ation of media flows at the organizations, and two different philosophies. The voice media gateway. network has always been separate from the data network Signaling gateway SS7-IP interface, coordinates SS7 because the characteristics of voice applications are very view of IP elements and IP view of different from the characteristics of data applications. SS7 elements. The traditional voice network is circuit switched. In- Media gateway Terminates PSTN lines and teractive voice traffic is sensitive to delay and jitter but packetizes media streams for IP can tolerate some packet loss. The voice philosophy was transport. to ensure the "five nines" of reliability-99.999 percent-because the lack of communication might be life threatening (i.e., the inability of placing a "911" call for help). Voice calls have always been networked Delay through dedicated lines to maintain no delay and re- In VoIP excessive end-to-end delay makes conversation liability. The data network, on the other hand, is packet inconvenient and unnatural. Each component in the switched. Data is less sensitive to delay and jitter, but transmission path-sender, network, and receiver-adds cannot tolerate loss. The data philosophy has been delay. ITU-TG.11 (One-Way Transmission Time) rec- concerned with providing reliable data transmission over ommends 150 ms as the maximum desired one-way la- unreliable media, regardless of delay. Bandwidth in the tency to achieve high-quality voice. Packet delay is the data world is largely shared, so congestion and delay are length of time it takes a packet to traverse the network. often present for multimedia applications such as voice. Users will experience difficulties in carrying on a normal Voice and Data network processes work very differ- conversation when the one-way network delay exceeds ently. Data can tolerate delay or latency at a certain 50 ms. Packet delay in excess of 50 ms can have a no- limitation, but voice application is very sensitive to delay, ticeable effect. However, some applications or use