SIGTRAN protocol

Chapter1 overview

SIGTRAN definition
.Two layers of protocols are included in the SIGTRAN protocol stack, i.e., transmission protocols
(such as SCTP/IP) and adaptation protocols (such as M3UA, IUA).

Introduction of M3UA

Chapter2 SCTP protocol
   2.1 overview
SCTP protocol introduction
.Stream Control Transmission Protocol (SCTP) is a reliable transport protocol that operates over a potentially unreliable connectionless packet service such as IP.
     -SCTP is designed to transfer SCN narrowband signaling over IP network.
     -Compared with the TCP, SCTP features higher reliability, real-time and multi-homed performance.

SCTP features
-Support for orderly/disorderly transmission of subscriber datagram in the flow.
-Multiple streams can be established in one association, and the data in the streams do not interfere with each other.
-Multi-home can be supported at one end or both ends of the association to improve the reliability of the link.
-The association must pass the COOKIE authentication before establishment to guarantee the security.

2.2 SCTP terms
SCTP transmission address
.A transport address of Stream Control Transmission Protocol (SCTP) is defined by the combination of an IP address and an SCTP port number.
.SCTP port number is used for the identification of the users at the same address, and it is identical to that of TCP port number in the concept.

Host and endpoint
.A Host is a computer, configured with one or multiple IP addresses. It is a typical physical entity.
.Endpoint is one of basic concepts of SCTP. An endpoint is the logical sender/receiver of SCTP packets. It is a typical logical entity. Association and stream

TSN and SSN
.TSN
-Transmission Sequence Number (TSN) is a 32-bit sequence number used internally by SCTP. One TSN is attached to each chunk containing user data to permit the receiving SCTP endpoint to acknowledge its receipt and detect duplicate deliveries. TSN is maintained on the basis of association.
.SSN
-SSN is the acronym of Stream Sequence Number. In each stream of an SCTP association, a 16-bit sequence number is assigned to each data chunk sent in the stream by the local end, in order to ensure the sequenced transmission in the stream. SSN is maintained on the basis of stream.
.TSN is maintained on the basis of association.
.For example: Endpoint A use two stream to connect endpoint B. Now block A,B,C,D will be transmit, the sequence of transmission is as following :block A use stream1,block B use stream2, block C use stream3, block D use stream4. And block5 is divided into D1 and D2.

CWND and RWND
.CWND: Congestion Window
    -An SCTP variable that limits the data, in number of bytes, a sender can transmit to a particular destination transport address before receiving an acknowledgement. SCTP is a sliding window protocol.
.RWND: Receiver Window.
   -An SCTP variable that a data sender uses to store the most recently calculated receiver window of its peer, in number of bytes.

2.3 SCTP function
SCTP function
.The functions of SCTP mainly include:
    -association startup and takedown
    -sequenced delivery within streams
    -user data fragmentation
    -acknowledgement and congestion avoidance
    -chunk bundling
    -packet validation
    -path management.

2.4 SCTP message structure
SCTP message

SCTP message type

Startup of association

.The startup of SCTP association is a four-way handshake process, which has four message interactions: INIT, INIT ACK, COOKIE ECHO and COOKIE ACK

Termination of association

.SCTP association can be terminated in two ways: One is GRACEFUL close, the other is UNGRACEFUL close.

.Just as their names imply, the former means that all data in queue by either endpoint is delivered to the respective peers before the association is shut down.

.The latter means that the association is directly aborted and the data is directly discarded.

Chap3 M3UA protocol introduction

3.1 overview

M3UA function

.M3UA (MTP3 User Adaptation) protocol supports the transport of any SS7 MTP3-User signaling (e.g., ISUP and SCCP messages) over IP using the services of the Stream Control Transmission Protocol.

.Also, provision is made for protocol elements that enable a seamless operation of the MTP3-User peers in the SS7 and IP domains. This protocol would be used between a Signaling Gateway (SG) and a Media Gateway Controller (MGC) or IP-resident Database, or between two IP-based applications.

M3UA protocol introduction

M3UA protocol introduction(continue)

M3UA protocol introduction

.M3UA also can be used to transfer signaling between two IPSP

3.2 basic concept

.AS

-A logical entity serving a specific Routing Key.

.ASP

-A process instance of an Application Server.

.IPSP

-A process instance of an IP-based application. An IPSP is essentially the same as an ASP, except that it uses M3UA in a point-to-point fashion. Conceptually, an IPSP does not use the services of a Signaling Gateway node.

Basic concept

.M3UA link state transition

.Relationship among M3UA Link, Linkset, Route and Entity

.M3UA route

-The path from source entity to destination entity is called a M3UA route.

    -One M3UA route corresponds to one M3UA Linkset at the home terminal.
.M3UA entity
   -The logical processing unit that accomplishes some special functions, such as AS, SP or a logic unit that only implements special message transfer function, such as SG can be classified as M3UA Entity. Each M3UA Entity is identified by a unique signaling point code.
   .M3UA LOCAL ENTITY: The logical entity to accomplish special function in local side.
   .M3UA DESTINATION ENTITY: The logic entity to accomplish special function in peer side.

3.3 M3UA message structure

.The general M3UA message format includes a common message header followed by zero or more variable length parameters.
    -The protocol messages for MTP3-User Adaptation require a message structure, which contains a version, message class, message type, message length, and message contents.

-All the parameters contained in a message are defined in a Tag Length-Value format as shown below.
MTP3 User

M3UA message introduction

.Management messages

.Transfer messages

.SS7 Signaling Network Management messages

.ASP State Maintenance messages

.ASP Traffic Maintenance messages

Establishment procedure

Data Transfer procedure

.Determine the correct Destination Entity.

.If the destination Entity is Accessible, then get the Available route to that destination entity.

.Get an Active Linkset belonging to this Route. .Determine an Active Link in the given Linkset.

.Determine whether to complete the optional fields of the DATA message. .Map the MTP-TRANSFER request primitive into the Protocol Data field of a DATA message

.Send the DATA message to the remote M3UA peer at the SGP, over the chosen M3UA link.

MTP_TRANSFER primitive handling at ASP