How does VoIP differ from PSTN?
The PSTN is based on copper wires forming a circuit between the two phones involved in a call. These phones do a specific task based on efficient communication of voice signals. PSTN has generally done 100 years of excellent service.
SIP relies on an IP environment where packets of information are transferred to specified addresses in the network, using a system of SIP servers.
| Issue | PSTN | SIP |
|---|---|---|
| What can be connected? | Phones, fax, answer-phones, specialist computer interfaces | SIP phones, Video clients, computers, pda’s, fax via computer/ SIP fax, messaging clients, mobile systems |
| Means of connection | Copper wired circuits | IP switched packets of data |
| Power to phones / devices | Carried along the copper wire ( self powering) | Either provided centrally on extra wires or by separate PSUs |
| Distribution | Wherever the Telephone company lays cable | Wherever stable IP networks can be connected |
| Understanding | Simple defined application product | Complex – learning on how to use and what it is capable of is needed |
| System failure | The system may be down for 1 hour per year – easily fixed in an exchange | Many points at which failure may occur |
