SDH Frame Structure• A single SDH frame is called a Synchronous Transmission Module (STM-1).Transmitted over a duration of 125 µs, the frame consists of 2430 octets organizedas 9 rows of 270 octets each. A single octet in an SDH frame represents a 64 kbpschannel (8 bits every 125 µs), several octets can be aggregated to form containersfor larger data rates.
SDH Section Overhead (SOH)• A relatively large number of 72 octets in an STM-1 frame have been reserved forvarious management and monitoring purposes. This so-called section overhead(SOH) is further divided into a regenerator section overhead (RSOH) and multiplexsection overhead (MSOH).
Administrative Unit (AU-4) and Virtual Container (VC-4)• The actual payload carried in an STM-1 frame is encapsulated in an administrative
unit (AU-4). The AU-4 consists of a VC-4 virtual container comprising 261 columnsplus a 9 octet wide AU-4 pointer that points to the first octet of the VC-4 payloadcontainer.
AU-4 Pointer• The SDH pointer mechanism is a very elegant way of multiplexing multiple datacontainers without the need to align the containers to a common frame start.Thus the frame buffers in SDH multiplexing equipment can be kept small and thetransmission delay due to buffering is minimized.
• The VC-4 container is allowed to float freely within the AU-4. The H1 and H2 pointerbytes form a word with a range of 0 to 782 which indicates the offset, in three byteincrements, between the pointer and the first byte of the VC-4. If the offset has thevalue 0 then the J1 byte of the VC-4 follows immediately after the H3 bytes of theAU-4 pointer
A. Steffen, 20.05.2002, KSy_SDH.ppt 6
ZürcherHochschuleWinterthurSDH Multiplexing Hierarchy - ETSI Branch
Network Elements and TopologiesNetwork Elements and Topologies
A. Steffen, 20.05.2002, KSy_SDH.ppt 8
ZürcherHochschuleWinterthurSDH Network Elements
Digital Cross-Connect (DCS / DXC)used in meshed networksmainly STM-N interfaceslarge switching matrix (1024 STM-1)Wideband DCS: VC-12 granularityBroadband DCS: AU-4 granularity
Add/Drop Multiplexer (ADM)used in ringstwo STM-N line interfaces (East/West)large number of tributary interfacesSTM-1, 140 / 34 / 2 Mbit/s(equipped up to full ring capacity)
Terminal Multiplexer (TMX / PTE)used as concentrator (hub)STM-1/4 (redundant) line interfacemainly 2 Mbit/s tributary interfaces
DefectsPersistent anomalies beyond a maximum time limitLoss of Signal (LOS)Loss of Frame Alignment (LOF)Loss of Pointer (LOP)Alarm Indication Signal (AIS), Remote Defect Indication (RDI)
FailuresPersistent defects beyond a maximum time limit
AlarmsMaintenance signals to alert downstream equipment that a defect or equipment failure has been detected
Fault and Performance MonitoringAnomalies, defects and failures are reported to OAM function
A. Steffen, 20.05.2002, KSy_SDH.ppt 24
ZürcherHochschuleWinterthur
Regenerator Section (RSOH)
LO PTE
Multiplex Section (MSOH)
HO PTE MS TE RS TE RS TE RS TE MS TE HO PTE LO PTE
Higher Order Path (POH)
Lower Order Path (POH)
SDH DefectsSignalling in forward and backward directions
