DFS类型有两种，它们是哪两种？（）

A.独立DFS

B.基于域DFS

C.服务器DFS

D.客户DFS

Frame Relay is simplified form of (1) , similar in principle to (2) , in which synchronous, frames of data are routed to different destinations depending on header information.

Packets are routed throught one or more Virtual Circuits known as (3) Most Virtual Circuits are (4) , which means that the network provider sets up all DLCI connections at subscription time. (5) are also part of the Frame Relay specification. They privide a link that only lasts only as long as the session.

1（）

A．Datagram Switching

B．Datagram Routing

C．Packet Switchig

D．packet Routing