Cisco Headend System Release 2.5 User Guide

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DHCT Status Reporting Utility

78-738186-01 Rev B

DHCT Delay Value Saturation Report,

Continued

Understanding the DHCT Delay Value Saturation Report

There are two parts to the DHCT Delay Value Saturation Report:
•

A graphical representation of the distribution of the various delay values of

DHCTs assigned to each QPSK modulator on the system
Note: Read Graphical Distribution of DHCT Delay Values, next in this section,

for help in interpreting the graphical representation.

•

A numerical analysis of the graphical representation of the various delay values of

DHCTs assigned to each QPSK modulator on the system
Note: Read Delay Value Analysis, later in this section, for help in interpreting the

graphical representation.

Graphical Distribution of DHCT Delay Values
The first part of the DHCT Delay Value Saturation Report contains a graph that

shows the distribution of the various delay values of DHCTs assigned to a specific

QPSK modulator. In the following example, the modulator is QPSKMOD1. The

horizontal axis of the graph plots units of time in microseconds (ms); the vertical axis

(not marked on the report) plots the relative number of DHCTs with each delay

value.

DHCT Delay Value Saturation Report - QPSKMOD1

  |------------------------------------------------------------------------------------------------------------------------------|
  | T    |
  |    | |
  | |    |
  |    T TT |
  | | ||     |
  | |T |T T     |
  | || T|T|    |
  | |T T||||     |
  | T T|| ||||T    |
  | | T||T T|||T|     |
  | T TTTT||| T|||T|    |
  | TTT T| T TTT|||||T|||||TT    |
  | TTTTTTTTTTT TT TTT||||||TT|||||T|T |
  | TTTT TTTTT||||TTT|T|TTTTTTTTTTTTT TTTTTTTT|||||||||||||||TT     |
  |+------+-----+---------+--------------+---------------+--------------+--------------+---------------+--------+-----+---+---+--|
  50 100 134 200 300 400 500 600 700 761 800 825 850 8

  =============>|<======================>|<====================================================================>|<===============
  ^ ^       ^ ^
  | | | |
TOO Far from Headend CORE POPULATION (300-761ms) Close to Headend Next to QPSK
  Distant but Within Range

The data in this graph shows that the QPSK called QPSKMOD1 supports two

distinct clusters of DHCTs. The first cluster of DHCTs is located close to the

headend, as confirmed by the Close to Headend label along the x-axis. These

DHCTs have a delay value centered around 700 ms.
The second cluster of DHCTs is located farther from the headend, as confirmed by

the Far from Headend but Within Range label along the x-axis. These DHCTs have

a delay value centered around 400 ms.
Having multiple clusters of DHCTs, as illustrated in this example, is normally not a

problem. Non-responding DHCTs begin to appear only when delay values fall

below the 134 microsecond range, as designated by the Too Distant label along the

x-axis.