Media Modules

The layer 2 and layer 3 media modules implement wire speed routing and bridging in ASICs. The routing and bridging ASICs can process 1.5 million packets per second of minimum-sized Ethernet frames.

NOTE: All layer 3 modules interoperate with layer 2 modules.

The ATM Uplink module provides LAN Emulation (LANE) connectivity over an ATM network and supports RFC 1483.

Bridging and routing are performed on the input side of each media module. Frames whose destination Media Access Control (MAC) address is on the same Virtual LAN (VLAN) as the interface on which they arrived are bridged. Frames that are going from one VLAN to another are routed. Some frames are both bridged and routed, as is the case with multicast.

The media modules’ features include:

• Onboard routing--See “Routing Overview” later in this chapter for more information about the onboard routing capability of the media modules.
• IEEE 802.3x full-duplex flow control--This allows the switch ports to send a pause command before input buffers overflow. Half-duplex ports support active backpressure (jamming).
• VLAN trunking or non-tagged access modes --This allows the switch ports to interoperate with popular tagged trunking schemes used by other vendors.
• Priority Queuing and Class of Service--These features allow you to prioritize traffic between particular stations or sets of stations to support jitter-sensitive applications.