3.2.2.2 ISUP Service Message (isot)
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. |
+------------------------------------------------------------------+
3.2.2.2.1 ISUP Encapsulation using TALI
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:
* discards the MTP Layer 2 information, CRC and flags
* places MTP Layer 3 into the SERVICE payload area of the TALI
packet
* The SYNC field is set
* The OPCODE is set to 'isot'
* The LENGTH is set to the number of octets in the SERVICE field
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.
-------------------------------------------------------------[Page 28]
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:
* validates the TALI header
* Allocates space for a new SS7 message
* extracts the MTP Layer 3 data from the SERVICE area and places it
in the new SS7 message
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.
3.2.2.3 MTP3 Service Message (mtp3)
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.
-------------------------------------------------------------[Page 29]
+------------------------------------------------------------------+
| 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. |
+------------------------------------------------------------------+
3.2.2.3.1 MTP3 Encapsulation using TALI
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:
* discards the MTP Layer 2 information, CRC and flags
* places MTP Layer 3 into the SERVICE payload area of TALI packet
* The SYNC field is set
* The OPCODE is set to 'mtp3'
* The LENGTH is set to the number of octets in the SERVICE field
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.
-------------------------------------------------------------[Page 30]
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:
* validates the TALI header
* Allocates space for a new SS7 message
* extracts the MTP Layer 3 data from the SERVICE area and places it
in the new SS7 message
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.
3.2.2.4 SAAL Service Message (saal)
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.
-------------------------------------------------------------[Page 31]
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. |
+------------------------------------------------------------------+
3.2.2.4.1 MTP3 and SAAL Peer to Peer Encapsulation using TALI
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:
-------------------------------------------------------------[Page 32]
* discards the MTP Layer 2 information, CRC and flags
* the MSU is passed from an MTP3 processing software layer to the
SSCF and SSCOP layers (the SAAL layers). These layers convert the
SS7 MSU into an SSCOP PDU. Part of this conversion includes
adding an SSCOP trailer.
* the SSCOP PDU (whether it is a peer to peer SAAL message or SS7
MSU in an SSCOP PDU) is copied into the SERVICE payload area of
the TALI packet
* The SYNC field is set
* The OPCODE is set to 'saal'
* The LENGTH is set to the number of octets in the SERVICE field
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.
-------------------------------------------------------------[Page 33]
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:
* validates the TALI header
* Allocates space for a new SSCOP PDU message
* extracts the SSCOP PDU data from the SERVICE area and places it in
the new SSCOP PDU message
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.
-------------------------------------------------------------[Page 34]
3.3 TALI Timers
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.
3.3.1 T1 Timer
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'.
3.3.2 T2 Timer
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.
3.3.3 T3 Timer
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.
3.3.4 T4 Timer
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'.
-------------------------------------------------------------[Page 35]
3.3.5 Recommended Defaults and Ranges for the TALI Timers
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.
3.4 TALI User Events
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.
3.4.1 Management Open Socket Event
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.
-------------------------------------------------------------[Page 36]
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()
3.4.2 Management Close Socket Event
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.
3.4.3 Management Allow Traffic Event
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.
3.4.4 Management Prohibit Traffic Event
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.
-------------------------------------------------------------[Page 37]
3.5 Other Implementation Dependent TALI Events
In addition to timers, each TALI implementation needs to be able to
detect, and react accordingly, for the following events:
* Connection Established. When the TCP socket connection is
initially established the TALI state machine must be notified.
* Connection Lost. When the TCP socket connection is lost, due to
socket errors during reads/writes, the TALI state machine must be
notified.
* Protocol Violations. Any violation of the TALI protocol as
discussed in 3.7.1.3.
3.6 TALI States
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.
-------------------------------------------------------------[Page 38]
+------------------------------------------------------------------+
| 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
3.7 TALI Version 1.0 State Machine
This section provides the state machine that must be followed by each
TALI implementation in order to be compliant with this specification.
3.7.1 State Machine Concepts
Before presenting the actual state machine, several concepts are
discussed.
3.7.1.1 General Protocol Rules
1. Neither side can send service data unless both sides are allowed.
2. Each side initializes to the prohibited state for both near end
and far end.
-------------------------------------------------------------[Page 39]
3. State changes between the NEx-FEx states 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 T1 expiration.
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 service 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 from NEA to NEP, after sending a 'proh', the
near end must continue to process received service data until a
'proa' is received or until a T3 timer expires.
3.7.1.2 Graceful Shutdown of a Socket
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.
3.7.1.3 TALI Protocol Violations
Each TALI implementation must detect when violations of the TALI
protocol have occurred and react accordingly. Protocol violations
include:
* Invalid sync code in a received message
-------------------------------------------------------------[Page 40]
* Invalid opcode in a received message
* Invalid length field in a received message
* Not receiving an 'allo' or 'proh', in response to the origination
of a 'test' , before the T2 timer expires
* Receiving Service Messages on a prohibited socket.
* TCP Socket errors - Connection Lost
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.
3.7.2 The State Machine
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 | |
-------------------------------------------------------------[Page 41]
+------------------------------------------------------------------+
|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 |
-------------------------------------------------------------[Page 42]
+------------------------------------------------------------------+
|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
3.8 TALI 1.0 Implementation Notes
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.
3.8.1 Failure on a TCP/IP Socket
* The failure to read or write from a TCP socket shall be detected
and generate a connection lost event.
-------------------------------------------------------------[Page 43]
3.8.2 Congestion on a TCP/IP Socket
* Message streams can be monitored for congestion via implementation
dependent methods.
* One possible definition of congestion for the previous requirement
might be when a TCP socket is blocked.
3.9 TALI 1.0 Limitations
Several limitations with the TALI 1.0 specification and
implementation are identified:
* For SCCP traffic, only UDT and XUDT Class 0 and Class 1 traffic
should be managed by this protocol.
* When the MTP3 Routing Label is not part of the data transmitted
across the wire, priority zero (0) traffic is used for all traffic
when the SIO is regenerated.
4. TALI Version 2.0
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.
-------------------------------------------------------------[Page 44]
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:
* Detailed information regarding how a TALI implementation can
identify itself as a 2.0 vs. a 1.0 implementation
* Detailed information regarding how to provide backward
compatibility for a connection to a far end that is only TALI 1.0
capable
* Detailed information regarding the new 2.0 opcodes
-------------------------------------------------------------[Page 45]
* Detailed information regarding any other changes to the
information presented in previous sections that need to be
implemented in order to be 2.0 compatible.
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.
4.1 Overview of TALI Version 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:
* 'mgmt'
* 'xsrv'
* 'spcl'
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:
* 'mgmt' - This opcode is intended to allow MANAGEMENT data, or data
that will manage the operation of the device, to pass between the
TALI endpoints. Examples of this management data include:
* configuration data, such as which SS7 traffic streams a peer
would like to receive over a specific socket
* SS7 Network Management data, such as information regarding
point code (un)availability and congestion.
* Enabling/disabling various socket options, such as options
regarding which messages are supported, or how to format data.
------------------------------------------------------------[Page 46]
* 'xsrv' - Extended Service Opcodes. It is envisioned that the TALI
protocol could be extended to carry other types of traffic that
are not covered by the 1.0 service data opcodes ('sccp', 'isot',
'mtp3', or 'saal'). By defining a new 'xsrv' service opcode, the
TALI protocol is opened up to the possibility of being used for
other types of data transport.
* 'spcl' - Special services. It is envisioned that vendors may want
to build special services into their TALI implementations that are
only activated when the implementation is connected to other
equipment implementing the same special services. This opcode is
intended to provide a general means to discover more information
regarding who the TALI session is connected to, and a means to
enable special features based on the vendor/implementation on the
far end.
-------------------------------------------------------------[Page 47]
+====+ +---------+ +============+
| | | 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
4.2 TALI Version Identification
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.
-------------------------------------------------------------[Page 48]
Recall from 1.0 that the 'moni' message was very loosely defined in
the 1.0 spec:
* The primary purpose of the 'moni' message was to provide a general
purpose ECHO capability. It was envisioned that an important task
that the ECHO capability could provide would be to measure Round
Trip TALI/TALI processing time.
* The data portion of the 'moni' message could be from 0-200 bytes
long. The use of the data area was completely implementation
specific.
* There were no requirements that an implementation ever send a
'moni'.
* If an implementation did send 'moni', it should use the T4 timer
to control the frequency of the outgoing 'moni'.
* The receiver of the 'moni' should not make any assumptions as to
the data portion of the 'moni'. The receiver should simply
convert the 'moni' into a 'mona' and return the message with the
same data portion.
TALI 2.0 implementations should use the 'moni' message to provide
version identification as per the following bullets:
* The primary purpose of the 'moni' message is now twofold:
* To provide version identification
* To continue to provide a general purpose ECHO capability that
can be used to measure Round Trip time or perform other
implementation specific tasks.
* The data portion of the 'moni' message is now divided into 2
portions
* A portion dedicated to version identification, 12 bytes long,
with a specific format that must be followed
* Followed by a free format section that can be used in a
completely implementation specific manner.
* The overall length of the data portion for a 'moni' should still
not exceed 200 bytes. This is required to maintain backward
compatibility with 1.0 implementations that may check for a
maximum length of 200 bytes on the 'moni' opcode.
-------------------------------------------------------------[Page 49]
* If a TALI implementation wants to identify itself as a version 2.0
node, it must send a 'moni' encoded as per Table 8. Every 'moni'
it sends should conform to the encoding in Table 8. The version
label should not change from 'moni' to 'moni'. The data following
the version label can change from 'moni' to 'moni' and can
continue to be used for RTT calculations, or other purposes.
* If a TALI implementation is trying to determine if the far end of
the TALI connection has implemented version 2.0, the
implementation must examine any received 'moni' messages that
arrive from the far end and see if they conform to the new
stricter 'moni' encoding in Table 8. On receiving 'moni', a TALI
2.0 node will compare the 12 bytes of data in the VER LABEL field
with a list of predetermined strings to determine the
functionality of the TALI node it is connected to. If the data
doesn't match any of the predetermined strings, the Far End is
assumed to be a TALI 1.0 node.
* Each TALI implementation must assume that the far end of the
connection is a 1.0 implementation until an arriving 'moni'
announces that the far end supports TALI version 2.0. If a 'moni'
never arrives, the implementation knows the far end has
implemented version 1.0 of the specification.
* TALI 1.0 implementations can receive newly encoded 'moni' messages
and simply ignore the data. The 1.0 implementations will continue
to operate as if the far end is always a 1.0 node (ignore the data
portion of the 'moni', convert 'moni' to 'mona', and return the
'mona').
* The next section provides more information regarding backwards
compatibility (2.0 implementations connected to devices that
implemented version 1.0 of the specification).
-------------------------------------------------------------[Page 50]
+------------------------------------------------------------------+
| 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.
4.3 Backwards Compatibility
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
-------------------------------------------------------------[Page 51]
node. In addition to the discussion in the previous section, the
following bullets provide details regarding how backwards
compatibility must be achieved:
* As documented in the version 1.0 specification, TALI 1.0
implementations that receive TALI messages with 'mgmt', 'xsrv',
and 'spcl' opcodes will treat the message as a Protocol Violation
(invalid opcode received). The Protocol Violation will cause the
socket to be dropped immediately.
* It is therefore required that a 2.0 implementation only send
'mgmt', 'xsrv', and 'spcl' opcodes, after it has used a received
'moni' message to determine that the far end is a 2.0 (or later)
implementation and has identified itself as a 2.0 (or later)
implementation.
* Each TALI 2.0 implementations must use the 'moni' as described in
the previous section to identify themselves as 2.0, and to learn
if the far end is 2.0.
* Each TALI 2.0 implementation should maintain a variable as part of
its state machine, 'far_end_version'. The 'far_end_version'
should be initialized to 1.0 when the socket is established. Each
time a 2.0 implementation receives 'moni', it should update the
'far_end_version' variable. If the 'moni' did not contain a
version label, the 'far_end_version' should be reset to 1.0. If
the 'moni' did contain a version label for 2.0 (or a later
version), the 'far_end_version' should be set accordingly.
* Each time a 2.0 implementation receives a new 2.0 opcode ('mgmt',
'xsrv', and 'spcl') from the far end, it should examine the '
far_end_version'. If the 'far_end_version' indicates the far end
is a 1.0 implementation, the received TALI message should be
treated as a Protocol Violation (invalid opcode). If the
'far_end_version' is 2.0 (or later), the 2.0 implementation should
process the received 'mgmt/xsrv/spcl' according to that nodes
capabilities for that opcode.
* Each time a 2.0 implementation receives a request to send a TALI
message with a 2.0 opcode ('mgmt/xsrv/spcl') from a higher layer
of software, it should examine the 'far_end_version'. If the
'far_end_version' indicates the far end is a 1.0 implementation,
the request to send the 2.0 opcode should be denied or ignored (an
implementation decision) and the 2.0 opcode must NOT be sent to
the far end. If the 'far_end_version' indicates the far end is
2.0 (or later), the request can be satisfied and the TALI message
with the 2.0 opcode can be sent to the far end.
-------------------------------------------------------------[Page 52]
* Each TALI 2.0 implementation can provide a varying level of
support for each of the three new 2.0 opcodes ('mgmt/xsrv/spcl').
In other words, an implementation may wish to only support SOME OF
the primitives within the new opcodes. The level of support for
each 2.0 opcode ('mgmt/xsrv/spcl') is independent of the other two
2.0 opcodes.
* The basic message structure for TALI messages using the new 2.0
opcodes is presented in Table 9.
* The minimal level of support that is required for each of the 2.0
opcodes (mgmt/xsrv/spcl) is to be able to receive TALI messages
with these opcodes, recognize the new opcode, and ignore the
message without affecting the state machine. The TALI state
should not change. The socket connection should stay up. In
other words, a 2.0 implementation can elect to ignore any received
'mgmt/xsrv/spcl' messages, if that implementation does not care to
support the capability intended by that particular opcode.
* A partial level of support for a 2.0 opcode could be implemented.
Partial support may consist of understanding the data structure
for the 2.0 opcode, but only supporting some of the variants of
the opcode. The message structure for each of the new 2.0 opcodes
consists of an extra 'Primitive' field that follows the TALI
opcode and message length fields. Each 'Primitive' is used to
differentiate a variant of the opcode. It is envisioned that each
new 2.0 opcode can be extended by adding new 'Primitives', as more
capabilities are defined for the opcode, without having to add new
TALI opcodes. A 2.0 implementation may understand and be willing
to act on some of the 'Primitives' for an opcode, but not others.
Receiving variants of a 2.0 opcode that an implementation does not
understand need to be ignored and not affect the 2.0 state
machine.
* The full level of support for a 2.0 opcode could be implemented.
This support would consist of understanding and fully supporting
every 'Primitive' within the 2.0 opcode.
-------------------------------------------------------------[Page 53]
+------------------------------------------------------------------+
| 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.
Next To :: Tekelec's Transport Adapter Layer Interface - Part 3
Credits
-- UnKnown --
|