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draft-benedyk-sigtran-tali-00

Description: Request For Comments

You can download source copies of the file as follows:

draft-benedyk-sigtran-tali-00.txt in text format.

Listed below is the contents of file draft-benedyk-sigtran-tali-00.txt.


Internet Engineering Task Force                           Tekelec
INTERNET DRAFT                                      David Sprague 
<draft-benedyk-sigtran-tali-00.txt>                 Robby Benedyk 
Category: Informational                               Dan Brendes
Expires: November 28, 1999                             John Mason

Transport Adapter Layer Interface
David Sprague, Dan Brendes, Robby Benedyk, John Mason, Tekelec 
May 28, 1999

Status of this document
This document is an Internet-Draft and is in full conformance with all 
provisions of Section 10 of RFC2026.  Internet-Drafts are working 
documents of the Internet Engineering Task Force (IETF), its areas, and 
its working groups. Note that other groups may also distribute working 
documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any 
time.  It is inappropriate to use Internet- Drafts as reference 
material or to cite them other than as "work in progress."

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt

The list of Internet-Draft Shadow Directories can be accessed at 
http://www.ietf.org/shadow.html

ABSTRACT

This document proposes the interfaces of a Signaling Gateway, which
provides interworking between the Switched Circuit Network (SCN) and an
IP network.  Since the Gateway is the central point of signaling
information, not only does it provide transportation of signaling from 
one network to another, but can also provide additional functions such 
as protocol translation, security screening, routing information, and 
seamless access to Intelligent Network(IN) services on both networks. 

The Transport Adapter Layer Interface (TALI) is the proposed interface, 
which provides TCAP, ISUP, and MTP messaging over TCP/IP.  In addition, 
TALI provides SCCP Management (SCMG), MTP Primitives, dynamic 
registration of circuits, and routing of call control messages based on 
circuit location.

Table of Contents
1  Introduction                                                 3
2  Architecture                                                 4
3  TALI                                                         5
       3.1  TALI Payload                                        7
       3.2  Message Components                                  8
            3.2.1  Point Code Substructure                      8
            3.2.2  Test                                         8
            3.2.3  Allow Socket                                 8
            3.2.4  Prohibit Socket                              9
            3.2.5  Prohibit Socket Acknowledge                  9
            3.2.6  Monitor                                      9
            3.2.7  Monitor Acknowledge                          9
            3.2.8  SCCP                                        10
            3.2.9  ISUP                                        10
            3.2.10 MTP3                                        10
            3.2.11 MTP Primitives                              11
            3.2.12 SCCP Primitives                             11
            3.2.13 Routing Key Registration                    12
            3.2.14 Routing Key Deregistration                  12
            3.2.15 Routing Key Substructure                    13
            3.2.16 Special                                     13 
4  Message Transport                                           13
       4.1  SCCP                                               13
       4.2  ISUP                                               14
       4.3  MTP3                                               14
       4.4  MTP Primitives                                     15
            4.4.1  MTP-PAUSE-INDICATION                        15
            4.4.2  MTP-RESUME-INDICATION                       15
            4.4.3  MTP-STATUS-INDICATION                       15
            4.4.4  MTP-STATUS-REQUEST                          15
       4.5  SCCP Primitives                                    16
       4.6  Routing Key Registration                           16
            4.6.1 Registering CICs                             16
            4.6.2 Registering Subsystems                       16
       4.7  Routing Key Deregistration                         17
       4.8  Special Service Message                            17
       4.9  Socket Management Messages                         17
5  Event Handling and State Machine                            18
       5.1  SS7 Message Handling Events                        26
            5.1.1  Implementation Dependent Event              26
       5.2  Management Events                                  27
            5.2.1  Management Open Socket                      27
            5.2.2  Management Close Socket                     27
            5.2.3  Management Allow Traffic                    27
            5.2.4  Management Prohibit Traffic                 27
       5.3  Peer Events                                        27
            5.3.1  Received Test Message                       27
            5.3.2  Received Allow Message                      27
            5.3.3  Received Prohibit Message                   27
            5.3.4  Received Prohibit Acknowledge Message       27
            5.3.5  Received Monitor Message                    27
            5.3.6  Received Monitor Acknowledge Message        28
5.4  General Protocol Rules                                    28
       5.5  Graceful Socket Shutdown                           28
6  Abbreviations                                               29
7  Acknowledgements                                            30
8  Author Information                                          30
                                                                Page 3
1 INTRODUCTION

This document is organized into the following 4 sections: 
- Introduction to the document
- Architecture 
- Protocol - TALI 
- Message Transport
- Event Handling, and State Machine

The following terms are used throughout this document.

Intelligent Network (IN):
A network that allows functionality to be distributed flexibly at a 
variety of nodes on and off the network and allows the architecture to 
be modified to control the services. 

Media Gateway (MG): 
A MG terminates SCN media streams, packetizes the media data,, if it 
is not already packetized, and delivers packetized traffic  to the 
packet network.  It performs these functions in reverse order for media 
streams flowing from the packet network to the SCN.

Media Gateway Controller (MGC): 
An MGC handles the registration and management of resources at the MG.  
The MGC may have the ability to authorize resource usage based on local 
policy.  For signaling transport purposes, the MGC serves as a possible
termination and origination point for SCN application protocols, such 
as SS7 ISDN User Part and Q.931/DSS1.

Signaling Gateway (SG): 
An SG is a signaling agent that receives/sends SCN native signaling at 
the edge of the IP network. The SG function may relay, translate or 
terminate SS7 signaling in an SS7-Internet Gateway. The SG function may 
also be co-resident with the MG function to process SCN signaling 
associated with line or trunk terminations controlled by the MG (e.g., 
signaling backhaul).

Switched Circuit Network (SCN):
The term SCN is used to refer to a network that carries traffic within 
channelized bearers of pre-defined sizes.  Examples include Public 
Switched Telephone Networks (PSTNs) and Public Land Mobile Networks 
(PLMNs).  Examples of signaling protocols used in SCN include Q.931, 
SS7 MTP Level 3 and SS7 Application/User parts.

                                                                Page 4
2 ARCHITECTURE

The Signaling Gateway provides an interface to the SCN, other Signaling 
Gateways, and Intelligent Network (IN) services on the SCN network; and 
to Media Gateway Controllers and IN Services on an IP network. 

Signaling Gateways are deployed in pairs for redundancy and 
reliability.  Multiple MGCs are served by both Signaling Gateways and 
operate either in a load sharing or "hot standby" configuration.  TALI 
provides for signaling transport and the appropriate signaling 
management functions for the MGCs under load sharing and communication 
failure cases.  TALI is not limited to MGCs, but may also provide 
signaling to IP based SCPs, and other devices equipped with an IP 
interface.  See Figure 2. 
                                                 
                              +-------+          /---------/
                              |       |          |         |
                              |       | SS7 Link |  SCP    |
   +------IP Network-+--------|  SG   |----------|         |
           |         |        |       |          +---------+
           |         |        |       |-----------------+-------+
           |         |        +-------+                 |       |
           |         |                                  | SSP   |
           |         |                                  |       | 
        +------+   +-----+                              +-------+    
        |      |   |     |                               ||   ||     
        |IP-SCP|   | MGC |                               ||   ||     
        |      |   |     |                               ||   ||     
        +------+   +-----+                               ||   ||    
                      |                                  ||   ||       
                   +-----+                               ||   ||     
                   |     |                               ||   ||     
                   |  MG |                  PRI or CAS   ||   ||    
                   |     |-------------------------------+|   ||    
                   +-----+--------------------------------+   ||    
                     ||                                       ||    
                     |+---------------------------------------+|    
                     +-----------------------------------------+   
                                     ISUP Trunk                   
                                                             
SG=Signaling Gateway               PRI=Primary Rate Interface (ISDN)
MGC=Media Gateway Controller       CAS=Circuit Associated Signaling
MG=Media Gateway                   ISUP=ISDN User Part
SCP=Service Control Point           
SSP=Signaling Switching Point
                                 Figure 1.
                                  

                                                                Page 5
                              +-------+          
                              |       |         
                              |       |  
   +------IP Network-+----+---|  SG   | 
           |         |    |   |       |          
           |         |    |   |       |     SS7 Link    +-------+
           |         |    |   +-------+-----------------|       |
           |         |    |       |                     | SSP   |
           |         |    +---+-------+-----------------|       | 
           |         |        |       |     SS7 Link    |       |   
        +------+   +-----+    |       |                 +-------+    
        |      |   |     |    |       |          
        |IP-SCP|   | MGC |    |   SG  |           
        |      |   |     |    |       |        
        +------+   +-----+    +-------+                      

                             Figure 2.

3 TALI
TALI is an adapter layer protocol used to support reliable 
communication between the SS7 Signaling Network and applications 
residing within the IP network. 

TALI provides:  
      Client / Server relationship between the user and the application
      Standard Berkeley sockets based connection oriented service
      Management control of the sockets
      Controlled flow of data across the socket
      Encapsulation of SCCP, TCAP and ISUP data within service 
      messages
      Identification of particular SCN protocol being carried
      Test and watchdog maintenance messages
      Graceful shutdown of socket
      Transport of multiple protocol types within a single underlying 
      Session

This version of TALI provides 3 SS7 signaling transport methods.  It 
should be noted TALI can be extended.  This version provides 
functionality for MTP over TCP/IP ('mtp3'), SCCP/TCAP over TCP/IP 
('sccp'), and ISUP over TCP/IP ('isot').  These three methods comprise 
the Service Messages.

- SCCP/TCAP Service Message ('sccp')
Provides delivery of SCCP/TCAP messages in a TCP/IP packet. Subsystem 
Management of the SCPs is provided via normal SCCP Management(SCMG) 
contained within UNITDATA messages.  
       
- MTP3 Service Message ('mtp3')
Provides delivery of MTP3 and User Data in a TCP/IP packet.

- ISUP Service Message ('isot')
Provides delivery of ISUP messages in a TCP/IP packet.

                                                                Page 6
Additional functions provided by TALI are socket management, socket 
test procedures, traffic management, and mechanisms for 
registration/deregistration of circuits.  These are outlined below:

- Socket Test ('test')
A periodic test message for service message availability.  Either a
'proh' or an 'allo' should be returned.

- Allow/Prohibit Service Messages ('allo'/'proh')
Allow/Disallow service messages to flow across this socket. 

- Prohibit Service Acknowledgment Message ('proa')
Acknowledges the Prohibit Service Message ('proh').
 
- Monitor/Monitor Acknowledge Socket ('moni'/'mona')
These messages provide a test of round-trip delay on a socket.  The 
'mona' is sent in response to a 'moni'.  Either side can initiate a 
'moni' to measure round trip delay on a congested socket.

- MTP Primitives ('mtpp')
This message delivers signaling management messages for events such as 
Signaling Point Availability/Unavailability and Signaling Point 
congestion status.

- SCCP Primitives ('scpp')
This message provides another mechanism for Subsystem Management of an 
SCP, via seven (7) SCMG messages.

- Routing Key Registration/Deregistration ('rkrg'/'rkdr')
It may be necessary for the Signaling Gateway to route signaling 
traffic based on Circuit Identification Code (CIC).  These message 
allows dynamic registration/deregistration of MG terminated circuits or 
CICs.  This message also allows registration of SCCP Subsystems. 

- Special ('spcl')
Intended for transport of other data formats not specified within TALI.  

                                                                Page 7
3.1 TALI Payload
The TALI payload follows:
==================================================================
OCTET| DESCRIPTION                              | TYPE   | ASCII
=====|==========================================|========| =======
1    | SYNC                                     | OCTETS | 'TALI'
------------------------------------------------------------------
5    | OPCODE                                   | OCTETS |            
     |  Test Service on this Socket             |        |  'test'
     |  Allow Service messages on this socket   |        |  'allo'
     |  Prohibit Service messages on this socket|        |  'proh'
     |  Prohibit Service messages Ack           |        |  'proa'
     |  Monitor Socket message on this socket   |        |  'moni'
     |  Monitor Socket message Ack              |        |  'mona'
     |  SCCP Service message                    |        |  'sccp'
     |  ISUP Service message                    |        |  'isot'
     |  MTP3 Service message                    |        |  'mtp3'
     |  MTP Primitives                          |        |  'mtpp'
     |  SCCP Primitives                         |        |  'scpp'
     |  Routing Key Registration                |        |  'rkrg'
     |  Routing Key De-Registration             |        |  'rkdr'
     |  Special Service Message                 |        |  'spcl'
-------------------------------------------------------------------
9    |  LENGTH (least significant byte first)   | OCTETS | 
     |  Non zero if message contains Service    |        |              
     |  or Monitor Socket message               |        |             
-------------------------------------------------------------------
11   | SERVICE MESSAGE DATA                     |        |             
     |                                          |        |             
===================================================================

                                                                Page 8
3.2 Message Components 

3.2.1 Point Code Substructure
======================================================================
OCTETS |  FIELD NAME   |  DESCRIPTION
       |               |                         
=======================|==============================================
0-3    |  Point Code   |  4 octets   
       |               |  Octet 0: Encoding
       |               |    0=ANSI
       |               |    1=NULL   (Octets 1-3 are undefined)
       |               |    2=ITU National
       |               |    3=ITU
       |               |  If ANSI:
       |               |    Octet 1=Network 
       |               |    Octet 2=Cluster                 
       |               |    Octet 3=Member
       |               |  If ITU National:
       |               |    Octet 1=Zone
       |               |    Octet 2=Area
       |               |    Octet 3=Id
       |               |  If ITU:
       |               |    Octet 1-3=Number
----------------------------------------------------------------------

3. 2.2 Test ('test')
======================================================================
OCTETS |  FIELD NAME   |  DESCRIPTION
       |               |                         
======================================================================
0-3    |  SYNC         |  'TALI'
----------------------------------------------------------------------
4-7    |  OPCODE       |  'test'
----------------------------------------------------------------------
8-9    |  Length       |   00
----------------------------------------------------------------------

3.2.3 Allow Socket ('allo')
======================================================================
OCTETS |  FIELD NAME   |  DESCRIPTION
       |               |                         
======================================================================
0-3    |  SYNC         |  'TALI'
----------------------------------------------------------------------
4-7    |  OPCODE       |  'allo'
----------------------------------------------------------------------
8-9    |  Length       |  00
----------------------------------------------------------------------

                                                                Page 9
3.2.4  Prohibit Socket ('proh')
======================================================================
OCTETS |  FIELD NAME   |  DESCRIPTION
       |               |                         
=======|===============|==============================================
0-3    |  SYNC         |  'TALI'
----------------------------------------------------------------------
4-7    |  OPCODE       |  'proh'
----------------------------------------------------------------------
8-9    |  Length       |   00
----------------------------------------------------------------------

3.2.5 Prohibit Socket Acknowledge ('proa')
======================================================================
OCTETS |  FIELD NAME   |  DESCRIPTION
       |               |                         
=======|===============|==============================================
0-3    |  SYNC         |  'TALI'
----------------------------------------------------------------------
4-7    |  OPCODE       |  'proa'
----------------------------------------------------------------------
8-9    |  Length       |  00
----------------------------------------------------------------------

3.2.6 Monitor ('moni')
======================================================================
OCTETS |  FIELD NAME   |  DESCRIPTION
       |               |                         
======================================================================
0-3    |  SYNC         |  'TALI'
----------------------------------------------------------------------
4-7    |  OPCODE       |  'moni'
----------------------------------------------------------------------
8-9    |  Length       |  0-200
----------------------------------------------------------------------
10-x   |  Data         |  Variable Length
----------------------------------------------------------------------

3.2.7 Monitor Acknowledge ('mona')
======================================================================
OCTETS |  FIELD NAME   |  DESCRIPTION
       |               |                         
======================================================================
0-3    |  SYNC         |  'TALI'
----------------------------------------------------------------------
4-7    |  OPCODE       |  'mona'
----------------------------------------------------------------------
8-9    |  Length       |  0-200
----------------------------------------------------------------------
10-x   |  Data         |  Data must match corresponding 'moni'
----------------------------------------------------------------------

                                                                Page 10
3.2.8  SCCP ('sccp')
======================================================================
OCTETS |  FIELD NAME   |  DESCRIPTION
       |               |                         
======================================================================
0-3    |  SYNC         |  'TALI'
----------------------------------------------------------------------
4-7    |  OPCODE       |  'sccp'
----------------------------------------------------------------------
8-9    |  Length       |  variable
----------------------------------------------------------------------
10-x   |  Data         |  SCCP and TCAP Data starting at the SCCP 
       |               |  message type
       |               |                         
----------------------------------------------------------------------

3.2.9  ISUP Data ('isot')
======================================================================
OCTETS |  FIELD NAME   |  DESCRIPTION
       |               |                         
======================================================================
0-3    |  SYNC         |  'TALI'
----------------------------------------------------------------------
4-7    |  OPCODE       |  'isot'
----------------------------------------------------------------------
8-9    |  Length       | variable 
----------------------------------------------------------------------
10-x   |  Data         | ISUP message starting at the SIO in the 
       |               | MTP3 header.  
       |               |                         
----------------------------------------------------------------------

3.2.10 MTP3 ('mtp3')
======================================================================
OCTETS |  FIELD NAME   |  DESCRIPTION
       |               |                         
======================================================================
0-3    |  SYNC         |  'TALI'
----------------------------------------------------------------------
4-7    |  OPCODE       |  'mtp3'
----------------------------------------------------------------------
8-9    |  Length       | variable 
----------------------------------------------------------------------
10-x   |  Data         | MTP3 and User Data starting at the SIO in the 
       |               | MTP3 header  
       |               |                         
----------------------------------------------------------------------

                                                                Page 11

3.2.11 MTP Primitives ('mtpp')
======================================================================
OCTETS |  FIELD NAME   |  DESCRIPTION
       |               |                         
======================================================================
0-3    |  SYNC         |  'TALI'
----------------------------------------------------------------------
4-7    |  OPCODE       |  'mtpp'
----------------------------------------------------------------------
8-9    |  Length       |  0012
----------------------------------------------------------------------
10-13  |  Primitive    | 0=Pause Indication
       |               | 1=Resume Indication
       |               | 2=Status Indication
       |               | 3=Status Request                      
----------------------------------------------------------------------
14-17  |  Concerned    | Point Code Substructure   
       |  Point Code   | 
-----------------------------------------------------------------------
       |               |              
18-21  |  Cause        | Used to carry congestion level status   
       |  Code         | (Primitives 2&3 Only)
       |               | 
----------------------------------------------------------------------

3.2.12 SCCP Primitives ('scpp')
======================================================================
OCTETS |  FIELD NAME   |  DESCRIPTION
       |               |                         
======================================================================
0-3    |  SYNC         |  'TALI'
----------------------------------------------------------------------
4-7    |  OPCODE       |  'scpp'
----------------------------------------------------------------------
8-9    |  Length       |  0016
----------------------------------------------------------------------
10-13  |  Primitive    | 0=Subsystem Allowed
       |               | 1=Subsystem Prohibited 
       |               | 2=Subsystem Test                       
       |               | 3=Subsystem Out of Service Request
       |               | 4=Subsystem Out of Service Grant 
       |               | 5=Susbystem Backup Routing
       |               | 6=Subsystem Normal Routing
----------------------------------------------------------------------
14-17  |  Affected     | Point Code Substructure
       |  Point Code   |
----------------------------------------------------------------------
18-21  |  Affected     | 
       |  Subsystem    | Affected Subsystem = 0-255
       |               | 
----------------------------------------------------------------------
22-25  |  Subsystem    | 
       |  Multiplicity |  0-3
       |  Indicator    | 
----------------------------------------------------------------------
                                                                Page 12

3.2.13 Routing Key Registration ('rkrg')
======================================================================
OCTETS |  FIELD NAME   |  DESCRIPTION
       |               |                         
======================================================================
0-3    |  SYNC         |  'TALI'
----------------------------------------------------------------------
4-7    |  OPCODE       |  'rkrg'
----------------------------------------------------------------------
8-9    |  Length       |  2 + 24(Key Count)
----------------------------------------------------------------------
10-11  |  Key Count    |  Number of Keys in the message, maximum 50
----------------------------------------------------------------------
12-x   |  Routing Key  |  Set of routing key sub-structures   
       |  Sub-Structure|    
----------------------------------------------------------------------

3.2.14 Routing Key Deregistration ('rkdr')
======================================================================
OCTETS |  FIELD NAME   |  DESCRIPTION
       |               |                         
======================================================================
0-3    |  SYNC         |  'TALI'
----------------------------------------------------------------------
4-7    |  OPCODE       |  'rkdr'
----------------------------------------------------------------------
8-9    |  Length       |  2 + 24(Key Count)
----------------------------------------------------------------------
10-11  |  Key Count    |  Number of Keys in the message, maximum 50
----------------------------------------------------------------------
12-x   |  Routing Key  |  Set of routing key sub-structures   
       |  Sub-Structure|    
----------------------------------------------------------------------

                                                                Page 13
3.2.15 Routing Key Sub-structure
======================================================================
OCTETS |  FIELD NAME   |  DESCRIPTION                                                 
======================================================================
0-3    |  Type         |  0=SCCP-REQ
       |               |  1=ISUP-REQ
       |               |  2=SCCP-IND
       |               |  3=ISUP-IND
----------------------------------------------------------------------
4-7    |  OPC          | Point Code Substructure
       |               |                   
----------------------------------------------------------------------
8-11   |  DPC          | Point Code Substructure 
       |               |                   
----------------------------------------------------------------------
12-15  | SSN           | Subsystem Number (Valid for types 0 and 2)
----------------------------------------------------------------------
16-17  | CIC Low       | CIC low end of range (Valid for types 1 and 3)
----------------------------------------------------------------------
18-19  | CIC High      | CIC high end of range(Valid for types 1 and 3)
----------------------------------------------------------------------
20-23  | Indication    | Indication  - Valid for Indications Only
       | Code          |   0=Success
       |               |   1=Fail
======================================================================

3.2.16  Special ('spcl')
======================================================================
OCTETS |  FIELD NAME   |  DESCRIPTION
       |               |                         
======================================================================
0-3    |  SYNC         |  'TALI'
----------------------------------------------------------------------
4-7    |  OPCODE       |  'spcl'
----------------------------------------------------------------------
8-9    |  Length       |  Variable
----------------------------------------------------------------------
10-x   |  Data         |  Non-TALI specific data
----------------------------------------------------------------------

4 Message Transport

4.1 SCCP 
On a SCCP MSU message arriving from the SS7 Network the Signaling 
Gateway takes the SS7 MSU:
+ discards the MTP Layer 2 information, CRC and flags
+ places the DPC from MTP Layer 3 into the Called Party Address field 
  of the SCCP layer; the Called Party Point Code is added to the Called 
  Party Address if it does not exist, 
+ places the OPC from MTP Layer 3 into the Calling Party Address field 
  of the SCCP layer if there is no Calling Party Point Code, 
+ places the modified SCCP and unchanged TCAP data in the service 
  payload area of the TALI packet,
+ The OPCODE is set to 'sccp',
+ The LENGTH is set to the number of octets in the SERVICE field.
                                                                Page 14
Since the routing information from MTP Layer 3 is placed in the SCCP 
part of the outgoing message, no routing information needs to be saved 
by the Signaling Gateway

On a data message arriving from the IP Network the Signaling Gateway:
+ validates the TALI header, 
+ Regenerate the SIO with the Sub-Service Field set to National 
  Network, priority of zero (0), Service Indicator set to SCCP
+ extracts the SCCP/TCAP data from the SERVICE area and places it in 
  the new SS7 message, 
+ sets the DPC to the SCCP Called Party Point Code, 
+ sets the OPC to the SCCP Calling Party Point Code, 
+ randomly generates the SLS
+ The Layer 2 data is properly formatted and the message is routed out 
  of the Signaling Gateway.

4.2 ISUP 
On an ISUP MSU message arriving from the SS7 Network the Signaling 
Gateway takes the SS7 MSU:
+ discards the MTP Layer 2 information, CRC and flags
+ places SIO, Routing Label, and ISUP data into the 
  SERVICE payload area of the TALI packet,
+ The OPCODE is set to 'isot'
+ The LENGTH is set to the number of octets in the SERVICE field.

Since the routing information is placed in the TALI Packet, no routing 
information needs to be saved by the Signaling Gateway.

On a data message arriving from the IP Network the Signaling Gateway 
takes:
+ validates the TALI header, 
+ extracts the MTP Layer 3 data from the SERVICE area and places it in 
  the new SS7 message, 
+ The Layer 2 data is properly formatted and the message is routed out 
  of the Signaling Gateway. 

4.3 MTP3 
On a MTP3 MSU message arriving from the SS7 Network the Signaling 
Gateway takes the SS7 MSU:
+ discards the MTP Layer 2 information, CRC and flags
+ places SIO, Routing Label, and User Data into the 
  SERVICE payload area of the TALI packet,
+ The OPCODE is set to "mtp3",
+ The LENGTH is set to the number of octets in the SERVICE field.

Since the routing information is placed in the TALI Packet, no routing 
information needs to be saved by the Signaling Gateway.

On a data message arriving from the IP Network the Signaling Gateway 
takes:
+ validates the TALI header, 
+ extracts the MTP Layer 3 data from the SERVICE area and places it in 
  the new SS7 message, 
+ The Layer 2 data is properly formatted and the message is routed out 
  of the Signaling Gateway. 
                                                                Page 15
4.4 MTP Primitives

4.4.1 MTP-PAUSE-INDICATION
The MTP-PAUSE-INDICATION is sent from the Signaling Gateway for the 
following events:
  1) On isolation of an SS7 Network Element
  2) In response to a message bound for an isolated Network Element 
  3) In response to a MTP-STATUS request concerning an unavailable node

On any of these three events, the Signaling Gateway performs the 
following:
+ The OPCODE is set to "mtpp",
+ The primitive is set to MTP-PAUSE-INDICATION,
+ The Concerned Point Code is placed in the Message Parameters field
+ The LENGTH is set to the number of octets in the Message Parameters   
  field.

4.4.2 MTP-RESUME-INDICATION
The MTP-RESUME-INDICATION is sent from the Signaling Gateway for the 
following events:
  1) On new availability of an SS7 Network Element
  2) In response to a MTP-STATUS request concerning an available node

On any of these two events, the Signaling Gateway performs the 
following:
+ The OPCODE is set to "mtpp",
+ The primitive is set to MTP-RESUME-INDICATION,
+ The Concerned Point Code is placed in the Message Parameters 
  field
+ The LENGTH is set to the number of octets in the Message Parameters 
  field.

4.4.3 MTP-STATUS-INDICATION
On a transition of congestion level of an SS7 Network Element, the 
Signaling Gateway does the following:
+ The OPCODE is set to "mtpp",
+ The primitive is set to MTP-STATUS-INDICATION,
+ The Concerned Point Code and Cause Code are placed in the Message
  Parameters field
+ The LENGTH is set to the number of octets in the Message Parameters 
  field.

4.4.4 MTP-STATUS-REQUEST
The MTP-STATUS-REQUEST is sent to query the status of a concerned point
code.  
+ The OPCODE is set to "mtpp",
+ The primitive is set to MTP-STATUS-REQUEST,
+ The Concerned Point Code is placed in the Message Parameters 
  field
+ The LENGTH is set to the number of octets in the Message Parameters 
  field.

                                                                Page 16
4.5 SCCP Primitives
SCCP Subsystem Management (SCMG) is provided through a set of SCCP 
primitives passed between the Signaling Gateway and the IP-SCP.  To 
send an SCCP primitive, the Signaling Gateway does the following:
+ The OPCODE is set to "scpp",
+ The primitive is set to either:
    00000000 - Subsystem Allowed  
    00000001 - Subsystem Prohibited 
    00000002 - Subsystem Test
    00000003 - Subsystem Out of Service Request
    00000004 - Subsystem Out of Service Grant
    00000005 - Subsystem Backup Routing
    00000006 - Subsystem Normal Routing
+ The Concerned Point Code, Subsystem, and Subsystem Multiplicity 
  Indicator (SMI) are placed in the Message Parameters field 
+ The LENGTH is set to the number of octets in the Message Parameters 
  field.

4.6 Routing Key Registration
The Routing Key Registration ('rkrg') message is sent to the Signaling 
Gateway to dynamically register Circuit Identification Codes (CIC) 
which are available for call processing, or SCCP Subsystems available 
for TCAP transactions.  The routing key sub-structure contains the type 
"ISUP-REQ" for registering CICs or "SCCP-REQ" for registering 
subsystems. 

4.6.1 Registering CICs
The registration message substructure contains the OPC, DPC, and range 
of CICs available.  All subsequent ISUP messages, which contain the 
specified range of CICs, are routed via the socket from which the 
'rkrg' was received.  A registration message can register 50 CIC 
ranges.  The CICs must be deregistered before use by another socket.

The Signaling Gateway indicates registration success by returning the 
'rkrg' with the type field set to 'ISUP-IND' in the registration sub-
structure, and the Indication Code set to success.  If the CICs can not 
be registered, a fail code is placed in the Indication Code.

4.6.2 Registering SCCP Subsystems
The registration message substructure contains the Subsystem and Point 
Code available.  All subsequent TCAP queries, which contain the 
specified Subsystem, are routed via the socket from which the 'rkrg' 
was received.  Multiple registration messages can be sent to register 
multiple Subsystems. 

The Signaling Gateway indicates registration success by returning the 
'rkrg' with the type field set to 'SCCP-IND' in the registration sub-
structure, and the Indication Code set to success.  If the Subsystem 
can not be registered, a fail cause code is placed in the Indication 
Code.

                                                                Page 17
4.7 Routing Key Deregistration
The Routing Key Deregistration 'rkdr' message is sent to the Signaling 
Gateway to indicate that the specified range of CICs or the specified 
Subsystems are no longer available for call processing or transaction 
capability.  The deregistration message contains the OPC, DPC, and 
range of CICs/Subsystems to be deregistered.  The type field is set to 
either ISUP-REQ or SCCP-REQ.

The Signaling Gateway indicates deregistration success by returning the 
'rkdr' with the type field set to 'ISUP-IND' or 'SCCP-IND' in the 
registration sub-structure, and the Indication Code set to success.  If 
the Subsystem or CICs can not be deregistered, a fail code is placed in 
the Indication Code.

4.8 Special Service Message  
The Special Service Message is available for transmission of any raw 
data between the Signaling Gateway and connected network element.  To 
send a special service message:
+ The OPCODE is set to "spcl",
+ The LENGTH is set to the number of octets in the Special Service 
  Message,

4.9 Socket Management Messages
The socket management messages are addressed in section 5 and include 
'test', 'allo', 'proh', 'proa', 'moni', and 'mona'.

                                                                Page 18
5 Event Handling and State Machine

The TALI State Machine and Event Handling:
+============+                                          +============+
|            |    |---------|   |------------------|    |            |
|    User    |    | Service |   | Mgmt. Open       |    | MANAGEMENT |
|    Part    |<-->| Message |   | Mgmt. Close      |<-->|            |
|            |    |         |   | Mgmt. Proh.      |    |            |
|            |    |---------|   | Mgmt. Allow      |    +============+
+============+          ^       |------------------|                             
                        |                      ^
                        |                      |
                        v                      v
+====================================================================+
|                         TALI State Machine                         |
|                                                                    |
+====================================================================+
         ^                    ^            ^                  ^
         |                    |            |                  |
         |                    |            |                  |
         |                    |            |                  |
         v                    |            |                  |   
  ---------    -----------------    ------------    ------------------
 | Received|  |                 |  |           |  |                  |
 | 'test'  |  | Connection est. |  | Protocol  |  | T1 Timer Expired | 
 | 'allo'  |  | Connection lost |  | Violation |  | T2 Timer Expired |
 | 'proh'  |  |                 |  |           |  | T3 Timer Expired |
 | 'proa'  |   -----------------    -----------   | T4 Timer Expired |     
 | 'moni'  |          ^                            ------------------
 | 'mona'  |          |                                  ^
 |    or   |          |                                  |
 | Service |          |                                  |
 | Message |          |                                  |
 |         |          |                                  |
  ---------           |                                  |
      ^               |                                  |
      |            +=================================================+
      |            |                                                 |
      |            |                  IMPLEMENTATION                 |
      |            |                    DEPENDENT                    |
      |            +=================================================+
      v
  +============+  
  |    PEER    |
  |            |
  +============+

                                                                Page 19
TALI STATES
======================================================================
Name              |        Description     
======================================================================
OOS               | NE prohibited - FE prohibited, socket is Out of  
                  | Service      
----------------------------------------------------------------------
Connecting        | NE prohibited - FE prohibited, Socket is attempting
                  | to connect.  Servers are 'accepting', Clients are 
                  | 'connecting'
----------------------------------------------------------------------
NEP-FEP           | Both sides are not ready to use the socket for 
                  | service PDUs
----------------------------------------------------------------------
NEP-FEA           | NE is not ready to use the socket for service PDUs
                  | FE is ready to use the socket for service PDUs
----------------------------------------------------------------------
NEA-FEP           | FE is not ready to use the socket for service PDUs
                  | NE is ready to use the socket for service PDUs
----------------------------------------------------------------------
NEA-FEA           | Both side are ready to use the socket for service 
                  | PDUs.  This is the only state where normal bi-
                  | directional data transfer occurs.
======================================================================

TALI TIMERS
======================================================================
NAME  | MIN   | MAX    | DEFAULT | DESCRIPTION
======================================================================
T1    | 100ms | 60 sec | 3 sec   | Send test PDU timer
----------------------------------------------------------------------
T2    | 100ms | 60 sec | 2 sec   | Response timer for a 'allo' or  
      |       |        |         | 'proh' response to test message
----------------------------------------------------------------------
T3    | 100ms | 60 sec | 5 sec   | Timer controls how long to process      
      |       |        |         | rcvd service data after an NE 
      |       |        |         | transition from NEA to NEP.  System 
      |       |        |         | is waiting for a 'proa' response to 
      |       |        |         | the first 'proh' sent when NE
      |       |        |         | transitions from NEA to NEP.
----------------------------------------------------------------------
T4    | 100ms | 60 sec | 60 sec  | Send 'moni' PDU timer
======================================================================
*T1 must be greater than T2

                                                                Page 20
Out of Service State
=====================================================================
|                      |                   STATE                     |
| EVENT                |                Out of Service               |
|   |                  |                   OOS                       |
|   V                  |                                             |
+----------------------+---------------------------------------------+
| T1 Timer Expired     |                                             |
+----------------------+---------------------------------------------+
| T2 Timer Expired     |                                             |
+----------------------+---------------------------------------------+
| T3 Timer Expired     |                                             |
+----------------------+---------------------------------------------+
| Received 'test'      |                                             |
+----------------------+---------------------------------------------+
| Received 'allo'      |                                             |
+----------------------+---------------------------------------------+
| Received 'proh'      |                                             |
+----------------------+---------------------------------------------+
| Received 'proa'      |                                             |
+----------------------+---------------------------------------------+
| Received 'moni'      |                                             |
+----------------------+---------------------------------------------+
| Received 'mona'      |                                             |
+----------------------+---------------------------------------------+
| Received 'isot',     |                                             |
| 'sccp', or 'mtp3'    |                                             |
+----------------------+---------------------------------------------+
|Connection Established|                                             |
+----------------------+---------------------------------------------+
| Connection Lost      |                                             |
+----------------------+---------------------------------------------+
| Protocol Violation   |                                             |
+----------------------+---------------------------------------------+
| Mgmt. Open Socket    | Open the Socket, New State=Connecting       |
+----------------------+---------------------------------------------+
| Mgmt. Close Socket   |                                             |
+----------------------+---------------------------------------------+
| Mgmt. Prohibit Socket| sock_allowed=FALSE                          |
+----------------------+---------------------------------------------+
| Mgmt. Allow Socket   | sock_allowed=TRUE                           |
+----------------------+---------------------------------------------+
| SCCP, ISUP, MTP3     | Reject data                                 |
+----------------------+---------------------------------------------+

                                                                Page 21

Connecting State
=====================================================================
|                      |                   STATE                     |
| EVENT                |                Connecting                   |
|   |                  |                                             |
|   V                  |                                             |
+----------------------+---------------------------------------------+
| T1 Timer Expired     |                                             |
+----------------------+---------------------------------------------+
| T2 Timer Expired     |                                             |
+----------------------+---------------------------------------------+
| T3 Timer Expired     |                                             |
+----------------------+---------------------------------------------+
| Received 'test'      |                                             |
+----------------------+---------------------------------------------+
| Received 'allo'      |                                             |
+----------------------+---------------------------------------------+
| Received 'proh'      |                                             |
+----------------------+---------------------------------------------+
| Received 'proa'      |                                             |
+----------------------+---------------------------------------------+
| Received 'moni'      |                                             |
+----------------------+---------------------------------------------+
| Received 'mona'      |                                             |
+----------------------+---------------------------------------------+
| Received 'isot',     |                                             |
| 'sccp', or 'mtp3'    |                                             |
+----------------------+---------------------------------------------+
|Connection Established| start T1, start T2,                         |
|                      | If sock_allowed                             |
|                      |   send 'allo', send 'test'                  |
|                      |   New State=NEA-FEP                         |
|                      | Else                                        |
|                      |   send 'proh', send 'test'                  |
|                      |   New State=NEP-FEP
+----------------------+---------------------------------------------+
| Connection Lost      |                                             |
+----------------------+---------------------------------------------+
| Protocol Violation   |                                             |
+----------------------+---------------------------------------------+
| Mgmt. Open Socket    |                                             |
+----------------------+---------------------------------------------+
| Mgmt. Close Socket   | Close socket,  New State=OOS                |
+----------------------+---------------------------------------------+
| Mgmt. Prohibit Socket| sock_allowed=FALSE                          |
+----------------------+---------------------------------------------+
| Mgmt. Allow Socket   | sock_allowed=TRUE                           |
+----------------------+---------------------------------------------+
| SCCP, ISUP, MTP3     | reject data                                 |
+----------------------+---------------------------------------------+

                                                                Page 22

Near End Prohibited-Far End Prohibited
=====================================================================
|                      |                 STATE                       |
| EVENT                |                NEP-FEP                      |
|   |                  |                                             |
|   V                  |                                             |
+----------------------+---------------------------------------------+
| T1 Timer Expired     | send test, start T1, start T2               |
+----------------------+---------------------------------------------+
| T2 Timer Expired     | Protocol Violation                          |
+----------------------+---------------------------------------------+
| T3 Timer Expired     | Protocol Violation                          |
+----------------------+---------------------------------------------+
| Received 'test'      | Send 'proh'                                 |
+----------------------+---------------------------------------------+
| Received 'allo'      | Stop T2, New State=NEP-FEA                  |
+----------------------+---------------------------------------------+
| Received 'proh'      | Stop T2, Send 'proa'                        |
+----------------------+---------------------------------------------+
| Received 'proa'      | Stop T3                                     |
+----------------------+---------------------------------------------+
| Received 'moni'      | Convert 'moni' to 'mona', send 'mona'       |
+----------------------+---------------------------------------------+
| Received 'mona'      | Implementation dependent                    |
+----------------------+---------------------------------------------+
| Received 'isot',     | Protocol Violation                          |
| 'sccp', or 'mtp3'    |                                             |
+----------------------+---------------------------------------------+
|Connection Established|                                             |
+----------------------+---------------------------------------------+
| Connection Lost      | Protocol Violation                          |
+----------------------+---------------------------------------------+
| Protocol Violation   | Stop all timers, Close the socket           |
|                      | New State=connecting                        |
+----------------------+---------------------------------------------+
| Mgmt. Open Socket    |                                             |
+----------------------+---------------------------------------------+
| Mgmt. Close Socket   | Stop all timers, Close the socket           |
|                      | New state=OOS                               |
+----------------------+---------------------------------------------+
| Mgmt. Prohibit Socket| sock_allowed=FALSE                          |
+----------------------+---------------------------------------------+
| Mgmt. Allow Socket   | sock_allowed=TRUE, send 'allo'              |
|                      | New state=NEA-FEP                           |
+----------------------+---------------------------------------------+
| SCCP, ISUP, MTP3     | reject data                                 |
+----------------------+---------------------------------------------+

                                                                Page 23

Near End Prohibited-Far End Allowed
=====================================================================
|                      |                 STATE                       |
| EVENT                |                NEP-FEA                      |
|   |                  |                                             |
|   V                  |                                             |
+----------------------+---------------------------------------------+
| T1 Timer Expired     | Send 'test', start T1, start T2             |
+----------------------+---------------------------------------------+
| T2 Timer Expired     | Protocol Violation                          |
+----------------------+---------------------------------------------+
| T3 Timer Expired     | Protocol Violation                          |
+----------------------+---------------------------------------------+
| Received 'test'      | Send 'proh'                                 |
+----------------------+---------------------------------------------+
| Received 'allo'      | Stop T2                                     |
+----------------------+---------------------------------------------+
| Received 'proh'      | Stop T2, send 'proa', New State=NEP-FEP     |
+----------------------+---------------------------------------------+
| Received 'proa'      | Stop T3                                     |
+----------------------+---------------------------------------------+
| Received 'moni'      | Convert 'moni' to 'mona', send 'mona'       |
+----------------------+---------------------------------------------+
| Received 'mona'      | Implementation dependent                    |
+----------------------+---------------------------------------------+
| Received 'isot',     | If T3 running, Process Data                 |
| 'sccp', or 'mtp3'    | Else Protocol Violation                     |
+----------------------+---------------------------------------------+
|Connection Established|                                             |
+----------------------+---------------------------------------------+
| Connection Lost      | Protocol Violation                          |
+----------------------+---------------------------------------------+
| Protocol Violation   | Stop all timers, Close the socket           |
|                      | New State=connecting                        |
+----------------------+---------------------------------------------+
| Mgmt. Open Socket    |                                             |
+----------------------+---------------------------------------------+
| Mgmt. Close Socket   | Stop all timers, Close the socket           |
|                      | New state=OOS                               |
+----------------------+---------------------------------------------+
| Mgmt. Prohibit Socket| sock_allowed=FALSE                          |
+----------------------+---------------------------------------------+
| Mgmt. Allow Socket   | sock_allowed=TRUE, send 'allo'              |
|                      | New state=NEA-FEA                           |
+----------------------+---------------------------------------------+
| SCCP, ISUP, MTP3     | Reject Data                                 |
+----------------------+---------------------------------------------+

                                                                Page 24

Near End Allowed-Far End Prohibited
=====================================================================
|                      |                 STATE                       |
| EVENT                |                NEA-FEP                      |
|   |                  |                                             |
|   V                  |                                             |
+----------------------+---------------------------------------------+
| T1 Timer Expired     | Send 'test', start T1, start T2             |
+----------------------+---------------------------------------------+
| T2 Timer Expired     | Protocol Violation                          |
+----------------------+---------------------------------------------+
| T3 Timer Expired     |                                             |
+----------------------+---------------------------------------------+
| Received 'test'      | send 'allo'                                 |
+----------------------+---------------------------------------------+
| Received 'allo'      | Stop T2, New State=NEA-FEA                  |
+----------------------+---------------------------------------------+
| Received 'proh'      | Stop T2, send 'proa'                        |
+----------------------+---------------------------------------------+
| Received 'proa'      |                                             |
+----------------------+---------------------------------------------+
| Received 'moni'      | convert 'moni' to 'mona', send 'mona'       |
+----------------------+---------------------------------------------+
| Received 'mona'      | Implementation dependent                    |
+----------------------+---------------------------------------------+
| Received 'isot',     | Protocol Violation                          |
| 'sccp', or 'mtp3'    |                                             |
+----------------------+---------------------------------------------+
|Connection Established|                                             |
+----------------------+---------------------------------------------+
| Connection Lost      | Protocol Violation                          |
+----------------------+---------------------------------------------+
| Protocol Violation   | Stop all timers, Close the socket           |
|                      | New State=connecting                        |
+----------------------+---------------------------------------------+
| Mgmt. Open Socket    |                                             |
+----------------------+---------------------------------------------+
| Mgmt. Close Socket   | Stop all timers, Close the socket           |
|                      | New state=OOS                               |
+----------------------+---------------------------------------------+
| Mgmt. Prohibit Socket| sock_allowed=FALSE, send 'proh', start T3   |
|                      | New State=NEP-FEP                           |
+----------------------+---------------------------------------------+
| Mgmt. Allow Socket   | sock_allowed=TRUE                           |
+----------------------+---------------------------------------------+
| SCCP, ISUP, MTP3     | reject data                                 |
+----------------------+---------------------------------------------+

                                                                Page 25

Near End Allowed-Far End Allowed
=====================================================================
|                      |                 STATE                       |
| EVENT                |                NEA-FEA                      |
|   |                  |                                             |
|   V                  |                                             |
+----------------------+---------------------------------------------+
| T1 Timer Expired     | Send 'test', start T1, start T2             |
+----------------------+---------------------------------------------+
| T2 Timer Expired     | Protocol Violation                          |
+----------------------+---------------------------------------------+
| T3 Timer Expired     |                                             |
+----------------------+---------------------------------------------+
| Received 'test'      | send 'allo'                                 |
+----------------------+---------------------------------------------+
| Received 'allo'      | stop T2                                     |
+----------------------+---------------------------------------------+
| Received 'proh'      | stop T2, flush or reroute data, send 'proa' |
|                      | New State=NEA-FEP                           |
+----------------------+---------------------------------------------+
| Received 'proa'      |                                             |
+----------------------+---------------------------------------------+
| Received 'moni'      | Convert 'moni' to 'mona', send 'mona'       |
+----------------------+---------------------------------------------+
| Received 'mona'      | Implementation dependent                    |
+----------------------+---------------------------------------------+
| Received 'isot',     | Process data                                |
| 'sccp', or 'mtp3'    |                                             |
+----------------------+---------------------------------------------+
|Connection Established|                                             |
+----------------------+---------------------------------------------+
| Connection Lost      | Protocol Violation                          |
+----------------------+---------------------------------------------+
| Protocol Violation   | Stop all timers, Close the socket           |
|                      | New State=connecting                        |
+----------------------+---------------------------------------------+
| Mgmt. Open Socket    |                                             |
+----------------------+---------------------------------------------+
| Mgmt. Close Socket   | Stop all timers, Close the socket           |
|                      | New state=OOS                               |
+----------------------+---------------------------------------------+
| Mgmt. Prohibit Socket| sock_allowed=FALSE, send 'proh', start T3   |
|                      | New state=NEP-FEA                           |
+----------------------+---------------------------------------------+
| Mgmt. Allow Socket   | sock_allowed=TRUE                           |
+----------------------+---------------------------------------------+
| SCCP, ISUP, MTP3     | Send data                                   |
+----------------------+---------------------------------------------+

                                                                Page 26
5.1 SS7 Message Handling Events

These events are the actual SS7 messages to be transported using TALI. 
The SS7 message handling part of the application provides an interface 
to the state machine interfaces to give the state machine data and 
accept data from the state machine. 

The state machine rejects new SS7 messages from the Message Handling 
process unless both the near and far end are allowed

5.1.1 Implementation Dependent Event

5.1.1.1 Connection Established Socket Event
The Connection Established Event occurs when an application (either 
client or server) has detected a successful connection to a peer.

5.1.1.2 Connection Lost Socket Event
The Connection Lost Event occurs when an application (either client or 
server) has detected that its connection to a peer has been lost.

5.1.1.3 T1 Timer Expired Event
The T1 Timer Expired Event occurs when a T1 timer has expired.  The T1 
timer represents the interval between the origination of Test Messages 
'test'.  

5.1.1.4 T2 Timer Expired Event
The T2 Timer Expired Event occurs when a T2 timer has expired.  A T2 
timer represents the amount of that the Peer has to return an Allow 
Message 'allo' message or a Prohibit Message 'proh' from the Far End 
in response to a Test Message 'test'.

5.1.1.5 T3 Timer Expired Event
The T3 Timer Expired Event occurs when a T3 timer has expired.  A T3 
timer controls how long to continue to process Service Data after a 
Management Prohibit Traffic Event has occurred.

5.1.1.6 T4 Timer Expired Event
The T4 Timer Expired Event occurs when a T4 timer has expired.  A T4 
timer represents the interval between the origination of Monitor 
Messages 'moni'.

5.1.1.7 Protocol Violation Event
A Protocol Violation Event occurs when the TALI detects an exceptional 
condition.  Protocol violations include:
- Invalid sync code in a received message
- Invalid length field in a received message
- Not receiving a Allow Message 'allo', or Prohibit Message 'proh', in 
  response to the origination of a Test Message 'test' , before the T2 
  timer expires
- Receiving Service messages on a prohibited socket. 
- Socket errors 

                                                                Page 27

5.2 Management Events

5.2.1 Management Open Socket Event
The client is responsible for initiating the socket connection. The 
server must be listening for connections for the connection to be 
completed.  Normally, the client would create a new socket instance and 
issue a connect.  The server would have already performed a bind, 
listen and accept. 

5.2.2 Management Close Socket Event
The client can close the socket by issuing a close to the socket. All 
outstanding messages are lost. 

5.2.3 Management Allow Traffic Event
Management can allow the flow of traffic on the open socket by issuing 
the Management Allow Event ('allo'). This changes the state of the near 
end to allowed. 

5.2.4 Management Prohibit Traffic Event
Management can prohibit the flow of traffic on the open socket by 
issuing the Management Prohibit Event ('proh'). This changes the state 
of the near end to prohibited.

5.3 Peer Events

5.3.1 Received Test Message ('test') Event
The Received Test Message Event occurs when a Test Message 'test' has 
been received from the far end.  The Near End sends a 'test' to inquire 
the State of the Far End Socket.  The response to a 'test' is either a 
Prohibit Message ('proh') or an Allowed Message ('allo').

5.3.2 Received Allow Message ('allo') Event
The Received Allow Message Event occurs when an Allow Message 'allo' 
has been received from the far end.  The reception of the 'allo' 
indicates the Far End is ready to receive Service messages.

5.3.3 Received Prohibit Message ('proh') Event
The Received Prohibit Message Event occurs when a Prohibit Message 
'proh' has been received from the far end.  The reception of the 'proh' 
indicates the Far End no longer wishes to receive Service messages.

5.3.4 Received Prohibit Acknowledge Message ('proa') Event
The Received Prohibit Allow Message Event occurs when a Prohibit Allow 
Message 'proa' has been received from the far end.  The 'proa' message 
is sent immediately upon reception of a Prohibit Message 'proh'.

5.3.5 Received Monitor Message ('moni') Event
The Received Monitor Message Event occurs when a Monitor Message 'moni' 
has been received from the far end. The objective of the Monitor 'moni' 
message is to measure and derive performance measurements on a Socket.  
Either end may send this message on a Socket in order to measure the 
round trip time on the socket.

                                                                Page 28

5.3.6 Received Monitor Acknowledge Message ('mona') Event
The Received Monitor Acknowledgment Message Event occurs when a Monitor 
Acknowledgment Message 'mona' has been received from the far end.  
Either End may send the Monitor Acknowledgment 'mona' message in 
response to a Monitor.  The Data Contents must be the contents of the 
Monitor Message.

5.3.7 Received Service Message ('sccp','isot','mtp3') Event
The Received Service Message Event occurs when a Service Message has 
been received from the far end.

5.4 General Protocol Rules
1)  Neither side can send user PDUs unless both sides are allowed.
2)  Each side initializes to the prohibit state for both near end and 
    far end.
3)  State changes are signaled with either an 'allo' or 'proh'.
4)  Each side can poll the far end's state with a test.  Upon sending 
    test, T1 and T2 should always be restarted.
5)  Each side polls the far end with a test every N (T1) seconds.
6)  The reply to a test is based on the state of the near end only.
7)  The reply to a test is either 'allo' or 'proh'.
8)  A far end signals the last user PDU has been transmitted with 
    either a 'proh' or a 'proa'.
9)  Upon receiving a 'proh', the receiver must always reply with 
    'proa'.
10) The NE cannot gracefully close a socket unless a 'proh' is sent and 
    'proa' is received.
11) On the transition to NEP, after sending a proh, the near end must 
    continue to process received service PDUs until a proa is received 
    or until a T3 timer expires.

5.5 Graceful Socket Shutdown
The state table treats a management request to close the socket as a 
'hard' shutdown. That is, it will close the socket immediately 
regardless of the current state.  Therefore, the correct steps to 
ensure a graceful shutdown of a socket (from the NEA_FEP or NEA_FEA 
states) is:

 1) Management issues a Management Prohibit Traffic Event on the 
    socket.
 2) Management will wait for T3 to expire.
 3) Management can then issue a Close Socket Event on the socket.

                                                                Page 29
6  Abbreviations:

CAS     Circuit Associated Signaling
DB      Database
FE      Far-End
IN      Intelligent Network
ISUP    ISDN User Part
MG      Media Gateway
MGC     Media Gateway Controller
MTP     Message Transfer Part
NE      Near-End
PRI     Primary Rate Interface
SCMG    SCCP Subsystem Management
SCN     Switched Circuit Network 
SCP     Service Control Point
SG      Signaling Gateway
SS7     Signaling System 7
SSP     Service Switching Point
TALI    Transport Adapter Layer Protocol
TCAP    Transmission Capabilities Application Part
TCP/IP  Transmission Control Protocol/Internet Protocol

                                                                Page 30
7. Acknowledgements
The authors would like to thank the following people for their comments and 
contributions to the document.

Ike Elliot -Level 3
Anita Marsh - Tellabs
Rich Garrett -USWest
Terry Thio -Cisco 
Philip W. Shryock -Compaq
Rahul Chopra -3Com
Fu Lin Wu -Telcordia
Prakash Iyer - Lucent

8. Author Information
David Sprague                       Dan Brendes
Tekelec                             Tekelec
5151 McCrimmon Pkwy.                5151 McCrimmon Pkwy.
Suite 216                           Suite 216
Morrisville, NC  27560              Morrisville, NC  27560
+1 919-460-5563                     +1 919-460-2162

Robby Benedyk                       John Mason
Tekelec                             Tekelec
5151 McCrimmon Pkwy.                5151 McCrimmon Pkwy.
Suite 216                           Suite 216
Morrisville, NC  27560              Morrisville, NC  27560
+1 919-460-5533                     +1 919-388-1306



Last modified: Fri, 14 Nov 2014 20:46:28 GMT  
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