Cisco Headend System Release 2.7 Guide De Montage
Chapter 1 Introducing GQAM Software Version 4.2.1
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CR 82667: Packets With No Payload Data No Longer Cause Pixilated Video
Previously, GQAMs did not filter “empty adaptation field only” packets from
incoming streams. A new grooming technique adopted by a single Mux vendor uses
program map table (PMT) extensions of empty adaptation fields to groom video
streams rather than the more conventional NULL packets to “stuff” variable bit rate
(VBR) to constant bit rate (CBR) streams. This reduces the GQAM’s ability to correct
clock accuracy errors which leads to occasional pixilation issues with video.
Previously, this issue was resolved with a Netcrypt patch that filtered the empty
adaption fields so they did not reach the GQAM. With the introduction of CR 82667,
the GQAM is compatible with this grooming method and the Netcrypt patch is no
longer required.
CR 86703: Trick Modes Occasionally Caused Dejitter Buffer Overflows on
GQAMs
Previously, using VOD trick modes (Pause, FF, or Rewind) on three or more set-tops
simultaneously could cause the GQAM jitter buffers to overflow. This overflow
occasionally caused momentary video impairments on other streams on both the
same QAM frequency and adjacent QAM frequencies. CR 86703 corrected this issue.
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