Key Features and Benefits
The Catalyst 3900 has the following features:
Twenty shielded Token Ring ports for 150−ohm shielded twisted pair (STP) or 100−ohm unshielded
twisted pair (UTP) connectivity
•
FlexSlot accommodating two expansion modules or one double−wide module for future expansion• Nine−pin EIA/TIA−232 interface for local console or modem connectivity• Automatic 4−, 16−, and 32Mbps speed adaptation• TokenChannel switch interconnect• MAC address and protocol (DSAP/SNAP) filters• IEEE and IBM Spanning−Tree Protocol•
The Catalyst 3920 provides the following features:
Twenty−four shielded Token Ring ports for 150−ohm STP or 100−ohm UTP connectivity• Nine−pin EIA/TIA−232 interface for local console or modem connectivity• Automatic 4−, 16− and 32Mbps speed adaptation• TokenChannel switch interconnect• MAC address and protocol (DSAP/SNAP) filters• Spanning−Tree Protocol•
When you need to upgrade the Catalyst 3900 or 3920 IOS, you can do so by using the same serial port that is
used for configuration. You can upgrade code by using Trivial File Transfer Protocol (TFTP) from a TFTP
server or uploaded through the workstation using HyperTerminal. Table E.7 shows key features of the
Catalyst 3900 series.
Table E.7: The key features of the Cisco Catalyst 3900 series.
Feature 3900 3920
Ports 20/24/28 24
Stack slot 1 1
Expansion slots 1 FlexSlot None
Backplane 520Mbps 520Mbps
Processor Intel 960SA Intel 960SA
DRAM Up to 8MB Up to 8MB
Stackable Yes Yes
Distribution Layer Switches
The Distribution layer is the demarcation point between the Access and Core layers. This level terminates the
traffic that originates in the Access layer connections and summarizes the traffic before passing it along to the
Core layer. It can best be described as the layer that provides policy−based connectivity.
The main focus of the Distribution layer is to define the boundaries for the network and to provide packet
manipulation of the network traffic. It provides isolation from topology changes, manages the size of the
routing table, and aggregates network traffic.
In addition, interdomain traffic is redistributed at the Distribution layer, and static and dynamic route
redistribution occurs at this point. This layer is also commonly used as the point at which remote sites connect
to the network. Let’s take a look at the different switches typically found at this layer.
In this section we’ll be looking at the following switches:
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