Chapter 4-Additional Conferencing Information
Polycom, Inc.
4-49
Causes of Packet Loss
Network congestion within a LAN or WAN, faulty or incorrectly configured network
equipment or faulty cabling are among the many causes of Packet Loss.
Effects of Packet Loss on Conferences
Packet Loss
affects the quality of:
•
Video –
frozen images, decreased frame rate, flickering, tiling, distortion, smearing,
loss of lip sync
•
Audio –
drop-outs, chirping, audio distortion
•
Content –
frozen images, blurring, distortion, slow screen refresh rate
Lost Packet Recovery
The
Lost Packet Recovery
(
LPR
) algorithm uses
Forward Error Correction
(
FEC
) to create
additional packets that contain recovery information. These additional packets are used to
reconstruct packets that are lost, for whatever reason, during transmission.
Dynamic
Bandwidth Allocation
(
DBA
) is used to allocate the bandwidth needed to transmit the
additional packets.
Lost Packet Recovery Guidelines
•
If packet loss is detected in the packet transmissions of either the video or Content
streams:
—
LPR
is applied to both the video and Content streams.
—
DBA
allocates bandwidth from the video stream for the insertion of additional
packets containing recovery information.
•
LPR
is supported in H.323 and
SIP
networking environments only.
•
In
LPR
-enabled
Continuous Presence
conferences:
—
Both
LPR
-enabled and non-
LPR
-enabled endpoints are supported.
—
The
LPR
process is not applied to packet transmissions from non-
LPR
-enabled
H.323, SIP and H.320 endpoints.
—
Non-LPR-enabled endpoints can be moved to
LPR
-enabled conferences.
—
LPR-enabled endpoints
cannot
be moved to non-
LPR
-enabled conferences.
•
In
LPR
-enabled
Video Switched
conferences:
—
H.323 and SIP endpoints are supported.
—
When cascading between conferences running on RMX and
MGC
(
Polycom
legacy
MCU
),
LPR
is not supported over the link between the two conferences.
—
Non-H.323 participants cannot be created, added or moved to
LPR
-enabled
Video
Switched
conferences.
•
When connecting via an
Entry Queue:
—
A participant using an
LPR
-enabled endpoint can be moved to a non-
LPR
-enabled
conference. The participant is connected with LPR enabled.
—
SIP and H.320 participants cannot be moved to
LPR
-enabled
Video Switched
conferences.
Enabling Lost Packet Recovery
LPR
is enabled or disabled in the
Conference Profile
dialog box.
Содержание RealPresence 2000
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