AX88615 ASIX [ASIX Electronics Corporation], AX88615 Datasheet - Page 13

• Manufacturer Part Number: AX88615
• Description: 5-Port 10/100BASE Ethernet Switch
• Manufacturer: ASIX [ASIX Electronics Corporation]

3.0 Functional Description
3.1 Basic Operation
In general, the basic operation of the switch is very simple. The switch receives incoming packets from one of its ports,
searches in the Look-Up Table for the Destination MAC Address and then forwards the packet to the destination ports,
if appropriate. If the destination MAC address is not found in the Look-Up Table, the switch treats the incoming packet
as a broadcast packet and forwards it to all ports except itself. Basically the switch automatically learns the port number
of attached network devices by examining the Source MAC Address of all incoming packets. The device is updated the
table with the Source MAC Address if the Source MAC Address does not exist the table.
3.2 Packet Filtering and Forwarding Process
During the receiving process, the switch will monitor the length of the received packet. Legal Ethernet packets should
have a length of no less 64 bytes and nor more than 1528 bytes. The switch discards any packet with illegal length.
After a packet is received, its Source MAC Address and Destination MAC Address are received. The Source MAC
Address is used to update the Look-Up Table and the Destination MAC Address is used to determine the destination port
of the packet. Once a MAC Address has been learned, and the packet is buffered, it must be forwarded, That is, the packet
forwarding mechanism for the switch is handled automatically based on the destination MAC Address.
Under the following conditions, received packets are filtered:
The switch supports three forwarding modes: Store-and-Forward, Fragment-Free and Auto.
3.3 MAC Address Learning and Aging Process
The switch can learn up to 8K unique MAC addresses with a hashing algorithm. Addresses are stored in the Look-Up
Table located in external SSRAM, then each packet updates the table.
The table lookup engine provides the switching information required routing the data packets. The address table is set up
through auto address learning dynamically. After the switch receives a packet, the Source MAC Address and Destination
MAC Address are received. The Source Address retrieved from the received packet is automatically stored in a SA
buffer. The switch will check for error and perform a SA search. The switch will update the Look-Up Table with the
Source MAC Address if there is no error.
The Look-Up Table is cleared on power-on, or hardware reset. When the aging option is enabled, the dynamically
Learned SA will be cleared if it is not refreshed in less than configured time (2 or 5 min).
3.4 Flow Control Process
The switch can operate at two different modes: half-duplex and full-duplex. Each port can be configured to have flow
control enabled or not. The switch supports 802.3X for full-duplex operation and uses back pressure for half-duplex.
In full-duplex mode, the switch will receive and transmit the packet in accordance to 802.3X. The transmission channel
and the receiving channel operate independently. If the occupancy of the buffer memory is above the FlowControlActive
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The switch will check all received packets for errors, e.g., FCS error, runt packet, long packet, etc.
Any packet handing to its own source port will be filtered. That is, its destination port is its source port.
The incoming packet will be discarded if the switch’s buffer memory is full.
Store-and-Forward Mode: An entry packet is received, checked and stored in the buffer memory before it
Fragment-Free Mode: It is a simple improvement on Cut-Through method. The switch will forward a
Auto Mode: In Auto mode, the switch select dynamically its optimized forwarding mode based on the
is forwarded. That is, each forwarded packet is correct.
packet whose packet length is more than 64 bytes. All runt packets will be filtered in Fragment-Free
mode.
current network quality of each port.
AX88615P 5-Port 10/100Mb Switch Controller PRELIMINARY
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ASIX ELECTRONICS CORPORATION
CONFIDENTIAL