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Импульс называется "Link pulse".
Смотреть надо стандарт "IEEE802.3" доступен бесплатно на IEEE.org
Вот кусочек оттуда:
link pulse:Communication mechanism used in 10BASE-T and 100BASE-T networks to indicate
link status and (in Auto-Negotiation-equipped devices)to communicate information about abilities and
negotiate communication methods.10BASE-T uses Normal Link Pulses (NLPs),which indicate link status
only.10BASE-T and 100BASE-T nodes equipped with Auto-Negotiation exchange information using a Fast
Link Pulse (FLP)mechanism that is compatible with NLP.(See IEEE 802.3 Clauses 14 and 28.)
И еще:
14.2.1.7 Link Integrity Test function requirements
In order to protect the network from the consequences of a simplex link segment failure,the MAU shall
monitor the RD circuit for RD_input and link test pulse activity.If neither RD_input nor a link test pulse is
received for a time “link_loss,”the MAU shall enter the Link Test Fail state and cause the input_idle mes-
sage to be sent on the DI circuit and the TD_idle message to be sent on the TD circuit (Figure 14 –6).The
value of “link_loss ”shall be between 50 ms and 150 ms.When RD_input or a number “lc_max ”of consec-?IEEE
Std 802.3,2000 Edition LOCAL AND METROPOLITAN AREA NETWORKS:
uti e link test pulses is recei ed on the RD circuit,the MAU shall exit the Link Test Fail state.The alue of
“lc_max ” shall be between 2 and 10 inclusi e..
Only link test pulses that occur within time “link_test_max ”of each other shall be considered consecuti e.
The alue of “link_test_max ”shall be between 25 ms and 150 ms.In addition,detected pulses that occur
within a time “link_test_min ”of a previous pulse or packet shall be ignored while in the Link Test Pass state.
In the Link Test Fail state,such pulses shall reset the counted number of consecuti e link test pulses to zero.
The alue of “link_test_min ”shall be between 2 ms and 7 ms.Re-enabling shall be deferred until the signals
on the RD and DO circuits become idle.The MAU shall not detect a link test pulse as RD_input .Addition-
ally,a MAU may exit the Link Test Fail Extend state and enter the Link Test Pass state when the RD circuit
becomes idle and the Jabber function has disabled transmission on the TD circuit.
While the MAU is not in the Link Test Pass state,the Link Integrity Test function shall disable the bit trans-
fer of the Transmit,Recei e,and Loopback functions,and the Collision Presence and SQE Test functions.
At PowerOn,in place of entering the Link Test Pass state as shown in Figure 14 –6,a MAU may optionally
enter the Link Test Fail Reset state.
For a MAU that implements the Auto-Negotiation algorithm de ?ned in Clause 28,the MAU shall enter the
LINK TEST FAIL RESET state at power-on as speci ?ed in Clause 28.For a MAU that does not implement
the Auto-Negotiation algorithm de ?ned in Clause 28,it is highly recommended that it also power-on in the
LINK TEST FAIL RESET state,although implementations may power-on in the LINK TEST PASS state.
For a MAU that implements the Auto-Negotiation function de ?ned in Clause 28,the Auto-Negotiation Tech-
nology Dependent Interface shall be supported.Supporting the Technology Dependent Interface requires
that in the Link Integrity Test function state diagram “link_status=OK ”is added to the LINK TEST PASS
state and “link_status=FAIL ” is added to the LINK TEST FAIL RESET state..Note these ISO message vari-
ables follow the con entions of Clause 21.
If a visible indicator is provided on the MAU to indicate the link status,it is recommended that the color be
green and that the indicator be labeled appropriately.It is further recommended that the indicator be on when
the MAU is in the Link Test Pass state and off otherwise.
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