draft-ietf-tsvwg-sctp-sack-immediately-04.txt   rfc7053.txt 
Network Working Group M. Tuexen Internet Engineering Task Force (IETF) M. Tuexen
Internet-Draft I. Ruengeler Request for Comments: 7053 I. Ruengeler
Updates: 4960 (if approved) Muenster Univ. of Appl. Sciences Updates: 4960 Muenster Univ. of Appl. Sciences
Intended status: Standards Track R. Stewart Category: Standards Track R. Stewart
Expires: March 01, 2014 Adara Networks ISSN: 2070-1721 Adara Networks
August 28, 2013 November 2013
SACK-IMMEDIATELY Extension for the Stream Control Transmission Protocol SACK-IMMEDIATELY Extension for
draft-ietf-tsvwg-sctp-sack-immediately-04.txt the Stream Control Transmission Protocol
Abstract Abstract
This document updates RFC 4960 by defining a method for the sender of This document updates RFC 4960 by defining a method for the sender of
a DATA chunk to indicate that the corresponding SACK chunk should be a DATA chunk to indicate that the corresponding Selective
sent back immediately and not be delayed. It is done by specifying a Acknowledgment (SACK) chunk should be sent back immediately and
bit in the DATA chunk header, called the I-bit, which can get set should not be delayed. It is done by specifying a bit in the DATA
either by the SCTP implementation or by the application using an SCTP chunk header, called the (I)mmediate bit, which can get set by either
stack. Since unknown flags in chunk headers are ignored by SCTP the Stream Control Transmission Protocol (SCTP) implementation or the
implementations, this extension does not introduce any application using an SCTP stack. Since unknown flags in chunk
interoperability problems. headers are ignored by SCTP implementations, this extension does not
introduce any interoperability problems.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on March 01, 2014. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7053.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The I-bit in the DATA Chunk Header . . . . . . . . . . . . . 3 3. The (I)mmediate Bit in the DATA Chunk Header . . . . . . . . . 3
4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Triggering at the Application Level . . . . . . . . . . . 4 4.1. Triggering at the Application Level . . . . . . . . . . . . 4
4.2. Triggering at the SCTP Level . . . . . . . . . . . . . . 4 4.2. Triggering at the SCTP Level . . . . . . . . . . . . . . . 4
5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Sender Side Considerations . . . . . . . . . . . . . . . 5 5.1. Sender-Side Considerations . . . . . . . . . . . . . . . . 5
5.2. Receiver Side Considerations . . . . . . . . . . . . . . 5 5.2. Receiver Side Considerations . . . . . . . . . . . . . . . 5
6. Interoperability Considerations . . . . . . . . . . . . . . . 5 6. Interoperability Considerations . . . . . . . . . . . . . . . . 5
7. Socket API Considerations . . . . . . . . . . . . . . . . . . 5 7. Socket API Considerations . . . . . . . . . . . . . . . . . . . 5
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
9. Security Considerations . . . . . . . . . . . . . . . . . . . 7 9. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
11.1. Normative References . . . . . . . . . . . . . . . . . . 7 11.1. Normative References . . . . . . . . . . . . . . . . . . . 7
11.2. Informative References . . . . . . . . . . . . . . . . . 7 11.2. Informative References . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction 1. Introduction
According to [RFC4960] the receiver of a DATA chunk should use According to [RFC4960], the receiver of a DATA chunk should use
delayed SACKs. This delaying is completely controlled by the delayed SACKs. This delay is completely controlled by the receiver
receiver of the DATA chunk and remains the default behavior. of the DATA chunk and remains the default behavior.
In specific situations the delaying of SACKs results in reduced In specific situations, the delaying of SACKs results in reduced
performance of the protocol: performance of the protocol:
1. If such a situation can be detected by the receiver, the 1. If such a situation can be detected by the receiver, the
corresponding SACK can be sent immediately. For example, corresponding SACK can be sent immediately. For example,
[RFC4960] recommends the immediate sending if the receiver has [RFC4960] recommends immediately sending the SACK if the receiver
detected message loss or message duplication. has detected message loss or message duplication.
2. However, if the situation can only be detected by the sender of 2. However, if the situation can only be detected by the sender of
the DATA chunk, [RFC4960] provides no method of avoiding a delay the DATA chunk, [RFC4960] provides no method of avoiding a delay
in sending the SACK. Examples of these situations include ones in sending the SACK. Examples of these situations include ones
which require interaction with the application (e.g. applications that require interaction with the application (e.g., applications
using the SCTP_SENDER_DRY_EVENT, see Section 4.1) and ones which using the SCTP_SENDER_DRY_EVENT, see Section 4.1) and ones that
can be detected by the SCTP stack itself (e.g. closing the can be detected by the SCTP stack itself (e.g., closing the
association, hitting window limits or resetting streams, see association, hitting window limits, or resetting streams, see
Section 4.2). Section 4.2).
To overcome the limitation described in the second case, this To overcome the limitation described in the second case, this
document describes a simple extension of the SCTP DATA chunk by document describes a simple extension of the SCTP DATA chunk by
defining a new flag, the I-bit. The sender of a DATA chunk indicates defining a new flag, the "I bit". By setting this bit, the sender of
by setting this bit that the corresponding SACK chunk should not be a DATA chunk indicates that the corresponding SACK chunk should not
delayed. be delayed.
2. Conventions 2. Conventions
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. The I-bit in the DATA Chunk Header 3. The (I)mmediate Bit in the DATA Chunk Header
The following Figure 1 shows the extended DATA chunk. Figure 1 shows the extended DATA chunk.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0 | Res |I|U|B|E| Length | | Type = 0 | Res |I|U|B|E| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TSN | | TSN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream Identifier | Stream Sequence Number | | Stream Identifier | Stream Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Protocol Identifier | | Payload Protocol Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \ \ \
/ User Data / / User Data /
\ \ \ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Extended DATA chunk format Figure 1: Extended DATA chunk format
The only difference between the DATA chunk in Figure 1 and the DATA The only difference between the DATA chunk in Figure 1 and the DATA
chunk defined in [RFC4960] is the addition of the I-bit in the flags chunk defined in [RFC4960] is the addition of the I bit in the flags
field of the DATA chunk header. field of the DATA chunk header.
This bit was Reserved in [RFC4960]. [RFC4960] specified that this [RFC4960] defines the Reserved field and specifies that these bits
bit should be set to 0 by the sender and ignored by the receiver. should be set to 0 by the sender and ignored by the receiver.
4. Use Cases 4. Use Cases
The setting of the I-bit can either be triggered by the application The setting of the I bit can either be triggered by the application
using SCTP or by the SCTP stack itself. The following two using SCTP or by the SCTP stack itself. The following two
subsections provide a non-exhaustive list of examples. subsections provide a non-exhaustive list of examples of how the I
bit may be set.
4.1. Triggering at the Application Level 4.1. Triggering at the Application Level
One example of a situation in which it may be desirable for an One example of a situation in which it may be desirable for an
application to trigger setting of the I-bit involves the application to trigger the setting of the I bit involves the
SCTP_SENDER_DRY_EVENT in the SCTP socket API [RFC6458]. Upper layers SCTP_SENDER_DRY_EVENT in the SCTP socket API [RFC6458]. Upper layers
of SCTP using the socket API as defined in [RFC6458] may subscribe to of SCTP that use the socket API as defined in [RFC6458] may subscribe
the SCTP_SENDER_DRY_EVENT for getting a notification as soon as no to the SCTP_SENDER_DRY_EVENT to be notified as soon as no user data
user data is outstanding anymore. To avoid an unnecessary delay is outstanding. To avoid an unnecessary delay, the application can
while waiting for such an event, the application can request the request that the I bit be set when sending the last user message
setting of the I-Bit when sending the last user message before before waiting for the event. This results in setting the I bit of
waiting for the event. This results in setting the I-bit of the last the last DATA chunk corresponding to the user message; this is
DATA chunk corresponding to the user message and is possible using possible using the extension of the socket API described in
the extension of the socket API described in Section 7. Section 7.
4.2. Triggering at the SCTP Level 4.2. Triggering at the SCTP Level
There are also situations in which the SCTP implementation can set There are also situations in which the SCTP implementation can set
the I-bit without interacting with the upper layer. the I bit without interacting with the upper layer.
If the association is in the SHUTDOWN-PENDING state, setting the If the association is in the SHUTDOWN-PENDING state, setting the I
I-bit reduces the number of simultaneous associations for a busy bit reduces the number of simultaneous associations for a busy server
server handling short living associations. handling short-lived associations.
Another case is where the sending of a DATA chunk fills the Another case is where the sending of a DATA chunk fills the
congestion or receiver window. Setting the I-bit in these cases congestion or receiver window. Setting the I bit in these cases
improves the throughput of the transfer. improves the throughput of the transfer.
If an SCTP association supports the SCTP Stream Reconfiguration If an SCTP association supports the SCTP Stream Reconfiguration
extension defined in [RFC6525], the performance can be improved by extension defined in [RFC6525], the performance can be improved by
setting the I-bit when there are pending reconfiguration requests setting the I bit when there are pending reconfiguration requests
that require that there be no outstanding DATA chunks. that require that there be no outstanding DATA chunks.
5. Procedures 5. Procedures
5.1. Sender Side Considerations
5.1. Sender-Side Considerations
Whenever the sender of a DATA chunk can benefit from the Whenever the sender of a DATA chunk can benefit from the
corresponding SACK chunk being sent back without delay, the sender corresponding SACK chunk being sent back without delay, the sender
MAY set the I-bit in the DATA chunk header. Please note that it is MAY set the I bit in the DATA chunk header. Please note that why the
irrelevant to the receiver why the sender has set the I-bit. sender has set the I bit is irrelevant to the receiver.
Reasons for setting the I-bit include, but are not limited to, the Reasons for setting the I bit include, but are not limited to (see
following (see Section 4 for the benefits): Section 4 for the benefits):
o The application requests to set the I-bit of the last DATA chunk o The application requests to set the I bit of the last DATA chunk
of a user message when providing the user message to the SCTP of a user message when providing the user message to the SCTP
implementation (see Section 7). implementation (see Section 7).
o The sender is in the SHUTDOWN-PENDING state. o The sender is in the SHUTDOWN-PENDING state.
o The sending of a DATA chunk fills the congestion or receiver o The sending of a DATA chunk fills the congestion or receiver
window. window.
o The sending of an Outgoing SSN Reset Request Parameter or an SSN/ o The sending of an Outgoing SSN Reset Request Parameter or an SSN/
TSN Reset Request Parameter is pending, if the association TSN Reset Request Parameter is pending, if the association
supports the Stream Reconfiguration extension defined in supports the Stream Reconfiguration extension defined in
[RFC6525]. [RFC6525].
5.2. Receiver Side Considerations 5.2. Receiver Side Considerations
On reception of an SCTP packet containing a DATA chunk with the I-bit Upon receipt of an SCTP packet containing a DATA chunk with the I bit
set, the receiver SHOULD NOT delay the sending of the corresponding set, the receiver SHOULD NOT delay the sending of the corresponding
SACK chunk, i.e., the receiver SHOULD immediately respond with the SACK chunk, i.e., the receiver SHOULD immediately respond with the
corresponding SACK chunk. corresponding SACK chunk.
6. Interoperability Considerations 6. Interoperability Considerations
According to [RFC4960] the receiver of a DATA chunk with the I-bit According to [RFC4960], the receiver of a DATA chunk with the I bit
set should ignore this bit when it does not support the extension set should ignore this bit when it does not support the extension
described in this document. Since the sender of the DATA chunk is described in this document. Since the sender of the DATA chunk is
able to handle this case, there is no requirement for negotiating the able to handle this case, there is no requirement for negotiating the
support of the feature described in this document. support of the feature described in this document.
7. Socket API Considerations 7. 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 set the I-bit. extended to provide a way for the application to set the I bit.
Please note that this section is informational only. Please note that this section is informational only.
A socket API implementation based on [RFC6458] needs to be extended A socket API implementation based on [RFC6458] needs to be extended
to allow the application to set the I-bit of the last DATA chunk when to allow the application to set the I bit of the last DATA chunk when
sending each user message. sending each user message.
This can be done by setting a flag called SCTP_SACK_IMMEDIATELY in This can be done by setting a flag called SCTP_SACK_IMMEDIATELY in
the snd_flags field of the struct sctp_sndinfo structure when using the snd_flags field of the struct sctp_sndinfo structure when using
sctp_sendv() or sendmsg(). If the deprecated struct sctp_sndrcvinfo sctp_sendv() or sendmsg(). If the deprecated struct sctp_sndrcvinfo
structure is used instead when calling sctp_send(), sctp_sendx(), or structure is used instead when calling sctp_send(), sctp_sendx(), or
sendmsg(), the SCTP_SACK_IMMEDIATELY flag can be set in the sendmsg(), the SCTP_SACK_IMMEDIATELY flag can be set in the
sinfo_flags field. When using the deprecated function sctp_sendmsg() sinfo_flags field. When using the deprecated function
the SCTP_SACK_IMMEDIATELY flag can be in the flags parameter. sctp_sendmsg(), the SCTP_SACK_IMMEDIATELY flag can be in the flags
parameter.
8. IANA Considerations 8. IANA Considerations
[NOTE to RFC-Editor:
"RFCXXXX" is to be replaced by the RFC number you assign this
document.
]
Following the chunk flag registration procedure defined in [RFC6096], Following the chunk flag registration procedure defined in [RFC6096],
IANA should register a new bit, the I-bit, for the DATA chunk. The IANA has registered a new bit, the I bit, for the DATA chunk.
suggested value is 0x08 and the reference should be RFCXXXX.
This requires an update of the "DATA Chunk Flags" registry for SCTP: The "Chunk Flags" registry for SCTP has been updated as described in
the following table.
DATA Chunk Flags DATA Chunk Flags
+------------------+-----------------+-----------+ +------------------+-----------------+-----------+
| Chunk Flag Value | Chunk Flag Name | Reference | | Chunk Flag Value | Chunk Flag Name | Reference |
+------------------+-----------------+-----------+ +------------------+-----------------+-----------+
| 0x01 | E bit | [RFC4960] | | 0x01 | E bit | [RFC4960] |
| 0x02 | B bit | [RFC4960] | | 0x02 | B bit | [RFC4960] |
| 0x04 | U bit | [RFC4960] | | 0x04 | U bit | [RFC4960] |
| 0x08 | I Bit | [RFCXXXX] | | 0x08 | I bit | [RFC7053] |
| 0x10 | Unassigned | | | 0x10 | Unassigned | |
| 0x20 | Unassigned | | | 0x20 | Unassigned | |
| 0x40 | Unassigned | | | 0x40 | Unassigned | |
| 0x80 | Unassigned | | | 0x80 | Unassigned | |
+------------------+-----------------+-----------+ +------------------+-----------------+-----------+
9. Security Considerations 9. Security Considerations
See [RFC4960] for general security considerations for SCTP. In See [RFC4960] for general security considerations for SCTP. In
addition, a malicious sender can force its peer to send packets addition, a malicious sender can force its peer to send packets
containing a SACK chunk for each received packet containing DATA containing a SACK chunk for each received packet containing DATA
chunks instead of every other. This could impact the network, chunks instead of every other received packet containing DATA chunks.
resulting in more packets sent on the network, or the peer because This could impact the network, resulting in more packets sent on the
the generating and sending of the packets has some processing cost. network, or the peer, because the generating and sending of the
However, the additional packets can only contain the most simplest packets has some processing cost. However, the additional packets
SACK chunk (no gap reports, no duplicate TSNs), since in case of can only contain the simplest SACK chunk (no gap reports, no
packet drop or reordering in the network a SACK chunk would be sent duplicate TSNs), since in cases of packet drops or reordering in the
immediately anyway. Therefore this does neither introduce a network a SACK chunk would be sent immediately anyway. Therefore,
significant additional processing cost on the receiver side. This this does not introduce a significant additional processing cost on
does not result in more traffic in the network than a receiver that the receiver side. This also does not result in more traffic in the
sends a SACK for every packet, which is already permitted. network, because a receiver sending a SACK for every packet is
already permitted.
10. Acknowledgments 10. Acknowledgments
The authors wish to thank Mark Allmann, Brian Bidulock, David Black, The authors wish to thank Mark Allmann, Brian Bidulock, David Black,
Anna Brunstrom, Gorry Fairhurst, Janardhan Iyengar, Kacheong Poon, Anna Brunstrom, Gorry Fairhurst, Janardhan Iyengar, Kacheong Poon,
and Michael Welzl for their invaluable comments. and Michael Welzl for their invaluable comments.
11. References 11. References
11.1. Normative References 11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC [RFC4960] Stewart, R., "Stream Control Transmission Protocol",
4960, September 2007. RFC 4960, September 2007.
[RFC6096] Tuexen, M. and R. Stewart, "Stream Control Transmission [RFC6096] Tuexen, M. and R. Stewart, "Stream Control Transmission
Protocol (SCTP) Chunk Flags Registration", RFC 6096, Protocol (SCTP) Chunk Flags Registration", RFC 6096,
January 2011. January 2011.
11.2. Informative References 11.2. Informative References
[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.
[RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control [RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control
Transmission Protocol (SCTP) Stream Reconfiguration", RFC Transmission Protocol (SCTP) Stream Reconfiguration",
6525, February 2012. RFC 6525, February 2012.
Authors' Addresses Authors' Addresses
Michael Tuexen Michael Tuexen
Muenster University of Applied Sciences Muenster University of Applied Sciences
Stegerwaldstr. 39 Stegerwaldstr. 39
48565 Steinfurt 48565 Steinfurt
DE DE
Email: tuexen@fh-muenster.de EMail: tuexen@fh-muenster.de
Irene Ruengeler Irene Ruengeler
Muenster University of Applied Sciences Muenster University of Applied Sciences
Stegerwaldstr. 39 Stegerwaldstr. 39
48565 Steinfurt 48565 Steinfurt
DE DE
Email: i.ruengeler@fh-muenster.de EMail: i.ruengeler@fh-muenster.de
Randall R. Stewart Randall R. Stewart
Adara Networks Adara Networks
Chapin, SC 29036 Chapin, SC 29036
US US
Email: randall@lakerest.net EMail: randall@lakerest.net
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