Connection Settings

Overview

A Connection Settings object is used to configure timeout, delay, and modem information for ports and/or devices. A single Connection Setting object can be shared across multiple devices and ports.  Often, default options will work in the Connection Setting object.

By default, a device will use the Connection Settings of its Port object.  If the device has a separate connection setting associated, it will override the connection settings of its port. This allows ports to be configured with commonly required settings, but also allows devices with specific needs, such as a longer reply timeout, to override the port settings.

Configuration

Connection Settings Tab

Poll Cycle Settings

A Poll Cycle is the set of request messages that are transmitted and processed for a device when a schedule comes due, or a when a non-scheduled event occurs (such as a demand poll or history collection request).

Poll Retries

Default = 2. The number of times a Poll Cycle should be attempted. Each attempt consists of sending the set of request messages that are due, or that belong to the requested event sequence.

• If a valid response is received for all the transmitted request messages, the Poll Cycle is considered complete. A complete Poll Cycle will end the scheduled or requested event and allow the poller to move on to the next device handled by that port.
• If any transmitted request messages did not receive a valid response (as determined by the Message Retries and Message Timeout properties), the Poll Cycle is considered incomplete. Incomplete Poll Cycles will be placed into a retry queue and attempted again later for up to the number of times configured in the Poll Retries property or until one of the attempts is complete (when all transmitted request messages receive a valid response). If none of the Poll Cycle Retries results in valid responses for all its transmitted request messages, the Poll Cycle is considered failed.

Fail Delay

Default = 30. The Fail Delay is a way to delay the time between Poll Retries of incomplete Poll Cycles. When a Poll Cycle is incomplete, it is placed into the retry queue (each port has its own retry queue). The Fail Delay applies to scheduled Poll Cycles only and defines a minimum delay period. If the retry queue grows due to many incomplete Poll Cycles, each Poll Cycle in the queue may wait longer than the configured Fail Delay time to get its turn. Incomplete Poll Cycles that occur due to non-scheduled events will be processed from the queue as soon as they reach the front of the queue, whether the Fail Delay time has elapsed or not.

Poll Message Settings

A poll message is a single request, or transmit, to a field device. Gathering data from a field device typically requires multiple poll messages.

Message Retries

Default = 2. The number of times a single message request should be attempted beyond the initial attempt. Each attempt consists of transmitting the request message and waiting for the response. If a valid response is received, the request message will be considered complete and the next request message will be transmitted if one is available. If a valid response is not received, the message will be transmitted again and a wait for the response will begin again. This sequence will be repeated for the number times configured in the Message Retries property. If a valid response is not received on any of the message tries, the request message is in the No-Response state.

Reply Timeout

Default = 2000 (Milliseconds). Each time a request message is transmitted, the poller will wait for the time configured in the Reply Timeout property. If no valid response is received within that time and there are Message Retries remaining, another attempt will be transmitted. If a valid response is received within the Reply Timeout period, the wait period will end (waiting until the full Reply Timeout period has elapsed is not required when a valid response is received) and polling will move to the next request message if one is available.

Initial Timeout

Default = 0 (Milliseconds). The Initial Timeout provides more granularity for the Reply Timeout period. This period defines the length of time to wait for the first received byte of a request message response. If the first byte is not received within the Initial Timeout period, the Reply Timeout is considered elapsed and the request message will be transmitted again if Message Retries are available. If no Message Retries are available, then polling will move to the next request message if one is available. Note: If this property’s value is zero, then the Initial Timeout check is disabled. This property will typically be configured with a zero value, making it disabled.

Inter-Character Timeout

Default = 0 (Milliseconds). The Inter-Character Timeout provides more granularity for the Reply Timeout period. This period defines the length of time to wait between any two bytes received as part of the request message response. If the Inter-Character Timeout period elapses between any two bytes, the Reply Timeout is considered elapsed and the request message will be transmitted again if Message Retries are available. If no Message Retries are available, then polling will move to the next request message if one is available. Note: If this property’s value is zero, then the Inter-Character Timeout check is disabled. This property will typically be configured with a zero value, making it disabled. One scenario where this property might be useful is with a slow communication link. If a response comes from a device over a slow link and just a few data bytes are received at a time, you can configure a long Reply Timeout, and set the Inter-Character Timeout to some non-zero value. This will ensure the port waits for the full response if it continues to receive data bytes. If a long gap occurs between the receipt of data bytes, the port will consider the response to have timed out instead of waiting for the full Reply Timeout period.

Skip Retries on Failed Devices

Default = Not selected. When a device performs a poll and cannot successfully retrieve all the data requested by the poller, it is in a failed state. When a device is in this state, the option to Skip Retries on Failed Devices will make the poller act as if the Message Retries property is set to zero. This can help improve performance if there are devices that are offline. It will prevent time spent on request message retries for devices that will not respond. However, enabling this option for devices on poor communication links may result in failure to collect data that might otherwise have been collected with Message Retries if this option were not enabled.

Abort Poll After First No-Response

Default = Not selected. When all configured Message Retries have been transmitted and no valid response has been received, a message is in a No-Response state. If this occurs, and the option to ‘Abort Poll After First No-Response’ is enabled, then no more request messages will be transmitted for the device during its current poll cycle. Polling for this device will continue the next time its schedule comes due, or if a non-scheduled event occurs (such as a demand poll).

Dialup Modem Tab

Command Retries

The maximum number of tries to issue a modem command with no response before continuing to another poll. Default = 2.

Command Timeout

The maximum amount of time in seconds to wait for the modem to respond.  Default = 2

Connect Timeout

Maximum amount of time in seconds to wait for the modems to establish a connection.  Default = 35.

Dial Prefix

The modem dial prefix.  Use ATDT for tone dialing, ATDP for pulse dialing or another custom setting.  Default = ATDT.

Connect String 

The string returned by the modem to indicate a connection to a remote modem.  Default = CONNECT.

Hangup String

The command string to hang up the modem and terminate the call.  Default = ATH0.

Modem Initialization

The initialization string used to configure the modem.  Default = ATE0Q0&C1&D2&S1V1X4.

Warmup Delay

The time to wait in milliseconds between connection to the remote modem and sending the first poll message.  Used for line stabilization.  Default = 0.

Between-Call Delay

The time to wait in seconds between finishing one call and beginning another.  Default = 0.

Hangup Delay. 0 (Default)

The amount of time in seconds after the last poll message before the hang up command is issued.  Default = 0.