3Com 3CRWDR300A-73-US User Guide - Page 87

Internet Settings 85 9 QoS Class: select CBR, UBR or VBR. ■ CBR (constant bit rate): the CBR service class is intended for real-time applications, for example, those requiring tightly constrained delay and delay variation, such as voice and video applications. The consistent availability of a fixed quantity of bandwidth is considered appropriate for CBR service. ■ VBR (variable bit rate): QoS class defined by the ATM Forum for ATM networks. VBR is subdivided into a real time (RT) class and non-real time (NRT) class. VBR (RT) is used for connections in which there is a fixed timing relationship between samples. VBR (NRT) is used for connections in which there is no fixed timing relationship between samples, but that still need a guaranteed QoS. Compare with ABR, CBR, and UBR. ■ UBR (unspecified bit rate): the UBR service class is intended for delay-tolerant or non-real-time applications, for example, those which do not require tightly constrained delay and delay variation, such as traditional computer communications applications. The UBR service may be considered as "best effort service". 10 PCR/SCR/MBS: PCR (Peak Cell Rate), SCR (Sustainable Cell Rate) and MBS (Maximum Burst Size) are configurable. 11 Click Apply.