Cisco Phone System

Cisco IP telephone technology?

http://www.starshipcorp.com/shop_dealer/images/Cisco%20IP%20Phone%20CP-7941G.jpeg My school has Cisco IP telephones in all offices. Like the one shown above. Whats the specialty of IP telephones as compared to the usual telephone at home? Does the IP telephone operate on the local intranet/ethernet? And the voice is sent as packets? Hence how can u guarantee about quality as packets might get lost/damaged due to network congestion? Also, if a certain institution has an IP phone system that means their internal calls are free of charge right? (As they already have an ethernet network)

Public Comments

1. An IP phone sends phone calls over the internet, rather than the phone lines. This does mean loss of data, as TCP is allowed to drop packets, so sometimes the other person may appear laggy. It depends on the service, but calls are either cheap or free.
2. IP telephone is a new telephone service. you are right !compared with usual telephone, voice is sent as packets through internet. therefore, the digital signals are sent through IP telephone instead of analog signal. although IP telephone is based on Internet, it uses special internet line. so the voice quality doesn't been influenced due to network congestion. of course, IP telephone system also not free. just like you want to surf the internet, you have to pay some network fees.it is cheaper than charge of normal telephone when you use IP telephone make a long-distance call.
3. Your questions show the extremely high degree of confusion and misunderstanding about Voice over Internet Protocol or VoIP. IP phones are more sophisticated than the regular phones. They plug into the Local Area Network using the standard CAT5 cables, not the old analog voice 4 wire lines. IP phones mate with the IP PBX module which is also connected to the LAN. You can move your IP phone from jack to jack on your LAN and the IP PBX finds and recognizes you (e.g. if your IP phone is ext. 309 on your phone system, moving the IP phone to a different jack on your LAN does not change your extension from the preset 309). VoIP uses packet switching which is an IP feature. It does not use the circuit switching of traditional phone systems. All other data on your LAN also uses packet switching as well. In traditional IP broadcasts, late arriving packets make no difference and lost packets are resent which is fine for data as the transmission is not time sensitive. Congestion causes late and lost packets. For voice, however, late or lost packets foul voice quality - often to an unacceptable degree causing Quality of Service (QoS) problems. VoIP addresses this by marking voice packets for priority over data. This means that in the event of congestion or back up, data packets are held until voice packets are sent. This works very well on your LAN and on your leased point to point lines because all the network hardware recognizes and provided priority to voice packets. Many feel that you can compensate for packet priority marking and processing by a larger capacity LAN and WAN which is not accurate. On the other hand, if the capacity of the LAN or WAN is undersized, priority will not completely compensate for undercapacity. For this reason you must address both priority and capacity - and this is one major reason people have either intermittant or continual problems with VoIP QoS. The Internet does not provide packet priority. All voice calls that use the Internet for transport are subject to QoS problems regardless of the voice carrier. This is one very misleading component of VoIP carriers who brag about their low cost. They cannot assure voice quality. Further, the so called low cost carrier also does not pay for the transmission of the call or the maintenance of the transportation line so it should be a lot less costly. Any single location company that has an internal phone system, whether it is VoIP or conventional, has "free" calls because they are calling on their own network. Of course, they already paid for their phone equipment, internal wiring, etc and continue to pay for maintenance. Any multi-location company that has point - to - point lines that link their locations have "free" calls, but they also pay for their equipment, maintenance and point to point line. It makes no difference if this is a VoIP or conventional phone system. This only means there is no per call fee since you already pay for the point to point line. If you go onto the Public Switched Telephone Network (PSTN) to complete a call, you usually have a per call fee. There are calling plans that cost more up front that reduce or eliminate per call fees in many cases.