|
Network Working Group Request for Comments: 3094 Category: Informational |
D. Sprague R. Benedyk D. Brendes J. Keller Tekelec April 2001 |
This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
Copyright © The Internet Society (2001). All Rights Reserved.
Readers should note that this memo presents a vendor's alternative to standards track technology being developed by the IETF SIGTRAN Working Group. The technology presented in this memo has not been reviewed by the IETF for its technical soundness or completeness. Potential users of this type of technology are urged to examine the SIGTRAN work before deciding to use the technology described here.
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 it 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 (Transaction Capability Application Part), ISUP (ISDN User Part), and MTP (Mail Transport Protocol) messaging over TCP/IP. In addition, TALI provides SCCP (Signalling Connection Control Part) Management (SCMG), MTP Primitives, dynamic registration of circuits, and routing of call control messages based on circuit location.
1. Introduction 4 2. Overview of the TALI Protocol 6 2.1 Traditional PSTN SS7 Networks 6 2.2 Converged SS7 Networks 8 2.3 TALI Protocol Stack Overview 10 2.3.1 An Alternate TALI Protocol Stack using the SAAL Layer 13 2.3.2 An Alternate TALI Protocol Stack using SCTP 15 2.4 Inputs to the TALI Version 1.0 State Machine 15 3. TALI Version 1.0 17 3.1 Overview of the TALI Message Structure 17 3.1.1 Types of TALI Fields 19 3.2 Detailed TALI Message Structure 20 3.2.1 TALI Peer to Peer Messages 20 3.2.1.1 Test Message (test) 20 3.2.1.2 Allow Message (allo) 21 3.2.1.3 Prohibit Message (proh) 21 3.2.1.4 Prohibit Acknowledgement Message (proa) 21 3.2.1.5 Monitor Message (moni) 22 3.2.1.6 Monitor Acknowledge Message (mona) 22 3.2.2 Service Messages 23 3.2.2.1 SCCP Service Message (sccp) 23 3.2.2.1.1 SCCP Encapsulation using TALI 25 3.2.2.2 ISUP Service Message (isot) 27 3.2.2.2.1 ISUP Encapsulation using TALI 27 3.2.2.3 MTP3 Service Message (mtp3) 28 3.2.2.3.1 MTP3 Encapsulation using TALI 29 3.2.2.4 SAAL Service Message (saal) 30 3.2.2.4.1 MTP3 and SAAL Peer to Peer Encapsulation using TALI 31 3.3 TALI Timers 34 3.3.1 T1 Timer 34 3.3.2 T2 Timer 34 3.3.3 T3 Timer 34 3.3.4 T4 Timer 34 3.3.5 Recommended Defaults and Ranges for the TALI Timers 35 3.4 TALI User Events 35 3.4.1 Management Open Socket Event 35 3.4.2 Management Close Socket Event 36 3.4.3 Management Allow Traffic Event 36 3.4.4 Management Prohibit Traffic Event 36 3.5 Other Implementation Dependent TALI Events 37 3.6 TALI States 37 3.7 TALI Version 1.0 State Machine 38 3.7.1 State Machine Concepts 38 3.7.1.1 General Protocol Rules 38 3.7.1.2 Graceful Shutdown of a Socket 39 3.7.1.3 TALI Protocol Violations 39
3.7.2 The State Machine 40 3.8 TALI 1.0 Implementation Notes 42 3.8.1 Failure on a TCP/IP Socket 42 3.8.2 Congestion on a TCP/IP Socket 43 3.9 TALI 1.0 Limitations 43 4. TALI Version 2.0 43 4.1 Overview of TALI Version 2.0 Features 45 4.2 TALI Version Identification 47 4.3 Backwards Compatibility 50 4.3.1 Generating Protocol Violations based on Received Messages 53 4.4 Overview of the TALI Message Structure 55 4.4.1 Types of TALI Fields 55 4.5 Detailed TALI Message Structures for New 2.0 Opcodes 58 4.5.1 Management Message (mgmt) 60 4.5.1.1 Routing Key Registration Primitive (rkrp) 61 4.5.1.1.1 RKRP Data Structures 65 4.5.1.1.1.1 Common Fields in all RKRP Messages 65 4.5.1.1.1.2 CIC Based Routing Key Operations 67 4.5.1.1.1.3 SCCP Routing Key Operations 71 4.5.1.1.1.4 DPC-SI, DPC and SI based Routing Key Operations 74 4.5.1.1.1.5 Default Routing Key Operations 76 4.5.1.1.1.6 Support for Multiple RKRP Registration Operations 78 4.5.1.1.1.6.1 Multiple Registrations Support 78 4.5.1.1.1.6.2 Multiple RKRP Operations in a Single Message 80 4.5.1.2 MTP3 Primitive (mtpp) 82 4.5.1.3 Socket Option Registration Primitive (sorp) 87 4.5.2 Extended Service Message (xsrv) 91 4.5.3 Special Message (spcl) 92 4.5.3.1 Special Messages Not Supported (smns) 93 4.5.3.2 Query Message (qury) 93 4.5.3.3 Reply Message (rply) 94 4.5.3.4 Unsolicited Information Message (USIM) 95 4.6 TALI Timers 95 4.7 TALI User Events 95 4.8 TALI States 96 4.9 TALI Version 2.0 State Machine 96 4.9.1 State Machine Concepts 96 4.9.1.1 General Protocol Rules 96 4.9.1.2 Graceful Shutdown of a Socket 97 4.9.1.3 TALI Protocol Violations 97 4.9.2 The State Machine 97 4.10 TALI 2.0 Specification Limitations 101 5. Success/Failure Codes 101 6. Security Considerations 102 7. References 102 8. Acknowledgments 103 9. Authors' Addresses 104 10. Full Copyright Statement 105
This document is organized into the following 6 sections:
- Introduction to the document - Overview of the TALI Protocol - TALI Version 1.0 - TALI Version 2.0 - Success/Failure Codes - Security Considerations
The following terms are used throughout this document.
Circuit Identification Code (CIC):
A field identifying the circuit being setup or released. Depending
on SI and MSU Type, this field can be 12, 14 or 32 bits.
Changeover/Changeback (co/cb):
SS7 MTP3 procedure related to link failure and re-establishment.
Far End (FE):
The remote endpoint of a socket connection.
Far End Allowed (FEA):
The FE is ready to use the socket for service PDUs.
Far End Prohibited (FEP):
The FE is not ready to use the socket for service PDUs.
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.
Management ATM Adaptation Layer (MAAL):
This layer is a component of SAAL. This layer maps requests and
indications between the System Management for the SG and the other
SAAL layers. MAAL includes interfaces to/from SSCOP, SSCF, and
system management. More information can be found in T1.652.
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.
MTP3 Framing (MTP3F):
TALI does not require full MTP3 procedures support but rather uses
the MTP3 framing structure (ie: SIO, Routing Label, etc)
Near End (NE):
The local endpoint of a socket connection.
Near End Allowed (NEA):
The NE is ready to use the socket for service PDUs.
Near End Prohibited (NEP):
The NE is not ready to use the socket for service PDUs.
Signaling ATM Adaptation Layer (SAAL):
This layer is the equivalent of MTP-2 for ATM High Speed Links
carrying SS7 Traffic as described in GR-2878-CORE [8]. SAAL includes
SSCF, SSCOP and MAAL.
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 MGC/MG functions to process
SCN signaling associated with line or trunk terminations controlled
by the MG (e.g., signaling backhaul).
Service Specific Coordination Function (SSCF):
This layer is a component of SAAL. This layer maps the services
provided by the lower layers of the SAAL to the needs of a specific
higher layer user. In the case of the STP, the higher layer user is
the MTP-3 protocol, and the SSCF required is that as defined by
T1.645: SSCF for Support of Signaling at the Network Node Interface
(SSCF at the NNI). More information can be found in T1.645. SSCF
provides the interface between SSCOP and MTP3 and includes the
following functions:
- Local Retrieve of messages to support link changeover procedures - Flow control with four levels of congestion
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.
Service Specific Connection Oriented Protocol (SSCOP):
This layer is a component of SAAL. This layer provides reliable
point to point data transfer with sequence integrity and error
recovery by selective retransmission. Protocol layer interfaces are
described in T1.637. Aspects of the protocol include flow control,
connection control, error reporting to layer management, connection
maintenance in the prolonged absence of data transfer, local data
retrieval by the user of the SSCOP, error detection of protocol
control information and status reporting. SSCOP provides the link
layer functions that are:
- In-Sequence Delivery - Flow Control - Error Detection/Correction - Keep Alive - Local Data Retrieval - Connection Control - Protocol Error Detection and Recovery
Signaling Transfer Point (STP):
Packet switches that provide CCS message routing and transport. They
are stored programmed switches that use information contained in the
message in conjunction with information stored in memory to route the
message to the appropriate destination signaling point.
The traditional PSTN SS7 network consists of 3 types of devices connected via dedicated SS7 signaling links.
The 3 primary device types for PSTN networks are:
There are 3 primary types of dedicated SS7 signaling links:
Figure 1 provides an overview of the traditional PSTN network. In this network, any of the links can be implemented via either 56 Kbps, DS1, or E1 links.
^
/ \
/SCP\
/-----\
/ \
/ \
/ \
/ \
/---\ +---+ +---+ /---\
| SSP |-----|STP|----|STP|-----| SSP |
\---/ \ /+-+-+\ /+-+-+ \ / \---/
\/ | \/ | \/
/\ | /\ | /\
/---\ / \+-+-+/ \+-+-+ / \ /---\
| SSP |/----|STP|----|STP|/----| SSP |
\---/ +---+ +---+ \---/
\ /
\ /
\ /
\ ^ /
\/ \/
/SCP\
/-----\
Figure 1: The Traditional PSTN Network
In the converged SS7 network, SS7 devices will reside on both the traditional PSTN network (with dedicated 56 Kbps and DS1 links) and on the IP network (with Ethernet links based on IP protocol). The services of SSPs, STPs, and SCPs can be provided by new types of devices that reside on IP networks. The IP network is not intended to completely replace the PSTN, rather devices on the 2 types of networks must be able to communicate with one another and convert from 1 lower layer protocol to the other.
Signaling Gateways are new devices that may also function as an STP in the converged network. SGs provide interfaces to:
SGs also continue to perform STP functions such as SS7 network management and some database services (such as GTT and LNP).
New devices on the IP network include:
Figure 2 provides an overview of the converged SS7 network.
----- +----+
/\ / \-------------| SG |
/ \----| SCN | +----+ +----+
/SCP \ \ /------| SG | |
------ ----- +----+ |
| | | |
| | | |
| | -----
| | / \ /\
| | | IP |----/ \
| /---\ \ / /SCP \
| | SSP | ----- ------
| \---/ / \
| | / \
/---\ | / \
| SSP | | +---+ +---+
\---/ +----+ |MGC| |MGC|
| | MG | +---+ +---+
| +----+\ \ /
| \ \ /
| \ -----
| \ / \
+----+ | IP |
| MG |-----------\ /
+----+ -----
Figure 2: The Converged SS7 Network
In theory, the TALI protocol can be used between 2 nodes to carry SS7 traffic across TCP/IP. Some of the areas that TALI could be used include:
- For SG to SG communication across IP - For SG to MGC communication across IP - For SG to IP based SCP communication across IP - For communication between multiple IP based SCPs - For communication between multiple MGCs - For communication between MGCs and MGs - For other IP devices such as DNS, Policy Servers, etc.
In reality, the communication between MGCs, or between MGC and MG is probably better suited to using other protocols. With respect to the Signaling Gateway implementation, the TALI protocol is used to carry SS7 traffic:
- For SG to SG communication - For SG to MGC communication - For SG to IP based SCP communication
The Transport Adapter Layer Interface is the proposed interface that provides SCCP, ISUP, and MTP messaging encapsulation within a TCP/IP packet between two switching elements. In addition, TALI provides SCCP Management (SCMG), MTP Primitives, dynamic registration of circuits, and routing of call control messages based on circuit location.
The major purpose of the TALI protocol is to provide a bridge between the SS7 Signaling Network and applications that reside within an IP network. Figure 3 provides a simple illustration that highlights the protocol stacks used for transport of SS7 MSUs on both the SS7 side and the IP side of the SG.
SS7 traffic SS7 traffic
via 56Kbps links via TALI
+-----------+ +----+ +--------+
|Traditional| | SG | | IP |
|SS7 Devices|<------>| |<-------->| Devices|
+-----------+ +----+ +--------+
SS7 SS7, TALI, TCP/IP
protocol stack protocol stack
+---------------+ +---------------+
|SS7 application| |SS7 application|
|layer | |layer |
+-------+-------+ +-------+-------+
| TCAP | ISUP | | TCAP | ISUP |
+-------+ | +-------+ |
| SCCP | | | SCCP | |
+-------+-------+ +-------+-------+
| MTP3 | | MTP3 |
+---------------+ +---------------+
| MTP2 | | TALI |
+---------------+ +---------------+
| MTP1 | | TCP |
| (& phy. | +---------------+
| layer) | | IP |
+---------------+ +---------------+
| MAC |
| (& phy. |
| layer) |
+---------------+
Figure 3: TALI Protocol to carry SS7 over TCP/IP
From Figure 3, several observations can be made:
Some of the facts concerning the TALI protocol which are important to understanding how TALI works that are not evident from Figure 3 include the following:
* Allows the user to control the graceful shutdown of each socket
This section presents a different, slightly more complex, TALI protocol stack that can be used in place of the protocol stack in the previous section.
Figure 3 in the previous section provided a simple illustration that highlighted the basic TALI protocol stack that can be used to transport SS7 MSUs between 56 Kbps links on the SS7 side of an SG and the IP devices.
Figure 4 below illustrates an alternate TALI protocol stack that includes the SAAL layer as part of the data transferred across the TCP/IP connection.
SS7 traffic SS7 traffic
via DS1 links via TALI
+-----------+ +----+ +--------+
|Traditional| | SG | | IP |
|SS7 Devices|<------>| |<-------->| Devices|
+-----------+ +----+ +--------+
SS7 DS1 SS7, TALI, TCP/IP
protocol stack protocol stack
+-----------------+ +-----------------+
| SS7 application | | SS7 application |
| layer | | layer |
+--------+--------+ +--------+--------+
| TCAP | ISUP | | TCAP | ISUP |
+--------+ | +--------+ |
| SCCP | | | SCCP | |
+--------+--------+ +--------+--------+
| MTP3 | | MTP3 |
+-----------------+ +-----------------+
| SAAL | | SAAL |
|(SSCF,MAAL,SSCOP)| |(SSCF,MAAL,SSCOP)|
+-----------------+ +-----------------+
| AAL5 | | TALI |
+-----------------+ +-----------------+
| ATM | | TCP |
| (& phy. | +-----------------+
| layer) | | IP |
+-----------------+ +-----------------+
| MAC |
| (& phy. |
| layer) |
+-----------------+
Figure 4: An Alternate TALI Protocol Stack with SAAL
The following bullets provide a discussion regarding the differences between these 2 protocol stacks, the reasons for having 2 protocol stacks, and the advantages of each:
across the TCP/IP connection. The TALI protocol stack without SAAL still guarantees correct sequencing of SS7 data (this sequencing is provided by sequence numbers in the TCP layer), however that protocol stack can not support SS7 changeover and changeback procedures.
The TALI protocol is dependent on a reliable transport layer below it. At the initial design of TALI, TCP was the only reliable, proven transport layer. Simple Control Transport Protocol (SCTP) is currently being designed as a transport later specifically for signalling. Once SCTP is a proven and accepted transport protocol, SCTP can then be used in place of TCP as shown in Figures 3 and 4.
Figure 5 illustrates the inputs that affect the TALI State Machine. Inputs to the state machine include:
* Timer events.
+====+ +============+
| | +---------+ +-------------+ | |
|User| | Service | | Mgmt. Open | | MANAGEMENT |
|Part|<-->| Message | | Mgmt. Close |<-->| |
| | | | | Mgmt. Proh. | | |
| | +---------+ | Mgmt. Allow | +============+
+====+ ^ +-------------+
| ^
| |
v v
+========================================================+
| TALI State Machine |
+========================================================+
^ ^ ^ ^
| | | |
| | | |
v | | |
+---------+ +-----------------+ +-----------+ +------------+
| Received| | Connection est. | | Protocol | | T1 Expired |
| 'test' | | Connection lost | | Violation | | T2 Expired |
| 'allo' | | | | | | T3 Expired |
| 'proh' | +-----------------+ +-----------+ | T4 Expired |
| 'proa' | ^ ^ +------------+
| 'moni' | | | ^
| 'mona' | | | |
| or | | | |
| Service | | | |
| Message | +========================================+
+---------+ | IMPLEMENTATION |
^ | DEPENDENT |
| +========================================+
|
v
+============+
| PEER |
| |
+============+
Figure 5: Overview of Inputs to the TALI 1.0 State Machine
This chapter provides the states, messages, message exchange rules and state machine that must be implemented to provide a TALI version 1.0 protocol layer.
Table 2 provides a summary of the messages and message structure used in TALI version 1.0.
+------------------------------------------------------------------+ | OCTET | DESCRIPTION | SIZE | VALUE | TYPE | +------------------------------------------------------------------+ | 0..3 | SYNC | 4 Octets | | 4 byte | | | | | | ASCII | +------------------------------------------------------------------+ | | TALI | | 'TALI' | | +------------------------------------------------------------------+ | 4..7 | OPCODE | 4 Octets | | 4 byte | | | | | | ASCII | +------------------------------------------------------------------+ | | Test Service | | 'test' | | | | Allow Service | | 'allo' | | | | Prohibit Service | | 'proh' | | | | Prohibit Service Ack | | 'proa' | | | | Monitor Socket | | 'moni' | | | | Monitor Socket Ack | | 'mona' | | | | SCCP Service | | 'sccp' | | | | ISUP Service over TALI | | 'isot' | | | | MTP3 Service over TALI | | 'mtp3' | | | | Service over SAAL | | 'saal' | | +------------------------------------------------------------------+ | 8..9 | LENGTH | 2 Octets | | integer | | | (least significant | | | | | | byte first) non-0 | | | | | | if Service or | | | | | | Socket monitor message| | | | +------------------------------------------------------------------+ | 10..X | DATA PAYLOAD | variable | | variable | +------------------------------------------------------------------+
Table 2: Message Structure for TALI 1.0
Table 3 indicates the valid values of the LENGTH field for each version 1.0 opcode. The LENGTH field is always an indication of the
# of bytes contained in the DATA PAYLOAD portion of a general TALI message.
+------------------------------------------------------------------+ | OPCODE | VALID LENGTH VALUES | COMMENTS | +------------------------------------------------------------------+ | test | 0 bytes | | +------------------------------------------------------------------+ | allo | 0 bytes | | +------------------------------------------------------------------+ | proh | 0 bytes | | +------------------------------------------------------------------+ | proa | 0 bytes | | +------------------------------------------------------------------+ | moni | 0-200 bytes | A maximum length is provided so | | | | that the maximum ethernet frame | | | | size is not exceeded. | +------------------------------------------------------------------+ | mona | 0-200 bytes | Mona reply length and content must| | | | match the original moni (with the | | | | exception of the opcode) | +------------------------------------------------------------------+ | sccp | 12-265 bytes | These are the valid sizes for the | | | | SCCP-ONLY portions of SCCP UDT | | | | MSUs | +------------------------------------------------------------------+ | isot | 8-273 bytes | The length is the number of octets| | | | in the MTP3 and higher layer(s) of| | | | the SS7 MSU. This length includes| | | | the SIO byte, the MTP3 routing | | | | label, the CIC code, and the | | | | ISUP Message Type field, and any | | | | other bytes that may exist as part| | | | of the SIF (Service Information | | | | Field) | +------------------------------------------------------------------+ | mtp3 | 5-280 bytes | The length is the number of octets| | | | in the MTP3 and higher layer(s) of| | | | the SS7 MSU. This length includes| | | | the SIO byte and the MTP3 routing | | | | labeld, and any other bytes that | | | | may exist as part of the SIF | | | | (Service Information Field) | +------------------------------------------------------------------+ | saal | 11-280 bytes | The length is the number of octets| | | | in the MTP3 and higher layer(s) of| | | | the SS7 MSU. This length includes| | | | the SIO byte and all bytes in the | | | | SIF (Service Information Field) | | | | field. The MTP3 routing label is | | | | part of the SIF field. Seven (7) |
| | | octets of SSCOP trailer is added | | | | to the message. The SSCOP trailer| | | | bytes are also included in the | | | | length. | +------------------------------------------------------------------+
Table 3: Valid Length Fields for Each Opcode in TALI 1.0
Several field types are used in the general TALI message structure.
+------------------------------------------------------------------+
|Field Type | Implementation Notes for that Type |
+------------------------------------------------------------------+
|4 byte | * 4 byte ASCII text strings are used to define the |
|ASCII text | sync code and the opcode of the basic TALI message.|
| | * These fields are case sensitive, the coding for |
| | each sync and opcode literal needs to match the |
| | case specified in Table 2. |
| | * The standard ASCII conversion table is used to |
| | transform each character into a byte. |
| | * The order of the ASCII characters is important. |
| | The first character in the string must be the |
| | first character transmitted across the wire. |
| | * For example, if the string being encoded is 'abCD',|
| | the order of the bytes as they are transferred |
| | over the wire must be: |
| | 1st byte: 0x61 ('a') 3rd byte: 0x43 ('C') |
| | 2nd byte: 0x62 ('b') 4th byte: 0x44 ('D') |
| | * The software for each implementation should be |
| | written in a manner that accounts for the required |
| | byte order of transmission (ie: the Big Endian/ |
| | Little Endian characteristics of the processor |
| | need to be dealt with in the software. |
+------------------------------------------------------------------+
|Integer | * A 1, 2 or 4 byte field to be treated as an integer |
| | value. Integer fields should be transmitted Least |
| | Significant Byte first across the wire. |
| | * The software for each implementation should be |
| | written in a manner that accounts for the required |
| | byte order of transmission (ie: the Big Endian/ |
| | Little Endian characteristics of the processor |
| | need to be dealt with in the software. |
+------------------------------------------------------------------+
|Variable | * The definition of the message structure for this |
| | field is governed by other specifications. |
| | * For example, when transferring MTP3 service data |
| | via a 'mtp3' opcode, the DATA PAYLOAD begins with | | | the SIO byte of the MTP3 routing label. The | | | structure for the entire DATA PAYLOAD is governed | | | by the MTP3 message structure defined in [1]. | +------------------------------------------------------------------+ |X byte | * ASCII text fields of sizes other than 4 bytes | |ASCII text | should be supported according to the same rules | | | presented for the 4 byte ASCII text fields. For | | | instance, an 8 byte string such as 'ab01cd23' could| | | be used, where the 'a' would be the first byte of | | | the field transmitted out the wire. | +------------------------------------------------------------------+
Table 4: Implementation Notes for each Type of TALI field
The following subsections provide more information regarding the TALI Peer to Peer messages that are implemented in version 1.0. The TALI peer to peer messages originate at the TALI layer of 1 end of the socket connection (the near end) and are terminated at the TALI layer of the far end of the connection.
The 'test' message is used by a TALI implementation to query the remote end of the TALI connection with respect to the willingness of the remote end to carry SS7 service data. This message asks the other end: are you ready to carry service data? This message is sent periodically by each TALI implementation based on a T1 timer interval. Upon receiving 'test', a TALI implementation must reply with either 'proh' or 'allo' to indicate the nodes willingness to carry SS7 service data over that TALI connection.
+------------------------------------------------------------------+ | Octets | Field Name | Description | +------------------------------------------------------------------+ | 0..3 | SYNC | 'TALI' | +------------------------------------------------------------------+ | 4..7 | OPCODE | 'test' | +------------------------------------------------------------------+ | 8..9 | LENGTH | Length = 0 | +------------------------------------------------------------------+
The 'allo' message is sent in reply to a 'test' query, or in response to some internal implementation event, to indicate that a TALI implementation IS willing to carry SS7 service data over the TALI session. This message informs the far end that SS7 traffic can be transmitted on the socket. 'allo' is one of the 2 possible replies to a 'test' message. Before SS7 traffic can be carried over a socket, both ends of the connection need to send 'allo' messages.
+------------------------------------------------------------------+ | Octets | Field Name | Description | +------------------------------------------------------------------+ | 0..3 | SYNC | 'TALI' | +------------------------------------------------------------------+ | 4..7 | OPCODE | 'allo' | +------------------------------------------------------------------+ | 8..9 | LENGTH | Length = 0 | +------------------------------------------------------------------+
The 'proh' message is sent in reply to a 'test' query, or in response to some internal implementation event, to indicate that a TALI implementation is NOT willing to carry SS7 service data over the TALI session. This message informs the far end that SS7 traffic can not be transmitted on the socket. 'proh' is one of the 2 possible replies to a 'test' message. As long as 1 end of the connection remains in the 'prohibited' state, SS7 traffic can not be carried over the socket.
+------------------------------------------------------------------+ | Octets | Field Name | Description | +------------------------------------------------------------------+ | 0..3 | SYNC | 'TALI' | +------------------------------------------------------------------+ | 4..7 | OPCODE | 'proh' | +------------------------------------------------------------------+ | 8..9 | LENGTH | Length = 0 | +------------------------------------------------------------------+
The 'proa' message is sent by a TALI implementation each time a 'proh' is received from the far end. This message is sent to indicate to the far end that his 'prohibit' message was received correctly and will be acted on accordingly.
+------------------------------------------------------------------+ | Octets | Field Name | Description | +------------------------------------------------------------------+ | 0..3 | SYNC | 'TALI' | +------------------------------------------------------------------+ | 4..7 | OPCODE | 'proa' | +------------------------------------------------------------------+ | 8..9 | LENGTH | Length = 0 | +------------------------------------------------------------------+
The 'moni' message provides a generic ECHO capability that can be used by each TALI implementation as that implementation sees fit. A TALI version 1.0 implementation does not have to originate a 'moni' message to be compliant with the 1.0 specification. The primary intent of this message is to provide a way for the TALI layer to test the round-trip message transfer time on a socket. A 'mona' message must be sent in reply to each received 'moni' message. The DATA portion of a 'moni' message is vendor implementation dependent. The DATA portion of each 'mona' reply must exactly match the DATA portion of the 'moni' that is replied to. Regardless of whether an implementation chooses to send 'moni' or not, 'mona' must be sent in response to each 'moni' in order to remain compliant with the TALI protocol.
+------------------------------------------------------------------+ | Octets | Field Name | Description | +------------------------------------------------------------------+ | 0..3 | SYNC | 'TALI' | +------------------------------------------------------------------+ | 4..7 | OPCODE | 'moni' | +------------------------------------------------------------------+ | 8..9 | LENGTH | Length | +------------------------------------------------------------------+ | 10..X | DATA PAYLOAD| Vendor Dependent | +------------------------------------------------------------------+
As mentioned above, the 'mona' must be sent in reply to each received 'moni'. The contents of the 'mona' DATA area must match the DATA area of the received 'moni' message.
+------------------------------------------------------------------+ | Octets | Field Name | Description | +------------------------------------------------------------------+ | 0..3 | SYNC | 'TALI' | +------------------------------------------------------------------+ | 4..7 | OPCODE | 'mona' | +------------------------------------------------------------------+ | 8..9 | LENGTH | Length | +------------------------------------------------------------------+ | 10..X | DATA PAYLOAD| Vendor Dependent | +------------------------------------------------------------------+
The following subsections provide more information regarding the TALI Service messages that are implemented in version 1.0. TALI Service messages are used to carry SS7 MSUs across the IP network. The information in this section includes details with respect to how to encapsulate SS7 MSUs into TCP/IP frames using each of the TALI service opcodes. The TALI service messages originate at the layer above TALI, are transported across the IP network via a TALI service message, and are delivered to the layer above TALI at the far end of the TALI connection.
The 'sccp' opcode is used to deliver SS7 MSUs with a Service Indicator of 3 (SCCP) over a TALI connection. This opcode is only used on TALI protocol stacks that are implemented without SAAL. The MTP3 layer of the SS7 MSU is NOT part of the data transferred across TCP/IP for this opcode; the data portion of the TALI 'sccp' message begins with the first byte of the SCCP data area in the SS7 MSU (after the MTP3 routing label). The first byte in the SCCP data area is an SCCP message type field.
Several restrictions on the SCCP messages that this TALI opcode can carry exist. These restrictions are as follows:
NOTE 1: SCCP Subsystem Management for the IP based SCP's is supported via this 'sccp' opcode. SS7 SCCP Management messages are controlled by an SCMG SS7 process. SCMG sends the management messages via SCCP UNITDATA (UDT) messages. Therefore, the SCMG messages can be sent across the TALI connection.
NOTE 2: 'sccp' TALI messages will not include the MTP3 header and therefore will not retain the original DPC/OPC of the SS7 MSU. Each TALI implementation needs to consider if/how to provide this DPC/OPC information in the SCCP portion of the message. For example the DPC can be replicated to the point code in the SCCP Called Party Address area and the OPC can be replicated to the point code in the SCCP Calling Party Address area.
+------------------------------------------------------------------+ | Octets | Field Name | Description | +------------------------------------------------------------------+ | 0..3 | SYNC | 'TALI' | +------------------------------------------------------------------+ | 4..7 | OPCODE | 'sccp' | +------------------------------------------------------------------+ | 8..9 | LENGTH | Length | +------------------------------------------------------------------+ | 10..X | SCCP Data | SCCP data starting at the first byte after| | | | the Layer 3 Routing Label (data does not | | | | include the SIO or Routing Label) | +------------------------------------------------------------------+
When an SCCP MSU arrives at an SG from a 56 Kbps or DS1 link and is routed within the SG for transmission to an IP device, the SG performs the following processing on the SS7 MSU:
* The LENGTH is set to the number of octets in the SERVICE field
Once the fully formed 'sccp' TALI packet is created, it is handed to the TCP socket layer and transmitted. The transmission process will add TCP, IP and MAC header information.
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 SG.
SS7 MSU
| Layer 3 | Layer 2 |
| | |
+----+---+-----+-----+-------+---+--+---+---+---+---+----+
|Flag|FCS|TCAP |SCCP |Routing|SIO|LI|FIB|FSN|BIB|BSN|Flag|
| | |Layer|Layer| Label | | | | | | | |
+----+---+-----+-----+-------+---+--+---+---+---+---+----+
| |
| |
| |
TALI +-----------+---+------+----+
Packet | Service |LEN|Opcode|SYNC|
+-----------+---+------+----+
| |
| |
| |
+---------------------------+------+------+------+
IP | TALI Packet |TCP | IP | MAC |
Packet | |Header|Header|Header|
+---------------------------+------+------+------+
Figure 6: Encapsulation of SCCP MSUs using the TALI 'sccp' opcode
When an 'sccp' TALI packet is received on by an SG from an IP device, the SG performs the following processing on the 'sccp' packet:
Once the 'sccp' packet is transformed back into a normal SS7 MSU, the MSU is routed within the SG according to the normal SS7 routing procedures.
The 'isot' opcode is used to deliver SS7 MSUs with a Service Indicator of 5 (ISUP) over a TALI connection. This opcode is only used on TALI protocol stacks that are implemented without SAAL. The MTP3 layer of the SS7 MSU IS part of the data transferred across TCP/IP for this opcode; the data portion of the TALI 'isot' message begins with the SIO byte of the MTP3 header in the SS7 MSU.
+------------------------------------------------------------------+ | Octets | Field Name | Description | +------------------------------------------------------------------+ | 0..3 | SYNC | 'TALI' | +------------------------------------------------------------------+ | 4..7 | OPCODE | 'isot' | +------------------------------------------------------------------+ | 8..9 | LENGTH | Length | +------------------------------------------------------------------+ | 10..X | ISUP Data | Raw ISUP data starting at the Layer 3 SIO | | | | field. | +------------------------------------------------------------------+
When an ISUP MSU arrives at an SG from a 56 Kbps or DS1 link and is routed within the SG to a IP device, the SG performs the following processing on the SS7 MSU:
Once the fully formed 'isot' TALI packet is created, it is handed to the TCP socket layer and transmitted. The transmission process will add TCP, IP and MAC header information.
Since the routing information is placed in the TALI Packet, no routing information needs to be saved by the SG.
SS7 MSU
| Layer 3 | Layer 2 |
| | |
+----+---+----+----+---+-------+---+--+---+---+---+---+----+
|Flag|FCS|ISUP|Msg.|CIC|Routing|SIO|LI|FIB|FSN|BIB|BSN|Flag|
| | |Part|Type| |Label | | | | | | | |
+----+---+----+----+---+-------+---+--+---+---+---+---+----+
| /
| /
| |
TALI +-----------------------+---+------+----+
Packet | Service |LEN|Opcode|SYNC|
+-----------------------+---+------+----+
| /
| ---------
| /
+----------------------------+------+------+------+
IP | TALI Packet |TCP | IP | MAC |
Packet | |Header|Header|Header|
+----------------------------+------+------+------+
Figure 7: Encapsulation of ISUP MSUs using the TALI 'isot' opcode
When an 'isot' TALI packet is received on an SG from an IP device, the SG performs the following processing on the 'isot' packet:
Once the 'isot' packet is transformed back into a normal SS7 MSU, the MSU is routed within the SG according to the normal SS7 routing procedures.
The 'mtp3' opcode is used to deliver SS7 MSUs with a Service Indicator of 0-2, 4, 6-15 (non-SCCP, non-ISUP) over a TALI connection. This opcode is only used on TALI protocol stacks that are implemented without SAAL. The MTP3 layer of the SS7 MSU IS part of the data transferred across TCP/IP for this opcode; the data portion of the TALI 'mtp3' message begins with the SIO byte of the MTP3 header in the SS7 MSU.
+------------------------------------------------------------------+ | Octets | Field Name | Description | +------------------------------------------------------------------+ | 0..3 | SYNC | 'TALI' | +------------------------------------------------------------------+ | 4..7 | OPCODE | 'mtp3' | +------------------------------------------------------------------+ | 8..9 | LENGTH | Length | +------------------------------------------------------------------+ | 10..X | Layer 3 MSU | Raw MSU data starting at the Layer 3 SIO | | | Data | field. | +------------------------------------------------------------------+
When an SS7 MSU with SI=0-2,4,6-15 arrives at an SG from a 56 Kbps or DS1 link and is routed within the SG to an IP device, the SG performs the following processing on the SS7 MSU:
Once the fully formed 'mtp3' TALI packet is created, it is handed to the TCP socket layer and transmitted. The transmission process will add TCP, IP and MAC header information.
SS7 MSU
| Layer 3 | Layer 2 |
| | |
+----+---+-----------+-------+---+--+---+---+---+---+----+
|Flag|FCS|Other Layer|Routing|SIO|LI|FIB|FSN|BIB|BSN|Flag|
| | |3 Data |Label | | | | | | | |
+----+---+-----------+-------+---+--+---+---+---+---+----+
| /
| ------
| /
TALI +----------------+---+------+----+
Packet | Service |LEN|Opcode|SYNC|
+----------------+---+------+----+
| /
| --
| /
+----------------------------+------+------+------+
IP | TALI Packet |TCP | IP | MAC |
Packet | |Header|Header|Header|
+----------------------------+------+------+------+
Figure 8: Encapsulation of SS7 MSUs with SI!=3,5,13 using 'mtp3'
When an 'mtp3' TALI packet is received by an SG from an IP device, the SG performs the following processing on the 'mtp3' packet:
Once the 'mtp3' packet is transformed back into a normal SS7 MSU, the MSU is routed within the SG according to the normal SS7 routing procedures.
The 'saal' opcode is used to deliver SS7 MSUs with any Service Indicator over a TALI connection. This opcode is only used on TALI protocol stacks that are implemented with SAAL. The 'saal' opcode is also used to transmit SAAL peer to peer packets (SSCF peer to peer packets and SSCOP peer to peer packets other than SS7 service data) over a TALI connection.
When used to transfer SS7 MSUs, the MTP3 layer of the SS7 MSU IS part of the data transferred across TCP/IP for this opcode; the data portion of the TALI 'saal' message begins with the SIO byte of the MTP3 header in the SS7 MSU and ends with the last byte of the SSCOP trailer.
When used to transfer SSCF/SSCOP peer to peer messages the data portion of the TALI 'saal' message includes the entire SSCOP PDU.
+------------------------------------------------------------------+ | Octets | Field Name | Description | +------------------------------------------------------------------+ | 0..3 | SYNC | 'TALI' | +------------------------------------------------------------------+ | 4..7 | OPCODE | 'saal' | +------------------------------------------------------------------+ | 8..9 | LENGTH | Length | +------------------------------------------------------------------+ | 10..X | Layer 3 | Raw MSU data starting at the Layer 3 SIO | | | Data | field. | +------------------------------------------------------------------+ | (X+1) | SSCOP | Zero (0) to three (3) octets of padding | | ..Y | Trailer | plus 4 octets for the trailer data. The | | | | total length of the Layer 3 Data and the | | | | SSCOP trailer must be a multiple of 4. | +------------------------------------------------------------------+
or
+------------------------------------------------------------------+ | Octets | Field Name | Description | +------------------------------------------------------------------+ | 0..3 | SYNC | 'TALI' | +------------------------------------------------------------------+ | 4..7 | OPCODE | 'saal' | +------------------------------------------------------------------+ | 8..9 | LENGTH | Length | +------------------------------------------------------------------+ | 10..X | SAAL Peer | Raw SSCF/SSCOP peer to peer packets are | | | to Peer | also transferred over the TALI connection | | | message | using this 'saal' opcode. | +------------------------------------------------------------------+
When an SS7 MSU (with any SI) arrives at an SG from a 56 Kbps or DS1 link and is routed within the SG for transmission to an IP device, the SG performs the following processing on the SS7 MSU:
Once the fully formed 'saal' TALI packet is created, it is handed to the TCP socket layer and transmitted. The transmission process will add TCP, IP and MAC header information.
Since the routing information is placed in the TALI Packet, no routing information needs to be saved by the SG.
SS7 MSU
| Layer 3 | Layer 2 |
| | |
+----+---+-----------+-------+---+--+---+---+---+---+----+
|Flag|FCS|Other Layer|Routing|SIO|LI|FIB|FSN|BIB|BSN|Flag|
| | |3 Data |Label | | | | | | | |
+----+---+-----------+-------+---+--+---+---+---+---+----+
| |
| |
| |
+-------+-----------------------+
|SSCOP | Service |
|Trailer| |
+-------+-----------------------+
| |
+-------+-----------------------+---+------+----+
|Service with SSCOP Trailer |LEN|Opcode|SYNC|
+-------+-----------------------+---+------+----+
| /
| -----------------
| /
+----------------------------+------+------+------+
| TALI Packet |TCP | IP | MAC |
| |Header|Header|Header|
+----------------------------+------+------+------+
Figure 9: Encapsulation of SAAL PDUs using the TALI 'saal' opcode
When an 'saal' TALI packet is received at the SG from an IP device, the SG performs the following processing on the 'saal' packet:
Once the 'saal' packet is transformed back into a normal DS1 SSCOP PDU, the SSCOP PDU is passed to the SAAL layer for receive processing. If the SSCOP PDU is a peer to peer pdu, it is processed completely in the appropriate SAAL layer. If the SSCOP PDU is an SS7 MSU, the MSU is transformed back to a normal SS7 MSU and is routed within the SG according to the normal SS7 routing procedures.
Version 1.0 of the TALI specification defined 4 TALI timers that are used as part of the TALI state machine. These timers are generically named 'T1' through 'T4'. Brief descriptions of each timer are provided in the following subsections. Timer expiration events for each of the T1-T4 timers appear as inputs to the TALI state machine. For exact processing of each timer (when to start/stop, how to process timer expirations), refer to the TALI state machine.
Both ends of the TALI connection have there own T1-T4 timers. The T1-T4 timer values can be set on each end of the connection independent of the settings on the far end. For each timer, a default value and range is recommended in the following sections.
The T1 timer represents the time interval between the origination of a 'test' message at each TALI implementation. Each time T1 expires, the TALI implementation should send a 'test'.
The T2 timer represents the amount of time that the Peer has to return an 'allo' or a 'proh' in response to a 'test'. If the far end fails to reply with 'allo' or 'proh' before T2 expires, the sender of the 'test' treats the T2 expiration as a protocol violation. Note that T2 must be < T1 in order for these timers to work as designed.
The T3 timer controls how long the near end should continue to process Service Data that is received from the far end after a Management Prohibit Traffic Event has occurred (at the near end). This timer is used when a transition from NEA-FEA (both ends allowed to send service data) to NEP-FEA (only far end willing to send service data) occurs. On that transition, it is reasonable to expect that the far end needs some amount of time to adjust its TALI state machine and divert service data traffic away from this socket. The T3 timer controls the amount of time the far end has to divert traffic.
The T4 timer represents the time interval between the origination of a 'moni' message at each TALI implementation. Each time T4 expires, the TALI implementation should send a 'moni'.
The following table provides the recommended default and configurable range for each TALI timer.
+------------------------------------------------------------------+ |Name| Min | Max |Default| Description | +------------------------------------------------------------------+ | T1 | 100ms | 60sec | 4 sec | Send test PDU timer | +------------------------------------------------------------------+ | T2 | 100ms | 60sec | 3 sec | Response timer for an allo or proh | | | | | | response to test message. | +------------------------------------------------------------------+ | T3 | 100ms | 60sec | 5 sec | Timer controls how long to process | | | | | | rcvd serv data after an NE | | | | | | transition from NEA to NEP. System | | | | | | is waiting for a proa response to | | | | | | the first proh send when NE | | | | | | transitions from NEA to NEP. | +------------------------------------------------------------------+ | T4 | 100ms | 60sec |10 sec | Send moni PDU timer | +------------------------------------------------------------------+
Table 5: Timers
NOTE: The value of T1 must be at least one (1) millisecond greater than T2. This is to prevent the system from a lockup in the T1 expired condition. If T1 is equal or less than T2, it will expire and restart T2 and not enforce responses to the test message.
Enforcement of minimum and maximum timer values is implementation dependent.
Each TALI implementation must provide several user event controls over the behavior of the TALI state machine for each TALI connection. The user interface to provide these capabilities is implementation specific.
The 'mgmt open socket' event, together with the 'mgmt close socket' event, allows the user to control when each defined TALI connection will form a TCP socket connection. When 'open socket' for a particular TALI connection occurs, the TALI connection should begin trying to form a TCP socket connection to the peer.
The steps that are taken to connect are dependent on the
client/server role of that end of the TALI connection. The exact
steps to perform these tasks are implementation dependent and may
differ based on the TCP stack being used.
In general, TALI clients form socket connections by using the BSD sockets calls:
Socket()
Bind()
Connect()
In general, TALI servers form socket connections by using the BSD sockets calls:
Socket()
Bind()
Listen()
Accept()
The 'mgmt close socket' event can be issued by the user when it is desired that the TCP socket for a TALI socket, be closed immediately, or discontinue its attempts to connect to the peer. After acting on 'close socket', the TALI connection will not be established until 'mgmt open socket' is issued.
The 'mgmt allow traffic' event, together with the 'mgmt prohibit traffic' event, allows the user to control when each defined TALI connection will be willing to carry SS7 service data over that particular TALI connection. When 'mgmt allow traffic' is issued, the TALI implementation becomes willing to carry service data. The TALI state for the near end should transition to NEA (near end allowed) if the connection is already established.
The 'mgmt prohibit traffic' event is the opposite of 'allow traffic'. When 'mgmt prohibit traffic' is issued, the TALI implementation becomes un-willing to carry SS7 service data over that particular TALI connection. The TALI state for the near end should transition to NEP (near end prohibited) if the connection is already established.
In addition to timers, each TALI implementation needs to be able to detect, and react accordingly, for the following events:
The TALI version 1.0 specification is based on a state machine that considers 6 TALI states. Each end of the TALI connection maintains its own TALI state.
+------------------------------------------------------------------+ | Name | Description | +------------------------------------------------------------------+ | OOS | The TALI connection is out of service. This usually| | | corresponds to a user event to 'close' the socket, | | | or a user event to 'deactivate the SS7 link'. | +------------------------------------------------------------------+ | Connecting | The TALI layer is attempting to establish a TCP | | | socket connection to the peer. Servers are | | | 'accepting', clients are 'connecting'. | +------------------------------------------------------------------+ | NEP-FEP | The TCP socket connection is established. Neither | | | side of the connection is ready to use the socket | | | for service PDUs. | +------------------------------------------------------------------+ | NEP-FEA | The TCP socket connection is established. The NE is| | | not ready to use the socket for service PDUs. The | | | FE is ready to use the socket for service PDUs. | +------------------------------------------------------------------+ | NEA-FEP | The TCP socket connection is established. The NE is| | | ready to use the socket for service PDUs. The FE is| | | not ready to use the socket for service PDUs. | +------------------------------------------------------------------+ | NEA-FEA | The TCP socket connection is established. Both | | | sides are ready to use the socket for service PDUs. | | | This is the only state where normal bi-directional | | | SS7 data transfer occurs. | +------------------------------------------------------------------+
Table 6: TALI States
This section provides the state machine that must be followed by each TALI implementation in order to be compliant with this specification.
Before presenting the actual state machine, several concepts are discussed.
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:
Each TALI implementation must detect when violations of the TALI protocol have occurred and react accordingly. Protocol violations include:
In the state machine that follows, State/Event combinations that should be treated as protocol violations are indicated via a 'PV' in the state/event cell. All of the 'PV' events are then processed as per the 'Protocol Violation' row in the table.
Internal Data required for State Machine:
boolean sock_allowed. This flag indicates whether the NE is allowed to carry Service Messages.
Initial Conditions:
sock_allowed = FALSE state = OOS no timers running +------------------------------------------------------------------+ | State| OOS |Connecting| NEP-FEP | NEP-FEA | NEA-FEP | NEA-FEA | |Event | | | | | | | +------------------------------------------------------------------+ |T1 Exp. | | |Send test|Send test|Send test|Send test| | | | |Start T1 |Start T1 |Start T1 |Start T1 | | | | |Start T2 |Start T2 |Start T2 |Start T2 | +------------------------------------------------------------------+ |T2 Exp. | | | PV | PV | PV | PV | +------------------------------------------------------------------+ |T3 Exp. | | | PV | PV | | | +------------------------------------------------------------------+ |T4 Exp. | | |Send moni|Send moni|Send moni|Send moni| | | | |Start T4 |Start T4 |Start T4 |Start T4 | +------------------------------------------------------------------+ |Rcv test| | |Send proh|Send proh|Send allo|Send allo| +------------------------------------------------------------------+ |Rcv allo| | | Stop T2 | Stop T2 | Stop T2 | Stop T2 | | | | | NEP-FEA | | NEA-FEA | |
+------------------------------------------------------------------+ |Rcv proh| | | Stop T2 | Stop T2 | Stop T2 | Stop T2 | | | | |Send proa|Send proa|Send proa|Flush or | | | | | | NEP-FEP | | reroute | | | | | | | |Send proa| | | | | | | | NEA-FEP | +------------------------------------------------------------------+ |Rcv proa| | | Stop T3 | Stop T3 | | | +------------------------------------------------------------------+ |Rcv moni| | |Convert |Convert |Convert |Convert | | | | | to mona | to mona | to mona | to mona | | | | |Send mona|Send mona|Send mona|Send mona| +------------------------------------------------------------------+ |Rcv mona| | |Implemen-|Implemen-|Implemen-|Implemen-| | | | |tation |tation |tation |tation | | | | |dependent|dependent|dependent|dependent| +------------------------------------------------------------------+ |Rcv | | | PV |If T3 run| PV |Process | | Service| | | | Process | | | | | | | |Else PV | | | +------------------------------------------------------------------+ |Connect.| | Start T1 | | | | | |Estab. | | Start T2 | | | | | | | | Start T4 | | | | | | | |(if non-0)| | | | | | | |if sock_ | | | | | | | | allowed | | | | | | | | = TRUE | | | | | | | | send allo| | | | | | | | send test| | | | | | | | NEA-FEP | | | | | | | |else | | | | | | | | send proh| | | | | | | | send test| | | | | | | | NEP-FEP | | | | | +------------------------------------------------------------------+ |Connect.| | | PV | PV | PV | PV | |Lost | | | | | | | +------------------------------------------------------------------+ |Protocol| | |Stop all |Stop all |Stop all |Stop all | |Violat. | | | timers | timers | timers | timers | | | | |Close the|Close the|Close the|Close the| | | | | socket | socket | socket | socket | | | | |Connect- |Connect- |Connect- |Connect- | | | | | ing | ing | ing | ing |
+------------------------------------------------------------------+ |Mgmt. |Open | | | | | | |Open |socket| | | | | | |Socket |Conne-| | | | | | | | cting| | | | | | +------------------------------------------------------------------+ |Mgmt. | |Close the |Stop all |Stop all |Stop all |Stop all | |Close | | socket | timers | timers | timers | timers | |Socket | |OOS |Close the|Close the|Close the|Close the| | | | | socket | socket | socket | socket | | | | |OOS |OOS |OOS |OOS | +------------------------------------------------------------------+ |Mgmt. |sock_ |sock_allo-|sock_all-|sock_all-|sock_all-|sock_all-| |Prohibit|allow-| wed=FALSE| owed= | owed= | owed= | owed= | |Socket |ed = | | FALSE | FALSE | FALSE | FALSE | | |FALSE | | | |send proh|send proh| | | | | | |start t3 |start t3 | | | | | | | NEP-FEP | NEP-FEA | | | | | | | | | +------------------------------------------------------------------+ |Mgmt. |sock_ |sock_allo-|sock_all-|sock_all-|sock_all-|sock_all-| |Allow |allow-| wed=TRUE | owed= | owed= | owed= | owed= | |Traffic |ed = | | TRUE | FALSE | TRUE | TRUE | | |TRUE | |send allo|send allo| | | | | | | NEA-FEP | NEA-FEA | | | +------------------------------------------------------------------+ |User |reject| reject | reject | reject | reject | send | |Part |data | data | data | data | data | data | |Msgs. | | | | | | | +------------------------------------------------------------------+
Table 7: TALI 1.0 State Machine
Several aspects of the expected TALI 1.0 implementation have not been
specifically addressed in the state machine or previous text (or else
they were presented but will be reiterated here). These
implementation notes in some cases have to do with the expected
behavior of the software layer above the TALI layer.
Several limitations with the TALI 1.0 specification and
implementation are identified:
Version 2.0 of the TALI specification provides several additions to the Version 1.0 specification. The 2.0 additions are provided by introducing three new TALI opcodes. The basic functionality and most of the details of the TALI 1.0 implementation are NOT changed by the 2.0 additions.
The table below provides a summary of the messages and message structure used in TALI version 2.0.
+------------------------------------------------------------------+ | OCTET | DESCRIPTION | SIZE | VALUE | TYPE | +------------------------------------------------------------------+ | 0..3 | SYNC | 4 Octets | | 4 byte ASCII | +------------------------------------------------------------------+ | | TALI | | 'TALI' | | +------------------------------------------------------------------+ | 4..7 | OPCODE | 4 Octets | | 4 byte ASCII | +------------------------------------------------------------------+ | | Test Service | | 'test' | | | | Allow Service | | 'allo' | | | | Prohibit Service | | 'proh' | | | | Prohibit Service Ack| | 'proa' | | | | Monitor Socket | | 'moni' | | | | Monitor Socket Ack | | 'mona' | | | | SCCP Service | | 'sccp' | | | | ISUP Service o/TALI | | 'isot' | | | | MTP3 Service o/TALI | | 'mtp3' | | | | Service o/SAAL | | 'saal' | | | | Management Message | | 'mgmt' | | | | Extended Service Msg| | 'xsrv' | | | | Special Message | | 'spcl' | | +------------------------------------------------------------------+ | 8..9 | LENGTH | 2 Octets | | integer | | | (least significant | | | | | | byte first) non-0 | | | | | | if Service or | | | | | | Socket monitor msg | | | | +------------------------------------------------------------------+ | 10..X | DATA PAYLOAD | variable | | variable | +------------------------------------------------------------------+
Due to the minimal amount of change from 1.0, this chapter will only provide:
Therefore, readers of this chapter should read this from the point of view of modifying an existing TALI 1.0 implementation to support the new 2.0 features.
A small number of changes to a 1.0 TALI implementation are required to support 2.0. Figure 10 illustrates the inputs that affect the 2.0 TALI State Machine. The reader may notice that the only differences from the inputs for 1.0 are as follows:
Three new TALI opcodes can be sent/received between a TALI node and its peer. The new opcodes are:
Three new User Part capabilities need to be supported by the layer of code above the TALI layer in each implementation. The user part needs to provide support for 'mgmt', 'xsrv', and 'spcl' data.
More information about the 3 new opcodes is provided in individual sections in this chapter. However, a brief description of the purpose of each of these opcodes is as follows:
+====+ +---------+ +============+
| | | Service | +-------------+ | |
|User| | Message,| | Mgmt. Open | | MANAGEMENT |
|Part|<-->| MGMT, | | Mgmt. Close |<-->| |
| | | XSRV, | | Mgmt. Proh. | | |
| | | SPCL | | Mgmt. Allow | +============+
+====+ +---------+ +-------------+
^ ^
| |
v v
+========================================================+
| TALI State Machine |
+========================================================+
^ ^ ^ ^
| | | |
v | | |
+---------+ | | |
| Received| +-----------------+ +-----------+ +------------+
| 'test', | | Connection est. | | Protocol | | T1 Expired |
| 'allo', | | Connection lost | | Violation | | T2 Expired |
| 'proh', | | | | | | T3 Expired |
| 'proa', | +-----------------+ +-----------+ | T4 Expired |
| 'moni', | ^ ^ +------------+
| 'mona', | | | ^
| 'mgmt', | | | |
| 'xsrv', | | | |
| 'spcl', | | | |
| or | +========================================+
| Service | | IMPLEMENTATION |
| Message | | DEPENDENT |
+---------+ +========================================+
^
|
v
+============+
| PEER |
| |
+============+
Figure 10: Overview of Inputs to the TALI 2.0 State Machine
The TALI 1.0 specification did not provide a simple means to perform TALI version identification. However, the general purpose 'moni' message from 1.0 can be used to solve this problem in 2.0.
Recall from 1.0 that the 'moni' message was very loosely defined in the 1.0 spec:
TALI 2.0 implementations should use the 'moni' message to provide version identification as per the following bullets:
+------------------------------------------------------------------+ | Octets | Field Name | Description | Field Type | +------------------------------------------------------------------+ | 0..3 | SYNC | 'TALI' |4 byte ASCII| +------------------------------------------------------------------+ | 4..7 | OPCODE | 'moni' |4 byte ASCII| +------------------------------------------------------------------+ | 8..9 | LENGTH | Length (includes the version | Integer | | | | label and data fields) | | +------------------------------------------------------------------+ | 10..21 | Ver. Label | 'vers xxx.yyy' | 12 byte | | | See note | | ASCII | +------------------------------------------------------------------+ | 22..X | DATA | Vendor Dependent | Variable | | | | Maximum length of this | | | | | message (as coded in octets 8| | | | | -9, and stored in bytes 10-X)| | | | | should not exceed 200 bytes. | | +------------------------------------------------------------------+
Table 8: Version Control 'moni' Message
NOTE: xxx.yyy = provides the Major and Minor release number of the
TALI specification being implemented.
001.000 = Tali version 1.0
002.000 = Tali version 2.0 // this specification.
002.001 = Tali version 2.1 // a minor change to 2.0
003.000 = Tali version 3.0
and so on.
The 'vers 002.000' field is an 12 byte field of field type 'ascii text'. As such, 'v' should be the first byte of the field that is transmitted out the wire.
As part of adding new functionality to the TALI specification, backwards compatibility from TALI version 2.0 to version 1.0 is required. Backwards compatibility is important since TALI 2.0 nodes may be connected to far ends that only support version 1.0; it is important that these 2 implementations continue to inter-operate, and that the 2.0 node falls back to supporting only 1.0 opcodes in this situation.
The previous section described how a TALI 2.0 implementation can use the 'moni' it sends to identify itself as a 2.0 node and how it can use the 'moni' it receives to determine if the far end is also a 2.0
node. In addition to the discussion in the previous section, the following bullets provide details regarding how backwards compatibility must be achieved:
+------------------------------------------------------------------+ | Octets | Field Name | Description | Field Type | +------------------------------------------------------------------+ | 0..3 | SYNC | 'TALI' |4 byte ASCII| +------------------------------------------------------------------+ | 4..7 | OPCODE | 'mgmt', 'xsrv' or 'spcl' |4 byte ASCII| +------------------------------------------------------------------+ | 8..9 | LENGTH | Length (length of the rest | Integer | | | | of this packet) | | +------------------------------------------------------------------+ | 10..13 | Primitive | 'wxyz', or a 4 byte text | 4 byte | | | See note | that is appropriate for the | ASCII | | | | given opcode | | +------------------------------------------------------------------+ | 14..X | DATA | The content of the data area | Variable | | | | is dependent on the opcode/ | | | | | primitive combination | | +------------------------------------------------------------------+
Table 9: Basic Message Structure for New 2.0 TALI Opcodes
NOTE: The Primitive field acts as a modifier for each opcode. Within an opcode, different operations or groups of operations can be defined and supported. The Primitive identifies each different operation or set of operations.
As implied by some of the bullets before Table 9, it is a goal of the 2.0 TALI specification to relax some of the error checking associated with the processing of received TALI messages.
Version 1.0 of this specification was very strict in detailing the fields that were checked for each received message. As each received message was processed, the SYNC code, opcode and length field of the message was checked; if any of these fields were invalid an internal protocol violation was generated. The processing of the protocol violation caused the socket to go down. In addition to the 3 specific checks (sync, opcode, length), the overall philosophy of version 1.0 was to treat any received data that the receiver did not understand, or which the receiver deemed to contain incorrectly coded fields as protocol violations.
Version 2.0 introduces the possibility of partial support for opcodes, partial support for primitives, and partial support for various fields (such as support for ANSI Pt Codes, but not ITU Pt Codes). Thus, the overall philosophy of how to treat received data that the receiver does not support needs to be relaxed from the
strict treatment in version 1.0. Version 2.0 implementations should be more tolerant when they receive messages they do not support (or which they believe contain incorrectly coded fields). This tolerance should include NOT treating these receives as protocol violations.
Version 2.0 implementations should perform the following level of strict/loose checks on the received messages:
The goals behind introducing this gentler treatment of errors in received data are as follows:
The basic message structure for all TALI messages is unchanged with the addition of new 2.0 opcodes. The base TALI header still consists of SYNC + OPCODE + LENGTH, as described in Table 2.
The message structure for the new 2.0 opcodes was shown in Table 9. These messages define an extra required field, PRIMITIVE, that follows the LENGTH field of Table 2.
Table 4 in the version 1.0 specification provided implementation notes for all the 'types of fields' found in the 1.0 specification. Version 2.0 of TALI continues to use all of the types provided in Table 4, and also defines some new fields that are used in TALI messages that use the new 2.0 opcodes. The following table introduces the new field types that are introduced with version 2.0. The types in Table 10 are used in addition to the types in Table 4 to implement the 2.0 TALI protocol.
+-----------+------------------------------------------------------+ |Field Type | Implementation Notes for that Type | +------------------------------------------------------------------+ |SS7 Point | Used to transmit point code information for ANSI or | |Code | ITU variants of point codes across the TALI interface| | | * The point code structure is 4 bytes. Byte 3 is used| | | to identify the TYPE of point code. The actual | | | point code is then encoded in bytes 0-2 (w/byte 0 | | | being the least significant byte and the first byte| | | transmitted across the wire) | | | * Byte 3: encoding of the type of point code (PC) | | | 0 = an ANSI Full PC | | | 1 = an ITU International Full PC w/ a 3/8/3 coding | | | scheme for zone/area/identifier | | | 2 = an ITU National Full PC w/ a raw 14 bit PC | | | 3 = unused | | | 4 = an ANSI Cluster PC | | | * For ANSI Full PC w/byte 3=0. These point codes are| | | 24 bit point codes as follows: | | | Byte 2 = Network | | | Byte 1 = Cluster | | | Byte 0 = Member | | | * For ITU International Full PC (3/8/3) w/byte 3=1. | | | These point codes use 14 bits (stored in the 14 | | | least significant bits in bytes 0&1). Byte 2 is | | | unused. The 14 bits should be interpreted as 3 | | | bits of zone, 8 bits of area and 3 bits of | | | signaling point identifier. The 3 bits of | | | signaling point identifier are the 3 least | | | significant bits. | | | * For ITU National Full PC w/byte 3=2. These point | | | codes use 14 bits (stored in the 14 least | | | significant bits in bytes 0&1). Byte 2 is unused. | | | The 14 bits represent a single 14-bit quantity that| | | constitutes the point code. | | | * For unused w/byte 3=3. Bytes 0 through 2 are | | | undefined. | | | * For ANSI C