DS33W41+ Maxim Integrated Products, DS33W41+ Datasheet - Page 71

• Manufacturer Part Number: DS33W41+
• Description: IC MAPPING ETHERNET 256CSBGA
• Manufacturer: Maxim Integrated Products

Specifications of DS33W41+

• Applications: Data Transport
• Interface: Parallel/Serial
• Voltage - Supply: 1.8V, 2.5V, 3.3V
• Package / Case: 256-CSBGA
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

8.16.5 Priority Coding with DSCP
The IETF RFC2474 (Differentiated Services) defines a Layer-3 alternate to 802.1p priority coding, known as
Differentiated Services Code Point (DSCP). DSCP is composed of a 6-bit value located in the second byte of the IP
header. When Priority Scheduling or Priority Forwarding are enabled, the priority value is inspected as each frame
arrives on the Ethernet Interfaces. The format of the DSCP tagged frame is shown in Figure 8-15. The device
supports DSCP priority carried in IPv4 or IPv6 packets. A user-programmed Priority Table is used to translate the
6-bit DSCP Priority into one of four Priority Levels for each Ethernet Interface. The received PCP value is used as
the address for the Priority Table lookup operation. The Priority Levels correspond to four separate queues. In
Priority Forwarding (Forwarding Mode 1), the four queues are in separate WAN Groups. In Priority Scheduling
operation, each WAN Group contains a set of four priority queues. These queues are collectively referred to as
LAN Queues in other portions of this document.
The priority mode (802.1p, DSCP, or none) for each Ethernet port can be independently selected using the
SU.LP1C and SU.LP2C registers. The DSCP function is a simple enable/disable function, with all of the other
parameters (Ethernet Frame Format, and Ethernet Type) being discovered by the device. See Section 8.16.6 for
more information on programming the priority table.
Figure 8-15. Differentiated Services Code Point (DSCP) Header Information
Rev: 063008
Ethernet Byte #
________________________________________________ DS33X162/X161/X82/X81/X42/X41/X11/W41/W11
17+
10
11
12
13
14
15
16
1
2
3
4
5
6
7
8
9
Bit 7
Bit 6
IP Version
Bit 5
DSCP Priority
Ethernet Type / Length (MSB)
Ethernet Type / Length (LSB)
< IP Header Continues…>
Destination Address (DA)
Source Address (SA)
Bit 4
Bit 3
Bit 2
IP TYPE
Bit 1
ECT
Bit 0
CE
71 of 375