Contemporary-control-systems Compact Managed Switches Software Manual for Web B Instrukcja Użytkownika Pobierz pdf (Strona 37)

TD020851-0MG

Middle Table — Map TOS Precedence and Priority Queue

Although TOS priority is supported by few TCP/IP implementations, it is provided as a

QoS option in managed switches from Contemporary Controls. One of the earliest

methods of QoS for Internet Protocol, TOS uses the second octet (the TOS field) of the

IP frame header — as described in RFC791 and RFC1349. The first three bits of this

octet set the priority (Precedence). The next four bits (known as the TOS bits) define

the tradeoffs among these four service objectives:

• minimize monetary cost (M-Type Priority) *

• maximize reliability (R-Type Priority)

• maximize t hroughput (T-Type Priority)

• minimize delay (D-Type Priority)

* This is sometimes referred to as “C-Type” priority or type of service.

The final bit of the TOS field was unused until DiffServ was defined.

Figure 32 — Map TOS Precedence and Priority Queue

1 2 ... 32 33 34 35 36 37 38 39 40 41 42 ... 82 83

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