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The TID, AID, CTAG, and General Block

The second part of the message, known as the "staging block", identifies the exact resource in the network element that will be acted on by the command. The staging block is constructed in the following format:

:TID:AID:CTAG:generalblock:

The Target Identifier (TID)

Every TL1 device is assigned a Target Identifier or (TID), which uniquely defines that device. The (TID) is the first command in the staging block sequence. The TID is subject to the following rules:

• The TID can be of maximum 20 ASCII characters and may only contain letters, numbers, and hyphens.
• In direct (or "point-to-point") routing, where commands are sent to an element over a private line, the TID value can be null.
• In indirect routing, where commands are sent over a shared or public line, a valid TID value is essential. If multiple devices will see the same command, you must specify a TID so you can select the device you wish to "talk" to.
• The TID value is also used to identify the source of a response message from a network element.

The Access Identifier (AID)

The Access identifier (AID) is found after the TID. It contains one or more simple or compound parameters. The parameters identify a specific entity within the associated target element to be acted upon by the input message. In other words, the TID defines a network element (Switch Bay 1), and the AID defines the specific segment (Shelf 3, Card 4) of that network element. The AID is often the field that uniquely identifies the alarm.

The Correlation Tag (CTAG)

A correlation tag (CTAG) is used to correlate a response or an acknowledgement to an earlier input message. When a response message is sent, it uses the same CTAG to indicate the command to which it is responding. It is, therefore, the user's responsibility to ensure that CTAGs are unique for each message. A replicated CTAG will not cause an error directly, but it will create uncertainty when responses are received with duplicate CTAGs. CTAGs are also used as serial numbers for autonomous alarm messages. If a number in the sequence is skipped (ex. 0001,0002,0003,0005), the user can see that an autonomous message was missed and send a "retrieve all alarms" command.

The General Block

The General block holds the information of the message. It also denotes how its information will be used by the NE. Certain types of large network elements that engage in switching may make an extension to the basic TL1 message. The general block is required for commands that have a payload and varies depending on the command. The General Block can also be used to specify delayed actions. To accomplish this functionality, the general block must contain an order number, date, and time for automatic execution. The delayed action feature of TL1 is helpful for busy operators who must perform service maintenance or run performance analysis. You may schedule actions that will be stored in a remote buffer and executed at a specific date and time.

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