IP175G datasheet(20/69 Pages) ETC2

20 / 69 page

IP175G/GI/GH/GHI

Data Sheet

20 / 69

November 27, 2012

IP175Gx-DS-R01.3

4.8

CoS

IP175G/GH supports two types of CoS. One is port base priority function and the other is frame base

priority function. IP175G/GH supports two levels of priority queues. A high priority packet will be queued

to the high priority queue to share more bandwidth. The ratio of bandwidth of high priority and low priority

queue is defined in MII register 20.1[15] or EEPROM 3[7].

4.8.1 Port base priority

The packets received from high priority port will be handled as high priority frames if the port base priority

is enabled. It is enabled by programming the corresponding bit in MII register 21.0[9] ~ 21.4[9] or

EEPROM register 65[1] ~73[1]. Each port of IP175G/GH can be configured as a high priority port

individually.

4.8.2 Frame base priority

4.8.2.1 VLAN tag and TCP/IP TOS

IP175G/GH examines the specific bits of VLAN tag and TCP/IP TOS for priority frames if the frame base

priority is enabled. The packets will be handled as high priority frames if the tag value meets the high

priority requirement, that is, VLAN tag or TCP/IP TOS field bigger than 3. It is enabled by programming

the corresponding bit in MII register 21.0[10]~21.7[10]. The frame base priority function of each port can

be enabled individually.

IP175G/GH supports an easy way to enable a sub set of CoS function without programming MII registers.

Frame base priority function of all ports is enabled if pin 37 COS_ENDIS is pulled low. The setting in

VLAN field

TCI difinition

bit [15:13] : User ptiority 7~0

TYPE= 8100 TCI(Tag Control Information)

bit 12 : Canoical Format Indicator (CFI)

Byte

12~13

14~15

bit [11:0] : VLAN ID

IP175G/GH uses bit[15:13] to define priority.

ToS field

IP header difinition

Byte 14

TYPE= 0800

IP header

bit [7:0] : IP protocol version number & header length

Byte

12~13

14~15

bit [11:0] : VLAN ID

IP175G/GH uses bit[15:13] to define priority.

Byte 15 : Service type

bit [7:5] : IP Priority (Precedence) from 7~0

bit 4 : No Delay (D)

bit 3 : High Throughput

bit 2 : High Reliability (R)

bit [1:0] : Reserved

IP175G/GH uses bit[7:5] to define priority.

0~3 : Low priority

4~7 : High priority

Figure 8

VLAN tag and TCP/IP TOS frame

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