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Signaling System No. 6 (SS6) was introduced in the 1970s as an early common channel signalling method for telecommunication trunks between international switching centers (ISCs). It is specified in CCITT Recommendations Q.251-Q.300. [1]
In telecommunication, signaling is the use of signals for controlling communications. This may constitute an information exchange concerning the establishment and control of a telecommunication circuit and the management of the network—in contrast to manual setup of circuits by users or administrators, for example the sending of a signal from the transmitting end of a telecommunication circuit to inform a user at the receiving end that a message is to be sent.
In telecommunications, trunking is a method for a system to provide network access to many clients by sharing a set of lines or frequencies instead of providing them individually. This is analogous to the structure of a tree with one trunk and many branches. Examples of this include telephone systems and the two-way radios commonly used by police agencies. Trunking, in the form of link aggregation and VLAN tagging, has been applied in computer networking as well.
The system had limited applications since at that time the predecessor systems Signaling System No. 5 (C5) and C4 were widely in use, but there was a need to experience common channel working on a fast digital basis.[ citation needed ]
The Signaling System No. 5 (SS5) is a multi-frequency (MF) telephone signaling system that was in use from the 1970s for International Direct Distance Dialing (IDDD). Internationally it became known as CCITT5 or CC5. It was also nicknamed Atlantic Code because it was used for the first IDDD connections between Europe and North America.
Traffic switching in the ISCs was then typically handled by crossbar switches or electronically controlled cross-points such as reed relays. The transmission media were likely satellite links or long terrestrial submarine cable channels. In some cases these were advantaged or multiplied with time-assignment speech interpolation (TASI) or digital circuit multiplication equipment (DCME). These transmission methods were not suited to line or inter-register signalling. Taking the signalling function away from the traffic channel could cut costs, and would later lead to Common Channel Signalling. There would be no need for filtering signalling away from speech, and the duty cycle of the costly trunk for each revenue earning call would be better. Signalling time in call set up and clear down would be significantly shorter than with C4 and C5. With telephone signalling not transmitted over the line, the opportunities for fraud were reduced.
In electronics, a crossbar switch is a collection of switches arranged in a matrix configuration. A crossbar switch has multiple input and output lines that form a crossed pattern of interconnecting lines between which a connection may be established by closing a switch located at each intersection, the elements of the matrix. Originally, a crossbar switch consisted literally of crossing metal bars that provided the input and output paths. Later implementations achieved the same switching topology in solid state semiconductor chips. The cross-point switch is one of the principal switch architectures, together with a rotary switch, memory switch, and a crossover switch.
A reed relay is a type of relay that uses an electromagnet to control one or more reed switches. The contacts are of magnetic material and the electromagnet acts directly on them without requiring an armature to move them. Sealed in a long, narrow glass tube, the contacts are protected from corrosion. The glass envelope may contain multiple reed switches or multiple reed switches can be inserted into a single bobbin and actuate simultaneously. Reed switches have been manufactured since the 1930s.
A transmission medium is a material substance that can propagate energy waves. For example, the transmission medium for sounds is usually a gas, but solids and liquids may also act as a transmission medium for sound.
The CCITT 6 signalling channel was typically a 2.4 kbit/s data link. Technology at the time was an M1040 or M1020 analogue Four-wire circuit presented private circuit link. Modems were slowly beginning to exceed these data rates over 4w circuits; these data links had the advantage that there was no national tail from the ISC out to a normal end point in the country. It was often the National Section that detracted the most from the quality and reliability of such links.
In telecommunication a data link is the means of connecting one location to another for the purpose of transmitting and receiving digital information. It can also refer to a set of electronics assemblies, consisting of a transmitter and a receiver and the interconnecting data telecommunication circuit. These are governed by a link protocol enabling digital data to be transferred from a data source to a data sink.
In telecommunication, a four-wire circuit is a two-way circuit using two paths so arranged that the respective signals are transmitted in one direction only by one path and in the other direction by the other path. Late in the 20th century, almost all connections between telephone exchanges were four-wire circuits, while conventional phone lines into residences and businesses were two-wire circuits.
A leased line is a private bidirectional or symmetric telecommunications circuit between two or more locations provided in exchange for a monthly rent. Sometimes known as a private circuit or data line in the UK.
The data circuit known with a DP designation, would have been terrestrial with no TASI or DCME, and the C6 signalling on the data link could perform for 48 or 96 traffic channels. It could function for up to 2,048 in the maximum. The question is whether two operators would have that many traffic channels between them, dependent on just one bearer for signalling and subject to occasional failure. It was of course practice to have standby route over a diverse path in case of outage on the original DP data circuit link.
A circuit ID is a company-specific identifier assigned to a data or voice network connection between two locations. This connection, often called a circuit, may then be leased to a customer referring to that ID. In this way, the circuit ID is similar to a serial number on any product sold from a retailer to a customer. Each circuit ID is unique, so a specific customer having many circuit connections sold to them would have many circuit IDs to refer to those connections. As an example of a use of the circuit ID, when a subscriber/customer has an issue with a circuit, they may contact the Controlling Local Exchange Carrier telecommunications provider, identifying the circuit that has the issue by giving the LEC that circuit ID reference. The LEC would refer to their internal records for this circuit ID to take corrective action on the designated circuit.
Finally it was considered possible that a mesh of such data channels could be set up between major centres, leading to a system where the link between country A and country B could perform the signalling functions for links to country A from country D for example.
CCITT No 6 was a method developed & implemented by administrations in a limited number of countries for use in correspondent International Switching of analogue telephone calls. The next development was correspondent and non-correspondent switching of telephone calls by new operators in the countries where more sophisticated methods were required.
