M2PA (MTP2-User Peer-to-Peer
Adaptation Layer)
The M2PA protocol supports the transport of Signaling System Number 7 (SS7) Message Transfer Part (MTP) Level 3 signaling messages over Internet Protocol (IP) using the services of the Stream Control Transmission Protocol (SCTP). M2PA is also used between SS7 Signaling Points using the MTP Level 3 protocol. The SS7 Signaling Points may also use standard SS7 links using the SS7 MTP Level 2 to provide transport of MTP Level 3 signaling messages.
There is a need for Switched Circuit Network (SCN) signaling protocol delivery over an IP network. This includes message transfer between the following:
The M2PA protocol supports the transport of Signaling System Number 7 (SS7) Message Transfer Part (MTP) Level 3 signaling messages over Internet Protocol (IP) using the services of the Stream Control Transmission Protocol (SCTP). M2PA is also used between SS7 Signaling Points using the MTP Level 3 protocol. The SS7 Signaling Points may also use standard SS7 links using the SS7 MTP Level 2 to provide transport of MTP Level 3 signaling messages.
There is a need for Switched Circuit Network (SCN) signaling protocol delivery over an IP network. This includes message transfer between the following:
- A Signaling Gateway (SG) and a Media Gateway Controller
(MGC)
- A SG and an IP Signaling Point (IPSP)
- An IPSP and an IPSP
This could allow for convergence of
some signaling and data networks. SCN signaling nodes would have access to
databases and other devices in the IP network domain that do not use SS7
signaling links. Likewise, IP telephony applications would have access to SS7
services. There may also be operational cost and performance advantages when
traditional signaling links are replaced by IP network "connections".
The delivery mechanism described here allows for full MTP3 message handling and network management capabilities between any two SS7 nodes, communicating over an IP network. An SS7 node equipped with an IP network connection is called an IP Signaling Point (IPSP). The IPSPs function as traditional SS7 nodes using the IP network instead of SS7 links.
The delivery mechanism supports:
The delivery mechanism described here allows for full MTP3 message handling and network management capabilities between any two SS7 nodes, communicating over an IP network. An SS7 node equipped with an IP network connection is called an IP Signaling Point (IPSP). The IPSPs function as traditional SS7 nodes using the IP network instead of SS7 links.
The delivery mechanism supports:
- Seamless operation of MTP3 protocol peers over an IP
network connection.
- The MTP Level 2 / MTP Level 3 interface boundary.
- Management of SCTP transport associations and traffic
instead of MTP2 Links.
- Asynchronous reporting of status changes to management.
The structure of the M2PA protocol
header is as follows:
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BSN
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Version
The version field contains the version of M2PA. The supported version is
1 - Release 1.0 of M2PA protocol.
Message Class
The only allowed value is 11 for M2PA Messages.
The version field contains the version of M2PA. The supported version is
1 - Release 1.0 of M2PA protocol.
Message Class
The only allowed value is 11 for M2PA Messages.
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Message Type
The following list contains the message types for the defined messages. |
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1
2 |
User Data
Link Status |
Message Length
The Message Length defines the length of the message in octets, including the Common Header.
BSN
Backward Sequence Number - This is the FSN of the message last received from the peer.
FSN
Forward Sequence Number -
This is the M2PA sequence number of the User Data message being sent.
The Message Length defines the length of the message in octets, including the Common Header.
BSN
Backward Sequence Number - This is the FSN of the message last received from the peer.
FSN
Forward Sequence Number -
This is the M2PA sequence number of the User Data message being sent.
M2UA is used for backhauling of SS7 MTP2-User signalling messages over IP using the Stream Control Transmission Protocol (SCTP). This protocol is used for communication between a Signalling Gateway (SG) and Media Gateway Controller (MGC). It is assumed that the SG receives SS7 signalling over a standard SS7 interface using the SS7 Message Transfer Part (MTP) to provide transport. The SG acts as a Signalling Link Terminal.
The M2UA header structure is as follows:
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M2UA
header structure
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Version
The version field contains the version of the M2UA adapation layer. The supported version is 1.0.
The version field contains the version of the M2UA adapation layer. The supported version is 1.0.
Spare
This field should be set to zero.
This field should be set to zero.
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Message class
The values for message class can be any of the following: |
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0
3 4 5 |
Management Messages (MGMT)
ASP State Maintenance Messages (ASPSM) ASP Traffic Maintenance Messages (ASPTM) MTP2 User Adaptation Messages (MAUP) |
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Message type
Management: |
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Error (ERR)
Notify (NTFY) |
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ASP State Maintenance:
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ASP Up (UP)
ASP Down (DOWN) ASP Up Ack (UP ACK) ASP Down Ack (DOWN ACK) |
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ASP Traffic Maintenance:
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ASP Active (ACTIVE)
ASP Inactive (INACTIVE) ASP Active Ack (ACTIVE ACK) ASP Inactive Ack (INACTIVE ACK) |
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MTP2 User Adaptatation:
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2 3 4 5 6 7 8 9 10 11 12 13 14 15 |
Data
Establish Request Establish Confirm Release Request Release Confirm Release Indication State Request State Confirm State Indication Data Retrieval Request Data Retrieval Confirm Data Retrieval Indication Data Retrieval Complete Indication Congestion Indication TTC Data |
Message length
The message length defines the length of the message in octets (including the header) and includes parameter padding bytes (if there are any).
The message length defines the length of the message in octets (including the header) and includes parameter padding bytes (if there are any).
Variable-length parameter format
M2UA messages consist of a common header (described above) followed by zero or more variable-length parameters, as defined by the message type. The variable-length parameter format is as follows:
M2UA messages consist of a common header (described above) followed by zero or more variable-length parameters, as defined by the message type. The variable-length parameter format is as follows:
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M2UA
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M3UA
M3UA supports the transport of any SS7 MTP3-User signalling (such as ISUP and SCCP messages) over IP, using the services of the Stream Control Transmission Protocol (SCTP). The protocol is used for communication between a Signalling Gateway (SG) and a Media Gateway Controller (MGC) or IP-resident database. It is assumed that the SG receives SS7 signalling over a standard SS7 interface using the SS7 Message Transfer Part (MTP) to provide transport.
The protocol consists of a common message header followed by parameters as defined by the message type.
The M3UA header structure is as follows:
M3UA supports the transport of any SS7 MTP3-User signalling (such as ISUP and SCCP messages) over IP, using the services of the Stream Control Transmission Protocol (SCTP). The protocol is used for communication between a Signalling Gateway (SG) and a Media Gateway Controller (MGC) or IP-resident database. It is assumed that the SG receives SS7 signalling over a standard SS7 interface using the SS7 Message Transfer Part (MTP) to provide transport.
The protocol consists of a common message header followed by parameters as defined by the message type.
The M3UA header structure is as follows:
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M3UA
header structure
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Version
The version field contains the version of the M3UA adapation layer. The supported version is 1.0.
The version field contains the version of the M3UA adapation layer. The supported version is 1.0.
Reserved
This field should be set to zero.
This field should be set to zero.
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Message class
The values for Message class can be any of the following: |
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0
1 2 3 4 9 |
Management (MGMT)
Transfer Messages SS7 Signalling Network Management (SSNM) ASP State Maintenance (ASPSM) ASP Traffic Maintenance (ASPTM) Routing Key Management (RKM) |
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Message type
Management: |
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0 Error (ERR)
1 Notify (NTFY) |
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Transfer:
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Payload Data (DATA)
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SS7 Signalling Network Management:
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Destination Unavailable (DUNA)
Destination Available (DAVA) Destination State Audit (DAUD) SS7 Network Congestion State (SCON) Destination User Part Unavailable (DUPU) Destination Restricted (DRST) |
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ASP State Maintenance:
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ASP Up (UP)
ASP Down (DOWN) Heartbeat (BEAT) ASP Up Ack (UP ACK) ASP Down Ack (DOWN ACK) Heartbeat Ack (BEAT ACK) |
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ASP Traffic Maintenance:
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2 3 4 |
ASP Active (ACTIVE)
ASP Inactive (INACTIVE) ASP Active Ack (ACTIVE ACK) ASP Inactive Ack (INACTIVE ACK) |
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Routing Key Management:
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2 3 4 |
Registration Request (REG REQ)
Registration Response (REG RSP) Deregistration Request (DEREG REQ) Deregistration Response (DEREG RSP) |
Message length
The message length defines the length of the message in octets, including the common header.
The message length defines the length of the message in octets, including the common header.
Variable-length parameters
M3UA messages consist of a common header followed by zero or more variable-length parameters, as defined by the message type. The format of variable-length parameters is as follows:
M3UA messages consist of a common header followed by zero or more variable-length parameters, as defined by the message type. The format of variable-length parameters is as follows:
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Reverved
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M3UA
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Parameter tag
The Parameter tag identifies the type of parameter. |
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0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 |
Reserved
Network Appearance Protocol Data 1 Protocol Data 2 Info String Affected Destinations Routing Context Diagnostic Information Heartbeat Data User/Cause Reason Traffic Mode Type Error Code Status Type/ID Congestion Indications Concerned Destination Routing Key Registration Result De-registration Result Local_Routing Key Identifier Destination Point Code Service Indicators Subsystem Numbers Originating Point Code List Circuit Range Registration Results De-registration Results |
Parameter length
Parameter length indicates the size of the parameter in bytes. The length includes the Parameter Tag, Parameter Length and Parameter Value fields.
Parameter length indicates the size of the parameter in bytes. The length includes the Parameter Tag, Parameter Length and Parameter Value fields.
Parameter value
The value of the parameter.
The value of the parameter.
The Stream Control Transmission
Protocol (SCTP) is designed to transport PSTN signalling messages over IP
networks, but is capable of broader applications. SCTP is an application-level
datagram transfer protocol operating on top of an unreliable datagram service
such as UDP. It offers the following services to its users:
- Acknowledged error-free non-duplicated transfer of user
data.
- Application-level segmentation to conform to discovered
MTU size.
- Sequenced delivery of user datagrams within multiple
streams, with an option for order-of-arrival delivery of individual
datagrams.
- Optional multiplexing of user datagrams into SCTP
datagrams, subject to MTU size restrictions.
- Enhanced reliability through support of multi-homing at
either or both ends of the association.
The design of SCTP includes
appropriate congestion avoidance behaviour and resistance to flooding and
masquerade attacks. The SCTP datagram is comprised of a common header and
chunks. The chunks contain either control information or user data.
The following is the format of the SCTP header:
The following is the format of the SCTP header:
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2
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Source
Port Number
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Destination
Port Number
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Verification
Tag
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Adler
32 Checksum
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Source Port Number
This is the SCTP sender's port number. It can be used by the receiver, in combination with the source IP Address, to identify the association to which this datagram belongs.
This is the SCTP sender's port number. It can be used by the receiver, in combination with the source IP Address, to identify the association to which this datagram belongs.
Destination Port Number
This is the SCTP port number to which this datagram is destined. The receiving host will use this port number to de-multiplex the SCTP datagram to the correct receiving endpoint/application.
This is the SCTP port number to which this datagram is destined. The receiving host will use this port number to de-multiplex the SCTP datagram to the correct receiving endpoint/application.
Verification Tag
The receiver of this 32 bit datagram uses the Verification tag to identify the association. On transmit, the value of this Verification tag must be set to the value of the Initiate tag received from the peer endpoint during the association initialization.
The receiver of this 32 bit datagram uses the Verification tag to identify the association. On transmit, the value of this Verification tag must be set to the value of the Initiate tag received from the peer endpoint during the association initialization.
For datagrams carrying the INIT
chunk, the transmitter sets the Verification tag to all 0's. If the receiver
receives a datagram with an all-zeros Verification tag field, it checks the
Chunk ID immediately following the common header. If the chunk type is not INIT
or SHUTDOWN ACK, the receiver drops the datagram. For datagrams carrying the
SHUTDOWN-ACK chunk, the transmitter sets the Verification tag to the Initiate
tag received from the peer endpoint during the association initialization, if
known. Otherwise the Verification tag is set to all 0's.
Adler 32 Checksum
This field contains an Adler-32 checksum on this SCTP datagram
This field contains an Adler-32 checksum on this SCTP datagram
Chunk Field Descriptions
The following is the field format for the chunks transmitted in the SCTP datagram. Each chunk has a chunk ID field, a chunk specific Flag field, a Length field and a Value field.
The following is the field format for the chunks transmitted in the SCTP datagram. Each chunk has a chunk ID field, a chunk specific Flag field, a Length field and a Value field.
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Chunk
ID
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Chunk
Flags
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Chunk
Length
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Chunk
Value (variable)
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Chunk ID
The type of information contained in the chunk value field. The values of the chunk ID are defined as follows:
The type of information contained in the chunk value field. The values of the chunk ID are defined as follows:
ID ValueChunk Type
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00000000
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Payload Data (DATA)
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00000001
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Initiation (INIT)
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0000001
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0Initiation Acknowledgment (INIT
ACK)
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00000011
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Selective Acknowledgment (SACK)
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00000100
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Heartbeat Request (HEARTBEAT)
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00000101
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Heartbeat Acknowledgment
(HEARTBEAT ACK)
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00000110
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Abort (ABORT)
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00000111
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Shutdown (SHUTDOWN)
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00001000
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Shutdown Acknowledgment (SHUTDOWN
ACK)
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00001001
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Operation Error (ERROR)
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00001010
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State Cookie (COOKIE)
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00001011
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Cookie Acknowledgment (COOKIE ACK)
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00001100
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Reserved for Explicit Congestion
Notification Echo (ECNE)
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00001101
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Reserved for Congestion Window
Reduced (CWR)
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00001110 to
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11111101 - reserved by IETF
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11111110
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Vendor-specific Chunk Extensions
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11111111
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IETF-defined Chunk Extensions
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Chunk Flags
The type of chunk flag as defined in the chunk ID defines whether these bits will be used. Their value is generally 0 unless otherwise specified.
The type of chunk flag as defined in the chunk ID defines whether these bits will be used. Their value is generally 0 unless otherwise specified.
Chunk Length
The size of the chunk in octets including the Chunk ID, Flags, Length and Value fields.
The size of the chunk in octets including the Chunk ID, Flags, Length and Value fields.
Chunk Value
This field contains the actual information to be transferred in the chunk. This is dependent on the chunk ID.
This field contains the actual information to be transferred in the chunk. This is dependent on the chunk ID.
Chunk Types
Initiation (INIT)
This chunk is used to initiate a SCTP association between two endpoints. The INIT chunk contains the following parameters. Unless otherwise noted, each parameter is only be included once in the INIT chunk.
Initiation (INIT)
This chunk is used to initiate a SCTP association between two endpoints. The INIT chunk contains the following parameters. Unless otherwise noted, each parameter is only be included once in the INIT chunk.
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Fixed Parameters
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Status
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Initiate Tag
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Mandatory
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Receiver Window Credit
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Mandatory
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Number of Outbound Streams
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Mandatory
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Number of Inbound Streams
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Mandatory
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Initial TSN
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Mandatory
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Variable Parameters
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Status
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IPv4 Address/Port
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Optional
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IPv6 Address/Port
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Optional
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Cookie Preservative
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Optional
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Reserved For ECN Capable
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Optional
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Host Name Address
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Optional
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Supported Address Types
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Optional
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Initiate Acknowledgement (INIT ACK)
The INIT ACK chunk is used to acknowledge the initiation of a SCTP association. The parameter part of INIT ACK is formatted similarly to the INIT chunk. It uses two extra variable parameters: The Responder Cookie and the Unrecognized Parameter.
The INIT ACK chunk is used to acknowledge the initiation of a SCTP association. The parameter part of INIT ACK is formatted similarly to the INIT chunk. It uses two extra variable parameters: The Responder Cookie and the Unrecognized Parameter.
Selective Acknowledgement (SACK)
This chunk is sent to the remote endpoint to acknowledge received Data chunks and to inform the remote endpoint of gaps in the received subsequences of Data chunks as represented by their TSNs.
The selective acknowledgement chunk contains the highest consecutive TSN ACK and Rcv Window Credit (rwnd) parameters. By definition, the value of the highest consecutive TSN ACK parameter is the last TSN received at the time the Selective ACK is sent, before a break in the sequence of received TSNs occurs; the next TSN value following this one has not yet been received at the reporting end. This parameter therefore acknowledges receipt of all TSNs up to and including the value given.
The Selective ACK also contains zero or more fragment reports. Each fragment report acknowledges a sub-sequence of TSNs received following a break in the sequence of received TSNs. By definition, all TSNs acknowledged by fragment reports are higher than the value of the Highest Consecutive TSN ACK.
This chunk is sent to the remote endpoint to acknowledge received Data chunks and to inform the remote endpoint of gaps in the received subsequences of Data chunks as represented by their TSNs.
The selective acknowledgement chunk contains the highest consecutive TSN ACK and Rcv Window Credit (rwnd) parameters. By definition, the value of the highest consecutive TSN ACK parameter is the last TSN received at the time the Selective ACK is sent, before a break in the sequence of received TSNs occurs; the next TSN value following this one has not yet been received at the reporting end. This parameter therefore acknowledges receipt of all TSNs up to and including the value given.
The Selective ACK also contains zero or more fragment reports. Each fragment report acknowledges a sub-sequence of TSNs received following a break in the sequence of received TSNs. By definition, all TSNs acknowledged by fragment reports are higher than the value of the Highest Consecutive TSN ACK.
Heartbeat Request (HEARTBEAT)
An endpoint should send this chunk to its peer endpoint of the current association to probe the reachability of a particular destination transport address defined in the present association. The parameter fields contain the time values.
An endpoint should send this chunk to its peer endpoint of the current association to probe the reachability of a particular destination transport address defined in the present association. The parameter fields contain the time values.
Heartbeat Acknowledgement (HEARTBEAT
ACK)
An endpoint should send this chunk to its peer endpoint as a response to a Heartbeat Request. The parameter field contains the time values.
An endpoint should send this chunk to its peer endpoint as a response to a Heartbeat Request. The parameter field contains the time values.
Abort Association (ABORT)
The Abort Association chunk is sent to the peer of an association to terminate the association. The Abort chunk may contain cause parameters to inform the receiver the reason for the abort. Data chunks are not bundled with the abort, control chunks may be bundled with an abort, but must be placed before the abort in the SCTP datagram or they will be ignored.
The Abort Association chunk is sent to the peer of an association to terminate the association. The Abort chunk may contain cause parameters to inform the receiver the reason for the abort. Data chunks are not bundled with the abort, control chunks may be bundled with an abort, but must be placed before the abort in the SCTP datagram or they will be ignored.
SHUTDOWN
An endpoint in an association uses this chunk to initiate a graceful termination of the association with its peer.
An endpoint in an association uses this chunk to initiate a graceful termination of the association with its peer.
Shutdown Acknowledgement (SHUTDOWN ACK)
This chunk is used to acknowledge the receipt of the SHUTDOWN chunk at the completion of the shutdown process. The SHUTDOWN ACK chunk has no parameters.
Operation Error (ERROR)
This chunk is sent to the other endpoint in the association to notify certain error conditions. It contains one or more error causes.
This chunk is sent to the other endpoint in the association to notify certain error conditions. It contains one or more error causes.
State Cookie (COOKIE)
This chunk is used only during the initialization of an association. It is sent by the initiator of an association to its peer to complete the initialization process. This chunk precedes any Data chunk sent within the association, but may be bundled with one or more Data chunks in the same datagram.
This chunk is used only during the initialization of an association. It is sent by the initiator of an association to its peer to complete the initialization process. This chunk precedes any Data chunk sent within the association, but may be bundled with one or more Data chunks in the same datagram.
Cookie Acknowledgement (COOKIE ACK)
This chunk is used only during the initialization of an association. It is used to acknowledge the receipt of a COOKIE chunk. This chunk precedes any Data chunk sent within the association, but may be bundled with one or more Data chunks in the same SCTP datagram.
This chunk is used only during the initialization of an association. It is used to acknowledge the receipt of a COOKIE chunk. This chunk precedes any Data chunk sent within the association, but may be bundled with one or more Data chunks in the same SCTP datagram.
Payload Data (DATA)
This contains the user data.
This contains the user data.
Vendor Specific Chunk Extensions
This chunk type is available to allow vendors to support their own extended data formats not defined by the IETF. It must not affect the operation of SCTP. Endpoints not equipped to interpret the vendor-specific chunk sent by a remote endpoint must ignore it. Endpoints that do not receive desired vendor specific information should make an attempt to operate without it, although they may do so (and report they are doing so) in a degraded mode.
This chunk type is available to allow vendors to support their own extended data formats not defined by the IETF. It must not affect the operation of SCTP. Endpoints not equipped to interpret the vendor-specific chunk sent by a remote endpoint must ignore it. Endpoints that do not receive desired vendor specific information should make an attempt to operate without it, although they may do so (and report they are doing so) in a degraded mode.
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