Black Box KV162A manual Planning and Installing an Expanded System Optional

CHAPTER 6: Planning and Installing an Expanded System (Optional)

3.There are several independent data pathways available to carry transmissions through any ServSwitch Multi: eight pathways for the SB model, four pathways for the EXP and Base Unit models, and only two for the MX model. Each expansion-port link between two ServSwitch Multis through a pair of Transmit and Receive Cards is going to require the use of one of these pathways through each of the two Switches every time signals are transmitted across the link. Whenever all of the pathways in a given Switch are active (carrying data) at the same time, any attempt by any other user in the system to independently select a computer channel on that Switch will be ignored.

Refer to Figure 6-6; let’s examine what happens if all of these Switches are ServSwitch Multi EXPs. Say the user on Switch 0 wants to access computer 1H. A Transmit Card on Switch 1 is connected to a Receive Card on Switch 0, so this would work if there were fewer users on Switch 1. But because there are four users on Switch 1, and all of them will be using at least one of Switch 1’s data pathways at all times, Switch 1 has no available pathways left. Therefore the user on Switch 0 can’t establish an independent connection to computer 1H (although he or she can share access to that computer—see Section 8.3.) However, as long as the user on Switch 2 has computer 2B selected, the user on Switch 0 can access computer 2K independently, because the user on Switch 2 is only occupying one of the four pathways through Switch 2.

If all of the switches in Figure 6-6 are ServSwitch Multi SBs, the user on Switch 0 has no problem independently accessing computer 1H. This connection would only be the fifth for Switch 1, which would still have three free data pathways available.

X

M

T

C C C C C

P P P P P U U U U U U U U U S S S S R R R R

I H G F E

SWITCH 1

C	U	X	C
P			P
U	S	M	U
	R	T
K			B

SWITCH 2

R

C

V

U S R

SWITCH 0

Figure 6-6. An expanded system that shows the importance of data-pathway availability.

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