3.3. SCTP Chunk Definitions - Continued
3.3.3. Initiation Acknowledgement (INIT ACK) (2)
The INIT ACK chunk is used to acknowledge the initiation of an SCTP association.
The parameter part of INIT ACK is formatted similarly to the INIT chunk. It uses two extra variable parameters: The State Cookie and the Unrecognized Parameter.
The format of the INIT ACK chunk is shown below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 2 | Chunk Flags | Chunk Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initiate Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertised Receiver Window Credit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Outbound Streams | Number of Inbound Streams |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initial TSN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Optional/Variable-Length Parameters /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Initiate Tag: 32 bits (unsigned integer)
The receiver of the INIT ACK records the value of the Initiate Tag parameter. This value MUST be placed into the Verification Tag field of every SCTP packet that the INIT ACK receiver transmits within this association.
The Initiate Tag MUST NOT take the value 0. See Section 5.3.1 for more on the selection of the Initiate Tag value.
If the value of the Initiate Tag in a received INIT ACK chunk is found to be 0, the receiver MUST destroy the association discarding its TCB. The receiver MAY send an ABORT for debugging purpose.
Advertised Receiver Window Credit (a_rwnd): 32 bits (unsigned integer)
This value represents the dedicated buffer space, in number of bytes, the sender of the INIT ACK has reserved in association with this window. During the life of the association, this buffer space SHOULD NOT be lessened (i.e., dedicated buffers taken away from this association).
Number of Outbound Streams (OS): 16 bits (unsigned integer)
Defines the number of outbound streams the sender of this INIT ACK chunk wishes to create in this association. The value of 0 MUST NOT be used, and the value MUST NOT be greater than the MIS value sent in the INIT chunk.
Note: A receiver of an INIT ACK with the OS value set to 0 SHOULD destroy the association discarding its TCB.
Number of Inbound Streams (MIS): 16 bits (unsigned integer)
Defines the maximum number of streams the sender of this INIT ACK chunk allows the peer end to create in this association. The value 0 MUST NOT be used.
Note: There is no negotiation of the actual number of streams but instead the two endpoints will use the min(requested, offered). See Section 5.1.1 for details.
Note: A receiver of an INIT ACK with the MIS value set to 0 SHOULD destroy the association discarding its TCB.
Initial TSN (I-TSN): 32 bits (unsigned integer)
Defines the initial TSN that the INIT ACK sender will use. The valid range is from 0 to 4294967295. This field MAY be set to the value of the Initiate Tag field.
Fixed Parameters Status
----------------------------------------------
Initiate Tag Mandatory
Advertised Receiver Window Credit Mandatory
Number of Outbound Streams Mandatory
Number of Inbound Streams Mandatory
Initial TSN Mandatory
Variable Parameters Status Type Value
-------------------------------------------------------------
State Cookie Mandatory 7
IPv4 Address (Note 1) Optional 5
IPv6 Address (Note 1) Optional 6
Unrecognized Parameter Optional 8
Reserved for ECN Capable (Note 2) Optional 32768 (0x8000)
Host Name Address (Note 3) Optional 11
Note 1: The INIT ACK chunks can contain any number of IP address parameters that can be IPv4 and/or IPv6 in any combination.
Note 2: The ECN Capable field is reserved for future use of Explicit Congestion Notification.
Note 3: The INIT ACK chunks MUST NOT contain more than one Host Name Address parameter. Moreover, the sender of the INIT ACK MUST NOT combine any other address types with the Host Name Address in the INIT ACK. The receiver of the INIT ACK MUST ignore any other address types if the Host Name Address parameter is present.
3.3.3.1. Optional or Variable-Length Parameters
State Cookie
Parameter Type Value: 7
Parameter Length: Variable size, depending on size of Cookie.
Parameter Value:
This parameter value MUST contain all the necessary state and parameter information required for the sender of this INIT ACK to create the association, along with a Message Authentication Code (MAC). See Section 5.1.3 for details on State Cookie definition.
Unrecognized Parameter:
Parameter Type Value: 8
Parameter Length: Variable size.
Parameter Value:
This parameter is returned to the originator of the INIT chunk when the INIT contains an unrecognized parameter that has a value that indicates it should be reported to the sender. This parameter value field will contain unrecognized parameters copied from the INIT chunk complete with Parameter Type, Length, and Value fields.
3.3.4. Selective Acknowledgement (SACK) (3)
This chunk is sent to the peer endpoint to acknowledge received DATA chunks and to inform the peer endpoint of gaps in the received subsequences of DATA chunks as represented by their TSNs.
The SACK MUST contain the Cumulative TSN Ack, Advertised Receiver Window Credit (a_rwnd), Number of Gap Ack Blocks, and Number of Duplicate TSNs fields.
By definition, the value of the Cumulative TSN Ack parameter is the last TSN received before a break in the sequence of received TSNs occurs; the next TSN value following this one has not yet been received at the endpoint sending the SACK. This parameter therefore acknowledges receipt of all TSNs less than or equal to its value.
The handling of a_rwnd by the receiver of the SACK is discussed in detail in Section 6.2.1.
The SACK also contains zero or more Gap Ack Blocks. Each Gap Ack Block acknowledges a subsequence of TSNs received following a break in the sequence of received TSNs. By definition, all TSNs acknowledged by Gap Ack Blocks are greater than the value of the Cumulative TSN Ack.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 3 |Chunk Flags | Chunk Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cumulative TSN Ack |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertised Receiver Window Credit (a_rwnd) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Gap Ack Blocks = N | Number of Duplicate TSNs = X |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Gap Ack Block #1 Start | Gap Ack Block #1 End |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ /
\ ... \
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Gap Ack Block #N Start | Gap Ack Block #N End |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Duplicate TSN 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ /
\ ... \
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Duplicate TSN X |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits
Set to all '0's on transmit and ignored on receipt.
Cumulative TSN Ack: 32 bits (unsigned integer)
This parameter contains the TSN of the last DATA chunk received in sequence before a gap. In the case where no DATA chunk has been received, this value is set to the peer's Initial TSN minus one.
Advertised Receiver Window Credit (a_rwnd): 32 bits (unsigned integer)
This field indicates the updated receive buffer space in bytes of the sender of this SACK; see Section 6.2.1 for details.
Number of Gap Ack Blocks: 16 bits (unsigned integer)
Indicates the number of Gap Ack Blocks included in this SACK.
Number of Duplicate TSNs: 16 bit
This field contains the number of duplicate TSNs the endpoint has received. Each duplicate TSN is listed following the Gap Ack Block list.
Gap Ack Blocks:
These fields contain the Gap Ack Blocks. They are repeated for each Gap Ack Block up to the number of Gap Ack Blocks defined in the Number of Gap Ack Blocks field. All DATA chunks with TSNs greater than or equal to (Cumulative TSN Ack + Gap Ack Block Start) and less than or equal to (Cumulative TSN Ack + Gap Ack Block End) of each Gap Ack Block are assumed to have been received correctly.
Gap Ack Block Start: 16 bits (unsigned integer)
Indicates the Start offset TSN for this Gap Ack Block. To calculate the actual TSN number the Cumulative TSN Ack is added to this offset number. This calculated TSN identifies the first TSN in this Gap Ack Block that has been received.
Gap Ack Block End: 16 bits (unsigned integer)
Indicates the End offset TSN for this Gap Ack Block. To calculate the actual TSN number, the Cumulative TSN Ack is added to this offset number. This calculated TSN identifies the TSN of the last DATA chunk received in this Gap Ack Block.
Duplicate TSN: 32 bits (unsigned integer)
Indicates the number of times a TSN was received in duplicate since the last SACK was sent. Every time a receiver gets a duplicate TSN (before sending the SACK), it adds it to the list of duplicates. The duplicate count is reinitialized to zero after sending each SACK.
3.3.5. Heartbeat Request (HEARTBEAT) (4)
An endpoint should send this chunk to its peer endpoint to probe the reachability of a particular destination transport address defined in the present association.
The parameter field contains the Heartbeat Information, which is a variable-length opaque data structure understood only by the sender.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 4 | Chunk Flags | Heartbeat Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Heartbeat Information TLV (Variable-Length) /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits
Set to 0 on transmit and ignored on receipt.
Heartbeat Length: 16 bits (unsigned integer)
Set to the size of the chunk in bytes, including the chunk header and the Heartbeat Information field.
Heartbeat Information: variable length
Defined as a variable-length parameter using the format described in Section 3.2.1, i.e.:
Variable Parameters Status Type Value
-------------------------------------------------------------
Heartbeat Info Mandatory 1
The Sender-Specific Heartbeat Info field should normally include information about the sender's current time when this HEARTBEAT chunk is sent and the destination transport address to which this HEARTBEAT is sent (see Section 8.3). This information is simply reflected back by the receiver in the HEARTBEAT ACK message (see Section 3.3.6). Note also that the HEARTBEAT message is both for reachability checking and for path verification (see Section 5.4). When a HEARTBEAT chunk is being used for path verification purposes, it MUST hold a 64-bit random nonce.
3.3.6. Heartbeat Acknowledgement (HEARTBEAT ACK) (5)
An endpoint should send this chunk to its peer endpoint as a response to a HEARTBEAT chunk (see Section 8.3). A HEARTBEAT ACK is always sent to the source IP address of the IP datagram containing the HEARTBEAT chunk to which this ack is responding.
The parameter field contains a variable-length opaque data structure.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 5 | Chunk Flags | Heartbeat Ack Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Heartbeat Information TLV (Variable-Length) /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits
Set to 0 on transmit and ignored on receipt.
Heartbeat Ack Length: 16 bits (unsigned integer)
Set to the size of the chunk in bytes, including the chunk header and the Heartbeat Information field.
Heartbeat Information: variable length
This field MUST contain the Heartbeat Information parameter of the Heartbeat Request to which this Heartbeat Acknowledgement is responding.
Variable Parameters Status Type Value
-------------------------------------------------------------
Heartbeat Info Mandatory 1
3.3.7. Abort Association (ABORT) (6)
The ABORT chunk is sent to the peer of an association to close the association. The ABORT chunk may contain Cause Parameters to inform the receiver about the reason of the abort. DATA chunks MUST NOT be bundled with ABORT. Control chunks (except for INIT, INIT ACK, and SHUTDOWN COMPLETE) MAY be bundled with an ABORT, but they MUST be placed before the ABORT in the SCTP packet or they will be ignored by the receiver.
If an endpoint receives an ABORT with a format error or no TCB is found, it MUST silently discard it. Moreover, under any circumstances, an endpoint that receives an ABORT MUST NOT respond to that ABORT by sending an ABORT of its own.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 6 |Reserved |T| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ zero or more Error Causes /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits
Reserved: 7 bits
Set to 0 on transmit and ignored on receipt.
T bit: 1 bit
The T bit is set to 0 if the sender filled in the Verification Tag expected by the peer. If the Verification Tag is reflected, the T bit MUST be set to 1. Reflecting means that the sent Verification Tag is the same as the received one.
Note: Special rules apply to this chunk for verification; please see Section 8.5.1 for details.
Length: 16 bits (unsigned integer)
Set to the size of the chunk in bytes, including the chunk header and all the Error Cause fields present.
See Section 3.3.10 for Error Cause definitions.
3.3.8. Shutdown Association (SHUTDOWN) (7)
An endpoint in an association MUST use this chunk to initiate a graceful close of the association with its peer. This chunk has the following format.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 7 | Chunk Flags | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cumulative TSN Ack |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits
Set to 0 on transmit and ignored on receipt.
Length: 16 bits (unsigned integer)
Indicates the length of the parameter. Set to 8.
Cumulative TSN Ack: 32 bits (unsigned integer)
This parameter contains the TSN of the last chunk received in sequence before any gaps.
Note: Since the SHUTDOWN message does not contain Gap Ack Blocks, it cannot be used to acknowledge TSNs received out of order. In a SACK, lack of Gap Ack Blocks that were previously included indicates that the data receiver reneged on the associated DATA chunks. Since SHUTDOWN does not contain Gap Ack Blocks, the receiver of the SHUTDOWN shouldn't interpret the lack of a Gap Ack Block as a renege. (See Section 6.2 for information on reneging.)
3.3.9. Shutdown Acknowledgement (SHUTDOWN ACK) (8)
This chunk MUST be used to acknowledge the receipt of the SHUTDOWN chunk at the completion of the shutdown process; see Section 9.2 for details.
The SHUTDOWN ACK chunk has no parameters.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 8 |Chunk Flags | Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits
Set to 0 on transmit and ignored on receipt.
3.3.10. Operation Error (ERROR) (9)
An endpoint sends this chunk to its peer endpoint to notify it of certain error conditions. It contains one or more error causes. An Operation Error is not considered fatal in and of itself, but may be used with an ABORT chunk to report a fatal condition. It has the following parameters:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 9 | Chunk Flags | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ one or more Error Causes /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits
Set to 0 on transmit and ignored on receipt.
Length: 16 bits (unsigned integer)
Set to the size of the chunk in bytes, including the chunk header and all the Error Cause fields present.
Error causes are defined as variable-length parameters using the format described in Section 3.2.1, that is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code | Cause Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Cause-Specific Information /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Cause Code: 16 bits (unsigned integer)
Defines the type of error conditions being reported.
Cause Code
Value Cause Code
--------- ----------------
1 Invalid Stream Identifier
2 Missing Mandatory Parameter
3 Stale Cookie Error
4 Out of Resource
5 Unresolvable Address
6 Unrecognized Chunk Type
7 Invalid Mandatory Parameter
8 Unrecognized Parameters
9 No User Data
10 Cookie Received While Shutting Down
11 Restart of an Association with New Addresses
12 User Initiated Abort
13 Protocol Violation
Cause Length: 16 bits (unsigned integer)
Set to the size of the parameter in bytes, including the Cause Code, Cause Length, and Cause-Specific Information fields.
Cause-Specific Information: variable length
This field carries the details of the error condition.
3.3.11. State Cookie Echo (COOKIE ECHO) (10)
This chunk is used only during the initialization of an association. It is sent from the INIT ACK sender to the INIT sender (see Section 5.1). This chunk MUST precede any DATA or SACK chunk sent within the association, but MAY be bundled with one or more DATA chunks or SACK chunk in the same SCTP packet.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 10 |Chunk Flags | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Cookie /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits
Set to 0 on transmit and ignored on receipt.
Cookie: variable size
This field must contain the exact cookie received in the State Cookie parameter from the previous INIT ACK.
An implementation SHOULD make the cookie as small as possible to ensure interoperability.
Note: A Cookie Echo does NOT contain a State Cookie parameter; instead, the data within the State Cookie's Parameter Value becomes the data within the Cookie Echo's Chunk Value. This allows an implementation to change only the first 2 bytes of the State Cookie parameter to become a COOKIE ECHO chunk.
3.3.12. Cookie Acknowledgement (COOKIE ACK) (11)
This chunk is used only during the initialization of an association. It is used to acknowledge the receipt of a COOKIE ECHO chunk. This chunk MUST precede any DATA or SACK chunk sent within the association, but MAY be bundled with one or more DATA chunks or SACK chunk's in the same SCTP packet.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 11 |Chunk Flags | Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits
Set to 0 on transmit and ignored on receipt.
3.3.13. Shutdown Complete (SHUTDOWN COMPLETE) (14)
This chunk MUST be used to acknowledge the receipt of the SHUTDOWN ACK chunk at the completion of the shutdown process; see Section 9.2 for details.
The SHUTDOWN COMPLETE chunk has no parameters.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 14 |Reserved |T| Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits
Reserved: 7 bits
Set to 0 on transmit and ignored on receipt.
T bit: 1 bit
The T bit is set to 0 if the sender filled in the Verification Tag expected by the peer. If the Verification Tag is reflected, the T bit MUST be set to 1. Reflecting means that the sent Verification Tag is the same as the received one.
Note: Special rules apply to this chunk for verification, please see Section 8.5.1 for details.
Note: This document contains Sections 3.3.3 through 3.3.13, completing the full description of SCTP chunk definitions. Chapter 4 and subsequent content will be continued in subsequent documents.