13
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How cascade connections operate
The method for cascading switching units is straightforward and requires no
hardware settings or lengthy configuration process. This is due to the
Port
Direct
communication system employed by certain advanced switching products
that allows them to locate each other and share information.
The method of linking switches is the same regardless of the cascade level, or
number of devices attached. Put simply:
•
A single cascade link is made by connecting a computer port of one
switch to a user port of the switch below it.
Such a single link would allow just one user from the higher switch to access
any of the computers (or other switches) attached to the lower one. However, a
single link can cause a bottleneck for multi-user systems, so it is commonplace
to make dual cascade links between switches. These allow two users to
simultaneously access computers situated anywhere within the cascade tree.
When dual cascade links are made between switches, each switch will
automatically recognise the dual links and treat them accordingly. The links
within a dual group will then be allocated to users according to their general
availability in that group, not as specific individual lines. To do this, each link
group has an access number, which is determined by the ports to which they are
connected on the switch.
For instance, a dual group connected to computer ports 1 and 2 of a switch
would always be known as 21, the next dual group connected to ports 3 and
4 would always carry the number 22, and so on. The diagram here summarises
the ports to which dual groups must be connected and the resulting group
numbers attained in the positions here
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The central purpose of the link group system is that each user can use a unique
address to locate a particular computer, however, as with the Internet, the route
to get there could be slightly different each time. This avoids any route blocking
that could easily be caused by other users occupying any specific link lines.
4
3
2
16
8
15
7
14
6
13
5
12
11
10
9
1
GROUP
21
GROUP
25
GROUP
26
GROUP
27
GROUP
28
GROUP
22
GROUP
23
GROUP
24
Port boundaries and numbering for dual link groups (model ACR6208A
uses groups 21 to 24 only)
Note: Single links and dual link groups may be mixed on one switch providing
the dual link groups lie within the appropriate port boundaries shown above
- see
Tips for successful cascading
for more details.
