Switching Traffic Flow - Cisco Catalyst 4500e Series Installation Manual

System Architecture

Switching Traffic Flow

All Catalyst 4500 series switches use a shared memory switching fabric. All forwarding decisions, QoS,
security policies and transmit queuing are implemented in the Supervisor Engine. Individual switching
modules are transparent, and only contain simple stub ASICs and PHYs; they do not perform buffering
or local switching. Classic switching modules and Classic IOS supervisor engines have a per slot
switching capacity of 6 Gbps, while E-series switching modules and supervisor engines have a per slot
switching capacity of 24 Gbps.
Frames flow into the switch through interfaces on the switching modules. Each switching module
connects to a backplane that supports a connection of up to 24 Gbps up to the supervisor engine. When
a frame reaches the supervisor engine, and a forwarding decision is made, the packet is sent out a port
on the same switching module, a different switching module, or the supervisor engine uplinks.
Figure 1-19
Figure 1-19
Over-subscription
Classic Catalyst 4500 Series 48 port 10/100/1000 E-Series Switching modules are 8:1 oversubscribed
and Catalyst 4500 E-Series 48 port 10/100/1000 Switching modules are 2:1 oversubscribed. On both
types of switching modules, there are multiplexing ASIC's which group the front panel ports and
multiplex them to the internal switch fabric. On a 48 port 10/100/1000 Classic Catalyst 4500 Series
switching module, eight front panel ports are multiplexed into a a single, nonblocking, full-duplex
Gigabit Ethernet connection to the internal switch fabric of the Catalyst 4500 Classic Supervisors or the
Supervisor 6-E. On the Catalyst 4500 E-series 48 port 10/100/1000 switching modules, six front panel
ports are multiplexed into a 3 gigabit nonblocking, full-duplex Ethernet connection to the internal switch
fabric on the Supervisor Engine 6-E.
If the data rate received for a port presents a potential overflow condition, flow control sends pause
frames to the remote port to temporarily stop traffic and prevent frame loss. For both Classic and E-series
switching modules each port operates independently so that flow control, or configuration of one port,
does not block or degrade the performance of another port in that group.
The 6 port 2.5:1 oversubscribed 10GbE X2 based switching module operates in a similar way. The six
front panel ports are multiplexed by groups of three into two ASICS, each having a 12 gigabit connection
into the internal switch fabric.
Catalyst 4500 E-Series Switches Installation Guide
1-36
shows a conceptual diagram of switching traffic flow through the system.
Switching Traffic Flow
6 Gbps per slot
Classic switching module
24 Gbps per slot
E-Series switching module
chassis
Uplinks
Supervisor Engine
Chapter 1 Product Overview
IP
network
OL-13972-01