Catalyst 3900
Token Ring Switch

This chapter provides information on the Catalyst 3900 Token Ring switch. The information is organized into the following sections:

• Product Overview

• Standard Features

• Expansion Modules

• Product Numbers

Product Overview

The Cisco Systems Catalyst 3900 is a second-generation Token Ring switch that combines unsurpassed performance and functionality with a cost-effective price, ideally suited for desktop connectivity. The Catalyst 3900 comes with 20 fixed ports and a unique FlexSlot that can accommodate two expansion modules or, in the future, one double-wide module. The Catalyst 3900 switch also offers an optional Stack Port module that enables up to eight units to be stacked together using the Catalyst Matrix switch.

An application-specific integrated circuit (ASIC) design results in low-latency, wire-speed switching of unicast, multicast, and broadcast frames at either half- or full-duplex speeds, regardless of whether they are source-route bridged (SRB), source-route transparently bridged (SRT), or source-route switched (SRS). Adaptive cut-through switching optimizes performance while providing protection from network errors by automatically switching to store-and-forward when errors reach a user-defined threshold.

To address the needs of delay-sensitive data, such as multimedia, this switching fabric contains two data queues. Frames assigned a priority of 5, 6, or 7, such as multimedia transmissions, are sent to the high-priority queue and given forwarding preference. Frames assigned a priority of 4 or lower are processed through the normal-priority queue.

For a bandwidth boost, SRS and dynamic ring learning enable the Catalyst 3900 switch to easily replace an existing Token Ring hub or Media Access Unit (MAU) with no configuration required. In the presence of source-routed traffic, the Catalyst 3900 automatically learns its ring number and forwards frames to downstream bridges based on next-hop information in the routing information field (RIF). Non-Source Routed (NSR) frames are transparently bridged. There is no need to reconfigure your existing network numbering plan when adding the Catalyst 3900 to the network infrastructure.

The Catalyst 3900 switch provides a wide range of connectivity options for maximum flexibility. Connecting a MAU, server, or end station is easy because the Catalyst 3900 enables direct station attachment and ring-in/ring-out (RI/RO) connections to scale ring segment size. Each port supports Dedicated Token Ring (DTR), the IEEE standard that defines direct station attachment at 4, 16, or 32 Mbps. Furthermore, ports 19 and 20 support RI/RO connectivity in addition to DTR. With the TokenChannel feature, you can group up to eight ports together as one logical port for a high-speed connection between switches.

Shielded RJ-45 ports support both 150-ohm shielded twisted-pair (STP) and 100-ohm unshielded twisted pair (UTP). There is no need for external media filters; neither is there a requirement for baluns to do impedance matching for different cable types.

Traffic filters that block or allow traffic are integrated into the bridging ASICs. As a result, enabling MAC address filtering on inbound ports and destination service access point (DSAP) and Subnetwork Attachment Point (SNAP) type filters on inbound and outbound ports has no effect on the media-rate performance of the switch. In addition, in configurations where SRT is used between ports or groups of ports, it is possible to control whether traffic is transparently bridged or source-route bridged on a per-protocol basis. This feature is ideal for environments that have redundant Systems Network Architecture (SNA) gateways and IP or IPX file servers that are not configured for SRB. With this capability, ports with SNA gateways can be configured to receive only SRB traffic, preserving the ability to have multiple gateways with the same MAC address, while also eliminating unnecessary transparently bridged traffic. Likewise, the switch ports with only IP or IPX servers can be configured to receive only the protocol traffic destined for them.

All-routes explorer reduction provides traffic control for networks with multiple user rings connected to dual-backbone segments. With this feature, when a client station sends an explorer frame, the switch forwards a copy of only one frame if it has not already been seen by the switch on any of its other ports. Therefore, in a dual-backbone configuration, each user ring receives only two copies of the broadcast. In this way, the client stations still learn backup paths to their servers, and the user rings are protected from unnecessary broadcast traffic. User-configurable broadcast thresholds are provided to protect end systems from excessive explorer traffic. Priority queues within the switch ensure that delay-sensitive traffic, such as multimedia applications, are forwarded first.

Figure 150 shows the front view of the Catalyst 3900. Table 93 summarizes the features of the Catalyst 3900, and Table 94 lists the environmental specifications.

Standard Features

The Catalyst 3900 provides the following features:

• 20 shielded Token Ring ports for 150-ohm STP or 100-ohm 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

• Support for the following bridging modes: SRS, SRB, SRT

• Adaptive cut-through switching

• Automatic 4/16/32-Mbps speed adaptation

• Automatic shared and dedicated adaptation (DTR)

• Two priority queues for multimedia traffic

• TokenChannel switch interconnect

• MAC address and protocol (DSAP/SNAP) filters

• All-routes explorer reduction

• Broadcast rate protection

• IEEE and IBM Spanning-Tree Protocol

Configurations larger than 20 Token Ring LAN segments can be constructed by:

• Connecting two Catalyst 3900 switches together using any of the ports on each switch, to form a TokenChannel. TokenChannels are two to eight parallel links that connect Catalyst 3900 switches. TokenChannels provide a capacity between the two Catalyst 3900 switches of up to 128 Mbps in half-duplex (HDX) mode and up to 256 Mbps if all ports in the TokenChannel are operating in full-duplex (FDX) mode.

• Connecting two Catalyst 3900 switches together using the optional stack port module in a back-to-back configuration.

• Connecting up to eight Catalyst 3900 switches together using the optional stack port module and a Catalyst Matrix.

To aid in network management, the Catalyst 3900 also maintains status information and a variety of statistics. Status information is available for each port and for each TokenChannel, if defined. Statistics are kept by port, by VLAN, and for the switch as a whole.

The Catalyst 3900 also contains an SNMP MIB-II-compliant management agent that allows a customer-supplied SNMP-based network management system (such as CiscoView) to remotely monitor and control the Catalyst 3900.

In addition, the Catalyst 3900 provides switched port analyzer support, which allows you to monitor traffic on any of the Token Ring ports using a customer-supplied monitoring device such as the Network General Sniffer.

If you need to upgrade the Catalyst 3900 software, you can upgrade through the same serial port used for configuration. The code can be downloaded from a customer-supplied programmable workstation using the Xmodem protocol. Code upgrades can also be accomplished using Trivial File Transfer Protocol (TFTP).

Expansion Modules

The Catalyst 3900 has a rear stack port that supports an optional Stack Port module providing a 280-Mbps link between back-to-back switches or between the Catalyst 3900 and the Catalyst Matrix switch for configuration requiring up to eight units in a stack.

Future expansion modules will include a four-port fiber module, a four-port copper module, a two-port copper ISL uplink, a two-port fiber ISL uplink, and an ATM OC-3uplink.

Product Numbers

The Catalyst 3900 ships with a power supply, power cable, and documentation. Table 95 lists the product numbers you can use to order the Catalyst 3900 and its expansion module. If a product number ends with an equal sign (=), the item can be ordered only as a spare. If a product number does not end with an equal sign, the item can be ordered as a spare or as a configurable part of a system order.