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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. The receiving end of the path
uses this identifier to make sure it is in continuous connection with the specified sender. The sender and
the receiver 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, including the following:
• Whether the path is carrying traffic.
• What type of traffic is carried.
• How the VC frames are mapped.
The sender and receiver must use the same C2 byte.
CPOS interface application scenarios
CPOS E1/T1 interfaces are typically used to aggregate E1 and T1 lines, as shown in Figure 4.
In actual applications, the connection between low-end devices and the CPOS interfaces might span
more than one transmission network and might require relay. This is similar to the scenario where
low-end devices are connected to a high-end device through one or multiple leased lines.
Figure 4 CPOS E1/T1 interface application scenario
Feature and hardware compatibility
Hardware CPOS interface
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