IP175C-DS-R03 datasheet(46/111 Pages) ETC2

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IP175C/IP175C LF/IP175CH/IP175CH LF

Data Sheet

2.9

CoS

IP175C/IP175CH supports two type of CoS. One is port base priority and the other is frame base priority.

IP175C/IP175CH supports two levels of priority queues.

2.9.1

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 “high priority port enable” bit in MII register 29.19~29.21or

EEPROM register 14~18. Each port of IP175C/IP175CH can be configured as a high priority port

individually.

2.9.2

Frame base priority

2.9.2.1

VLAN tag and TCP/IP TOS

IP175C/IP175CH examines the specific bits in VLAN tag and TCP/IP TOS for priority frames if the frame

base priority is enabled. A high priority packet will be queued into the high priority queue; this action will

ensure more bandwidth is allocated for the high priority packets in the transmission. The packets will be

handled as high priority frames if the tag value meets the high priority requirement, that is, priority bits in

a VLAN tag bigger than 3 or TCP/IP TOS field not equal to 3’b000. It is enabled by programming the

“class of service enable” bit in MII register 29.19~29.21 or EEPROM register 14~18. The frame base

priority function of each port can be enabled individually.

The ratio of bandwidth of high priority and low priority queue is defined in MII register 30.12[4] or

EEPROM 60[4].

byte

TYPE = 8100

VLAN field

TCI (tag control information)

12~13

14~15

TCI definition:

Bit[15:13]: User Priority 7~0

Bit 12: Canonical Format Indicator (CFI)

Bit[11~0]: VLAN ID.

IP175C uses bit[15:13] to define priority.

byte

TYPE = 0800

TOS field

IP HEADER

12~13

14~15

IP header definition:

Byte 14

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

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

IP175C uses bit[4:2] to define priority.

Mar 09, 2007

46/111

IP175C/IP175CH-DS-R14

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