Signaling network SS7 is a common channel signaling №7. This network is a set of telephone signaling protocols around the world use to configure the majority of telephone exchanges. With this technology, you can get a smart phone network, which will have broad functionality for end users, as well as provides an opportunity to convergence (for example, with VoIP-networks and the public switched telephone network).
Telephone network SS7 network is a dedicated data packet of variable length (up to 274 bytes). These packages are called signal units.
Hosts SS7 signaling points are called (SP — Signaling Point). The attributes of the signal points are:
SPC — Signaling Point Code — code signal points (14-bit)
NI — Network Indicator — Network ID (2 bits)
NI = 10 — a national network
NI = 11 — departmental or regional network
NI = 00 — international network
SPC code can address the signaling messages between nodes within the same network SS7, for example within a national network. It is not sufficient for addressing messages between signaling points different SS7 networks.
SS7 node types
SS7 network has channels and nodes. Nodes are the physical elements of SS7, but the channels are signaling pathways exchange of data between the nodes.
Often in the SS7 network using 3 devices:
- service switching device (SSP — Service Switching Point),
- signal transmission apparatus (STP — Signal Transfer Point)
- device management service called another alarm device (SCP — Service Control Point).
The advantages of using SS7:
- Expansion of services without having to replace the equipment. Thanks to the introduction SS7 operators can generate new services. Thus, there is no need to replace the old to the new equipment. Thanks to the introduction SS7 you can perform the following services:
- conversion of telephone numbers (eg, toll free — free number is converted to a regular subscriber number PSTN)
- Automatic Caller ID
- blocking subscriber numbers
- automatic redirect
- Call Hold
- prepaid calls.
You get a universal structure for the organization messaging, voice and data networking and maintenance of the telephone network. Once the connection is established, the protocol starts to share user information, call routing, billing and interaction with intelligent services.
Solve problems with security. The subscriber does not have access to the signaling channel since moved to separate signaling channel.
You can use the packet-switched network. This is one of the most visible manifestations of the trends implementation of open information systems. Signaling network SS7 — an important link between the circuit-switched networks and communication networks, based on the protocol IP.
SS7 signaling system enables high speed connection setup and data transfer (without loss or duplication), switching traffic to alternative routes in case of failure, a convenient structure for processing messages broadcast phone number.
High efficiency. At the switching station requires several times less equipment performance (service one thousand call signaling channel) and reliability (due to alternative signal routing, and redundancy of channels).
Where to use SS7
SS7 network is intended for operators of local, long-distance communication, as well as used in wireless networks. I can even say more — SS7 telephone network has become almost an integral part of the cellular and telephone networks. Not for the first ten years of its use in the public telephone networks.
SS7 standard adopted by the International Telecommunication Union (International Telecommunications Union, ITU), but in each country version of SS7 have their own characteristics.
SS7 standard defines the procedures and protocols by which the device (switching stations) can exchange information in networks PSTN. SS7 channels are used to transmit information about the connection establishment and routing. In networks for SS7 PSTN can use a dedicated signaling network (digital overlay network) — channels on 56/64 kbit / s. The special SS7 network and backup channels make it more reliable and secure.
Why use SS7
Scope of the SS7 signaling network extends to broadband networks, and computer telephony applications.
Further development of public telephone networks depends on the widespread introduction of SS7. The fact that the channels are used to transmit SS7 data connection setup and routing, and a dedicated network and reservation channels make it more reliable and secure.
The technology provides a powerful incentive to the rapid development of both the concept of intelligent networks and modern concepts of converged networks.
SS7 signaling network forms the basis of creation of intelligent services. They can be realized in the form of a packet and the telephone network using suitable protocols. The main thing is that any telecommunications task or application should use it if you need access to the telephone network.
How to install intelligent networks
Intelligent network — a network that offers customers additional communication services. That the company can provide subscribers with services such network nodes must be SS7: Service Control Point (Service Control Point, SCP) and service switching points (Service Switching Point, SSP).
To be able to send and receive messages, you must have transit points for transfer of signaling messages (Signal Transfer Point, STP) — packet switches network SS7, which carry out switching or routing in the network (usually the network SS7 STP implemented on automatic switching nodes or transit switches and in regional networks of local operators — on long-distance stations, networks of mobile operators — in the switching center MSC).
Points SCP is responsible for call forwarding, caller identification, etc.. Function. This allows you to cost-effectively develop services, regardless of the switching equipment.
How to implement SS7
Manufacturers of active telephone and network equipment problem of constructing multi-service networks, voice and data decide differently. Thus, the market offers a lot of options, among them becomes difficult to find the right price and quality goods.
Usually proizvoiteli offer solutions most frequently requested by customers. For network integration features switches and media gateways (Media Gateway, MG), which support SS7. Gateways SS7, consisting of gateway controller physical layer (Media Gateway Controller, MGC) and signaling gateway (Signaling Gateway, SG), provides an interface IP and SS7, simplify the creation of a single network multiprotocol environment. An example of such a gateway is Terratel SIP / E1 Gatewau.
This gateway supports SS7 and therefore can access the databases of telephone network, which will provide users with services IN (prompting the appropriate telephone network service). Control the operation of media gateway controller receives a signal from the information packet and telephone networks and process it. In an IP network, this information is transmitted over IP (for example, H.323 or SIP protocols).