Chapter Summary Continued
X.25 is the oldest of the switched or relayed services and provides the least efficient service due to its error checking.
Frame Relay is an enhancement over X.25 because it is faster and does not provide redundant error checking.
ATM is similar to Frame Relay, except that it is a WAN as well as a LAN protocol.
ISDN is a leased digital line that can support X.25 and Frame Relay connections among others. ISDN comes in PRI and BRI.
BRI provides 128 Kbps throughput over two B-channels, and 16 Kbps over one D-channel that is used for signaling.
PRI provides 23 channels of 64 Kbps each plus one, 64 Kbps D-channel. This allows PRI to offer 1.544 Mbps throughput.