SCTP Overview
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Tutorial of SCTP and Sigtran

Tutorial of SCTP and Sigtran

Invited Lecture, Beijing University of Posts and Telecommunication, April 3, 2000..

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SCTP Overview SCTP Overview Presentation Transcript

  • SCTP Overview John Loughney NRC/COM Helsinki April 4th, 2000NOKIA John A. Loughney 3 April 2000
  • Introduction • Based on NRC “IP Based 3G Protocols” • SCTP •S= Simple (maybe Stream …) •C= Control •T= Transmission •P= Protocol • SIGTRAN = Signaling Transport • IETF reference implementation should be ready this week.NOKIA John A. Loughney 3 April 2000
  • Why? • IP is everywhere but it an old protocol (RFC 793, September 1981) • TCP has acknowledged deficiencies. • Head-of-line blocking • Vulnerable to attacks • Poor support for multihoming. • New, demanding applications & services are IP based. • IP Telephony • Streaming Audio & Video • 3G • Advancing Hardware Design • Bandwidth, bandwidth, bandwidth ...NOKIA John A. Loughney 3 April 2000
  • SCTP Goals • SCTP is designed to transport both PSTN signaling messages and provide general transport solution. • SCTP is an kernel-level datagram transfer protocol operating over IP offering: • acknowledged error-free non-duplicated transfer of user data • data segmentation to conform to discovered path MTU size, • sequenced delivery of user datagrams within multiple streams, with an option for order-of-arrival delivery of individual messages • optional multiplexing of user messages into SCTP datagrams, subject to MTU size restrictions • network-level fault tolerance through supporting of multi-homing at either or both ends of an association. • Appropriate congestion avoidance behavior. • Resistance to flooding and masquerade attacks.NOKIA John A. Loughney 3 April 2000
  • Work So Far • Architectural Framework For Signaling Transport document • RFC 2719 • SCTP - Simple Control Transmission Protocol draft • draft submitted - draft-ietf-sigtran-sctp07.txt • SCCP user adaptation layer: used by TCAP, RANAP, etc. • Draft submitted - draft-loughney-sigtran-sua00.txt • MTP level 3 user adaptation layer: used by ISUP and SCCP. • Draft submitted - draft-ietf-sigtran-m3ua02.txt • MTP level 2 user adaptation layer: used by MTP level 3 • draft submitted - draft-ietf-sigtran-m2ua-03.txt • Q.921 User adaptation layer: used by q931/DSS1 • draft submitted - draft-ietf-sigtran-iua-01.txtNOKIA John A. Loughney 3 April 2000
  • Functional Description of SCTP _____________ ____________________ | | | Sequenced delivery | | Association | | within streams | | | |____________________| | startup | ..| | ____________________________ | and | | User Data Segmentation | | | |____________________________| | takedown | ..| | ____________________________ | | | Acknowledgement | | | | and | | | | Congestion Avoidance | ..| | |____________________________| | | | | ____________________________ | | | Chunk Multiplex | | | |____________________________| | | | | ________________________________ | | | Message Validation | | | |________________________________| | | | | ________________________________ | | | Path Management | |______________ |________________________________|NOKIA John A. Loughney 3 April 2000
  • SCTP Association _____________ _____________| SCTP User | | SCTP User || Application | |Application ||-------------| |-------------|| SCTP | | SCTP || Transport | | Transport || Service | | Service ||-------------| |-------------|| |One or more ---- One or more| || IP Network |IP address / IP address| IP Network || Service |appearances / appearances| Service ||_____________| ---- |_____________| SCTP Node A |<-------- Network transport ------->| SCTP Node B * Usage of multiple port / address pairs is implementation specific.NOKIA John A. Loughney 3 April 2000
  • Data Transfer +--------------------------+ | User Messages | +--------------------------+ SCTP user ^ | ==================|==|================================= | v (1) +------------------+ +--------------------+ | SCTP DATA Chunks | |SCTP Control Chunks | +------------------+ +--------------------+ ^ | ^ | | v (2) | v (2) +--------------------------+ | SCTP datagrams | +--------------------------+ SCTP ^ | ===========================|==|======================== | v IP (1) SCTP sender will segment user messages larger than the current path MTU into multiple data chunks., when converting user messages into Data chunks . The segmented message will normally be reassembled from data chunks before delivery to the user by the SCTP receiver. (2) Multiple data and control chunks may be multiplexed by the sender into a single SCTP datagram for transmission, as long as the final size of the datagram does not exceed the current path MTU. The receiver will de-multiplex the datagram back into the original chunks.NOKIA John A. Loughney 3 April 2000
  • Endpoint A Example Endpoint Z {app sets association with Z} (build TCB) INIT [INIT Tag=Tag_A & other info] -------- (Start T1-init timer) (Enter COOKIE-WAIT state) ---> (compose temp TCB and Cookie_Z) /--- INIT ACK [Veri Tag=Tag_A, / INIT Tag=Tag_Z, (Cancel T1-init timer) <-----/ Cookie_Z, & other info] (destroy temp TCB) COOKIE [Cookie_Z] ----------- (Start T1-init timer) (Enter COOKIE-SENT state) ---> (build TCB enter ESTABLISHED state) /---- COOKIE-ACK / (Cancel T1-init timer, <-----/ enter ESTABLISHED state) {app sends 1st user data; strm 0} DATA [TSN=init TSN_A Strm=0,Seq=1 & user data]- (Start T3-rxt timer) ---> /---- SACK [TSN ACK=init TSN_A,Frag=0] (Cancel T3-rxt timer) <------/ {app sends 2 datagrams;strm 0} /---- DATA / [TSN=init TSN_Z <--/ Strm=0,Seq=1 & user data 1] SACK [TSN ACK=init TSN_Z, /---- DATA Frag=0] ---------/ [TSN=init TSN_Z + 1, <------/ Strm=0,Seq=2 & user data 2] --->NOKIA John A. Loughney 3 April 2000
  • TCP Drawbacks • TCP provides reliable data transfer with strict order-of- transmission delivery. Some applications need only reliable transfer, while others need only partial ordering of the data. In both of these cases the head-of-line blocking offered by TCP causes unnecessary delay. • TCP stream support is often an inconvenience. Applications must add their own record marking to delineate their messages, and must make explicit use of the push facility to ensure that a complete message is transferred in a reasonable time. • The limited scope of TCP sockets complicates the task of providing highly-available data transfer capability using multi- homed hosts. • TCP is relatively vulnerable to denial of service attacks, such as SYN attacks.NOKIA John A. Loughney 3 April 2000
  • Differences between TCP & SCTP • SCTP is connection-oriented in nature, but the SCTP association is a broader concept than the TCP connection. • The term "stream" is used in SCTP to refer to a sequence of user messages. This is in contrast to its usage in TCP, where it refers to a sequence of bytes.NOKIA John A. Loughney 3 April 2000
  • Congestion Control (1/3) • The congestion control algorithms used by SCTP are based on RFC 2581 "TCP Congestion Control". • SCTP congestion control is always applied to the entire association, and NOT to individual streams. • The Selective Acknowledgment function (SACK) is designed into SCTP, rather than an enhancement that is added to the protocol later as is the case for TCP. SCTP SACK carries the same semantic meaning with that of TCP SACK. • Multi-homing in SCTP, may lead differing data paths between the two points, thus a separate set of congestion control parameters for each of the paths.NOKIA John A. Loughney 3 April 2000
  • Congestion Control (2/3) • Congestion control variables similar to TCP: • Receiver advertised window size (rwnd, in octets), which is set by the receiver based on its available buffer space for incoming packets. • Congestion control window (cwnd, in octets), which is adjusted by the sender based on observed network conditions. • Slow-start threshold (ssthresh, in octets), which is used by the sender to distinguish slow start and congestion avoidance phases. • SCTP also requires one additional control variable, partial_bytes_acked, which is used during congestion avoidance phase to facilitate cwnd adjustment. • Unlike TCP, an SCTP sender MUST keep a set of these control variables for EACH destination address of its peer (when its peer is multi-homed).NOKIA John A. Loughney 3 April 2000
  • Congestion Control (3/3) • A straightforward implementation Fast Retransmission on Gap Reports, requires that the sender keeps a counter for each TSN hole first reported by a SACK; the counter keeps track of whether 3 subsequent SACKs have reported the same hole. • TCP-like fast-recovery is achieved automatically, because cwnd in SCTP indirectly bounds the number of outstanding TSNs, with no adjustment to the congestion control window size.NOKIA John A. Loughney 3 April 2000
  • SS7 over IP Architecture ****** SS7 ******* SS7 ************ IP ******* *SEP *--------* STP *------* SG *-------*ISEP * ****** ******* ************ ******* +-----+ +-----+ |S7AP | |S7AP | +-----+ +---------+ +-----+ |Adap.| | Adap. | |Adap.| |layer| | layer | |adap | +-----+ +-----+ +---------+ +-----+ |MTP | |MTP | |MTP |SCTP| |SCTP | | | | | | +----+ +-----+ | | | | | | IP | | IP | +-----+ +-----+ +---------+ +-----+ SEP = Signaling End Point STP = Signaling Transfer Point SG = Signaling Gateway ISEP = IP Signaling Endpoint S7AP = SS7 Application protocolNOKIA John A. Loughney 3 April 2000
  • SIGTRAN in 3GPP • 3GPP Rel 99 Packet Architecture • RANAP (Iu interface) • RNSAP (Iur interface) • 3GPP Rel 00 - All IP architecture • MAP over SIGTRAN • CAP over SIGTRAN • R-SGW • T-SGWNOKIA John A. Loughney 3 April 2000
  • Open Issues • Bounded transfer delay -> No Changes. • Inadequate congestion control. -> No Changes. • On failover, ability to not do slow start on failover link • Load balancing in SCTP. -> No Changes. • SCTP support of load balancing in the ULP. • Host names -> Slight Change in Draft. • Modified TSN windowing calculation. -> Slight Change in Draft. • Cancel chunk operation -> Slight change & future study. • Per-stream rwnd -> Future Study. • Support of source address selection, IP source routing and per- source/Destination address pair congestion control. -> Future Study. • Adding / deleting addresses in an association. -> Future Study.NOKIA John A. Loughney 3 April 2000
  • Uses of SCTP? • Already specified for carrying SS7 protocols in 3GPP. • RANAP, RSNAP • MAP/TCAP, CAP/TCAP • HTTP • AAA • SIP • MEGACO protocol • BICC (Bearer Independent Call Control)NOKIA John A. Loughney 3 April 2000
  • Effects on Other Protocols • IKE (Internet Key Exchange) needs to be modified to more fully support multihoming. • SCTP implementation may use TCP-like socket calls, to more easily allow integration of existing protocols.NOKIA John A. Loughney 3 April 2000
  • Areas to Study • Performance studies and simulations. • Applying existing TCP optimizations to SCTP. • SCTP over wireless devices. • Creative uses of multihoming. • Fair queuing when assigning TSNs to different streams.NOKIA John A. Loughney 3 April 2000
  • MTP-3 User Adaptation Layer John A. Loughney Nokia Research CenterNOKIA John A. Loughney 3 April 2000
  • ISUP Transport ******** SS7 ***************** IP ******** * SEP *---------* SG *--------* ASP * ******** ***************** ******** +------+ +------+ | ISUP | (NIF) | ISUP | +------+ +------+-+------+ +------+ | MTP3 | | MTP3 | | M3UA | | M3UA | +------| +------+ +------+ +------+ | MTP2 | | MTP2 | | SCTP | | SCTP | +------+ +------+ +------+ +------+ | L1 | | L1 | | IP | | IP | +------+ +------+ +------+ +------+ |_______________| |______________| SEP - SS7 Signaling End Point SCTP - Simple Common Transport Protocol NIF – Nodal Interworking FunctionNOKIA John A. Loughney 3 April 2000
  • Major Terminology • Application Server (AS) - A logical entity serving a specific Routing Key. • Application Server Process (ASP) - An Application Server Process serves as an active or standby process of an Application Server (e.g., part of a distributed virtual switch or database element). • Routing Key: At the SG, the Routing Key describes a set of SS7 parameter/parameter-ranges that uniquely defines the range of signaling traffic configured to be handled by a particular Application Server. • Routing Context – from the perspective of an ASP, the Routing Context uniquely identifies the range of traffic associated with a particular Application Server, which the ASP is configured to receive from the SG.NOKIA John A. Loughney 3 April 2000
  • SCCP Transport ******** SS7 ***************** IP ******** * SEP *---------* *--------* * * or * * SG * * ASP * * STP * * * * * ******** ***************** ******** +------+ +---------------+ +------+ | SCCP | | SCCP | | SCCP | +------+ +------+-+------+ +------+ | MTP3 | | MTP3 | | M3UA | | M3UA | +------| +------+ +------+ +------+ | MTP2 | | MTP2 | | SCTP | | SCTP | +------+ +------+ +------+ +------+ | L1 | | L1 | | IP | | IP | +------+ +------+ +------+ +------+ |_______________| |______________| STP - SS7 Signaling Transfer PointNOKIA John A. Loughney 3 April 2000
  • Example (1/2) ******** ************** * *_________________________________________* ******** * Host1 * * _________* * ASP1 * * * SG1 * SCTP Associations | * ******** * * *_______________________ | * ******** * * * | | * * ASP2 * * * * | | * ******** * * * | | * ******** * * * | | * * ASP3 * * ******** | | * ******** * | | * . * ******** | | * . * * *_______________________________| * * * * | * ******** * * SG2 * SCTP Associations | * * ASPn * * * *____________ | * ******** * * * | | ************** * * | | ************** * * | |_________________* ******** * Host2 * * |____________________________* * ASP1 * * ******** * ******** * * ******** * * * ASP2 * * * ******** * * ******** * * * ASP3 * * * ******** * * . * * . * * * * ******** * * * ASPn * * * ******** * ************** . . .NOKIA John A. Loughney 3 April 2000
  • Example (2/2) +--------+ | | +------------+ SG 1 +--------------+ +-------+ | | "STP" | | ---- | SEP +---+ +--------+ +---/ | or | | ASPs | | STP +---+ +--------+ +--- / +-------+ | | | | ---- +------------+ SG 2 +--------------+ | "STP" | +--------+NOKIA John A. Loughney 3 April 2000
  • Messages • Transfer Messages • Data 0101 • SS7 Signaling Network Management (SSNM) Messages • Destination Unavailable (DUNA) 0201 • Destination Available (DAVA) 0202 • Destination State Audit (DAUD) 0203 • SS7 Network Congestion State (SCON) 0204 • Destination User Part Unavailable (DUPU) 0205 • Application Server Process Maintenance (ASPM) messages • ASP Up 0301 • ASP Down 0302 • Heartbeat 0303 • ASP Active 0401 • ASP Inactive 0402 • Management (MGMT) Messages • Error 0000 • Notify 0001NOKIA John A. Loughney 3 April 2000
  • Basic Introduction • Removed explicit SCN protocol id & protocol ID • Cleaned-up SG configuration terminology • Expanded to include n+k redundancy, load-sharing • Better description of fail-over operation • Added ability for ASP to route SS7 traffic across redundant SGs • Added point code lists in SSNM messaging • Made SSNM DAUD (audit) more flexible • Added state change notification SG-ASPs in AS to allow better coordination. • User cases expanded • Added optional M3UA-level heartbeatNOKIA John A. Loughney 3 April 2000
  • Current Issues • Impact of future registration protocol Component • Implementation-dependent parameters or messages (agreed, to be added) • New SS7 Network unavailable message (agreed, to be added) • Nodal inter-working function still confusing. • More use cases (agreed, to be added) • Timer provisional values required. • ASP graceful shutdown required • Provide consistent use of MUST, SHALL, MAY …NOKIA John A. Loughney 3 April 2000
  • New Issues • Add case of SG sending UPU into SS7 when all ASPs in SPMC are unavailable. • Use of TCP • IP to IP M3UA. • Specify explicit data recovery from a failed SCTP association (use like SS7 changeover?) • SCON from ASP to SG to indicate ASP nodal congestion?NOKIA John A. Loughney 3 April 2000
  • SCCP User Adaptation Layer Update from the 47th IETF Meeting: Adelaide, Australia draft-loughney-sigtran-sua-00.txt John A. LoughneyNOKIA John A. Loughney 3 April 2000
  • Why • SCCP-users can run over IP. • There are existing, proprietary solutions (i.e. - TCAP over IP). • All IP 3G Networks are currently in development, which use application protocols over SCCP, but IP for transport. • Point-to-point and via Signaling Gateways. • Simplifies the protocol stack.NOKIA John A. Loughney 3 April 2000
  • How • Keep SCCP-User lower interface intact. • Allow protocol options. • Connection-less & connection oriented, etc. • Transfer SCCP-User messages over SCTP/IP. • CAP/TCAP, MAP/TCAP, RANAP, etc. • Allow flexible protocol & architectural implementation. • Support for distributed IP-based signaling nodes. • Inter-work with legacy SS7 networks.NOKIA John A. Loughney 3 April 2000
  • General Architecture Protocol Stack ******** SS7 *************** IP ******** * SEP *---------* *--------* * * or * * SG * * ASP * * STP * * * * * ******** *************** ******** +------+ +------+ | AP | | AP | +------+ +------+------+ +------+ | SCCP | | SCCP | SUA | | SUA | +------+ +------+------+ +------+ | MTP3 | | MTP3 | | | | +------| +------+ SCTP | | SCTP | | MTP2 | | MTP2 | | | | +------+ +------+------+ +------+ | L1 | | L1 | IP | | IP | +------+ +------+------+ +------+ | | | | +----------------+ +-------------+NOKIA John A. Loughney 3 April 2000
  • General Architecture Example Signaling SCTP Associations AS3 Gateway ASP1 AS1 ASP2 ASP1 ASP3 SS7 ASP2Network AS2 AS4 ASP1 ASP1 ASP2 ASP2 Note: The Signaling Gateway may be realized as a cluster. Application Servers may be distributed as well. NOKIA John A. Loughney 3 April 2000
  • All-IP Architecture Protocol Stack ******** IP ******** * *--------* * * AS * * AS * *(ASP) * *(ASP) * ******** ******** +------+ +------+ | AP | | AP | +------+ +------+ | SUA | | SUA | +------+ +------+ | SCTP | | SCTP | +------+ +------+ | IP | | IP | +------+ +------+ | | +---------------+NOKIA John A. Loughney 3 April 2000
  • All-IP Architecture Example AS1 SCTP Associations AS3 ASP1 ASP1 ASP2 ASP2 ASP3 AS2 AS4 ASP1 ASP1 ASP2 ASP2 ASP3NOKIA John A. Loughney 3 April 2000
  • Messages • Data Transfer Messages Data Transfer (DATRA) Data Acknowledge (DAACK) • Connection Messages connection request (CONRE) connection acknowledge (CONAK) release request (RELRE) release complete (RELCO) reset confirm (RESCO) reset request (RESRE) • Application Server Process Maintenance (ASPM) Messages ASP Up (ASPUP) ASP Down (ASPDN) ASP Active (ASPAC) ASP Inactive (ASPIA) ASP Takeover (ASPTO) Notify (NTFY) No Active ASP (NAASP) • SUA Management Messages Error (ERR) Audit (AUD) Stream Configuration (SCO) Stream Configuration Acknowledge (SCA) • SS7 Signaling Network Management (SSNM) Messages Destination Unavailable (DUNA) Destination Available (DAVA) Destination State Audit (DAUD) SS7 Network Congestion State (SCON) Destination User Part Unavailable (DUPU) • Other Vendor-Specific Message (VEND)NOKIA John A. Loughney 3 April 2000
  • To Do • Improve all-IP architecture. • Administrative resources for AS. • Avoid dual client & server ASP. • Avoid association setup collision • Specify in a more detailed way which protocols features are mandatory and those that are optional. • Add more use cases & examples. • Rework management messages. • Application Server Process Maintenance Messages. • SS7 Management Messages • Approve draft for WG statusNOKIA John A. Loughney 3 April 2000