Cisco ONS 15454 SDH Specifications download pdf (Page 320)

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Cisco ONS 15454 SDH Installation and Operations Guide, R3.3

May 2002

Chapter 8 SDH Performance Monitoring

Enabling Pointer Justification Count Parameters

8.4 Enabling Pointer Justification Count Parameters

Pointers provide a way to align the phase variations in VC4 payloads. Pointer justification counts

indicate frequency adjustments on SDH networks. The VC4 payload pointer is located in the H1 and H2

bytes of the AU pointers section and it is a count of the number of bytes the VC4 POH J1 byte is away from

the H3 byte, not including the section overhead bytes.

When a network is out of synch, jitter, and wander occurs on the transported signal. Excessive wander

can cause terminating equipment to slip. It also causes slips at the SDH and PDH boundaries. 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.

Figure 8-11 shows pointer justification count parameters on the Performance Monitoring screen. You

can enable PPJC and NPJC performance monitoring parameters for LTE cards. See Table 8-4 on

page 8-18 for a list of Cisco ONS 15454 SDH LTE cards.

Figure 8-11 Viewing pointer justification count parameters

To avoid problems with data when timing differences exist, dummy bytes can be inserted into the VC4.

There are negative (NPJC) and positive (PPJC) pointer justification count parameters. NPJC is a count

of path-detected (NPJC-Pdet) or path-generated (NPJC-Pgen) negative pointer justifications. H3 bytes

are called negative justification bytes and carry extra payload data for one frame during a pointer

decrease.

PPJC is a count of path-detected (PPJC-Pdet) or path-generated (PPJC-Pgen) positive pointer

justifications. The three bytes following the last H3 byte in the VC4 are called positive justification bytes

and carry three dummy bytes of information for one frame during a pointer increment.

A consistent large 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.

71050

Pointer justification counts Performance tab Card view

1 2 ... 315 316 317 318 319 320 321 322 323 324 325 ... 503 504

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Cisco ONS 15454 SDH Specifications Page 320