Switching Equipment
- The Lucent 4ESS is a digital switch widely used as a Class 4 switch in the United States. It was developed by AT&T's Western Electric division, before that division was spun off as Lucent. The first 4ESS was installed in Chicago in 1976. The last 4ESS in the AT&T Long Lines network was installed in 1999.
- The Lucent 5ESS, a Class 5 switching system, is sometimes used as a Class 4 switch (or as a mixed Class 4/5 switch) in markets that are too small to justify a 4ESS switch.
- The Nortel DMS-250, a larger variant of the DMS-100, is a popular competitor to Lucent's 4ESS, especially among telephone companies that were not previously a part of AT&T. Other DMS switches can also be used as tandems.
- The Nortel SP1 4-Wire was an early electronic switch used as a Class 4 switch.
Other Class 5 digital switches are often used as Class 4 switches for smaller applications.
Read more about this topic: Class 4 Telephone Switch
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