Abstract: After the demands for network bearer service SLA （NSLA） in NGI are analyzed,taking possible application scenarios of NSLA as well as new features of IPv6 into account,this paper defines four QoS parameters for IPv6 NSLA：IP packet transfer delay （IPTD）, IP

Key words: Quality of service, Network bearer service SLA （NSLA）, IP packet throughput capability （IPTC）, IP packet delay variation （IPDV） ,IP packet fail ratio （IPFR）