5 2 Space Division Switching 1 
Digital Switching
SPACE DIVISION SWITCHING
• The simplest switching structure is a rectangular array of crosspoints as shown in Figure 5.2.
• This switching matrix can be used to connect any one of N inlets to any one of M outlets.
• If the inlets and outlets are connected to two-wire circuits, only one cross-point per connection is required.
• Rectangular cross-point arrays are designed to provide intergroup
(transit) connections only, that is, from an inlet group to an outlet group. • Applications for this type of an operation occur in the following:
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–
–
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Remote concentrators.
Call distributors.
The portion of a PBX or end-office switch that provides transit switching.
Single stages in multiple stage switches.
SPACE DIVISION SWITCHING
SPACE DIVISION SWITCHING
• In most of the foregoing applications, it is not necessary that the inlets be connectable to every outlet.
• In situations involving large groups of outlets, considerable savings in total cross-points can be achieved if each inlet can access only a limited number of outlets.
• When such a situation occurs "limited availability" is said to exist.
• By overlapping the available outlet groups for various inlet groups, a technique called "grading" is established.
• An example of a graded switching matrix is shown in Figure 5.3.
• Notice that if outlet connections are judiciously chosen, the adverse effect of limited availability is minimized.
• For example, if inlets 1 and 8 in Figure 5.3 request a connection to the outlet group, outlets 1 and 3 should be chosen instead of outlets
1 and 4 to avoid future blocking for inlet 2.
SPACE DIVISION SWITCHING
SPACE DIVISION SWITCHING
•
•
•
•
•
•
Graded switching structures were often used for access to large trunk groups in electromechanical switches where cross-points were expensive and individual switching modules were limited in size.
Intragroup switching, as for loop-to-loop switching, requires each loop to be connectable to every other loop.
Thus
SPACE DIVISION SWITCHING
• The simplest switching structure is a rectangular array of crosspoints as shown in Figure 5.2.
• This switching matrix can be used to connect any one of N inlets to any one of M outlets.
• If the inlets and outlets are connected to two-wire circuits, only one cross-point per connection is required.
• Rectangular cross-point arrays are designed to provide intergroup
(transit) connections only, that is, from an inlet group to an outlet group. • Applications for this type of an operation occur in the following:
–
–
–
–
Remote concentrators.
Call distributors.
The portion of a PBX or end-office switch that provides transit switching.
Single stages in multiple stage switches.
SPACE DIVISION SWITCHING
SPACE DIVISION SWITCHING
• In most of the foregoing applications, it is not necessary that the inlets be connectable to every outlet.
• In situations involving large groups of outlets, considerable savings in total cross-points can be achieved if each inlet can access only a limited number of outlets.
• When such a situation occurs "limited availability" is said to exist.
• By overlapping the available outlet groups for various inlet groups, a technique called "grading" is established.
• An example of a graded switching matrix is shown in Figure 5.3.
• Notice that if outlet connections are judiciously chosen, the adverse effect of limited availability is minimized.
• For example, if inlets 1 and 8 in Figure 5.3 request a connection to the outlet group, outlets 1 and 3 should be chosen instead of outlets
1 and 4 to avoid future blocking for inlet 2.
SPACE DIVISION SWITCHING
SPACE DIVISION SWITCHING
•
•
•
•
•
•
Graded switching structures were often used for access to large trunk groups in electromechanical switches where cross-points were expensive and individual switching modules were limited in size.
Intragroup switching, as for loop-to-loop switching, requires each loop to be connectable to every other loop.
Thus