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10-15
Cisco ONS 15454 SDH Reference Manual, R5.0
April 2008
Chapter 10 Circuits and Tunnels
10.9 Path Trace
10.9 Path Trace
SDH J1 and J2 path trace are repeated, fixed-length strings composed of 64 consecutive bytes. You can
use the strings to monitor interruptions or changes to circuit traffic. Table 10-5 shows the
ONS 15454 SDH cards that support J1 path trace. Cards that are not listed in the table do not support the
J1 byte.
Table 10-6 shows cards that support J2 path trace.
If the string received at a circuit drop port does not match the string the port expects to receive, an alarm
is raised. Two path trace modes are available:
• Automatic—The receiving port assumes that the first string it receives is the baseline string.
• Manual—The receiving port uses a string that you manually enter as the baseline string.
10.10 Path Signal Label, C2 Byte
One of the overhead bytes in the SDH frame is the C2 byte. The SDH standard defines the C2 byte as
the path signal label. The purpose of this byte is to communicate the payload type being encapsulated
by the high-order path overhead (HO-POH). The C2 byte functions similarly to EtherType and Logical
Link Control (LLC)/Subnetwork Access Protocol (SNAP) header fields on an Ethernet network; it
allows a single interface to transport multiple payload types simultaneously. Table 10-7 provides the C2
byte hex values.
Table 10-5 ONS 15454 SDH Cards Capable of Path Trace
J1 Function Cards
Transmit and receive E3-12
DS3i-N-12
G-Series
ML-Series
Receive only OC3 IR 4/STM1 SH 1310
OC12/STM4-4
OC48 IR/STM16 SH AS 1310
OC48 LR/STM16 LH AS 1550
OC192 LR/STM64 LH 1550
Table 10-6 ONS 15454 SDH Cards Capable of J2 Path Trace
J2 Function Cards
Transmit and Receive E1-42
Receive Only STM1E-12