GE GE-DS-82, 82-POE user manual TOS/DSCP Configuration, Precedence, Tos Mbz, DiffServ

Chapter 4: Web-Based Management

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Precedence

TOS

MBZ

Pv4 Packet Header Type of Service Octet

The four TOS bits provide 15 different priority values, however only five values have a defined meaning.

DiffServ Code Point (DSCP) - is the traffic prioritization bits within an IP header that are encoded by certain applications and/or devices to indicate the level of service required by the packet across a network. DSCP are defined in RFC2597 for classifying traffic into different service classes. The Managed Switch extracts the codepoint value of the DS field from IPv4 packets and identifies the priority of the incoming IP packets based on the configured priority.

4 bit 4 bit 6 bit 2 bit

VER=0100

Header

Size

DiffServ

RES

Preamble

Destination

Address

Source

Address

VLAN

TAG

(Optional)

Ethernet

Type

(0800)

Data

FCS

6 bytes 6 bytes 4 bytes 2 bytes 2 bytes 46-1517 bytes 4 bytes

The DSCP is six bits wide, allowing coding for up to 64 different forwarding behaviors. The DSCP retains backward compatibility with the three precedence bits so that non- DSCP compliant, TOS-enabled devices, will not conflict with the DSCP mapping. Based on network policies, different kinds of traffic can be marked for different kinds of forwarding.

TOS/DSCP Configuration

The TOS/DSCP page provides fields for defining output queue to specific DSCP fields. When TCP/IP's TOS/DSCP mode is applied, the Managed Switch recognizes TCP/IP Differentiated Service Codepoint (DSCP) priority information from the DS-field defined in RFC2474.

Enable TOS/DSCP for traffic classification and then the DSCP to priority mapping column is configurable, as Figure 81 shows:

114 GE-DS-82 and 82-PoE Ethernet Managed Switch User Manual