Content

| 7.5 |  | Voice Quality Issues |
| 7.5.5 |  | Traffic classification |

Classification
Equally as important as queuing, however, is a QoS mechanism called classification. It is important to differentiate at all points in the network between voice and data traffic so that queuing techniques can be applied in places such as the WAN edge. Classification therefore "marks" voice and data frames differently so that they can be treated differently by the other switches and routers that make up the intelligent IP network. Two standards-based methods are utilized. At Layer 2, 802.1p defines classes of service (CoSs) pertaining to that Ethernet segment. At Layer 3, the IP layer, the IP type of service (ToS) field can carry different values end to end through the network.

The ability to change the Layer 2 and Layer 3 classification parameters to values desired by the network designer is a function inherent in the Cisco AVVID architecture and available in the IP phone integrated switch and some Catalyst switching platforms. The ability of the network manager to manipulate these values at different points in the network defines a parameter called the "trust boundary". For example, if it is trusted that the end stations and phones will set their QoS values correctly so that end-to-end QoS can be maintained, the trust boundary includes the end stations. If, however, it cannot be guaranteed that all end stations behave properly and set their own priority values correctly, then the ability to properly manipulate these parameters is available in the Catalyst switch infrastructure.