AM79C985 Advanced Micro Devices, AM79C985 Datasheet - Page 47

• Manufacturer Part Number: AM79C985
• Description: enhanced Integrated Multiport Repeater Plus (eIMR+)
• Manufacturer: Advanced Micro Devices

Appendix A
Security
EAVESDROP PROTECTION
The eIMR+/HIMIB devices are capable of providing
network eavesdrop protection. This feature is protected
by a software key. An application note containing the
necessary software key and implementation details is
available from AMD. A brief description of eavesdrop
protection is given below. For more information, contact
your local AMD sales representative.
FEATURES SUMMARY
Eavesdrop protection is based on the concept that con-
fidential data should only be received by specified se-
cure stations. The eIMR+/HIMIB devices are capable of
repeating packets only to ports considered secure for a
packet’s destination address. On all other ports, trans-
mission can be disrupted by transmitting a pattern of
alternating 1s and 0s.
The eIMR+/HIMIB can disrupt packet transmission, as
described above, on ports not having a valid address.
Valid addresses are determined by comparing a
TCLK
CLK
STR
Note: TCLK illustrates internal eIMR+ chip clock phase relationship.
Figure A1. STR Input Signal from Am79C987 HIMIB Device
AUI
TP0
Am79C985
TP1
TP2
packet’s destination address with the two address reg-
isters associated with each repeater port: Last Source
Address Register and Preferred Source Address Reg-
ister. Eavesdrop protection can be masked on a port-
by-port basis. Disruption of multicast packets can also
be masked on a port-by-port basis. If the destination
address is a broadcast address, the packet is transmit-
ted unmodified on all ports.
In many instances, a station targeted with a specific
destination address will not reside within the same re-
peater as the originating station. To ensure that packets
arrive at the intended destination, eIMR+/HIMIB ports
can be programmed to pass packets with an invalid des-
tination address undisturbed if no other port on the re-
peater has a valid address that matches the destination
address. The eIMR+/HIMIB devices can determine if
there is a match on the repeater by monitoring its ports
and by monitoring signals on the eIMR+/HIMIB expan-
sion bus.
TP3
TP4
TP5
TP6
TP7
20651B-34
A-1