Q-Flex Satellite Modem Installation and Operating Handbook
6-50
6.2.2.4 Round-trip Satellite Delay
Range:
0ms to 9999ms; step size: 1ms
Description:
This sets a satellite round-trip delay that is used in conjunction with TCP
acceleration. It controls the size of the modem’s internal packet buffer to
match the bandwidth-delay product for the link (i.e. the link’s data capacity
multiplied by the end-to-end delay). This helps to maintain the throughput
at its maximum level when TCP acceleration is on.
Table 6-52 Round-trip Satellite Delay
6.2.2.5 Header Compression
This is an On/Off control that controls header compression.
IP, UDP and RTP header compression is supported in accordance with the Robust
Header Compression (ROHC) standard RFC 3095 (profiles 2 and 3). ROHC typically
reduces the 40 bytes of IP, UDP and RTP header, which is typically used with Voice over
IP data, down to between 1 and 3 bytes. Ethernet header compression is also supported
in addition and this reduces 14 bytes of Ethernet frame down to typically 1 byte. Overall
savings from compression from both types of compression (e.g. for a G.729 voice stream)
can be as high as 60%.
When header compression is on, Ethernet, UDP, TCP, RTP and IP packet headers are
compressed in order to save satellite bandwidth. The relative bandwidth saving is greater
for smaller packets.
The compressed packets will be either bridged or routed as determined by the
IP mode
setting.
Selective compression of packets can be controlled via the
Edit->IP->Header
Compression
screen, which allows routes to be added.
6.2.2.6 Payload Compression
This is an On/Off control that controls header compression.
When payload compression is on, the payload of IP packets are compressed in order to
save satellite bandwidth.
The compressed packets will be either bridged or routed as determined by the
IP mode
setting.
6.2.2.7 ACM Mode
Table 6-47
lists the modes available with respect to Adaptive Coding and Modulation
(ACM). ACM converts any unused link margin into additional IP throughput.
