Clearing the way
- By Paul Korzeniowski
- May 28, 2001
IP was optimized to support simple data transmissions over Ethernet networks and performs that task very well. With the recent emergence of desktop video and voice applications, the network protocol is now being asked to support multimedia transmissions.
Problems arise because voice and video have different transmission requirements than data. Currently, information travels across IP networks in a random fashion. In a series of 10 packets, packet No. 8 may arrive before packet No. 6. The computer system at the other end shuffles the packets so the information is presented correctly to an end user.
Packet arrival order is not important with most data applications because the user will sit and wait as information appears. But it is vital with video and voice transmissions. If packets arrive in the improper sequence, a picture may fluctuate or a voice may sound garbled. If two workers are conversing, they may find the fluctuation annoying. If two doctors are examining medical images, the flickering could be catastrophic.
A related problem is bandwidth contention. On an Ethernet network, bandwidth is parceled out on the fly. A user may begin sending a large file when no one else is using the network and the transmission will start out fine. Another user may begin to access a database and the transmission for both could slow to a crawl.
Video and voice applications cannot tolerate such fluctuations. If available bandwidth shrinks, such a transmission will jar or possibly break completely. These applications need to be assured that bandwidth will be available during an entire session.
Quality-of-service (QOS) features solve these problems by opening a clear communication line between two endpoints and maintaining it during the entire transmission. The other applications cannot interfere with the data flow.
With QOS, an organization can prioritize different types of traffic and ensure that voice and video applications have sufficient bandwidth to run without interference.