Specifications

Alarm Descriptions
VTM Series Installation and Operation Handbook
5-12
ETR 290 1
st
Priority
The ETR 290 1
st
Priority menu contains the TS Sync Loss alarm, Sync Byte Error
alarm, PAT Error alarm, Continuity Count Error alarm, PMT Error alarm, and PID
Error alarm.
TS Sync Loss
The actual synchronization of the transport stream (TS) depends upon two things.
First, synchronization depends upon the number of correct sync bytes necessary for the
device to synchronize. Secondly, synchronization depends upon the number of
distorted sync bytes that the device cannot control. Five consecutive sync bytes should
be sufficient for sync acquisition, and two or more consecutive corrupted sync bytes
should indicate sync loss. The TS Sync Loss alarm activates when two or more
consecutive corrupted sync bytes occur for a period in excess of the duration setting.
Sync Byte Error
Sync Byte Error activates as soon as the correct sync byte (0x47) does not appear after
188 or 204 bytes. This structure is used throughout the channel encoder and decoder
chains for synchronization. Every sync byte is checked for correctness since the
encoders might not necessarily check the sync byte. Some encoders use the sync byte
flag signal on the parallel interface to control the randomizer re-seeding and byte
inversion without checking that the corresponding byte is a valid sync byte.
PAT Error
The PAT Error alarm activates when the PAT table is missing for a period in excess of
the duration setting.
Continuity Count Error
The Continuity Count Error alarm preconditions are “Incorrect Packet Order” and
“Lost Packet.” The preconditions could cause problems for the Integrated Receiver
Decoder (IRD), which is not equipped with additional buffer storage and intelligence.
It is not necessary for the test equipment to distinguish between these two
preconditions. The conditions are logically OR-ed together with the third precondition
into one indicator. “Packet Loss” shows that a packet loss can occur on any
asynchronous transfer mode (ATM) link, where one lost ATM packet would cause the
loss of a complete MPEG-2 packet. The precondition “a packet occurs more than
twice” could be symptomatic of a larger problem which the service provider should
keep under observation.
PMT Error
The PMT Error alarm occurs when there is no PMT and the corresponding program is
not decodable.