STS payload pointer (H1, H2)
{"Image DocumentName": "STS payload pointer (H1, H2)", "Image ImageDescription": "I - Increment Bits. D - Decrement Bits. NDF Not Set = NDF Set = Concatenation Flag. H1. H2. 1. X. I. D Not. Used. New Data Flag. Pointer Offset. The content of the STS payload pointer bytes is shown above. Bits 7 and 8 of H1 together with bits 1-8 of H2 carry the pointer offset. If the first byte of the next SPE frame was the byte immediately following the H3 byte, the offset would contain the value 00 hex. The bits of the pointer offset are grouped into I bits and D bits. These bits are used to flag increment operations and decrement operations respectively. A pointer processor monitoring an incoming pointer keeps track of the current offset and continuously compares the next received value with the current value. An increment operation is detected when the I bits of the received value are inverted with respect to the current value. Similarly, a decrement operation is detected when the D bits of the received value are inverted with respect to the current value. Bits 1-4 of H1 contain the new data flag. This flag is used to notify downstream pointer processors of a change in the pointer value to a new value unrelated to the previous value. This would be used at a cross-connect system for example, when an outgoing STS-1 that was carrying an SPE from one particular incoming STS-1 suddenly starts carrying an SPE from a different incoming STS-1 due to a provisioning command. Since there is no phase relationship between the two SPEs, the pointer value will change. The new data flag is set to 1001 in the first STS-1 frame that contains the new pointer offset value, and then returns to its normal value of When an STS-1 is concatenated to another STS-1, its pointer offset contains the value This is the concatenation flag and it effectively disables the pointer processing circuitry for this STS-1. When a failure is detected at the path layer, path AIS is generated downstream to provide a keep-alive signal. Path AIS is detected by all ones in the H1-2 pointer bytes. 70.", "Image XResolution": "37", "Image YResolution": "37", "Image ResolutionUnit": "Pixels/Centimeter", "Image Software": "SlidePlayer", "Image YCbCrPositioning": "Centered"}