SDH Networks - Total Management Network (TMN)

TMN in the SDH network

The principle of telecommunications management network(TMN) technology was established in 1989 with the publication by the CCITT(now ITU-T) of Recommendation M.3010. 

The functions of a TMN are summed up in the expression “Operation, administration, maintenance and provisioning” (OAM&P). This includes monitoring the network performance and the checking of error messages, among other things. To provide these functions, TMN uses object-oriented techniques based on the OSI reference model. The TMN model comprises one manager handling several agents. 

The agents in turn each handle several managed objects(MO). The manager is included in the operating system (OS) which forms the “control center” for the network as a whole or in part. In a SDH network, the agents are located in the  network elements (NE),  such as switches, etc. AMO may be a physical unit (e.g. a plug-in card, multiplex section, etc.) but can also occur as a logical element (e.g. a virtual connection). 

TMN also distinguishes between logical management units. For  example, one management unit operates at network level, handling individual NEs. Another management unit operates at the service level, e.g. for  monitoring billing charges. These tasks are performed in modern telecommunications networks by using the common management information protocol (CMIP). 

The simple network management protocol(SNMP) is often mentioned in this context; this is basically a simplified form  of CMIP.  SNMP is mainly used in data communications, however, and cannot cope with the requirement of large telecommunications networks. The Q3 interface,  which is where the exchange of data between manager and agent takes  place, is the point of reference for CMIP.  

CMIP is also used where several TMNs or their  managers are linked  together  via the X interface. Since large quantities of data are not generally required for exchanging information in the TMN, the capacity of the embedded communication channels(ECC) or data communication channels(DCC) is sufficient when managing SDH networks. 

Channels D1 to D3 with a capacity of 192kbit/s(DCCP) are used for SDH-specific NE management. Channels D4 to D12 with a capacity of 576kbit/s(DCCM) can be used for non SDH specific purposes.

To distinguish the implementation in the section overhead (SOH) data channels from the Q interface, the term QECC protocol is used. To summarize, such networks are called SDH management networks (SMN); these are primarily responsible for managing network elements. SMNs can also be subdivided into sub-networks(SMS).