Voice over IP

VoIP server, 

VoIP clients,  computing devices.  include: hard phones(looks like a normal phone actually a phone buit-in software), soft phones(usually installed on normal laptop,ipad, etc..)
 accounts & passwd, extension..

Voice gateway,  allows you use the VoIP phone communicate with the normal phone.

protocol  such as SIP(free open source protocol)

codec

latency  45ms,   75ms--100ms,   not exceed 100ms.

QoS,
 

Voice over IP

原文：http://41080138.blog.51cto.com/2587513/1680624