M 2 UA AND M 2 PA Submitted

M 2 UA AND M 2 PA Submitted by, Srinivas Kommineni, Gayathri Sarivisetti, Vivek Nemarugommula.

Agenda o o o Introduction of SS 7 M 2 UA M 2 PA Differences between M 2 UA and M 2 PA Conclusion References

SS 7 Protocols o Common Channel Signaling System No. 7 (i. e. , SS 7 or C 7) is a global standard for telecommunications defined by the International Telecommunication Union (ITU) Telecommunication Standardization Sector (ITU-T). o The standard defines the procedures and protocol by which network elements in the public switched telephone network (PSTN) exchange information over a digital signaling network to effect wireless (cellular) and wireline call setup, routing and control.

Standard SS 7 Layer Summary

Message Transfer Part o The lowest level, MTP Level 1, is equivalent to the OSI Physical Layer. MTP Level 1 defines the physical, electrical, and functional characteristics of the digital signaling link. o MTP Level 2 ensures accurate end-to-end transmission of a message across a signaling link. Level 2 implements flow control, message sequence validation, and error checking. o MTP Level 3 provides message routing between signaling points in the SS 7 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 to the OSI Network Layer.

SCCP & TCAP o o Signaling Connection Control Part (SCCP): SCCP is used as the transport layer for TCAP-based services. SCCP provides global title translation (GTT) capabilities above MTP Level 3. TCAP supports the exchange of non-circuit related data between applications across the SS 7 network using the SCCP connectionless service.

SS 7 Classic o o The term SS 7 classic differentiates between SS 7 over IP and narrowband 64 -kilobit SS 7 classic is signaling for call delivery that follows a separate physical path from the bearer channel to set up calls.

Evolution to SS 7 over IP o o A Signaling Transport (sigtran) working group is focusing on how the existing SS 7 protocol might run over IP. The first step is converting elements—such as simple control transport protocol (SCTP) to run directly over IP, thus replacing transmission control protocol (TCP) and user datagram protocol (UDP) to provide a reliable transport for signaling in the telephony networks.

Uses of SS 7 Network The SS 7 network and protocol are used for: o basic call setup, management, and tear down o wireless services such as personal communications services (PCS), wireless roaming, and mobile subscriber authentication o local number portability (LNP) o toll-free (800/888) and toll (900) wireline services o efficient and secure worldwide telecommunications

Introduction (M 2 UA) o M 2 UA is a protocol for transporting SS 7 MTP 2 -User signaling e. g. , MTP 3 messages over IP using the services of the Stream Control Transmission Protocol (SCTP). o The M 2 UA protocol is the layer between SCTP and MTP 3 that separates the physical SS 7 termination from the actual signaling point within the network.

M 2 UA Overview M 2 UA deployments consist of 2 entities, the client and the server. o The server provides physical SS 7 termination and communicates with the client over an SCTP association using IP. o The client houses the MTP 3 and thus is the point code addressable element within the SS 7 network.

M 2 UA in the SG to MGC Application

Architecture of M 2 UA

Common Message Header

M 2 UA Message Header

Applications o o o M 2 UA serves several purposes. The first purpose is to provide a mechanism for the transport of SS 7 MTP 2 user signaling (e. g. , MTP 3 messages) over IP using SCTP. The second purpose is to allow remote placement of SS 7 link terminations and back haul SS 7 traffic to a centralized point in the network.

Services Provided by the M 2 UA Adaptation Layer o o The SS 7 MTP 3/MTP 2(MTP 2 -User) interface is retained at the termination point in the IP network, so that the M 2 UA protocol layer is required to provide the equivalent set of services to its users as provided by the MTP Level 2 to MTP Level 3. Support for MTP Level 2 / MTP Level 3 interface boundary Support for communication between Layer Management modules on SG and MGC Support for management of active associations between SG and MGC

Functions Provided by the M 2 UA Layer o o o Mapping Flow Control / Congestion SCTP Stream Management Seamless SS 7 Network Management Interworking Active Association Control

Security o o M 2 UA is designed to carry signaling messages for telephony services. As such, M 2 UA MUST involve the security needs of several parties: the end users of the services; the network providers and the applications involved. As a transport protocol, M 2 UA has the following security objectives: * Availability of reliable and timely user data transport. * Integrity of user data transport. * Confidentiality of user data.

Threats * Blind Denial of Service Attacks * Flooding * Masquerade * Improper Monopolization of Services o When the network in which M 2 UA runs in involves more than one party, it MAY NOT be reasonable to expect that all parties have implemented security in a sufficient manner. In such a case, it is recommended that IPSEC is used to ensure confidentiality of user payload.

M 2 PA-Message Transport protocol peer-to-peer adaptation layer o o o M 2 PA is the peer-to-peer equivalent of M 2 UA. M 2 PA allows communication between SS 7 systems over IP rather than T-1 or E-1 TDM links. An M 2 PA link may be used in place of an MTP 2 link, removing the need for dedicated and expensive SS 7 hardware. The M 2 PA protocol is the layer between SCTP and MTP Level 3. M 2 PA provides a means for peer MTP 3 layers in SGs to communicate directly, it extends the reach of SS 7 over the IP network.

Role of M 2 PA in Evolution to SS 7 over IP o M 2 PA allows the classical SS 7 link to be replaced by SS 7 over IP while maintaining the SS 7 link topology.

Purpose of M 2 PA o o Provides a mechanism for the transport of SS 7 MTP 2 user signaling (e. g. , MTP 3 messages) over IP using SCTP. Enables seamless operation between MTP 2 user peers in the SS 7 and IP space.

M 2 PA Symmetrical Peer-to-Peer Architecture

M 2 PA Symmetrical Peer-to-Peer Architecture o o MTP 3 is adapted to the SCTP layer using M 2 PA. All primitives between MTP 3 and MTP 2 are supported by M 2 PA.

Architecture of M 2 PA in a Signaling Gateway

M 2 PA in IP Signaling Gateway

Architecture of M 2 PA in a Signaling Gateway o o o SG is an IPSP that is equipped with both traditional SS 7 and IP network connections. Architecture is applicable for an SG to SG connection, used to bridge SS 7 network islands. SG and the IPSP communicate through an IP link using the M 2 PA protocol. Messages sent from the SEP to the IPSP (and vice versa) are routed by the SG. MTP 3 is present on each SG to provide routing and management of the MTP 2/M 2 PA links. Because of the presence of MTP 3, each SG would require its own SS 7 point code. M 2 PA has no knowledge of the upper SS 7 layer.

M 2 PA in IP Signaling Gateway o o o The IPSP's MTP 3 uses its underlying M 2 PA as a replacement for MTP 2. Communication between the two layers MTP 3/M 2 PA is defined by the same primitives as in SS 7 MTP 3/MTP 2. M 2 PA uses the SCTP association as an SS 7 link. The M 2 PA/SCTP/IP stack can be used in place of an MTP 2/MTP 1 stack.

Functions Provided by M 2 PA o o o à à MTP 2 Functionality: M 2 PA provides MTP 2 functionality that is not provided by SCTP; thus, together M 2 PA and SCTP provide functionality similar to that of MTP 2. SCTP provides reliable, sequenced delivery of messages. M 2 PA functionality includes: Data retrieval to support the MTP 3 changeover procedure. Reporting of link status changes to MTP 3. Processor outage procedure. Link alignment procedure.

SCTP Association Management o o SCTP allows a user-specified number of streams to be opened during initialization. Responsibility of M 2 PA to ensure proper management of the streams. M 2 PA uses two streams in each direction for each association. - Stream 0 is designated for Link Status messages. - Stream 1 is designated for User Data messages, as well as Link Status messages that must remain in sequence with the User Data messages. Separating results in M 2 PA to prioritize the messages in a manner similar to MTP 2.

M 2 PA Association State Transition Diagram

Description of M 2 PA Association states o o o IDLE: State of the association during power up initialization ASSOCIATING: M 2 PA is attempting to establish an SCTP association. ESTABLISHED: SCTP association is established.

M 2 PA Link State Control M 2 PA link moves from one state to another in response to various events. The events that may result in a change of state include: - MTP 3 primitive requests - Receipt of messages from the peer M 2 PA - Expiration of timers - SCTP notifications o

M 2 PA Applications

M 2 PA Applications o M 2 PA used in SS 7 offloading applications Communication between node SEP 1 and SEP 2 is done via two SGs. Both SEP 1 and SEP 2 are connected to two different Signaling Gateways via SS 7 interface. These Signaling Gateways are connected to each other via SIGTRAN (M 2 Pa + SCTP) and acts as STP Nodes. Signaling messages from SEP 1 and SEP 2 are passed via these two Signaling Gateways. This application can be termed as SS 7 offload. o M 2 PA used in IP based signaling points In this case Signaling Points are connected to each other using IP network. These IP based signaling points (IPSP) uses M 2 PA links instead of MTP 2 links. These IP bases signaling points can also connect to signaling points in SS 7 network, via M 2 PA based Signaling Gateway.

Services provided by M 2 PA o o o M 2 PA receives the primitives sent from MTP 3 to its lower layer. M 2 PA processes these primitives or maps them to appropriate primitives at the M 2 PA/SCTP interface. Also M 2 PA sends primitives to MTP 3 similar to those used in the MTP 3/MTP 2 interface.

Types of messages o o o Message Signal Units (MSUs) Link Status Signal Units (LSSUs) Fill-In Signal Units (FISUs)

Types of messages (contd. . ) o o o MSUs originate at a higher level than MTP 2, and are destined for a peer at another node. M 2 PA passes these messages from MTP 3 to SCTP as data for transport across a link. These are called User Data messages in M 2 PA. LSSUs allow peer MTP 2 layers to exchange status information. Analogous messages are needed for M 2 PA. The Link Status message serves this purpose. FISUs are transmitted continuously when no other signal units are waiting to be sent. FISUs also carry acknowledgement of messages. Since an IP network is a shared resource, it would be undesirable to have a message type that is sent continuously as is the case with FISUs. Furthermore, SCTP does not require its upper layer to continuously transmit messages. Therefore, M 2 PA does not provide a protocol data unit like the FISU. The M 2 PA User Data message is used to carry acknowledgement of messages. If M 2 PA needs to acknowledge a message, and it has no MTP 3 message of its own to send, an empty User Data message can be sent.

M 2 PA Procedures o o o Messages passed between MTP 3 and M 2 PA are the same as those passed between MTP 3 and MTP 2. M 2 PA interprets messages from MTP 3 and sends the appropriate message to SCTP. Likewise, messages from SCTP are used to generate a meaningful message to MTP 3. LINK Initialization – Alignment An example of the message flow used to bring an SS 7 link in service is shown The purposes of the alignment procedure are: n (1) To provide a handshaking procedure so that both endpoints are prepared to send SS 7 traffic, and to prevent traffic from being sent before the other end is ready. n (2) To verify that the SCTP association is suitable for use as an SS 7 link.

Link Initialization - Alignment

Link Initialization o o o If SCTP fails to establish the association, and M 2 PA has received a Start Request from its MTP 3, then M 2 PA SHALL report to MTP 3 that the link is out of service. The Link Status Out of Service message replaces the SIOS message of MTP 2 After the association is established, M 2 PA SHALL send a Link Status Out of Service message to its peer. Prior to the beginning of alignment, M 2 PA MAY send additional Link Status Out of Service messages. M 2 PA MAY send additional Link Status Alignment until it receives Link Status Alignment, Link Status Proving Normal, or Link Status Proving Emergency from the peer. If proving is performed, then during the proving period (i. e. , after M 2 PA starts the proving period timer T 4), M 2 PA SHALL send Link Status Proving messages to its peer at an interval defined by the protocol parameter Proving_Interval The Link Status Ready message is used to verify that both ends have completed proving. When M 2 PA starts timer T 1, it SHALL send a Link Status Ready message to its peer in the case where MTP 2 would send a FISU after proving is complete.

Link Initialization - Proving

Message Transmission and Reception Link Initialization – In Service o Messages are transmitted using the Data Request primitive from MTP 3 to M 2 PA. o The message is passed from MTP 3 of the source to MTP 3 of the destination.

Link Status Indication o If SCTP sends a Communication Lost primitive to M 2 PA, M 2 PA notifies MTP 3 that the link is out of service. MTP 3 responds in its usual way.

Processor Outage o o o The Link Status Processor Outage message replaces the SIPO message of MTP 2. M 2 PA SHALL send a Link Status Processor Outage message to its peer at the beginning of a processor outage condition where MTP 2 would send SIPO. M 2 PA MAY send additional Link Status Processor Outage messages as long as that condition persists. M 2 PA sends a Link Status message to its peer. The peer M 2 PA notifies MTP 3 of the outage. MTP 3 can then follow the processor outage procedures. When the local processor outage condition ends, M 2 PA SHALL send a Link Status Processor Recovered message to its peer on the User Data stream. This message is used to signal the end of the processor outage condition, instead of an MSU or FISU, as is used in MTP 2. Upon receiving the Link Status Processor Recovered message, the M 2 PA in RPO SHALL respond with a Link Status Ready message on the User Data stream. When M 2 PA experiences a local processor outage, it MAY put the link out of service by sending a Link Status Out of Service message, if this is allowed by the applicable MTP 2 standard

Processor Outage

Flow control o o o M 2 PA SHALL send a Link Status Busy message to its peer at the beginning of a receive congestion condition. M 2 PA MAY send additional Link Status Busy messages as long as that condition persists. When the condition ends, M 2 PA SHALL send a Link Status Busy Ended message to its peer When the peer M 2 PA receives the first Link Status Busy message, it SHALL start the Remote Congestion timer T 6 if there are messages in the retransmission buffer awaiting acknowledgement (i. e. , T 7 is running). M 2 PA SHALL stop the T 7 timer if it is running. Additional Link Status Busy messages received while T 6 is running do not cause T 6 to be reset and do not cause T 7 to be started. While T 6 is running, T 7 SHALL NOT be started. When the peer M 2 PA receives the Link Status Busy Ended message and T 6 has not expired, it SHALL stop T 6 (if T 6 is running) and start T 7 (if there are messages awaiting acknowledgement in the retransmission buffer). The peer M 2 PA SHOULD continue receiving and acknowledging messages while the other end is busy, but MUST NOT send User Data messages after receiving Link Status Busy and before receiving Link Status Busy Ended.

Flow Control o Level 2 Flow Control- Congestion Ceases

Level 2 Flow Control-Timer T 6 Expires

MTP 3 Signaling Link Congestion o M 2 PA SHALL detect transmit congestion in its buffers according to the requirements for signaling link transmit congestion in MTP 3 o M 2 PA notifies MTP 3 of congestion onset and abatement. The notification includes the congestion level, if there are levels of congestion defined.

Link Deactivation • MTP 3 can request that a link be taken out of service. • M 2 PA SHALL send a Link Status Out of Service message to its peer at the beginning of a condition where MTP 2 would send SIOS. M 2 PA MAY send additional Link Status Out of Service messages as long as that condition persists.

Link Changeover o o o o The objective of the changeover is to ensure that signaling traffic carried by the unavailable signaling link is diverted to the alternative signaling links as quickly as possible while avoiding message loss, duplication, or mis-sequencing. MTP 3 performs a changeover because the link went out of service. MTP 3 selects a different link to retransmit the unacknowledged and unsent messages. MTP 2's Forward and Backward Sequence Numbers are only seven bits long. Hence, it is necessary for MTP 3 to accommodate the larger sequence numbers. This is done through the use of the Extended Changeover Order (XCO) and Extended Changeover Acknowledgement (XCA) messages instead of the Changeover Order (COO) and Changeover Acknowledgement (COA) messages. If M 2 PA receives a Retrieval Request and FSNC request from MTP 3, M 2 PA SHALL retrieve from its buffers and deliver to MTP 3 BSNT - Backward Sequence Number to be Transmitted FSNC - Forward Sequence Number of last message accepted by remote level 2 For emergency changeover, MTP 3 retrieves only the unsent messages for transmission on the alternate links. If M 2 PA receives a Retrieval Request and FSNC request with no FSNC value, or with an invalid FSNC, then M 2 PA SHALL retrieve from its buffers and deliver to MTP 3.

Link Changeover

Security Issues o M 2 PA is designed to carry signaling messages for telephony services. As such, M 2 PA MUST involve the security needs of several parties: - the end users of the services - the network providers - the applications involved

M 2 PA Protocol Extensions o This protocol may be extended through IANA (Internet Assigned Numbers Authority) in three ways: - through definition of additional message classes, - through definition of additional message types, and - through definition of additional message parameters.

Differences between M 2 PA and M 2 UA o o o M 2 PA: IPSP processes MTP 3/MTP 2 primitives. M 2 UA: MGC transports MTP 3/MTP 2 primitives between the SG's MTP 2 and the MGC's MTP 3 (via the NIF) for processing. M 2 PA: SG-IPSP connection is an SS 7 link. M 2 UA: SG-MGC connection is not an SS 7 link. It is an extension of MTP to a remote entity. M 2 PA: SG is an SS 7 node with a point code. M 2 UA: SG is not an SS 7 node and has no point code. M 2 PA: SG can have upper SS 7 layers, e. g. , SCCP. M 2 UA: SG does not have upper SS 7 layers since it has no MTP 3. M 2 PA: relies on MTP 3 for management procedures. M 2 UA: uses M 2 UA management procedures.

M 2 PA and M 2 UA similarities o o Both transport MTP 3 messages. Both present an MTP 2 upper interface to MTP 3.

Specification Issues o o In M 2 PA/SCTP, there is no mechanism for immediately stopping acknowledgement of incoming messages. No Link Status Out of Service message - If M 2 PA keeps an association up when the link is out of service, there should be a Link Status Out of Service message. M 2 PA could then inform its peer that it is in the Out of Service state. o M 2 PA draft does not give clear advice on when to abort an association because of poor association performance.

Benefits of SS 7 o. IP o o o reduced infrastructure costs. enhanced efficiency. new opportunities to deploy revenuegenerating applications and services.

Conclusions o o The goal of SS 7 is to provide a signaling network, and performance characteristics to facilitate communication between carrier grade network elements in circuit switched and mobile networks. The purpose is to provide a mechanism for the transport of SS 7 MTP 2 user signaling (e. g. , MTP 3 messages) over IP using SCTP. M 2 PA provides MTP 2 functionality that is not provided by SCTP; thus, together M 2 PA and SCTP provide functionality similar to that of MTP 2. M 2 PA interprets messages from MTP 3 and sends the appropriate message to SCTP. Likewise, messages from SCTP are used to generate a meaningful message to MTP 3.

Questions 1. Differences between M 2 UA and M 2 PA? - Refer slide # 57. 2. What functions does M 2 PA support? a. ) seamless operation of MTP 3 protocol peers over an IP network connection. b. ) The MTP 2/MTP 3 interface boundary, management of SCTP transport associations, and traffic instead of MTP 2 Links. c. ) Asynchronous reporting of status changes to management. 3. Services Provided by the M 2 UA Adaptation Layer ? - Refer slide # 17.

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