Datasheet

11-18
Cisco ONS 15454 SDH Reference Manual, R7.0
October 2008
Chapter 11 Circuits and Tunnels
11.11 Path Signal Label, C2 Byte
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.
11.11 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 11-8 provides the C2
byte hex values.
If a circuit is provisioned using a terminating card, the terminating card provides the C2 byte. A
low-order path circuit is terminated at the cross-connect card and the cross-connect card generates the
C2 byte (0x02) downstream to the VC terminating cards. The cross-connect generates the C2 value
(0x02) to the terminating card. If an STM-N circuit is created with no terminating cards, the test
equipment must supply the path overhead in terminating mode. If the test equipment is in pass-through
mode, the C2 values usually change rapidly between 0x00 and 0xFF. Adding a terminating card to an
STM-N circuit usually fixes a circuit having C2 byte problems.
Table 11-7 ONS 15454 SDH Cards Capable of J2 Path Trace
J2 Function Cards
Transmit and Receive E1-42
Receive Only STM1E-12
Table 11-8 STM Path Signal Label Assignments for Signals
Hex Code Content of the STM Synchronous Payload Envelope (SPE)
0x00 Unequipped
0x01 Equipped—nonspecific payload
0x02 Tributary unit group (TUG) structure
0x03 Locked tributary unit (TU-n)
0x04 Asynchronous mapping of 34,368 kbps or 44,736 kbps into container-3 (C-3)
0x12 Asynchronous mapping of 139,264 kbps into container-4 (C-4)
0x13 Mapping for asynchronous transfer mode
(ATM)
0x14 Mapping for Distributed Queue Dual Bus (DQDB)
0x15 Asynchronous mapping for Fiber Distributed Data Interface
(FDDI)
0xFE 0.181 Test signal (TSS1 to TSS3) mapping SDH network (see ITU-T G.707)
0xFF Virtual container-alarm indication signal (VC-AIS)