t71l6808a TM Technology Inc., t71l6808a Datasheet - Page 7

• Manufacturer Part Number: t71l6808a
• Description: Octal 10/100 Switch With Embedded Memory
• Manufacturer: TM Technology Inc.

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Preliminary T71L6808A
(bandwidth and available space in transmit queues). The T71L6808A will discard broadcast or
multicast packets if the number of those packets exceeds the threshold .
Data Transmission
The T71L6808A transmits all packets in accordance to IEEE 802.3 standard. The T71L6808A will
send the packets with a guaranteed minimum IPG (Inter Packet/Frame Gap) of 96BT even if the
received packets have an IPG less than the minimum requirement. The IPG is 9.6us for 10Mbps
Ethernet and is 960ns for 100Mbps fast Ethernet.
During a transmit process the packet data is read from the memory buffer and forwarded to the
destination port’s PHY device in di-bits. Seven bytes of preamble signal (10101010) will be
generated first before the SFD (10101011). Frame data is sent after the SFD along with four-bytes
of FCS at the end.
Back off Algorithm
The T71L6808A implements the truncated exponential back off algorithm compliant to 802.3
standard. The collision counter will be restarted after 16 consecutive collision.
Head-Of-Line Blocking
The T71L6808A incorporate a simple mechanism to prevent Head-Of -Line blocking problem when
flow control is disabled. When flow control function is disabled, the T71L6808A will first check the
destination address of incoming packet. If the destined port is congested, the T71L6808A will
discard this packet to avoid the blocking of next packet which is going to loose traffic port.
Flow Control
The T71L6808A supports IEEE 802.3x full duplex flow control and half duplex back pressure
congestion control. The IEEE 802.3x flow control's ability is auto-negotiated between remote device
and the T71L6808A by writing the flow control ability via MDIO to external connected PHY. The
T71L6808A adopts a special back-pressure design, forwarding one packet successfully after 28
force collisions, to avoid the connected repeater being partitioned. The full duplex flow control
ability can be enabled or disabled via ENFCTRL pin. And the half duplex back pressure function
can be enabled or disabled via the ENBKPRS pin.
Port-based VLAN
T71L6808A can be divided up to 2 different VLAN groups by programming VLAN. Broadcast
Taiwan Memory Technology, Inc. reserves the right
P. 7
Publication Date:May. 2001
to change products or specifications without notice.
Revision:0.A