H3C Technologies H3C SR8800 - Manual (Page 40)

33
• SOH
Section overhead (SOH) consists of regenerator section overhead (RSOH) and multiplex section
overhead (MSOH).
The regeneration section trace message J0 is included in 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 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.
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 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 J1 byte at the receiving and transmission ends should be matched.
In addition, the path signal label byte C2 is also included in the higher-order path overhead to
indicate the multiplexing structure of VC frames and the property of payload, for instance, whether
the path is carrying services, what type of services 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 router in low-speed access aggregation. STM-1 CPOS is
especially suitable for aggregating E1/T1 channels.
At present, some government agencies and enterprises use low-end and mid-range network devices to
access transmission networks through E1/T1 leased lines. Users who require bandwidth between E1 (2
Mbps)/T1 (1.5 Mbps) and E3 (34 Mbps)/T3 (44 Mbps), 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 router where the low-end routers are uniquely identified by
timeslots.
In actual applications, the connection between these low-end routers and the CPOS interfaces may span
more than one transmission network and as such, may 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. Figure
11 shows such an application scenario.