Datasheet

15-4
Cisco ONS 15454 SDH Reference Manual, R7.0
October 2008
Chapter 15 Performance Monitoring
15.3 Pointer Justification Count Performance Monitoring
Note The E1 card and STM-1 card can monitor far-end IPPM. For all other cards listed in Table 15-2, far-end
IPPM is not supported. However, SDH path PM parameters can be monitored by logging into the far-end
node directly.
The ONS 15454 SDH performs IPPM by examining the overhead in the monitored path and by reading
all of the near-end path PM values in the incoming direction of transmission. The IPPM process allows
the path signal to pass bidirectionally through the node completely unaltered.
For detailed information about specific IPPM parameters, locate the card name in the following sections
and review the appropriate definition.
15.3 Pointer Justification Count Performance Monitoring
Pointers are used to compensate for frequency and phase variations. Pointer justification counts indicate
timing errors on SDH networks. When a network is out of synchronization, jitter and wander occur on
the transported signal. Excessive wander can cause terminating equipment to slip.
Slips cause different effects in service. Voice service has intermittent audible clicks. Compressed voice
technology has short transmission errors or dropped calls. Fax machines lose scanned lines or experience
dropped calls. Digital video transmission has distorted pictures or frozen frames. Encryption service
loses the encryption key causing data to be transmitted again.
Pointers provide a way to align the phase variations in VC4 payloads. The VC4 payload pointer is located
in the H1 and H2 bytes of the AU pointers section and is a count of the number of bytes the VC4 path overhead
(POH) J1 byte is away from the H3 byte, not including the section overhead bytes. Clocking differences are
measured by the offset in bytes from the pointer to the first byte of the VC4 POH called the J1 byte.
Clocking differences that exceed the normal range of 0 to 782 can cause data loss.
There are positive (PPJC) and negative (NPJC) pointer justification count parameters. PPJC is a count
of path-detected (PPJC-Pdet) or path-generated (PPJC-Pgen) positive pointer justifications. NPJC is a
count of path-detected (NPJC-Pdet) or path-generated (NPJC-Pgen) negative pointer justifications
depending on the specific PM name.
A consistent pointer justification count indicates clock synchronization problems between nodes. A
difference between the counts means the node transmitting the original pointer justification has timing
variations with the node detecting and transmitting this count. Positive pointer adjustments occur when
the frame rate of the POH is too slow in relation to the rate of the VC4.
You must enable PPJC and NPJC performance monitoring parameters for LTE cards. See Table 15-2 on
page 15-3 for a list of Cisco ONS 15454 SDH LTE cards. In CTC, the count fields for PPJC and NPJC
PM parameters appear white and blank unless they are enabled on the card view Provisioning tab.
For detailed information about specific pointer justification count PM parameters, locate the card name
in the following sections and review the appropriate definition.
15.4 Performance Monitoring Parameter Definitions
Table 15-3 gives definitions for each type of performance monitoring parameter found in this chapter.