ACD81024 データシートの表示（PDF） - Unspecified

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ACD81024

24 Ports Single Chip 10Base-T Ethernet Switch Designed For Desktop Environment

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General speaking, ACD81024 is designed to comply

with IEEE 802.3 standard. ACD81024 has also been

proved to work perfectly with IEEE 802.3 compatible

devices. However, there are a few creative features

implemented on ACD81024 which deviate a little from

IEEE 802.3 standard. The following is a description

on these features:

Collision Backoff Time Period

Since ACD81024 does not store the received traffic,

each output port of ACD81024 does not schedule the

retransmission as a bridge type device does. When

collision is detected on an output port, both the

source DTE and the destination DTE will receive a

Jam pattern to force collision detection on both sides.

ACD81024 behaves like a middle man. It is the

source and destination DTEs which will follow the

truncated binary exponential backoff process defined

by the CSMA/CD scheme to control the retransmis-

sion time. Moreover, if there are multiple source

DTEs trying to send data to the same destination

DTE at same time, ACD81024 will remove the Back

Pressure signal applied to one of these source ports

to allow the attached source DTE to start sending

data to the destination DTE. ACD81024 also monitors

the number of consecutive collisions occurred on

each port. When the number of collisions on a port is

higher than the threshold value of three, the port has

higher priority than other input ports to get the com-

munication channel. Therefore, ACD81024 eliminates

the draw backs of the Channel Capturing feature on

networks using repeater hubs.

Collision-Jam Propagation Delay

ACD81024 does not isolate the collision domain

between its input port and output port. Instead, it uses

Jam plus Back Pressure signal for congestion control.

IEEE 802.3 specifies that the collision-jam propaga-

tion delay on a repeater set with internal 10-Base-T

MAUs on input and output ports should be less than

20.5 bit times. Since ACD81024 is a switching device,

collision cannot be detected until the destination port

is identified. As a result, the collision-jam propagation

delay on ACD81024 is 150 bit times. Therefore, care

should be taken when using ACD81024 in a

multisegment networking environment. The summa-

tion of the round trip delay should not exceed 512 bit

times, and ACD81024 contributes 150 bit times for

round trip propagation delay.

ACD Confidential. Do Not Reproduce. Use under Non-Disclosure agreement only.

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