IP178G datasheet(19/76 Pages) ETC2

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IP178G

Data Sheet

19 / 76

December 19, 2012

IP178G-DS-R01.3

Functional Description

4.1

Switch Engine and Queue Management

4.1.1

Switch Engine

IP178G integrates an 8-port switch controller, SSRAM, and 8 10/100 Ethernet transceivers. Each of the

transceivers complies with the IEEE 802.3, IEEE 802.3u, and IEEE 802.3x specifications. IP178G offers

all the rich features of a high-speed broadband wire Internet services including non-blocking switch fabric

4.1.2

Packet Forwarding

IP178G utilizes the “store & forward” method to handle packet transfer. IP178G 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

IP178G 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 IP178G defers transmission when it

receives a jam or a pause frame. The source address (SA) of pause control frame will be [ IP178G 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, IP178G 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.

The flow control function can be enabled by programming registers 0.4[11:10] ~ 7.4[11:10] for 8 PHY.

4.1.4

Backpressure

In half duplex mode, the IP178G supports backpressure flow control. When set BK_EN of MII

off the link partner. IP178G supports carrier-sense based backpressure. When the carrier-sense based

backpressure is enabled, MII register 20.1[7] is set to “0”, and IP178G 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 IP178G 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 47 BF_STM_DIS or programming MII register 20.1[6].

IP178G handles multicast frame as a broadcast frame in broadcast storm protection function if MII

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