SCTP ABORT报文

SCTP ABORT报文
SCTP端点发送ABORT数据块来中止到对等端的偶联，ABORT数据块中可以包含原因参数用来通知接收ABORT数据块的一方中止该偶联的原因。
DATA数据块不能同ABORT数据块捆绑在一个SCTP分组中。
控制数据块(除INIT、INIT ACK和SHUTDOWN COMPLETE)均可以同ABORT进行捆绑在一个SCTP分组中，但这些控制块都应放在SCTP分组中的ABORT数据块之前，否则这些控制数据块将被接收方忽略。
如果一个端点收到了格式错误或与不存在的偶联相关的ABORT消息，则应当舍弃该消息。此外，在任何情况下，端点收到一个ABORT消息后，都不能通过发送ABORT消息作为响应。
一、 SCTP ABORT报文格式

       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
      +-------------------------------+-------------------------------+ ---
      |     Source Port Number        |     Destination Port Number   |  ^
      +-------------------------------+-------------------------------+  |
      |                      Verification Tag                         |  Common Header
      +---------------------------------------------------------------+  |
      |                           Checksum                            |  V
      +---------------+-------------+-+-------------------------------+ ---
      |   Type = 6    |Reserved     |T|           Length              |
      +---------------+-------------+-+-------------------------------+
      |               zero or more Error Causes                       |
      +                                                               +
      |                      ... ...                                  |
      +---------------------------------------------------------------+

二、 SCTP ABORT报文格式释义

字段	长度	描述
Source Port Number	16比特	源端口号，识别SCTP发送端点的SCTP端口号。接收方可以使用源端口号、源IP地址、目的端口号和目的IP地址标识该SCTP分组所属的偶联。
Destination Port Number	16比特	目的端口号，为目的端点的SCTP端口号。接收主机可以使用目的端口号将SCTP分组复用到正确的端点或应用中。
Verification Tag	32比特	验证标签是偶联建立时，本端端点为这个偶联生成一个随机标识。偶联建立过程中，双方会交换这个TAG，到了数据传递时，发送端必须在公共分组头中带上对端的这个TAG，以备校验。在包含ABORT数据块的分组中，验证标签必须要从触发这个ABORT发送的分组中复制。
Checksum	32比特	SCTP通过对用户数据使用ADLER-32算法，计算出一个32位的校验码，带在数据报中，在接收端进行同样的运算，通过检查校验码是否相等来验证用户数据是否遭到破坏。
Type	8比特	Type=6：中止(ABORT)
Reserved	7比特	在发送方设置为全0，并在接收方忽略。
T	1比特	当发送方有一个TCB被破坏时则该T比特设置为0，如果发送方没有TCB，则把该比特设置为1。
Length	16比特	设置为该数据块的长度，包括数据块头和所有包含的差错原因字段。
zero or more Error Causes	变长	ABORT数据块还可以包含0个或多个差错原因参数。

三、SCTP ABORT报文示例

Frame 1: 64 bytes on wire (512 bits), 64 bytes captured (512 bits)
    Encapsulation type: Ethernet (1)
    Arrival Time: Aug 18, 2011 16:09:25.809661000
    [Time shift for this packet: 0.000000000 seconds]
    Epoch Time: 1313654965.809661000 seconds
    [Time delta from previous captured frame: 0.000000000 seconds]
    [Time delta from previous displayed frame: 0.000000000 seconds]
    [Time since reference or first frame: 0.000000000 seconds]
    Frame Number: 1
    Frame Length: 64 bytes (512 bits)
    Capture Length: 64 bytes (512 bits)
    [Frame is marked: False]
    [Frame is ignored: False]
    [Protocols in frame: eth:ethertype:ip:sctp]
    [Coloring Rule Name: SCTP ABORT]
    [Coloring Rule String: sctp.chunk_type eq ABORT]
Ethernet II, Src: 00:0f:e2:d5:c5:29 (00:0f:e2:d5:c5:29), Dst: 00:25:9e:17:0d:85 (00:25:9e:17:0d:85)
    Destination: 00:25:9e:17:0d:85 (00:25:9e:17:0d:85)
        Address: 00:25:9e:17:0d:85 (00:25:9e:17:0d:85)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
    Source: 00:0f:e2:d5:c5:29 (00:0f:e2:d5:c5:29)
        Address: 00:0f:e2:d5:c5:29 (00:0f:e2:d5:c5:29)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
    Type: IP (0x0800)
    Padding: 000000000000
    Frame check sequence: 0xa89c09f1 [correct]
        [FCS Good: True]
        [FCS Bad: False]
Internet Protocol Version 4, Src: 10.168.168.9 (10.168.168.9), Dst: 10.21.112.2 (10.21.112.2)
    Version: 4
    Header Length: 20 bytes
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00: Not-ECT (Not ECN-Capable Transport))
        0000 00.. = Differentiated Services Codepoint: Default (0x00)
        .... ..00 = Explicit Congestion Notification: Not-ECT (Not ECN-Capable Transport) (0x00)
    Total Length: 40
    Identification: 0x5c7a (23674)
    Flags: 0x02 (Don't Fragment)
        0... .... = Reserved bit: Not set
        .1.. .... = Don't fragment: Set
        ..0. .... = More fragments: Not set
    Fragment offset: 0
    Time to live: 61
    Protocol: SCTP (132)
    Header checksum: 0x5c0e [validation disabled]
        [Good: False]
        [Bad: False]
    Source: 10.168.168.9 (10.168.168.9)
    Destination: 10.21.112.2 (10.21.112.2)
    [Source GeoIP: Unknown]
    [Destination GeoIP: Unknown]
Stream Control Transmission Protocol, Src Port: diameter (3868), Dst Port: 3876 (3876)
    Source port: 3868
    Destination port: 3876
    Verification tag: 0x0bbf238b
    [Assocation index: 0]
    Checksum: 0x4f4f2668 (not verified)
    ABORT chunk
        Chunk type: ABORT (6)
            0... .... = Bit: Stop processing of the packet
            .0.. .... = Bit: Do not report
        Chunk flags: 0x00
            .... ...0 = T-Bit: Tag not reflected
        Chunk length: 8
        User initiated ABORT cause
            Cause code: User initiated ABORT (0x000c)
            Cause length: 4

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