best effort delivery
(BE) what it says, no guarantees, all traffic treated equally, the lack of QoS
integrated services
(IntServ) rfc 1633, end-to-end QoS for real-time applications such as voice and video; explicit management of network resources for specific user packet streams
differentiated services
(DiffServ) unlike IntServ, no advance reservations required. preferred
see below for ToS evolution (this is a great intro which quickly goes deep; take human bites)
http://fengnet.com/book/ios_mpls/ch13lev1sec1.html
Figure 13-1 shows the IPv4 packet header with an 8-bit type of service
(ToS) field. The ToS field was conventionally used to provide QoS in IP
networks. However, since the advent of the Diff-Serv model, it has been
replaced by the implementation of IP Precedence or DSCP values.
Figure 13-1. IP Packet Header
The higher order 3 bits in the TOS field, shown in Figure 13-1,
map to the IP Precedence value assigned to the IP packet. The
predefined values used to identify the IP Precedence are shown in Table 13-1.
IP Precedence Value
|
Binary Value
|
Priority
|
|---|---|---|
0
|
000
|
Routine
|
1
|
001
|
Priority
|
2
|
010
|
Immediate
|
3
|
011
|
Flash
|
4
|
100
|
Flash Override
|
5
|
101
|
Critical
|
6
|
110
|
Internetwork Control
|
7
|
111
|
Network Control
|
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