draft-ietf-tsvwg-sctp-failover-09.txt   draft-ietf-tsvwg-sctp-failover-10.txt 
Network Working Group Y. Nishida Network Working Group Y. Nishida
Internet-Draft GE Global Research Internet-Draft GE Global Research
Intended status: Standards Track P. Natarajan Intended status: Standards Track P. Natarajan
Expires: June 27, 2015 Cisco Systems Expires: September 10, 2015 Cisco Systems
A. Caro A. Caro
BBN Technologies BBN Technologies
P. Amer P. Amer
University of Delaware University of Delaware
K. Nielsen K. Nielsen
Ericsson Ericsson
December 24, 2014 March 9, 2015
SCTP-PF: Quick Failover Algorithm in SCTP SCTP-PF: Quick Failover Algorithm in SCTP
draft-ietf-tsvwg-sctp-failover-09.txt draft-ietf-tsvwg-sctp-failover-10.txt
Abstract Abstract
One of the major advantages of SCTP is the support of multi-homed One of the major advantages of SCTP is the support of multi-homed
communication. A multi-homed SCTP end-point has the ability to communication. A multi-homed SCTP end-point has the ability to
withstand network failures by migrating the traffic from an inactive withstand network failures by migrating the traffic from an inactive
network to an active one. However, if the failover operation as network to an active one. However, if the failover operation as
specified in [RFC4960] is followed, there can be a significant delay specified in RFC4960 is followed, there can be a significant delay in
in the migration to the active destination addresses, thus severely the migration to the active destination addresses, thus severely
reducing the effectiveness of the SCTP failover operation. reducing the effectiveness of the SCTP failover operation.
This memo complements [RFC4960] by the introduction of the This document complements RFC4960 by the introduction of a new path
Potentially Failed path state and the associated new failover state, the Potentially Failed (PF) path state, and an associated new
operation called SCTP-PF to apply during a network failure. In failover operation to apply during a network failure. The algorithm
addition, the memo complements [RFC4960] by introducing of defined is called SCTP Potentially Failed Algorithm, SCTP-PF for
short. In addition, the document complements RFC4960 by introducing
alternative switchover operation modes for the data transfer path alternative switchover operation modes for the data transfer path
management after the recovery of a failed primary path. These modes management after the recovery of a failed primary path. These modes
offers for more performance optimal operation in some network can allow improvements in the performance of the operation in some
environments. The implementation of the additional switchover network environments. The implementation of the additional
operation modes is optional. switchover operation modes is an optional part of SCTP-PF.
The procedures defined in the document require only minimal The procedures defined in the document require only minimal
modifications to the current specification. The procedures are modifications to the current specification. The procedures are
sender-side only and do not impact the SCTP receiver. sender-side only and do not impact the SCTP receiver.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on June 27, 2015. This Internet-Draft will expire on September 10, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 3 2. Conventions and Terminology . . . . . . . . . . . . . . . . . 4
3. Issues with the SCTP Path Management . . . . . . . . . . . . 4 3. Issues with the SCTP Path Management . . . . . . . . . . . . 4
4. SCTP with Potentially-Failed Destination State (SCTP-PF) . . 5 4. SCTP with Potentially-Failed Destination State (SCTP-PF) . . 5
4.1. SCTP-PF Concept . . . . . . . . . . . . . . . . . . . . . 5 4.1. SCTP-PF Concept . . . . . . . . . . . . . . . . . . . . . 5
4.2. SCTP-PF Algorithm in Detail . . . . . . . . . . . . . . . 6 4.2. Specification of the SCTP-PF Algorithm . . . . . . . . . 6
4.3. Optional Feature: Permanent Failover . . . . . . . . . . 9 4.2.1. Dormant State Operation . . . . . . . . . . . . . . . 10
5. Socket API Considerations . . . . . . . . . . . . . . . . . . 11 4.3. Permanent Failover . . . . . . . . . . . . . . . . . . . 12
5.1. Support for the Potentially Failed Path State . . . . . . 11 4.3.1. Background . . . . . . . . . . . . . . . . . . . . . 12
4.3.2. Permanent Failover Algorithm . . . . . . . . . . . . 12
5. Socket API Considerations . . . . . . . . . . . . . . . . . . 13
5.1. Support for the Potentially Failed Path State . . . . . . 14
5.2. Peer Address Thresholds (SCTP_PEER_ADDR_THLDS) Socket 5.2. Peer Address Thresholds (SCTP_PEER_ADDR_THLDS) Socket
Option . . . . . . . . . . . . . . . . . . . . . . . . . 12 Option . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.3. Exposing the Potentially Failed Path State 5.3. Exposing the Potentially Failed Path State
(SCTP_EXPOSE_POTENTIALLY_FAILED_STATE) Socket Option . . 13 (SCTP_EXPOSE_POTENTIALLY_FAILED_STATE) Socket Option . . 16
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14 6. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
8. Proposed Change of Status (to be Deleted before Publication) 14 8. Proposed Change of Status (to be Deleted before Publication) 17
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . 14 9.1. Normative References . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . 15 9.2. Informative References . . . . . . . . . . . . . . . . . 17
Appendix A. Discussions of Alternative Approaches . . . . . . . 16 Appendix A. Discussions of Alternative Approaches . . . . . . . 18
A.1. Reduce Path.Max.Retrans (PMR) . . . . . . . . . . . . . . 16 A.1. Reduce Path.Max.Retrans (PMR) . . . . . . . . . . . . . . 18
A.2. Adjust RTO related parameters . . . . . . . . . . . . . . 16 A.2. Adjust RTO related parameters . . . . . . . . . . . . . . 19
Appendix B. Discussions for Path Bouncing Effect . . . . . . . . 17 Appendix B. Discussions for Path Bouncing Effect . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 Appendix C. SCTP-PF for SCTP Single-homed Operation . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction 1. Introduction
The Stream Control Transmission Protocol (SCTP) as specified in The Stream Control Transmission Protocol (SCTP) as specified in
[RFC4960] supports multihoming at the transport layer -- an SCTP [RFC4960] supports multihoming at the transport layer -- an SCTP
endpoint can bind to multiple IP addresses. SCTP's multihoming endpoint can bind to multiple IP addresses. SCTP's multihoming
features include failure detection and failover procedures to provide features include failure detection and failover procedures to provide
network interface redundancy and improved end-to-end fault tolerance. network interface redundancy and improved end-to-end fault tolerance.
In SCTP's current failure detection procedure, the sender must In SCTP's current failure detection procedure, the sender must
experience Path.Max.Retrans (PMR) number of consecutive failed timer- experience Path.Max.Retrans (PMR) number of consecutive failed timer-
based retransmissions on a destination address before detecting a based retransmissions on a destination address before detecting a
path failure. The sender fails over to an alternate active path failure. The sender fails over to an alternate active
destination address only after failure detection. Until detecting destination address only after failure detection. Until detecting
the failover, the sender continues to transmit data on the failed the failover, the sender continues to transmit data on the failed
path, which degrades the SCTP performance. Concurrent Multipath path, which degrades the SCTP performance. Concurrent Multipath
Transfer (CMT) [IYENGAR06] is an extension to SCTP that allows the Transfer (CMT) [IYENGAR06] is an proposed extension to SCTP that
sender to transmit data on multiple paths simultaneously. Research allows the sender to transmit data on multiple paths simultaneously.
[NATARAJAN09] shows that the current failure detection procedure Research [NATARAJAN09] shows that the current failure detection
worsens CMT performance during failover and can be significantly procedure worsens CMT performance during failover and can be
improved by employing a better failover algorithm. significantly improved by employing a better failover algorithm.
This document specifies an alternative failure detection procedure This document specifies an alternative failure detection and failover
for SCTP that improves the SCTP performance during a failover. procedure, the SCTP Potentially Failed algorithm, that improves the
performance of SCTP multi-homed operation during a failover.
Also the operation after the recovery of a failed path impacts the For multi-homed SCTP the operation after the recovery of a failed
performance of the protocol. With procedures specified in [RFC4960], path equally well impacts the performance of the protocol. With the
SCTP will, after a failover from the primary path, switch back to the procedures specified in [RFC4960], SCTP will, after a failover from
primary path for data transfer as soon as this path becomes available the primary path, switch back to the primary path for data transfer
again. From a performance perspective, as confirmed in research as soon as this path becomes available again. From a performance
[CARO02], such a switchback of the data transmission path is not perspective, as confirmed in research [CARO02], such a switchback of
optimal in general. As an optional alternative to the switchback the data transmission path is not optimal in general. As an optional
operation of [RFC4960], this document specifies the Permanent alternative to the switchback operation of [RFC4960], this document
Failover procedures proposed by [CARO02]. specifies the Permanent Failover procedures proposed by [CARO02].
Additional discussions for alternative approaches that do not require Additional discussion for alternative approaches that do not require
modifications to [RFC4960] and path bouncing effects that might be modifications to [RFC4960], as well as discussion of path bouncing
caused by frequent switchover are provided in the Appendices. effects that might be caused by frequent switchover, are provided in
the Appendices.
While the Potentially Failed algorithm primarily is motivated for
improvement of the SCTP multi-homed operation, the feature applies
also to SCTP single-homed operation. Here the algorithm serves to
provide increased failure detection on idle associations, whereas the
failover or switchback aspects of the algorithm will not be
activated. This is discussed in more detail in Appendix C.
2. Conventions and Terminology 2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Issues with the SCTP Path Management 3. Issues with the SCTP Path Management
This section describes issues in the SCTP as specified in [RFC4960] This section describes issues in the SCTP as specified in [RFC4960]
skipping to change at page 4, line 38 skipping to change at page 4, line 51
destination address. If it fails to receive acknowledgments, the destination address. If it fails to receive acknowledgments, the
error count for the destination address is increased. If the error error count for the destination address is increased. If the error
counter exceeds the tunable protocol parameter Path.Max.Retrans counter exceeds the tunable protocol parameter Path.Max.Retrans
(PMR), the SCTP endpoint considers the destination address to be (PMR), the SCTP endpoint considers the destination address to be
inactive. inactive.
The failover process of SCTP is initiated when the primary path The failover process of SCTP is initiated when the primary path
becomes inactive (the error counter for the primary path exceeds becomes inactive (the error counter for the primary path exceeds
Path.Max.Retrans). If the primary path is marked inactive, SCTP Path.Max.Retrans). If the primary path is marked inactive, SCTP
chooses a new destination address from one of the active destinations chooses a new destination address from one of the active destinations
and start using this address to send data to. If the primary path and starts using this as the destination address for sending data.
becomes active again, SCTP uses the primary destination address for If the primary path becomes active again, SCTP reverts to using the
subsequent data transmissions and stop using the non-primary one. primary destination address for subsequent data transmissions and
stop using the non-primary one.
One issue with this failover process is that it usually takes a One issue with this failover process defined in [RFC4960] is that it
significant amount of time before SCTP switches to the new usually takes a significant amount of time before SCTP switches to
destination address. Let's say the primary path on a multi-homed the new destination address. Let's say the primary path on a multi-
host becomes unavailable and the RTO value for the primary path at homed host becomes unavailable and the RTO value for the primary path
that time is around 1 second, it usually takes over 60 seconds before at that time is around 1 second, it usually takes over 60 seconds
SCTP starts to use the non-primary path for initial data before SCTP starts to use the non-primary path for initial data
transmission. This is because the recommended value for transmission. This is because the recommended value for
Path.Max.Retrans in the [RFC4960] is 5, which requires 6 consecutive Path.Max.Retrans in the [RFC4960] is 5, which requires 6 consecutive
timeouts before the failover takes place. Before SCTP switches to timeouts before the failover takes place. Before SCTP switches to
the non-primary address, SCTP keeps trying to send packets to the the non-primary address, SCTP keeps trying to send packets to the
primary address and only retransmitted packets are sent to the non- primary address and only retransmitted packets are sent to the non-
primary address and thus can be received by the receiver. This slow primary address and thus can be received by the receiver. This slow
failover process can cause significant performance degradation and is failover process can cause significant performance degradation and is
not acceptable in some situations. not acceptable in some situations.
Another issue is that once the primary path becomes active again, the Another issue with RFC4960 failover and switchback operation is that
traffic is switched back. This is not optimal in some situations. once the primary path becomes active again, the traffic is
This is further discussed in Section 4.3. unconditionally switched back to use this path. This is not optimal
in some situations. This is further discussed in Section 4.3.
4. SCTP with Potentially-Failed Destination State (SCTP-PF) 4. SCTP with Potentially-Failed Destination State (SCTP-PF)
To address the issues described in Section 3, this section extends To address the issues described in Section 3, this document extends
SCTP path management scheme by adding the Potentially Failed state SCTP path management scheme by adding the Potentially Failed state
and the associated failover operation. We use the term SCTP-PF to and associated protocol operation. The algorithm is called SCTP
denote the resulting SCTP path management operation. Potentially Failed algorithm. SCTP-PF for short. The resulting SCTP
path management operation is called SCTP Potentially Failed
operation.
4.1. SCTP-PF Concept 4.1. SCTP-PF Concept
SCTP-PF as defined stems from the following two observations about The introduction of the Potentially Failed state stems from the
SCTP's failure detection procedure: following two observations about SCTP's failure detection procedure:
o To minimize the performance impact during failover, the sender o To minimize the performance impact during failover, the sender
should avoid transmitting data to the failed destination address should avoid transmitting data to the failed destination address
as early as possible. In the current SCTP path management scheme, as early as possible. In the current SCTP path management scheme,
the sender stops transmitting data to a destination destination the sender stops transmitting data to a destination address only
only after the destination is marked Failed (inactive). Thus, a after the destination address is marked Failed (inactive). Thus,
smaller PMR value is better because the sender can transition a a smaller PMR value is better because the sender can transition a
destination address to the Failed (inactive) state quicker. destination address to the Failed (inactive) state quicker.
o Smaller PMR values increase the chances of spurious failure o Smaller PMR values increase the chances of spurious failure
detection where the sender incorrectly marks a destination address detection where the sender incorrectly marks a destination address
as Failed (inactive) during periods of temporary congestion. As as Failed (inactive) during periods of temporary congestion. As
[RFC4960] recommends for a coupling of the PMR value and the [RFC4960] recommends for a coupling of the PMR value and the
protocol parameter Association.Max.Retrans (AMR) value such protocol parameter Association.Max.Retrans (AMR) value such
spurious failure detection risks to carry over to spurious spurious failure detection risks to carry over to spurious
association failure detection and closure. Larger PMR values are association failure detection and closure. Larger PMR values are
preferable to avoid spurious failure detection. preferable to avoid spurious failure detection.
From the above observations it is clear that tuning the PMR value From the above observations it is clear that tuning the PMR value
involves the following tradeoff -- a lower value improves performance involves the following trade off -- a lower value improves
but increases the chances of spurious failure detection, whereas a performance but increases the chances of spurious failure detection,
higher value degrades performance and reduces spurious failure whereas a higher value degrades performance and reduces spurious
detection in a wide range of path conditions. Thus, tuning the failure detection in a wide range of path conditions. Thus, tuning
association's PMR value is an incomplete solution to address the the association's PMR value is an incomplete solution to address the
performance impact during failure. performance impact during failure.
SCTP-PF defined in this document introduces a new "Potentially- SCTP-PF defined in this document introduces the new Potentially
Failed" (PF) destination state in SCTP's path management procedure. Failed (PF) destination address state in SCTP's path management
The PF state was originally proposed to improve CMT performance procedure. The new Potentially Failed (PF) destination address state
applies to SCTP single-homed operation as well as to SCTP multi-homed
[NATARAJAN09]. The PF state is an intermediate state between the operation. The PF state was originally proposed to improve CMT
Active and Failed states. SCTP's failure detection procedure is performance [NATARAJAN09]. The PF state is an intermediate state
modified to include the PF state. The new failure detection between the Active and Failed states. SCTP's failure detection
algorithm assumes that loss detected by a timeout implies either procedure is modified to include the PF state. The new failure
severe congestion or failure en-route. After a number of consecutive detection algorithm assumes that loss detected by a timeout implies
timeouts on a path, the sender is unsure, and marks the corresponding either severe congestion or failure en-route. After a number of
destination address as PF. A PF destination address is not used for consecutive timeouts on a path, the sender is unsure, and marks the
data transmission except in special cases (discussed below). The new corresponding destination address as in the PF state. A PF
failure detection algorithm requires only sender-side changes. destination address is not used for data transmission except when it
is the only destination address available (e.g., for single-homed
SCTP) or in other special cases (discussed below). The new failure
detection algorithm requires only sender-side changes.
4.2. SCTP-PF Algorithm in Detail 4.2. Specification of the SCTP-PF Algorithm
The SCTP-PF operation is specified as follows: The SCTP-PF operation is specified as follows:
1. The sender maintains a new tunable parameter called Potentially- 1. The sender maintains a new tunable parameter called
Failed.Max.Retrans (PFMR). The RECOMMENDED value of PFMR = 0 PotentiallyFailed.Max.Retrans (PFMR). The RECOMMENDED value of
when SCTP-PF is used. When PFMR is larger or equal to PMR, PFMR is 0 when SCTP-PF is used. The PFMR defines a new
SCTP-PF is turned off. intermediate PF threshold on the destination address error
counter at exceed of which the destination address is classified
as PF and related PF state actions are to be taken. By standard
RFC4960 semantics a destination address is classified as
Inactive once the error counter exceeds PMR. Setting PFMR
larger to or equal to PMR does not result in definition of a PF
threshold for the destination address. I.e., PFMR set larger to
or equal to PMR means that the destination address never will be
classified as PF.
2. The error counter of an active destination address is 2. The error counter of an active destination address is
incremented as specified in [RFC4960]. This means that the incremented as specified in [RFC4960]. This means that the
error counter of the destination address will be incremented error counter of the destination address will be incremented
each time the T3-rtx timer expires, or at times where a each time the T3-rtx timer expires, or each time a HEARTBEAT
HEARTBEAT sent to an idle, active address is not acknowledged chunk is sent when idle and not acknowledged within an RTO.
within an RTO. When the value in the destination address error When the value in the destination address error counter exceeds
counter exceeds PFMR, the endpoint MUST mark the destination PFMR, the endpoint MUST mark the destination address as in the
transport address as PF. PF state.
3. The sender SHOULD avoid data transmission to PF destination 3. The PFMR threshold defines the point the destination address no
addresses. When the destination addresses are all in PF state longer is considered a good candidate for data transmission and
or some in PF state and some in inactive state, the sender MUST a SCTP-PF sender SHOULD NOT send data to destination addresses
choose one destination address in PF state and transmit data to in PF state when alternative destination addresses in active
this destination. The sender SHOULD choose the destination state are available. Specifically this means that:
address in PF state with the lowest error count (fewest
consecutive timeouts) for data transmission and transmit data to i When there is outbound data to send and the destination
this destination. When there are multiple PF destinations with address presently used for data transmission is in PF state,
same error count, the sender SHOULD let the choice among the the sender SHOULD choose a destination address in active
multiple PF destination address with equal error count be based state, if one exists, and failover to deploy this destination
on the [RFC4960], section 6.4.1, principles of choosing most address for data transmission.
divergent source-destination pairs when executing (potentially
consecutive) retransmission. This means that the sender SHOULD ii When retransmitting data that has timed out and the sender
attempt to pick the most divergent source - destination pair thus by [RFC4960], section 6.4.1, should attempt to pick a
from the last source - destination pair on which data were new destination address for data retransmission, the sender
transmitted or retransmitted. Rules for picking the most SHOULD choose an alternate destination transport address in
divergent source-destination pair are an implementation decision active state if one exists.
and are not specified within this document. A sender may choose
to deploy other strategies than the above when choosing among iii When there is outbound data to send and the SCTP user
multiple PF destinations with equal error count. In all cases, explicitly requests to send data to a destination address in
the sender MUST NOT change the state of chosen destination PF state, the sender SHOULD send the data to an alternate
address and it MUST NOT clear the destination's error counter as destination address in active state if one exists.
a result of choosing the destination address for data
When choosing among multiple destination address in active state
the following considerations are given:
A. An SCTP sender should comply with [RFC4960], section 6.4.1,
principles of choosing most divergent source-destination
pairs compared with, for i.: the destination address in PF
state that it performs a failover from, and for ii.: the
destination address towards which the data timed out. Rules
for picking the most divergent source-destination pair are
an implementation decision and are not specified within this
document.
B. A SCTP-PF sender MAY choose to send data to a destination
address in PF state, even if destination addresses in active
state exist, have the SCTP-PF sender other means of
information available that disqualifies the destination
address in active state from being preferred. However, the
discussion of such mechanisms is outside of the scope of the
SCTP_PF operation specified in this document.
In all cases, the sender MUST NOT change the state of chosen
destination address, whether this state be active or PF, and it
MUST NOT clear the error counter of the destination address as a
result of choosing the destination address for data
transmission. transmission.
4. HEARTBEAT chunks SHOULD be sent to PF destination(s) once per 4. When the destination addresses are all in PF state or some in PF
RTO, which requires to ignore HB.interval for PF destinations. state and some in inactive state, the sender MUST choose one
If a HEARTBEAT chunk is not acknowledged, the sender SHOULD destination address in PF state and transmit or retransmit data
increment the error counter and exponentially back off the RTO to this destination address using the following rules:
value. If error counter is less than PMR, the sender SHOULD
transmit another packet containing HEARTBEAT chunk immediately
after T3-timer expiration. When data is transmitted to a PF
destination, the transmission of HEARTBEAT chunk MAY be omitted
as receipt of SACK chunks or a T3-rtx timer expiration can
provide equivalent information. It is RECOMMENDED that
HEARTBEAT chunks are send to PF destinations regardless of
whether the Path Heartbeat function (Section 8.3 of [RFC4960])
is enabled for the destination address or not.
5. When the sender receives a HEARTBEAT ACK from a PF destination, A. The sender SHOULD choose the destination in PF state with
the sender MUST clear the destination's error counter and the lowest error count (fewest consecutive timeouts) for
transition the PF destination address back to Active state. data transmission and transmit or retransmit data to this
When the sender resumes data transmission on the destination destination.
address, it MUST do this following the prescriptions of
Section 7.2 of [RFC4960].
6. Additional (PMR - PFMR) consecutive timeouts on a PF destination B. When there are multiple PF destinations with same error
address confirm the path failure, upon which the destination count, the sender should let the choice among the multiple
address transitions to the Inactive state. As described in PF destination with equal error count be based on the
[RFC4960], the sender (i) SHOULD notify ULP about this state [RFC4960], section 6.4.1, principles of choosing most
transition, and (ii) transmit HEARTBEAT chunks to the Inactive divergent source-destination pairs when executing
destination address at a lower frequency as described in (potentially consecutive) retransmission. Rules for picking
Section 8.3 of [RFC4960] (when this function is enabled for the the most divergent source-destination pair are an
destination address). implementation decision and are not specified within this
document.
7. When all destinations are in inactive state (association dormant C. A sender MAY choose to deploy other strategies than the
state) the sender MUST also choose one destination address to above when choosing among multiple PF destinations have the
transmit data to. The sender SHOULD choose the destination SCTP-PF sender other means of information available that
address in inactive state with the lowest error count (fewest qualifies a particular destination address for being used.
consecutive timeouts) for data transmission and transmit data to The SCTP-PF protocol operation specified in this document
this destination. When there are multiple destination addresses makes no assumption of the existence of such other means of
with same error count in inactive state, the sender SHOULD information and specifies for the above as the default
attempt to pick the most divergent source - destination pair operation of an SCTP-PF sender.
from the last source - destination pair on which data were
transmitted or retransmitted following [RFC4960]. Rules for The sender MUST NOT change the state and the error counter of
picking the most divergent source-destination pair are an any destination address regardless of whether it has been chosen
implementation decision and are not specified within this for transmission or not.
document. Therefore, a sender SHOULD allow for incrementing the
destination error counters up to some reasonable limit larger 5. HEARTBEAT chunks MUST be send to PF destination addresses
than PMR+1, thus changing the prescriptions of [RFC4960], regardless of whether the Path Heartbeat function (Section 8.3
section 8.3, in this respect. The exact limit to apply is not of [RFC4960]) is enabled for the destination address or not.
specified in this document but it is considered reasonable to The HB.interval of the Path Heartbeat function of [RFC4960] MUST
require for such to be an order of magnitude higher than the PMR be ignored for destination addresses in PF state, instead
value. A sender MAY choose to deploy other strategies than the HEARTBEAT chunks are sent to destination addresses in PF state
above. For example, a sender could choose to prioritize the once per RTO. The HEARTBEAT sending begins upon that a
last active destination address during dormant state. The destination address reaches the PF state. When a HEARTBEAT
strategy to prioritize the last active destination address is chunk is not acknowledged within the RTO, the sender increments
optimal when some paths are permanently inactive, but suboptimal the error counter and exponentially back off the RTO value. If
when paths' instability is transient. While the increment of the error counter is less than PMR, the sender transmits another
the error counters above PMR+1 is a prerequisite for the error packet containing the HEARTBEAT chunk immediately after timeout
counter values to serve to guide the path selection in dormant expiration on the previous HEARTBEAT. When data is being
state, then it is noted that by virtue of the introduction of transmitted to a destination address in the PF state, the
the Potentially Failed state, one may deploy higher values of transmission of a HEARTBEAT chunk MAY be omitted in case receipt
PMR without compromising the efficiency of the failover of a SACK of or a T3-rtx timer expiration on the outstanding
operation, and thus making the increase of path error counters data can provide equivalent information. Likewise the timeout
above PMR+1 less critical as the dormant state will be less of a HEARTBEAT chunk MAY be ignored if data is outstanding
likely to happen. The downside of increasing the PMR value towards the destination address.
relative to the AMR value, however, is that the per destination
address failure detection and notification of such to ULP 6. When the sender receives a HEARTBEAT ACK from a destination
thereby is weakened. In all cases the sender MUST NOT change address in PF state, the sender MUST clear the error counter of
the state of the chosen destination address and it MUST NOT the destination address and transition the destination address
clear the destination's error counter as a result of choosing back to active state. When the sender resumes data transmission
the destination address for data transmission. on the destination address, it MUST do this following the
prescriptions of Section 7.2 of [RFC4960].
7. Additional (PMR - PFMR) consecutive timeouts on a destination
address in PF state confirm the path failure, upon which the
destination address transitions to the inactive state. As
described in [RFC4960], the sender (i) SHOULD notify the ULP
about this state transition, and (ii) transmit HEARTBEAT chunks
to the inactive destination address at a lower frequency as
described in Section 8.3 of [RFC4960] (when this function is
enabled for the destination address).
8. Acknowledgments for chunks that have been transmitted to 8. Acknowledgments for chunks that have been transmitted to
multiple destinations (i.e., a chunk which has been multiple destinations (i.e., a chunk which has been
retransmitted to a different destination address than the retransmitted to a different destination address than the
destination address to which the chunk was first transmitted) destination address to which the chunk was first transmitted)
SHOULD NOT clear the error count of an inactive destination MUST NOT clear the error count for an inactive destination
address and SHOULD NOT transition a PF destination address back address and MUST NOT transition a PF destination address back to
to Active state, since a sender cannot disambiguate whether the active state, since a sender cannot disambiguate whether the ACK
ACK was for the original transmission or the retransmission(s). was for the original transmission or the retransmission(s). The
The same ambiguity concerns the related congestion window same ambiguity concerns the related congestion window growth.
growth. The bytes of a newly acknowledged chunk which has been The bytes of a newly acknowledged chunk which has been
transmitted to multiple destination addresses SHOULD be transmitted to multiple destination addresses SHOULD be
considered for contribution to the congestion window growth considered for contribution to the congestion window growth
towards the destination address where the chunk was last sent. towards the destination address where the chunk was last sent.
The contribution of the ACKed bytes to the window growth is The contribution of the ACKed bytes to the window growth is
subject to the prescriptions described in Section 7.2 of subject to the prescriptions described in Section 7.2 of
[RFC4960] is fulfilled. A SCTP sender MAY apply a different [RFC4960] is fulfilled. A SCTP sender MAY apply a different
approach for both the error count handling and the congestion approach for both the error count handling and the congestion
control growth handling based on unequivocally information on control growth handling based on unequivocally information on
which destination (including multiple destination addresses) the which destination (including multiple destination addresses) the
chunk reached. This document makes no reference to what such chunk reached. This document makes no reference to what such
unequivocally information could consist of, neither how such unequivocally information could consist of, neither how such
unequivocally information could be obtained. The implementation unequivocally information could be obtained. The design of such
of such an alternative approach is left to implementations. an alternative approach is left to implementations.
9. Acknowledgments for chunks that has been transmitted to one 9. Acknowledgments for chunks that has been transmitted to one
destination address only MUST clear the error counter of the destination address only MUST clear the error counter for the
destination address and MUST transition a PF destination address destination address and MUST transition a PF destination address
back to Active state. This situation can happen when new data back to Active state. This situation can happen when new data
is sent to a destination address in PF state. It can also is sent to a destination address in the PF state. It can also
happen in situations where the destination address is in PF happen in situations where the destination address is in the PF
state due to the occurrence of a spurious T3-rtx timer and state due to the occurrence of a spurious T3-rtx timer and
Acknowledgments start to arrive for data sent prior to Acknowledgments start to arrive for data sent prior to
occurrence of the spurious T3-rtx and data has not yet been occurrence of the spurious T3-rtx and data has not yet been
retransmitted towards other destinations. This document does retransmitted towards other destinations. This document does
not specify special handling for detection of or reaction to not specify special handling for detection of or reaction to
spurious T3-rtx timeouts, e.g., for special operation vis-a-vis spurious T3-rtx timeouts, e.g., for special operation vis-a-vis
the congestion control handling or data retransmission operation the congestion control handling or data retransmission operation
towards a destination address which undergoes a transition from towards a destination address which undergoes a transition from
active to PF to active state due to a spurious T3-rtx timeout. active to PF to active state due to a spurious T3-rtx timeout.
But it is noted that this is an area which would benefit from But it is noted that this is an area which would benefit from
additional attention, experimentation and specification for additional attention, experimentation and specification for
Single Homed SCTP as well as for Multi Homed SCTP protocol Single Homed SCTP as well as for Multi Homed SCTP protocol
operation. operation.
10. SCTP stack SHOULD provide the ULP with the means to expose the 10. The SCTP stack SHOULD provide the ULP with the means to expose
PF state of its destinations as well as the means to notify the the PF state of its destinations as well as the means to notify
state transitions from Active to PF, and vice-versa. When doing the state transitions from Active to PF, and vice-versa. When
this, such an SCTP stack MUST provide the ULP with the means to doing this, such an SCTP stack MUST provide the ULP with the
suppress exposure of PF state and associated state transitions means to suppress exposure of PF state and associated state
as well. transitions as well.
4.3. Optional Feature: Permanent Failover 4.2.1. Dormant State Operation
In a situation with complete disruption of the communication in
between the SCTP Endpoints, the aggressive HEARTBEAT transmissions of
SCTP-PF on destination addresses in PF state may make the association
enter dormant state faster than a standard [RFC4960] SCTP
implementation given the same setting of Path.Max.Retrans (PMR) and
Association.Max.Retrans (AMR). For example, an SCTP association with
two destination addresses typically would reach dormant state in half
the time of an [RFC4960] SCTP implementation in such situations.
This is because a SCTP PF sender will send HEARTBEATS and data
retransmissions in parallel with RTO intervals when there are
multiple destinations addresses in PF state. This argument pressumes
that RTO << HB.interval of [RFC4960]. One could use higher values of
PMR, which makes the dormant state situations less likely to happen.
The downside of increasing the PMR value is that destination address
failure detections and notifications of such events to ULP is
weakened.
A design goal of SCTP-PF is that it should provide the same level of
disruption tolerance as an [RFC4960] SCTP implementation with the
same Path.Max.Retrans (PMR) and Association.Max.Retrans (AMR)
setting. For this reason, SCTP-PF SHOULD perform the following
operations during dormant state, while this is an implementation
decision in [RFC4960].
a. When the destination addresses are all in inactive state, the
sender MUST choose one destination when data is transmitted. The
sender MUST NOT change the state and the error counter of any
destination address regardless of whether it has been chosen for
transmission or not.
b. The sender SHOULD choose the destination in inactive state with
the lowest error count (fewest consecutive timeouts) for data
transmission. When there are multiple destinations with same
error count in inactive state, the sender SHOULD attempt to pick
the most divergent source - destination pair from the last source
- destination pair where failure was observed. Rules for picking
the most divergent source-destination pair are an implementation
decision and are not specified within this document. To support
differentiation of inactive destination addresses based on their
error count SCTP will need to allow for increment of the
destination address error counters up to some reasonable limit
above PMR+1, thus changing the prescriptions of [RFC4960],
section 8.3, in this respect. The exact limit to apply is not
specified in this document but it is considered reasonable to
require for such to be an order of magnitude higher than the PMR
value. A sender MAY choose to deploy other strategies that the
strategy defined by here. The strategy to prioritize the last
active destination address,i.e., the destination address with the
fewest error counts is optimal when some paths are permanently
inactive, but suboptimal when a path instability is transient.
An SCTP-PF implementation MAY keep the operation during dormant state
an implementation decision, but it should be careful not to
compromise the fault tolerance of the SCTP operation.
The above prescriptions for SCTP-PF dormant state handling SHOULD NOT
be coupled to the value of the PFMR, but solely to the activation of
SCTP-PF logic in an SCTP implementation. It is further noted that
also a standard [RFC4960] SCTP implementation can use this mode of
operation to improve the fault tolerance (which some implementations
already do).
4.3. Permanent Failover
This section describes an OPTIONAL switchback feature called
Permanent Failover which is beneficiary to deploy in certain
situations.
4.3.1. Background
In [RFC4960], an SCTP sender migrates the traffic back to the In [RFC4960], an SCTP sender migrates the traffic back to the
original primary destination address once this address becomes active original primary destination address once this address becomes active
again. As the CWND towards the original primary destination address again. As the CWND towards the original primary destination address
has to be rebuilt once data transfer resumes, the switch back to use has to be rebuilt once data transfer resumes, the switch back to use
the original primary address is not always optimal. Indeed [CARO02] the original primary address is not always optimal. Indeed [CARO02]
shows that the switch back to the original primary may degrade SCTP shows that the switch back to the original primary may degrade SCTP
performance compared to continuing data transmission on the same performance compared to continuing data transmission on the same
path, especially, but not only, in scenarios where this path's path, especially, but not only, in scenarios where this path's
characteristics are better. In order to mitigate this performance characteristics are better. In order to mitigate this performance
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the extent to which it is desired for the mode of operation to the extent to which it is desired for the mode of operation to
enforce traffic distribution over a number of network paths. I.e., enforce traffic distribution over a number of network paths. I.e.,
load distribution of traffic from multiple SCTP associations may be load distribution of traffic from multiple SCTP associations may be
sought to be enforced by distribution of the set primary paths with sought to be enforced by distribution of the set primary paths with
[RFC4960] switchback operation. However as [RFC4960] switchback [RFC4960] switchback operation. However as [RFC4960] switchback
behavior is suboptimal in certain situations, especially in scenarios behavior is suboptimal in certain situations, especially in scenarios
where a number of equally good paths are available, it is recommended where a number of equally good paths are available, it is recommended
for SCTP to support also, as alternative behavior, the Permanent for SCTP to support also, as alternative behavior, the Permanent
Failover switch over modes of operation. Failover switch over modes of operation.
4.3.2. Permanent Failover Algorithm
The Permanent Failover operation requires only sender side changes. The Permanent Failover operation requires only sender side changes.
The details are: The details are:
1. The sender maintains a new tunable parameter, called 1. The sender maintains a new tunable parameter, called
Primary.Switchover.Max.Retrans (PSMR). The PSMR MUST be set Primary.Switchover.Max.Retrans (PSMR). The PSMR MUST be set
greater or equal to the PFMR value. Implementations MUST reject greater or equal to the PFMR value. Implementations MUST reject
any other values of PSMR. any other values of PSMR.
2. When the path error counter on a set primary path exceeds PSMR, 2. When the path error counter on a set primary path exceeds PSMR,
the SCTP implementation MUST autonomously select and set a new the SCTP implementation MUST autonomously select and set a new
primary path. primary path.
3. The primary path selected by the SCTP implementation MUST be the 3. The primary path selected by the SCTP implementation MUST be the
path which at the given time would be chosen for data transfer. path which at the given time would be chosen for data transfer.
A previously failed primary path MAY come in use as data transfer A previously failed primary path can be used as data transfer
path as per normal path selection when the present data transfer path as per normal path selection when the present data transfer
path fails. path fails.
4. The recommended value of PSMR is PFMR when Permanent Failover is 4. The recommended value of PSMR is PFMR when Permanent Failover is
used. This means that no forced switchback to a previously used. This means that no forced switchback to a previously
failed primary path is performed. An implementation of Permanent failed primary path is performed. An implementation of Permanent
Failover MUST support the setting of PSMR = PFMR. An Failover MUST support the setting of PSMR = PFMR. An
implementation of Permanent Failover MAY support setting of PSMR implementation of Permanent Failover MAY support setting of PSMR
> PFMR. > PFMR.
5. It MUST be possible to disable the Permanent Failover and obtain 5. It MUST be possible to disable the Permanent Failover and obtain
the standard switchback operation of [RFC4960]. the standard switchback operation of [RFC4960].
This specifications RECOMMENDS a default configuration that uses To support optimal operation in a wider range of network scenarios,
standard RFC4960 switchback, i.e., switch back to the old primary it it proposed for an SCTP-PF implementation to implement Permanent
destination once the destination address becomes active again. Failover operation as an optional feature. The implementation of the
However, to support optimal operation in a wider range of network Permanent Failover feature is optional for an SCTP-PF implementation.
scenarios, an implementation MAY implement Permanent Failover For an SCTP implementation that implements Permanent Failover, this
operation as detailed above and MAY enable it based on network specification RECOMMENDS that the standard RFC4960 switchback
configurations or users' requests. operation is retained as the default operation.
5. Socket API Considerations 5. Socket API Considerations
This section describes how the socket API defined in [RFC6458] is This section describes how the socket API defined in [RFC6458] is
extended to provide a way for the application to control and observe extended to provide a way for the application to control and observe
the SCTP-PF behavior. the SCTP-PF behavior.
Please note that this section is informational only. Please note that this section is informational only.
A socket API implementation based on [RFC6458] is, by means of the A socket API implementation based on [RFC6458] is, by means of the
skipping to change at page 13, line 8 skipping to change at page 15, line 45
uint16_t spt_pathpfthld; uint16_t spt_pathpfthld;
uint16_t spt_pathcpthld; uint16_t spt_pathcpthld;
}; };
spt_assoc_id: This parameter is ignored for one-to-one style spt_assoc_id: This parameter is ignored for one-to-one style
sockets. For one-to-many style sockets the application may fill sockets. For one-to-many style sockets the application may fill
in an association identifier or SCTP_FUTURE_ASSOC. It is an error in an association identifier or SCTP_FUTURE_ASSOC. It is an error
to use SCTP_{CURRENT|ALL}_ASSOC in spt_assoc_id. to use SCTP_{CURRENT|ALL}_ASSOC in spt_assoc_id.
spt_address: This specifies which peer address is of interest. If a spt_address: This specifies which peer address is of interest. If a
wildcard address is provided, this socket option applies to all wild card address is provided, this socket option applies to all
current and future peer addresses. current and future peer addresses.
spt_pathmaxrxt: Each peer address of interest is considered spt_pathmaxrxt: Each peer address of interest is considered
unreachable, if its path error counter exceeds spt_pathmaxrxt. unreachable, if its path error counter exceeds spt_pathmaxrxt.
spt_pathpfthld: Each peer address of interest is considered spt_pathpfthld: Each peer address of interest is considered
potentially failed, if its path error counter exceeds potentially failed, if its path error counter exceeds
spt_pathpfthld. spt_pathpfthld.
spt_pathcpthld: Each peer address of interest is not considered the spt_pathcpthld: Each peer address of interest is not considered the
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For one-to-many style sockets the application may fill in an For one-to-many style sockets the application may fill in an
association identifier or SCTP_FUTURE_ASSOC. It is an error to association identifier or SCTP_FUTURE_ASSOC. It is an error to
use SCTP_{CURRENT|ALL}_ASSOC in assoc_id. use SCTP_{CURRENT|ALL}_ASSOC in assoc_id.
assoc_value: The potentially failed path state is exposed if and assoc_value: The potentially failed path state is exposed if and
only if this parameter is non-zero. only if this parameter is non-zero.
6. Security Considerations 6. Security Considerations
Security considerations for the use of SCTP and its APIs are Security considerations for the use of SCTP and its APIs are
discussed in [RFC4960] and [RFC6458]. There are no new security discussed in [RFC4960] and [RFC6458]. The logic described here is
considerations introduced in this document. for sender-side only enabled by configuration and does not have any
impacts on protocol messages on the wire. No new chunk type or new
field parameter is not required in this document.
7. IANA Considerations 7. IANA Considerations
This document does not create any new registries or modify the rules This document does not create any new registries or modify the rules
for any existing registries managed by IANA. for any existing registries managed by IANA.
8. Proposed Change of Status (to be Deleted before Publication) 8. Proposed Change of Status (to be Deleted before Publication)
Initially this work looked to entail some changes of the Congestion Initially this work looked to entail some changes of the Congestion
Control (CC) operation of SCTP and for this reason the work was Control (CC) operation of SCTP and for this reason the work was
skipping to change at page 16, line 7 skipping to change at page 18, line 41
Natarajan, P., Ekiz, N., Amer, P., and R. Stewart, Natarajan, P., Ekiz, N., Amer, P., and R. Stewart,
"Concurrent Multipath Transfer during Path Failure", "Concurrent Multipath Transfer during Path Failure",
Computer Communications , 5 2009. Computer Communications , 5 2009.
[RFC6458] Stewart, R., Tuexen, M., Poon, K., Lei, P., and V. [RFC6458] Stewart, R., Tuexen, M., Poon, K., Lei, P., and V.
Yasevich, "Sockets API Extensions for the Stream Control Yasevich, "Sockets API Extensions for the Stream Control
Transmission Protocol (SCTP)", RFC 6458, December 2011. Transmission Protocol (SCTP)", RFC 6458, December 2011.
Appendix A. Discussions of Alternative Approaches Appendix A. Discussions of Alternative Approaches
This section lists alternative approaches for the issues desribed in This section lists alternative approaches for the issues described in
this document. Although these approaches do not require to update this document. Although these approaches do not require to update
RFC4960, we do not recommend them from the reasons described below. RFC4960, we do not recommend them from the reasons described below.
A.1. Reduce Path.Max.Retrans (PMR) A.1. Reduce Path.Max.Retrans (PMR)
Smaller values for Path.Max.Retrans shorten the failover duration. Smaller values for Path.Max.Retrans shorten the failover duration.
In fact, this is recommended in some research results [JUNGMAIER02] In fact, this is recommended in some research results [JUNGMAIER02]
[GRINNEMO04] [FALLON08]. For example, if when Path.Max.Retrans=0, [GRINNEMO04] [FALLON08]. For example, if when Path.Max.Retrans=0,
SCTP switches to another destination address on a single timeout. SCTP switches to another destination address on a single timeout.
This smaller value for Path.Max.Retrans can results in spurious This smaller value for Path.Max.Retrans can results in spurious
failover, which might be a problem. failover, which might be a problem.
Unlike SCTP-PF, the interval for heartbeat packets is governed by Unlike SCTP-PF, the interval for heartbeat packets is governed by
'HB.interval' even during failover process. 'HB.interval' is usually 'HB.interval' even during failover process. 'HB.interval' is usually
set in the order of seconds (recommended value is 30 seconds). When set in the order of seconds (recommended value is 30 seconds). When
the primary path becomes inactive, the next HB can be transmitted the primary path becomes inactive, the next HEARTBEAT can be
only seconds later. Meanwhile, the primary path may have recovered. transmitted only seconds later. Meanwhile, the primary path may have
In such situations, post failover, an endpoint is forced to wait on recovered. In such situations, post failover, an endpoint is forced
the order of seconds before the endpoint can resume transmission on to wait on the order of seconds before the endpoint can resume
the primary path. However, using smaller value for 'HB.interval' transmission on the primary path. However, using smaller value for
might help this situation, but it will be the waste of bandwidth in 'HB.interval' might help this situation, but it will be the waste of
most cases. bandwidth in most cases.
In addition, smaller Path.Max.Retrans values also affect In addition, smaller Path.Max.Retrans values also affect
'Association.Max.Retrans' values. When the SCTP association's error 'Association.Max.Retrans' values. When the SCTP association's error
count (sum of error counts on all ACTIVE paths) exceeds count (sum of error counts on all ACTIVE paths) exceeds
Association.Max.Retrans threshold, the SCTP sender considers the peer Association.Max.Retrans threshold, the SCTP sender considers the peer
endpoint unreachable and terminates the association. Therefore, endpoint unreachable and terminates the association. Therefore,
Section 8.2 in [RFC4960] recommends that Association.Max.Retrans Section 8.2 in [RFC4960] recommends that Association.Max.Retrans
value should not be larger than the summation of the Path.Max.Retrans value should not be larger than the summation of the Path.Max.Retrans
of each of the destination addresses, else the SCTP sender considers of each of the destination addresses, else the SCTP sender considers
its peer reachable even when all destinations are INACTIVE. To avoid its peer reachable even when all destinations are INACTIVE. To avoid
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path related parameters (CWND, ssthresh, RTT, error count, etc) per path related parameters (CWND, ssthresh, RTT, error count, etc) per
each destination address. These parameters cannot be affected by each destination address. These parameters cannot be affected by
path bouncing. In addition, when SCTP migrates the data transfer to path bouncing. In addition, when SCTP migrates the data transfer to
another path, it starts with the minimal or the initial CWND. Hence, another path, it starts with the minimal or the initial CWND. Hence,
there is little chance for packet reordering or duplicating. there is little chance for packet reordering or duplicating.
Second, even if all communication paths between the end-nodes share Second, even if all communication paths between the end-nodes share
the same bottleneck, the SCTP-PF results in a behavior already the same bottleneck, the SCTP-PF results in a behavior already
allowed by [RFC4960]. allowed by [RFC4960].
Authors' Addresses Appendix C. SCTP-PF for SCTP Single-homed Operation
For a single-homed SCTP association the only tangible effect of the
activation of SCTP-PF operation is enhanced failure detection in
terms of potential notification of the PF state of the sole
destination address as well as, for idle associations, more rapid
entering, and notification, of inactive state of the destination
address and more rapid end-point failure detection. It is believed
that neither of these effects are harmful, provided adequate dormant
state operation is implemented, and furthermore that they may be
particularly useful for applications that deploys multiple SCTP
associations for load balancing purposes. The early notification of
the PF state may be used for preventive measures as the entering of
the PF state can be used as a warning of potential congestion.
Depending on the PMR value, the aggressive HEARTBEAT transmission in
PF state may speed up the end-point failure detection (exceed of AMR
threshold on the sole path error counter) on idle associations in
case where relatively large HB.interval value compared to RTO (e.g.
30secs) is used.
Authors' Addresses
Yoshifumi Nishida Yoshifumi Nishida
GE Global Research GE Global Research
2623 Camino Ramon 2623 Camino Ramon
San Ramon, CA 94583 San Ramon, CA 94583
USA USA
Email: nishida@wide.ad.jp Email: nishida@wide.ad.jp
Preethi Natarajan Preethi Natarajan
Cisco Systems Cisco Systems
510 McCarthy Blvd 510 McCarthy Blvd
Milpitas, CA 95035 Milpitas, CA 95035
USA USA
Email: prenatar@cisco.com Email: prenatar@cisco.com
Armando Caro Armando Caro
BBN Technologies BBN Technologies
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