The egress martin setting (appearing in Apex 2.0, ApexPlus 2.0 and GigaPlus 3.0) allows for some end-user fine tuning of the QoS strictness of the internal switch. Since the RF throughput varies with different packet sizes, a range is provided so a user can select tighter QoS compliance, or maximum bandwidth.
The default setting of 10% should work fine for most cases. Setting it smaller, like 5%, will provide tighter QoS control, but come at the expense of reduced throughput for smaller packets. At a smaller setting, there is less of a chance of a higher priority packet being dropped at the expense of a low priority packet.
With a larger setting, like 20%, maximum throughput will be observed, but there is an increased likely-hood of dropping a critical packet while allowing a lower priority packet through.
The setting mostly impacts small frame sizes and has no measurable difference on latency, as long as the traffic is below the RF rate. A larger percentage setting will allow more packets in each burst, especially for smaller packets. Please see the linked images below for a graphical representation of how the setting affects live traffic.
|TrangoLINK ApexPlus 18 GHz
80 MHz QAM256
with varying Egress Percentage Setting
(No QoS tags)
Throughput (Layer 2-3) Mbps
Back-to-Back (Layer 2-3) packets per burst