Catalyst 5000/5500 Architectures
As previously discussed in this chapter, the Catalyst 5000 line
of switches uses a shared bus architecture to transport incoming frames from
source to destination. The Catalyst 5000 uses a total of three buses to move
data, communicate configuration and network management information, and
determine which ports should forward or discard frames.
The following describes the bus types on the Catalyst 5000
series:
-
Switching or data bus (dBus)—
The dBus is used to switch frames between line cards. The data bus is 48 bits
wide and operates at 25 MHz, yielding 1.2 Gbps of bus bandwidth.
-
Management bus (mBus)— The
mBus carries configuration information from the NMP to each module and
statistical information from each module to the NMP, using the Serial
Communication Protocol (SCP).
-
Results/index bus (rBus)— The
rBus carries port-select information from the central EARL ASIC to the ports.
This information determines which ports forward the packet and which flush it
from the buffer.
The Catalyst 5500 series implements these same three buses,
plus two additional data buses, each providing 1.2 Gbps of bandwidth, yielding
3.6 Gbps of total bus bandwidth. To maintain backward compatibility with the
Catalyst 5000 line cards, the chassis of the 5500 series were designed so that
newer line cards connected to all three buses, while still allowing older
Catalyst 5000 line cards to connect to a single bus. Figure 3-5 illustrates the types of the connections on the
Catalyst 5500 backplane.
The Catalyst 5500 introduced a 5-Gbps Asynchronous Transfer
Mode (ATM) cell switch bus for use with an optional ATM switch processor based
on Cisco Lightstream 1010 technology. As with all Catalyst switches, Slot 1 is
reserved for a Supervisor module. Switching modules installed in Slots 1–5
connect to all three 1.2-Gbps buses providing 3.6 Gbps of total bandwidth.
While Gigabit Ethernet modules are available for the Catalyst
5000 and 5500 series, certain restrictions apply to where they can be installed
to provide enough bandwidth to enable all the ports. Gigabit Ethernet modules
should be installed in slots with connections to all three 1.2-Gbps buses. Slot
13 is reserved for the ATM switch processor (ASP). A detailed discussion of the
ATM switching capabilities on the Catalyst 5500 is beyond the scope of this
book. More information on Catalyst 5500 ATM switching capabilities is available
on the Cisco website at
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