The terms EMS, NMS and OSS are often misunderstood and used interchangeably. This can, sometimes, lead to a confusion on which system can do what functions. Therefore I am attempting to clarify these terms in a simple way. This may help you in making informed decisions when procuring management systems.


But before understanding the terms for management systems, one should understand what FCAPS is, in relation to management systems. In fact every management system should perform FCAPS. The five alphabets in FCAPS stand for the following:


F- Fault Management – i.e.  Reading and reporting of faults in a network; for example link failure or node failure.


C-Configuration Management- Relates to loading/changing configuration on network elements and configuring services in network.


A-Account Management- Relates to collection of usage statistics for the purpose of billing.


P- Performance Management- Relates to reading performance related statistics, for example reading utilization, error rates, packet loss, and latency.


S-Security Management- Relates to controlling access to assets of network. This includes authentication, encryption and password management.


Ideally, any management system should do all of the FCAPS functions described above. However, some commercial solutions allow only some of the FCAPS functions. In that case, there will be a need for additional management system to do the rest of the FCAPS functions. The FCAPS applies to all types of management systems including EMS, NMS and OSS.


Now that we covered the general functions of management systems, let’s understand the terms, EMS, NMS and OSS.


EMS stands for “Element Management System”. It is also called Element manager. EMS can manage (i.e. FCAPS) a single node/element or a group of similar nodes. For example it can configure, read alarms etc. on a particular node or group of nodes.


NMS (Network Management System) on the other hand manages a complete network i.e. it covers all the functions of EMS as well as does FCAPS with relation to the communication between different devices.


So the difference between EMS and NMS is that NMS can understand the inter-relationship between individual devices, which EMS cannot. Although EMS can manage a group of devices of the same type but it treats all the devices in a group as single devices and does not recognize how individual devices interact with one another.


So to sum up:

  1. I.e. NMS = EMS + link/connectivity management of all devices+ FCAPS on network basis.


NMS can manage different types of network elements/technologies of a same vendor.


An example would clarify. An EMS would be able to give individual alarms on nodes. But NMS can correlate the alarms on different nodes; it can, thus find out root cause alarms when a service is disrupted. It can do so because it has network wide view and intelligence.


OSS (Operation Support Systems) takes a step further. It can not only manage a single vendor but can also manage multiple vendors. OSS will be needed in addition to vendor specific NMS. OSS will interact with individual NMSs and provide one dashboard for FCAPS management.


OSS, thus, can give a single view of the network end to end including all vendors. An example would be a service provisioning tool that can create an end to end service between Cisco and Juniper routers. This would need an OSS that can talk to the NMS of the both vendors for this purpose or can even configure the network elements directly.


After explaining the terms EMS, NMS and OSS, I would end up my blog by asking


  • Does your management system do all the FCAPS functions or some?


  • Do you prefer to have one network management system that does all FCAPS or different ones depending on different specialized functions?


Or may be I should ask, are you using any management system at all


Would love to hear your opinion!