Operation, administration and maintenance

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Operation, Administration and Maintenance or OAM , translated as "Operation, Administration and Maintenance", is a fixed term in public high-speed data networks. These data networks not only transport their payload, but also standardized management information that serves these functions. The international standardization organization ITU-T has defined such management information for the ATM network protocol and for the PDH and SDH methods used in broadband ISDN .

ATM is a network protocol that is transported over PDH or SDH connections. Five levels are defined, the lower three levels F1, F2 and F3 of which relate to the physical layer (radio signals, wired electrical signals or optical signals) and the transmission layer (see OSI layer model ), the upper two levels F4 and F5 of which relate to the Refer to the ATM layer.

  • F1 denotes the lowest level between the transmitter / receiver, where there is no change to the data
  • F2 describes the level between two LT (Line Terminals)
  • F3 denotes the entire transmission path

In SDH and ATM technology there are “paths” and “channels”, with each path containing a number of channels. Because paths and channels are not real lines, but only represent a reserved fraction of the bandwidth of a line, they are called virtual.

  • F4 represents the Virtual Path ( VP ) level
  • F5 represents the virtual channel ( VC ) level

Paths and channels are defined in both SDH and ATM technology, but not in PDH technology. ATM can be transmitted over both PDH and SDH links. If ATM is transmitted via SDH, there are also two levels F4 and F5, namely for both.

OAM at ATM level

The following functions are defined on the ATM layer (F4 and F5).

  • Fault Management - AIS ( Alarm Indication Signal ) and RDI (Remote Defect Indication) are used to notify other network nodes about errors, for example interruptions in a line. CC (Continuity Check) is used for permanent monitoring of a connection
  • Performance monitoring - measurement of cell loss
  • Activation / Deactivation - Activation and deactivation of performance monitoring.

OAM functions can be carried out over the entire route of a VCC (Virtual Channel Connection) or VPC (Virtual Path Connection) (end-to-end), but also over a partial route (segment) by defining segments.

To distinguish between OAM cells and user cells, VCCs 3 and 4 are used at VP level, and values ​​4 and 5 in the PT field of the cell header are used at VC level. The payload of the OAM cells contains an identifier of the function as well as function-specific fields.

literature

  • ITU-T G-SERIES RECOMMENDATIONS, TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS
    • Recommendations G.770-G.779: Operations, administration and maintenance features of transmission equipment