H3C Technologies H3C SR8800 - Manual (Page 52)

45
SONET SDH Rate
STS-3 STM-1 155.52 Mbps
STS-12 STM-4 622.080 Mbps
STS-48 STM-16 2488.320 Mbps
Overhead bytes
SDH provides hierarchical monitoring and management functions. It provides section level monitoring
and path level monitoring. Section level monitoring is subdivided into regenerator section level
monitoring and multiplex section level monitoring, while the path level monitoring is subdivided into
higher-order path level monitoring and lower-order path level monitoring. These monitoring functions are
implemented using overhead bytes.
NOTE:
SDH provides a variety of overhead bytes, but only those involved in E-CPOS configuration are discussed
in this section.
• SOH
The SOH consists of the RSOH and the MSOH.
The regeneration section trace message J0 is included in the RSOH to send the section access point
identifier repeatedly. Based on the identifier, the receiver can make sure that it is in continuous
connection with the sender. This byte can be any character in the network of the same operator.
If the networks of two operators are involved, the sending and receiving devices at network
borders must use the same J0 byte. With the J0 byte, operators can detect and troubleshoot faults
in advance or use less time to recover networks.
• POH
The payload of an STM-N frame includes the path overhead (POH), which monitors low-speed
tributary signals.
While the SOH monitors the section layer, the POH monitors the path layer. The POH is divided
into the higher-order path overhead and the lower-order path overhead.
The higher-order path overhead monitors lower-level paths.
Similar to the J0 byte, the higher-order VC-N path trace byte J1 is included in the higher-order path
overhead to send the higher-order path access point identifier repeatedly. Based on the identifier,
the receiving end of the path can make sure that it is in continuous connection with the specified
sending end. The sender and the recipient must use the same J1 byte.
In addition, the path signal label byte C2 is included in the higher-order path overhead to indicate
the multiplexing structure of VC frames and the properties of payload such as whether the path is
carrying services, what type of services are carried, and how they are mapped. The sender and
the recipient must use the same C2 byte.