307 lines
8.9 KiB
Plaintext
307 lines
8.9 KiB
Plaintext
How to use the YSS7 (Yet Another SS7 Stack)
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===========================================
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YSS7 is a library usable mainly for telephony call signalling and related
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services. It implements a subset of the ITU Signalling System no. 7 and it
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also implements a subset of ISDN (Integrated Services Digital Network).
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The library is written in C++ and uses the base classes provided by Yate
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(Yet Another Telephony Engine) for its basic needs. As a result it supports
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any operating system supported by Yate but with some limitations regarding
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low level drivers and protocol support.
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The architecture of the classes in YSS7 loosely follows the layers defined
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in SS7. Each layer talks to the next one through standard interfaces. Multiple
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inheritance is used so one object can simultaneously implement an interface
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to a lower layer, an interface to a higher layer and some local processing.
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The base of any usage of YSS7 is the SignallingEngine class. Typically only
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one instance of this class is created although it is possible to create
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multiple, completely independent engines. The SignallingEngine object holds
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together all parts of the stack (which are derived from SignallingComponent)
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and periodically calls a timer method to allow for a simple implementation of
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asynchronous processing and timeouts.
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Each other signalling object is derived from SignallingComponent so that it
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keeps the connection to the engine. Because many classes are using multiple
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inheritance the SignallingComponent class is usually inherited virtually to
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make sure only one copy exists per signalling object.
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A protocol stack is built by first creating an empty SignallingEngine object
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and then populating it with instances of the different layers. In most cases
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it is unnecessary to explicitely add an object to the engine if it is
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connected to another component as the base SignallingComponent class will do
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so automatically. However, the components that are created the first time have
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to be explicitely added to the engine.
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Example:
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SignallingEngine* engine = new SignallingEngine;
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SS7Router* router = new SS7Router;
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engine->insert(router);
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// now the router is managed by the engine
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SS7MTP3* network = new SS7MTP3;
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router->attach(network);
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// the network is now implicitely inserted in the engine
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SS7MTP2* link = new SS7MTP2;
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network->attach(link);
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// now the data link is inserted in the engine as well
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The Interfaces of YSS7
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======================
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An interface is a base class that provides some functionality to an object.
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Actually usable classes inherit an interface to provide that functionality.
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SignallingInterface
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-------------------
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This class is an abstraction of Layer 1 (hardware).
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- talks to the hardware through specific code
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- pushes received data to a SignallingReceiver
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- sends out data to the hardware
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- notifies a SignallingReceiver about status changes and errors
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- receives activation and deactivation commands
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SignallingReceiver
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------------------
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The purpose of this class is to talk to Layer 1
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- gets data pushed from a SignallingInterface
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- sends out data to the hardware by calling methods of SignallingInterface
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- receives notification events from a SignallingInterface
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Inherited by: SS7MTP2, ISDNQ921
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SS7Layer2
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---------
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Provides Data Link control to interface to a L2User, usually SS7 Layer 3 (MTP3)
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- pushes Message Signal Units (MSU) to user
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- sends out MSUs received from user interface
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- generates notifications about data link status to upper layers
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- activates or deactivates the link as requested from the upper layers
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Inherited by: SS7MTP2, SS7M2PA, SS7M2UA
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SS7L2User
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---------
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Connects to a SS7 Layer 2 interface
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- pushes MSUs to Layer 2
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- receives MSUs and notifications from Layer2
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Used internally by: SS7MTP3
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SS7Layer3
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---------
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Provides SS7 network layer functions to a L3User, usually a SS7Router
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- forwards messages to a router to be distributed
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- properly label and send out MSUs received from services
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Inherited by: SS7MTP3, SS7M3UA
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SS7L3User
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---------
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Connects to a SS7 Layer 3 interface
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- forwards messages to the connected Layer 3
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- sends messages to Layer 3
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Used internally by: SS7Router
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SS7Layer4
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---------
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Application (Layer 4) interface
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- gets messages from a SS7Router
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- sends messages to a SS7Router
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- receives network status notifications
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Inherited by: SS7ISUP, SS7TUP, SS7SCCP
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SCCP
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----
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Abstract Signalling Connection Control Part
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- performs end-to-end routing of messages
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Inherited by: SS7SCCP, SS7SUA
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SCCPUser
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--------
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Interface to Signalling Connection Control Part
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- sends and receives messages to / from SCCP
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Inherited by: SS7ASP
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ASPUser
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-------
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Interface to Application Service Part
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- sends and receives messages to / from ASP
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Inherited by: SS7TCAP
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TCAPUser
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--------
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Interface to a TCAP implementation
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- sends and receives commands, queries and answers to / from TCAP
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ISDNLayer2
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----------
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Interfaces to an ISDN Layer 3 (Q.931) implementation
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- pushes Q.921 messages to upper layer
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- sends out Q.921 messages from upper layer
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- generate network status changes notifications
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Inherited by: ISDNQ921, ISDNIUA
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ISDNLayer3
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----------
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Interfaces to an ISDN Layer 2 (Q.921) implementation
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- sends Q.921 messages to network
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- receives Q.921 messages from network
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- receives network status notifications
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Inherited by: ISDNQ931
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SIGTRAN
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-------
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Generic interface for transporting signalling over SCTP/IP
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- creates and connects to SCTP sockets
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- sets up alternative routing
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- transfers data to / from the IP network
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- generates network status notifications
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Inherited by: SS7M2PA, SS7M2UA, SS7M3UA, SS7SUA, ISDNIUA
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SignallingCallControl
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---------------------
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This class provides an uniform interface to telephony call control
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- receive requests for call setup, teardown, transfer, etc.
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- acknowledge or reject requests
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- report call status and events
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Inherited by: SS7ISUP, SS7TUP, ISDNQ931
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SignallingCall
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--------------
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Each instance of this class represents one phone call
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SignallingEvent
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---------------
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These object are used to transport event notifications and all related
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information between the library and the user application.
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The Implementations of YSS7
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===========================
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Implementations are fully usable classes that implement the actual
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functionality and also talk to other components through interfaces.
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SS7MTP2
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-------
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Provides an implementation of ITU MTP2 on top of a synchronous (HDLC) hardware
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interface.
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Implements: SS7Layer2, SignallingReceiver
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SS7MTP3
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-------
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Provides an implementation of ITU MTP3 on top of one or more Data Links (SS7
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Layer 2) and takes care of load balancing and link failover.
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Implements: SS7Layer3, SS7L2User
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SS7Router
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---------
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This class is used to route messages between multiple Layer 3 and Layer 4
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components. Usually there is one router per signalling engine.
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- forwards messages to Layer 3
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- distributes messages to Layer 4 according to service type
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SS7ISUP, SS7TUP
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-------------------------
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These 2 classes implement SS7 telephony call control according to different
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subprotocols used around the world.
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Implement: SS7Layer4, SignallingCallControl
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SS7SCCP
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-------
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Implementation of SS7 Signalling Connection Control Part
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Implements: SS7Layer4, SCCP
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SS7ASP
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------
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Implementation of SS7 Application Service Part
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Implements: SCCPUser
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SS7TCAP
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-------
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Implementation of SS7 Transactional Capabilities Application Part
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Implements: ASPUser
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SS7M2PA, SS7M2UA
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----------------
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SIGTRAN implementations of SS7 Layer 2 over SCTP/IP
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Implement: SS7Layer2, SIGTRAN
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SS7M3UA
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-------
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SIGTRAN implementation of SS7 Layer 3 over SCTP/IP
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Implements: SS7Layer3, SIGTRAN
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SS7SUA
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------
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SIGTRAN implementation of SCCP over SCTP/IP
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Implements: SCCP, SIGTRAN
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ISDNQ921
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--------
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Provides an implementation of ITU Q.921 on top of a synchronous (HDLC) hardware
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interface.
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Implements: ISDNLayer2, SignallingReceiver
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ISDNQ931
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--------
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Provides an implementation of ITU Q.931 telephony call control on top of Q.921
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Implements: ISDNLayer3, SignallingCallControl
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ISDNIUA
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-------
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SIGTRAN implementation of Q.921 over SCTP/IP
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Implements: ISDNLayer2, SIGTRAN
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Standards and Recommendations
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=============================
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Basic SS7 concepts
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ITU-T: Q.700
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Message Transfer Part (MTP)
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ITU-T: Q.701 - Q.704, Q.706, Q.707
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Telephone User Part (TUP)
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ITU-T: Q.721 - Q.725
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Supplementary services
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ITU-T: Q.730 - Q.739
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ISDN User Part (ISUP)
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ITU-T: Q.761 - Q.764, Q.766
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Signalling Connection Control Part (SCCP)
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ITU-T: Q.711 - Q.714, Q.716
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Transaction Capabilities
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ITU-T: Q.771 - Q.775
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Operations Maintenance and Administration Part (OMAP)
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ITU-T: Q.750 - Q.755
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ISDN User-Network Interface - Link Layer specification
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ITU-T: Q.921
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ISDN User-Network Interface - Layer 3 specification for Basic Call Control
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ITU-T: Q.931
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ISDN Service Indicator Codings
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ITU-T: Q.939
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Usage of the Cause and Location Codes
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ITU-T: Q.850
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MTP2 User Peer-to-Peer Adaptation Layer
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IETF: RFC 4165
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MTP2 User Adaptation Layer
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IETF: RFC 3331
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MTP3 User Adaptation Layer
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IETF: RFC 3332
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SCCP User Adaptation Layer
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IETF: RFC 3868
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ISDN Q.921 User Adaptation Layer
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IETF: RFC 4233
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