- PSTN carries Voice
- Internet Carries Data – data network
- Recently, PSTNs are customized to carry data
- You can also carry voice over the data network like the Internet – called IP Telephony or VOIP.
How to connect to the Voice Network – PSTN
Just connect to the phone line – applies to one user only
How multiple users can connect to the Voice Network – PSTN
- Key System-Most basic multiuser support – good for very small offices
- PBX
- centrax
Key System
- Uses a few trunk lines to connect to the LE or CO-central Office
- When users call, one of the free lines is used
- Each trunk line is associated with a number
- Incoming calls come to a central phone that can be forwarded to others
- Individual users can also pick the phone
- Good only when < 50 users are involved
- Recent Key Systems come with features like: Caller ID, Voice Mail, Conference Calls
- Not much scalable
- Push button to select a line
PBX
- Works like a telephone exchange
- Has more outgoing trunk lines
- Users can call outside or inside independently
- Users can press 9 or a special key to make calls to outside
- Internal calls never leaves the internal network, hence, PBX provides security
- More scalable than the Keysystem
- Can associate a number with a particular phone
- Have features like analog extensions, digital extensions
Centrex System
- Similar to the PBX but the telephone company handles the Centrex equipments
- The Centrex equipments do not have to be in the same building like PBX, hence Centrex is more popular withing big enterprises
- Less setup cost, more running cost
- Each phone set has a public phone number associated
- Scalable
- Can connect multiple sites without PSTN. Hence, providing IP telephony through Centrex system is easier and practical
- Installation cheaper
From: http://sitestree.com/?p=5027
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Post Data:2012-03-04 19:04:09
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