Cisco Systems RJ-45-to-AUX manual ∙ Synergy Advanced Multipurpose Bus Arbiter Samba Asic

∙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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