RFC 4666
Signaling System 7 (SS7) Message Transfer Part 3 (MTP3) - User Adaptation Layer (M3UA)
1.4. Functional Areas
1.4.1. Signalling Point Code Representation
For example, within an SS7 network, a Signalling Gateway might be charged with representing a set of nodes in the IP domain into the SS7 network for routing purposes. The SG itself, as a signalling point in the SS7 network, might also be addressable with an SS7 Point Code for MTP3 Management purposes. The SG Point Code might also be used for addressing any local MTP3-Users at the SG such as a local SCCP layer.
An SG may be logically partitioned to operate in multiple SS7 network appearances. In such a case, the SG could be addressable with a Point Code in each network appearance, and it represents a set of nodes in the IP domain into each SS7 network. Alias Point Codes [8] may also be used within an SG network appearance. Where an SG contains more than one SGP, the MTP3 routeset, SPMC, and remote AS/ASP states of each SGP SHOULD be coordinated across all the SGPs. Rerouting of traffic between the SGPs MAY also be supported. Application Servers can be represented under the same Point Code of the SG, under their own individual Point Codes, or grouped with other Application Servers for Point Code preservation purposes. A single Point Code may be used to represent the SG and all the Application Servers together, if desired. If an ASP or group of ASPs is available to the SS7 network via more than one SG, each with its own Point Code, the ASP(s) will typically be represented by a Point Code that is separate from any SG Point Code. This allows, for example, these SGs to be viewed from the SS7 network as "STPs", each having an ongoing "route" to the same ASP(s). Under failure conditions where the ASP(s) become(s) unavailable from one of the SGs, this approach enables MTP3 route management messaging between the SG and SS7 network, allowing simple SS7 rerouting through an alternate SG without changing the Destination Point Code Address of SS7 traffic to the ASP(s). Where a particular AS can be reached via more than one SGP, the corresponding Routing Keys in the SGPs should be identical. (Note: It is possible for the SGP Routing Key configuration data to be temporarily out of sync during configuration updates). +--------+ | | +------------+ SG 1 +--------------+ +-------+ | SS7 links | "STP" | IP network | ---- | SEP +---+ +--------+ +---/ \ | or | |* | ASPs | | STP +---+ +--------+ +---\ / +-------+ | | | | ---- +------------+ SG 2 +--------------+ | "STP" | +--------+ Figure 1. Example with mated SGs * Note: SG-to-SG communication (i.e., "C-links") is recommended for carrier grade networks, using an MTP3 linkset or an
equivalent, to allow rerouting between the SGs in the event of
route failures. Where SGPs are used, inter-SGP communication
might be used. Inter-SGP protocol is outside of the scope of this
document.
The following example shows a signalling gateway partitioned into
two network appearances.
SG
+-------+ +---------------+
| SEP +--------------| SS7 Ntwk.|M3UA| ----
+-------+ SS7 links | "A" | | / \
|__________| +-----------+ ASPs |
| | | \ /
+-------+ | SS7 Ntwk.| | ----
| SEP +--------------+ "B" | |
+-------+ +---------------+
Figure 2. Example with multiple network
1.4.2. Routing Contexts and Routing Keys
1.4.2.1. Overview
The distribution of SS7 messages between the SGP and the Application
Servers is determined by the Routing Keys and their associated
Routing Contexts. A Routing Key is essentially a set of SS7
parameters used to filter SS7 messages, whereas the Routing Context
parameter is a 4-octet value (integer) that is associated to that
Routing Key in a 1:1 relationship. The Routing Context therefore can
be viewed as an index into a sending node's Message Distribution
Table containing the Routing Key entries.
Possible SS7 address/routing information that comprise a Routing Key
entry includes, for example, the OPC, DPC, and SIO found in the MTP3
routing label. Some example Routing Keys are: the DPC alone, the
DPC/OPC combination, or the DPC/OPC/SI combination. The particular
information used to define an M3UA Routing Key is application and
network dependent, and none of the above examples are mandated.
An Application Server Process may be configured to process signalling
traffic related to more than one Application Server, over a single
SCTP Association. In ASP Active and ASP Inactive management
messages, the signalling traffic to be started or stopped is
discriminated by the Routing Context parameter. At an ASP, the
Routing Context parameter uniquely identifies the range of signalling
traffic associated with each Application Server that the ASP is
configured to receive.
1.4.2.2. Routing Key Limitations
Routing Keys SHOULD be unique in the sense that each received SS7 signalling message SHOULD have a full or partial match to a single routing result. An example of a partial match would be a default Routing Key that would be the result if there are no other Routing Keys to which the message belongs. It is not necessary for the parameter range values within a particular Routing Key to be contiguous.1.4.2.3. Managing Routing Contexts and Routing Keys
There are two ways to provision a Routing Key at an SGP. A Routing Key may be configured statically using an implementation dependent management interface, or dynamically using the M3UA Routing Key registration procedure. When using a management interface to configure Routing Keys, the message distribution function within the SGP is not limited to the set of parameters defined in this document. Other implementation- dependent distribution algorithms may be used.1.4.2.4. Message Distribution at the SGP
To direct messages received from the SS7 MTP3 network to the appropriate IP destination, the SGP must perform a message distribution function using information from the received MTP3-User message. To support this message distribution, the SGP might, for example, maintain the equivalent of a network address translation table, mapping incoming SS7 message information to an Application Server for a particular application and range of traffic. This could be accomplished by comparing elements of the incoming SS7 message to currently defined Routing Keys in the SGP. These Routing Keys could in turn map directly to an Application Server that is enabled by one or more ASPs. These ASPs provide dynamic status information regarding their availability, traffic- handling capability and congestion to the SGP using various management messages defined in the M3UA protocol. The list of ASPs in an AS is assumed to be dynamic, taking into account the availability, traffic-handling capability, and congestion status of the individual ASPs in the list, as well as configuration changes and possible failover mechanisms.
Normally, one or more ASPs are active (i.e., currently processing traffic) in the AS, but in certain failure and transition cases it is possible that there may be no active ASP available. Broadcast, loadsharing, and backup scenarios are supported. When there is no matching Routing Key entry for an incoming SS7 message, a default treatment MAY be specified. Possible solutions are to provide a default Application Server at the SGP that directs all unallocated traffic to a (set of) default ASPs, or to drop the message and provide a notification to layer management. The treatment of unallocated traffic is implementation dependent.1.4.2.5. Message Distribution at the ASP
The ASP must choose an SGP to direct a message to the SS7 network. This is accomplished by observing the Destination Point Code (and possibly other elements of the outgoing message, such as the SLS value). The ASP must also take into account whether the related Routing Context is active or not (see Section 4.3.4.3). Implementation Note: Where more than one route (or SGP) is possible for routing to the SS7 network, the ASP could, for example, maintain a dynamic table of available SGP routes for the SS7 destinations, taking into account the SS7 destination availability/restricted/congestion status received from the SGP(s), the availability status of the individual SGPs, and configuration changes and failover mechanisms. There is, however, no M3UA messaging to manage the status of an SGP (e.g., SGP- Up/Down/Active/Inactive messaging). Whenever an SCTP association to an SGP exists, the SGP is assumed to be ready for the purposes of responding to M3UA ASPSM messages (refer to Section 3).1.4.3. SS7 and M3UA Interworking
In the case of SS7 and M3UA interworking, the M3UA adaptation layer is designed to provide an extension of the MTP3-defined user primitives.1.4.3.1. Signalling Gateway SS7 Layers
The SG is responsible for terminating MTP Level 3 of the SS7 protocol, and offering an IP-based extension to its users.
From an SS7 perspective, it is expected that the Signalling Gateway transmits and receives SS7 Message Signalling Units (MSUs) over a standard SS7 network interface, using the SS7 Message Transfer Part (MTP) [7,8,9]. As a standard SS7 network interface, the use of MTP Level 2 signalling links is not the only possibility. ATM-based High Speed Links can also be used with the services of the Signalling ATM Adaptation Layer (SAAL) [19,20]. Note: It is also possible for IP-based interfaces to be present, using the services of the MTP2-User Adaptation Layer (M2UA) [24] or M2PA [25]. These could be terminated at a Signalling Transfer Point (STP) or Signalling End Point (SEP). Using the services of MTP3, the SG could be capable of communicating with remote SS7 SEPs in a quasi- associated fashion, where STPs may be present in the SS7 path between the SEP and the SG.1.4.3.2. SS7 and M3UA Interworking at the SG
The SGP provides a functional interworking of transport functions between the SS7 network and the IP network by also supporting the M3UA adaptation layer. It allows the transfer of MTP3-User signalling messages to and from an IP-based Application Server Process where the peer MTP3-User protocol layer exists. For SS7 user part management, it is required that the MTP3-User protocols at ASPs receive indications of SS7 signalling point availability, SS7 network congestion, and remote User Part unavailability, as would be expected in an SS7 SEP node. To accomplish this, the MTP-PAUSE, MTP-RESUME, and MTP-STATUS indication primitives received at the MTP3 upper layer interface at the SG need to be propagated to the remote MTP3-User lower layer interface at the ASP. MTP3 management messages (such as TFPs or TFAs received from the SS7 network) MUST NOT be encapsulated as Data message Payload Data and sent either from SG to ASP or from ASP to SG. The SG MUST terminate these messages and generate M3UA messages, as appropriate.1.4.3.3. Application Server
A cluster of application servers is responsible for providing the overall support for one or more SS7 upper layers. From an SS7 standpoint, a Signalling Point Management Cluster (SPMC) provides complete support for the upper layer service for a given point code.
As an example, an SPMC providing MGC capabilities could provide complete support for ISUP (and any other MTP3 user located at the point code of the SPMC) for a given point code. In the case where an ASP is connected to more than one SGP, the M3UA layer must maintain the status of configured SS7 destinations and route messages according to the availability/congestion/restricted status of the routes to these SS7 destinations.1.4.3.4. IPSP Considerations
Since IPSPs use M3UA in a point-to-point fashion, there is no concept of routing of messages beyond the remote end. Therefore, SS7 and M3UA interworking is not necessary for this model.1.4.4. Redundancy Models
1.4.4.1 Application Server Redundancy
All MTP3-User messages (e.g., ISUP, SCCP) that match a provisioned Routing Key at an SGP are mapped to an Application Server. The Application Server is the set of all ASPs associated with a specific Routing Key. Each ASP in this set may be active, inactive, or unavailable. Active ASPs handle traffic; inactive ASPs might be used when active ASPs become unavailable. The failover model supports an "n+k" redundancy model, where "n" ASPs is the minimum number of redundant ASPs required to handle traffic and "k" ASPs are available to take over for a failed or unavailable ASP. Traffic SHOULD be sent after "n" ASPs are active. "k" ASPs MAY be either active at the same time as "n" or kept inactive until needed due to a failed or unavailable ASP. A "1+1" active/backup redundancy is a subset of this model. A simplex "1+0" model is also supported as a subset, with no ASP redundancy.1.4.5. Flow Control
Local Management at an ASP may wish to stop traffic across an SCTP association to temporarily remove the association from service or to perform testing and maintenance activity. The function could optionally be used to control the start of traffic on to a newly available SCTP association.
1.4.6. Congestion Management
The M3UA layer is informed of local and IP network congestion by means of an implementation-dependent function (e.g., an implementation-dependent indication from the SCTP of IP network congestion). At an ASP or IPSP, the M3UA layer indicates IP network congestion to local MTP3-Users by means of an MTP-STATUS primitive, as per current MTP3 procedures, to invoke appropriate upper-layer responses. When an SG determines that the transport of SS7 messages to a Signalling Point Management Cluster (SPMC) is encountering IP network congestion, the SG MAY trigger SS7 MTP3 Transfer Controlled management messages to originating SS7 nodes, per the congestion procedures of the relevant MTP3 standard. The triggering of SS7 MTP3 Management messages from an SG is an implementation-dependent function. The M3UA layer at an ASP or IPSP MAY indicate local congestion to an M3UA peer with an SCON message. When an SG receives a congestion message (SCON) from an ASP and the SG determines that an SPMC is now encountering congestion, it MAY trigger SS7 MTP3 Transfer Controlled management messages to concerned SS7 destinations according to congestion procedures of the relevant MTP3 standard.1.4.7. SCTP Stream Mapping
The M3UA layer at both the SGP and ASP also supports the assignment of signalling traffic into streams within an SCTP association. Traffic that requires sequencing SHOULD be assigned to the same stream. To accomplish this, MTP3-User traffic may be assigned to individual streams based on, for example, the SLS value in the MTP3 Routing Label, subject of course to the maximum number of streams supported by the underlying SCTP association. The following rules apply (see Section 3.1.2): 1. The DATA message MUST NOT be sent on stream 0. 2. The ASPSM, MGMT, RKM classes SHOULD be sent on stream 0 (other than BEAT, BEAT ACK and NTFY messages). 3. The SSNM, ASPTM classes and BEAT, BEAT ACK and NTFY messages can be sent on any stream.1.4.8. SCTP Client/Server Model
It is recommended that the SGP and ASP be able to support both client and server operation. The peer endpoints using M3UA SHOULD be
configured so that one always takes on the role of client and the other the role of server for initiating SCTP associations. The default orientation would be for the SGP to take on the role of server while the ASP is the client. In this case, ASPs SHOULD initiate the SCTP association to the SGP. In the case of IPSP to IPSP communication, the peer endpoints using M3UA SHOULD be configured so that one always takes on the role of client and the other the role of server for initiating SCTP associations. The SCTP and TCP Registered User Port Number Assignment for M3UA is 2905.1.5. Sample Configuration
1.5.1. Example 1: ISUP Message Transport
******** SS7 ***************** IP ******** * SEP *---------* SGP *--------* ASP * ******** ***************** ******** +------+ +---------------+ +------+ | ISUP | | (NIF) | | ISUP | +------+ +------+ +------+ +------+ | MTP3 | | MTP3 | | M3UA | | M3UA | +------| +------+-+------+ +------+ | MTP2 | | MTP2 | | SCTP | | SCTP | +------+ +------+ +------+ +------+ | L1 | | L1 | | IP | | IP | +------+ +------+ +------+ +------+ |_______________| |______________| SEP - SS7 Signalling End Point SCTP - Stream Control Transmission Protocol NIF - Nodal Interworking Function In this example, the SGP provides an implementation-dependent nodal interworking function (NIF) that allows the MGC to exchange SS7 signalling messages with the SS7-based SEP. The NIF within the SGP serves as the interface within the SGP between the MTP3 and M3UA. This nodal interworking function has no visible peer protocol with either the MGC or SEP. It also provides network status information to one or both sides of the network. For internal SGP modeling purposes, at the NIF level, SS7 signalling messages that are destined to the MGC are received as MTP-TRANSFER indication primitives from the MTP Level 3 upper layer interface,
translated to MTP-TRANSFER request primitives, and sent to the local M3UA-resident message distribution function for ongoing routing to the final IP destination. Messages received from the local M3UA network address translation and mapping function as MTP-TRANSFER indication primitives are sent to the MTP Level 3 upper-layer interface as MTP-TRANSFER request primitives for ongoing MTP Level 3 routing to an SS7 SEP. For the purposes of providing SS7 network status information, the NIF also delivers MTP-PAUSE, MTP-RESUME, and MTP-STATUS indication primitives received from the MTP Level 3 upper-layer interface to the local M3UA-resident management function. In addition, as an implementation and network option, restricted destinations are communicated from MTP network management to the local M3UA-resident management function.1.5.2. Example 2: SCCP Transport between IPSPs
******** IP ******** * IPSP * * IPSP * ******** ******** +------+ +------+ |SCCP- | |SCCP- | | User | | User | +------+ +------+ | SCCP | | SCCP | +------+ +------+ | M3UA | | M3UA | +------+ +------+ | SCTP | | SCTP | +------+ +------+ | IP | | IP | +------+ +------+ |________________| This example shows an architecture where no Signalling Gateway is used. In this example, SCCP messages are exchanged directly between two IP-resident IPSPs with resident SCCP-User protocol instances, such as RANAP or TCAP. SS7 network interworking is not required; therefore, there is no MTP3 network management status information for the SCCP and SCCP-User protocols to consider. Any MTP-PAUSE, MTP- RESUME, or MTP-STATUS indications from the M3UA layer to the SCCP layer should consider the status of the SCTP Association and underlying IP network and any congestion information received from the remote site.
1.5.3. Example 3: SGP Resident SCCP Layer, with Remote ASP
******** SS7 ***************** IP ******** * SEP *---------* *--------* * * or * * SGP * * ASP * * STP * * * * * ******** ***************** ******** +------+ +---------------+ +------+ | SCCP-| | SCCP | | SCCP-| | User | +---------------+ | User | +------+ | _____ | +------+ | SCCP | | | | | | SCCP | +------+ +------+-+------+ +------+ | MTP3 | | MTP3 | | M3UA | | M3UA | +------| +------+ +------+ +------+ | MTP2 | | MTP2 | | SCTP | | SCTP | +------+ +------+ +------+ +------+ | L1 | | L1 | | IP | | IP | +------+ +------+ +------+ +------+ |_______________| |______________| STP - SS7 Signalling Transfer Point In this example, the SGP contains an instance of the SS7 SCCP protocol layer that may, for example, perform the SCCP Global Title Translation (GTT) function for messages logically addressed to the SG SCCP. If the result of a GTT for an SCCP message yields an SS7 DPC or DPC/SSN address of an SCCP peer located in the IP domain, the resulting MTP-TRANSFER request primitive is sent to the local M3UA- resident network address translation and mapping function for ongoing routing to the final IP destination. Similarly, the SCCP instance in an SGP can perform the SCCP GTT service for messages logically addressed to it from SCCP peers in the IP domain. In this case, MTP-TRANSFER indication primitives are sent from the local M3UA-resident network address translation and mapping function to the SCCP for GTT. If the result of the GTT yields the address of an SCCP peer in the SS7 network, then the resulting MTP- TRANSFER request primitive is given to the MTP3 for delivery to an SS7-resident node. It is possible that the above SCCP GTT at the SGP could yield the address of an SCCP peer in the IP domain, and that the resulting MTP-TRANSFER request primitive would be sent back to the M3UA layer for delivery to an IP destination.
For internal SGP modeling purposes, this may be accomplished with the use of an implementation-dependent nodal interworking function within the SGP that effectively sits below the SCCP and routes MTP-TRANSFER request/indication messages to/from both the MTP3 and the M3UA layer, based on the SS7 DPC or DPC/SI address information. This nodal interworking function has no visible peer protocol with either the ASP or SEP. Note that the services and interface provided by the M3UA layer are the same as in Example 1 and that the functions taking place in the SCCP entity are transparent to the M3UA layer. The SCCP protocol functions are not reproduced in the M3UA protocol.1.6. Definition of M3UA Boundaries
This section provides a definition of the boundaries of the M3UA protocol. They consist of SCTP, Layer Management, and the MTP3-User. +-----------+ | MTP3-User | +-----------+ | | +-----------+ +------------+ | M3UA |-----| Layer Mgmt | +-----------+ +------------+ | | +-----------+ | SCTP | +-----------+1.6.1. Definition of the Boundary between M3UA and an MTP3-User
From ITU Q.701 [7]: MTP-TRANSFER request MTP-TRANSFER indication MTP-PAUSE indication MTP-RESUME indication MTP-STATUS indication1.6.2. Definition of the Boundary between M3UA and SCTP
An example of the upper-layer primitives provided by the SCTP are provided in Reference [18], Section 10.
1.6.3. Definition of the Boundary between M3UA and Layer Management
M-SCTP_ESTABLISH request Direction: LM -> M3UA Purpose: LM requests that ASP establish an SCTP association with its peer. M-SCTP_ESTABLISH confirm Direction: M3UA -> LM Purpose: ASP confirms to LM that it has established an SCTP association with its peer. M-SCTP_ESTABLISH indication Direction: M3UA -> LM Purpose: M3UA informs LM that a remote ASP has established an SCTP association. M-SCTP_RELEASE request Direction: LM -> M3UA Purpose: LM requests that ASP release an SCTP association with its peer. M-SCTP_RELEASE confirm Direction: M3UA -> LM Purpose: ASP confirms to LM that it has released SCTP association with its peer. M-SCTP_RELEASE indication Direction: M3UA -> LM Purpose: M3UA informs LM that a remote ASP has released an SCTP Association or that the SCTP association has failed. M-SCTP_RESTART indication Direction: M3UA -> LM Purpose: M3UA informs LM that an SCTP restart indication has been received. M-SCTP_STATUS request Direction: LM -> M3UA Purpose: LM requests that M3UA report the status of an SCTP association. M-SCTP_STATUS confirm Direction: M3UA -> LM Purpose: M3UA responds with the status of an SCTP association.
M-SCTP STATUS indication Direction: M3UA -> LM Purpose: M3UA reports the status of an SCTP association. M-ASP_STATUS request Direction: LM -> M3UA Purpose: LM requests that M3UA report the status of a local or remote ASP. M-ASP_STATUS confirm Direction: M3UA -> LM Purpose: M3UA reports the status of local or remote ASP. M-AS_STATUS request Direction: LM -> M3UA Purpose: LM requests that M3UA report the status of an AS. M-AS_STATUS confirm Direction: M3UA -> LM Purpose: M3UA reports the status of an AS. M-NOTIFY indication Direction: M3UA -> LM Purpose: M3UA reports that it has received a Notify message from its peer. M-ERROR indication Direction: M3UA -> LM Purpose: M3UA reports that it has received an Error message from its peer or that a local operation has been unsuccessful. M-ASP_UP request Direction: LM -> M3UA Purpose: LM requests that ASP start its operation and send an ASP Up message to its peer. M-ASP_UP confirm Direction: M3UA -> LM Purpose: ASP reports that it has received an ASP UP Ack message from its peer. M-ASP_UP indication Direction: M3UA -> LM Purpose: M3UA reports that it has successfully processed an incoming ASP Up message from its peer.
M-ASP_DOWN request Direction: LM -> M3UA Purpose: LM requests that ASP stop its operation and send an ASP Down message to its peer. M-ASP_DOWN confirm Direction: M3UA -> LM Purpose: ASP reports that it has received an ASP Down Ack message from its peer. M-ASP_DOWN indication Direction: M3UA -> LM Purpose: M3UA reports that it has successfully processed an incoming ASP Down message from its peer, or the SCTP association has been lost/reset. M-ASP_ACTIVE request Direction: LM -> M3UA Purpose: LM requests that ASP send an ASP Active message to its peer. M-ASP_ACTIVE confirm Direction: M3UA -> LM Purpose: ASP reports that it has received an ASP Active Ack message from its peer. M-ASP_ACTIVE indication Direction: M3UA -> LM Purpose: M3UA reports that it has successfully processed an incoming ASP Active message from its peer. M-ASP_INACTIVE request Direction: LM -> M3UA Purpose: LM requests that ASP send an ASP Inactive message to its peer. M-ASP_INACTIVE confirm Direction: LM -> M3UA Purpose: ASP reports that it has received an ASP Inactive Ack message from its peer. M-ASP_INACTIVE indication Direction: M3UA -> LM Purpose: M3UA reports that it has successfully processed an incoming ASP Inactive message from its peer. M-AS_ACTIVE indication Direction: M3UA -> LM Purpose: M3UA reports that an AS has moved to the AS-ACTIVE state.
M-AS_INACTIVE indication Direction: M3UA -> LM Purpose: M3UA reports that an AS has moved to the AS-INACTIVE state. M-AS_DOWN indication Direction: M3UA -> LM Purpose: M3UA reports that an AS has moved to the AS-DOWN state. If dynamic registration of RK is supported by the M3UA layer, the layer MAY support the following additional primitives: M-RK_REG request Direction: LM -> M3UA Purpose: LM requests that ASP register RK(s) with its peer by sending an REG REQ message M-RK_REG confirm Direction: M3UA -> LM Purpose: ASP reports that it has received REG RSP message with a registration status of successful from its peer. M-RK_REG indication Direction: M3UA -> LM Purpose: M3UA informs LM that it has successfully processed an incoming REG REQ message. M-RK_DEREG request Direction: LM -> M3UA Purpose: LM requests that ASP deregister RK(s) with its peer by sending a DEREG REQ message. M-RK_DEREG confirm Direction: M3UA -> LM Purpose: ASP reports that it has received DEREG REQ message with a deregistration status of successful from its peer. M-RK_DEREG indication Direction: M3UA -> LM Purpose: M3UA informs LM that it has successfully processed an incoming DEREG REQ from its peer.2. Conventions
In this document, the keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL are to be interpreted as described in [21].
3. M3UA Protocol Elements
The general M3UA message format includes a Common Message Header followed by zero or more parameters as defined by the Message Type. For forward compatibility, all Message Types may have attached parameters even if none are specified in this version.3.1. Common Message Header
The protocol messages for MTP3-User Adaptation require a message header that contains the adaptation layer version, the message type, and message length. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Version | Reserved | Message Class | Message Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ \ / / All fields in an M3UA message MUST be transmitted in network byte order, unless otherwise stated.3.1.1. M3UA Protocol Version: 8 bits (unsigned integer)
The version field contains the version of the M3UA adaptation layer. The supported versions are as follows: 1 Release 1.03.1.2. Message Classes and Types
The following list contains the valid Message Classes: Message Class: 8 bits (unsigned integer) The following list contains the valid Message Type Classes: 0 Management (MGMT) Messages 1 Transfer Messages 2 SS7 Signalling Network Management (SSNM) Messages 3 ASP State Maintenance (ASPSM) Messages 4 ASP Traffic Maintenance (ASPTM) Messages 5 Reserved for Other SIGTRAN Adaptation Layers
6 Reserved for Other SIGTRAN Adaptation Layers
7 Reserved for Other SIGTRAN Adaptation Layers
8 Reserved for Other SIGTRAN Adaptation Layers
9 Routing Key Management (RKM) Messages
10 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined Message Class extensions
Message Type: 8 bits (unsigned integer)
The following list contains the message types for the defined
messages.
Management (MGMT) Messages (see Section 3.8)
0 Error (ERR)
1 Notify (NTFY)
2 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined MGMT extensions
Transfer Messages (see Section 3.3)
0 Reserved
1 Payload Data (DATA)
2 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined Transfer extensions
SS7 Signalling Network Management (SSNM) Messages (see Section
3.4)
0 Reserved
1 Destination Unavailable (DUNA)
2 Destination Available (DAVA)
3 Destination State Audit (DAUD)
4 Signalling Congestion (SCON)
5 Destination User Part Unavailable (DUPU)
6 Destination Restricted (DRST)
7 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined SSNM extensions
ASP State Maintenance (ASPSM) Messages (see Section 3.5)
0 Reserved
1 ASP Up (ASPUP)
2 ASP Down (ASPDN)
3 Heartbeat (BEAT)
4 ASP Up Acknowledgement (ASPUP ACK)
5 ASP Down Acknowledgement (ASPDN ACK)
6 Heartbeat Acknowledgement (BEAT ACK)
7 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined ASPSM extensions
ASP Traffic Maintenance (ASPTM) Messages (see Section 3.7)
0 Reserved
1 ASP Active (ASPAC)
2 ASP Inactive (ASPIA)
3 ASP Active Acknowledgement (ASPAC ACK)
4 ASP Inactive Acknowledgement (ASPIA ACK)
5 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined ASPTM extensions
Routing Key Management (RKM) Messages (see Section 3.6)
0 Reserved
1 Registration Request (REG REQ)
2 Registration Response (REG RSP)
3 Deregistration Request (DEREG REQ)
4 Deregistration Response (DEREG RSP)
5 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined RKM extensions
3.1.3. Reserved: 8 Bits
The Reserved field SHOULD be set to all '0's and ignored by the
receiver.
3.1.4. Message Length: 32-Bits (Unsigned Integer)
The Message Length defines the length of the message in octets,
including the Common Header. The Message Length MUST include
parameter padding octets, if there are any.
Note: A receiver SHOULD accept the message whether or not the final
parameter padding is included in the message length.
3.2. Variable-Length Parameter Format
M3UA messages consist of a Common Header followed by zero or more
variable-length parameters, as defined by the message type. All the
parameters contained in a message are defined in a Tag Length-Value
format, as shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Parameter Tag | Parameter Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Parameter Value /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where more than one parameter is included in a message, the
parameters may be in any order, except where explicitly mandated. A
receiver SHOULD accept the parameters in any order.
Unless explicitly stated or shown in a message format diagram, only
one parameter of the same type is allowed in a message.
Parameter Tag: 16 bits (unsigned integer)
The Tag field is a 16-bit identifier of the type of parameter. It
takes a value of 0 to 65534. Common parameters used by adaptation
layers are in the range of 0x00 to 0x3f. M3UA-specific parameters
have Tags in the range 0x0200 to 0x02ff. The parameter Tags
defined are as follows:
Common Parameters. These TLV parameters are common across the
different adaptation layers:
Parameter Name Parameter ID
============== ============
Reserved 0x0000
Not Used in M3UA 0x0001
Not Used in M3UA 0x0002
Not Used in M3UA 0x0003
INFO String 0x0004
Not Used in M3UA 0x0005
Routing Context 0x0006
Diagnostic Information 0x0007
Not Used in M3UA 0x0008
Heartbeat Data 0x0009
Not Used in M3UA 0x000a
Traffic Mode Type 0x000b
Error Code 0x000c
Status 0x000d
Not Used in M3UA 0x000e
Not Used in M3UA 0x000f
Not Used in M3UA 0x0010
ASP Identifier 0x0011
Affected Point Code 0x0012
Correlation ID 0x0013
M3UA-Specific parameters. These TLV parameters are specific to the
M3UA protocol:
Network Appearance 0x0200
Reserved 0x0201
Reserved 0x0202
Reserved 0x0203
User/Cause 0x0204
Congestion Indications 0x0205
Concerned Destination 0x0206
Routing Key 0x0207
Registration Result 0x0208
Deregistration Result 0x0209
Local Routing Key Identifier 0x020a
Destination Point Code 0x020b
Service Indicators 0x020c
Reserved 0x020d
Originating Point Code List 0x020e
Reserved 0x020f
Protocol Data 0x0210
Reserved 0x0211
Registration Status 0x0212
Deregistration Status 0x0213
Reserved by the IETF 0x0214 to 0xffff
The value of 65535 is reserved for IETF-defined extensions.
Values other than those defined in specific parameter descriptions
are reserved for use by the IETF. An RFC is required to make use
of parameter values "Reserved by the IETF".
Parameter Length: 16 bits (unsigned integer)
The Parameter Length field contains the size of the parameter in
octets, including the Parameter Tag, Parameter Length, and
Parameter Value fields. Thus, a parameter with a zero-length
Parameter Value field would have a Length field of 4. The
Parameter Length does not include any padding octets. If the
parameter contains subparameters, the Parameter Length field will
include all the octets of each subparameter, including
subparameter padding octets (if there are any).
Parameter Value: variable length
The Parameter Value field contains the actual information to be
transferred in the parameter.
The total length of a parameter (including Tag, Parameter Length,
and Value fields) MUST be a multiple of 4 octets. If the length
of the parameter is not a multiple of 4 octets, the sender pads
the Parameter at the end (i.e., after the Parameter Value field)
with all zero octets. The length of the padding is NOT included
in the parameter length field. A sender MUST NOT pad with more
than 3 octets. The receiver MUST ignore the padding octets.
3.3. Transfer Messages
The following section describes the Transfer messages and parameter
contents.
3.3.1. Payload Data Message (DATA)
The DATA message contains the SS7 MTP3-User protocol data, which is
an MTP-TRANSFER primitive, including the complete MTP3 Routing Label.
The DATA message contains the following variable-length parameters:
Network Appearance Optional
Routing Context Conditional
Protocol Data Mandatory
Correlation Id Optional
The following format MUST be used for the Data Message:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0200 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0006 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Routing Context |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0210 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Protocol Data /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0013 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Correlation Id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Network Appearance: 32 bits (unsigned integer)
The Network Appearance parameter identifies the SS7 network
context for the message and implicitly identifies the SS7 Point
Code format used, the SS7 Network Indicator value, and the MTP3
and possibly the MTP3-User protocol type/variant/version used
within the specific SS7 network. Where an SG operates in the
context of a single SS7 network, or if individual SCTP
associations are dedicated to each SS7 network context, the
Network Appearance parameter is not required. In other cases, the
parameter may be configured to be present for the use of the
receiver.
The Network Appearance parameter value is of local significance
only, coordinated between the SGP and ASP. Therefore, in the case
where an ASP is connected to more than one SGP, the same SS7
network context may be identified by different Network Appearance
values, depending on which SGP a message is being transmitted/
received.
Where the optional Network Appearance parameter is present, it
MUST be the first parameter in the message, as it defines the
format of the Protocol Data field.
IMPLEMENTATION NOTE: For simplicity of configuration, it may be
desirable to use the same NA value across all nodes sharing a
particular network context.
Routing Context: 32 bits (unsigned integer)
The Routing Context parameter contains the Routing Context value
associated with the DATA message. Where a Routing Key has not
been coordinated between the SGP and ASP, sending of Routing
Context is not required. Where multiple Routing Keys and Routing
Contexts are used across a common association, the Routing Context
MUST be sent to identify the traffic flow, assisting in the
internal distribution of Data messages.
Protocol Data: variable length
The Protocol Data parameter contains the original SS7 MTP3
message, including the Service Information Octet and Routing
Label.
The Protocol Data parameter contains the following fields:
Service Indicator
Network Indicator
Message Priority
Destination Point Code
Originating Point Code
Signalling Link Selection Code (SLS)
User Protocol Data, which includes
MTP3-User protocol elements (e.g., ISUP, SCCP, or TUP
parameters)
The Protocol Data parameter is encoded as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originating Point Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Point Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SI | NI | MP | SLS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ User Protocol Data /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Originating Point Code: 32 bits (unsigned integer)
Destination Point Code: 32 bits (unsigned integer)
The Originating and Destination Point Code fields contains the OPC
and DPC from the routing label of the original SS7 message in Network
Byte Order, justified to the least significant bit. Unused bits are
coded `0'.
Service Indicator: 8 bits (unsigned integer)
The Service Indicator field contains the SI field from the original
SS7 message justified to the least significant bit. Unused bits are
coded `0'.
Network Indicator: 8 bits (unsigned integer) The Network Indicator contains the NI field from the original SS7 message justified to the least significant bit. Unused bits are coded `0'. Message Priority: 8 bits (unsigned integer) The Message Priority field contains the MP bits (if any) from the original SS7 message, both for ANSI-style and TTC-style [26] message priority bits. The MP bits are aligned to the least significant bit. Unused bits are coded `0'. Signalling Link Selection: 8 bits (unsigned integer) The Signalling Link Selection field contains the SLS bits from the routing label of the original SS7 message justified to the least significant bit and in Network Byte Order. Unused bits are coded `0'. User Protocol Data: variable-length octet string The User Protocol Data field contains an octet string of MTP-User information from the original SS7 message, starting with the first octet of the original SS7 message following the Routing Label [7][8][26]. Correlation Id: 32 bits (unsigned integer) The Correlation Id parameter uniquely identifies the MSU carried in the Protocol Data within an AS. This Correlation Id parameter is assigned by the sending M3UA.3.4. SS7 Signalling Network Management (SSNM) Messages
3.4.1. Destination Unavailable (DUNA)
The DUNA message is sent from an SGP in an SG to all concerned ASPs to indicate that the SG has determined that one or more SS7 destinations are unreachable. It is also sent by an SGP in response to a message from the ASP to an unreachable SS7 destination. As an implementation option, the SG may suppress the sending of subsequent "response" DUNA messages regarding a certain unreachable SS7 destination for a certain period to give the remote side time to react. If there is no alternate route via another SG, the MTP3-User at the ASP is expected to stop traffic to the affected destination via the SG as per the defined MTP3-User procedures.
The DUNA message contains the following parameters:
Network Appearance Optional
Routing Context Conditional
Affected Point Code Mandatory
INFO String Optional
The format for DUNA Message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0200 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0006 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Context /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0012 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected PC 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ ... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected PC n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Network Appearance: 32-bit unsigned integer
The description of Network Appearance in Section 3.3.1 applies,
with the exception that Network Appearance does not have to be the
first parameter in this message.
Routing Context: n x 32 bits (unsigned integer)
The conditional Routing Context parameter contains the Routing
Context values associated with the DUNA message. Where a Routing
Key has not been coordinated between the SGP and ASP, sending of
Routing Context is not required. Where multiple Routing Keys and
Routing Contexts are used across a common association, the Routing
Context(s) MUST be sent to identify the concerned traffic flows
for which the DUNA message applies, assisting in outgoing traffic
management and internal distribution of MTP-PAUSE indications to
MTP3-Users at the receiver.
Affected Point Code: n x 32 bits
The Affected Point Code parameter contains a list of Affected
Destination Point Code fields, each a three-octet parameter to
allow for 14-, 16-, and 24-bit binary formatted SS7 Point Codes.
Affected Point Codes that are less than 24 bits are padded on the
left to the 24-bit boundary. The encoding is shown below for ANSI
and ITU Point Code examples.
ANSI 24-bit Point Code
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Network | Cluster | Member |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MSB-----------------------------------------LSB|
ITU 14-bit Point Code
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask |0 0 0 0 0 0 0 0 0 0|Zone | Region | SP |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MSB--------------------LSB|
It is optional to send an Affected Point Code parameter with more
than one Affected PC, but it is mandatory to receive it.
Including multiple Affected PCs may be useful when receipt of an
MTP3 management message or a linkset event simultaneously affects
the availability status of a list of destinations at an SG.
Mask: 8 bits (unsigned integer)
The Mask field can be used to identify a contiguous range of
Affected Destination Point Codes. Identifying a contiguous range
of Affected DPCs may be useful when receipt of an MTP3 management
message or a linkset event simultaneously affects the availability
status of a series of destinations at an SG.
The Mask parameter is an integer representing a bit mask that can
be applied to the related Affected PC field. The bit mask
identifies how many bits of the Affected PC field are significant
and which are effectively "wildcarded". For example, a mask of
"8" indicates that the last eight bits of the PC are "wildcarded".
For an ANSI 24-bit Affected PC, this is equivalent to signalling
that all PCs in an ANSI Cluster are unavailable. A mask of "3"
indicates that the last three bits of the PC are "wildcarded".
For a 14-bit ITU Affected PC, this is equivalent to signaling that
an ITU Region is unavailable. A mask value equal (or greater
than) the number of bits in the PC indicates that the entire
network appearance is affected; this is used to indicate network
isolation to the ASP.
INFO String: variable length
The optional INFO String parameter can carry any meaningful UTF-8
[10] character string along with the message. Length of the INFO
String parameter is from 0 to 255 octets. No procedures are
presently identified for its use, but the INFO String MAY be used
for debugging purposes. An INFO String with a zero-length
parameter is not considered an error (a zero length parameter is
one in which the Length field in the TLV will be set to 4).
3.4.2. Destination Available (DAVA)
The DAVA message is sent from an SGP to all concerned ASPs to
indicate that the SG has determined that one or more SS7 destinations
are now reachable (and not restricted), or in response to a DAUD
message, if appropriate. If the ASP M3UA layer previously had no
routes to the affected destinations, the ASP MTP3-User protocol is
informed and may now resume traffic to the affected destination. The
ASP M3UA layer now routes the MTP3-user traffic through the SG
initiating the DAVA message.
The DAVA message contains the following parameters:
Network Appearance Optional
Routing Context Conditional
Affected Point Code Mandatory
INFO String Optional
The format and description of the Network Appearance, Routing
Context, Affected Point Code, and INFO String parameters are the same
as for the DUNA message (See Section 3.4.1).
3.4.3. Destination State Audit (DAUD)
The DAUD message MAY be sent from the ASP to the SGP to audit the
availability/congestion state of SS7 routes from the SG to one or
more affected destinations.
The DAUD message contains the following parameters:
Network Appearance Optional
Routing Context Conditional
Affected Point Code Mandatory
INFO String Optional
The format and description of DAUD Message parameters are the same as
for the DUNA message (See Section 3.4.1).
It is recommended that during normal operation (traffic handling) the
mask field of the Affected Point Code parameter in the DAUD message
be kept to a zero value in order to avoid SG overloading.
3.4.4. Signalling Congestion (SCON)
The SCON message can be sent from an SGP to all concerned ASPs to
indicate that an SG has determined that there is congestion in the
SS7 network to one or more destinations, or to an ASP in response to
a DATA or DAUD message, as appropriate. For some MTP protocol
variants (e.g., ANSI MTP) the SCON message may be sent when the SS7
congestion level changes. The SCON message MAY also be sent from the
M3UA layer of an ASP to an M3UA peer, indicating that the congestion
level of the M3UA layer or the ASP has changed.
IMPLEMENTATION NOTE: An M3UA node may maintain a timer to control
congestion notification validity, if desired. This timer will be
useful in cases where the peer node fails to indicate congestion
abatement.
The SCON message contains the following parameters:
Network Appearance Optional
Routing Context Conditional
Affected Point Code Mandatory
Concerned Destination Optional
Congestion Indications Optional
INFO String Optional
The format for SCON Message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0200 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0006 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Context /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0012 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected PC 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ ... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected PC n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0206 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| reserved | Concerned DPC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0205 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Cong. Level |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format and description of the Network Appearance, Routing
Context, Affected Point Code, and INFO String parameters are the
same as for the DUNA message (see Section 3.4.1).
The Affected Point Code parameter can be used to indicate
congestion of multiple destinations or ranges of destinations.
Concerned Destination: 32 bits
The optional Concerned Destination parameter is only used if the
SCON message is sent from an ASP to the SGP. It contains the
point code of the originator of the message that triggered the
SCON message. The Concerned Destination parameter contains one
Concerned Destination Point Code field, a three-octet parameter to
allow for 14-, 16-, and 24-bit binary formatted SS7 Point Codes.
A Concerned Point Code that is less than 24 bits is padded on the
left to the 24-bit boundary. Any resulting Transfer Controlled
(TFC) message from the SG is sent to the Concerned Point Code
using the single Affected DPC contained in the SCON message to
populate the (affected) Destination field of the TFC message
Congested Indications: 32 bits
The optional Congestion Indications parameter contains a
Congestion Level field. This optional parameter is used to
communicate congestion levels in national MTP networks with
multiple congestion thresholds, such as in ANSI MTP3. For MTP
congestion methods without multiple congestion levels (e.g., the
ITU international method) the parameter is not included.
Congestion Level field: 8 bits (unsigned integer)
The Congestion Level field, associated with all of the Affected
DPC(s) in the Affected Destinations parameter, contains one of the
following values:
0 No Congestion or Undefined
1 Congestion Level 1
2 Congestion Level 2
3 Congestion Level 3
The congestion levels are defined in the congestion method in the
appropriate national MTP recommendations [7,8].
3.4.5. Destination User Part Unavailable (DUPU)
The DUPU message is used by an SGP to inform concerned ASPs that a remote peer MTP3-User Part (e.g., ISUP or SCCP) at an SS7 node is unavailable. The DUPU message contains the following parameters: Network Appearance Optional Routing Context Conditional Affected Point Code Mandatory User/Cause Mandatory INFO String Optional The format for DUPU message parameters is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag = 0x0200 | Length = 8 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Network Appearance | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag = 0x0006 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ \ / Routing Context / \ \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag = 0x0012 | Length = 8 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Mask = 0 | Affected PC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag = 0x0204 | Length = 8 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Cause | User | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag = 0x0004 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ \ / INFO String / \ \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
User/Cause: 32 bits
The Unavailability Cause and MTP3-User Identity fields, associated
with the Affected PC in the Affected Point Code parameter, are
encoded as follows:
Unavailability Cause field: 16 bits (unsigned integer)
The Unavailability Cause parameter provides the reason for the
unavailability of the MTP3-User. The valid values for the
Unavailability Cause parameter are shown in the following table.
The values agree with those provided in the SS7 MTP3 User Part
Unavailable message. Depending on the MTP3 protocol used in the
Network Appearance, additional values may be used; the
specification of the relevant MTP3 protocol variant/version
recommendation is definitive.
0 Unknown
1 Unequipped Remote User
2 Inaccessible Remote User
MTP3-User Identity field: 16 bits (unsigned integer)
The MTP3-User Identity describes the specific MTP3-User that is
unavailable (e.g., ISUP, SCCP, etc.). Some of the valid values
for the MTP3-User Identity are shown below. The values align with
those provided in the SS7 MTP3 User Part Unavailable message and
Service Indicator. Depending on the MTP3 protocol variant/version
used in the Network Appearance, additional values may be used.
The relevant MTP3 protocol variant/version recommendation is
definitive.
0 to 2 Reserved
3 SCCP
4 TUP
5 ISUP
6 to 8 Reserved
9 Broadband ISUP
10 Satellite ISUP
11 Reserved
12 AAL type 2 Signalling
13 Bearer Independent Call Control (BICC)
14 Gateway Control Protocol
15 Reserved
The format and description of the Affected Point Code parameter
are the same as for the DUNA message (see Section 3.4.1.) except
that the Mask field is not used and only a single Affected DPC is
included. Ranges and lists of Affected DPCs cannot be signaled in
a DUPU message, but this is consistent with UPU operation in the
SS7 network. The Affected Destinations parameter in an MTP3 User
Part Unavailable message (UPU) received by an SGP from the SS7
network contains only one destination.
The format and description of the Network Appearance, Routing
Context, and INFO String parameters are the same as for the DUNA
message (see Section 3.4.1).
3.4.6. Destination Restricted (DRST)
The DRST message is optionally sent from the SGP to all concerned
ASPs to indicate that the SG has determined that one or more SS7
destinations are now restricted from the point of view of the SG,
or in response to a DAUD message, if appropriate. The M3UA layer
at the ASP is expected to send traffic to the affected destination
via an alternate SG with a route of equal priority, but only if
such an alternate route exists and is available. If the affected
destination is currently considered unavailable by the ASP, The
MTP3-User should be informed that traffic to the affected
destination can be resumed. In this case, the M3UA layer should
route the traffic through the SG initiating the DRST message.
This message is optional for the SG to send, and it is optional
for the ASP to act on any information received in the message. It
is for use in the "STP" case described in Section 1.4.1.
The DRST message contains the following parameters:
Network Appearance Optional
Routing Context Conditional
Affected Point Code Mandatory
INFO String Optional
The format and description of the Network Appearance, Routing
Context, Affected Point Code, and INFO String parameters are the
same as for the DUNA message (see Section 3.4.1).
(page 45 continued on part 3)
