SS7 Signaling System

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SS7 Signaling SystemBy Common Technologies Department

Course Code: OIA0005

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ObjectivesUpon completion of this course,you will be able to: Understand the basic concepts in SS7 Understand the important composition of SS7 signalling units Understand the basic signalling procedures of SS7

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ContentsChapter 1 Chapter 2 Fundamentals of SS7 Message Transfer Part

Chapter 3Chapter 4 Chapter 5 Chapter 6 Chapter 7

Telephone User PartISDN User Part Signaling Connection Control Part Transaction Capabilities Application Part Intelligent Network Application Part3

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Chapter One

Fundamentals of SS7

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An Introduction to Signaling

In a telephony context, signaling means the passing of information and instructions from one point to another relevant to the setting up and supervision of a telephone call. By tradition, Signaling has been divided into two types: Subscriber Signaling i.e. signaling between a subscriber terminal (telephone) and the local exchange, and Trunk Signaling i.e. signaling between exchanges.Local Exchange Local Exchange

Subscriber Signalling

Trunk Signalling

Subscriber Signalling

c c s

c a s

c c s

c a s

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Subscriber Signaling

Calling Party A_NumberHOOK OFF DIAL TONE NUMBER RINGING TONE RINGING SIGNAL B ANSWER

Called Party B_Number

CONVERSATION

HOOK

ON

HOOK

ON

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Channel Associated Signaling (CAS)

Characteristic for CAS is that for each speech channel there is one unambiguously defined signaling path, either On-speech-path, i.e. the signals are transferred in the speech channel (in-band signaling) or Channel-associated, i.e. the signals are transferred in a separate signaling channel, for example the line signals are transferred in time slot 16 in PCM system.All of these signaling systems have a number of limitations like: Relatively slow, Limited information capacity, etc.

Switch 1

Switch 2

Voice Trunk Signaling Link7

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Common Channel Signaling (CCS)

In type of CCS, signaling for numerous circuits can be handled by a few fast signaling data links. The signaling is performed in both directions, with one signaling channel in each direction.The signaling information that will be transferred is grouped into signal units (data packets). Besides the signaling information itself, there is also need for speech circuit identification and address information (label) and information for error control. SS7 is a kind of CCS signaling system.Voice Trunk

SP

SPSignaling Link

STP

STP8

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Evolution of SS7

Common Channel Signaling System No. 7 (i.e., SS7 or C7), which was specified in 1979/80, is intended primarily for digital networks, both national and international, where the high transmission rate (64 kb/s)can be exploited. It may also be used on analog lines. SS7 signaling has not only been designed to control the setting up and supervision of telephone calls but of non -voice services also.

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Advantages of Using SS7

SS7 has several advantages compared with traditional signaling systems. Some obvious advantages are the following:FAST - the time for call set up is reduced to less than one second in most cases. HIGH CAPACITY - each signaling link can handle the signaling for several thousand simultaneous calls. ECONOMICAL - much less signaling equipment is required, compared to traditional signaling systems.

RELIABLE - by using alternate signaling routes, the signaling network can be made very secure.FLEXIBLE - the system can contain many more signals, for example, and can be used for other purposes than telephony.10

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Definition of CCS7 Signalling System

In CCS7, signalling links are independent of voice

channels. These signalling links form a network dedicated to the transmission of signalling, which is called CCS7 signalling network. It is a multifunctional supporting network, can be used in telephone network, circuit-switch data network, ISDN network, and intelligent network, etc.. Fundamentally, CCS7 signalling network is a packet switching data network used for dedicated purpose.11

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Three Elements in CCS7 Signalling Network

A CCS7 signalling network is composed of three elements:

signalling Point (SP), signalling Transfer Point (STP) and signalling Link.

Link

Voice Channel12

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Three Elements in CCS7 Signalling Network SP (Signalling Point)SP is the originating or destination point of a CCS7 message. In each signalling network, a SP has an exclusive signalling point code: SPC (14 bits). Since the four signalling networks assign the SPCs independently, only NI+SPC can uniquely locate a SP.Notes: In data setting we usually describe SPC in Hex. Following are some examples of SPC shown in binary and hex. SPC (binary) SPC (Hex) 00 0000 1011 0101 00b5 10 0011 1101 0111 23d713

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OPC and DPC ( I )

DPC: Destination Point Code OPC: Originating Point Code A message going from one SP to another SP should bear the SPC of the originating SP and the terminating SP, which are called OPC and DPC respectively. If we compare sending a message to sending a letter, OPC and DPC are similar to the sender's address and receiver's address.

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Three Elements in CCS7 Signalling Network STP (Signalling Transfer Point)STP is the network node which transfers CCS7 messages.

LinkLink is the data channel which connects the nodes (SPs and STPs) in CCS7 signalling network. Digital link, 64 kb/s

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Signaling Route & Signaling Route Set

The pre-determined path, that a message takes through the signaling network between the origination point and the destination point is called a Signaling Route. It may consist of a succession of SP/STPs and the interconnecting SLs. All the Signaling Routes that may be used between an origination point and a destination point by a message traversing the signaling network is the Signaling Route Set for that signaling relation.

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Working Modes of CCS7 Signalling NetworkWorking mode refers to the relationship between the signalling link and the voice channels the link serves. Presently two modes are in use: Associated mode The messages between two adjacent points are conveyed over a link-set directly interconnecting those signalling points, i.e., the link is parallel to the voice path.

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Working Modes of CCS7 Signalling Network

Quasi-associated mode In the quasi-associated mode the message which is going to arrive at a SP goes through a path which is predetermined and via one or more STPs.

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When the links between any two offices are transferred by a STP, how will be the link path?

Note: the sole purpose of using signalling is to serve the voice path.19

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When the links between any two offices are transferred by a STP, how will be the link path?

Note: the arrows show the paths that signalling messages go through. Remember, a signalling path always starts from one end of the voice path it is going to serve, and ends up at the other end of the voice path.

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An Example of Signaling Network

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SS7 Protocol Stack

The OSI Reference Model and the SS7 Protocol Stack

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Chapter Two

Message Transfer Part

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MTP Level 1

The lowest level, MTP Level 1 defines the physical, electrical, and functional characteristics of the digital signaling link. Physical interfaces defined include E-1 (2048 kb/s; 32 64 kb/s channels), DS-1 (1544 kb/s; 24 64 kp/s channels), V.35 (64 kb/s), DS-0 (64 kb/s), and DS-0A (56 kb/s).

MTP Level 1 is equivalent to the OSI Physical Layer.

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MTP Level 2

MTP Level 2 ensures accurate end-to-end transmission of a message cross a signaling link. Level 2 implements flow control, message sequence validation, and error checking. When an error occurs on a signaling link, the message (or set of messages) is retransmitted. MTP Level 2 is equivalent to the OSI Data Link Layer.

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MTP Level 3

MTP Level 3 provides message routing between signaling points in the SS7 network. MTP Level 3 re-routes traffic away from failed links and signaling points and controls traffic when congestion occurs. MTP Level 3 is equivalent in function to the OSI Network Layer.

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Signaling Unit (SU)

An SS7 message is called a signal unit (SU). There are three kinds of signal units: Fill-In Signal Units (FISUs), Link Status Signal Units (LSSUs), and Message Signal Units (MSUs)

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Fill-in Signal Units (FISUs)

Fill-In Signal Units (FISUs) are transmitted continuously on a signaling link in both directions unless other signal units (MSUs or LSSUs) are present. FISUs carry basic level 2 information only (e.g., acknowledgment of signal unit received by a remote signaling point). Because a CRC checksum is calculated for each FISU, signaling link quality is checked continuously by both signaling points at either end of the link.28

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Link Status Signal Unit (LSSUs)

Link Status Signal Units (LSSUs) carry one or two octets (8-bit bytes) of link status information between signaling points at either end of a link. The link status is used to control link alignment and to indicate the status of a signaling point (e.g., local processor outage) to the remote signaling point.29

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Message Signal Units (MSUs)

Message Signal Units (MSUs) carry all call control, database query and response, network management, and network maintenance data in the signaling information field (SIF). MSUs have a routing label which allows an originating signaling point to send information to a destination signaling point across the network.30

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Length Indicator (LI)

LI Value 0 1..2

Signal Unit Type Fill-In Signal Unit (FISU) Link Status Signal Unit (LSSU)

3..63

Message Signal Unit (MSU)

The value of the LI (Length Indicator) field determines the signal unit type. The 6-bit LI can store values between zero and 63. If the number of octets which follow the LI and precede the CRC is less than 63, the LI contains this number. Otherwise, the LI is set to 63. An LI of 63 indicates that the message length is equal to or greater than 63 octets (up to a maximum of 273 octets). The maximum length of a signal unit is 279 octets: 273 octets (data) + 1 octet (flag) + 1 octet (BSN + BIB) + 1 octet (FSN + FIB) + 1 octet (LI + 2 bits spare) + 2 octets (CRC).31

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Flag

The flag indicates the beginning of a new signal unit and implies the end of the previous signal unit (if any). The binary value of the flag is 0111 1110. Before transmitting a signal unit, MTP Level 2 removes "false flags" by adding a zero-bit after any sequence of five one-bits. Upon receiving a signal unit and stripping the flag, MTP Level 2 removes any zero-bit following a sequence of five one-bits to restore the original contents of the message. Duplicate flags are removed between signal units.

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CRC (Cyclic Redundancy Check)

The CRC value is used to detect and correct data transmission errors.

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BSN, BIB, FSN & FIB

BSN (Backward Sequence Number) is used to acknowledge the received signal units by the remote signaling point. The BSN contains the sequence number of the signal unit being acknowledged. BIB (Backward Indictor Bit) indicates a negative acknowledgment by the remote signaling point when toggled. FSN (Forward Sequence Number) contains the sequence number of the signal unit. FIB (Forward Indicator Bit) is used in error recovery like the BIB.

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Basic Error Correction MethodFSN=63

FSN

A

BSNBSN=63 BIB=FIB

B

Positive AcknowledgementFSN=63

FSN

A

BSNNegative Acknowledgement

B35

BSN=62 BIB=Toggled Value of FIB

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SIO (Service Information Octet)

Service Information OctetSubService Field Service Indicator

DC BA International Network International Reserved National Network National Reserved 0 0 1 1 0 1 0 1Spare

DCBA 0000 0001 0010 0011 0100 0101 0110 0111 to 1111 Signaling Network Management Maintenance Test Message Spare SCCP Telephone User Part ISDN User Part Data User Part

Network Indicator

Spare

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SIF (Signaling Information Field)

The SIF in an MSU contains the routing label and signaling information (e.g., SCCP, TCAP, and ISUP message data).

LSSUs and FISUs contain neither a routing label nor an SIO as they are sent between two directly connected signaling points. For more information about routing labels, refer to the description below.

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MTP Level 3 Routing Label

MTP Level 3 routes messages based on the routing label in the signaling information field (SIF) of MSUs. The routing label is comprised of the destination point code (DPC), originating point code (OPC), and signaling link selection (SLS) field.Signaling Points Codes are numeric addresses which uniquely identify each signaling point in the SS7 network. The DPC in a message indicates the receiving signaling point, and the OPC in a message indicates the originating signaling point. The message is distributed to the appropriate user part (e.g., ISUP or SCCP) indicated by the service indicator in the SIO. The selection of outgoing link is based on information in the DPC and SLS.38

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MSU - Message Signal Unit

F CK

SIF

SIO LI

Error Correction

F

ROUTING LABEL SLS OPC DPC NI(Spare)

SI

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ITU-T point codes are pure binary numbers which may be stated in terms of zone, area/network, and signaling point identification numbers. For example, the point code 5557 (decimal) may be stated as 2-1825 (binary 010-10110110-101). The point code always uses 3-segment format.40

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Signaling Link Selection (SLS)

The selection of outgoing link is based on information in the DPC and Signaling Link Selection field. The SLS is used to: Ensure message sequencing. Any two messages sent with the same SLS will always arrive at the destination in the same order in which they were originally sent. Allow equal load sharing of traffic among all available links. In theory, if a user part sends messages at regular intervals and assigns the SLS values in a round-robin fashion, the traffic level should be equal among all links (within the combined linkset) to that destination. MTP Level 3 re-routes traffic away from failed links and signaling points and controls traffic when congestion occurs.41

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OPC and DPC ( II )In the following two figures, what's the DPC and OPC of the messages?

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Answer

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Chapter Three

Telephone User Part

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Overview of TUP

The Telephone User Part defines the necessary telephone signaling functions in SS7 for international as well as national telephone traffic. It provides the same features for telephone signaling as other ITU-T signaling systems. The telephone signals are transferred in the signaling network as the form of signaling messages, which are the contents in the SIF field in the Message Signal Units (MSUs).

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TUP Message Structure

MSU of TUP F8

CK16

SIF SIO8n,n 2 8 2

LI6

Error Correction16

F8Transmission Direction

Signal Infor

H1 H0

Label

12CIC SLS

14

14

OPCRouting Label

DPC

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TUP Signals

Message Group

H1 H0 0000

0000

0001

0010

0011

0100

0101

0110

0111

1000

1001

1010

1011

1100

1101

1110

1111

Spare, reserved for national use IAM GSM GRQ ACM SEC ANU ANC RLG MGB CGH CGC ANN BLO MBA NNC CBK BLA MGU ADI CLF UBL MUA CFL RAN UBA HGB SSB FOT CCR HBA UNN CCL RSC HGU HUA GRS GRA SGB SBA SGU SUA LOS SST ACB DPN MPR EUM IAI SAM COT SAO CCF

FAM FSM BSM SBM UBM CSM CCM GRM

0001 0010 0011 0100 0101 0110 0111 1000 1001

Reserved ACC Spare, reserved for international and national use

CNM

1010 1011

NSB NCB NUB NAM

1100 1101 Spare, reserved for national use 1110 1111

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An Example of TUP Signals

IAM -- Initial Address Message0001 0001Address signals n 8 Number of address signals 4 Message Indicators 12S P A R E

A-Category

H14

H04

Routing Label40Transmission Direction

2

6

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Commonly Used TUP Signals

IAM or IAI The Initial Address Message (IAM) is the first message of a call set -up. It generally includes all of the information required to route the call. IAI is the same as IAM, but IAI has the caller identification. Generally, IAI is sent from LS to TS. SAM or SAO The remaining digits, if any, may be sent individually (SAO Subsequent Address Message with One digit) or grouped together (SAM - Subsequent Address Message). Efficiency can be gained by grouping together as many digits as possible.

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ACM The Address Complete Message will be originated by the last Signaling System No. 7 exchange. It is sent as an acknowledgment signal if the B -subscriber is free and contains information like charging, echo suppresser information etc. ANC or ANN The signals Answer Charge and Answer No Charge are sent as a result of the first off-hook signal from the B subscriber. In the case of ANC signal, the charging process should be initiated after receiving the ANC signal.50

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CBKA Clear Back signal is sent if the B -subscriber hooks on first. This signal does not disconnect the established speech channel. CLF The Clear Forward signal is sent when the A -subscriber hooks on. All exchanges must respond by releasing the speech (or data) circuit and send a Release Guard (RLG) as an acknowledgment. RLG The Release Guard signal is the last signal in the signaling procedure of a call. After this signal has been sent, the speech circuit will be released and available for new traffics again.51

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An Example of a Toll Call (A Hooks on)LSAIAISAM SAO ACM

TSAIAM SAM SAO ACM

LSB

Ringing

ANCCLF RLG

ANC CLF RLG52

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An Example of a Toll Call (B Hooks on)LSAIAISAM SAO ACM

TSAIAM SAM SAO ACM

LSB

Ringing

ANC CBKCLF RLG

ANC

CBKCLF RLG53

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An Example of Requesting Calling NumberLSAIAMGRQ GSM ACM ANC

LSB

CBK CLF

RLG

GRQ: General Request Message GSM: General Group Reset Message

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Chapter Four

ISDN User Part

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Overview of ISUP

The ISDN User Part (ISUP) defines the protocol and procedures used to set-up, manage, and release trunk circuits that carry voice and data calls over the public switched telephone network (PSTN) or ISDN network. ISUP is capable of processing ISDN specific information which is more complex than telephony signaling. ISUP is used for both ISDN and non-ISDN calls. Calls that originate and terminate at the same switch do not use ISUP signaling.

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ISUP Message Structure

Unlike TUP, SLS is an independent 4-bit, no longer part of CIC. And ISUP uses Message Type instead of H1 and H0.

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Commonly Used ISUP Signals

Initial Address Message (IAM) An IAM is sent in the "forward" direction by each switch needed to complete the circuit between the calling party and called party until the circuit connects to the destination switch. An IAM contains the called party number in the mandatory variable part and may contain the calling party name and number in the optional part. Address Complete Message (ACM) An ACM is sent in the "backward" direction to indicate that the remote end of a trunk circuit has been reserved. The originating switch responds to an ACM message by connecting the calling party's line to the trunk to complete the voice circuit from the calling party to the called party. The originating switch also sends a ringing tone to the calling party's line.58

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Commonly Used ISUP Signals

Answer Message (ANM) When the called party answers, the destination switch terminates the ringing tone and sends an ANM to the originating switch. The originating switch initiates billing after verifying that the calling party's line is connected to the reserved trunk.Release Message (REL) A REL is sent in either direction indicating that the circuit is being released due to the cause indicator specified. An REL is sent when either the calling or called party "hangs up" the call (cause = 16). An REL is also sent in the backward direction if the called party line is busy (cause = 17). Release Complete Message (RLC) A RLC is sent in the opposite direction of the REL to acknowledge the release of the remote end of a trunk circuit and end the billing cycle as appropriate.

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Basic ISUP Call Control

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Chapter Five

Signaling Connection Control Part

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Where is SCCP?

INAPTUP ISUP

CAPTCAP SCCP

MAP

MTP

INAP: IN Application Protocol CAP: CAMEL Application Part TUP: Telephone User Part MTP: Message Transfer Part

MAP: Mobile Application Part TCAP: Transaction Capability Application Part ISUP: ISDN User Part SCCP: Signaling Connection Control Pa62

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What is SCCP?

In SS7 signaling systemSCCP and MTP layer three together are responsible for signaling network layer function. SCCP expands the MTP functions in the following points:Enable to convey various non-circuit-related signaling message.

Provide enhanced addressing and routing function, and enable to achieve the direct global transmission between different SS7 networks by using GT addressing.Expand the user part of MTP. SCCP supports up to 256 kinds of sub systems in stead of 16 in MTP. Enable to provide connectionless service and connectionoriented service.63

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Service Functions of SCCP Network

According to the various service requirements, SCCP provides four classes of service: two connectionless services and two connection-oriented services. The four classes are: Class 0: Basic connectionless class. Class 1: In-sequence delivery connectionless class. Class 2: Basic connection-oriented class. Class 3: Flow control connection-oriented class.

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Addressing and Routing Functions of SCCP

The SCCP routing provides a powerful addressing information translation function on behalf of its users. The routing function also responds to the MTP and SCCP congestion reports.

SCCP Addressing makes use of three separate elements:DPC; Global Title (GT); Sub-System Number (SSN);

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Primitive

In SS7 system, the information exchange between two adjacent layers is called primitive which includes primitive name, primitive type and primitive parameters. There are four types of primitives: Request Indication Response

Confirmation

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Primitives between SCCP and SCCP-User

Primitives between SCCP and SCCP-User (TCAP) are N_Primitives. The connectionless services use the following N_Primitives: N_UNITDATA_REQis used when SCCP-User requires SCCP to send data. N_UNITDATA_INDis used when SCCP reports the received data to SCCP-User. N_NOTICE_INDis used when SCCP reports the reason why the SCCP-User data cannot be sent to peer point. N-Primitives can be traced on SSP maintenance terminals.67

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N_UNITDATA Parameters

N-UNITDATA_IND and N-UNITDATA_REQ have the same parameters. SCCP-USER Octet (83H) Routing Label (DPCOPCSLS) Sequence Control (SLS) Protocol Class (81H) Parameter Location Pointer (Called Address, Caller Address, User Data Pointer) Called Address (Destination Address) Caller Address (Originating Address) User Data (SCCP-User Data to be sent by SCCP transparently, SCCP makes no change to them)

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N_NOTICE Parameters

N_NOTICE has the same parameter structure with N_UNITDATA, but the Protocol Class is changed to return reason.

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SCCP Message Types

There are 17 kinds of SCCP messages. Among them UDT (Unit Data) and UDTS (Unit Data Service) are used for connectionless services. The codes for UDT and UDTS are 09H and 0AH. INAP only uses UDT messages.

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Chapter Six

Transaction Capabilities Application Part

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Applications of TCAP

Applications of TCAP: Data Exchange between switching systems Switching systems access network database center Network databases establish remote operation dialogue Examples of TCAP applications: Mobile service applications

Free phone service (800-service) Credit Card calling Operation & Maintenance applications72

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Dialogue

Dialogue is the association established between two TC users exchanging data. Whenever two signaling points are going to exchange data, they will setup a dialogue via TCAP. It is TCAP that initiates, maintains and releases of a dialogue. But TCAP does not care the functions of the dialogue. The procedure of message exchange between two signaling points is similar to man-machine dialogue mode, which involves all necessary messages such as BEGIN and END.

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Component

Component is the protocol data unit exchanged between TC users. i.e. the information exchanged in a dialogue is just a set of components. Components are defined by TC-Users. Components include the invoke operation by initiator and the returned result of the operation. The operation is decided by applications, e.g. number translation.

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The Relationship Between Dialogue and Component

A dialogue has one or more components. A service procedure is just one dialogue. i.e. all the operations of a service procedure constitute a dialogue, the dialogue is the carrier of the operations.

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Categories of TCAP Components

Invoke (INV) is used to send an operation request to remote TCUser. Return Result-Last (RR-L) is used to return the components of final result of last INV operation. Return Result-not Last (RR-NL) is used to return the components of non-final result of last INV operation. Return Error (RE) is used to return the components of error information, in which an error code is embedded. Reject (RJ) is used to reject last INV operation, in which a reason code is embedded.76

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Classes of TCAP Operations

According to different requirements of operation results, TCAP are classified into 4 classes: Class 1: Result will be returned no matter the operation is successful or not. i.e. a RR-L, RR-NL or RE must be returned. Class 2: Only when the operation fails, a RE will be returned. Class 3: Only when the operation succeeds, a RR-L or RR-NL will be returned. Class 4: No result returned no matter the operation is successful or not.77

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TC Primitives

TCAP and TC-User exchange data via TC_Primitives. There are 16 kinds of TC_Primitives, among them there 9 Component TC-Primitives which are related to components and 7 Dialogue TC-Primitives which are related to dialogues. The TC_Primitives from TCAP to TC-User are Indication primitives, from TC-User to TCAP are Request primitives.

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Component TC_Primitives (1)

TCINVOKE is used to invoke an operation. TCRESULTL is used to return the result of an operation. TCRESULTNL is similar to TCRESULTL, but only returns the middle result. Note: all above primitives have both Indication and Request types.

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TCUERROR is a Request Primitive which is used to return the error code when the operation fails although TC-User has received the correct operation request.

TCUREJECTis a Request Primitive which is used to return reject code when TC-User has received an incorrect operation request.TCUCANCEL is a Request Primitive which is used for TCUser to request TCAP to cancel an operation.

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TCLCANEL is an Indication Primitive which is used to notify TC-User an operation is overtime. TCLREJECT is an Indication Primitive which is used to reject an operation by local TCAP. TCRREJECTis an Indication Primitive which is used to reject an operation when remote TCAP rejects the operation.

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Types of TCAP Dialogues

There are two types of TCAP dialogues. Unstructured Dialogue in which only unidirectional (UNI) messages are included. No response to be returned from opposite point in unstructured dialogue (e.g. a dialogue for sending an alarm message). Intelligent Network seldom uses this kind of dialogues. Structured Dialogue has initiating, maintaining and ending processes. It has BEGIN, CONTINUE and END or ABORT messages. Intelligent Network just uses this kind of dialogues.

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Dialogue TC_Primitives (1)

TCUNI

TC-User or TCAP request to begin a UNI dialogue. Request or indicate to begin a dialogue. Request or indicate to maintain a dialogue.

TCBEGIN

TCCONTINUE TCEND

Request or indicate to end a dialogue.

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Dialogue TC_Primitives (2)

TCUABORTRequest to abort a dialogue. TCPABORTIndicate TC-User to abort a dialogue because of the error in transaction layer. TCNOTICEIndicate TC-User that the network service provider cannot provide the required service (e.g. STP does not support INAP).

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An Example of TCAP ProcessNode2 (SCP) SSP begins a dialogue to query the balance of a calling card subscriber. SCP asks SSP to return the password.

Node1 (SSP) TC-Begin

TC-Invoke (Invoke) TC-Continue TC-Invoke (Invoke) TC-Continue

TC-Result-L (RR-L)TC-End TC-Result-L (RR-L)

SSP returns the password.

SCP returns balance of the subscriber.85

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Chapter Seven

Intelligent Network Application Part

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The Functions of INAP

INAP defines operation criterion among the IN functional entities SSF, SCF, SRF and SDF. INAP is transmitted by SCCP UDT data, using connectionless services.

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The Relationship Between INAP and SCCP

INAP usually uses DPC+SSN routing mode of SCCP. INAP can also use GT routing mode of SCCP.

INAP uses class 0 and class 1 connectionless services of SCCP.

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INAP Operation CategoriesClass 1: Result will be returned no matter the operation is successful or not. i.e. a RR-L, RR-NL or RE must be returned. Class 2: Only when the operation fails, a RE will be returned. Class 3: Only when the operation succeeds, a RR-L or RR-NL will be returned. Class 4: No result returned no matter the operation is successful or not.89

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INAP Operations

INAP is a kind of TC-User. In INAP protocol, all INAP operations are also classified into 4 classes. Class 1 Class 2 Class 3 Activate Service Filtering, P&C Initial DP, RRBE AT

Class 4

RC, BER

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IDP: Initial DP

IDP is the first INAP message sent from SSP to SCP, requesting SCP to establish the control relationship for an IN call. The parameters included in IDP are: access code, service key (the unique identifier of an IN service), caller number, called number, number attributes, etc.

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RRBE: Request Report BCSM Event

RRBE is sent from SCP to SSP, requesting SSP to configure DP dynamically. When SSP meets these DPs in later call process, SSP will report call information to SCP. RRBE provides SCP the condition of controlling calls. The parameters of RRBE include DP type, DP condition, etc. One RRBE can configure several DPs.92

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CTR: Connect To Resource

CTR is sent from SCP to SSP, requesting SSP to connect the user to IP. CTR provides the users the condition of using IP. If IP is integrated with SSP, SSP makes only the internal connection with IP. If IP is independent from SSP, SSP communicates IP via TUP messages, connecting the users to IP through PSTN voice channels.93

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P&C: Prompt & Collect User Information

P&C is sent from SCP to SSP, requesting IP to play voice prompts the users and collect the users input. P&C needs IP to return operation results.

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DFC: Disconnect Forward Connect

DFC is sent from SCP to SSP, requesting SSP to disconnect the connection between the users and IP.

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AC: Apply Charging

AC is sent from SCP to SSP, requesting SSP to charge the call. The parameters of AC include: charge class, the balance of the subscriber, charging party, etc.

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Connect

Connect is sent from SCP to SSP, requesting SSP to connect the users to the designated number.

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ACR: Apply Charging Report

ACR is sent from SSP to SCP, reporting the charge result. The parameters in ACR include: the call start time, call end time, call length, caller number, called number, charging number, fee, etc.

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ERB: Event Report BCSM

ERB is sent from SSP to SCP when SSP detects the DPs configured by SCP in last RRBE message, reporting the call information to SCP.

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RC: Release Call

RC is sent from SCP to SSP, requesting SSP to release the occupied IN call resources.

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PA: Play announcement

PA is sent from SCP to SSP, requesting IP to play voice prompts to the users. PA does not need result return from IP.

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SRR: Specialized Resource Report

SRR is sent from SSP to SCP, notifying SCP the end of playing announcement.

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AT: Activity Test

SCP sends AT to SSP every 6 minutes when the call is established to check the communication between SSP and SCP. If SSP can return AT_ack, the communication is good. If no AT_ack returns to SCP, the communication is broken, and SCP will release the resources occupied this IN call.

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An Example of INAP (FPH Service)

SSP Initial DP

SCP

Request Report BCSM Event

Apply ChargingConnect

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An Example of INAP (Continue)

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SCCPTCAP and INAP (FPH Service)INAPTC-BEGIN-REQ TC-INVOKE-REQ N_UNITDATA-IND TC-CONTINUE-IND Request Report Bcsm Event TC-INVOKE-IND TC-CONTINUE-IND Apply Charging TC-INVOKE-IND TC-CONTINUE-IND Connect TC-INVOKE-IND TC-CONTINUE-REQ TC-INVOKE-REQ TC-CONTINUE-REQ Event Report BCSM TC-INVOKE-REQ TC-END-IND Release Call TC-INVOKE-IND N_UNITDATA-IND UDT MSU N_UNITDATA-REQ UDT MSU N_UNITDATA-REQ UDT MSU N_UNITDATA-IND N_UNITDATA-IND UDT UDT MSU UDT MSU

APInitialDP

TCAPN_UNITDATA-REQ

SCCPUDT

MTPMSU

SCP

MSU

Apply Charging Report

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Summary

Chapter 1 Chapter 2

Fundamentals of SS7 Message Transfer Part

Chapter 3Chapter 4 Chapter 5 Chapter 6 Chapter 7

Telephone User PartISDN User Part Signaling Connection Control Part Transaction Capabilities Application Part Intelligent Network Application Part107

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Thank you !

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Documents

SS7 Signaling System