ip178a ETC-unknow, ip178a Datasheet - Page 18

• Manufacturer Part Number: ip178a
• Description: 8-port 10/100 Ethernet Integrated Switch
• Manufacturer: ETC-unknow

Back off Algorithm
IP178A provides two parameters to modify its back off
algorithm. They are Modbck and Drop16. IP178A
implements the IEEE802.3 standard binary exponential
back off algorithm (Modbck=0) and modified back off
algorithm (Modbck=1) when it works at half duplex mode.
If Modbck is set, the maximum back off time is limited to
eight-slot time. The minimum defer time is separated into
the two periods. The first period consists of the first
64-bit time and the 2
bit-time. In the case of minimum defer time IP178A
transmits a packet after 96-bit time immediately in spite
of the status of cable on the 2
consecutive collisions, the transmitting packet is dropped
if Drop16 is set.
Operation Parameter
IP178A supports many optional functions. They can be
configured to fit different requirements by setting
appropriate parameters. These parameters can be fed
into IP178A through EEPROM interface or through pins.
Flow Control
IP178A provides two mode of flow control. Backpressure
is for half duplex mode and IEEE802.3x flow control is
for full duplex.
Preliminary, Specification subject to change without notice
IP178A-DS-P05
Sep. 09, 2002
nd
period consists of the rest 32
nd
period. After 16
18
Backpressure
The backpressure is used for flow control in half duplex
mode if Bk_en is turned on. When the buffer of a port is
full, it will start to send jam signals. The remote station
will defer transmission after detecting the jam signals.
Carrier based backpressure is sent by IP178A, when the
buffer of a port is full. IP178A sends jam packets
continuously to defer the remote station. The length of
jam packet is 1518 byte and the IPG is equal to 96-bit
time. If the port has packets to transmit during this period,
it transmits the queuing packet instead of the jam
packets. After the queuing packets are transmitted,
IP178A resumes to jam the segment by sending jam
packets if the buffer of a port is full. If a collision occurs,
the back off algorithm is skipped and the jam packets are
generated immediately. The definition of buffer full for
carrier base backpressure is there is only one empty
buffer for a port.
(Advance Version)
IP178A