Differentiated Services - Hirschmann RS20 User Manual

Network Load Control
Bits (0-2): IP Precedence Defined Bits (3-6): Type of Service Defined Bit (7)
111 - Network Control
110 - Internetwork Control
101 - CRITIC / ECP
100 - Flash Override
011 - Flash
010 - Immediate
001 - Priority
000 - Routine
Table 13: ToS field in the IP header

Differentiated Services

The newly defined Differentiated Services field in the IP header
fig. 39) - often known as the DiffServ code point or DSCP, replaces the
ToS field and is used to mark the individual packets with a DSCP. Here
the packets are divided into different quality classes. The first 3 bits of the
DSCP are used to divide the packets into classes. The next 3 bits are
used to further divide the classes on the basis of different criteria. In
contrast to the ToS byte, DiffServ uses six bits for the division into
classes. This results in up to 64 different service classes.
Bits 1
0
Differentiated Services Codepoint
Class Selector
Codepoints
Figure 39: Differentiated Services field in the IP header
The different DSCP values get the device to employ a different forwarding
behavior, namely Per-Hop Behavior (PHB). PHB classes:
Class Selector (CS0-CS7): For reasons of compatibility to TOS/IP
Precedence
Expedited Forwarding (EF): Premium service.
Reduced delay, jitter + packet loss (RFC2598)
Basic Configuration
Release 6.0 07/2010
0000 - [all normal]
1000 - [minimize delay]
0100 - [maximize throughput]
0010 - [maximize reliability]
0001 - [minimize monetary cost]
2 3
(DSCP) RFC 2474
4 5 6
Currently
Unused
(CU)
8.4 QoS/Priority
0 - Must be zero
(see
7
145