Link Access Procedure Balanced Mode) may be used. That is, as in the case of LAPD, the LAAPB frame transmitted from the subscriber terminal 10 is converted into a LAPF frame by the frame handler (FH) 21c.
[0038]
Next, a second embodiment of the present invention will be described with reference to FIG. In the present embodiment, the description will be focused on differences from the first embodiment.
[0039]
In the present embodiment, the subscriber accommodation unit 13a includes the frame handler (FH) provided in the line processing unit 13b in the first embodiment. The line concentrator 20b ′ takes out one arbitrarily defined B channel or D channel from the channel structure of the ISDN basic interface or the primary group interface. The frame handler 20e performs the same processing as the frame handler 21c in the first embodiment.
[0040]
Therefore, in the present embodiment, the channel of the IP connection subscriber is dropped by the concentrator switch unit 20b in the subscriber accommodation unit (SBM) 13a, multiplexed by the frame handler 20e, and the line processing unit (ASM) 13b. Connecting. In the line processing unit (ASM) 13b, the distribution switch unit 21b sets a path to the frame distribution unit 21e and connects to the IP network side via the frame distribution unit 21e and the IP network interface 21f. .
[0041]
As a result, in the present embodiment, after the PPP data is multiplexed by the subscriber accommodation unit (SBM) 13a, it is connected to the line processing unit (ASM) 13b. Therefore, the subscriber accommodation unit (SBM) 13a and the line processing are processed. Further reduction of the transmission path to the unit (ASM) 13b can be expected.
[0042]
As described above, according to the above-described embodiment, in the subscriber exchange for public communication service, the channel structure based on the ISDN basic interface or the primary group interface in which the distribution switch 21b is multiplexed for each subscriber terminal device. A predetermined one B channel or D channel is taken out from within the frame, and a frame handler (FH) 21c takes out PPP frame data from the data in the channel from each subscriber terminal device taken out for each subscriber terminal device. A path to the economical IP network is obtained by adding an in-device header for identifying a subscriber in the exchange to the frame and then performing frame multiplexing, and the IP network interface 21f transmits the multiplexed frame to the outside. Can be obtained.
[0043]
As a result, it is possible to significantly reduce the resources used in the exchange when accessing the IP network via the subscriber exchange. Furthermore, it becomes possible to connect the PPP terminator installed at the ISP access point and the exchange with a multiplexed line, and the increase in equipment on the PPP terminator side can be suppressed.
[0044]
In addition, the subscriber can expect an economic effect of reducing the charge burden in the IP connection via the public communication network.
[0045]
【The invention's effect】
According to the present invention, line efficiency can be improved when connecting to an IP network using an ISDN network.
[Brief description of the drawings]
FIG. 1 is a diagram showing a network configuration in a first embodiment according to the present invention.
FIG. 2 is a diagram showing a functional configuration of a subscriber exchange according to the first embodiment of the present invention.
FIG. 3 is a diagram for explaining a distribution process between a packet including a control signal and a packet including data in a frame handler.
FIG. 4 is a diagram for explaining frame distribution processing in a frame distribution unit.
FIG. 5 is a diagram showing a protocol stack in the network according to the first embodiment of the present invention.
6A is a frame format of data input to a subscriber switch, and FIG. 6B is a frame format of data output from the subscriber switch.
7A is a diagram illustrating a LAPD frame format, and FIG. 7B is a diagram illustrating a LAPF frame format;
FIG. 8 is a diagram illustrating an X.X. It is a figure which shows a 25-PPPoE conversion table.
FIG. 9 is a diagram showing a functional configuration of a subscriber exchange according to the second embodiment of the present invention.
FIG. 10 is a diagram illustrating an example of a network configuration at the time of conventional IP connection.
FIG. 11 is a diagram showing a functional configuration of a conventional exchange.
FIG. 12 is a diagram showing a protocol stack in a conventional network.
[Explanation of symbols]
10. Terminal (subscriber terminal equipment)
11. Terminal adapter (TA)
12 Network termination unit (DSU)
13. Local exchange 13a. Subscriber accommodation (SBM)
13b. Line processor (ASM)
14 PPP termination device 20a. OCU (ISDN subscriber circuit)
20b. Concentration switch sections 20c, 21a, 21h. SDH transmission interface 20e. PPP frame multiplexing processor 21b. Distribution switch part 21c. PPP frame multiplex processing unit and frame handler 21d. I subscriber line signal processor (ISIG)
21e, 40. Frame distribution unit 21f, 42. IP network interface unit 21g. Processor

Claims (2)

A PPP (Point-to-Point Protocol) frame , a LAPD (Link Access Procedure on the D-channel) frame, or a LAPB (Link Access Procedure Balanced) frame transmitted through one of a plurality of subscriber lines. Receiving means for receiving information including a frame ;
Identifying means for identifying a subscriber of the information by identifying the subscriber line through which the received information has been transmitted;
Multiplexing means for converting the accepted LAPD frame or LABP frame into a PPP frame included in the information, converting the received LAPD frame or LABP frame into a LAPF (Link Access Procedure for Frame Mode Bearer Service) frame, and adding the identification information to multiplex the PPP frame When,
A PPP frame multiplexing apparatus comprising: output means for referring to the identification information and converting the PPP frame into PPPoE (Point-to-Point Protocol over Ethernet) for each subscriber ; The multiplexing of the PPP frame is performed in X. Frame multiplexing device according to claim 1, wherein performing by multiplexing the 25 packets.

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