Presentation on theme: "Integrated Services Digital Network"— Presentation transcript:
1Integrated Services Digital Network ISDNIntegrated Services Digital Network
2interaction is possible What is ISDN ?1. End-to-end digital connectivity2. Enhanced subscriber signaling3. A wide variety of new services (due to 1 and 2)4. Standardized access interfaces and terminalsOriginal idea in the 1980’sISDN is not a “new” network separated from the PSTN. Interworking with “normal” PSTN equipment is very important.interaction is possibleISDN terminalPSTN terminal
3Evolution of the PSTN / ISDN Step 1: all-analogue network (before 1960)
4Evolution of the PSTN / ISDN Step 2: digital transmission in the core network ( )PDH transmission systems ( Mbit/s)
5Evolution of the PSTN / ISDN Step 3: digital switching of 64 kbit/s channels ( )Time switching technology
6Evolution of the PSTN / ISDN Step 4: common channel signalling in the core network ( )SS7
7Evolution of the PSTN / ISDN Step 5: PDH systems are being replaced by SDH ( )SDH transmission systems (155, 620 Mb/s)
8Evolution of the PSTN / ISDN Step 6: digital access lines (ISDN, ADSL) installed ( )End-to-end digital user dataEnd-to-end digital signalling
9Success of a new concept depends on: Public network => standardization important (there may be different equipment vendors, operators …) => open interfacesCritical mass of services, subscribers, and terminal equipment is needed before concept can be made comercially attractive (chicken and egg problem)Problem-free evolution & concept integrationDoes the user need this new concept?
10Digital access: several alternatives ISDNmodemADSLBit rate (kb/s) x 64 max much largerConnection fast slow fastsetup timePopularity little great increasingHowever, large impact on signalling protocols
11PSTN vs. ISDN user access 300 … 3400 Hz analogue transmission band“poor-performance” subscriber signalingPSTNBasic Rate Access ISDN2 x 64 kbit/s digital channels (B channels)16 kbit/s channel for signaling (D channel)30 x 64 kbit/s digital channels (B channels)64 kbit/s channel for signaling (D channel)concatenation of B channels possiblePrimary Rate Access ISDN
12Telecommunication services Basic telecommunication servicesBearer services provide the capability of transmitting signals between network access points. Higher-level functionality of user terminals is not specified.Teleservices provide the full communication capability by means of network functions, terminals, dedicated network elements, etc.Supplementary servicesA supplementary service modifies or supplements a basic telecommunication service. It cannot be offered to a customer as a stand-alone service.
13Services examples Some typical teleservices Telephony (normal, high quality)Telefax (Group 3, Group 4)Video-telephonySome typical bearer servicesSpeech (transparency not guaranteed)64 kbit/s unrestricted3.1 kHz audio (non-ISDN interworking)Some typical supplementary servicesCLIP / CLIRCall forwarding / waiting / holdCharging supplementary services
17OSI reference model 7. Application 6. Presentation 5. Session A (protocol residing in a) lower layer provides certain services to a (protocol in a) higher layer6. Presentation5. SessionProtocol Data Units (PDU)4. Transport3. NetworkHeadersRx endTx end2. Data Link1. Physical
18Relation between network connection elements and OSI model 7. ApplicationSome examples:6. PresentationGateway (GW), Interworking function (IWF)5. Session4. Transport3. NetworkRouter, Switching function2. Data LinkBridge, Relaying function1. PhysicalSDH cross-connect
19Tasks of OSI layers: 7. Application 6. Presentation 5. Session User application6. PresentationCompression & coding5. SessionDialogue control4. TransportEnd-to-end flow & error control3. NetworkSwitching & routing2. Data LinkLink-layer flow & error control1. PhysicalMultiplexing & transport of bits
21Signalling protocols for end-to-end connection User interfacePSTN NetworkUser interfaceSS7Q.931Q.931ISUPISUPQ.931Q.931DSS1DSS1MTP 3MTP 3Q.921Q.921MTP 2MTP 2Q.921Q.921I.430I.430MTP 1MTP 1I.430I.430contains the signalling messages for call control
22Layered DSS1 signaling structure DSS1 = Digital Subscriber Signalling system no.1Layer 1:Bit sequence structure, framing & multiplexingLayer 2:Link control (HDLC-type protocol called LAPD)Layer 3:Signaling messages (application layer)I.430Q.921Q.931
23LAPD (Q.921) is used forEstablishing data link connections identified by the Data Link Connection Identifier (DLCI = SAPI + TEI)Frame delimiting, alignment and transparency, allowing recognition of frames transmitted over the D-channelFlow control: (a) to maintain the sequential order of frames across a data link connection, (b) temporarily stopping transmissionError Control: detection of errors on a data link connection, recovery from errors, and notification to the management entity of unrecoverable errors
24Q.931 Call-related messages Call establishment messages: ALERTINGCALL PROCEEDINGCONNECTCONNECT ACKNOWLEDGEPROGRESSSETUPSETUP ACKNOWLEDGECall clearing messages:DISCONNECTRELEASERELEASE COMPLETESimilar functions as ISUP in SS7
25Typical content of ISDN Set-up message Called party (user B) number & numbering planCalling party (user A) number (+ CLIP/CLIR)Bearer capability (64 kbit/s unrestricted, speech, 3.1 kHz audio, packet mode B-channel, packet mode D-channel)Channel identification (B1, B2, or D channel request)Low-layer compatibility (type of bit rate adaptation, type of modem …)High-layer compatibility (teleservice-related issues)Keypad facilityShow to B?
26Structure of Q.931 message (Release) Message type: RELEASE Significance: Local Direction: BothInfo Element Direction Type LengthProtocol Both M 1discriminatorCall reference Both M 2-Message type Both M 1Cause Both ODisplay n u OSignal n u OCause description may require many bytes
27Setup of a PSTN call off-hook SS7 ISUP dial tone B number ringing tone User AExchange AExchange BUser Boff-hookSS7 ISUPdial toneB numberringing toneringing toneuser B answersconnection ok
28Setup of an ISDN call using Q.931 User AExchange AExchange BUser BSetupoff-hookSetupCall proceedSS7 ISUPAlert“ring”AlertConnectuser B answersConnectconnection ok
29Intelligent Network concept SS7Common ChannelSignalling System Nr. 7INIntelligent Network concept
30History of inter-exchange signalling Before 1970, only channel-associated signalling (CAS) was used. In CAS systems, signalling always occurs in-band (i.e. over voice channels).CASSS6 = CCIS (common channel interoffice signaling) was widely deployed in North America, but not in Europe (=> concentrating on SS7 instead).CCISStarting from 1980 (mainly in Europe), CAS was being replaced by SS7. The use of stored program control (SPC) exchanges made this possible. Like CCIS, signalling messages are transmitted over separate signalling channels. Unlike CCIS, SS7 technology is based on protocol stacks.SS7
31Channel-associated signalling (CAS) CAS means in-band signalling over voice channels.signalling possiblesignalling not possible (yet)ExchangeExchangeExchangecircuit switched connectionCAS has two serious draw-backs:1) Setting up a circuit switched connection is very slow.2) Signalling to/from databases is not possible (setting up a circuit switched connection to the database would be extremely inconvenient).
32Common channel signalling (CCS) In practice, CCS = SS7 (except maybe North America).In Finnish: CCS = yhteiskanavamerkinanto (YKM)signalling possible anywhere anytimeExchangeExchangeDatabaseThe packet-switched signalling network is separated from circuit switched connections. Consequently:1) Signalling to/from databases is possible anytime.2) End-to-end signalling is possible before call setup and also during the conversation phase of a call.
33CAS vs. CCS Tokyo Oulu Exch User A (calling user) Exch Exch User B (called user)ExchDatabase1) Accessing databaseEspoo2) Signalling before call setup3) Signalling during conversation phase(user-to-user => digital access technology required)
34Signalling points (SP) in SS7 Every SP is identified by a unique signalling point codeSignalling Transfer Point (only related to SS7 network)STPSTPSignalling Point (in a database, such as HLR in GSM)SPMAP INAP CAPApplication protocols used in SS7STPExchangeSPSignalling Point (signalling termination in an exchange)ISUP
35Intelligent Network (IN) Concept Intelligence => access to various databasesOperator implements service logic (IN Service)STPSCPService Control Point(a network element containing the service logic, is often also called database or register)MAP INAP CAPExchangeSSPService Switching Point(enables service triggering in an exchange)ISUP
36Typical call-related IN procedure (1) 3.SCP2.4.SSP1.5.ExchangeExchange1. Call routing proceeds up to Exchange2. Trigger activated in Basic Call State Model at SSP3. SSP requests information from SCP (database)4. SCP provides information5. Call routing continues (routing to next exchange)
37Typical call-related IN procedure (2) 3.SCP2.4.SSP1.5.ExchangeExchange2. Trigger activated in Basic Call State Model at SSPTypical triggers:Called number (or part of number)Access code or ID informationTime (hour, day) or location (mobile system)Calling number (or part of number)
38Typical call-related IN procedure (3) 3.SCP2.4.SSP1.5.ExchangeExchange4. SCP provides informationExample: Number translation in SCPSSP sends 800 number ( )SCP translates into ”real” number whichcan be used for routing the call( )translation may be based on several variables
39IN service examples “Traditional” IN services: - Freephone / customised charging schemes- Virtual Privat Network (VPN)- Number portability- Televoting“IN” in mobile networks:- Mobility management (HLR, VLR = databases)- Security management (Authentication ...)- CAMEL IN in mobile networks (CustomisedApplications for Mobile networks Enhanced Logic)
40Protocol layers (”levels”) of SS7 Application protocolsTUPISUPMAPCAPINAPTCAPSCCProutingMTP level 3MTP level 2 (link-layer protocol)MTP level 1 (64 kbit/s PCM time slot)MTP - Message Transfer PartSCCP - Signalling Connection Control PartUP - User Part AP - Application Part
41Application protocols in SS7 TUP (Telephone User Part) – is being replaced by ISUPISUP (ISDN User Part) – for all signalling related to setting up, maintaining, and releasing circuit switched connectionsMAP (Mobile User Part) – for transactions between exchanges (MSC, GMSC) and databases (HLR, EIR, AuC) in mobile networksINAP (Intelligent Network Application Part) for IN applications in fixed networksCAP (CAMEL Application Part) for extended IN functionality in mobile networks (where MAP is not sufficient ...)
42MTP functions MTP level 1 (signalling data link level): MTP level 2 (signalling link level):MTP level 3 (signalling network level):Physical transmission (e.g. 64 kbit/s PCM time slot)HDLC-type frame-based protocol for flow control, error control (using ARQ), and signalling network supervision and maintenance functions.Routing in the signalling network (using OPC, DPC) between SPs with level 4 users (see SIO at level 2).
43MTP level 2 frame formats Level 3 signalling messageMSU (Message Signal Unit)FCKSIFSIOLIControlFNetwork:NationalInternationalUser part:TUPISUPSCCPNetworkmanagementLSSU (Link Status Signal Unit)FCKSFLIControlFFISU (Fill-In Signal Unit)FCKLIControlF
44MTP level 2 frames MSU (Message Signal Unit): Contains signalling messages (User Part SIO)The received frame is MSU if LI > 2 (number of octets)LSSU (Link Status Signal Unit):Contains signalling messages for link supervisionThe received frame is LSSU if LI = 1 or 2FISU (Fill-In Signal Unit):Can be used to monitor quality of signalling linkThe received frame is FISU if LI = 0
45Routing information in SS7 message Level 3 signalling message in SIF (Signalling Information Field)Routing labelMTP management message:SLC – 4 bit signalling link codeSLCOPCDPCMTP SCCP message:SLS – 4 bit signalling link selectionSLSOPCDPCMTP TUP message:CIC – 12 bit circuit ID codeCICOPCDPC
46Structure of SS7 ISUP message Level 3 signalling message in SIF (Signalling Information Field)Routing labelMTP ISUP message:SLS – 4 bitCIC – 12 bitMax octetsCICSLSOPCDPCITU-T structureANSI => differentOpPMaVPMaFPMTCMTC: Message Type Code (name of ISUP message)MaFP: Mandatory Fixed Part (no LI, no parameter names required)MaVP: Mandatory Variable Part (LI, no parameter names required)OpP: Optional Part (LI and parameter names required)
47Difference between SLS and CIC SLS defines the signalling link which is used for transfer of signalling information.CIC defines the circuit (used for a certain circuit switched connection) with which the ISUP message is associated.signalling linkSTPExchangeSSPSSPExchangecircuit
48Role of DPC and OPC in SS7DPC – Destination Point Code (14 bit SPs)Termination point of application transactionKey information for routing within SS7 networkDPC is inserted by the originating MTP ”user”.OPC – Originating Point Code (14 bit)Originating point of application transactionThe ”network indicator” in the SIO octet determines whether the DPC or OPC is an international, national, or network dependent SP identifier.FCKSIFSIOLIControl
49Same signalling point codes can be reused at different network levels InternationalSPC = 277NationalSPC = 277Network specificSPC = 277SPC = 277 means different SPs at different network levels
51ISUP (Integrated Services User Part) Essential for circuit-switching related signallingNot only ISDN (can be generally used in PSTN)Features:Establishment / release of circuit switched connections (basic call control) using link-by-link signallingEnd-to-end signalling between two exchanges (for this purpose SCCP + ISUP is used)General (non-user-related) circuit managementsee Bhatnagar, p.77
52Example: link-by-link routing Using MTP-level routing table, STP routes message to DPC = 22STPSTPOutgoing MTP MSU:OPC = 22 CIC = 20DPC = 60 SLS = 2SL 2SPC = 15SPC = 18SL 4SL 7ExchangeSPC = 82ExchangeSPC = 22ExchangeSPC = 60Circuit 20Circuit 14Outgoing message:OPC = 82 CIC = 14DPC = 22 SLS = 4Processing in (transit) exchange(s):Received message is sent to user (ISUP) that gives B-number to exchange. Exchange performs number analysis and selects new DPC (60) and CIC (20)
53MTP + ISUP in SS7The routing capability of MTP is rather limited (routing tables are entirely based on signalling point codes).Exchanges perform the routing through the network(s) during the establishment of circuit switched connections on an exchange-to-exchange basis, using the dialed digits and routing tables.exchange IDCountry code National region Subscriber number
54Example: link-by-link signalling Using MTP-level routing table, STP routes message to DPC = 22Otherwise like link-by-link routing,only difference is hereSTPSTPOutgoing MTP MSU:OPC = 22 CIC = 20DPC = 60 SLS = 2SL 2SPC = 15SPC = 18SL 4SL 7ExchangeSPC = 82ExchangeSPC = 22ExchangeSPC = 60Circuit 20Circuit 14Outgoing message:OPC = 82 CIC = 14DPC = 22 SLS = 4Processing in (transit) exchange(s):Using routing table and incoming routing label, exchange inserts DPC (60) and CIC (20) into outgoing routing label (no number analysis … )
55Setup of a call using ISUP User AExchange ATransit exchangeExchange BUser BSetupIAMIAMSetupQ.931Link-by-link routing (number analysis)AlertACMACMAlertConnectANMANMConnectLink-by-link signalling (no number analysis)Charging of call starts now
56Some basic ISUP messages user A user BIAM – Initial Address MessageACM – Address Complete MessageANM – Answer MessageREL – Release MessageRLC – Release Complete
57Signalling sequence 1 (call setup) User ALE ATELE BUser BOff hookLocal exchange detects setup request and returns dial toneDial toneB numberLocal exchange:analyzes B numberdetermines that call should be routed via transit exchange (TE)
58Signalling sequence 2 (call setup) User ALE ATELE BUser BInitial address message (IAM)ISUP message IAM is sent to transit exchange.Transit exchange analyzes B number and determines that call should be routed to local exchange of user B (LE B).IAM message is sent to LE B.Within all exchanges, the path is cut through (circuit switched path between user A and LE B).
59Signalling sequence 3 (call setup) User ALE ATELE BUser BAddress completemessage (ACM)Ringing signalRinging toneorRinging signal is sent to user B (user B is alerted).Ringing tone is sent to user A.(Ringing tone is generated locally at LE A or is sent from LE B through circuit switched path)
60Signalling sequence 4 (call setup) Conversation over this “pipe”User ALE ATELE BUser BAnswer message (ANM)User B answersCharging starts nowUser B answers, connection is cut through at LE B.Charging of the call starts when ANM message is received at LE A.Conversation can take place over the bi-directional circuit switched connection.
61E.164 numbering scheme 00 358 9 1234567 International number 9 1234567 9National numberUser numberPrefixCountry code358Area code9or mobile network code40In each exchange, the B number is analyzed at call setup and a routing program (algorithm) selects the next exchange to which the call is routed.
62Signalling sequence (call release) Conversation over this “pipe”Signalling sequence (call release)User ALE ATELE BUser BOn hookRelease (REL)Charging stopsRelease complete (RLC)The connection links are released one by one.(“Hanging links” are blocked from further use)
63SCCP (Signalling Connection Control Part) Essential for non-circuit-switching related signallingFeatures:Essential for end-to-end signalling & database accessGlobal Title Translation (GTT) for enhanced routingSubSystem Number (SSN) analysis at destination4 Transport Service ClassesOSI Layer 3 functionalityOSI Layer 4 functionality
64SS7 connection setup using SCCP Signalling connection, not circuit switched connection (= call)User(AP)User applicationsUser(AP)User(AP)User(AP)SCCPSCCPGT translationSCCPSSN analysisMTPMTPMTPSSP STP SCP
65Global title translation (GTT) Global title translation (GTT) is required when the originating exchange (SSP) knows a ”global title” but does not know the DPC of the database (SCP).SSPSTPSCPGlobal title (GT) examples:Translation in STP0800 number => SCPIMSI => HLRGT => DPC + SSN
66Why GTT in STP network node? Global title translation (GTT) is usually done in an STP.Advantage: Advanced routing functionality (= GTT) needed only in a few STPs with large packet handling capacity, instead of many SSPs (exchanges).SSPSSPSCPSCPSSPSTPSSPSCPSSP
67Example: SCCP connection with GTT No SCCP functionalitySTPSTPSCCP functionalitySTPSPC = 32SCCPSCCPMSC/VLR located in EspooHLR located in OsloSPC = 82SPC = 99Outgoing message:OPC = 82 DPC = 32SCCP: IMSI global titleProcessing in STP:Received message is given to SCCP for GTT. SCCP finds the DPC of the HLR: DPC = 99
68Four classes of service in SCCP Class 0: Basic connectionless class. Each information block (SCCP message) is transmitted from one SCCP user to another SCCP user independently.Class 1: Sequenced (MTP) connectionless class. All messages use the same SLS code.Class 2: Basic connection-oriented class. Virtual connections are set-up and released + using same SLS code + segmentation & reassembly (SAR)Class 3: Flow-control connection-oriented class. VC control + same SLS codes + SAR + flow control
69Signalling in GSM core network ISUP for signalling between exchanges (MSC, GMSC)MAP for signalling to/from databases (VLR, HLR, AuC, EIR)MM / CMRRBSSMAP / DTAPMAPTCAPMAPSCCPISUPBSSAPBSSAPTCAPMTPSCCPSCCPSCCPHLRMTPMTPA interfaceBSCMSC / VLRto GMSC
70Further information on SS7 Tutorials:Modarressi, Skoog: ”SS7: a tutorial”, IEEE Comm. Magazine, July 1990Jabbari: ”CCSS7 for ISDN and IN”, Proc. IEEE, Feb. 1991Books:Bhatnagar: Engineering networks for synchronization, CCS7, and ISDN, IEEE Press, 1997Van Bosse: Signaling in telecommunication networks, Wiley, 1998Web material:(the course book)