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ISDN Integrated Services Digital Network. What is ISDN ? 1. End-to-end digital connectivity 2. Enhanced subscriber signaling 3. A wide variety of new.

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Presentation on theme: "ISDN Integrated Services Digital Network. What is ISDN ? 1. End-to-end digital connectivity 2. Enhanced subscriber signaling 3. A wide variety of new."— Presentation transcript:

1 ISDN Integrated Services Digital Network

2 What is ISDN ? 1. End-to-end digital connectivity 2. Enhanced subscriber signaling 3. A wide variety of new services (due to 1 and 2) 4. Standardized access interfaces and terminals ISDN is not a “new” network separated from the PSTN. Interworking with “normal” PSTN equipment is very important. ISDN terminal PSTN terminal interaction is possible Original idea in the 1980’s

3 Step 1: all-analogue network (before 1960) Evolution of the PSTN / ISDN

4 Step 2: digital transmission in the core network ( ) PDH transmission systems ( Mbit/s) Evolution of the PSTN / ISDN

5 Step 3: digital switching of 64 kbit/s channels ( ) Time switching technology Evolution of the PSTN / ISDN

6 Step 4: common channel signalling in the core network ( ) SS7 Evolution of the PSTN / ISDN

7 Step 5: PDH systems are being replaced by SDH ( ) SDH transmission systems (155, 620 Mb/s) Evolution of the PSTN / ISDN

8 Step 6: digital access lines (ISDN, ADSL) installed ( ) End-to-end digital user data End-to-end digital signalling Evolution of the PSTN / ISDN

9 Success of a new concept depends on: Public network => standardization important (there may be different equipment vendors, operators …) => open interfaces Critical mass of services, subscribers, and terminal equipment is needed before concept can be made comercially attractive (chicken and egg problem) Problem-free evolution & concept integration Does the user need this new concept?

10 Digital access: several alternatives ISDNmodem Bit rate (kb/s) 2 x 64max. 50 much larger Connection fast slow fast setup time Popularity little great increasing ADSL However, large impact on signalling protocols

11 PSTN vs. ISDN user access 300 … 3400 Hz analogue transmission band “poor-performance” subscriber signaling 2 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 possible PSTN Basic Rate Access ISDN Primary Rate Access ISDN

12 Telecommunication services Basic telecommunication services Bearer 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 services A supplementary service modifies or supplements a basic telecommunication service. It cannot be offered to a customer as a stand-alone service.

13 Services examples Some typical teleservices  Telephony (normal, high quality)  Telefax (Group 3, Group 4)  Video-telephony Some typical bearer services  Speech (transparency not guaranteed)  64 kbit/s unrestricted  3.1 kHz audio (non-ISDN interworking) Some typical supplementary services  CLIP / CLIR  Call forwarding / waiting / hold  Charging supplementary services

14 Basic rate access – user interface Exchange Terminal Adaptor ISDN terminal Network Termination Non-ISDN terminal Line Interface Circuit Line Interface Circuit Bi-directional 192 kbit/s 160 kbit/s echo canceling or time compression R S/TU Exchange Subscriber (premises) network

15 Primary rate access – user interface PBX Line Termination Line Termination Standard 2 Mb/s TDM connection (PDH or SDH) PBX equipment manufacturer specific solutions Exchange U 64 kb/s D channel in one PCM time slot

16 ISDN Signalling Protocols

17 7. Application 6. Presentation 5. Session 4. Transport 3. Network 2. Data Link 1. Physical OSI reference model A (protocol residing in a) lower layer provides certain services to a (protocol in a) higher layer Protocol Data Units (PDU) Headers Tx end Rx end

18 7. Application 6. Presentation 5. Session 4. Transport 3. Network 2. Data Link 1. Physical Relation between network connection elements and OSI model SDH cross-connect Gateway (GW), Interworking function (IWF) Router, Switching function Bridge, Relaying function Some examples:

19 7. Application 6. Presentation 5. Session 4. Transport 3. Network 2. Data Link 1. Physical Tasks of OSI layers: Multiplexing & transport of bits Switching & routing Link-layer flow & error control End-to-end flow & error control User application Compression & coding Dialogue control

20 Typical protocol interaction End node End node Intermediate nodes End node End node Phy Link Net Tran App : Phy Link Net Tran App : Phy Link Net Phy Link Phy Link Phy Switch, routerRelay, bridge

21 Signalling protocols for end-to-end connection ISUP Q.931 Q.921 I.430 Q.931 Q.921 I.430 MTP 3 MTP 2 MTP 1 Q.931 Q.921 I.430 Q.931 Q.921 I.430 ISUP MTP 3 MTP 2 MTP 1 contains the signalling messages for call control User interface PSTN Network DSS1 SS7 DSS1

22 Layered DSS1 signaling structure DSS1 = Digital Subscriber Signalling system no.1 Layer 1: Bit sequence structure, framing & multiplexing Layer 2: Link control (HDLC-type protocol called LAPD) Layer 3: Signaling messages (application layer) I.430 Q.921 Q.931

23 LAPD (Q.921) is used for Establishing 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-channel Flow control: (a) to maintain the sequential order of frames across a data link connection, (b) temporarily stopping transmission Error Control: detection of errors on a data link connection, recovery from errors, and notification to the management entity of unrecoverable errors

24 Q.931 Call-related messages Call establishment messages: ALERTING CALL PROCEEDING CONNECT CONNECT ACKNOWLEDGE PROGRESS SETUP SETUP ACKNOWLEDGE Call clearing messages: DISCONNECT RELEASE RELEASE COMPLETE Similar functions as ISUP in SS7

25 Typical content of ISDN Set-up message Called party (user B) number & numbering plan Calling 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 facility Show to B?

26 Structure of Q.931 message (Release) Message type: RELEASE Significance: Local Direction: Both Info ElementDirectionTypeLength Protocol Both M 1 discriminator Call reference Both M 2- Message type Both M 1 Cause Both O 2-32 Display n  u O Signal n  u O 2-3 Cause description may require many bytes

27 Setup of a PSTN call Exchange AExchange BUser AUser B ringing tone user B answers off-hook connection ok SS7 ISUP dial tone B number ringing tone

28 Setup of an ISDN call using Q.931 Exchange AExchange BUser AUser B Setup Alert Connect Alert Connect Call proceed “ring” user B answers off- hook connection ok SS7 ISUP

29 SS7 Common Channel Signalling System Nr. 7 IN Intelligent Network concept

30 History of inter-exchange signalling SS6 = CCIS (common channel interoffice signaling) was widely deployed in North America, but not in Europe (=> concentrating on SS7 instead). Starting 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. Before 1970, only channel-associated signalling (CAS) was used. In CAS systems, signalling always occurs in-band (i.e. over voice channels). CAS CCIS SS7

31 Channel-associated signalling (CAS) CAS means in-band signalling over voice channels. 2) Signalling to/from databases is not possible (setting up a circuit switched connection to the database would be extremely inconvenient). Exchange circuit switched connection signalling possiblesignalling not possible (yet) CAS has two serious draw-backs: 1) Setting up a circuit switched connection is very slow.

32 Common channel signalling (CCS) The packet-switched signalling network is separated from circuit switched connections. Consequently: In practice, CCS = SS7 (except maybe North America). In Finnish: CCS = yhteiskanavamerkinanto (YKM) Exchange signalling possible anywhere anytime Database 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.

33 CAS vs. CCS 2) Signalling before call setup Exch User A (calling user) Database 1) Accessing database 3) Signalling during conversation phase (user-to-user => digital access technology required) OuluTokyo Espoo User B (called user) Exch

34 Signalling points (SP) in SS7 Every SP is identified by a unique signalling point code Exchange STP SP STP Signalling Point (in a database, such as HLR in GSM) Signalling Transfer Point (only related to SS7 network ) Signalling Point (signalling termination in an exchange) STP MAP INAP CAP ISUP Application protocols used in SS7

35 Intelligent Network (IN) Concept Exchange STP SCP SSP Service Control Point (a network element containing the service logic, is often also called database or register) Service Switching Point (enables service triggering in an exchange) MAP INAP CAP Intelligence => access to various databases ISUP Operator implements service logic (IN Service )

36 Typical call-related IN procedure (1) SSP Exchange SCP Exchange 1. Call routing proceeds up to Exchange 2. Trigger activated in Basic Call State Model at SSP 3. SSP requests information from SCP (database) 4. SCP provides information 5. Call routing continues (routing to next exchange)

37 SSP Exchange SCP Exchange 2. Trigger activated in Basic Call State Model at SSP Typical triggers: Called number (or part of number) Access code or ID information Time (hour, day) or location (mobile system) Calling number (or part of number) Typical call-related IN procedure (2)

38 SSP Exchange Exchange Example: Number translation in SCP SSP sends 800 number ( ) SCP translates into ”real” number which can be used for routing the call ( ) 4. SCP provides information SCP Typical call-related IN procedure (3) translation may be based on several variables

39 IN 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 (Customised Applications for Mobile networks Enhanced Logic )

40 Application protocols Protocol layers (”levels”) of SS7 MTP - Message Transfer Part SCCP - Signalling Connection Control Part UP - User PartAP - Application Part CAP INAP MAP ISUP TCAP SCCP TUP MTP level 3 MTP level 2 (link-layer protocol) MTP level 1 (64 kbit/s PCM time slot) routing

41 Application protocols in SS7 TUP (Telephone User Part) – is being replaced by ISUP ISUP (ISDN User Part) – for all signalling related to setting up, maintaining, and releasing circuit switched connections MAP (Mobile User Part) – for transactions between exchanges (MSC, GMSC) and databases (HLR, EIR, AuC) in mobile networks INAP (Intelligent Network Application Part) for IN applications in fixed networks CAP (CAMEL Application Part) for extended IN functionality in mobile networks (where MAP is not sufficient...)

42 MTP 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).

43 MTP level 2 frame formats F F CK SIF SIO LI Control F F F F CK SF LI Control F F F F CK LI Control F F MSU (Message Signal Unit) LSSU (Link Status Signal Unit) FISU (Fill-In Signal Unit) Level 3 signalling message Network: National International User part: TUP ISUP SCCP Network management

44 MTP 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 supervision The received frame is LSSU if LI = 1 or 2 FISU (Fill-In Signal Unit): Can be used to monitor quality of signalling link The received frame is FISU if LI = 0

45 Routing information in SS7 message Level 3 signalling message in SIF (Signalling Information Field) SLC OPC DPC MTP management message: SLC – 4 bit signalling link code CIC OPC DPC MTP TUP message: CIC – 12 bit circuit ID code SLS OPC DPC MTP SCCP message: SLS – 4 bit signalling link selection Routing label

46 Level 3 signalling message in SIF (Signalling Information Field) Routing label OpP MaVP MaFP MTC CIC SLS OPC DPC MTP ISUP message: SLS – 4 bit CIC – 12 bit Max octets ITU-T structure ANSI => different MTC: 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) Structure of SS7 ISUP message

47 Difference 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. Exchange SSP STP Exchange SSP circuit signalling link

48 Role of DPC and OPC in SS7 DPC – Destination Point Code (14 bit  SPs) Termination point of application transaction Key information for routing within SS7 network DPC is inserted by the originating MTP ”user”. OPC – Originating Point Code (14 bit) Originating point of application transaction The ”network indicator” in the SIO octet determines whether the DPC or OPC is an international, national, or network dependent SP identifier. F F CK SIF SIO LI Control F F

49 Same signalling point codes can be reused at different network levels SPC = 277 International National Network specific SPC = 277 means different SPs at different network levels

50 Functions at signalling network level MTP user ISUP SCCP MTP user ISUP SCCP Signalling link MTP level 2 Signalling link MTP level 2 Message distribution Message distribution Message discrimination Message discrimination Message routing Message routing Signalling message handling Signalling network management

51 ISUP (Integrated Services User Part) Essential for circuit-switching related signalling Features: Establishment / release of circuit switched connections (basic call control) using link-by-link signalling End-to-end signalling between two exchanges (for this purpose SCCP + ISUP is used) General (non-user-related) circuit management Not only ISDN (can be generally used in PSTN) see Bhatnagar, p.77

52 Example: link-by-link routing Exchange SPC = 82 Circuit 14 SPC = 22SPC = 60 Circuit 20 SPC = 18SPC = 15 STP SL 4 Outgoing MTP MSU: OPC = 22 CIC = 20 DPC = 60 SLS = 2 SL 2 SL 7 STP Outgoing message: OPC = 82 CIC = 14 DPC = 22 SLS = 4 Processing 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) Using MTP-level routing table, STP routes message to DPC = 22

53 MTP + ISUP in SS7 The 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 Country code National region Subscriber number exchange ID

54 Example: link-by-link signalling Exchange SPC = 82 Circuit 14 SPC = 22SPC = 60 Circuit 20 SPC = 18SPC = 15 STP SL 4 Outgoing MTP MSU: OPC = 22 CIC = 20 DPC = 60 SLS = 2 SL 2 SL 7 STP Outgoing message: OPC = 82 CIC = 14 DPC = 22 SLS = 4 Processing 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 … ) Using MTP-level routing table, STP routes message to DPC = 22 Otherwise like link-by-link routing, only difference is here

55 Setup of a call using ISUP Exchange AExchange BTransit exchangeUser AUser B Setup IAM Setup Alert Connect ACM ANM ACM ANM Alert Connect Charging of call starts now Link-by-link routing (number analysis)Q.931 Link-by-link signalling (no number analysis)

56 Some basic ISUP messages IAM – Initial Address Message ACM – Address Complete Message ANM – Answer Message REL – Release Message RLC – Release Complete user A user B

57 User AUser B Off hook Dial tone B number Local exchange detects setup request and returns dial tone Local exchange: analyzes B number determines that call should be routed via transit exchange (TE) LE ALE BTE Signalling sequence 1 (call setup)

58 User ALE ALE BTEUser B Initial 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). Signalling sequence 2 (call setup)

59 User AUser B Address complete message (ACM) LE ALE BTE Ringing signal Ringing tone Ringing 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) Signalling sequence 3 (call setup) or

60 User AUser B Answer message (ANM) LE ALE BTE User B answers User 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. Charging starts now Conversation over this “pipe” Signalling sequence 4 (call setup)

61 International number National number User number Prefix Country code Area code In 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. or mobile network code40 E.164 numbering scheme

62 User AUser BLE ALE BTE Conversation over this “pipe” On hook Release (REL) Release complete (RLC) The connection links are released one by one. (“Hanging links” are blocked from further use) Charging stops Signalling sequence (call release)

63 SCCP (Signalling Connection Control Part) Essential for non-circuit-switching related signalling Features: Essential for end-to-end signalling & database access Global Title Translation (GTT) for enhanced routing SubSystem Number (SSN) analysis at destination 4 Transport Service Classes OSI Layer 3 functionality OSI Layer 4 functionality

64 SS7 connection setup using SCCP Signalling connection, not circuit switched connection (= call) SCCP GT translation SCCP GT translation SSP STP SCP MTP User (AP) User (AP) User (AP) User (AP) User (AP) User (AP) User (AP) User (AP) MTP SCCP SSN analysis SCCP SSN analysis User applications

65 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). STP SCP SSP Global title translation (GTT) Global title (GT) examples: 0800 number => SCP IMSI => HLR Translation in STP GT => DPC + SSN

66 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). Why GTT in STP network node? STP SSP SCP SSP

67 Example: SCCP connection with GTT SCCP STP MSC/VLR located in Espoo HLR located in Oslo STP SPC = 82SPC = 99 SPC = 32 No SCCP functionality SCCP functionality Outgoing message: OPC = 82 DPC = 32 SCCP: IMSI global title Processing in STP: Received message is given to SCCP for GTT. SCCP finds the DPC of the HLR: DPC = 99

68 Four 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

69 A interface Signalling in GSM core network MAP TCAP MM / CM RR BSSMAP / DTAP MM / CM RR BSSMAP / DTAP MAP ISUP BSSAP TCAP BSSAP SCCP MTP SCCP MTP BSCMSC / VLR to GMSC HLR SCCP MTP ISUP for signalling between exchanges (MSC, GMSC) MAP for signalling to/from databases (VLR, HLR, AuC, EIR)

70 Further information on SS7 Tutorials: Modarressi, Skoog: ”SS7: a tutorial”, IEEE Comm. Magazine, July 1990 Jabbari: ”CCSS7 for ISDN and IN”, Proc. IEEE, Feb Books: Bhatnagar: Engineering networks for synchronization, CCS7, and ISDN, IEEE Press, 1997 Van Bosse: Signaling in telecommunication networks, Wiley, 1998 Web material: (the course book)


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