107
Making Measurements
Measuring Cell Transfer Delay and Cell Delay Variation
Measuring Cell Transfer Delay and Cell Delay
Variation
Description Cell transfer delay may occur because of physical layer switching and
propagation delay over long transmission paths. At the ATM layer,
queueing and cell multiplexing may cause additional and varying delay
(CDV). CDV is accentuated when a virtual circuit is multiplexed with a
highly variable traffic load or when congestion is approached in ATM
switches. Delay may also be caused by traffic shaping.
Cell transfer delay and CDV should not affect data transfer applications
but will affect audio and video services. For telephony and video
conferencing, the round trip delay may make communication difficult.
Constant Bit Rate services require the CDV to be controlled to minimize
the depth of reconstruction buffers and to minimize jitter in the service
clock recovery at the receive end
HOW TO: 1 Set up the PHYSICAL LAYER interface, see
“Selecting the Physical Receive Interface for ATM payloads” page 25.
2 Set up the ATM LAYER see page 104. The CELL
PAYLOAD must be the test cell.
3 Press to start a test.
RECEIVE
ATM
RECEIVE
ATM
RUN/STOP
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