9.3 Structure of ACS networks

Despite the fact that the signaling network relies on a network of channels that transmit basic information (voice and data), the structure of signaling networks may be different. The main goal will be to ensure reliability. In most cases, a structure is built that provides several alternative paths. When considering the formats of the ACS network, attention was drawn to the signaling link selection feature (SLS). It allows you to organize roundabout routes. For this, a network should be built that has several alternative signaling paths. Therefore, a “signaling mesh network” is being built, where each of the previous signaling nodes is connected to at least two of the following. In addition to network methods of ensuring reliability, methods of station redundancy of ACS equipment and allocation of backup channels (with the exception of the 16th channel intended for this purpose) are also used, to which the signaling system links are transferred consistently when communication is lost in the main signaling direction.

Network management functions of the OKS number 7

These functions were also considered, as they are reflected in the format of the network management of the ACS. Therefore, we limit ourselves to their listing.

• The functions of the control signaling traffic in violation of networks of alarm systems.
• Functions for measuring signaling traffic.
• The procedure for the transition to the reserve and the transfer of traffic to an alternative link.
• The procedure for returning to the original link.
• The procedure to prohibit control of the signaling link when performing testing or maintenance.
• Management of signal traffic in case of overload.
• Alarm link management (link activation, deactivation).

The main procedures of these processes are given in the recommendations of ITU-T Q.701-704 of the White Paper.

Next generation network

The next generation network (NGN - Next Generation Network) [19, 20, 36, 55, 68, 70] is a broad term that reflects the evolution of communication networks and access networks [61]. The main idea of ​​this type of networks is to create a unified transport network for all types of information and services (speech, mobile and still image, data and all multimedia services) by transmitting packages such as those used, for example, on the Internet. NGN generally uses the Internet protocols that were discussed in the previous course.

NGN can provide services related to broadband to provide a given quality of service (maintain the value of QoS) regardless of the technology of the transport network. Such a network supports the communication of mobile objects.

The main components of the new generation network:

• The core network, which consistently (by allocating sites or using the overlay method) turns the transport networks used for various services into a single transport network (more often based on the principles of Internet or Ethernet). It is assumed that the voice service will be transformed from the circuit-switched Public Switched Telephone Network architecture to a packet-switched voice network (VoIP) network. A voluntary commercial transition from existing services such as X.25, Frame Relay to Internet services (IP) and virtual private networks (VPN) or technical simulation of existing services on the NGN network is also contemplated.
• The subscriber access network assumes a transition from “two-wire” access to xDSL as the first step of access at local stations to the next step - installing a digital subscriber Line Access Multiplexer (DSLAM), an integral voice transmission port, which allows remove the switching station.
• In the cable network (trunk section), a transition from voice transmission at a constant speed to a service that provides multiservice services (VoIP and SIP) is assumed.

NGN is characterized by a clear separation between the transport part and the services that are transmitted through this transport network. This means that if the service provider wants to introduce a new service, he can do it at the application level without going into the details of the transport layer, i.e., the service is independent of the characteristics of the transport layer. For example, a service that includes voice transmission may be independent of the access network and contain more than one type of terminal (telephone, personal computer, etc.).

NGN is based on technologies including Internet protocols and Multiprotocol Label Switching (MPLS - Multiprotocol Label Switching). At the application layer, H.323 is applied, which is superior to the ITU protocol. Initially, H.323 was more popular, although its popularity suffered due to the difficult connection to the network address translation (NAT) and security programs. For this reason, local voice service (VoIP) services have been developed with extensive use of SIP.

However, in voice networks, large companies use H.323 in the core network.

For speech applications, an important component is the Softswitch, a programmable device that performs call service control functions, signaling, and functions that establish a connection through one or more networks, that is, a programmable device that controls voice transmission over IP.

This allows you to correctly adjust the various protocols in the NGN.

The most important functions of the Softswitch: creating interfaces with existing telephone networks using signaling (SG - SignalingGateways) and information gateways (MG - Media Gateways). However, the term Softswitch defines the equipment of a different manufacturer and performing various functions.

Often the term "Gatekeeper" is used in the literature in the NGN. Initially, it was a device designed to switch channels (PSTN, ACS No. 7) to a packet form and converts speech and data from analog or digital form. This information passes through one or many gateways. Transport Gateway Control Protocols (MGCP) are used to control telephony gateways and interact with transport gateway controllers. Softswitch call control functions are sometimes distinguished in the Call Agent function, but the term Softswitch is broader and more accurate. [A.B. Goldstein, B.S. Goldstein SOFTSWITCH SPb. BHV - St. Petersburg, 2006, 368 p.]. The European Telecommunications Standards Institute (ETSI) and the 3rd Generation Partnership Project (3GPP) have defined the standard NGN for multimedia services on the Internet as an IP Multimedia Subsystem (IMS - IPMultimedia Subsystem) [IP Multimedia Subsystem is a universal architecture for services. Nikolay Silakov. October 10, 2006].

The IMS architecture has been developed for use in third generation mobile networks. Support for the Session Initiation Protocol (SIP) allows you to apply a unified approach to the implementation of applications and access, as well as integrate applications offered by third-party companies (for example, content providers).

The concept of creating an IMS architecture was so successful that some standardization bodies proposed using it for multiservice solutions in their market sectors. The European Telecommunications Standards Institute ETSITSPAN Working Group (Telecom & Internet converged Services & Protocols for Advanced Networks - converged telecommunications and Internet services for modernized networks) develops specifications for fixed networks, mainly applying in 3GPR developments. Organization Cable Labs, which develops standards for networks of cable operators, in the Fast Cable 2.0 specification provides for the introduction of SIP. And everywhere at the core lies the idea of ​​IMS.

The concept of IMS really embodies the principle that this architecture should have the ability to establish a large number of communication sessions, and the subscribers participating in these sessions can use different access devices. Subscribers are offered all sorts of services, delivery of which is based on a common approach.

In particular, this architecture should have the ability to solve problems such as the implementation of several services within a single communication session. So, voice calls can quite often be accompanied by a determination of the availability of the called party (the so-called "attendance service"). At the same time, the served subscriber should have no problems with different types of terminal equipment. In particular, the establishment of a communication session should be guaranteed in the case when the terminal used does not have certain functionality. This means that during a video telephone call, it is possible to receive it without the video component, or the video will be redirected to another device.

Brief summary

• Intellectual networks are based on the resources of public telephone networks and provide the user with access and performance of a certain set of intellectual services.
• The architecture of the intelligent network platform contains: a regular telephone node, a service switching node, intelligent peripherals, a service control node, an operational management system, and a service creation environment.
• The generic predictive call service model uses the following concepts: call status point, event detection point.
• The ACS network, ideally, largely repeats the public network. Each of the nodes and each station of a long-distance, zone and local (urban or rural) network has an alarm system.
• The system of connected ACS is not always economically justified, or it cannot be strictly implemented, given emergency situations, so there is a need to create a quasi-connected network. In this case, the ACS network begins to acquire a character distinct from the public network that it accompanies.
• In Russia, two formats of signaling point codes have been adopted, the size of which, in accordance with ITU-T recommendations, is 16 bits. They contain a network indicator (IC) consisting of 2 binary characters (IC) and a signaling point code consisting of 14 binary characters (CPS).
• Next Generation Network (NGN) is a broad term that reflects the evolution of communication networks and access networks. The main idea of ​​this type of networks is to create a single transport network for all types of information and services (speech, moving and still image, data and all multimedia services) by transmitting packets.