17-29
Cisco ONS 15454 DWDM Reference Manual, R8.5
78-18343-02
Chapter 17 Performance Monitoring
17.10 Pointer Justification Count Performance Monitoring
17.10 Pointer Justification Count Performance Monitoring
For the MultiService Transport Platform (MSTP), only the MXP_2.5G_10G card uses pointer
justification counts. Pointers are used to compensate for frequency and phase variations. Pointer
justification counts indicate timing errors on 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.
For ONS 15454 ANSI nodes, pointers provide a way to align the phase variations in STS and VT
payloads. The STS payload pointer is located in the H1 and H2 bytes of the line overhead. Clocking
differences are measured by the offset in bytes from the pointer to the first byte of the STS synchronous
payload envelope (SPE) called the J1 byte. Clocking differences that exceed the normal range of 0 to 782
can cause data loss.
For ONS 15454 ETSI nodes, 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-P) or path-generated (PPJC-PGEN-P) positive pointer justifications.
NPJC is a count of path-detected (NPJC-PDET-P) or path-generated (NPJC-PGEN-P) negative pointer
justifications depending on the specific PM name. PJCDIFF is the absolute value of the difference
between the total number of detected pointer justification counts and the total number of generated
pointer justification counts. PJCS-PDET-P is a count of the one-second intervals containing one or more
PPJC-PDET or NPJC-PDET. PJCS-PGEN-P is a count of the one-second intervals containing one or
more PPJC-PGEN or NPJC-PGEN.
A consistent pointer justification count indicates clock synchronization problems between nodes. A
difference between the counts means that the node transmitting the original pointer justification has
timing variations with the node detecting and transmitting this count. For ONS 15454 SONET nodes,
positive pointer adjustments occur when the frame rate of the SPE is too slow in relation to the rate of
the STS-1. For ONS 15454 SDH nodes, positive pointer adjustments occur when the frame rate of the
path overhead (POH) is too slow in relation to the rate of the VC4.
In CTC, the count fields for PPJC and NPJC PMs appear white and blank unless they are enabled on the
card view Provisioning tab.
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