See IP Telephones

IP Telephones

Traditional phones operate over the Public Switched Telephone Network (PSTN). (Sometimes this is called POTS (Plain Old Telephone Service). IP Phones, on the other hand, use VoIP tech to enable phone calls over an IP network (such as the Internet).

”IP Phone” typically refers specifically to hardware: a physical telephone. Most IP phones look nearly identical to regular landline telephones, but they will have RJ45 network ports rather than typical phone jacks. A number of companies, including Cisco, produce IP phones.

IP phones need to be connected to a network switch just like any other end host device. IP phones are commonly used by workers at their desks, where there is likely to be a desktop workstation that also needs an Ethernet connection. It would be cumbersome to run two separate cables from the switch to each desk in an office, and that would mean taking double the number of interfaces on the switch for every desk. Furthermore, it is common for workers to use software on their desktop to track and manage phone calls, so the IP phone and the workstation PC, so it makes sense to have them directly connected. This is why many IP phones have a small 3-port switch built-in. One port is the “uplink” and connects to the external switch. Another is the “downlink” which is used to connect to the PC (It could be used for any end-host but a PC is most common). The final port connects internally to the phone itself. This way you only need a single switch interface for each desk. All the traffic from the PC will be pass through the phone’s internal switch.


Why is it important to reduce the number of switch interfaces we use?

Because enterprise switches are expensive, and the more interfaces we use the more switches we need to buy.


IP Telephones are commonly powered with Power over Ethernet (PoE).

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