.4 kbps 28 kbps 17 kbps CHAPTER 3.3 VolP Technology All of these QoS schemes are discussed in more detail solution and works on data coming to and from the elsewhere. For our purposes here we will discuss how specified ports or port range. these QoS mechanisms can be used to optimize voice quality in a converged network. In order for a VoIP solution to function well, the Differential services (DiffServ, DSCP, network must be able to give voice packets priority over ordinary data packets or sufficient bandwidth must always be available. There are several strategies available The Differential Services Code Point (DSCP) priori- to provide this prioritization. These strategies include tization scheme redefines the existing ToS byte in the using CoS, prioritizing ports, prioritizing services, and IP header by combining the first 6 bits into 64 pos- using IEEE 802.1 p/Q to set the priority bits. sible combinations. This use of the ToS byte is still evolving but can be used now by vop media control- lers, IP telephones, and other network elements such CoS versus QoS as routers and switches in the LAN and WAN. Please note that older routers may require a DSCP The concepts of CoS and QoS are often confused. CoS is setting of 40 (101,000), which is backward compatible to a classification method only. CoS does NOTensure a level the original ToS byte definition of critical. The ToS byte is of QoS, but is the method used by queuing mechanisms to an OSI model layer 3 solution and works on IP packets on limit delay and other factors to improve QoS. Most CoS the LAN and possibly the WAN depending on the service strategies assign a priority level, usually 0-7 or 0-63, to provider. a frame or packet respectively. Common CoS models include the IP TOS (Type Of Service) byte, Differenti- ated Services Code Point (DiffServ or DSCP, defined in RFC 2474 and others), and the IEEE 802.1 p/Q. IEEE 802.1 p/Q QoS involves giving preferential treatment through queuing, bandwidth reservation, or other methods based Yet another prioritization s