7.0 Gateway NE

Gateway NE has the capability to route input messages from the EMS to the NEs. And it also routes the autonomous messages from the NEs to the EMS. This article speaks more about this GNE in detail.

7.1 TL1 Deployment Scenario

In TL1, there are two major types of NE deployment. One is the deployment in a ring or bus topology and the other is deployment in a linear topology. Systems such as SONET, SDH, etc., are examples of deployment in a ring topology. A system such as IDLC is an example for deployment in linear or non-ring topology.
SONET systems interconnect the devices in a ring manner. Any command to the NEs should pass through this ring. IDLC system interconnects the devices in a linear manner. A manager, which communicates with the devices, requires a TCP/IP connection.

7.2 Need for Gateway GNE

In SONET systems, a command can reach an NE after passing the intermittent NEs. A device as such cannot pass on the command. Hence, at least one of the devices should be a gateway element so that it passes the command to the intended device.

Figure 1.0

In SONET systems, apart from the normal operations channel, there is another channel called Data Communication Channel (DCC). Used only for administrative and management operations. A command, sent through DCC travels through all NEs in the path before reaching the target NE. NEs present in between the GNE and the ENDNE (target NE) are called Intermediate NEs (INEs).

Figure 2.0

For security reasons, some NEs have restrictions on the number of "simultaneous user sessions". While managing such elements, the management applications and the craft operators face a "resource constraint problem" accentuated by the user session restrictions. Installing a GNE and routing the messages from multiple operators via the GNE solve this problem. Refer to figure 3.0.

Figure 3.0 

Note :You can correlate GNE with the proxy feature of other management protocols. Without GNE, the management of TL1 networked devices will become difficult.

7.3 How GNE Works

A gateway network element has the ability to route information between NEs and the OSSs. It holds a persistent connection with the manager to enable message routing. The TIDs in the input command help GNE to identify the target NE. GNE maintains the list of TIDs of the NEs connected to it. Whenever GNE receives a TL1 input message, it routes the message to the appropriate NE by referring the TID. The GNE will also route the autonomous messages from the NEs to the OSS.
If the device is IP based, then the GNE opens up a TCP/IP connection, sends the command, and then closes the TCP/IP connection. In a SONET system, there is a dedicated channel called Embedded Operations Channel (EOC). GNE uses separate EOC commands such as ENT-EOCRE, ED-EOCRE, DLT-EOCRE, RTRV-EOCRE (refer to GR199) to add, delete, edit, and retrieve EOC entries in the GNE table.
Some networks use multiple communication channels, such as TCP/IP and X2.5. The routing entries for such channels will be different. Hence, for every protocol, you have to implement TL1 commands, similar to those of EOC commands. This enables the GNE to route messages in these channels over the specified protocol.

7.4 Building TL1 Agent for GNE

For an NE to act as a gateway NE, its agent should support the following.
· It should maintain  a routing table (TID, subtended NE details(e.g. IP address and portnumber).
· It should also implement TL1 Messages for manipulating routing table.
The differentiation between NE and GNE lies in the agent that is installed in it. GNE’s agent should have the capability to interpret the commands and identify the target NE. It should then send the command to the target NE, by opening a session. If the command is intended for the GNE itself, it executes the command on itself.