Other vendors have built stand-alone network appliances. And one vendor has taken this a step further by creating an Ethernet IP telephone. Vendors designing IP telephony products face two fundamental issues. One is latency, or in laymen's terms the time required for data to travel from point A to point B. Latency does not in of itself destroy data, but it makes for awkward conversation when it climbs above a few tenths of a second. The other fundamental issue is packet loss.
Network performance can fluctuate from moment to moment.
Sometimes data will be transmitted immediately, sometimes it will be delayed or not sent at all. In many respects, the problems facing designers are similar to digital cellular network design in that the underlying transport medium provides no guarantee that data will arrive intact. Therefore, vendors must assume the underlying network is unreliable and compensate for this by using error correction and interpolation techniques to minimize and compensate for lost or severely delayed packets. These problems are not insurmountable by any means, but they do require serious attention. Common IP Telephony Gateway Architectures Vendors have taken several approaches to IP telephony.