User`s manual

User’s Manual v.13 QVidium

H.264 HD Video Codecs™

Technologies, Inc. Page 37 of 67

measures and calculates the Round Trip Time and Number Retries. Automatic mode only

uses three parameters: Target Latency and Burst-Drop time and Robust mode. In most

cases automatic mode and the default parameters should be adequate.

Of the required parameters, the first parameter, Target Latency, specifies the total delay, in

milliseconds, allotted for the request, retransmission, and recovery process. The ARQ mechanism

will attempt as many retries as possible within this target latency time. Thus, larger target latency

times increase the delay before video is output, but allows for more chances of requesting and

recovering any missing packets. However, automatic mode also sets an internal maximum limit

based on its measurements that may be less than the target latency time.

The Burst Drop delay can be specified to delay any retransmission requests for a time equal to

the maximum expected packet loss time, such as from dynamic router changes of other sources of

burst loss.

Robust Mode can also be selected for Auto mode of operation. When selected (checked), a

minimum of two tries will be attempted for recovering any missing packets. When not selected

(unchecked), ARQ will always try at least once to recover any missing packets.

To help with firewall configuration and to handle potential port conflicts, the user can change the

default port that ARQ uses to send upstream retransmission requests, ARQ Port. However, you

must make certain that the same ARQ port number is set in both the encoder as in the decoder.

Although the automatic measurement of the round-trip time uses multiple measurements to take

into account random network delays, for some networks you might wish to specify a larger round-

trip value, or to specify a larger number of retries in case the upstream link loses some of the

retransmission request messages. In automatic robust-mode of ARQ operation, the system

automatically measures the round-trip time and divides that number into your specified Target

Latency to determine the number of retries to use. However in Manual Mode, you can force ARQ

to always use a specified number or retransmission requests.

Note: For testing ARQ error correction, select ARQ transport at both the encoder and decoder and

use the default ARQ parameters at the decoder (receiver). Please also be certain that ARQ has

also been selected at the encoder.