Comtech EF Data MDX420 SkyWire Manual - Manual (Page 113)

MDX420 SkyWire™ Satellite Network Gateway SkyWire QoS
MN-MDX420 Revision 6 C–3
C.2.2 IPv4 Packets with a Type of Service field (RFC 791)
When a packet doesn't contain an IEEE tag, and it's an IPv4 packet with a Type of Service field
(TOS), SkyWire uses the information contained in the TOS Precedence field to determine the
appropriate queue. The Type of Service field is contained in the second byte of the IPv4 header
and supports 8 levels of precedence with 7 (Network Control) being the highest and 0 (Routine)
being the lowest. The following diagrams illustrate the format of the IPv4 Type of Service
information and their mapping to the available queues. Please note, in IPv4, the Type of Service
field and Differentiated Services field (discussed in the next section) occupy the same location in
the IP header, therefore, only one of these fields will be present in any particular IPv4 header.
IPv4 Type of Service Field
Precedence
3 bits
D
1 bit
Reserved
2 bits
T
1 bit
R
1 bit
R = Reliability
T = Throughput
D = Delay
Precedence
111 = Network Control
110 = Internetwork Control
101 = Critical / ECP
100 = Flash Override
011 = Flash
010 = Immediate
001 = Priority
000 = Routine
Network Queue
Precedence 6 and 7
Critical Queue
Prededence 4 and 5
Immediate Queue
Precedence 2 and 3
Routine Queue
Precedence 0 and 1
Queue
Manager
Packets In Packets Out
IPv4 Type of Service Traffic Flow