
4
Copyright © 1997 Cisco Systems, Inc.
6-7CSE: Networking Fundamentals — WAN Basics
© 1999, Cisco Systems, Inc.
www.cisco.com
• A logical circuit ensuring reliable
communication between two devices
• Switched virtual circuits (SVCs)
– Dynamically established on demand
– Torn down when transmission is complete
– Used when data transmission is sporadic
• Permanent virtual circuits (PVCs)
– Permanently established
– Save bandwidth for cases where certain
virtual circuits must exist all the time
• Used in Frame Relay, X.25, and ATM
WAN Virtual Circuits
WAN Virtual Circuits
6-8CSE: Networking Fundamentals — WAN Basics
© 1999, Cisco Systems, Inc.
www.cisco.com
OSI Reference Model
Physical
Layer
Data
Link
Layer
Network Layer
LLC
Sublayer
MAC
Sublayer
SMDS
X.21bis
EIA/TIA-232
EIA/TIA-449
V.24 V.35
HSSI G.703
EIA-530
HDLC
PPP
WAN Protocols
LAPB
X.25 PLP
Frame Relay
SDLC
WAN Protocols
WAN Protocols
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