1 Wszelkie prawa zastrzeone. adna cz niniejszej publikacji nie moe by reprodukowana i przekazywana w jakiejkolwiek formie zapisu. Na prawach rkopisu. Wydrukowano z materiałów dostarczonych przez Autora w Drukarni Cyfrowej Kserkop sp. z o.o. w Krakowie. Wydawnictwo Wydziału Elektrotechniki, Automatyki, Informatyki i Elektroniki Akademia Górniczo-Hutnicza Kraków 2007 ISBN
2 Slajd 1 Signalling systems Krzysztof Wajda Telecommunications Department AGH University of Science and Technology Slajd 2 References ATM Forum standards ITU Recommendations D. Ginsburg, ATM. Solutions for enterprise networking, Addison-Wesley, 1999 D. Minoli, G. Dobrowski, (Principles of signaling for Cell Relay and Frame Relay, Artech House, 1995 Lectures available at: Papers from IEEE Communication Magazine Slajd 3 Goals of the course introduction of main problems and definitions related to signalling desciption of functions accomplished by signalling detailed desciption of Signalling System No 7 signalling in intelligent networks and advanced services B-ISDN environment and signalling for contemporary networks
3 Slajd 4 Signalling is closely related to three significant areas of modern telecommunications: Intelligent Networks Asynchronous Transfer Mode Multimedia communications Slajd 5 Necessity of signalling systems Slajd 6 Outline Telecommunication services Short history of signalling Basic definitions and categories Correlation between switching and signalling technology Access and trunk signalling Signalling systems requirements Call control process
4 Slajd 7 Short history of signalling Signalling is directly related to technological progress in telecommunications Special relations with switching technology and telephone network concepts Slajd 8 Short history of signalling (1) Alexander Graham Bell invented the telephone first telephone exchange served by an operator (21 subscribers) introduction of first trunk lines Almon Strowger invented the stepping relay Slajd 9 Short history of signalling (2) Messrs Keith from Erickson & Erickson invented the rotary dialer first automatic subscriber trunk dialing system inaugurated in Bavaria replacing dc trunk signalling with a 50 Hz ac separation of subscriber loop signalling and inter-office signalling
5 Slajd 10 Short history of signalling (3) using of valve amplifiers moved the signalling into Hz T. Skillman proposed multifrequency coding introduction of concept of compelled signalling first digital PCM TDM trunk lines Slajd 11 Short history of signalling (4) first common-channel signalling system (CCS) 198x - emerging of the concept of broadband networks first set of ATM standards (CCITT) Slajd 12 Definition of signalling Signalling: process of generating and transferring of information pertaining to call management and to network management
6 Slajd 13 Basic definitions and categories call connection phases of call classification of signalling concepts and systems Slajd 14 Call vs connection Call means formal association between two parties involving activation of information transfer protocol; has also meaning as object which can be created and destroyed. Many calls taken together create traffic stream. Connection has mainly technical meaning; it is creation of technical means for information transportation In telephone environment call = connection In B-ISDN environment we can have one call composed of many connections Slajd 15 Classification (topological criterion) Inter-Customer Premises Equipment Signalling Intra-CPE Signalling Customer Line Signalling Interoffice Signalling Special Services Signalling Advanced Services Signalling
7 Slajd 16 Classification (physical method criterion) dc signalling in-band, monofrequency in-band, multifrequency out-band, monofrequency code-type common channel Slajd 17 Signalling in the access loop dc signalling DTMF (Dual Tone MultiFrequency) Slajd 18 Intranetwork signalling dc ac in-band signalling out-of-band signalling MF (multifrequency) codes common channel signalling
8 Slajd 19 Classification (functional criterion) Supervisory: monitoring the status of a line or circuit (idle, busy) Adressing: transferring routing and destination signals Alerting: anouncing the incoming call Billing: generation and collection of biling information Slajd 20 Correlation between switching and signalling technology There is tight relation between main technologies used in switching and transmision equipment and signalling concepts It was easier to change the signalling concept than intra-network technology There is strong pressure to preserve usage of old technology in new changing environment - issues of interworking Slajd 21 Correlation between switching and signalling technology switching technology step-by-step cross-bar electronic SPC signalling dc, ac, MF, out-band MF, out-band message based
9 Slajd 22 Access and trunk signalling These are two main areas of signalling systems implementation:» access network, expensive and difficult to change rapidly, sometimes private, with private terminals (often old-fashioned)» trunk network, interoffice, inter-node, telecom operator based; easier to replace Slajd 23 Signalling systems requirements reliability limited delay robustness under different conditions self-tuning to traffic patterns compliance of national and international version of signalling systems congestion control Slajd 24 Latency of signalling Dial-pulse DTMF ISDN Encoding 1 of 10 digits 1 of 10 digits plus # and * message-based Signalling latency > 1s/digit < 1s/digit 16 kbit/s to 2 Mbit/s
10 Slajd 25 Outline Telecommunication services Short history of signalling Basic definitions and categories Correlation between switching and signalling technology Access and trunk signalling Signalling systems requirements Call control process Slajd 26 Call control process Phases of call control process:» call initiation» call acknowledgement» sending adressing information» transfer of information» call release Slajd 27 Introduction to SS7
11 Slajd 28 Common Channel Signalling This concept was possible with significant advances in network software engineering SS6 as first attempt to CCS This is out-of-band signalling method in which common data channel conveys signalling messages related to a number of trunks Slajd 29 CCS6 - CCIS CCIS - Common Channel Interoffice Signalling CCS6 - Signalling System No. 6 introduced in 1976 by AT&T Features of CCS6:» not a layered system» only for trunk signalling» routing based on the basis of permanent virtual signalling circuits Slajd 30 CCS6 - drawbacks large efforts to manage banded routing limited lengths low speed links non-modular structure
12 Slajd 31 SS7 Work on SS7 began in mid 1970s CCITT (ITU-T currently) as leading force 800 service and calling card service as first attempts to new concept used layered approach to system construction Slajd 32 SS7 supports signalling for: Public Switched Telephone Networks ISDN Public mobile networks Operations, administrations and maintenance as a basis for interactions with network data bases and service control points for advanced services Slajd 33 SS7 network structure Sie sygnalizacyjna SS7 Sie telefoniczna - centrala telefoniczna STP Signalling Transfer Point - SP signalling point
13 Slajd 34 Signalling network elements SP - Signalling Point STP - Signal Transfer Point signalling links SCP - Service Control Points OAM - Operation, Administration and Maintenance centres Slajd 35 Signalling network structure Reflects the structure of telecommunication network to be served by signalling and administration aspects Signalling system can be planned:» purely on a per signalling relation basis - associated signalling for large traffic volumes and some quasiassociated signalling for low volume signalling relations» as an independent network with regard to common channel signalling needs - this leads to mainly quasi-associated signalling with scarce associated signalling for high volume traffic patterns Slajd 36 Worldwide signalling network Structured into two functionally independent levels:» international» national such structure helps to split responsibility and separates numbering plans
14 Slajd 37 Signalling point modes Originating point of the message is a signalling point at which message is generated, i.e. there is location of the source User Part function Destination point of the message is a signalling point to which message is destined, i.e. there is location of the receiving User Part function Signalling point at which a message is received on one signalling link and transferred to another link is a Signal Transfer Point (STP) Slajd 38 Signalling relation Signalling relation exists between two nodes when they are capable of exchanging signalling messages through signalling network Slajd 39 Signalling modes Mode refers to the type of association between path taken by the signalling message and its corresponding signalling relation:» Associated» Non-associated» Quasi-associated
15 Slajd 40 Associated mode Messages corresponding to a signalling relation between two points are transported over a link set directly inteconnecting those signalling points exchange A exchange SP signalling link set signalling relation exchange B Slajd 41 Non-associated mode Messages corresponding to a particular signalling relation between two points are transported over two or more linksets in tandem passing through one or more signalling points other than the origin and destination of messages exchange A exchange C exchange SP signalling link set signalling relation exchange B Slajd 42 Quasi-associated mode It is limited case of the non-associated mode - route (path) taken by message through signalling network is pre-determined and fixed (at a given point in time) exchange A exchange C exchange SP signalling link set signalling relation exchange B
16 Slajd 43 SS7 - main building blocks Message Transfer Part (MTP): block which ensures reliable transmission of functional signalling messages with high availability User Parts (UP): block which provides functions to manage number of services Slajd 44 SS7 protocol model Model OSI Model SS7 OMAP ASEs application l. TCAP ISDN-UP presentation l. session l. Puste transport l. SCCP network l. MTP Level 3 data link l. physical l. MTP Level 2 MTP Level 1 OMAP = Operations Maintenence and Administration Part ASE = Application Service Element TCAP = Transaction Capabilities Application Part ISDN-UP = ISDN User Part SCCP = Signaling Connection Part MTP = Message Transfer Part Slajd 45 SS7 - building blocks MTP SCCP TUP ISDN-UP DUP TC
17 Slajd 46 Institutions engaged in standardization process of SS7 ITU-T (former CCITT) Bellcore ANSI all national standard institutes Slajd 47 ITU-T recommendations Key recommendations General description Q.700 Q.771-Q.775 MTP Q.701-Q.704, Q.706, Q.707 TUP Q.721-Q.725 Supplementary services Q.730 DUP Q.741 Q.701-Q.704, Q.706, Q.707 ISDN-UP Q.761-Q.764, Q.766 Q.721-Q.725 SCCP Q.711-Q.714, Q.716 Q.730 Transaction Capabilities Q.771-Q.775 Q.771-Q.775 Operations, maintenance and administration part (OMAP) Q.795 Q.771-Q.775 Slajd 48 ITU-T recommendations Additional recommendations Signalling network structure Q.705 Q.771-Q.775 Numbering of international Q.708 signalling point codes Hypothetical signalling reference Q.709 connection PBX application Q.710 Test specifications Q.780-Q783 Q.701-Q.704, Q.706, Q.707 Monitoring and measurements Q.791 Q.721-Q.725
18 Slajd 49 Basic architectural and functional components of SS7 Slajd 50 Signalling link MTP - structure and functions Physical layer requirements and standards Signalling unit formats Link protocol operation Error detection and recovery Flow control issues Slajd 51 MTP Provides a reliable transfer and delivery of signalling messages across the signalling network Consists of levels 1-3 of SS7 protocol:» Signalling Data Link Functions (Level 1)» Signalling Link functions (Level 2)» Signalling Network Functions (Level 3) Uses datagram mode Signalling link przsło sygnalizacyjne
19 Slajd 52 MTP functional diagram Signalling Link User Message Processing Common Transfer Functions link control functions Signalling Data Link link control functions Common Transfer Functions User Message Processing MTP Users MTP users MTP Slajd 53 Signalling Data Link Functions Signalling Data Link is a bidirectional transmission path for transfer of signalling messages; two data channels operating together in opposite directions with the same data rate analog signalling link (4 khz) accessible by modems digital data links:» 56 kbit/s (ANSI standard)» 64 kbit/s (ITU-T standard) minimum data rate allowed is 4.8 kbit/s (delay requirements) Slajd 54 Signalling link functions Correspond to the OSI s data link layer (layer 2), provide reliable transfer of signalling messages between two adjacent signalling points, signalling units have variable length and are called signal units.
20 Slajd 55 Signal unit formats Slajd 56 Signal unit formats F B F CK SIF SIO LI I FSN BSN F B B I n, n> Time a) Basic format of MSU F B F CK SF LI I FSN BSN F B B I lub Time b) Format of LSSU F B F CK LI I FSN BSN F B B I Time c) Format of FISU BIB: Backward indicator bit BSN: Backward sequence number CK: Check bits F: Flag SIO: Service information octet FIB: Forward indicator bit FSN: Forward sequence number LI: Length indicator SF: Status field SIF: Signal information field N: Number of octets in the SIF Slajd 57 Length indicator 6 bits field (range 0-63) indicates number of octets following the length indicator octet and preciding check bits Three types:» LI=0; Fill in signal unit» LI=1 or 2; Link status signal unit» LI>2; message signal unit - when signalling information field is 62 octets or more, LI=63
21 Slajd 58 Service Information Octet divided into service indicator and the subservice field, service indicator associates signalling information with particular user part (only in MSU). Slajd 59 Sequence numbering + indicator bits Forward sequence number is the sequence number of the signal unit this field belongs Backward sequence number is the sequence number of a signal unit being acknowledged Both fields range from 0 to 127 Indicator bits (forward and backward) together with sequence numbers are used in basic error control Slajd 60 Signalling information field (SIF) consists of an integral number of octets in the range from 2 to 272, but: up to 62 bytes in international networks, up to 272 bytes in national networks, format and codes of SIF are defined in description of user parts.
22 Slajd 61 Status field Used in LSSU, Identified by a length indicator value equal to 1 or 2 (when LI=1, the status field consists of 1 octet, etc.) Slajd 62 Check bits Error detection is done by means of 16 check bits provided at each signal unit» the reminder after multiplication by x 16 and then division (modulo 2) by the generator polynomial x + x + x + 1 of the content of the signal unit existing between, but not including, the final bit of the opening flag and the first bit of the check, excluding bits inserted for transparency. Slajd 63 Zero insertion and deletion The flag code should not to be imitated by any other part of the signal unit. To ensure it, the transmitting signalling link terminal inserts a 0 after every sequence of five consecutive 1s before the flags are attached and the signal unit is transmitted, At the receiving end, after flag detection and removal, each 0 which directly follows a sequence of five consecutive 1s is deleted, bit stuffing.
23 Slajd 64 Transmitted items within level 2 new message signal units MSU, yet not acknowledged message signal units MSU, link status signal units LSSU, fill-in signal units FISU, flags. Slajd 65 Signalling link functions signal unit delimitation signal unit alignment error detection error correction initial alignment signalling link error monitoring flow control Slajd 66 Signal unit delimitation 8-bit pattern called flag indicates the beginning and the end of each signal unit it is necessary to ensure that flag pattern cannot be repeated inside the message unit loss of alignment:» receiving more than 6 consecutive 1 s» receiving too long signal unit» will cause a change in the mode of operation of signal unit error rate monitor
24 Slajd 67 Error detection Performed by means of 16 check bits They are located at the end of signal unit Received check bits are compared with check bits generated by receiving terminal by operating on the preceding bitsof signal unit If error is detected (inconsistency), signal unit is discarded Slajd 68 Error correction Two ways of error correction:» Basic method applies for signalling links with one-way propagation delay less than 15 ms» Preventive cyclic retransmission method applies for intercontinental links with propagation delay greater than or equal 15 ms Slajd 69 Basic method of error correction (1) non-compelled, positive/negative acknowledgement, retransmission error correction system, transmitted signal unit is stored in the transmitting buffer until receiving of positive acknowledgement, negative acknowledgement of certain signal unit causes interruption of transmission of new signal units and retransmission of all not yet positively acknwledged signal units (go-back-n).
25 Slajd 70 Basic method of error correction (2) Positive acknowledgement 0 n FIB FSN BIB BSN n 0 BSN BIB FSN FIB A B Slajd 71 Basic method of error correction (3) Negative acknowledgement 0 n FIB FSN BIB BSN n-1 1 Repeat MSU with BSN+1! BSN BIB FSN FIB A B Slajd 72 Basic method of error correction (3) Retransmission 1 n FIB FSN BIB BSN n 1 BSN BIB FSN FIB A B
26 Slajd 73 Preventive cyclic retransmission method non-compelled, positive/negative acknowledgement, cyclic retransmission, forward error correction system transmitted signal unit is retained at the transmitting end terminal - until receiving positive acknowledgement when there are no new signal units to be transmitted - all yet not positively acknowledged units are again retransmitted cyclically Slajd 74 Preventive cyclic retransmission method - abnormal situation When the number of unacknowledged MSU s exceeds thresholds - error correction is not sufficient to be done by cyclic retransmission forced retransmission is invoked: transmission of new MSU is stopped and all unacknowledged MSUs are retransmitted forced retransmission continue until the counts of unacknowledged MSUs and octets are below specific threshold value threshold value enables to control link performance Slajd 75 Initial alignment Used after switch-on and during restoration after a link failure, based on compelled exchange of status information between two signalling points.
27 Slajd 76 Signalling link error monitoring signal unit error rate monitor - used when signalling link is in service - provides one of the criterion to consider link to be out of service» based on a signal unit error counter incremented and decremented by leaky bucket method» during loss of alignement, the signal error rate monitor is incremented proportionally to the length of period of alignment loss alignment error rate monitor - employed when the link is in proving state» based on linear count of signal unit errors Slajd 77 Signal unit error rate monitor Based on a signal unit error counter Each errored unit the counter is increased by one, for each 256 signal units received (errored or not), a positive count is decremented by 1 When he counter reaches value 64 an excessive error rate indication is sent to level 3 - signalling link is in the out-of-service state Slajd 78 Signal unit error rate monitor When more than six consecutive 1s are received or the maximum length of a signal unit is exceeded - loss of alignment occurs and error rate monitor enters an octet-counting mode Being in octet counting mode error rate monitor increments the counter every 16 octets received Octet counting mode is changed back to alignment mode when the first correct signal unit is detected
28 Slajd 79 Alignment error rate monitor It is a linear counter that is operated during alignment proving periods The counter is set to zero at start of a proving period and the count is incremented by 1 for each signal unit received (or after each 16 octets in the octet counting mode) The proving period is aborted when the threshold for the the alignment error rate monitor is exceeded before the end proving-period Slajd 80 Flow control Initiated when receiving end detects congestion receiving terminal notifies transmitting end about congestion by sending approppriate link status signal unit no acknowledgements of incoming signal units during congestion, transmitting end is periodically informed about that state too long congestion period causes link to be indicated as failed (3 to 6 s) Slajd 81 Flow control Signalling Indication Processor Outage Signalling Indication Processor Outage (SIPO) is sent by level 2 whenever an explicit indication is sent from level 3 or there is recognition of level 3 failure SIPO informs far end that signalling messages can not be transferred to level 3 (and above) The far end level 2 sends fill-in-signal units and inform its level 3 of SIPO condition The far end level 3 reroutes traffic according to signalling network management procedures
29 Slajd 82 Link state control function provides directives to the other signalling link functions (switching function) Slajd 83 Network layer issues for SS7 Slajd 84 Network layer issues Network management Message handling processes Message routing Traffic management Flow control Failure recovery
30 Slajd 85 Signalling network functions (level 3) Correspond to the lower sublayer of the OSI s network layer provide procedures for the transfer of messages between signalling points two basic categories:» signalling message handling» signalling network management Slajd 86 Message structure inside SIF F B MTP F CK SIF SIO LI I FSN I BSN F B B CK F LI SF SIF SIO FSN BSN FIB BIB Check Bitsg Flag Length Indicator Status Field Signaling Information Field Service Information Field Forward Sequence Number Backward Sequence Number Forward Indicator Bit Backward Indicator Bit First Bit Transmitted SIF field will be revisited when describing User Parts (UP) TUP TUP Message Information Elements H1 Message Type H0 Label Message Group B ISUP ISUP Message Information Elements Message Type Label C SCCP E O P User Message/Data SCCP Message Header Message Type Label D Includes Called And Calling Party Adresses And Local References* (*CO Only) TCAP Component Portion Component n Component 2 Component 1 Transaction Portion TUP = Telephone User Part ISUP = ISDN User Part SCCP = Signaling Connection User Part TCAP = Transaction Capabilities Application Part Slajd 87 Signalling message handling Consists of message routing, discrimination and distribution performed at each signalling point based on the content of Routing Label and Service Information Octet Routing Label:» Destination Point Code (DPC)» Origination Point Code (OPC)» Signalling Link Selection (SLS)» these fields have different length in ITU-T and ANSI specifications
31 Slajd 88 Signalling network functions Level 4 Level 3 User Parts MTP Signaling Network Functions Signaling Message Handling Level 2 Message Transfer Part Message Distribution Message Discrimination Message Routing Signaling Network Management Signalling Traffic Management Signalling Route Management Signalling Link Management Testing and Maintenance (MTP) Signalling Message Flow Indications and Controls Slajd 89 Message routing Based on DPC and SLS fields, sometimes on SIO Ussually more than one signalling link can be used to send message to DPC Selection is made on SLS-field basis - implementation of load sharing Link set it is set of links between two signalling points Slajd 90 Routing label Length (bit) n 8 SLS OPC DPC 0/3 4/5 14/24 14/24 Routing label First Bit Transmitted Label k/l: k is value for CCITT l is value for ANSI OPC - Origination Point Code DPC - Destination Point Code SLS - Signalling Link Selection
32 Slajd 91 Load sharing chooses among links belonging to link set the objective of load sharing is to spread the load, to keep it balanced can be done over links in the same link set or over links not belonging to the same link set collection of link sets used by load sharing is called a combined link set load sharing do not preserve sequence of messages, so when this is necessary, the SLS field should be kept the same Slajd 92 How SLS field works? SLS= xxx1 A xxx0 B xx11 D G xx01 xx10 C xx00 E H I Slajd 93 General structure of signalling system functions Level 4 Level 3 Level 2 Level 1 User Parts TUP D Signalling network functions Signalling message handling Message Transfer Part C Signalling link Signalling link functions B Signalling data link A DUP Signalling network management Other type Testing and maintenance TUP DUP Signalling message flow Controls and indications Telephone User Part Data User Part
33 Slajd 94 Detailed structure of signalling system functions Level 4 User Parts TUP DUP D Signalling link management Level 3 Level 2 Level 1 A Message Transfer Part C Signalling network functions B Signalling data link Signalling message handling Signalling link Message Signalling Transmission Message Switching discrimination functions link distribution functions channels Message routing SCCP Other type Signalling Network Management Signalling traffic managemnet Signalling route management Testing and maintenance Signalling message flow Controls and indications Slajd 95 Signalling Connection Control Part (SCCP) Relation of SCCP to MTP Connection-oriented and connectionless services SCCP routing SCCP management Slajd 96 Relation of SCCP to MTP SCCP enhances services accomplished by MTP to provide the functional equivalent of OSI s network layer SCCP has enhanced addressing ability: DPC plus Subsystem Numbers (SSN) to identify local users at the node SCCP has ability to use global addresses, such as dialed digits (using global addresses needs their translation to DPC+SSN)
34 Slajd 97 SCCP - service classes Class 0: Basic connectionless class Class 1: Sequenced connectionless class Class 2: Basic connection-oriented class Class 3: Flow control connection-oriented class Slajd 98 Class 0 of SCCP User-to-user information block is called Network Service Data Unit (NSDU) and is transported independently, possibly out of sequence (pure connectionless class) Slajd 99 Class 1 of SCCP Particular stream of NSDUs is supposed to be delivered in sequence There is association (by SCCP) between stream units and sequence control parameter All messages in one stream unit have the same SLS code
35 Slajd 100 Class 2 of SCCP Bidirectional transfer of NSDUs is done through virtual circuit Messages belonging to the same signalling connection have the same SLS field Segmentation and reassembly capability is provided (when NSDU is longer than 255 octets) Slajd 101 Class 3 of SCCP Capabilities of class 2 are supported with addition of flow control Detection of message loss and missequencing is provided There is notification of higher layers about message loss and mis-sequencing Slajd 102 SCCP functions SCCP Users SCCP MTP N-Connect Request N-Connect Response N-Data Request N-Exped. Data Request N-Data Acknowledgment Request N-Disconnect Request N-Reset Request N-Reset Response N-Inform Request N-Connect Indication N-Connect Confirmation N-Data Indication N-Exped. Data Indication N-Data Acknowledgment Indication N-Disconnected Indication N-Reset Indication N-Reset Confirmation N-Inform Indication Request Type 1 Request Type 2 Reply SCCP SCCP Connection-Oriented CO Message Control (SCOC) Routing SCCP Failure Routing Control (SCRC) MTP - Transfer Indication MTP - Transfer Request N-Unitdate Request N-Unitdate Indication N-Notice Indication SCCP Connectionless Control (SCLC) S S S S S O O S S S R G A P T CL Message Routing Failure Message Received for Unavailable Local SS N-Coordination Request N-Coordination Response N-State Request N-Coordination Indication N-Coordination Confirmation N-State Indication N-PC State Indication SCCP Management (SCMG) MTP - Pause Indication MTP - Resume Indication MTP - Status Indication
36 Slajd 103 Signalling network structures Slajd 104 Basic SS7 network structure STP STP SP SP STP STP SP - Signalling Point STP - Signalling Transfer Point Slajd 105 Basic structure - mesh-type Mesh type or quad-type The STPs are combined ( mated ) on a pairwise basis Mesh-type network has 100% redundacy (any single failure causes traffic to be diverted to alternative paths) Each component should be engineered in such way to allow twice its peak load There is necessity to fulfil diversity criterion: split of quad pairs into different physical transmission paths
37 Slajd 106 Alternate signalling network structure A Associated STP 2 STP 1 C Associated B Mix of associated and quasi-associated signalling modes Associated signalling mode can be used as first choice route Quasi-associated signalling mode can be used as backup in case the associated path fails Slajd 107 Generalization of mesh-network Cluster (1,3) Cluster (1,2) STP 2 Cluster (2,3) Cluster (2,6) STP 1 STP 3 Cluster (2,4) Cluster (1,6) Cluster (3,4) STP 6 STP 4 Cluster (1,5) Cluster (3,5) Cluster (5,6) STP 5 Cluster (4,6) Cluster (4,5) Slajd 108 Generalization of mesh-network Backbone network of fully connected STPs Clusters of offices (SPs) are connected to different pairs of STPs When STP fails - its load is split to number of STPs When signalling link fails - also split of traffic
38 Slajd 109 SS7 node codes Slajd 110 Signalling Area Network Code (SANC) Country designations were decided before wide deployment of IP networks ITU Point Code Format is different than the ANSI (North American) Zone ID Network ID Signalling Point ID 3 bits 8 bits 3 bits Slajd 111 ITU Zone IDs Zone ID Geographical Region Europe North America, Mexico, the Caribean, Greenland Middle East and Asia South Asia, Australia, New Zealand Africa South America
39 Slajd 112 Country Codes Code Network Poland Poland Liechtenstein Slajd 113 SS7 User Parts Slajd 114 Data User Part (DUP) Functions of DUP are now realized by ISUP Many telecom administrations do not use DUP
40 Slajd 115 Telephone User Part Supports telephone services Migration towards ISDN Main functions:» connecting and disconnecting of calls» enabling access of users to set of additional features Slajd 116 TUP - Groups of messages FAM - Forward address message group FSM - Forward set-up message group BSM - Backward set-up request message group SBM - Successful backward set-up information group UBM - Unsuccessful backward information message group CSM - Call supervision message group CCM - Circuit Supervision message group Slajd 117 TUP - message label H1 H0 CIC OPC DPC
41 Slajd 118 Message structure F B MTP F CK SIF SIO LI I FSN I BSN F B B First Bit Transmitted CK Check Bitsg F Flag LI Length Indicator SF Status Field SIF Signaling Information Field SIO Service Information Field FSN Forward Sequence Number BSN Backward Sequence Number FIB Forward Indicator Bit BIB Backward Indicator Bit TUP TUP Message Information Elements H1 Message Type H0 Label Message Group B ISUP ISUP Message Information Elements Message Type Label C SCCP E O P User Message/Data SCCP Message Header Message Type Label D Includes Called And Calling Party Adresses And Local References* (*CO Only) TCAP Component Portion Component n Component 2 Component 1 Transaction Portion TUP = Telephone User Part ISUP = ISDN User Part SCCP = Signaling Connection User Part TCAP = Transaction Capabilities Application Part Slajd 119 ISUP Slajd 120 ISDN ISDN service is a modern digital technology for access and intranetwork The basic ISDN bearer capability is circuit-switched mode unrestricted digital transmission, supporting ondemand, point-to-point, bidirectional and symmetric digital connectivity
42 Slajd 121 ISDN - access configuration 2B+D two 64kbit/s channels + 16 kbit/s packet/signalling channel (Basic Rate Access) 23B+D 23 x 64 kbit/s + 16 kbit/s packet/signalling channel (Primary Rate Access) n x 64 + D n x 64 kbit/s channels (n from 1 to 23) 30B+D 30 x 64 kbit/s + 64 kbit/s packet/signalling channel H0+D A nonchannelized 384 kbit/s channel plus 64 kbit/s packet/signalling channel H11 A nonchannelized (signalling within another D-channel interface) H12 A nonchannelized (signalling within another D-channel interface) Slajd 122 SS7 for ISDN User-network signalling (DSS1) ISUP Basic call process Supplementary services Slajd 123 ISDN network User Plane switch ISDN User Plane User switch ISDN switch ISDN User Control Plane SS7 Control Plane
43 Slajd 124 ISDN signalling Call control Message functional definitions and content Information elements coding Description of various control procedures Slajd 125 User and network signalling in ISDN DSS1 SS7 DSS1 TE S/T ISDN benchmark services S/T TE teleservices Slajd 126 DSS1 User-network signalling Limited number of services Narrowband services
44 Slajd 127 Messages for Circuit Mode Connection Control - DSS1 Call Establishment Messages:» ALERTING» CALL PROCEEDING» CONNECT» CONNECT ACKNOWLEDGE» PROGRESS» SETUP» SETUP ACKNOWLEDGE Slajd 128 Messages for Circuit Mode Connection Control - DSS1 Call Information Phase Messages» RESUME» RESUME ACKNOWLEDGE» RESUME REJECT» SUSPEND» SUSPEND ACKNOWLEDGE» SUSPEND REJECT Slajd 129 Messages for Circuit Mode Connection Control - DSS1 Call Clearing Messages» DISCONNECT» RELEASE» RELEASE COMPLETE Miscellaneous Messages» INFORMATION» NOTIFY» STATUS» STATUS ENQUIRY
45 Slajd 130 Brief description of Q.931 Messages Each message contains:» The protocol discriminator» The length of the call reference value» The call reference (CR does not have endto-end significance across ISDN)» The message type» Other IEs Slajd 131 Brief description of Q.931 Messages ALERTING*: message sent by the called user to the network and by the network to the calling user to indicate that called-user alerting has been initiated CALL PROCEEDING*: message sent by the called user to the network or by the network to the calling user. In the networkuser direction, it indicates that the requested call establishment information will be accepted CONNECT*: message sent by the called user to the network or by the network to the calling user to indicate call acceptance by the called user Slajd 132 Brief description of Q.931 Messages CONNECT ACKNOWLEDGE. This message is sent by the network to the called user to indicate the user has been awarded the call. It may also be sent by the calling user to the network to allow symmetric call control procedures. DISCONNECT. This message is sent by the user to request the network to clear an end-to-end connection, or is sent by the netw ork to indicate that the end-to-end connection is cleared. INFORMATION. This message is sent by the user or the network to provide additional information. It may be used to provide information for call establishment or miscellaneous callrelate information.
46 Slajd 133 Brief description of Q.931 Messages NOTIFY. This message is sent by the user or network to indicate information pertaining to a call, such as user suspended. PROGRESS. This message is sent by the user or the network to indicate the progress of a call in the event of interworking or in relation with the provision of inband information or pattems. Slajd 134 Brief description of Q.931 Messages RELEASE. This message is sent by the user or the network to indicate that the equipment sending the message has disconnected the channel (if any) and intends to release the channel and the call reference, and that the receiving equipment should release the channel and prepare to release the call reference after sending. RELEASE COMPLETE. This message is sent by the user or network to indicate that the equipment sending the message has released the channel (if any) and call reference,the channel is available for reuse,and the receiving equipment will release the call reference. Slajd 135 Brief description of Q.931 Messages RESUME.This message is sent by the user to request the network to resume a suspended call. RESUME ACKNOWLEDGE. This message is sent by the network to the user to indicate completion of a request to resume a suspended call. RESUME REJECT. This message is sent by the network to the user to indicate failure of a request to resume a suspended call.
47 Slajd 136 Brief description of Q.931 Messages SETUP. This key message is sent by the calling user to the network and by the network to the called user to initiate call establishment.this message is discussed more below. SETUP ACKNOWLEDGE. This message is sent by the network to the calling user (or by the called user to the network) to indicate that call establishment has been initiated,but additional information may be required. STATUS. This message is sent by the user or the network in response to a STATUS ENQUIRY message or at any time during a call to report certain error conditions. Slajd 137 Brief description of Q.931 Messages STATUS ENQUIRY. This message is sent by the user or the network at any time to solicit a STATUS message from the peer layer 3entity (sending a STATUS message in response to a STATUS ENQUIRY message is mandatory). SUSPEND. This message is sent by the user to request the network to suspend a call. SUSPEND ACKNOWLEDGE. This message is sent by the network to the user to indicate completion of a request to suspend a call. SUSPEND REJECT. This message is sent by the network to the user to indicate failure of a request to suspend a call. Slajd 138 Brief description of Q.931 Messages SEGMENT,CONGESTION CONTROL, and USER lnformation messages are not shown above since they are not for basic call control
48 Slajd 139 Information elements used in ISDN Signalling Most important: protocol discriminator call reference message type Slajd 140 Information elements used in ISDN Signalling Single-Octet Information Elements» Shift BCC» More data BCC» Sending complete BCC» Congestion level BCC» Repeat indicator BCC Slajd 141 Information elements used in ISDN Signalling Variable-Iength Information Elements» Segmented message BCC» Bearer capability BCC» Cause BCC» Call identity BCC» Call state BCC» Channel identification BCC» Progress indicator BCC» Network-specific facilities BCC
49 Slajd 142 Information elements used in ISDN Signalling Notification indicator BCC Display BCC Date/time Other Keypad facility BCC Signal BCC Information rate Other End-to-end transit delay Other Transit delay selection and indication Other Packet layer binary parameters Other Slajd 143 Information elements used in ISDN Signalling Packet layer window size Packet size Closed user group Reverse charge indication Calling-party number Calling-party subaddress Called-party number Called-party subaddress Redirecting number Other Other Other Other BCC BCC BCC BCC BCC Slajd 144 Information elements used in ISDN Signalling Transit network selection Restart indicator Low-layer compatibility High-layer compatibility User-user Escape for extension BCC BCC BCC BCC BCC Other BCC: basic call control and possibly other procedures. Other: used in other than basic call control.
50 Slajd 145 ISDN-UP (ISUP) Provides signalling functions for basic bearer services and supplementary services, for switched voice and non-voice (data) applications in an ISDN Provides all functions accomplished by TUP plus additional functions for non-voice services, ISDN and Intelligent Network services First version of ISUP was published in 1984 CCITT Red Book, then enhanced in 1988 Blue Book Slajd 146 ISUP The ISUP meets the requirements defined by ITU for worldwide international telephone and circuit-switched data traffic The ISUP is also suitable for national applications. Most signaling procedures, information elements, and messages specified for international use are also applicable in national versions. There are some fields reserved in order to allow national administrations and private operating agencies to introduce network-specific signaling messages and elements of information within the protocol structure There is necessity to tune an international version of ISUP to national requirements Slajd 147 ISUP ISUP messages have variable lengths (up to 272 octets including MTP level headers) All ISUP messages have:» routing label indetifying the origin and destination of the message» Circuit Identification Code (CIC)» Message Type Code» Mandatory Fixed Part» Mandatory Variable Part» Optional Part
51 Slajd 148 Detailed structure of ISUP message Order of Bit Transmission Order of Octet» Routing Label» Transmission Circuit Identification Code Message Type Code Mandatory Parameter A Mandatory Parameter F Pointer to Parameter M Mandatory Fixed Part Pointer to Parameter P Pointer to Optional Part Start Parameter M Length Indicator» Parameter M» Mandatory Variable Part Parameter P Length Indicator Parameter P Parameter Name = X Parameter X Length Indicator Parameter X Parameter name = Z Optional Part Parameter Z Length Indicator» Parameter Z» Slajd 149 Optional Parameter Field End Basic Bearer Service Basic service offered by ISUP is controlling of circuit-switched network connections between subscriber-line exchange terminations User-network signalling is accomplished by DSS1 protocol on the D-channel Call set-up and release needs interworking of DSS1 and ISUP procedures Slajd 150 ISDN-UP message scenario Originating Destination Exchange Transit Exchange Exchange Set-up IAM1 Call Proceedings IAM2 Set-up Call Proceedings Alerting Alerting ACM2 ANM2 ACM1 ANM1 Connect Connect B-Channel End-to-End Ckt. Conn. 'a' 'b' B-Channel Disconnect REL1 REL RLC1 REL2 RLC2 Disconnect REL RLC RLC
52 Slajd 151 Supplementary Services for ISDN Slajd 152 Supplementary services Supplementary services add more functionality to calls established in ISDN network They invoke some functions which are terminal-specific Typical supplementary services are: user-touser signalling, closed-user group, call forwarding, calling line identification, etc. Slajd 153 Number Identification Supplementary Services Calling line identification presentation (CLIP) Calling line identification restriction (CLIR) Connected line identification presentation (COLP) Connected line identification restriction (COLR) Direct Inward Dialing Service Multiple Subscriber Number (MSN Supplementary Service Malicious Call Identification ( MCID) Supplementary Services Sub-addressing Supplementary Services (SUB)
53 Slajd 154 Supplementary services (details) Q.731 Stage 3 description for number identification supplementary services using signalling system No. 7 Clause 1 (02/92) Direct-dialling-in (DDI) Clause 3 (1993) Calling line identification presentation (CLIP) Clause 4 (1993) Calling line identification restriction (CLIR) Clause 5 (1993) Connected line identification presentation (COLP) Clause 6 (1993) Connected line identification restriction (COLR) Clause 8 (02/92) Sub-addressing (SUB) Slajd 155 DDI Direct-Dialling-In (DDI) enables a user to directly call another user on an integrated services private branch exchange or other private system without attendant intervention. This supplementary service shall be based on the use of the ISDN number. At least the significant part of the ISDN number shall be passed to the private ISDN, in order to progress the call to the destination. Direct-Dialling-In shall apply to public ISDNs having either a closed or an open numbering plan. This service shall be provided/withdrawn after pre-arrangement with the service provider. The service provider shall allocate a set of ISDN numbers. Slajd 156 MSU The Multiple Subscriber Number (MSN) supplementary service provides the possibility for assigning multiple numbers (not necessarily consecutive) to a single public or private interface. This enables the selection of one or multiple distinct terminals attached to the same interface. The service provider shall fix the length of the numbers to be transmitted to the user's installation. They may comprise the least significant digit up to the full integrated services digital network ISDN number (E.164)
54 Slajd 157 MSU Multiple Subscriber Number provides the possibility for assigning multiple integrated services digital network numbers to a single interface. For example, this service:» 1) allows dialling from a line connected to a public network directly to terminals connected to a basic access which bas subscribed to Multiple Subscriber Number (e.g. in a passive bus configuration);» 2) enables the network to determine which ISDN number is applicable on originating calls (e.g. for charging purposes, for notification to the called party and application for supplementary services). Slajd 158 MSU Administrations:» may not have knowledge or control over what is connected to the basic access, e.g. an network termination 2 (NT2) or passive bus;» may have different numbering methods;» may agree that common international terminal specifications are desired. Slajd 159 CLIP Calling Line Identifcation Presentation (CLIP) is a supplementary service offered to the called party which provides the calling party's ISDN-number, possibly with sub-address information, to the called party. When Calling Line ldentification Presentation is applicable and activated, the network provides the called party with the number of the calling party at call set-up on all incoming calls. The calling party number may be accompanied by a subaddress.the network should be capable of transmitting at least 15 digits [maximum length of an integrated services digital network (ISDN) number]. In addition, if provided by the calling party, the network should be capable of transmitting a subaddress.
55 Slajd 160 Sub-addressing The sub-addressing supplementary service allows tbe called (served) user to expand his addressing capacity beyond the one given by the ISDN number. A sub-address, if presented by a calling user, is delivered unaffected to the called (served) user. Only the served user defines tbe significance of tbe sub-address. Applications can be for example:» 1) to select or to prefer a specific terminal at tbe called customer's termination;» 2) to invoke a specific process in a terminal at the called customer's termination. Tbe maximum size of the sub-address is 20 octets. Slajd 161 Supplementary services Q.732 Stage 3 description for call offering supplementary services using Signalling System No. 7 Clause 2 (1993) Call diversion services Clause 3 (1993) Call forwarding no answer Clause 4 (1993) Call forwarding unconditional Clause 5 (1993) Call deflection Slajd 162 Call forwarding unconditional Call forwarding unconditional permits a "served user" to have the network send to another number all incoming calls for the served user's ISDN number (or just those associated with a specified basic service). The served user's originating service is unaffected. If this service is activated, calls are forwarded no matter what the condition of the termination. Other call forwarding services provide for call forwarding based on condition, e.g. Call Forwarding Busy and Call Forwarding No Reply. The forwarded-to number is registered with the network for use for all calls.
56 Slajd 163 Supplementary services Q.733 Stage 3 description for call completion supplementary services using Signalling System No. 7 Clause 1 (02/92) Call waiting (CW) Clause 2 (1993) Call hold (HOLD) Clause 4 (1993) Terminal portability (TP) Slajd 164 Supplementary services Q.734 Stage 3 description for multiparty supplementary services using Signalling System No. 7 Clause 1 (1993) Conference calling Clause 2 (1993) Three-party service Slajd 165 Community of interest supplementary services Are aimed at a specific group of users who share special communication needs it is preliminary attempt to VPNs Closed User Group (CUG) Private Numbering Plan (PNP) Multi-level precedence and preemption Priority Service Outgoing Call Barring
57 Slajd 166 Supplementary services (details) Q.735 Stage 3 description for community of interest supplementary services using SS No. 7 Clause 1 (1993) Closed user group (CUG) Clause 3 (1993) Multi-level precedence and preemption Q.737 Stage 3 description for additional information transfer supplementary services using SS No. 7 Clause 1 (1993) User-to-user signalling (UUS) Slajd 167 Closed User Group A closed user group consists of a group of users who have a restricted access arrangements and features. A user can be a member of one or more CUGs. Restriction categories:» Call permitted only within the CUG» Calls within the CUG and incoming calls only from users outside the CUG» Calls within the CUG and outgoing calls only to users outside the CUG» Calls within the CUG and both incoming and outgoing calls to users outside the CUG Typically if a user is a member of many CUGs, one CUG is registered with the network as preferential CUG. Slajd 168 List of ISUP Messages (38 messages) Address Complete Message (ACM). A message sent in the backward direction indicating that all the address signals required for routing the call to the called party have been received. Answer Message (ANM). A message sent in the backward direction indicating that the call has been answered. In semiautomatic working, this message has a supervisory function. In automatic working, this message is used in conjunction with charging information in order to:» (1) start metering the charge to the calling subscriber» (2) start measurement of call duration for international accounting purposes.
58 Slajd 169 List of ISUP Messages Blocking (BLO). A message sent only for maintenance purposes to the exchange at the other end of a circuit to cause an engaged condition of that circuit for subsequent calls going out from that exchange. When a circuit is used in the ` `bothway 'mode of operation, an exchange receiving the blocking message must be capable of accepting incoming calls on the concerned circuit unless it has also sent a blocking message. Under certain conditions, a blocking message is also a proper response to a reset circuit message. Slajd 170 List of ISUP Messages Blocking Acknowledgment (BLA). A message sent in response to a blocking message indicating that the circuit has been blocked. Call Progress (CPG). A message sent in the backward direction indicating that an event has occurred during call setup which should be relayed to the calling party. Charge Information (CRG) (national use). Information sent in either direction for accounting and/or call-charging purposes. Slajd 171 List of ISUP Messages Circuit Group Blocking (CGB). A message sent to the exchange at the other end of an identified group of circuits to cause an engaged condition of this group of circuits for subsequent calls going out from that exchange. An exchange receiving a circuit group unless it has also sent a blocking message. Under certain conditions, a circuit group blocking message is also a proper response to a reset circuit message.