SCTP(流控制传输协议)是Internet协议套件传输层中的计算机网络通信协议。最初该协议用于电信网络中的七号信令系统(SS7)消息传输，提供用户数据报协议(UDP)的面向消息特性，同时确保可靠、按顺序传输具有拥塞控制的消息如传输控制协议(TCP)。与UDP和TCP不同，SCTP支持多宿主和冗余路径以提高弹性和可靠性。SCTP由Internet工程任务组(IETF)在RFC4960中标准化。
在4G和5G移动蜂窝通信系统中SCTP是eNB与MME(4G)，eNB与eNB之间通信使用的协议连接；在5G网络中SCTP是gNB与AMF，gNB与gNB之间使用的协议连接。
图1.4G和5G中SCTP链路图
一、SCTP协议栈
在4G和5G网络中SCTP用于X2和S1，Xn与NG之间接口，它们使用的协议栈结构分别如下。
图2.4G和5G中SCTP协议栈结构
二、SCTP数据结构
SCTP数据在4G和5G中结构相同，通过接口进行数据包捕获(如Wireshark捕获)后您将看到它们由:IP+SCTP+S1AP(or NGAP)+承载数据(Payload)构成。
图3.4G和5G中SCTP数据结构
三、SCTP建立
SCTP需要初始握手来建立两个端点之间连接。如下表所示SCTP要经过4步握手(TCP经过3次握手)完成SCTP初始设置过程。
图4.5G中SCTP建立流程
四、SCTP建立报文
4.1 INIT(初始建立请求)
Internet Protocol Version 4, Src: 10.0.0.185, Dst: 10.0.0.162
0100 .... = Version: 4
.... 0101 = Header Length: 20 bytes (5)
Differentiated Services Field: 0x02 (DSCP: CS0, ECN: ECT(0))
0000 00.. = Differentiated Services Codepoint: Default (0)
.... ..10 = Explicit Congestion Notification: ECN-Capable Transport codepoint '10' (2)
Total Length: 68
Identification: 0x0000 (0)
Flags: 0x40, Don't fragment
0... .... = Reserved bit: Not set
.1.. .... = Don't fragment: Set
..0. .... = More fragments: Not set
Fragment Offset: 0
Time to Live: 64
Protocol: SCTP (132)
Header Checksum: 0x24da [validation disabled]
[Header checksum status: Unverified]
Source Address: 10.0.0.185
Destination Address: 10.0.0.162
Stream Control Transmission Protocol, Src Port: 48041 (48041), Dst Port: 38412 (38412)---SCTP源端口号(48041),目的地端口号(38412）
Source port: 48041
Destination port: 38412
Verification tag: 0x00000000
[Association index: 65535]
Checksum: 0x0ffaab98 [unverified]
[Checksum Status: Unverified]
INIT chunk (Outbound streams: 8, inbound streams: 65535)
Chunk type: INIT (1)(链路类型--初始建立)
0... .... = Bit: Stop processing of the packet
.0.. .... = Bit: Do not report
Chunk flags: 0x00
Chunk length: 36
Initiate tag: 0x8d10a6cf
Advertised receiver window credit (a_rwnd): 106496
Number of outbound streams: 8
Number of inbound streams: 65535
Initial TSN: 3757580128
Supported address types parameter (Supported types: IPv4)
Parameter type: Supported address types (0x000c)
0... .... .... .... = Bit: Stop processing of chunk
.0.. .... .... .... = Bit: Do not report
Parameter length: 6
Supported address type: IPv4 address (5)
Parameter padding: 0000
ECN parameter
Parameter type: ECN (0x8000)
1... .... .... .... = Bit: Skip parameter and continue processing of the chunk
.0.. .... .... .... = Bit: Do not report
Parameter length: 4
Forward TSN supported parameter
Parameter type: Forward TSN supported (0xc000)
1... .... .... .... = Bit: Skip parameter and continue processing of the chunk
.1.. .... .... .... = Bit: Do report
Parameter length: 4
4.2 INIT_ACK(初始建立应答)
Internet Protocol Version 4, Src: 10.0.0.162, Dst: 10.0.0.185
0100 .... = Version: 4
.... 0101 = Header Length: 20 bytes (5)
Differentiated Services Field: 0x02 (DSCP: CS0, ECN: ECT(0))
0000 00.. = Differentiated Services Codepoint: Default (0)
.... ..10 = Explicit Congestion Notification: ECN-Capable Transport codepoint '10' (2)
Total Length: 292
Identification: 0x0000 (0)
Flags: 0x40, Don't fragment
0... .... = Reserved bit: Not set
.1.. .... = Don't fragment: Set
..0. .... = More fragments: Not set
Fragment Offset: 0
Time to Live: 64
Protocol: SCTP (132)
Header Checksum: 0x23fa [validation disabled]
[Header checksum status: Unverified]
Source Address: 10.0.0.162
Destination Address: 10.0.0.185
Stream Control Transmission Protocol, Src Port: 38412 (38412), Dst Port: 48041 (48041)---SCTP源端口号(38412),目的地端口号(48041）
Source port: 38412
Destination port: 48041
Verification tag: 0x8d10a6cf
[Association index: 65535]
Checksum: 0x30678470 [unverified]
[Checksum Status: Unverified]
INIT_ACK chunk (Outbound streams: 8, inbound streams: 8)
Chunk type: INIT_ACK (2)(链路类型--初始建立)
0... .... = Bit: Stop processing of the packet
.0.. .... = Bit: Do not report
Chunk flags: 0x00
Chunk length: 260
Initiate tag: 0x790ad620
Advertised receiver window credit (a_rwnd): 106496
Number of outbound streams: 8
Number of inbound streams: 8
Initial TSN: 4169966867
State cookie parameter (Cookie length: 228 bytes)
Parameter type: State cookie (0x0007)
0... .... .... .... = Bit: Stop processing of chunk
.0.. .... .... .... = Bit: Do not report
Parameter length: 232
State cookie: 4124569d7e0548bdbfbc4c54e0af0c95e938d9f500000000000000000000000000000000…
ECN parameter
Parameter type: ECN (0x8000)
1... .... .... .... = Bit: Skip parameter and continue processing of the chunk
.0.. .... .... .... = Bit: Do not report
Parameter length: 4
Forward TSN supported parameter
Parameter type: Forward TSN supported (0xc000)
1... .... .... .... = Bit: Skip parameter and continue processing of the chunk
.1.. .... .... .... = Bit: Do report
Parameter length: 4
4.3 COOKIE_ECHO（COOKIE应答)
Internet Protocol Version 4, Src: 10.0.0.185, Dst: 10.0.0.162
0100 .... = Version: 4
.... 0101 = Header Length: 20 bytes (5)
Differentiated Services Field: 0x02 (DSCP: CS0, ECN: ECT(0))
0000 00.. = Differentiated Services Codepoint: Default (0)
.... ..10 = Explicit Congestion Notification: ECN-Capable Transport codepoint '10' (2)
Total Length: 264
Identification: 0x0000 (0)
Flags: 0x40, Don't fragment
0... .... = Reserved bit: Not set
.1.. .... = Don't fragment: Set
..0. .... = More fragments: Not set
Fragment Offset: 0
Time to Live: 64
Protocol: SCTP (132)
Header Checksum: 0x2416 [validation disabled]
[Header checksum status: Unverified]
Source Address: 10.0.0.185
Destination Address: 10.0.0.162
Stream Control Transmission Protocol, Src Port: 48041 (48041), Dst Port: 38412 (38412)---SCTP源端口号(48041),目的地端口号(38412）
Source port: 48041
Destination port: 38412
Verification tag: 0x790ad620
[Association index: 65535]
Checksum: 0xa00fe0f7 [unverified]
[Checksum Status: Unverified]
COOKIE_ECHO chunk (Cookie length: 228 bytes)
Chunk type: COOKIE_ECHO (10)(链路类型--COOKIE应答)
0... .... = Bit: Stop processing of the packet
.0.. .... = Bit: Do not report
Chunk flags: 0x00
Chunk length: 232
Cookie: 4124569d7e0548bdbfbc4c54e0af0c95e938d9f500000000000000000000000000000000…
4.4 COOKIE_ACK(COOKIE反馈）
Internet Protocol Version 4, Src: 10.0.0.162, Dst: 10.0.0.185
0100 .... = Version: 4
.... 0101 = Header Length: 20 bytes (5)
Differentiated Services Field: 0x02 (DSCP: CS0, ECN: ECT(0))
0000 00.. = Differentiated Services Codepoint: Default (0)
.... ..10 = Explicit Congestion Notification: ECN-Capable Transport codepoint '10' (2)
Total Length: 36
Identification: 0x0000 (0)
Flags: 0x40, Don't fragment
0... .... = Reserved bit: Not set
.1.. .... = Don't fragment: Set
..0. .... = More fragments: Not set
Fragment Offset: 0
Time to Live: 64
Protocol: SCTP (132)
Header Checksum: 0x24fa [validation disabled]
[Header checksum status: Unverified]
Source Address: 10.0.0.162
Destination Address: 10.0.0.185
Stream Control Transmission Protocol, Src Port: 38412 (38412), Dst Port: 48041 (48041)---SCTP源端口号(38412),目的地端口号(48041）
Source port: 38412
Destination port: 48041
Verification tag: 0x8d10a6cf
[Association index: 65535]
Checksum: 0xa018cd9c [unverified]
[Checksum Status: Unverified]
COOKIE_ACK chunk
Chunk type: COOKIE_ACK (11)(链路类型--COOKIE反馈)
0... .... = Bit: Stop processing of the packet
.0.. .... = Bit: Do not report
Chunk flags: 0x00
Chunk length: 4
联系客服
