Overhead Bytes; Cpos Interface Application Scenario - HP HSR6800 Configuration Manual

Overhead bytes

SDH provides layered monitoring and management of precise division.
It provides monitoring at section and channel levels, where sections are subdivided into regenerator and
multiplex sections, and channels are subdivided into higher-order and lower-order paths. These
monitoring functions are implemented using overhead bytes.
SDH provides a variety of overhead bytes, but only those involved in CPOS configuration are discussed
in this section.
SOH
The section overhead (SOH) is further classified into the regenerator section overhead (RSOH) and the
multiplex section overhead (MSOH).
The regeneration section trace message J0 is included in RSOH to repeatedly send the section access
point identifier, based on which the receiver can make sure 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.
The SOH monitors the section layer, and the POH monitors the path layer. The POH is divided into the
higher-order path overhead and the lower-order path overhead.
Higher-order path overhead monitors paths at the VC-4/VC-3 level.
Similar to the J0 byte, the higher-order VC-N path trace byte J1 is included in the higher-order path
overhead to repeatedly send the higher-order path access point identifier, based on which the receiving
end of the path can make sure it is in continuous connection with the specified sender. 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
traffic, what type of traffic are carried, and how they are mapped. The sender and receiver must use the
same C2 byte.

CPOS interface application scenario

CPOS is used to enhance the capability of a device in low-speed access redistribution. STM- 1 CPOS is
especially suitable for aggregating E1/T1 channels.
Some government agencies and enterprises use low-end and mid-range devices to access transmission
networks through E1/T1 leased lines. Users who require bandwidth between E1 and T3 (44 Mbps), for
a data center for example, lease multiple E1/T1 lines.
The bandwidth of all these users is aggregated to one or more CPOS interfaces through a transmission
network, and then connected to a high-end device where the low-end devices are uniquely identified by
timeslots.
In actual applications, the connection between these low-end devices and the CPOS interfaces might
span more than one transmission network and as such, might require relay. This is similar to the scenario
where low-end devices are connected to a high-end device through one or multiple E1/T1 leased lines.
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