AlphaNet Data Protocol

Introduction

The AlphaCom/AlphaNet Data Protocol (ACDP protocol) is used for:

• Data communication between AlphaCom Exchanges in AlphaNet, including other types of exchanges such as TouchLine MPC
• Data communication between AlphaCom Exchanges and External Devices such as RIOs and PC based Control Handlers
• Advanced internal control of the AlphaCom. Event Handler can use DP messages as general Action Commands.

The Data Protocol is made generally available from software version AMC 06.00. Previous AMC softwares are NOT compatible with this protocol descriptions.

Protocol properties

• Binary format for speed. Readable ASCII hex format can be used as an alternative for easier debugging
• The physical layer of the protocol is RS485, RS422 or RS232
• Data link layers with message checksum for reliability, and with acknowledgment and re-transmission of erroneous messages
• Network layer for routability when several exchanges are connected
• Variable length fields and optional fields so that the protocol can be used also in future systems with different requirements regarding number of digits in addresses, station numbers etc.
• A systematic way of addressing exchange resources both as directory numbers and physical addresses
• Addressed messages. Commands are addressed to a specific device, and response is returned to the device issuing the command only. In addition, there is a few status broadcast messages
• Addressed messages can be routed in a network. The input and output messages have identical frame format, and thus can be sent via transit exchanges. The same protocol is used both to control a single exchange, and as the AlphaNet protocol
  

Message example

Here is a HEX coded example of a message with network layer header and application data. This is basically what you send to the exchange in the “simple link layer” format. We assume that you use exchange node 01, the PC is device 01, and that there is a station 107 and 102. The message DIAL_DIGITS looks like this, with spaces between fields for clarity only:

Network        Application   Application Message 
layer header   header        parameters    _         
0101 0141 01   41 1234 0050  3201107F 20102F
Src  Dest Hop  Cl Ref  Msg   P1       P2
dev  dev  cnt  ss      id    Station  Digits to dial

Message Formats - Grouped by Function

Common notes

• NET_OBJ_REF parameters: Where an entity class is given (Example: {ECL_ABSENT}), the parameter must be either a LOCAL_ENTITY format reference of the correct class or a directory number that maps to an entity of the correct class, or a Null value, if allowed.

Except: ECL_USER and ECL_STATION can be used interchangeably, and will be converted to the other type when needed. As a side effect of this, the returned directory number reference for a ECL_STATION type object may be different from the one in the command message, or even invalid, if the directory number or user reference in the command message is not the one of the default user of the station.

• NET_OBJ_REF parameters are by default output in the LOCAL_DIRNO format by AlphaCom and TouchLine. Exceptions are noted in each case.
• For the reason above and other reasons, NET_OBJ_REF parameters in command messages can not be relied upon to match the corresponding NET_OBJ_REF parameters in response messages. If one need to sort responses of the same message type from each other, the message reference field in the application header should be used.

Explanation of table format, explanations are in italic font:

• Over time, more parameters will be added to existing messages. These parameters are often marked “(optional)”, and the AMC version which introduced them is shown to the right in the explanation of each parameter.

- Note that it’s the exchange that processes the DP message that adds default values when it creates an internal representation of the message. If you send a “short” message to a remote node in AlphaNet, all default fields will be filled in in that exchange. Example: SEND_MAIL without A station name will get the name from the same dir.no in the remote exchange (if existing). See comment under Simple Link Layer, page 70.

• In general, NULL is not allowed as NET_OBJ_REF parameter.

It’s described explicitly when it can be used, e.g. to switch call forwarding OFF. Hint: Some DP messages works correctly only if you leave the NET_OBJ_REF parameter out, rather than supplying an explicit NULL field.

• Note that all messages may cause the response message ILLEGAL_PARAM, indicating that the exchange has problems recognizing either the message number, or a parameter value of a message. In these cases the documented response message will NOT be returned.

- ILLEGAL_PARAM refers to the problem parameter using a number from 1 and up. This is the number you will find in to the left of each parameter in the table.

- In AlphaNet, if you get an ILLEGAL_PARAM from a remote node indicating that an optional parameter is required, remember that the AMC versions indicated for optional parameters refers to the receiving node, not the local node generating the message.

• Some messages may seem to have too few parameters. Keep in mind that:

- the network layer header contains node and device address for both a source and a destination

- the reference field is always identical in a “command” and the returned “response”.

• AlphaNet: To control a station in a network you must address the DP message to that station’s node. Messages are in general ONLY routed according to the network layer header. If you send a message to an exchange, and use a node number as part of the (A) Subscriber field which is different from the addressed node, the command will be ignored or cause an error response. The messages which deviates from this rule is documented explicitly!

Station Connect Operations

Message	Description
CALL_SETUP	Sets up a coversation between two users
CONN_REQUEST	Sets up a coversation between two users
CONN_REFERENCE	Positive response from the exchange to CONN_REQUEST
CONN_REF_ACK	The external application acknowledges the CONN_REFERENCE
STATION_BUSY	Negative response to CONN_REQUEST
RESOURCE_BUSY	Negative response to CONN_REQUEST
NO_ACCESS	Negative response to CONN_REQUEST
STATION_DOWN	Negative response to CONN_REQUEST
DISCON_ST	Disconnect station from ongoing feature
DISC_REQ	Conversation established with CONN_REQUEST: The external application disconnects a conversation.
DISC_REQ_ACK	Conversation established with CONN_REQUEST: The AlphaCom acknowledges the DISC_REQ message
DISCONNECTED	Conversation established with CONN_REQUEST: Conversation was disconnected, e.g. the user pressed C-key
DISCONNECTED_ACK	Conversation established with CONN_REQUEST: Acknowledge of the DISCONNECTED message
CALL_STATUS_BC	Broadcast message telling the status of a call
CONN_STATUS_BC	Broadcast message telling that a connection is established
DISCON_STATUS_BC	Broadcast message telling that a connection is disconnected
PARK_INQ_BROKER	Park station from conversation, enter Inquiry call state
UNPARK	Unpark station from Inquiry call state station, return to conversation
REQ_TRANSF_CALL	Transfer call in an Inquiry Call situation.

Station Keyboard & Display emulation

Note that the exchange remembers the M-key state and the handset state forever (it’s not “cleared” e.g. by conversation cancel).

Message	Description
DIAL_DIGITS	Simulate digit dialing from a station
DIAL_DAK	Dial DAK on a station
SINGLE_DIGIT	Dial one digit on a station
DIGIT_RELEASE	The station has released a digit press
M_KEY	Order station to press M-key
M_KEY_RELEASE	Order station to release M-key
HANDSET_OFF	Order station to lift handset
HANDSET_ON	Order station to replace handset
C_KEY	Order station to press C-key
DISPLAY_TEXT	Send text and control characters to a station
ST_BUSY_BC	Broadcast message: Intercom station is busy
ST_FREE_BC	Broadcast message: Intercom station is free

Station Features and Status

Message	Description
PROGRAM	Set audio program for single station or a predefined group of stations
PROGRAM_ACK	Positive response to PROGRAM
PROGRAM_NAK	Negative response to PROGRAM
PROG_CONF	Set Simplex conference for predefined group of stations or a single station
PROG_CONF_ACK	Positive response to PROG_CONF
PROG_CONF_NAK	Negative response to PROG_CONF
CONF_TALK	Set Simplex conference speaker
CONF_TALK_STOP	Stop station form feeding Simplex conference
AUDIO_DETECT	Triggers the event Simplex_Conference_Audio
O_DUPL_CONF	Include/exclude a station or a group into/from an Open Duplex Conference
OD_CONF_ENTERED	The participant has entered an Open Duplex Conference
OD_CONF_LEAVE	The participant has left the Open Duplex Conference
ALARM_MSG	Set up (or disconnect) an ASVP Alarm message to a single station or a predefined group of stations
ALARM_MSG_ACK	Positive response to ALARM_MSG
ST_GROUP_DISCON	Switch off Group Call audio at a station that receives Group Call audio at the moment
SET_CALL_REQ_MODE	Turn on/off message “your call is registered, please wait”, then ringing/flashing at a station
CALL_TRANSFER	Set or remove call transfer for a station
CALL_TRANSFER_OK	Positive response to CALL_TRANSFER
CALL_TRANSFER_NOK	Negative response to CALL_TRANSFER
SET_REQ_TRANSF	Set transfer of Call Request for an intercom station
GET_REQ_TRANSF	Get the Call Request Transfer status for an intercom station
REQ_TRANSF	Response to the SET_REQ_TRANSF and GET_REQ_TRANSF messages
SET_ABSENCE	Set absence status for an intercom station
GET_ABSENCE	Get absence status for an intercom station
ABSENCE_STATUS	Response to SET_ABSENCE and GET_ABSENCE messages
WAKE_UP	Register or remove wake­up request
WAKE_UP_ACK	Positive response to WAKE_UP
WAKE_UP_NAK	Negative response to WAKE_UP
SET_GRP_FILT	Set group call filter for a station
GROUP_MEMBERSHIP	Set group membership in NVRAM for a station
EXT_FEATURE_BC	Broadcast message when a directory number (feature 50) is dialed on a station
SET_STATION_COS	Set COS membership in NVRAM for a station
MODIFY_COS_CONTENTS	Modify feature membership in COS in NVRAM

Station Mail Operations

Message	Description
SEND_MAIL	Send a mail message to an intercom station
SEND_TXT_MAIL	Send a mail message with free text to an intercom station
SEND_MAIL_ACK	Response to the SEND_MAIL and SEND_TEXT_MAIL messages
CANCEL_MAIL	Delete one or more mail/call request/alarm messages queued at a station
SET_MAIL_TIMEOUT	Set the timer of a mail queue entry
COPY_MAIL	Send a copy of a mail in own queue to a new destination (station or group)
MAILQ_NAVIG	Do operation on mail queue, or step current mail in mail queue
DELETE_MAIL	Delete a mail entry in the queue for an intercom station
DELETE_MAIL_ACK	Response to the DELETE_MAIL message
GET_FIRST_MAIL	Get the first mail entry in the queue for an intercom station
GET_LAST_MAIL	Get the last mail entry in the queue for an intercom station
GET_NEXT_MAIL	Get the next mail entry in the queue for an intercom station
GET_PREV_MAIL	Get the previous mail entry in the queue for an intercom station
GET_THIS_MAIL	Get the identified mail entry in the queue for an intercom station
EXT_MAIL	Response to the GET_x_MAIL messages
Q_ELEM_ADDED	Broadcast message. Reports that a mail message has been added to a station’s mail queue
Q_ELEM_REMOVED	Broadcast message. Reports that a mail message has been removed from a station’s mail queue

General Exchange Control

Message	Description
SET_SYSTEM_TIME	Set the internal clock to the given date and time
GET_SYSTEM_TIME	Ask a device (AlphaCom) for date and time
SYSTEM_TIME	Response to the GET_SYSTEM_TIME and SET_SYSTEM_TIME message
PUT_STRING	Output String to Exchange serial port after adding appropriate framing depending on selected port
LOG_STRING	Output String to System Log
EXECUTE_COMMAND	Send a command string to the exchange to be executed there
EVENT_REPORT	Report an event to the event/action system
SET_TIMER	Start or stop a timer
WRITE_USER_DEF_DATA	Write User Defined Data (UDD)
SET_DIRNO_TXT	Change the display text of a directory number (station or feature)
NAME_EXTENSION	Special exchange mode using two line names: Send the second line through AlphaNet
SNV	Update specific system settings (NVRAM) values
STATUS_REPORT	Report equipment Presence and Error/OK status
COMMAND_RESPONSE	General response message to messages
ILLEGAL_PARAM	Negative response
DPMT_INVALID	Reserved value for internal use
DUMMY	Test message: Should be routed, accepted and ignored

Device Control and Status

A device shall not respond to any message before it’s operative except RESET_DEVICE and GET_DEVICE.

Message	Description
RESET_TAKEN	A device reports that it has done an internal reset
RESET_DEVICE	Reset a device
GET_DEVICE	Get information from an external device
DEVICE_INFO	Response to the GET_DEVICE message
PING	Test device: “Are you there?”
PONG	Response to the PING message. “Yes, I’m here.”

Remote Control

Message	Description
SET_LOGICAL_RCO	Set or clear a logical RCO
RCO_CHANGED	New RCO state reported from the exchange
RCI_CHANGED	New RCI state reported from the exchange

RIO Protocol

There are a number of messages for RIO control. The message sequences, timing and error procedures are described in a separate document. Note that all inputs or outputs “owned” by the exchange can NOT be controlled in parallel by an external computer. Responses are always returned to the device that controls a pin.

Message	Description
GET_PIN_COUNTS	Query a RIO about number of output and input pins and support for non mandatory features
PIN_COUNTS	Response to the GET_PIN_COUNTS message
SET_RCO	Turn the given remote control output on
SET_RCO_OK	Positive response to the SET_RCO message
SET_RCO_FAILED	Negative response to the SET_RCO message
CLEAR_RCO	Turn the given remote control output off
CLEAR_RCO_OK	Positive response to the CLEAR_RCO message
CLEAR_RCO_FAILED	Negative response to the CLEAR_RCO message
PULSE_RCO	Generate a pulse with the defined length
PULSE_RCO_OK	Positive response to the PULSE_RCO message
PULSE_RCO_FAILED	Negative response to the PULSE_RCO message
POLL_RCI	Poll the given remote control input once
SCAN_RCI_ONCE	Scan input until defined condition is met, then report to exchange
SCAN_RCI_ACK	Positive response to the SCAN_RCI_ONCE message
RCI_IS_ON	Response to the POLL_RCI and SCAN_RCI_ONCE messages, input pin is on
RCI_IS_OFF	Response to the POLL_RCI and SCAN_RCI_ONCE messages, input pin is off
SCAN_END_ACK	Acknowledgment to the RCI_IS_OFF and RCI_IS_ON messages

AlphaNet

This is messages related to audio control between exchanges. AlphaNet also uses other messages like station emulation, mails, and system maintenance.

Message	Description
AUDIO_PATH_SETUP	Set up audio path between a source node and a destination node (possibly via transit nodes)
AUDIO_CODEC	Message sent in the direction of start node, from end node or trans-coding nodes along the path
AUDIO_PATH_OK	End to end message: Audio path is ready
AUDIO_LINK_OK	Response to AUDIO_PATH_SETUP. Channel number is OK
AUDIO_PATH_STATE	SIP Response to AUDIO_PATH_SETUP
STATION_INFO	SIP update of number and display text
AUDIO_LINK_NOT_AVAILABLE	Response to AUDIO_PATH_SETUP from next node: Channel not granted
AUDIO_PATH_DISCONNECT	Release the end­to­end audio path. Normal disconnect from source or destination
AUDIO_LINK_RELEASE	Used to release audio path backwards stepwise from node to node when setup meets busy or faulty link
STATION_LISTEN	Message from remote exchange. Set station in listen mode. Shut mic
STATION_CONVERSATION	Message from remote exchange. Set station in conversation mode. Stop tone and open mic.
STATION_TRANSFER	Message from remote exchange: Transfer of B subscriber.
CHECK_AUDIO_PATH	Check of established audio path at regular intervals
AUDIO_PATH_CHECK_OK	Positive response to CHECK_AUDIO_PATH
AUDIO_CH_LOOPBACK_REQ	Request for loopback audio connection. Used by the Audio Channel Testing process
AUDIO_CH_LOOPBACK_ACK	Positive acknowledge of AUDIO_CH_LOOPBACK_REQ
AUDIO_CH_FAULTY	Response to AUDIO_CH_LOOPBACK_REQ: Requested channel was faulty
LOOPBACK_IMPOSSIBLE	Response to AUDIO_CH_LOOPBACK_REQ
AUDIO_CH_DISCON	Disconnect a audio channel after loopback test
AUDIO_CH_TONE_REQ	Request a peer exchange to put a 500Hz tone on a audio channel
AUDIO_M_PATH_SETUP	Communication in a multi-node network
AUDIO_M_PATH_OK	Contains statuses for an AUDIO_M_PATH_SETUP from one or more destination exchanges
AUDIO_M_LINK_OK	Per­ hop positive response to AUDIO_M_PATH_SETUP
AUDIO_M_PATH_BACKTRACK	AUDIO_M_PATH_SETUP failed
VCP_MEET_REQ	Request answer to global group call
BUILD_GLOB_GRP	Broadcast message to all exchanges to make them rebuild global group indexes
GLOB_GRP_MEMB	A exchange tells which global groups this exchange is member of by broadcasting this to all exchanges
RESET_AUDIO_LINK	Reset audio link between nodes. Message not used in current AlphaCom version
CONF_JOIN	Exchange wants to join conference, asks root-exchange to setup connection back to sender
CONF_MEMB_CHK	Ask whether any neighbor exchange has any ordinary member left in conference
CONF_ORD_MEMB	An exchange tells its neighbors that it has ordinary member left in conference
CONF_IS_ROOT	Broadcast message. Sender informs that it is root of conference
CONF_NOT_ROOT	Broadcast message. Sender informs that it is no longer root of conference
AUDIO_M_FEED_REQ	Global Simplex Conference: Some station is pressing the M-key when participating in a conference
AUDIO_M_FEED_STOP	Global Simplex Conference: The station is releasing the M-key
AUDIO_PATH_DELAY	Set Duplex switch delay

System Maintenance

Message	Description
SET_NODE_NUMBER	Change the node number of an exchange
ROUTE_ALPHAPRO_MSG	Send AlphaPro message via AlphaNet to/from a remote node
CONSOLE_REQ	Log on to system debug console (TST)
CONSOLE_DISC	Log off from system debug console (TST)

Appendix: Link layers in detail

ISO Data Link Layer

Transmission Control Characters used

The following control characters are used in the protocol: The first 32 characters, ASCII 0 ­ 31 (0x00 ­ 0x1F) is not allowed in the payload of an message. Note that the message’s Block Check Character can have any value, including the reserved transmission control characters!

STX ­ Start of text

STX is a transmission control character which precedes a text and which is used to terminate a heading. STX is transmitted by the Master Device.

ETX ­ End of text

ETX is a transmission control character which terminates a text. ETX is only transmitted by the Master Device and calls for a reply from the Slave Device. ETX is followed by a BCC, “block check character”.

EOT ­ End of transmission

EOT is a transmission control character used to indicate the conclusion of the transmission of one text. EOT may be transmitted by a Control, Master or Slave Device. The Control Device transmits EOT to anticipate the reception of a forward supervisory sequence. The Master Device in the system transmits EOT to relinquish its right to transmit in favor of the Control Device.

ENQ ­ Enquiry

ENQ is a transmission control character used as a request for a response from a remote device. ENQ is transmitted by the Control Device during polling and by the Master Device during selecting.

ACK ­ Acknowledge

ACK is the transmission character transmitted by a receiver as an affirmative response to the sender.

NAK ­ Negative acknowledge

NAK is a transmission control character transmitted by a receiver as a negative response to the sender.

Device Id

The Device Id is an UINT1 value which is unique within an exchange.

Selecting a device in another exchange (Routing)

If the Master Device has a message to a device in another exchange, the Router is selected. The Router has device id 204 (0xCC) and answers the enquiry, and receives the message, on behalf of the destination device. This means that each device has to know which AlphaCom module they belong to. The Master Device has completed its transmission upon receipt of ACK from the Router. Acknowledgment / handshake between devices on different modules must be handled at the application layer.

Broadcast

The Master Device uses a broadcast id when selecting for a broadcast message. It is the responsibility of the Master Device to ACK the selecting supervisory by transmitting the positive acknowledge character ACK.

Stentofon Data Link Layer

Frame Description

Encoding type 0 means that the field is binary data. - Data needs no reformatting. Encoding type 1 means that the field contains hexadecimal data. - Data is represented by ASCII characters `0’ ... `9’ and `A’ ... `F’. - Each byte of original binary data is converted to 2 ASCII characters. The data are converted back to binary form before they are sent to the Network Layer. - If the character ` ‘’ ‘ (double quote, 0x22) is received within a hexadecimal message, the rest of the message is uncoded (ASCII text). The ` ‘’ ‘ is stripped off, and its position is handed over to the Network Layer, so that if the message is to be retransmitted, the double quote is reinserted and the ASCII text part will not be coded to hexadecimal. - When a hexadecimal encoding type is used, a CR (carriage return) character is added at the end of the field to increase readability. This character is also stripped off before the data is sent to the Network Layer.

Information/Message Frame

The Information/Message Frame type (type 1) typically will have a Network Layer Frame as payload.

Idle Frame

A special version of the message frame is the Idle Frame, defined by a field containing a Network Layer Frame with only the address header (no payload message code and parameters). When no data are ready for transmission for a given time, idle frames are transmitted at regular intervals to check the quality of the data channel, and also to detect interruption of the channel (watchdog function). Idle frames are also used for resynchronization of sequence numbers. Idle frames are acknowledged in the same way as data messages. The format of the idle frame is as follows, where the size of each field is 1 byte:

 = <source node><source device><destinatin node><destination device> 

Acknowledge Frame

The ACK frame (type 2) is used to acknowledge frames that are correctly received. The sequence number is derived from the frame it acknowledges.

Negative Acknowledge Frame

The NAK frame (type 3) is used to request for retransmission of a given message. ACK and NAK frames will have priority for sending before any other messages.

Link Control, Supervision and Error Recovery Procedures

As the protocol may be used on intercontinental links with long delays (up to 500 ­ 600 ms roundtrip delay on a satellite |hop), special precautions must be taken to secure transmission quality without introducing too long delay in the forward path when conditions are good. Therefore, a sliding window mechanism is used to maintain correct sequencing of messages in case of transmission errors.

Sliding Window Protocol

A sliding window protocol with sending window size 7 is used. This means that 7 messages may be sent on the link before a response is required for any of them. At the receiving end, window size 1 is used, i.e. if a message is lost, the lost message plus all messages after the lost one must be retransmitted.

At the transmitting end, the Message Frames are numbered with a sequence number and inserted into a window buffer when sent, and removed when acknowledged. Before a new frame is sent, the previous frame must be completed (STOP_FLAG sent). When the buffer is full, transmission of new frames has to wait until an acknowledge is received. The Acknowledge Frame carries the same sequence number as the frame it acknowledges. If an acknowledge is received for a frame that is not the oldest one in the window buffer, it means that an Acknowledge Frame is lost or skipped at the receiving end, and the acknowledged frame and any older frames are removed from the buffer. If a NAK frame is received, the corresponding frame plus the newer frames (if any) are retransmitted, and the older frames are removed from the buffer.

At the receiving end, incoming frames are checked for errors, and if OK, an ACK frame with the same sequence number is transmitted back to the sender. The frame is then decoded to binary form (if necessary) and sent to the Network Router. If an error is detected, either in the current frame or if there is a frame sequence number missing, NAK frame is sent back to the sender with the sequence number of the frame with error or missing. The receiver then discards all received frames until the one with the correct sequence number is received, and normal operation is resumed. Since an Idle Frame is only transmitted when the window buffer is empty, it is used to synchronize sequence numbering at the other end of the link. After a reset, the transmission always starts with at least one Idle Frame.

Link Supervision

If there is no response from the other end of a link within a given time (calculated from the normal delay of the link) after the last frame is sent, the contents of the window buffer is retransmitted. If no response is obtained after 2 attempts, the window buffer is cleared, transmitter reset, and Idle frames transmitted with specific intervals. If contact with the other end is re­established, an OK­message is sent to the Network Router so that data communication can be resumed.

Simple implementation

An external computer can run with a sliding window size of one, i.e. for each message you send you must wait for the acknowledge from the AlphaCom. Sending/receiving NAKs can also be skipped as both ends always must have (fast) timeouts to handle errors.