Signaling Blog

Connection request (CR)
Sent by SCCP to another SCCP peer to request a setting up of a logical connection between them so that data transfer between them can take place in a connection-orientated fashion.

Code: 0 0 0 0 0 0 0 0

Connection Confirm (CC)
Sent in response to a CR message to indicate to that the node has performed the setup of the requested signalling logical connection.

Code: 0 0 0 0 1 0 1 0

Connection Refused (CREF)
Sent by the destination or an intermediate SCCP node in response to a CR message to indicate that the setup of a logical connection has been refused.

Code: 0 0 0 0 0 0 1 1

Data Acknowledgement (AK)
May be sent when using protocol class 3 to control the window flow control.

Code: 0 0 0 0 1 0 0 0

Data Form 1 (DT1)
Sent by either end of a signalling connection to pass SCCP user data transparently between two SCCP nodes. DT1 is used in protocol class 2 only.

Code: 0 0 0 0 0 1 1 0

Data Form 2 (DT2)
Sent by eith er end of a signalling connection to pass SCCP user data transparently between two SCCP nodes. DT2 is used in protocol class 3 only.

Code: 0 0 0 0 0 1 1 1

Expedited Data (ED)
Performs the same function as the DT2 message but includes the capability to bypass the flow control mechanism and as such is used in protocol class 3 only.

Code: 0 0 0 0 1 0 1 1

Expedited Data Acknowledgement (EA)
Used to acknowledge a ED message. Each ED message must be acknowledged before another one is sent.

Code: 0 0 0 0 1 1 0 0

Extended Unitdata (XUDT)
Used by SCCP to transmit data along with optional parameters, using connectionless mode, (protocol classes 0 and 1).

Code: 0 0 0 1 0 0 0 1

Extended Unitdata Service (XUDTS)
Sent back in response to a XUDT message only if the XUDT message cannot be delivered to its destination. Only used when the optional field in XUDT is set to “return on error”. (Used in connectionless protocol classes 0 and 1).

Code: 0 0 0 1 0 0 1 0

Inactivity Test (IT)
May be sent periodically by either end of a signalling connection to check if the signalling connection is active, and to audit the consistency of connection data at both ends.
It is used in connection-orientated classes 2 and 3.

Code: 0 0 01 0 0 0 0

Long Unitdata (LUDT)
Used by SCCP to transmit data along with optional parameters, using connectionless mode, (protocol classes 0 and 1). If ATM is the underlying network, it allows sending of NSDU sizes up to 3952 octets without segmentation.

Code: 0 0 0 1 0 0 1 1

Long Unitdata Service (LUDTS)
Sent back in response to a LUDT message only if the LUDT message cannot be delivered to its destination. Only used when the optional field in LUDT is set to “return on error”. (Used in connectionless protocol classes 0 and 1).

Code: 0 0 0 1 0 1 0 0

Protocol Data Unit Error (ERR)
Sent on detection of any protocol errors. It is used during the data transfer phase in connection-orientated classes 2 and 3.

Code: 0 0 0 0 1 1 1 1

Release complete (RLC)
Sent in response to the RLSD message to indicate that the RLSD message was received, and the necessary procedures have been performs. It is used during connection release phase in connection-orientated classes 2 and 3.

Code: 0 0 0 0 0 1 0 1

Released (RLSD)
Sent to indicate that the sending SCCP wishes to release a signalling connection and that the associated resources have been brought into the disconnect pending condition. It also indicates that the receiving node should release the connection and it’s associated resources.
It is used during connection release phase in connection-orientated classes 2 and 3.

Code: 0 0 0 0 0 1 0 0

Reset confirm (RSC)
Sent in response to a RSR message to indicate that RSR has been received and that the necessary procedure has been performed. It is used during the data transfer phase in connection-orientated class 3.

Code: 0 0 0 0 1 1 1 0

Reset Request (RSR)
Sent to indicate that the sending SCCP wishes to initiate a reset procedure (re-initialisation of sequence numbers) with the receiving SCCP. It is used during the data transfer phase in protocol class 3.

Code: 0 0 0 0 1 1 0 1

Subsystem Backup Routing (SBR) (A)
Optional message sent prior to rerouting traffic to the backup subsystem. Provides more connectivity information so that the end node can determine the traffic mix received for a subsystem.

Code: 1 1 1 1 1 1 0 1

Subsystem Normal Routing (SNR) (A)
Optional message sent prior to rerouting traffic to the primary subsystem, to the backup of the now allowed subsystem. Allows the end node to update the traffic mix information that the subsystem is receiving.

Code: 1 1 1 1 1 1 1 0

Subsystem Routing Status Test (SRT) (A)

Optional message sent to verify the routing status of a sub-system marked as under backup routing.

Code: 1 1 1 1 1 1 1 1

Subsystem Allowed (SSA)
Used by SCCP subsystem management to inform SCMG at concerned destinations that a formely prohibited subsystem (such as VLR/HLR) is now available, or a previously unavailable SCCP is now available.The node receiving the SSA will as a consequence update its translation tables.

Code: 0 0 0 0 0 0 0 1

Subsystem Prohibited (SSP)
Used by SCCP subsystem management to inform SCMG at concerned destinations of a failure of a subsystem (such as VLR/HLR).The receiving end of an SSP message will update its translation tables; as a consequence traffic could be re-routed to a backup subsystem if available.

Code: 0 0 0 0 0 0 1 0

Subsystem Status Test (SST)
Used by SCCP subsystem management to to verify the status of a subsystem marked prohibited or the status of an SCCP marked unavailable. The receiving node checks the status of the named subsystem and, if the subsystem is allowed, an SSA message is sent in response. If the subsystem is prohibited, no reply is sent.

Code: 0 0 0 0 0 0 1 1

Subsystem Out-of-service-request (SOR)
Used by SCCP subsystem management to allow subsystems to go out-of-service without degrading performance of the network.

Code: 0 0 0 0 0 1 0 0

Subsystem Out-of-service-grant (SOG)
Used by SCCP subsystem management in response to a Subsystem Out of Service Request message, to the requesting SCCP if both the requested SCCP and the backup of the affected subsystem agree to the request.

Code: 0 0 0 0 0 1 0 1

SCCP Subsystem-congested (SSC)
Sent when an SCCP node experiences congestion.

Code: 0 0 0 0 0 0 1 0

Unitdata (UDT)
Used by SCCP to transmit data, using connectionless mode (protocol classes 0 and 1).

Code: 0 0 0 0 1 0 0 1

Unitdata Service (UDTS)
Sent back in response to a UDT message only if the UDT message cannot be delivered to its destination. Only used when the optional field in UDT is set to “return on error”. (Used in connectionless protocol classes 0 and 1).

Code: 0 0 0 0 1 0 1 0

Key:
(A) MESSAGES SUPPORTED IN ANSI ONLY [ANSI SCCP 96]

All other messages are supported by both ITU [Q.711-Q.714 96] and ANSI [ANSI SCCP 96]