Specifications

A-5
Cisco 1700 Series Router Software Configuration Guide
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Chapter A Networking Concepts
WAN Technologies
• It uses fiber media/digital transmission links. These types of physical
connections have a high level of data integrity, so Frame Relay does not need
to perform error checking. Error checking is time-consuming and can
decrease WAN performance.
• It does not need to perform flow control procedures because these types of
procedures are done by upper-layer protocols. Frame Relay uses a simple
congestion notification mechanism to inform user devices when the network
become congested. Congestion notification alerts the higher-layer protocols
that flow control is needed.
Current Frame Relay standards support permanent virtual circuits (PVCs) that are
configured and managed in a Frame Relay network. The Cisco 1700 router
supports switched virtual circuits (SVCs) for DTE interfaces.
Frame Relay also has Local Management Interface (LMI) extensions for
supporting large, complex internetworks. Any LMI extension known as common
should be implemented in internetworks that support the LMI specification. Other
LMI extensions are known as optional.
The LMI extensions are as follows:
• Virtual circuit status messages (common)—Provide communication and
synchronization between the network and the user device, periodically report
the addition of new PVCs and the deletion of existing PVCs, and provide
information about PVC integrity.
• Multicasting (optional)—Allows a sender to transmit a single frame to
multiple recipients, supporting the efficient routing of protocol messages and
address resolution procedures that typically must be sent to many destinations
simultaneously.
• Global addressing (optional)—Gives connection identifiers global rather than
local significance, allowing them to be used to identify a specific interface to
the Frame Relay network. Global addressing makes the Frame Relay network
resemble a LAN, with respect to addressing.