Allied Telesis AT-MR840TF - Manual (Page 24)

Product Description
4
Jabber Lock-up Protection
Jabber lock-up protects the hub from being overrun with excessively long data
packets by isolating segments that contain these oversized packets (exceed
maximum packet length). Therefore, jabber lock-up automatically prevents
data which exceeds the allowed duration (usually 5 ms) from reaching the hub,
or if the hub has been continuously transmitting for more than 65,536 bit times.
This protection scheme automatically interrupts transmission for 96 bit times.
Fragment Extension
If the total packet length received is less than 96 bits, including preamble, the
packet length is expanded to 96 bits by appending a jam sequence to the
original fragment.
Jam Signal
If one port detects a carrier, the hub repeats all received data form this port to
another port. If a collision is detected while sending data to a port, the hub
sends the jam signal to all connected ports. If the collision status continues on
only one port even after 96 bits of jam signal have been sent, the jam signal is
sent to ports in the non-collision status.
Functional Block Diagram
Figure 3 shows the relationship between the major components of the
AT-MR840TF hub; Table 1 lists and identifies these components.
Figure 3: AT-MR840TF Functional Block Diagram
RX TX
10Base-FL (ST/SC)
10Base-T (RJ45)
(2) (2) (2) (2)
8 7 6 5 4 3 2 1
(1) (1)
(3)
(4) (4)
MR840TF_Book Page 4 Tuesday, November 11, 1997 3:46 PM