DP83251V datasheet(13/96 Pages) NSC

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30 Functional Description (Continued)

CONCENTRATOR CONFIGURATIONS

There are 2 types of Concentrators Single Attach and Dual

Attach These Concentrators can be designed with or with-

out the MAC(s) Its configuration is determined based upon

its type and the number of active MACs in the Concentrator

Using the PLAYER devices a Concentrator can be built with

many different configurations without the need of any exter-

nal logic

Both the DP83251 and DP83255 can be used to build a

Single Attach Concentrator Only the DP83255 is recom-

mended for the Dual Attach Concentrator design

See Application Note 675 Designing FDDI Concentrators

and Application Note 741 Differentiating FDDI Concentra-

tors for futher information

Concepts

A Concentrator is comprised of 2 parts the Dual Ring Con-

nect portion and the Master Ports

The Dual Ring Connection portion connects the Concentra-

tor to the dual ring directly or to another Concentrator If the

Concentrator is connected directly to the dual ring it is a

part of the ‘‘Dual Ring Tree’’ If the Concentrator is connect-

ed to another Concentrator it is a ‘‘Branch’’ of the ‘‘Dual

Ring Tree’’

The Master Ports connect the Concentrator to its ‘‘Slaves’’

A Slave could be a Single Attach Station or another Con-

centrator (thus forming another Branch of the Dual Ring

Tree)

When a MAC in a concentrator is connected to the Primary

or Secondary Ring it is required to be situated at the exit

port of that concentrator (ie its PH

IND is connected to

the IND Interface of the last Master Port in the Concentrator

(PHY

M n) that is connected to that ring)

A Concentrator can have two MACs connected to both the

Primary and Secondary rings In addition a Roving MAC can

be included in the Concentrator configuration A Roving

MAC can be used to test the stations connected to the Con-

centrator before allowing them to join the Dual Ring This

may require external multiplexers

Single Attach Concentrator

A Single Attach Concentrator is a Concentrator that has

only one PHY at the Dual Ring Connect side It cannot

therefore be connected directly to the Dual Ring A Single

Attach Concentrator is a Branch to the Dual Ring Tree It is

connected to the ring as a Slave of another Concentrator

Multiple Single Attach Concentrators can be connected to-

gether hierarchically to build multiple levels of branches in a

Dual Ring

The Single Attach Concentrator can be connected to either

the Primary or Secondary ring depending on the connection

with its Concentrator (the Concentrator that it is connected

to a slave)

Figure 3-10 shows a Single Attach Concentrator with a Sin-

gle MAC

Dual Attach Concentrator

A Dual Attach Concentrator is a Concentrator that has two

PHYs at the Dual Ring Connect side It is connected directly

to the dual ring and is a part of the Dual Ring Tree

The Dual Attach Concentrator is connected to both the Pri-

mary and Secondary rings

Dual Attach Concentrator with Single MAC

Figure 3-11 shows a Dual Attach Concentrator with a Single

MAC

Because the Concentrator has one MAC it can only trans-

mit and receive frames on the ring where the MAC is con-

nected The Concentrator can only repeat frames on the

other ring

Dual Attach Concentrator with Dual MACs

Figure 3-12 shows Dual Attach Concentrator wih Dual

MACs

Because the Concentrator has two MACs it can transmit

and receive frames on both the Primary and Secondary

rings

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