During Auth 48, the authors of draft-ietf-pwe3-static-pw-status found some issues with the acknowledgement procedures in Section 5.3 of the draft that we feel should be addressed before publication. Since the draft has already been through WG and IETF last call, we would like to highlight the proposed changes to the working group and solicit feedback. Best regards, Matthew Section 5.3, 3rd paragraph: Reason for change: The current suggested default refresh timer value is too short to allow scaling to very large numbers of PWs while minimising the overhead. It is also inconsistent with the suggested default requested in an ACK packet. Therefore we suggest increasing the default to 600secs. OLD: The suggested default value for the refresh timer is 30 seconds. NEW: The suggested default value for the refresh timer is 600 seconds. Section 5.3, 4th paragraph: Reason for change: The current text requires that a receiving PE must acknowledge a PW status message of 'clear all faults' in order to force a transmitter to stop sending PW status messages at 1 second intervals. We are concerned that a mandatory acknowledgement adds an unnecessary complexity to the protocol which is inconsistent with the use of the acknowledgement as per the following section (5.3.1). Additionally, we are also concerned that this may cause problems if a transmitter is flapping between 'clear all faults' and a non-zero value, and if the acknowledgement is lost. We therefore suggest that the acknowledgement to 'clear all faults' be made optional, and that the transmitter behavior be changed so that it sends up to 3 status messages of zero in a row, and then goes silent. OLD: To clear a particular status fault, the PE need only send an updated message with the corresponding bit cleared. If the PW status code is zero, the PW OAM message will be sent like any other PW OAM status message using the procedures described above; however, it MUST be acknowledged with a packet with a timer value of zero. This will cause the PE sending the PW status notification message with a PW status code equal to zero to stop sending and to continue normal operation. NEW: To clear a particular status fault, the PE need only send an updated message with the corresponding bit cleared. If the PW status code is zero, the PW OAM message will be sent like any other PW OAM status message using the procedures described above; however, transmission will cease after 3 PW status messages have been sent. A PW status message of zero MAY be acknowledged as per the procedures described in Section 5.3.1. If it is acknowledged, then a timer value of zero MUST be used. This SHOULD cause the PE sending the PW status notification message with a PW status code equal to zero to stop sending and to continue normal operation. Section 5.3.1, 1st paragraph: Reason for change: The procedures currently defined in this paragraph can lead to a receiver of the static status message timing out if it requests, throught the use of the ACK mechanism, a longer refresh timer from the transmitter. This is because the current text implies that the transmitter change its referesh timer immediately on receipt of the ack packet from the receiver. The new text clarifies that the refresh timer be updated at the end of the current refresh interval, as well as making some other editorial clarifications. OLD: The PE receiving a PW OAM message containing a PW status message can acknowledge the PW status message by simply building an almost identical reply packet with the A bit set, and transmitting it on the PW ACH back to the source of the PW status message. The timer value set in the reply packet SHOULD then be used by the PE as the new transmit interval. If the transmitting PE does not want to use the new timer value (for local policy reasons, or because it simply cannot support it), it MUST refresh the PW OAM message with the timer value it desires. The receiving PE will then set its timeout timer according to the timer value that is in the packet received, regardless of what timer value it sent. The receiving PE MUST NOT retry to set the timer value more than once per timer value. NEW: A PE receiving a PW OAM message containing a PW status message MAY acknowledge the PW status message by simply building a reply packet with the same format and status code as the received PW OAM message, but with the A bit set, and transmitting it on the PW ACh back to the source of the PW OAM message. The receiving PE MAY use the refresh timer field in the acknowledgement packet to request a new refresh interval from the originator of the PW OAM message. The timer value set in the reply packet SHOULD then be used by the originator of the PW OAM message as the new transmit interval. If the requested refresh timer value is used, the PW OAM message transmission interval is only set to the new value and the new value sent in the next PW OAM message, when the current timer expires. If the transmitting PE does not want to use the new timer value (for local policy reasons, or because it simply cannot support it), it MUST refresh the PW OAM message with the timer value it desires. The receiving PE will then set its timeout timer according to the new refresh timer value that is in the packet received, regardless of what timer value it requested. The receiving PE MUST NOT request a new refresh timer value more than once per refresh interval. |
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