CC BY
4
Mirsagdiyev Orifjon Alimovich, Tashkent Institute of Railway Transport Engineering Assistant
of the Department "Electrical connection and radio", E-mail: oamirsagdiev@yandex.ru Xalikov Abdulxak Abdulxairovich, Tashkent Institute of Railway Transport Engineering Doctor
of Technical Sciences, Professor of the Department "Electrical connection and radio", E-mail: xalikov-abdulxak@mail.ru
MODELS OF SERVICE CALLS IN THE RAILWAY NETWORKS
Abstract: Currently, the rail network communication share on the network operational technological communication (OTC) and overall technological communication (OvTC). They operate separately. In each of these networks are set switching stations serving only their subscribers.
Keywords: network operational technological communication, overall technological communication, network, model, dispatch communication.
1. Call service networks in OTC and OvTC the transmission of user information in a single commu-
Call service networks and resources in networks nication session. In this case, the individual channels are
OTC and OvTC fundamentally different. In the network OTC basic subscribers are dispatcher and subordinates them to performers who are united in the following dispatch communication. Dispatch circle is an isolated subnet OTC, which closes all calls. For each dispatcher circle offers a shared network resource: analog network -a group voice frequency channel, digitally - a group the main digital channel E0 (64 kbit/s). Calls coming in, served without losses and without expectations. The only time indicator of the digital service system is the time to establish the connection. This time in the digital network depends on the number of switching stations involved in the connection, signaling traffic load control devices. In the digital network to dispatch communication, affecting the safety of trains, this time should not exceed 2 seconds [1, 6-9].
In OvTC network subnet is not allocated, and the subscribers serviced primarily through a system with a loss of call. The exception is the call centers used to organize manual intercity stations (MIS) with semi-automatic and connections for passengers (booking and reservation of tickets, help desk). In these centers, calls from the subscribers served by the system with the expectation. Resource OvTC network is only available for
formed between subscriber user devices.
When you create digital networks with circuit, switching OTC attempts were partial federated systems OTC and OvTC. For example, switching stations were set up with distributed switching field, part of which was allocated for the OTC, and the other - for OvTC. Normative documents on the creation of digital systems allow for OTC systems the union of OTC and OvTC level connection management systems. These control systems presented a requirement for logical separation of call control functions in networks OTC and OvTC.
When switching to packet switching technology there are new preconditions for unification systems OTC and OvTC. Effective packet network transmission of information from different subnets on the same channels. In such a network, the principle of the separation of call control and switching processes, as well as the allocated function to provide additional services, for example conferencing. Therefore, in the packet network call control functions in the OTC and OvTC systems can be combined in a shared server, which controls the process of connections, user access to network services, distribution of network resources.
2. Model service call in the united network
It is possible to examine the following model of service call to the the united network, taking into account the features of systems and OTC and OvTC:
MODEL 1 - with a combined stream of information of all subscribers dispatch communication network OTC and all users of ObTS network;
MODEL 2 - with the union of the flow of information subscribers dispatch communication network OTC, except subscribers train dispatcher communication (TDC) and all the users ObTS network; TDC subscribers are provided with a dedicated resource network constantly. Consider the model 1.
MODEL 1 - shared resources for all subscribers OTC and OvTC. The subscribers are divided into three classes, depending on the priority of the call service. In the first class with the highest priority, include subscribers TDC circles. This class of subscribers serviced with an absolute priority, and thus no losses and standby. The second class is formed by subscribers of other dispatching circles: energy-dispatch communication (EDC), the service dispatch communication (SDC), linear-directional communication (LDC), wagons and administrative communication (VAC) and other. Here also may include subscribers of different dispatchers movement control, for example, DLU - dispatcher ofloading and unloading, DTLC - dispatcher to manage transportation ofliquid cargo and others. Calls from these subscribers are served with a relative priority when employment network resources calls are in the queue. The third class includes subscribers ObTS and they served no priorities for system calls loss. Calls may be lost for two reasons: due to the employment of all network resources and thus interrupt the connection. The latter occurs when a call from a first-class, and the absence of a free resource network [2, 80-85].
Table 1.
In figure 1 showing scheme of the model. The model calls three groups of sources, with the number of calls the group of sources corresponds to the number of subscribers of class. From the first and second sources of independent groups received primitive call flows, from the third - a simple call flow. Network resources are characterized by permissible number of concurrent connections - V. For call the second group of sources provides queuing, which are not limited by length. In queue calls are when the number of concurrent connections reaches the value V. Calls in the third group are lost with a probability Pp - due to reaching the limit established connections with probability Pl - in the case of interruption of the connection to subscribers of the first class. The intensity of the call receipts for the first (A.1) and second (A 2) source groups are defined by the formulas: X1 = (N1 - i)a1; X 2 = (N2 - i)a2 N1 and N2 - the number of circles for the dispatch of the first and second classes of subscribers; a1 and a2 - the intensity of the receipts of calls in one round for the dispatch of the first and second classes of subscribers, respectively;- i - the number of dispatch circles which are in a call condition.
The flow from the third group of sources - the simplest and is characterized by the intensity of calls A3. The intervals between calls are distributed exponentially. In this group, the number of sources is not limited. All call arrives intensities per unit of time adopted an hour. The duration of calls to subscribers of all classes is subject to an exponential law.
In the process of modeling the task of determining the value of V for specified load parameters must be addressed and indicators of quality of service calls.
The simulation was performed for two variants of the original data, given in table 1. Initial data
Variants Sources group 1 Sources group 2 Sources group 3
N1 t1, c al call./hour N2 t2, c a2 call./hour t3, c A3 call./hour
1. 10 26 47 20 40 12 90 800
2. 1200
In the model, the following quality service call rates can be obtained by:
- for the second class of subscribers: chance expectations Px; the average waiting time for all calls j and expectant caller j ;
- for subscribers of third class: of probability Pp, Pl and the probability of the common challenges of losses P. t1, t2, t3 - the average duration of calls to the appropriate sources of group. The following values have been taken V: in the first variant - from 24 to 40, the second variant - from 28 to 52.
Figure 1.
The simulation results are presented in graphs The dependense of Ihe probability of expectation Pe!! from V
1
\
2
24 29 34 39 44 49 54
V
Figure 2. 1 - variant 2; 2 - variant 1
0,8 0,7 0,6 0,5 ^ 0,4 0,3 0,2 0,1 0
The dependence of llie waiting time y from V
i
2
\
I
\
>
22
27
32
37 42 V
47
52
57
Figure. 3. 1 - variant 2; 2 - variant 1
Figure 4. Variant 1: 1 - Pc; 2 - Pp; 3 - P,
Figure 5. Variant 2: 1
Conclusion
To evaluate the results obtained in the simulation is necessary to set parameters of quality of service calls. Compare the model under the current system, in which the service calls from each group of sources occurs separately. In this case, for each group of sources in the network are allocated their own resources, with the first and second groups of sources the number of concurrent conTable
- P ; 2 - P; 3 - P,
c' p' l
nections equals the number of sources. Then, in each version 1 and 2 for the first and second groups of sources need to 30 simultaneous connections. In the third group for the service, subscribers need the following number of simultaneous connections: Variant 1-31, variant 2-42. Table 2 shows the values of the total number of concurrent connections V for the model and the system with a separate call service.
System of service of calls V
Variant 1 Variant 2
The reviewed model 39 51
A separate call service 61 72
The table shows that in case of association of groups of sources need to network resources by 35% (Variant 1) and 32% (Variant 2) less. Taking into account that for the subscribers of the second class wait-
ing is rare and short time, and for subscribers of third class - Interrupt are very rare, it can be concluded about the appropriateness of the model in practice.
References:
1. Лебединский А. К. Оценка качества передачи речи в сетях с коммутацией каналов и пакетов // Автоматика, связь, информатика. -2011. - № 11. - С. 6-9.
2. Теория телетрафика и ее приложения / В. В. Крылов, С. С. Самохвалова // СПб.: BHV - Петербург, -2005. - 288 с.
