QUALITY OF SERVICE
As new entertainment-based applications are deployed over home networks, Quality of Service (QoS) features will be needed to arbitrate between traffic flows that are competing for different resources on the network. QoS allows home networking applications to prioritize individual services. An example is videoconferencing, which uses QoS to guarantee enough bandwidth to deliver high-quality video. Any application that is deployed in an in-home network must provide the following guarantees.
Minimum latency— Latency is best described as the amount of time it takes for a packet of multimedia data to get from the sending appliance to the receiving appliance on the in-home network. The latency delay can have a serious impact on the quality of the multimedia stream of data that is flowing around a house.
Minimum jitter impact— Whereas the exact sequence of regular network traffic that arrives at the receiving host isn't always important, multimedia-based information must always be delivered to the receiving device in sequence. Jitter in the transmission signal causes dropped packets and decreases the overall performance of an in-home network.
Coexistence parameters— This value is used to measure the impact of broadcasting unpredictable bursts of multimedia data across a home network. This type of traffic behavior can cause gaps in the multimedia data stream.
Bandwidth— Rich multimedia applications such as home video distribution systems require large amounts of bandwidth. QoS needs to guarantee that these types of applications do not overpower all other network traffic on a home network.
So what type of technologies are able to support services such as QoS? ATM provides QoS guarantees that other transport protocols such as TCP/IP are unable to deliver. Ethernet is able to give you speeds of 100 Mbps, but only ATM can give the QoS services required for real-time communications within a home. Many of the home networking technologies that we discussed in previous chapters also provide QoS mechanisms. Implementing and managing a QoS-aware network is a complex task for most people. Fortunately, companies like Microsoft are integrating QoS components into the next release of operating systems, which should make life easier for all of us.