4.2 Tabular method, or the method of the universal program

Its characteristic features are:

• The mathematical task of objects, which is expressed in writing algorithms in the form of recursive or tabular functions.
• Description of processes from the point of view of the automaton model.

Objects

The objects on which actions are carried out are station sets, switching fields. In this case, the station will be considered. Sometimes virtual objects are used for processing. An example of a real object is the set of analog subscriber line, considered in "Algorithms of individual functions performed in program-controlled stations". The processing request follows from the kit towards the external environment after the subscriber has picked up the handset.

According to the concept of an object, it has the attributes necessary to work with this object. For example, these may be:

1. Type of kit. This attribute in our example allows us to determine the list of programs for processing a subscriber call.
2. Kit number. The station may have hundreds of thousands of sets of the same type. The number allows you to determine which of them need to work.
3. The status of the kit. This attribute indicates the stage at which work is performed by the external environment with this set (the set is free, busy, blocked, etc.) The value of this attribute, in contrast to the attributes discussed above, changes during work.

Each of these attributes can be numbered and represented as a function parameter, called a subscriber set - f _AK (x ₁ , x ₂ , x ₃ , ... ... x _n ).

Other kits have similar attributes. For example, considered in the example of establishing a connection in a fully decentralized system ("Switching fields on the microelectronic element base"), the multi-frequency set receiver (MFEL) has the same attributes as the subscriber set:

1. Type of kit
2. Kit number
3. Kit status

However, it has several characteristic attributes, for example:

1. Number of accepted digit (possible values ​​1, 2, 3, ...)
2. 1st digit value
3. 2nd digit value
4. etc.

These attributes are also involved in call processing.

Dynamic object - connection

Objects can be virtual (imaginary), which do not really exist, but are described logically and are displayed only in memory. One of these important objects is the connection.

For many systems, the connection exists in real equipment, displaying a temporary set of devices that implement the physical connection of the two end terminals.

Let's give an example. It has already been considered in detail in the section "Establishing a connection in fully decentralized switching systems" ("Switching fields on microelectronic element base", Fig. 2.18). Below (Fig. 4.2) we present an abbreviated version to illustrate the concept of a virtual object "connection". In this example, the subscriber set (AK1) is connected to the multi-frequency transmitter module (MCHP) for transmitting the dialing number. According to the algorithm considered earlier, the subscriber dials the number of the incoming subscriber, after which another part of the multi-frequency transceiver (MCPP) dialing is connected to the module of subscriber analog lines of the incoming subscriber (subscriber set AK2) to determine its state. After these actions, a new "connection" object appears at the station, which is displayed using the addresses of the bundle. To do this, the attribute number of the address of the bundle - N _{CB is} added to the attributes of the real object. Its value indicates the type numbers and the number of the kit connected to the data. Then the function, reflecting, for example, the object AK1 as a function with the help of its attributes (parameters), has the form

f _AK1 = f (N _type , N _AK1 , N _CB ),

Where

N _type - the _type number of the kit, in this case the type AK (usually this type is assigned the number 1);

N _AK1 - the number of the set among its type of AK (for example, from 100 to 10000, depending on the capacity of the station);

N _MCPP - a set number among its own type of MPPP (for example, from 100 to 10000 depending on the capacity of the station);

N _CB - communication number (values ​​are determined by the type and number in the type of sets involved in the connection).

Similarly, the object considered in the example is shown.

f _MCPP = f (N _type , N _MCPP , N _{CB ,,} N ₁ , ..., N _K ).

enlarge image
Fig. 4.2. The principle of creating and displaying the "connection" object a) a conditional image of the connection of real equipment, b) a distributed display of the connection using a communication address. c) centralized mapping of the connection using the communication address.

The only difference is in the number of the type, which must take the value assigned to this type of kit, and in the additional parameters of the characteristic of the dialed number, which are mentioned above, designated N ₁ , N ₂ ..., N _k .

Note that the "connection" object is dynamic. It changes during the process of establishing a connection. In the processes that provide data transfer, it does not necessarily have an analogue of the connection of real equipment. It can display virtual path or channel parameters. Functionally, the “connection” object can be mapped in two ways: decentralized (Fig. 4.2b), centralized (Fig. 4.2c).

In the decentralized method, the connection is displayed by recording the number and type of the previous device in place of the variable "communication address" (N _CB ) of the subsequent device (this is shown by arrows). For reliability, the type and number of the last device is written to the communication address of the first device (the "ring" is closed).

With the centralized method, a new virtual device is created - a “process” in which the communication addresses — the numbers and the type of participants in the connection — are written to the variable addresses.

The connection object may also have its attributes (for example, a connection category) that are not listed here.

Servers

According to the concept of architecture of distributed computing resources (one of which is CORBA), the objects act as clients that are serviced by servers. The servers used in the tabular approach were previously considered in the form of algorithms for individual functions. The problem is that, at the request of the client, only certain functions must be called and in a certain order. For this, the method in question offers a tabular record of a function (universal program).

For further study, we will clarify the terms used.

Universal program

This is one of the main results of the theory of computability, the stated method is its first application, in addition to mathematics. Without going into mathematical details, give a quote [12, 33]:

"Universal programs are programs that, in a sense, implement all programs. At first, the existence of a universal program seems implausible. Nevertheless, it is not difficult to verify that it exists. The bottom line is that a universal program does not have to contain all other programs. It should be able to encode and decode the numbers of all programs that can be recorded and valid in a given programming language. "

You can add that the program is a sequence of given commands. The number of such sequences is large, but not infinite and can be listed. It is amenable to the natural description in the form of their numbers. A theoretical study of universal programs is beyond the scope of this course.