IP175G datasheet(14/69 Pages) ETC2

14 / 69 page

IP175G/GI/GH/GHI

Data Sheet

14 / 69

November 27, 2012

IP175Gx-DS-R01.3

Functional Description

4.1

Switch Engine and Queue Management

4.1.1 Switch Engine

IP175G/GH integrates an 5-port switch controller, SSRAM, and 5 10/100 Ethernet transceivers. Each of

the transceivers complies with the IEEE 802.3, IEEE 802.3u, and IEEE 802.3x specifications.

IP175G/GH offers all the rich features of a high-speed broadband wire Internet services including

non-blocking switch fabric

4.1.2 Packet Forwarding

IP175G/GH utilizes the “store & forward” method to handle packet transfer. IP175G/GH begins to

forward a packet to a destination port after the entire packet is received. A received packet will be

forwarded to the destination port only if it is error free; otherwise, it will be discarded.

4.1.3 Flow control

IP175G/GH jams or pauses a port, which causes output queue over the threshold. Its link partner will

defer transmission after detecting the jam or pause frame. A port of IP175G/GH defers transmission

when it receives a jam or a pause frame. The source address (SA) of pause control frame will be

[ IP175G/GH OUI (0090C3), port number]. For example, the SA of port 1 pause control frame will be “ 00

90 C3 00 00 01”.

When CoS is enabled, IP175G/GH may disable the flow control function for a short term to guarantee the

bandwidth of high priority packets. A port disables its flow control function for 2 ~ 3 seconds when it

receives a high priority packet. It doesn’t transmit pause frame or jam pattern during the period but it still

responses to pause frame or jam pattern.

4.1.4 Backpressure

In half duplex mode, the IP175G/GH supports backpressure flow control. When set BK_EN of MII

back off the link partner. IP175G/GH supports carrier-sense based backpressure. When the

carrier-sense based backpressure is enabled, MII register 20.1[7] is set to “0”, and IP175G/GH transmits

null packets continuously to prevent link partner’s transmission when the buffer is not available.

4.1.5 Broadcast storm protection

A port of IP175G/GH begins to drops broadcast packets if the received broadcast packets are more

than the threshold defined in MII register 21.9[15:14] BF_STM_THR_SEL [1:0] in 10ms (100Mbps) or

100ms (10Mbps)

The function can be enabled by pulling low pin 36 BF_STM_DIS or programming MII register

20.1[6].

IP175G/GH handles multicast frame as a broadcast frame in broadcast storm protection function if

MII register 21.30[12] is set to “0”

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