Abstract: The V5 connection is access network (AN) and between local switchboard (LE) the standardized open connection. This article first briefly introduced that the V5 connection agreement structure, then gives in the IDS2000 synthesis digital communication system the V5 connection to realize the method; Introduced emphatically the third agreement the software realizes the method, and carries on some discussions to the embedded system programming.
Key word: Access network V5 connection real-time operating system local switchboard
Introduction
Access network’s concept is develops by the traditional subscriber’s line. In recent years, because telephone business’s development, the new service type increased, to the line band width request’s enhancement as well as each kind of emerging technology (was specially fiber optic communications technology) the development, enabled traditional the subscriber’s line concept to develop into access network’s concept gradually. Most recent several years, International Telecommunication Union (ITU) formal definition user access network. After introduction access network, the existing telecommunication network will reduce the end office quantity, the simplified junction network complex degree, is advantageous in the junction network management.
The access network covers the scope may limit by three kind of connections, as shown in Figure 1. The connection standardization, the comprehensive immediate influence to access network’s construction cost and the access network could load bearing professional ability, for this reason, ITU-T overall evaluation each kind of need, pass finally about between the access network and the local switchboard standardized V5.1 and V5.2 connection suggestion [1,2].
The V5 connection is one kind the applicable scope is broad in the access network, the standardized degree high new opening digital interface, applies, many kinds of service development and the network renewal vital role regarding equipment’s development. The V5 connection’s standardization has represented the important network evolution direction, affects profoundly. Its significance lies in the switchboard to be possible to support many kinds of types through this connection user turning on, moreover V5 connection’s openness means that the switchboard and access network’s technology and the service evolution are completely independent.
Access network’s development may switchboard’s limit, not cause the access network market to open completely.
First, V5 connection agreement structure
Narrow band V5 connection including V5.1 and V5.2 connection. The V5.1 connection by 1 2048Kb/s link constitution, through the time slot transmission common control signal, supports simulation telephone turning on, (2B D) and uses in half permanent connection based on the 64Kb/s comprehensive service digit network basic access, not adding outside the belt signaling information other simulation turning on and digital turning on. These turning on type has the assignment load-carrying channel assignment, namely in the user port and the V5.1 connection the load-carrying channel has the fixed corresponding relationships. The V5.2 connection on demand must be possible by 1~16 2048Kb/s link constitution, besides to support the V5.1 connection the service, but also supports ISDN PRI (30B D) to turn on, it enables the V5.2 connection based on call’s time slot assignment to have the centralized function. The V5.1 connection is the V5.2 connection subset, the V5.1 connection must be able to promote to the V5.2 connection.
The V5 connection agreement is composed of 3, the access network side and the local switchboard side assume are asymmetrical arrange, between the level and the level information transmission uses primitive realizes, but uses the mapping with the straton level’s information transmission.
The V5 connection physics level by 1~16 2048Kb/s link constitutions, electrical and the physical property conforms to G.703 to suggest that the frame structure conforms to the G.704/G.706 suggestion. Each frame is composed of 32 time slots: Time slot TS0 serves as the frame localization and the CRC-4 regulations; Time slot TS15, TS16 and TS31 may serve as the correspondence circuit (the C circuit), the delivery signaling information and the control information, assign through the assignment; Other time slots may serve as the load-carrying channel.
The V5 connection’s data link layer only speaking of the C circuit. The second agreement (LAPV5) standard suggested in Q.921 stipulated the LAPD agreement and the regulations will be the foundation, the permission will come up nimbly the different information flow multiplying to the C circuit. The second agreement divides into two sublayers: Seal function sublayer (LAPV5-EF) and data link sublayer (LAPV5-DL). In addition, in the second function should also include frame relay function (AN-FR).
The V5 connection’s third agreement bunch including the PSTN agreement, the controlling agreement, the link control protocol, the BCC agreement and the safekeeping agreement (latter three kind of agreements is the V5.2 connection unique). The PSTN agreement is responsible to process and the PSTN service related signaling; The controlling agreement is responsible for the user port status indicator and the control, coordinated both sides under network management control data assignment; The link control protocol is responsible to be coordinated and to control AN, LE both sides link blocking, the link to relieve blocking and the link marking function; The BCC agreement uses for a specific 2048Kb/s link on the load-carrying channel based on the call distribution for the user the port; The safekeeping agreement provides the V5.2 connection when presents the breakdown to correspond the way cut protection function.
As shown in Figure 2, when the third agreement has the signaling information needs to transmit, through the data link sublayer (LAPV5-DL), requested that the seal function sublayer (LAPV5-EF), with the seal function address transmission data link sublayer end-to-end data which assigns.
Second, V5 connection realization
The author once participated in the IDS2000 synthesis digital communication system (access network side) the V5.2 connection opening development work. The IDS2000 synthesis digital communication system is the electric power automation research institute to satisfy one kind of synthesis turning on equipment which the electric power communications network need to develop develops. This equipment has the V5 connection, causes the IDS2000 system to be possible very conveniently through the opening connection and the gross-austausch equipment interconnection, the audio frequency Z connection which or the specific interface originally substituted has turned on when gross-austausch equipment uses.
The V5 connection agreement is divided 3 structures. The physical level and the data link layer partial functions realize by the hardware, this in ultra large scale integrated circuit swift development’s today, the difficulty already is not too big. Mitel Corporation produces large-scale E1 connection chip MT9075 is one kind of very appropriate chip [3]. MT9075 is one kind of list E1 connection, synthesized the framing and LIU. The important characteristic including data link turning on, the warning, the interrupt, the link returns and diagnoses, and in has inlaid two HDLC controllers (MT8952), is suitable specially in the V5 connection (seal function sublayer function and the HDLC agreement similar).
The V5 connection’s third agreement contains the content to be many, realizes by the software. This article mainly unifies the embedded system programming to introduce that the V5 connection the third software architecture, realizes regarding the agreement detail gives unnecessary detail not much.
1. real-time multi-duty operating system [4]
At present, an embedded application domain’s development tendency is uses real-time multi-duty operating system RTOS (Real Time Operating System). The RTOS widespread use and the application complication concerns. In the past 1 monolithic integrated circuit application procedure controlled the peripheral device and the fulfillment duty were not many, adopts the subroutine module which 1 main loop and several orders transferred then to satisfy requests; But 1 embedded control system possibly must simultaneously control/surveillance many peripheral devices now, the request real-time response, has many processing duties, between each duty has many information transmissions, if still used the original method, has two problems: First, the interrupt possibly cannot obtain the prompt response, the process time is excessively long; Second, the system task are many, must consider each kind of possibility are also many, if each resources the dispatcher improper will create the deadbolt lock, will reduce the software reliability, the programming duty quantity becomes the index to increase. Is precisely this kind of situation appearance, is promoting the RTOS application rapidly expand.
Regarding the V5 connection, the system software work load is quite big, including 5 core protocol function’s processing, must manage many timers, has many user ports to need to monitor, and requests the real-time processing, if uses traditional the software programming method, very difficult to realize. In the IDS2000 system, the author uses VRTX the real-time multi-duty operating system [5] achievement to develop the platform, reduced software’s work load greatly, but uses the object-oriented programming method and the event driven news mechanism, enables the agreement procedure to have the redundant reliability, controllable, to be possible to observe, easy to maintain and the management.
2.V5 interface software diagram
As shown in Figure 3, the V5 interface software mainly includes:
(1) the data link layer module (only includes data link sublayer function, seal function sublayer completes by hardware board);
(2) PSTN protocol processing module;
(3) controlling agreement processing module (including user port state machine, assignment control state machine, common control state machine);
(4) link control protocol processing module (including link control state machine, link control L3 state machine);
(5) BCC protocol processing module;
(6) safekeeping agreement module;
(7) V5 connection AN side system administration module;
(8) V5 connection AN side resource management module;
(9) timer administration module;
(10) message handling module;
(11) user port module;
(12) 10ms timer interruption.
In the above module, the module 1~7 complete the V5 connection agreement the core function. And, the data link layer module the news which produces to module 2~7 carries on processing, hands over meets the oral plate by the V5 hardware to complete the seal function, transmits again for the LE side entity; The PSTN protocol processing module major function is establishes the user port condition and between the LE side domestic agreement entity relation; The controlling agreement module uses in expressing the user port status indicator and the control, but also and the system initiation, starts, the assignment related; V5 the connection AN side system administration module is the important part which the protocol function realizes normally, in AN and LE, between different FSM or between second agreement entity not direct correspondence, but is coordinated through the system administration between the V5 connection each agreement entity the operation. Moreover, the system administration is responsible from AN or in the LE each kind of functional module receives with the processing related condition and the breakdown information. Between the system administration or the service platform or the network management system and the V5 connection’s bridge, it is responsible to receive the maintenance order, and to V5 connection execution corresponding operation, momentarily to upper formation network management reporting technology system’s movement condition.
The module 8~12 complete the V5 connection agreement the auxiliary function. And the user port module is responsible for the user port status scan and the control, direct and hardware port relation; An side resource management module coordinates the BCC protocol processing module to complete in the V5 connection the BCC protocol function; The message handling module is to lighten operating system’s burden to set up, it is responsible for co-operating system administration various modules the news formation; The timer administration module is responsible for the timer which produces, in the management system management system to need, when the timer overflows, sends a message to the corresponding module; the 10ms timer interruption procedure is responsible for in the dispatching system needs the periodic movement the duty, the use “the signal quantity” (semaphores) the correspondence mechanism complete.
3. limited state machine
In the above program module, has the massive limited state machines (FSM), like in controlling agreement’s user port FSM, common control FSM, in the BCC agreement’s load-carrying channel connects FSM and so on. The limited state machine describes the communication protocol process general way, is one object-oriented description method, with realizes the procedure to have nothing to do with specifically. The limited state machine has the limited condition collection, in time which assigns willfully, must have the only determination condition, must rely on under some condition external input specific news triggering, can cause the condition shift or carry out some kind of task.
The limited state machine speaking of system other softwares is equal to one “the flight recorder”. It may receive the limited news group, may also transmit the specific news group, but its internal structure does not know for system other parts. Its function receives completely by it and sends a message the order to decide.
The limited state machine’s this description way is very suitable with the object-oriented method to realize. In the tradition realizes in the method, the state variable and the condition table may visit outside the state machine module, easy to be destructed. Object-oriented realized the method to provide one kind more structurized and more direct-viewing FSM realizes the method, favored “the data hideaway”, moreover these merits increased even more obviously along with the FSM scale. We only need probably define a FSM base class, using the seal, inherits with the polymorphism characteristic, FSM which is very easy from formerly to define in the base which class derives needs, reduced software’s work load easy greatly, the software also to maintain.
4. the timer realizes the mechanism
The timer regarding realizes the communication protocol function to have the very vital role correctly. In the V5 connection agreement has the massive timers, when the traffic load is big, possibly has several hundred timers also to move. Timer’s design is completes the V5 connection protocol function correctly an important part.
In this system is responsible by the timer management advancement to manage in the V5 connection all timers. Because each kind of timer requests the precision is various, selecting time’s length carries on the surveillance and the counting accumulation to various timers is the question key: The time-gap is too small, affects the systems operation efficiency; The time-gap is too long, affects timer’s precision. In order to solve this problem, in the system has established three kind of different resolution timers: 10ms, 100ms and 1s (resolution refers to counting interval gap).
If some application advancement must use the timer, information and so on news which must first transmit a news to the timer management advancement, in after the news should contain applies for timer’s resolution, preset count value, overflow, should transmit. After the timer management advancement receives this news, puts according to timer’s resolution it to the appropriate formation in fixed time, start fixed time. If the timer counting is zero, then expressed that this timer overflows, the timer management advancement should to the corresponding application advancement transmission overflow news, simultaneously be supposed to release this timer. If the application advancement requests to give up a timer on own initiative, should transmit a release timer news to the timer management advancement. In the news should contain applies for timer’s marking, the resolution as well as the overflow goal advancement, the target audience and so on. After the timer management advancement receives this news, seeks in the appropriate timer formation after this timer, its release. The timer management process management other each application advancement applies timer. In the timer management advancement, three chain tables use in depositing these 3 kind of different resolution separately the timer.
The timer management advancement completes the following some basic functions:
(1) manages 10ms, 100ms and the 1s three kind of timer chain tables.
(2), when the 10ms timing separation, should traversal the 10ms timer chain table, completes to the chain table in various timers’ counting processing. If has the timer to overflow, approaches the corresponding advancement transmission overflow news, and releases this timer from the timer chain table. Similarly, when 100ms or 1s timing separation at the appointed time, also deals with 100ms or the 1s timer chain table makes same processing.
(3) processes receives from other advancements to the news. When receives from other advancement transmission application timer’s news, should insert the timer which in the corresponding resolution timer chain table applies; In receives release timer’s news which comes after other advancements, should seek to this timer, and its release.
5. the compilation may the re-entry function
In the V5 connection has the massive functions to need to compile. Is different with the traditional programming environment, in this system, the V5 interface software movement in the multi-duty environment, the function reenterability (reentrancy) appears very important.
So-called may the re-entry function be refers to one to be possible by many task call process, the duty when the transfer does not need to worry whether the data will make a mistake. When compiles the function should as far as possible only use the local variable, regarding the global variable which must use needs to perform to protect (for example uses closes measures and so on interrupt, signal quantity), like this constitutes the function is certainly may the re-entry; But compiler whether to have may the re-entry storehouse, serves the operating system with it related, like under DOS Borland C and Microsoft C/C and so on do not have to be possible the re-entry function storehouse, this is because DOS is a single user, the single duty operating system.
In order to guarantee that each transfer function the task control oneself private variable, in one may in the re-entry C function, such variable declaration be the local variable, the C compiler deposits such variable in the transfer stack or the register. Under the VRTX operating system the compilation may the re-entry function, probably need to follow the following principle:
(1) will possess the local variable declaration will be auto or the register (register) the type;
(2) do not use static or the extern variable as far as possible, when inevitably uses the global variable, must protect;
(3) assigns the big construction of data with VRTX storehouse function sc_gblock.
Third, V5 connection development tendency
In the long run, to overcome existing a series of SNI (service node connection) the function limit, must develop SNI which attaches, specially module and B-ISDN turning on SNI. At present, as the foundation VB5 connection standardized work is carrying on take ATM. The VB5 reference point may divide into VB5.1 and VB5.2LIANG a form.
ITU-T already passed about the VB5 reference point suggestion, stipulated VB5 both to support AN and the SN direct connection, and supported both’s long-distance connection; Both supports based on the ATM B-ISDN turning on, and supports each kind of non-ATM the turning on. In addition, VB5 should also support turns on each kind of SN the turning on function, and can simultaneously connect many different SN. The related VB5 technical frame also waits for further studying and developing.
