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Sigtran Introduction

Sigtran Introduction. Disheng.chen. Agenda. ■ SCTP ■ M3UA ■ UI. file 1 record 0. file 1 record 1. file 2 record 0. file 2 record 1. file 3 record 0. file 3 record 1. file 2 record 0. file 2 record 1. file 3 record 1. file 3 record 0. file 1 record 1. file 1 record 0.

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Sigtran Introduction

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  1. Sigtran Introduction Disheng.chen

  2. Agenda ■SCTP ■ M3UA ■UI

  3. file 1record 0 file 1record 1 file 2record 0 file 2record 1 file 3record 0 file 3record 1 file 2record 0 file 2record 1 file 3record 1 file 3record 0 file 1record 1 file 1record 0 file 3record 0 file 3record 1 SCTP VS TCP TCPEndpointA TCPEndpointB file 3record 1 file 3record 0 file 2record 1 file 2record 0 file 1record 1 file 1record 0 TCP connection received buffered Stream 0 file 1record 0 SCTPEndpointB SCTPEndpointA file 1record 1 file 2record 1 file 2record 0 Stream 1 SCTP association Stream 2 received buffered

  4. SCTP Multihoming 10.11.23.14 10.11.23.16 Path0 Path2 Path1 2905 2905 MGC Path3 SG 10.11.23.15 10.11.23.17

  5. SCTP vs TCP ■SCTP was designed to overcome the TCP head-of-line blocking problem with… ● …unordered delivery feature ● … multi-streaming ● … multi-homing ■ Reordering is done based on stream sequence numbers (SSN) separately for each stream ■Number of incoming and outgoing streams is negotiated when association is established

  6. SCTP Terminology (RFC2960, RFC3309, RFC4960) •Transport Address • a SCTP port + an IP address (IPV4/IPV6) •Endpoint • logical sender/receiver. a source port + one or more source IP + a dest port + one or more dest IP. •Association • a Connection between 2 endpoints. •Path • a route taken from one host to a specific destination transport address of its peer end point. a source port + a source IP + a dest port + a dest IP. •Stream • a unidirectional logical channel, usually with in-sequence delivery. Unordered delivery also possible. •Chunck • A unit of information within an SCTP packet, consisting of a chunk header and chunk-specific content.

  7. SCTP Endpoint Own_ip:10.11.23.15 10.11.23.14 Remote_ip: 10.11.23.16 10.11.23.17 Own port: 2905 Remote port:2905 remote_ip:10.11.23.15 10.11.23.14 own_ip: 10.11.23.16 10.11.23.17 Own port: 2905 Remote port: 2905 Associaton MGC SG EndPoint1 EndPoint2

  8. SCTP Packet Format IP-Proto:Ox84 32Bit Source Port Dest.Port SCTP Common Header(12 Bytes) Verification Tag Checksum(CRC32C) Type Flags Length SCTP Chunk 1 (>=4 Bytes) Chunk specific Data … … SCTP Chunk n (>=4 Bytes)

  9. SCTP important chunck types • Association Setup • Initiation(INIT):1 • Initiation Acknowledgement(INIT ACK):2 • State Cookie(COOKIE ECHO):10 • Cookie Acknowledgement(COOKIE ACK):11 • Association Teardown • Abort(ABORT):6 • Shutdown(SHUTDOWN):7 • Shutdown Ackn. (SHUTDOWN ACK):8 • Operation Error(ERROR):9 • Data Transmission: • Payload Data(DATA):0 • Selective Acknowledgement(SACK):3 • Path Management: • Heartbeat Request(HEARTBEAT):4 • Heartbeat Ackn. (HEARTBEAT ACK):5

  10. SCTP data chunck ■Data chunk carries two sequencenumbers: ●32 Bit Trans mission Sequence Number (TSN) used solely for reliable delivery ●16 Bit Stream Sequence Number (SSN) used for reordering within a stream ■Flags may be set for: ●Segmentation ●Unordered Delivery ■ Payload Protocol ID can be used to identify user application 1: IUA; 2: M2UA; 3: M3UA; 4: SUA; 5: M2PA; 6: V5UA; 10: DUA 32 Bit Flags: U B E Type Length TSN Stream ID Stream SN Payload Protocol ID User Data The (U)nordered bit, if set to '1', indicates that this is an unordered DATA chunk, and there is no Stream Sequence Number assigned to this DATA chunk. Therefore, the receiver MUST ignore the Stream Sequence Number field.

  11. SCTP Association setup Host A Host B INIT (List of IP addresses,A1,A2,…） INIT ACK (Cookie, List of addresses,B1,B2, …) COOKIE ECHO (Cookie) Resource Allocation COOKIE ACK

  12. SCTP Association Teardown (Abort) ■Two methods for termination of an association have been defined: ●Association Abort (see below) ●Graceful Termination Host B Host A ABORT(32 bit verification) association is gone !

  13. SCTP Association Teardown (Graceful) ■Standard covers also all the pathological cases Host A Host B CLOSE Flush Queues SHUTDOWN Flush Queues SHUTDOWN ACK SHUTDOWN COMPLETE

  14. SCTP stream concept For IUA/M2UA, Interface Identifier has a one to one relationship with a SS7 Link. Each message received is routed to the corresponding Stream.

  15. SCTP stream concept SCTP User Processes P3 P1 P2 P4 1 5 1 SCTP Stream Queues 2 17 18 19 New SCTP Packet 2 3 16 7

  16. SCTP Multihoming AS 0 AS 1 SCTP associations ASP a IP address a’ IP address x’ ASP x IP address a IP address x SignallingGateway ASP b IP address b’ IP address y’ ASP y IP address b IP address y IP address c’ IP address z’ ASP c ASP z IP address c IP address z = multi-homing

  17. SCTP Multihoming ■each host selected one path as primary path ●say:A1-B1 and B3-A2 ■carries main data load (except retransmissions) ■idle paths are heart-beaten (~once in 30 secs) ■path states can be active or inactive

  18. SCTP Multihoming ■one path fails: ■A experiences ratrans mission timeouts ■A increases a path error counter ■so does B with its hearts-beats (slower!) ■std. threshold for setting path inactive:5 ■A will mark path to B1 inactive ■retrans missions will go to another path(B2,B3)

  19. Agenda ■SCTP ■M3UA ■UI

  20. AS and ASP Vidio Server call server Media Resource Server Web server • Application Server (AS) : A logical entity serving a specific • application instance. • Application Server Process (ASP) - A process instance of an • Application Server.

  21. Sigtran Framework Architecture (one scenario) Sigtran

  22. OPC 1-1-1 DPC 4-4-4 OPC 1-1-1 OPC 1-1-1 OPC 1-1-1 DPC 2-2-2 DPC 2-2-2 DPC 4-4-4 M3UA Routing based on DPC (same rule can be applied to OPC) MTP3 Route table: Number of routes : 4 ------------------------------------------------------------------------------- Route-ID Network-ID DPC Direction(*) Protocol Cmblinkset-ID Restart ------------------------------------------------------------------------------- 0 0 1-1-1 Down ITU 0 ITU92 1 0 3-3-3 Down ITU 2 ITU92 2 0 2-2-2 Up ITU 1 ITU92 3 0 4-4-4IP ITU 3 ITU9 ------------------------------------------------------------------------------- SS7 link SCTP association User Data ASP1(PC: 2-2-2) ASP1 Germany MTP3 SP A(PC: 1-1-1) ASP2(PC: 2-2-2) ASP2 M3UA AS1 Cmblinkset 0 Cmblinkset 2 ASP4 AS2 A7510 ASP4(PC: 4-4-4) France SP B(PC: 3-3-3) M3UA Route Filter Parameter (for M3UA packets sent to AS) --------------------------------------------------------- AS OPC OPC-Mask DPC DPC-Mask SLS SLS-Mask SIO SIO-Mask 1 1-1-1 14 2-2-2 0 0 4 0 4 23-3-3 14 4-4-4 0 0 4 0 4 OPC-Mask=14 means ignore the OPC field

  23. OPC 1-1-1 DPC 2-2-2 OPC 1-1-1 OPC 1-1-1 DPC 2-2-2 DPC 4-4-4 M3UA Routing based on Service Type MTP3 Route table: Number of routes : 4 ------------------------------------------------------------------------------- Route-ID Network-ID DPC Direction(*) Protocol Cmblinkset-ID Restart ------------------------------------------------------------------------------- 0 0 1-1-1 Down ITU 0 ITU92 1 0 3-3-3 Down ITU 2 ITU92 2 0 2-2-2 Up ITU 1 ITU92 3 0 4-4-4IP ITU 3 ITU92 4 0 7-9-8down ITU 0 ITU92 ------------------------------------------------------------------------------- SS7 link Down: to tdm Up: to IP IP: to IP SCTP association ISUP SCCP ASP1(PC: 2-2-2) ASP1 Germany MTP3 ASP2(PC: 2-2-2) SP A(PC: 1-1-1) ASP2 M3UA AS1 ISUP Cmblinkset 0 7-9-8 Cmblinkset 2 ASP4 AS2 SCCP A7510 ASP4(PC: 5-5-5) France SP B(PC: 3-3-3) M3UA Route Filter Parameter (for M3UA packets sent to AS) --------------------------------------------------------- AS OPC OPC-Mask DPC DPC-Mask SLS SLS-Mask SIO SIO-Mask 1 1-1-1 14 2-2-2 0 0 4 50 23-3-3 14 4-4-40 0 4 30 Question: if DPC-Mask=0 for AS1 and AS2 , what will happen? DPC-Mask=14 means ignore the DPC field

  24. OPC 1-1-1 OPC 1-1-1 DPC 5-5-5 DPC 2-2-2 M3UA Routing based on Service Type MTP3 Route table: Number of routes : 4 ------------------------------------------------------------------------------- Route-ID Network-ID DPC Direction(*) Protocol Cmblinkset-ID Restart ------------------------------------------------------------------------------- 0 0 1-1-1 Down ITU 0 ITU92 1 0 3-3-3 Down ITU 2 ITU92 2 0 2-2-2 Up ITU 1 ITU92 3 0 5-5-5IP ITU 3 ITU92 ------------------------------------------------------------------------------- SS7 link Down: to tdm Up: to IP IP: to IP SCTP association ISUP SCCP Germany MTP3 ASP2(PC: 2-2-2) 5-5-5 SP A(PC: 1-1-1) ASP2 M3UA AS1 ISUP Cmblinkset 0 Cmblinkset 2 A7510 France SP B(PC: 3-3-3) M3UA Route Filter Parameter (for M3UA packets sent to AS) --------------------------------------------------------- AS OPC OPC-Mask DPC DPC-Mask SLS SLS-Mask SIO SIO-Mask 1 1-1-1 14 2-2-2 14 0 4 50 23-3-3 14 4-4-414 0 4 30 Question: if DPC-Mask=0 for AS1 and AS2 , what will happen? DPC-Mask=14 means ignore the DPC field

  25. OPC 1-1-1 OPC 1-1-1 DPC 3-3-3 DPC 3-3-3 DPC 3-3-3 OPC 1-1-1 MTP3 Loopback routing : confused SS7 link Route table: Number of routes : 5 ------------------------------------------------------------------------------- Route-ID Network-ID DPC Direction(*) Protocol Cmblinkset-ID Restart ------------------------------------------------------------------------------- 0 0 1-1-1 Down ITU 0 ITU92 1 03-3-3 Down ITU 2 ITU92 2 0 2-2-2 Up ITU 1 ITU92 3 03-3-3 IP ITU ITU92 4 0 1-1-1 IP ITU ITU92 ------------------------------------------------------------------------------- Scope SGW1 SCTP association ISUP Germany SP A(PC: 1-1-1) SGW(PC: 2-2-2) MGC(PC: 2-2-2) M3UA MTP3 Cmblinkset 0 STP A7510 Cmblinkset 2 France SP B(PC: 3-3-3) M3UA Route Filter Parameter (for M3UA packets sent to AS) --------------------------------------------------------- AS OPC OPC-Mask DPC DPC-Mask SLS SLS-Mask SIO SIO-Mask 1 1-1-1 14 2-2-2 0 0 4 0 4 In the same network, the same DPC is configured for both TDM and IP direction, confused.

  26. M3UA Terminology • Routing Key - A set of SS7 parameters and parameter values that uniquely define the range of signalling traffic to be handled by an AS. A routing key is essentially a set of SS7 used to filter SS7 messages. Normally a routing key may be consist of : 1) DPC 2) SIO + DPC 3) SIO + DPC +OPC 4) SIO + DPC + OPC + SLS (CIC) 7510: 1) Routing key is named as route filter. 2) SIO is pationed into two parts: SSF + SI. 3) SSF is defined as m3ua network paramter. 4) SI is defined as route filter parameter.

  27. M3UA Terminology • Routing Context - A value that uniquely identifies a Routing Key. 7510 use AS id as routing context. • Application Server (AS) - A logical entity serving a specific Routing Key. AS and Routing Key has a 1:1 relationship. 7510 is an SGP, it don’t provide any mtp3 user service, on 7510, AS is the image of MGC service entity. • Signalling Process- A process instance that uses M3UA to communicate. with other signalling processes. on 7510, ASP is the image of remote ASP. ASP and SCTP association has a 1:1 relationship.

  28. transfer PSTN IP MGC1 LS1 ASP1 network2 Germany AS1 ASP2 AS2 SEP2 MGC2 SEP3 1-2-2 AS3 ASP3 AS4 ASP4 France 2-2-2 network2 SGW

  29. M3UA Terminology • Network Appearance – an integer shared by SG and AS. Used to identifies the specific SS7 network that an SS7 node belongs to. 7510 use network id as network appearance. • Signalling Point Management Cluster (SPMC) - The complete set of AS under a single MTP entity in a specific Network Appearance. SG may also be a member of SPMC. • IP Server Process (IPSP) - A process instance of an IP-based application. Essentially same as an ASP, except that it uses M3UA in a point-to-point fashion

  30. M3UA Application Model : SGP-ASP (7510 ) SEP Signalling Gateway ASP NIF ISUP ISUP MTP3 MTP3 M3UA M3UA MTP2 MTP2 SCTP SCTP SS7 IP L1 L1 IP IP SG don’t provide any MTP3 User Service.

  31. M3UA Application Model : IPSP-IPSP IPSP1 IPSP2 SCCP User SCCP User SCCP SCCP M3UA M3UA SCTP SCTP IP IP No MTP function is required. No SGP function is rquired.

  32. M3UA Application Model: SGP Resident SCCP Layer SEP/STP Signalling Gateway MGC SCCP USER SCCP SCCP SCCP MTP3 MTP3 M3UA M3UA MTP2 MTP2 SCTP SCTP E1/T1 ethernet L1 L1 IP IP SG perform the SCCP Global Title Translation (GTT) function.

  33. M3UA Architecture Model: mated SGs. + + + SG 1 “STP” + + + + SS7 links IP network SEP OR STP + + + ASPs + * + + + + + + SG 2 “STP” + + + + + + Mtp2/M2PA SG 1 and SG 2 have the same Routing Key (they serve the same AS).

  34. M3UA Architecture Model SG + + + + M3UA SS7 Ntwk “A” SEP + SS7 links + + ASPs + + SS7 Ntwk “B” + + SEP + + + + + + An SG is patitioned into multiple networks.

  35. M3UA Common Message Header The common message header is same for IUA/M2UA/M3UA/V5UA.

  36. M3UA Message Class 0 Management (MGMT) Message 1 Transfer Messages 2 SS7 Signalling Network Management (SSNM) Messages 3 ASP State Maintenance (ASPSM) Messages 4 ASP Traffic Maintenance (ASPTM) Messages 5 Reserved for Other Sigtran Adaptation Layers 6 Reserved for Other Sigtran Adaptation Layers 7 Reserved for Other Sigtran Adaptation Layers 8 Reserved for Other Sigtran Adaptation Layers 9 Routing Key Management (RKM) Messages 10-127 Reserved by the IETF 128-255 Reserved for IETF-Defined Message Class extensions

  37. SSF SI SLS slc OPC DPC M3UA and MTP3 mapping (Transfer message type) 0 Reserved 1 Payload Data (DATA) 2 to 127 Reserved by the IETF 128 to 255 Reserved for IETF-Defined Transfer extensions MTP3 message format First bit transmitted

  38. M3UA Data Fields : SI – Service Indicator DCBA DCBA Service indicator Sub-service field First bit transmitted 4 4 SI value(4bits) Service Signaling network management messages 0x0 Signaling network testing and maintenance messages 0x1 spare 0x2 0x3 SCCP 0x4 TUP 0x5 ISUP Data User Part (call and circuit-related messages 0x6 Data User Part (facility registration and cancellation messages 0x7 0x8 Reserved for MTP Testing User Part 0x9 Broadband ISUP Satellite ISUP 0xa spare 0xb~0xf

  39. M3UA Data Fields : NI and MP The network indicator codes are allocated as follows: bits D C 0 0 International network 0 1 Spare (for international use only) 1 0 National network 1 1 Reserved for national use NI – Network Indicator MP – Message Priority DCBA DCBA Service indicator Sub-service field First bit transmitted 4 4

  40. M3UA Data Fields : SLS, OPC , DPC, SLC OPC DPC SIO First bit transmitted ITU 4 8 14 24 14 24 ANSI Figure 14/Q.704 Standard label structure

  41. M3UA SSNM Message Types 0 Reserved 1 Destination Unavailable (DUNA) 2 Destination Available (DAVA) 3 Destination State Audit (DAUD) 4 Signaling Congestion (SCON) 5 Destination User Part Unavailable (DUPU) 6 Destination Restricted (DRST) 7 to 127 Reserved by the IETF 128 to 255 Reserved for IETF-Defined SSNM extensions Note: except DAUD & SCON, other message types are sent from SG to ASP.

  42. OPC 1-1-1 DPC 2-2-2 M3UA and MTP3 interactive : UPU MTP3 Route table: Number of routes : 4 ------------------------------------------------------------------------------- Route-ID Network-ID DPC Direction(*) Protocol Cmblinkset-ID Restart ------------------------------------------------------------------------------- 0 0 1-1-1 Down ITU 0 ITU92 1 0 3-3-3 Down ITU 2 ITU92 2 0 2-2-2 Up ITU 1 ITU92 3 0 4-4-4IP ITU 3 ITU9 ------------------------------------------------------------------------------- SS7 link SCTP association User Data ASP1(PC: 2-2-2) UPU (AS1 not active) ASP1 Germany MTP3 SP A(PC: 1-1-1) ASP2(PC: 2-2-2) ASP2 AS1 M3UA AS2 Cmblinkset 2 ASP4 France ASP4(PC: 4-4-4) SP B(PC: 3-3-3) A7510 M3UA Route Filter Parameter (for M3UA packets sent to AS) --------------------------------------------------------- AS OPC OPC-Mask DPC DPC-Mask SLS SLS-Mask SIO SIO-Mask 1 1-1-1 14 2-2-2 0 0 4 0 4 23-3-3 14 4-4-4 0 0 4 0 4 • If AS is not active or pending, when message with DPC 2-2-2 reach SGW from mtp link, SGW will reply with UPU

  43. M3UA and MTP3 interactive : DUPU MTP3 Route table: Number of routes : 4 ------------------------------------------------------------------------------- Route-ID Network-ID DPC Direction(*) Protocol Cmblinkset-ID Restart ------------------------------------------------------------------------------- 0 0 1-1-1 Down ITU 0 ITU92 1 0 3-3-3 Down ITU 2 ITU92 2 0 2-2-2 Up ITU 1 ITU92 3 0 4-4-4IP ITU 3 ITU9 ------------------------------------------------------------------------------- SS7 link SCTP association User Data APC 1-1-1 ASP1(PC: 2-2-2) DUPU UPU ASP1 Germany MTP3 DUPU SP A(PC: 1-1-1) APC 1-1-1 ASP2(PC: 2-2-2) APC 1-1-1 ASP2 AS1 M3UA AS2 Cmblinkset 2 ASP4 France ASP4(PC: 4-4-4) SP B(PC: 3-3-3) A7510 DUPU APC 1-1-1 • If a UPU is received from tdm link, SGW will send DUPU to All Active ASPs in the same network.

  44. M3UA SSNM DUPU message format User value: 0 to 2 Reserved 3 SCCP 4 TUP 5 ISUP 6 to 8 Reserved 9 Broadband ISUP 10 Satellite ISUP 11 Reserved 12 AAL type 2 Signalling 13 Bearer Independent Call Control (BICC) 14 Gateway Control Protocol 15 Reserved

  45. M3UA and MTP3 interactive : DUNA/DAVA/DRST MTP3 Route table: Number of routes : 4 ------------------------------------------------------------------------------- Route-ID Network-ID DPC Direction(*) Protocol Cmblinkset-ID Restart ------------------------------------------------------------------------------- 0 0 1-1-1 Down ITU 0 ITU92 1 0 3-3-3 Down ITU 2 ITU92 2 0 2-2-2 Up ITU 1 ITU92 3 0 4-4-4IP ITU 3 ITU92 ------------------------------------------------------------------------------- SS7 link SCTP association User Data DUNA STP A(PC: 1-1-1) ASP1(PC: 2-2-2) APC 1-1-1 ASP1 Germany DUNA MTP3 ASP2(PC: 2-2-2) APC 1-1-1 ASP2 M3UA AS1 AS2 Cmblinkset 2 ASP4 France ASP4(PC: 4-4-4) A7510 DUNA APC1-1-1 STP B(PC: 3-3-3) TFP--->DUNA TFA--->DAVA TFR--->DRST • For a MTP3 route to ‘down’ direction, if it becomes unreachable, a DUNA will be sent to All ASPs in the same network (in case ASP is active). If it becomes reachable, then a DAVA will be sent to All ASPs.

  46. M3UA and MTP3 interactive : DUNA/DAVA/DRST MTP3 Route table: Number of routes : 5 ------------------------------------------------------------------------------- Route-ID Network-ID DPC Direction(*) Protocol Cmblinkset-ID Restart ------------------------------------------------------------------------------- 0 0 1-1-1 Down ITU 0 ITU92 1 0 3-3-3 Down ITU 2 ITU92 2 0 2-2-2 Up ITU 1 ITU92 3 0 4-4-4IP ITU 3 ITU92 4 0 7-7-7Down ITU 4 ITU92 ------------------------------------------------------------------------------- SS7 link SCTP association User Data DUNA STP A(PC: 1-1-1) ASP1(PC: 2-2-2) APC 7-7-7 TFP ASP1 DUNA Germany MTP3 ASP2(PC: 2-2-2) APC7-7-7 APC 7-7-7 ASP2 SP 7-7-7 M3UA AS1 AS2 Cmblinkset 2 ASP4 France ASP4(PC: 4-4-4) A7510 DUNA APC 7-7-7 STP B(PC: 3-3-3) TFP--->DUNA TFA--->DAVA TFR--->DRST • For a MTP3 route to ‘down’ direction, if it becomes unreachable, a DUNA will be sent to All ASPs in the same network (in case ASP is active). If it becomes reachable, then a DAVA will be sent to All ASPs.

  47. M3UA SSNM DUNA/DAVA/DAUD/DRST message format

  48. M3UA SSNM Affected Point Code format Mask: identifies how many bits of a Point Code are wildcarded.

  49. M3UA and MTP3 interactive : SCON –Remote Congestion MTP3 Route table: Number of routes : 4 ------------------------------------------------------------------------------- Route-ID Network-ID DPC Direction(*) Protocol Cmblinkset-ID Restart ------------------------------------------------------------------------------- 0 0 1-1-1 Down ITU 0 ITU92 1 0 3-3-3 Down ITU 2 ITU92 2 0 2-2-2 Up ITU 1 ITU92 3 0 4-4-4IP ITU 3 ITU92 ------------------------------------------------------------------------------- SS7 link SCTP association User Data SCON Sp A(PC: 1-1-1) ASP1(PC: 2-2-2) APC 1-1-1, L=2 TFC ASP1 SCON Germany MTP3 ASP2(PC: 2-2-2) APC 1-1-1, L=2 ASP2 APC 1-1-1, L=2 Congestion level=2 M3UA AS1 AS2 Cmblinkset 2 ASP4 France ASP4(PC: 4-4-4) A7510 SCON APC 1-1-1, L=2 SP B(PC: 3-3-3) When TFC is received , MTP3 record the congestion level, and generate a SCON to M3UA. Later, if MTP3 receive a message from M3UA, and message priority < TFC congestion level, then SCON will be generated to M3UA.

  50. M3UA and MTP3 interactive : SCON –Remote congestion MTP3 Route table: Number of routes : 4 ------------------------------------------------------------------------------- Route-ID Network-ID DPC Direction(*) Protocol Cmblinkset-ID Restart ------------------------------------------------------------------------------- 0 0 1-1-1 Down ITU 0 ITU92 1 0 3-3-3 Down ITU 2 ITU92 2 0 2-2-2 Up ITU 1 ITU92 3 0 4-4-4IP ITU 3 ITU92 ------------------------------------------------------------------------------- SS7 link SCTP association User Data Sp A(PC: 1-1-1) AS1 ASP1(PC: 2-2-2) ASP1 Germany MTP3 SCON DPC 1-1-1, MP=1 ASP2 APC 1-1-1, L=2 M3UA ASP2(PC: 2-2-2) DPC 1-1-1, MP=1 Cmblinkset 2 ASP4 France A7510 SP B(PC: 3-3-3) ASP4(PC: 4-4-4) AS2 When TFC is received , MTP3 record the congestion level, and generate a SCON to M3UA. Later, if MTP3 receive a message from M3UA, and message priority < TFC congestion level, then SCON will be generated to M3UA.

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