SIGNALs in TelecomCAS, CCS7RTTC, HYD

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IntroductionA signalling system uses a language which enables two switching equipments to converse for the purpose of setting up calls. Telephony started with the invention of magneto telephone which used a magneto to generate the ringing current

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Types of Signalling Subscriber Line signalling Inter-exchange Signaling

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Subscriber Line signallingCalling Subscriber Line Signaling Called subscriber line signals

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Calling Subscriber Line SignalingAddress signal Decadic Dialling Multifrequency Push-button Dialling End of selection signal Answer Back Signal Release signal Permanent Line (PG) Signal

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The address digits may be transmitted as a sequence of interruption of the DC loop by a rotary dial or a decadic push-button key pad. The number of interruption (breaks) indicate the digit, exept0, for which there are 10 interruptions. The rate of such interruptions is 10 per second and the make/break ration is 1:2. There has to be a inter-digital pause of a few hundred milliseconds to enable the exchange to distinguish between consecutive digits. This method is, therefore, relatively slow and signals cannot be transmitted during the speech phase.

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It uses two sets of four voice frequencies a signal comprising of two frequencies. one from each group. Hence, it is also called Dual-Tone Multi frequency (DTMF) dialling

By this method, the dialling time is reduced and almost 10 digits can be transmitted per second.

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Called subscriber line signalsRing Signal Answer Signal Release Signal Register Recall Signal

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Inter-exchange signalingInter-exchange signaling can be transmitted over each individual inter exchange trunk. The signals may be transmitted using the same frequency band as for speech signals (inband signaling), or using the frequencies outside this band (out-of-band signaling). The signaling may bei. Pulsedii. Continuousiii. Compelled

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Supervisory signals Answer SignalBlocking Signal: To block the circuitClear-Back Signal: Indicate that the called party is cleared(in Reverse Direction)Clear-forward Signal: Terminate that call, to release the all switching units held Metering SignalReanswer Signal: In backward direction, indicating called party lifts the handset after clearSeizure Signal: Seize the Circuit

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Supervisory signalsSeizure-ACK SignalUnblocking- ACK SignalInter Exchange Signals: a) Line Signals: Related to Trasmission lines b) Register Signals: Related to Switching equippments

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Register signalsRegister signals are interchanged between registers during a phase between receipt of trunk seizure signal and the exchange switching to the speech phase. These signals are proceed-to-send (PTS) signals, address signals, and signals indicating the result of the call attempt.

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CSMFTo reduce transmission time and to increase reliability, a number of frequencies are used in groups. Normally 2 out of 6 frequencies are used. To make the system more reliable compelled sequence is used. Hence, this system is normally called compelled sequence Multi-frequency (CSMF) signalingIn CCITT terminology it is termed as R2 system.

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SIGNAL FREQUENCY INDEX AND WEIGHT CODE There is a provision for having 15 combinations using two out of six frequencies viz., 1380, 1500, 1620, 1740, 1860 and 1980 Hz, for forward signals and another 15 combination using two out of six frequencies viz., 1140,1020, 900, 780, 660 and 540 Hz, for backward signals. In India, the higher frequency in the forward group i.e., 1980 Hz, and the lower frequency in the backward group, i.e., 540 hz, are not used. Thus, there are 10 possible combinations in both the directions

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Inter Exchange SignallingWhen more than two exchanges are involved in setting up the connections the signaling may be done in either of the two modesEnd-to-end signalingLink-By-Link signalingGenerally supervisory (or line) and subscriber signaling is necessarily on link-by-link basis. Address component may be signalled either by end-to-end or link-by-link depending upon the network configuration.

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R2 MF Signalling CCITT standardized the R2 signaling system to be used on national and international routes. However, the Indian environment requires lesser number of signals and hence, a slightly modified version is being used.

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Signalling Freqs.FORWARD SIGNALS BACKWARD SIGNALS Each signal is acknowledged appropriately at the other end after the receiver checks the presence of only 2 and only 2 out of 5 proper frequencies.

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Digital Signalling Inter exchange signalling can be transmitted over a channel directly associated with the speech channel, channel-associated signalling (CAS) , or over a dedicated link common to a number of channels, common channel signalling (CCS). The information transmitted for setting up and release of calls is same in both the cases

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Channel- Associated signalling Though the speech sampling rate is 8 Khz, the signals do not change as rapidly as speech and hence, a lower sampling rate of 500 Hz, for digitization of signals can suffice. Based on this concept, TS 16 of each frame of 125 microseconds is used to carry signals of 2 speech channels, each using 4 bits

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Signalling Chl.

TS 16 of F1 contains signal for speech channels 1 and 16 being carried in TS 1 and TS 17, respectively, TS16 of F2 contains signals of speech channels 2 and 17 being carried in TS2 and TS 18, respectively and so on,

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Signalling Chl.Although four bits per channel are available for signalling only two bits are used. As the transmission is separate in the forward and backward direction, the bits in the forward link are called af and bf, and those in the backward link are called ab and bb. Values for these bits are assigned

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IntroductionControl information has to be transferred between the exchanges for call control and for the use of facilities. In digital, processor-controlled communication network, the amount and variety of the information to be transferred is accordingly larger. The information can no longer be economically transported by the conventional channel-associated signaling systems. For this reason, a new, efficient signaling system is required in digital, processor-controlled communication networks.

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Main Features

Internationally standardized (national variations possible).Suitable for the national, international and intercontinental network level.Suitable for various communication services such as telephony, text services, data services digital network (ISDN).

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Features contd.high performance and flexibility along with a future-oriented concept which well meet new requirements. high reliability for message transfer.processor-friendly structure of messages

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Features contd.use of the signalling links for transferring user data also. used on various transmission mediacable (copper, optical fiber)radio relay satellite (up to 2 satellite links)use of the transfer rate of 64 k bit/s typical in digital networks.used also for lower bit rates and for analog signaling links if necessary.automatic supervision and control of the signaling network.

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Signalling via a Common Channel Signalling link

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Signaling Points The SPs are the sources (originating points) and the sinks (destination points) of signaling traffic. In a communication network these are primarily the exchangesAll SPs in the signaling network are identified by means of a code within the framework of a corresponding numbering plan and, therefore, can be directly addressed in a signaling message.

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Signaling Transfer Points The STPs switch signaling messages received to another STP or to a SP on the basis of the destination address. No call processing of the signaling messages occurs in a STP

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Signalling Links A signaling link consists of a signaling data link (two data channels operating together in opposite directions at the same data rate) and its transfer control functions. A channel of an existing transmission link is used as the signaling data link

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Signalling LinksGenerally, more than one signaling link exists between two SPs in order to provide redundancyIn the case of failure of a signaling link, signaling traffic is rerouted to fault-free alternative routes.All the signaling links between two SPs are combined in a signaling link set.

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Signalling ModesAssociated mode : The signaling link is routed together with the circuit group belonging to the link . The signaling link is directly connected to SPs which are also the terminal points of the circuit group.This mode of signaling is recommended when the capacity of the traffic between the SPs is heavily utilized.

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Associated Mode of SignallingEXGE ASP

EXGE BSP

CIRCUIT GROUPSIGNALING LINK

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Quasi-associated Mode The signaling link and the speech circuit group run along different routes. The signaling for the circuit group is carried out via one or more defined STPs This signaling mode is favourable for traffic relations with low capacity utilization, as the same signaling link can be used for several destinations.

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Quasi-associated Mode

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Signalling RoutesThe route defined for the signalling between an originating point and a destination point is called the signalling route. The signalling traffic between two SPs can be distributed over several different signalling routes. All signalling routes between two SPs are combined in a signalling route set.

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Signaling Function PartsThe signaling functions in CCS7 are distributed among the following parts :Message transfer part (MTP)Function specific User Parts (UP)The functions of the MTP and the UP of CCS7 are divided into 4 levels. Levels 1 to 3 are allotted to the MTP while the UPs form level 4

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Functional Levels of CCS

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MTPThe message transfer part (MTP) is used in CCS7 by all user parts (UPs) as a transport system for message exchange. Messages to be transferred from one UP to another are given to the MTP. The MTP ensures that the messages reach the addressed UP, in the correct order, without information loss, duplication or sequence alteration and without any bit errors.

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Message exchange between two Signalling Points

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Functional LevelsLevel I (Signaling Data Link) defines the physical, electrical and functional characteristics of a signaling data link and the access units. Level 1 represents the bearer for a signaling link. In a digital network, 64-kbit/s channels are generally used as signaling data links

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Functional LevelsLevel 2 defines the functions and procedures for a correct exchange of user messages delimitation of the signal units by flags.error detection using check bits.error correction by retransmitting signal units.error rate monitoring on the signalling data link.restoration of fault-free operation

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Functional LevelsLevel 3 defines the inter working of the individual signaling links. A distinction is made between the two following functional areas : Message handling, i.e. directing the messages to the desired signalling line, or to the correct UP.Signaling network management, i.e. control of the message traffic, for example, by means of changeover of signaling links if a fault is detected and change back to normal operation after the fault is corrected.

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Signal Units (SU)The MTP transport messages in the form of SUs of varying length.There are three different types of SUs : Message Signal Units (MSU). Link Status Signal Units (LSSU). Fill-in Signal Units (FISU).

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Thank U

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SIGNALING LINK