Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1998-03-19
2001-04-24
Olms, Douglas (Department: 2661)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S241000
Reexamination Certificate
active
06222854
ABSTRACT:
BACKGROUND
The present invention concerns data transfer over a network and pertains particularly to a link monitor state machine used in a physical media access sublayer of 100BASE-TX technology.
The IEEE 802.3 committee has defined a standard technology for 100 megabits per second networking over category five (CAT-5) Unshielded Twisted Pair (UTP) cabling. This technology is known as 100BASE-TX and is defined in Clauses 24 and 25 of the specification IEEE 802.3u-1995.
Within the 100BASE-TX technology physical sublayer (PHY), as defined in Clauses 24 and 25 of the specification IEEE 802.3u-1995, there is a Physical Coding Sublayer (PCS), a Physical Media Access (PMA) sublayer, and a Physical Media Dependent (PMD) sublayer. The PCS defines how data is encoded and decoded, how the Carrier Sense (CS) and Collision Detection (CD) functions work, and the interface between higher and lower layers in the protocol specification. The PMA defines the mapping of code bits, generation of a control signal (link_status) which indicates the availability of the PMD, generation of control signals to the PCS that indicate Carrier Sense, Collision Detection and Physical Layer Errors, and clock recovery. The PMD defines the signaling method and the various physical parameters that are necessary to address the link's physical requirements. Within the PMA, as defined in the specification IEEE 802.3u-1995, there is a state machine which is described as the LINK MONITOR state machine. It is described in section 24.3.4.4 and by a diagram depicted in
FIGS. 24-15
. This state machine is intended to provide a mechanism which determines whether the underlying physical layer is providing reliable data.
The LINK MONITOR state machine described in section 24.3.4.4 and by a diagram depicted in
FIGS. 24-15
of the specification IEEE 802.3u-1995 assumes that if a link has been connected and the signal energy is sufficient to cause an indication of “signal_status ON” for more than 330 micro-seconds, then the link must be reliable. However, a link which exceeds the signal amplitude requirements to generate a “signal_status ON” may in fact have a Bit Error Rate (BER) that is substantially above the acceptable level as defined by requirements set out in the specification IEEE 802.3u-1995. A link which has a Bit Error Rate (BER) that is substantially above the acceptable level is unreliable.
When using the LINK MONITOR state machine described in section 24.3.4.4 of the specification IEEE 802.3u-1995, once a link has been enabled to operate, it will go to a state known as “LINK UP,’ and stay there until either the signal_status goes to OFF or a control signal is asserted to bring the link down. The BER of the link has no direct impact on link_status.
The 100BASE-TX technology uses a protocol known as Carrier-Sense, Multiple Access with Collision Detection (CSMA-CD). The CSMA-CD protocol depends on the reliable ability of each node to detect when another node in the network is transmitting (Carrier Sense) and when more than one node in the network is transmitting (Collision Detection). If bit errors occur during a packet, a re-transmission may occur which reduces network performance. However, if a protocol error occurs, the impact upon network performance degrades substantially.
The 100BASE-TX technology uses a continuous signaling mechanism to communicate across the link. This means that the lack of “Carrier” is actually a stream of bits known as “IDLE” symbols. If a bit error occurs in the reception of the IDLE symbols, then “Carrier Sense” or “Collision” may be detected. Therefore, this System absolutely depends on a reliable BER to operate properly. An unacceptable BER on any link in the network will result in substantial disruption and degradation of network performance.
SUMMARY OF THE INVENTION
In accordance with the preferred embodiment of the present invention, a network node is connectable to a network. The node includes a physical media access sublayer. The physical media access sublayer includes a link monitor state machine. The link monitor state machine includes an evaluate link state, an evaluate carrier state, an increment criteria state and a link down state. In the evaluate state, an idle timer is started. The evaluate carrier state is entered from the evaluate link state when a carrier event is detected before expiration of the idle timer. In the evaluate carrier state, a valid carrier timer is started. The increment criteria state is entered from the evaluate carrier state if a status error is detected or if the carrier event completes before expiration of the valid carrier timer. In the increment criteria state, a false carrier count is incremented. The link down state is entered from the increment criteria state if the false carrier count, after being incremented, is equal to a false carrier count limit.
Additionally in the preferred embodiment, in the increment criteria state, if the idle timer is not already at a maximum value, the current value of the idle timer is increased. Also, the link monitor state machine additionally includes a decrement criteria state which is entered from the evaluate link state upon expiration of the idle timer. In the decrement criteria state, if the idle timer is not already at a minimum value, a current value of the idle timer is reduced.
Additionally in the preferred embodiment, in the link down state, the idle timer is set to the minimum value and a link status is set to fail. Also, the link monitor state machine additionally includes a hysteresis state and a link ready state. The hysteresis state is entered from the link down state, upon reception of a signal status on. In the hysteresis state, a stabilizer timer is started. A link ready state is entered from the hysteresis state, upon reception of a signal status on. In the link ready state, the link status is set to ready. Upon a link control being enabled, the evaluate link state is entered.
Also, in the preferred embodiment, the link monitor state machine additionally includes a valid carrier state. The valid carrier state is entered from the evaluate carrier state when the valid carrier timer expires and the carrier status is off. In the valid carrier state, the false carrier count is set to zero, and if the idle timer expires, the decrement criteria state is entered.
Also, in the preferred embodiment, the link monitor state machine additionally includes a link up state. The link up state is entered from the decrement criteria state. In the link up state, the link status to is set to OK. In the link up state, upon a link control being equal to enable, the evaluate link state is entered. Also, in the link up state, upon link_control equaling SCAN_FOR_CARRIER, the link down state is entered.
In the valid carrier state, if the carrier status is on, the evaluate carrier state is entered. In the valid carrier state, if the idle timer expires, the decrement criteria state is entered. In the valid carrier state, if the carrier status is on, the evaluate carrier state is entered.
The present invention allows the upper layers of the 100BASE-TX as defined in Clauses 24 and 25 of the specification IEEE 802.3u-1995, to rely upon the Physical Coding Sublayer (PCS), the Physical Media Access (PMA) sublayer, and the Physical Media Dependent (PMD) sublayer. Instead of getting false “Carrier Sense” or false “collision Detection”, the protocol will perform reliably, or the link will indicate Link_status=Fail and disconnect itself from the network.
REFERENCES:
patent: 5577069 (1996-11-01), Lau
patent: 5754540 (1998-05-01), Liu
patent: 5754552 (1998-05-01), Allmond
patent: 6141352 (2000-10-01), Gandy
IEEE Std 802.3u (CSMA/CD) Chapter 24 and 25, (1995), pp. 157-197.
Hewlett--Packard Company
Olms Douglas
Pizarro Ricardo M.
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