Product specifications

Chapter 2: Product Overview Efficient Networks
®
Router family
Technical Reference Guide
Page 2-4 Efficient Networks
®
Virtual Connections
The router’s wide area network (WAN) interface uses Asynchronous Transfer Mode
(ATM) virtual connections (VCs) to transport data. The system provides unlimited VC
support.
ATM
Asynchronous Transfer Mode (ATM) is a networking technology that provides support
for a wide variety of services and applications.
ATM is based on the transfer of fixed-length cells (53-byte) containing a header and
an information field. The header is used to route the cells through the ATM network
backbone. ATM defines the connections by two main parameters:
• Virtual Path Identifier (VPI) - The VPI is an 8-bit field in the header of an ATM
cell.
• Virtual Channel Identifier (VCI) - The VCI is a 16-bit field in the header of an
ATM cell.
These parameters, used together, provide information that identifies the cell’s
destination as it passes through ATM switches.
When there is no data to transfer, the ATM link (endpoint-to-endpoint) will send cells
across the link until data is present; at that point, the data is incorporated into the
stream of cells. When multiple VCs are needed simultaneously, the data is
multiplexed to share the link bandwidth.
Routing and Bridging
The 5900 Series Business Gateway does not operate in an explicit bridging or routing
mode, but can operate as a bridge, as a router, or as both as defined by the
configuration of the specified protocol. The following sections describe routing and
bridging and how the two functions operate together.
Routing
Routing is the process that determines where data is sent. A router can route user
data from source to destination over different LAN and WAN links. Routing relies on
routing address tables to determine the best path for each packet to take.
The routes within a routing address table are established in two ways:
• You can enter specific static routes. For each route, you enter the address for
a remote destination with path details and a value for the perceived cost of
that route (path latency).
• The routing tables can also be built dynamically; i.e., the location of remote
stations, hosts, and networks are updated from broadcast packet
information.