What is DDM for Optical Transceiver?
Today, optical transceivers from vendors in the market basically support digital diagnostic monitoring (DDM) function, which can monitor optical transceiver parameters (e.g., operating temperature, transmit optical power and receive optical power, etc.) in real time to help network management units to predict and locate faults. This article will focus on the optical transceiver DDM and the methods to query the optical transceiver DDM information for you.
What Does DDM Mean?
DDM (Digital Diagnostic Monitoring) follows the SFF-8472 multi-source protocol (developed by the industry organization SFF Committee) and is a means of real-time parameter monitoring of optical transceivers that allows users to monitor the parameters of the optical transceiver in real time, including received optical power, transmitted optical power, operating temperature, supply voltage and laser bias current.
Brief Description of the DDM Principle
Optical transceiver DDM works based on the standard parameter values defined in the SFF-8472 protocol, which regulates the standard parameter values or ranges to be followed by the software and hardware of optical transceivers and network equipment (such as switches, etc.), ensuring the interoperability of the products provided by different network equipment suppliers and optical transceiver suppliers, in short, a common set of OAM parameters can be shared by the entire communications industry. It is worth noting that some of today’s products are now more accurate than the requirements of the protocol. The following table shows the SFF-8472 protocol parameter standards for optical transceivers.
DDM Function Detailed Explanation
As can be seen from the above, optical transceiver DDM is a means of monitoring parameters, it has not only alarm and warning functions, but also fault prediction and fault location functions.
As we all know, only when the working environment of the optical transceiver meets the standard, it can ensure its best performance. If the environmental parameters of the optical transceiver are out of the standard range, it will lead to the degradation of the performance of the optical transceiver and the occurrence of false codes. And support DDM optical transceiver when its environmental parameters exceed the specified standard range (such as voltage exceeds the specified range, receive optical power overload, temperature exceeds the operating temperature range, etc.), it will send an alarm to the system, showing that the transceiver is in a bad state, at this time the transmitter will stop sending data, and similarly the receiver will also refuse to receive data.
Fault prediction refers to finding potential link failures before system performance is affected, that is, allowing network managers to ensure uninterrupted service and repair failures by switching services to alternate links or replacing potentially failing optical transceivers in advance of the failure. The failure prediction of optical transceiver DDM mainly refers to the monitoring of laser bias current to predict the deterioration of the laser, so as to ensure its replacement before it breaks down. Principle: The optical transceiver will control the output power will be at a stable level by increasing the bias current of the laser, while the aging of the laser (caused by long working hours) will reduce the quantum efficiency of the laser, and the bias current of the laser will also be affected by it, thus affecting the optical power of the optical transceiver.
Quickly locating the fault location is critical for business systems. The DDM-enabled optical transceivers can quickly locate link faults through comprehensive analysis of alarm flags or alarm conditions, monitoring parameter information, and optical transceiver pinout, thereby reducing system fault repair time.
How to Check the DDM Information?
Optical transceiver DDM information can be viewed directly through SNMP and commands. For details, see the following.
1. Check DDM Information through SNMP
Before understanding the detailed operation steps, let’s have a brief understanding of SNMP protocol.
SNMP (i.e. Simple Network Management Protocol) is a standard protocol dedicated to managing network nodes in IP networks, which mainly consists of three key components: network management system, managed devices, and agents. A managed device is a network node that exists in the managed network as an SNMP manager. These managed devices can be routers, servers, switches, bridges, hubs, computers, printers. An agent is a network management software transceiver that exists in the managed device and mainly controls the management information of the local machine, delivered in an SNMP-compatible format. Network Management System (i.e. NMS) is mainly used to run applications, monitor and control the managed devices, and it can provide a lot of computing and memory resources needed for network management.
A management information base (i.e., MIB) is a collection of management objects that are accessed through SNMP. the MIB is stored in a tree structure, and each SNM device (SNMP Agent) has its own MIB, such as CISCO-ENTITY-SENSOR-MIB.
An object identifier (i.e., OID) is a key value with a unique identifier provided by the SNMP Agent. Usually the OID is a long string of numbers with the name of the parent node as the prefix of the child node name, separated by dots.
(1) Monitoring DDM Information through SNMP
When your optical transceiver supports DDM, you can enable this function and then use Net-SNMP (snmpwalk) to query it.
Take Cisco ASR9k switch as an example, read the received optical power and transmitted optical power of the optical transceiver through SNMP.
Note: The Cisco ASR9k switch is IOS-XR operating system, version 5.3.1. the MIB is “CISCO-ENTITY-SENSOR-MIB” and the OID is 188.8.131.52.184.108.40.206.220.127.116.11.1.
A. Executing the following command through the Net-SNMP tool.
B. Then the command line interface will display the received optical power and transmitted optical power values.
2 View DDM Information by Command
Since the MIB and OID will be different for different brands of equipment vendors, some equipment can also directly obtain DDM information through simple commands.
For example, Brocade switch can get the DDM information of a certain optical transceiver by the command “show optic port-number”.
Huawei switches can view the interface optical transceiver DDM information by the display command.
Execute the command display transceiver [ interface interface-type interface-number | slot slot-id ] [ verbose ] to view the information of the optical transceiver on the device interface.
Execute the command display transceiver diagnosis interface [ interface-type interface-number ] to display the optical transceiver diagnosis parameters.
Through the above introduction, I believe you must have a full understanding of DDM, and know how to query the optical transceiver DDM information. However, it should be noted that not all optical transceivers support DDM, and you must check whether the optical transceiver supports this function before querying the DDM information of the optical transceiver. Otherwise, everything is in vain.