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Table of Contents
Preface.
1. Introduction and Overview.
IP Networking Basics.
How Messages are Delivered in an IP Network.
IP Protocols.
IP Multi-homing.
What Is SCTP?
Where Does SCTP Fit in the IP Architecture?
Motivation for Developing SCTP.
TCP Limitations.
UDP Limitations.
SCTP Enhancements Over TCP and UDP.
A Short History of SCTP Development.
Early Works Before IETF and MDTP.
IETF Refinements.
Major General SCTP Issues Debated in IETF.
Do We Really Need a New Transport Protocol?
Over UDP vs. Over IP.
Organization of This Book.
Summary.
Questions.
2. SCTP Endpoint and Association. SCTP Transport Address.
SCTP Endpoint.
Multi-homed SCTP Endpoint.
SCTP Association.
Operation of an SCTP Association.
Functional View of an Association.
Functional Responsibilities of an SCTP Endpoint.
Operation States of an Association.
IETF Debate And Issues.
Summary.
Questions.
3. Format of SCTP Messages. Basic Layout—the Bits on the Wire.
The SCTP Common Header.
Elements in a Chunk.
Defined Chunk Types and Extensibility.
General Rules When Dealing with Chunks.
Chunk Parameters.
Other Considerations.
Basic Chunk Descriptions.
The INIT Chunk.
The INIT-ACK Chunk.
The COOKIE-ECHO Chunk.
The COOKIE-ACK Chunk.
The DATA Chunk.
The SACK Chunk.
The HEARTBEAT Chunk 98.
The HEARTBEAT-ACK Chunk.
The SHUTDOWN chunk.
The SHUTDOWN-ACK Chunk.
The SHUTDOWN-COMPLETE Chunk.
The ERROR Chunk.
The Error Cause Parameters.
The ABORT Chunk.
IETF Debate And Issue.
Summary.
Questions.
4. Setup of an Association. The INIT Chunk.
Formulating the Chunk.
INIT Parameters.
Timer and Retransmission For INIT.
The INIT-ACK Response.
Formulating the Response.
INIT-ACK Parameters.
Preventing Resource Attacks.
The COOKIE-ECHO Chunk.
Formulating the Chunk.
Bundling Data with the COOKIE-ECHO.
Timer and Retransmission For COOKIE-ECHO.
The COOKIE-ACK Chunk.
Validating and Unpacking the Cookie.
Formulating The COOKIE-ACK.
Bundling DATA and SACK with COOKIE-ACK.
Address Usage When Starting An Association.
Chunk Rejections During an Association Setup.
When an INIT Is Unacceptable?
When is a Cookie Not Worth Eating?
Handle Unexpected Initialization Chunks.
Association Tie-Tags and their values.
Handle Overlapping Initialization Chunks.
Case Study #1: Initialization Collision.
Case Study #2: Peer Restart.
A lost COOKIE-ACK.
IETF Debate and Issues.
Summary.
Questions.
5. User Data Transfer. User Message Transfer Overview.
How User Messages Are Sent.
How User Messages Are Received.
Summary on Data Transfer Overview.
Obey The Transmission Rules.
Congestion Window And Receiver Window.
Rules for Data Transmission.
Acknowledgment Rules.
Where to Send a SACK?
When to Send a SACK?
What to Report in a SACK?
Revoke an Acknowledgment by Receiver.
Process Received SACK by Data Sender.
Management of Retransmission Timer.
Determine Retransmission Time-out (RTO).
Retransmission Timer Rules.
Handle Retransmission Timer Expiration.
Multi-homed Data Sender and Receiver.
Selection of Primary Transport Address.
Transfer Data Between Multi-homed Endpoints.
Sending SACK on Duplicate Data.
Stream Identifier and Stream Sequence Number.
Ordered and Un-ordered Message Delivery.
Passing Payload Protocol Identifier.
Fragmentation and Bundling Of User Messages.
When to Fragment?
How to Fragment a User Message?
Reassembling Fragmented Message at Data Receiver.
User Message Bundling.
Adler-32 Checksum.
Generation of Adler-32 Checksum by Data Sender.
Validate Adler-32 Checksum by Data Receiver.
Error Handling.
Handle Data Chunk with Invalid Stream Identifier.
Handle Empty Data Chunk.
Handle Out-of-state Data.
IETF Debate and Issues.
Summary.
Questions.
6. Congestion Control and Avoidance. The Cause of Network Congestion Collapse.
Basic Concept of Congestion Control.
SCTP Congestion Control Algorithm.
How Does Your cwnd Grow?
How Does Your cwnd Shrink?
Interesting Details of the Algorithms.
Path MTU Discovery.
A Refresher on How PMTU Works.
PMTU Discoveryin SCTP.
Explicit Congestion Notification.
IETF Debate and Issues.
Summary.
Questions.
7. Failure Detection and Recovery. What Types of Failure SCTP Detects.
Destination Address Unreachable.
Peer Endpoint Unreachable.
How To Detect an Unreachable Address.
Use HEARTBEAT to Monitor Reachability.
Address Unreachability Detection Algorithm.
More on Using Heartbeat.
Handle Unreachable Primary Destination Address.
How To Detect an Unreachable Peer.
Association Entering Dormant State.
Fault Resilience Communication and Routing Configuration.
Maximize Path Diversity.
Asymmetric Multi-homing Configuration.
Effects of Source Address Selection.
IETF Debate and Issues.
Summary.
Questions.
8. Auxiliary SCTP Packet Handling Functions. Handle Out-of-the-blue SCTP Packets.
SCTP Packet Verification Tag Rules.
Basic Verification Tag Rules.
Special Verification Tag Rules.
IETF Debate and Discussion.
Summary.
Questions.
9. Close of an Association. The Graceful Shutdown.
Sending SHUTDOWN.
Receiving SHUTDOWN.
Sending SHUTDOWN-COMPLETE.
Race Condition And Lost Message.
The Abortive Shutdown.
Abort Usage.
Sending ABORT.
Receiving ABORT.
IETF Debate and Issues.
Summary.
Questions.
10. IANA And Future Extension Of SCTP. SCTP Port Assignment.
IETF Chunk Extensions.
IETF Parameter Extensions.
IETF Extensions to the Error Causes.
Payload Protocol Identifier.
Summary.
11. A Socket API For SCTP. A Quick Review of the TCP SOCKET API.
The Application Server Side.
The Application Client Side.
Applying the Typical TCP API to SCTP.
The Un-typical SCTP API.
A View of a Client.
The Receiving Side View.
Common API Mechanisms for Both Models.
Using the sendmsg and recvmsg Calls with SCTP.
Notification Information.
Summary.
Questions.
12. Comparing SCTP to TCP. The Similarities Between SCTP and TCP.
Start-up.
Reliability and Ordering.
Congestion Control.
Closing Down.
The Differences between SCTP and TCP.
Differences at Start-up.
Head of Line Blocking.
Message Oriented Boundaries.
Un-ordered Delivery.
Selective Acknowledgment.
Multi-homing.
A Closing Difference.
Summary.
Questions.
13. Using Streams In SCTP. A File Transfer Application.
A Call Control Application.
A Web Browser.
Summary.
Questions.
14. A User Space Implementation Of SCTP. The Big Picture.
Data Structures.
Events and the API.
Association Setup.
When an Upper Layer Issues an Associate Primitive.
When a Peer Sends the SCTP Endpoint an INIT.
Data Transfer.
SACK Processing.
Inbound DATA Processing
Finishing Off By Sending.
Congestion Control, PMTU, And RTO.
Congestion Control.
PMTU Discovery.
RTO Calculation.
Fault Management.
Tag and Out-of-the-blue Handling.
Association Close-down.
At the Upper Layers Request.
Reception of a SHUTDOWN.
Summary.
Glossary and Abbreviations. References. Index. 0201721864T10022001
Preface
This book describes, from the two primary designers' view, the design and operation of the Stream Control Transmission Protocol (SCTP)--a new general-purpose IP transport protocol recently standardized by the Internet Engineering Task Force (IETF).
For those who are familiar with TCP/IP networking, SCTP can be simply viewed as a "super-TCP," that is, a TCP-like, general-purpose reliable data transport protocol with an enhanced set of capabilities.
SCTP is a key piece of the puzzle for making IP a truly viable technology choice in building the next-generation commercial grade infrastructure for telecommunications and e-commerce. For instance, SCTP has been required by the 3rd Generation Partnership Project (3GPP) to carry call signaling traffic in the third-generation cellular systems, and recommended by the IETF to carry the mission-critical Authentication, Authorization, and Accounting (AAA) messages in any future IP service networks.
Telecommunications Magazine selected SCTP as one of the "10 Hottest Technologies of Year 2001" in a cover story in its May 2001 issue.
Why Do We Need SCTP?
The basic design of TCP/IP has worked remarkably well and remained largely unchanged. All the while the Internet has gone through its exponential growth, from a network of only a few nodes connecting a few university campuses, to a truly global Internet with tens of millions of hosts.
The Internet's explosive growth, witnessed by the nineties, continues into the new millennium. At the same time, IP technology has been steadily transforming itself into a cornerstone of the new information-era economy. One of the most visible results of this transformation is that IP technology is beginning to see more and more commercial uses. This is in sharp contrast to the seventies and eighties, when almost the only mention of TCP/IP was heard in academic and research communities.
It is inevitable that this commercialization process has brought with it new requirements to the technology. The original design of TCP, which was conceived and incubated in a mostly academic and research environment, has started to show its limitations in meeting some of these new commercial requirements.
It is this commercialization challenge on IP technology that has brought on the birth of SCTP.
When we first brought the original idea of SCTP (then called MDTP) to the IETF, we were trying to create a protocol to solve a very particular and practical problem; that is, how to transport telephony signaling messages using IP technology in commercial-grade systems. But, at the end of the process, the success of SCTP has grown far beyond our widest expectations.
Readers
This book is written with two different groups of readers in mind. The first group consists of those who want to understand SCTP. These readers may include programmers who need to work with SCTP, managers who want to make informed decisions about SCTP, students who want to learn the basics of SCTP, etcetera. For them, this book can serve as an easy-to-read alternative to the IETF standards specification.
In this book they will find not only detailed explanations of all the basic parts and operations of the protocol, often accompanied by a good deal of examples and diagrams, but also a thorough item-by-item comparison between functions of SCTP and TCP/UDP. Some of the chapters also give this group of readers guidance on which parts of the chapter they can safely skip without hindering their understanding of the general protocol operation.
The second group of readers we have in mind consists of the implementers of SCTP. For them, this book can be used as an annotation to the IETF standards specification. It is our hope that they will find some helpful clarifications of certain complex internal mechanisms of the protocol through the examples and illustrations we put in the book. Moreover, the recounts we have in the book on many important IETF debates and consensus-building processes may give them some insight into the protocol design. This in turn may improve their understanding over the rationale behind those same key design decisions.
Prerequisites
We assume that the readers have preliminary knowledge about TCP/IP and IP networking. (An excellent book for this is W. Richard Stevens' and Gary R. Wright's The TCP/IP Illustrated, Volume 1: The Protocols, published by Addison-Wesley.) Moreover, some experience with C programming and Unix systems will be very helpful, though it is not an absolute requirement.
For those who would like to refresh their knowledge of IP networking, we have a short review of the IP networking basics at the beginning of Chapter 1.
Coverage
This book covers all aspects of SCTP standards as defined in the IETF's Request for Comments 2960 (RFC2960) (Stewart et al. 2000). We also include a preview of the proposed SCTP sockets API (application programming interface) extension, which is a work in progress in the IETF.
A CD-ROM containing the open-source user-space SCTP reference implementation is included in this book. Readers who want to read the reference implementation code can find a chapter at the end of the book explaining the overall design and internal structures of the code. This code has been compiled and tested with FreeBSD 4.2, Linux 2.2.17 and 2.4.1, and Solaris 2.8.1 operating systems. Updates and new releases of this open-source SCTP reference implementation can be found at http://www.sctp.org.
For those interested in doing experiments with the SCTP reference implementation, a good tool to use to capture and analyze SCTP traffic is the Ethereal Network Analyzer, which is freely downloadable from http://www.ethereal.com.
0201721864P10152001
Index
Numerics- 3GPP (Third Generation Partnership Project) 329
A- a_rwnd (advertised receive window credit) 145-146
- calculating 145
- for INIT messages 46
- ABORT chunk 33
- description of 40
- fields of 72-73
- receiving 249-250
- in SCTP packets 233-234
- sending 248-249
- using 248
- abortive shutdown 248-250
- accept() function 259
- acknowledgment
- cumulative 138
- delayed 138-139
- generation of 28
- revoking 146-148
- to SCTP sender 131
- additive increase multiplicative decrease (AIMD) 180
- ADDRESS_ADDED state 274
- ADDRESS_AVAILABLE state 274
- ADDRESS_MADE_PRIM state 274
- ADDRESS_REMOVED state 274
- ADDRESS_UNREACHABLE state 274
- addresses 2-3
- ambiguity in detecting the reachability of 208-208
- broadcast 22
- heartbeat period of 205
- hostname 48, 48
- inactive 160
- multicast 22
- source 161
- unicast 22
- unreachability detection algorithm for 205-206
- unreachable 201-204
- unresolvable 69
- use in association set-up 97-101
- address-unreachability detection algorithm 205-206
- Adler-32 checksum 37
- generation by data senders 171
- validation by data receivers 172
- advertised receive window credit (a_rwnd) 46
- calculating 145
- AF_INET 259
- AIMD (additive increase multiplicative decrease) 180
- ancillary data 268
- API (application programming interface) 24, 297
- application programming interface. See API
- ASSOCIATE primitive 30
- association 21, 24-25
- asymmetric multi-homing configuration of 220-221
- between single-homed and multi-homed endpoints 220-221
- chunk rejections during setup of 101-102
- CLOSED state 237-238
- definition of 329
- dormant state of 216-218
- duplication of 307-308
- four-way initiation sequence of 13
- functional view of 26-27
- graceful shutdown of 238-239
- operation states of 30-33
- setup of 298
- shutdown of 237-238
- peer endpoint request 322
- upper-layer request 321-322
- tie-tags 104-105
- use of addresses when starting 97-101
- See also chunks
- See also endpoints
- association PMTU 166-166
- changes in 167
- definition of 329
- asymmetric multi-homing 220-222
- AUTOCLOSE option 265
B- B bit 56
- bandwidth 281
- Big Endian. See network byte order
- bind() system call 24
- Birds of a Feather (BOF) 329
- BOF (Birds of a Feather) 329
- broadcast addresses 22
- buffer space 139
- receive 145-146
- bundling 13
- of data 28
- DATA chunk with COOKIE-ACK chunk 96-97
- data with COOKIE-ECHO chunk 91
- definition of 329
- disabling 128
- SACK chunk with COOKIE-ACK chunk 96-97
- of user messages 169-170
C- calculateRTO() function 317
- call processing centers 15
- CANT_START_ASSOC notification 273
- cause code
- of cookie received while shutting down error 72
- of invalid mandatory parameter error 70
- of invalid stream identifier error 67
- of missing mandatory parameter error 67
- of no user data error 71
- of out of resource error 68
- of stake cookie error 68
- of unrecognized chunk type error 69
- of unrecognized parameter error 71
- of unresolvable address error 69
- cause length
- of cookie received while shutting down error 72
- of invalid mandaratory parameter error 70
- of invalid stream identifier error 67
- of missing mandatory parameter error 67
- of no user data error 71
- of out of resource error 68
- of stale cookie error 68
- of unrecognized chunk type error 69
- of unrecognized parameter error 71
- of unresolvable address error 69
- chunk flags
- for ABORT chunk 72
- for COOKIE-ACK chunk 55
- for COOKIE-ECHO chunk 54
- for DATA chunk 55
- for HEARTBEAT chunk 61
- for HEARTBEAT-ACK chunk 61
- for INIT-ACK chunk 51
- for OPERATIONAL ERROR chunk 65
- for SACK chunk 59
- for SHUTDOWN chunk 63
- for SHUTDOWN-ACK chunk 64
- for SHUTDOWN-COMPLETE chunk 64
- chunk header 330
- chunk length 38
- of ABORT chunk 73
- of COOKIE-ACK chunk 55
- of COOKIE-ECHO chunk 54
- of DATA chunk 57
- of HEARTBEAT chunk 61
- of HEARTBEAT-ACK chunk 61
- of INIT messages 46
- of INIT-ACK chunk 51
- of OPERATIONAL ERROR chunk 65
- of SACK chunk 59
- of SHUTDOWN chunk 63
- of SHUTDOWN-ACK chunk 64
- of SHUTDOWN-COMPLETE chunk 64
- chunk parameters 42-44
- data 43
- definition of 330
- length 43
- optional 42
- permanent 42, 332
- type 43
- chunk type 38
- bit patterns 43
- by number 38-41
- extensibility of 254-255
- for ABORT chunk 72
- for COOKIE-ACK chunk 55
- for COOKIE-ECHO chunk 54
- for DATA chunk 55
- for HEARTBEAT chunk 61
- for HEARTBEAT-ACK chunk 61
- for INIT messages 46
- for INIT-ACK chunk 51
- for OPERATIONAL ERROR chunk 65
- for SACK chunk 59
- for SHUTDOWN chunk 63
- for SHUTDOWN-ACK chunk 64
- for SHUTDOWN-COMPLETE chunk 64
- reserved values for 254-255
- selecting the values of 42
- chunks 35
- ABORT 72-73
- control 35, 41
- COOKIE-ACK 55
- COOKIE-ECHO 54-55, 89-90
- DATA 55-58
- data 35, 41
- definition of 330
- elements in 37-38
- ERROR 65
- flags 38
- forming SCTP packets from 127-128
- general rules in dealing with 41-42
- header 330
- HEARTBEAT 60-61
- INIT 44-47
- INIT-ACK 50-53
- length 38
- OPERATIONAL ERROR 65, 65
- out-of-the-blue 173
- parameter length 43
- parameter type 43
- parameters 42-44
- parameters data 43
- rejections during association setup 101-102
- SACK 58-60
- SHUTDOWN 62-63
- SHUTDOWN-ACK 63-64
- SHUTDOWN-COMPLETE 64-65
- types 38
- by number 38-41
- unrecognized 69
- See also association
- See also endpoints
- client-side applications 259-261
- CLOSE primitive 33
- close() function 260
- CLOSED state 30, 32
- of association 237-238
- procedures for entering 247
- CMSG_HDR structure 265
- command channel 288
- commercial telephone services 9
- common header 36-37
- communication nodes 4
- multi-homed 6
- protocols 5
- communication software 3
- COMMUNICATION_LOST notification 273
- COMMUNICATION_UP notification 273
- communications 1
- complex cookies 306
- processing of 308-309
- congestion 10
- avoidance of 28
- control of 13
- congestion avoidance algorithm 184
- congestion avoidance mechanism 132
- congestion collapse 177-178
- congestion control 280, 315-316
- algorithms 178-180, 186-193
- basic concepts of 178-180
- for SCTP (Stream Control Transmission Protocol) 180-186
- congestion window (cwnd) 132, 180
- decreasing 185
- increasing 183
- congestion window reduce (CWR) 197
- connect() function 259-260
- connection-oriented communications 1
- control chunks 35, 41
- cookie preservative parameter 48, 82
- description of 48
- cookie received while shutting down error 71-72
- COOKIE_ECHOED state 30, 308
- handlin