Telex 38109-977 manual Number of Users Number of Crosspoints

Table 4.1 Number of Users vs. Number of Crosspoints

Number of Users	Number of Crosspoints
10	100
25	625
50	2,500
100	10,000
200	40,000
400	160,000

As you can see in Table 4.1, while a ten-user system “only” requires 100 crosspoints for all possible communications paths, a 100-user system requires 10,000 crosspoints. Now, realize the number of crosspoints has a direct correlation to power consumption, physical size, and cost. It becomes apparent that with a traditional architecture, crosspoint matrices have a pretty small limit on maximum practical size.

When McCurdy Radio Industries introduced their 9500 series matrix intercom product, 50 ports required a rack frame 3 RU in height, and weighed 20 pounds. At the time, the size limitation was understood, but not regarded as a problem because it was thought that no one would ever need more than 50 users in a single intercom matrix. Today, we can look back and put that statement in the same category as IBM’s assertion in the 1950’s that “the world market for computers is 5 systems – TOPS,” or the apocryphal Bill Gates quotation to the effect of, “Who will ever need more than 640K of memory?” In 1985, the market for systems as large as a 50-user intercom was primarily limited to the major television networks.

C h a p t e r 4 - I n t r o d u c t i o n t o M a t r i x I n t e r c o m S y s t e m s 49