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An STM-1 frame. The first nine columns contain the overhead and the pointers. For the sake of simplicity, the frame is shown as a rectangular structure of 270 columns and nine rows but the protocol does not transmit the bytes in this order. For the sake of simplicity, the frame is shown as a rectangular structure of 270 columns and nine rows.
The STM-1 frame is on the basic transmission format for SDH (Synchronous Digital Hierarchy). An STM-1 frame has a byte-oriented structure with 9 rows and 270 columns of bytes, for a total of 2,430 bytes (9 rows * 270 columns = 2430 bytes). Each byte corresponds to a 64 kbit/s channel. [3] TOH: Transport Overhead (RSOH + AU4P + MSOH)
In SDH, the Synchronization Status Message (SSM) provides traceability of synchronization signals and it is therefore required to extend the SSM functionality to Synchronous Ethernet to achieve full interoperability with SDH equipment. In SDH, the SSM message is carried in fixed locations within the SDH frame.
An STM-4 frame consists of 36 rows each containing 270 bytes. This is a direct multiple of STM-1, which consists of 9 rows each containing 270 bytes. The frame frequency of 32 kHz has also been chosen as a 4x multiple of that of STM-1, so that one byte of frame corresponds to the transmission capacity of a 64 kbit/s channel.
The frame structure defined in G.709 is constructed of 4 areas: OPUk [3] is the area in which payload is mapped. ODUk [3] contains the OPUk with additional overhead bytes (e.g. TTI, BIP8, GCC1/2, TCM etc.). OTUk [3] is the section and includes framing, TTI, BIP8 and GCC0 bytes.
After traversing SDH paths, the traffic is processed in the reverse fashion: virtual concatenation path processing to recreate the original synchronous byte stream, followed by decapsulation to converting the synchronous data stream to an asynchronous stream of Ethernet frames. The SDH paths may be VC-4, VC-3, VC-12 or VC-11 paths.
Ethernet over PDH over SONET/SDH (EoPoS) is one of many techniques that provided Ethernet connectivity over non-Ethernet networks. EoPoS is a standardized method for transporting native Ethernet frames over the existing telecommunications optical infrastructure use both the established Plesiochronous Digital Hierarchy (PDH) and Synchronous Digital Hierarchy (SONET/SDH) transport technologies.
Packet over SONET/SDH, abbreviated POS, is a communications protocol for transmitting packets in the form of the Point to Point Protocol (PPP) over SDH or SONET, which are both standard protocols for communicating digital information using lasers or light emitting diodes (LEDs) over optical fibre at high line rates. POS is defined by RFC 2615 ...