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Synergy Advanced Multipurpose Bus Arbiter (SAMBA) ASIC•
EARL ASIC
The Encoded Address Recognition Logic (EARL) ASIC performs functions that are very similar to those of
the Content Addressable Memory (CAM) table. Switches use this CAM to make filtering and forwarding
decisions. The EARL ASIC connects directly to the data switching bus, allowing the ASIC access to all the
frames that cross the switching fabric. The switch makes forwarding decisions based on the destination Media
Access Control (MAC) address.
Note The CAM table contains the MAC address of the interfaces connected to the port and the time the switch
last read a frame from that source port and address. The CAM table receives updated information by
examining frames it receives from a segment; it then updates the table with the source MAC address
from the frame.
The EARL ASIC aids in building a table containing all the information the switch has extracted from
incoming frames. This information includes the source MAC address, the port of arrival, the virtual LAN
(VLAN) membership of the port of arrival, and the time the frame was received. This table can contain up to
128,000 entries. Entries in the table are removed after the time to live (TTL) has expired. The default TTL at
which entries are removed is 300 seconds; this time can be set from 1 to 20 minutes.
The EARL ASIC tags each frame as it arrives at the switch before the frame is buffered. This tagging includes
the source port’s identity, the VLAN, and a checksum. This tagging should not be confused with the tagging
used in trunking for Inter−Switch Link (ISL) or 802.1Q, discussed in Chapter 5. The tagging the EARL places
in the frame is removed before the frame exits the switch. The EARL ASIC’s placement is shown in Figure
4.2.
Figure 4.2: EARL ASIC placement on the Crescendo architecture.
EARL+ ASIC
The Encoded Address Recognition Logic Plus (EARL+) ASIC allows the EARL to support Token Ring line
modules. The EARL+ ASIC is an enhancement to the EARL ASIC and is used on the Supervisor Engine III
Module.
SAINT ASIC
The Synergy Advanced Interface and Network Termination (SAINT) ASIC allows a switch interface to
support both half−duplex and full−duplex Ethernet. This ASIC has a second responsibility to handle frame
encapsulation and de−encapsulation, and gathering statistics for trunked ports.
SAMBA ASIC
The Synergy Advanced Multipurpose Bus Arbiter (SAMBA) ASIC and the EARL ASIC work in tandem to
let ports access the bus, thus allowing frames to be forwarded correctly. Both the Supervisor Engine and the
installed line modules utilize this ASIC; it can support up to 13 separate line modules.
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