Comtech EF Data SLM-5650A Vipersat - Manual (Page 115)

Appendix B - Automatic Switching B-17
ToS Switching
ToS Remarking
For situations where the application device is not capable of stamping a packet
with a ToS value or where the application traffic is generated by a variety of
different host and protocols ToS remarking should be considered. ToS remark-
ing refers to a device, such as a router, that has the capability of re-stamping
packets with a user defined ToS value. Devices that support remarking often
allow users to assign a ToS value to packets that match, certain source or desti-
nation IP addresses, port numbers, and/or protocols.
Example 1 : A user wants to switch up whenever a host performs an FTP across
the satellite. A device that supports remarking can be placed between the appli-
cations and the remote modem. The device can then be configured to stamp all
traffic that utilized FTP port 21 with a particular ToS value. The remote modem
can then be configured to detect this value and switch to a specific SCPC bit
rate.
Example 2 : A remote customer is using an IP based video encoder to transmit
video over the satellite. The encoder does not have the option to assign a ToS
value for prioritization. Again, a remarking device can be placed between the
encoder and the remote modem and configured to assign a ToS value to all
packets received from the encoder.
Figure B-8 provides an example of a router performing ToS remarking for VoIP
phones.
Figure B-8 ToS Remarking Application
ToS to DSCP Value Conversions
Application devices or remarking devices often have different ways of display-
ing or configuring the ToS or DSCP values used to mark packets. Some devices
require the user to input the ToS value while others require input of the DSCP
value. Depending on the manufacturer these values may be displayed in binary,
hexadecimal, or decimal formats.