net and will support advanced multimedia applications, such as teleimmersion, virtual reality, and telerobotics. 6bone An experimental network used as an environment for IPv6 research. More than 1,173 networks in some 60 countries were connected to the 6bone IPv6 network. 6bone ceased to operate in 2006, and IANA reclaimed all 6bone prefixes. 6to4 A technique for enabling IPv4-to-IPv6 interworking and coexistence that interconnects IPv6 networks over IPv4 networks without explicitly defined tunnels. 8-PSK (eight phase-shift keying) A PSK modulation scheme in which 3 bits at a time are encoded. A (access) link A link that interconnects an STP with either an SSP or an SCP. The SSP and SCP, collectively, are referred to as the signaling endpoints. A message sent to and from the SSPs or SCPs first goes to its home STP, which in turn processes or routes the message. AAA (authentication, authorization, and accounting) A network server used for access control. Authentication identifies the user, authorization implements policies that deter- mine which resources and services a valid user may access, and accounting keeps track of time and data resources used for billing and analysis. AAL (ATM adaptation layer) The ATM layer that is responsible for the adaptation of the information of the higher layer to the ATM cells. It is composed of two layers, the Segmentation and Reassembly sublayer and the Convergence sublayer. ATM adaptation layer 1 supports CBR voice and video network services. ATM adaptation layer 2 supports VBR voice and video network services. ATM adaptation layer 3 supports VBR connection-oriented data services. ATM adapta- tion layer 4 supports VBR connectionless data services. ATM adaptation layer 5 supports connec- tionless VBR data (e.g., IP or signaling) over ATM. The native stream (whether it's real-time, analog, voice, MPEG-2 compressed video, or TCP/IP) goes through the AAL, where it is seg- mented into 48-byte cells. ABR (available bit rate) One of the ATM service classes. ABR supports VBR data traffi