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Stream Control Transmission Protocol (SCTP): A Reference Guide: A Reference Guide

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Stream Control Transmission Protocol (SCTP): A Reference Guide: A Reference Guide


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  • Copyright 2002
  • Dimensions: 7-5/16" x 9-1/2"
  • Pages: 384
  • Edition: 1st
  • Book
  • ISBN-10: 0-201-72186-4
  • ISBN-13: 978-0-201-72186-7

"This book...offers inside insights (by two of the SCTP designers) into the design of the protocol and discusses why the protocol operates as it does. This insight takes much of the 'black magic' out of SCTP and makes the protocol more accessible."
--From the Foreword by Mark Allman

Named one of the Top 10 Hottest Technologies of 2001 by Telecommunications Magazine, Stream Control Transmission Protocol (SCTP) is considered by many to be the TCP of the future. Originally designed for Internet telephony, SCTP has also proven itself a superb general purpose transport protocol for IP network data communications. More robust and secure than TCP, SCTP is the technology of choice for building next generation commercial grade infrastructures for telecommunications and e-commerce. Anyone involved with the technical aspects of Internet communications should have a working knowledge of this new transmission protocol, which is rapidly being adopted by standardization bodies and networking organizations.

Written by the creators of SCTP, Stream Control Transmission Protocol (SCTP): A Reference Guide is a comprehensive, practical, guide to SCTP technology. Examining the protocol in depth, the book provides useful perspective on design rationale and highlights SCTP's improvements over TCP in the areas of security and reliability. The book also demonstrates how to take full advantage of SCTP to make IP-based communications more reliable and robust.

Topics covered include:

  • An item-by-item comparison between the functions of SCTP and TCP/UDP
  • SCTP packet formats
  • Setup and closing of an association
  • User data transfer
  • Congestion control and avoidance, covering the SCTP Congestion Control Algorithm
  • Failure detection and recovery, covering the interaction with multihoming and route arrangements
  • "Out-of-the-blue" SCTP packets and verification tag rules
  • IANA and future extension of SCTP
  • A preview of the proposed SCTP Socket API extension
  • Use of Streams in SCTP, featuring file transfer, call control, and Web browser applications

Numerous examples and diagrams throughout the book clarify important concepts and techniques. The final chapter presents a user space implementation of SCTP, and the accompanying CD-ROM contains the open source code for this implementation.

An important complement to the official IETF standards specification, this book is required reading for all Internet programmers, developers, managers, and implementors of SCTP.



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Table of Contents


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.



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.



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 DATA Chunk.

The SACK Chunk.

The HEARTBEAT Chunk 98.


The SHUTDOWN chunk.



The ERROR Chunk.

The Error Cause Parameters.

The ABORT Chunk.

IETF Debate And Issue.



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.


Formulating the Chunk.

Bundling Data with the COOKIE-ECHO.

Timer and Retransmission For COOKIE-ECHO.


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.


IETF Debate and Issues.



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.



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.



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.



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.



9. Close of an Association.

The Graceful Shutdown.


Receiving SHUTDOWN.


Race Condition And Lost Message.

The Abortive Shutdown.

Abort Usage.

Sending ABORT.

Receiving ABORT.

IETF Debate and Issues.



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.


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.



12. Comparing SCTP to TCP.

The Similarities Between SCTP and TCP.


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.


A Closing Difference.



13. Using Streams In SCTP.

A File Transfer Application.

A Call Control Application.

A Web Browser.



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.


Glossary and Abbreviations.


Index. 0201721864T10022001


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.


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.


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.


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.



3GPP (Third Generation Partnership Project) 329
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
cumulative 138
delayed 138-139
generation of 28
revoking 146-148
to SCTP sender 131
additive increase multiplicative decrease (AIMD) 180
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
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 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
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 SACK chunk 59
for SHUTDOWN chunk 63
for SHUTDOWN-ACK 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 SACK chunk 59
of SHUTDOWN chunk 63
of SHUTDOWN-ACK 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 SACK chunk 59
for SHUTDOWN chunk 63
for SHUTDOWN-ACK chunk 64
reserved values for 254-255
selecting the values of 42
chunks 35
ABORT 72-73
control 35, 41
COOKIE-ECHO 54-55, 89-90
DATA 55-58
data 35, 41
definition of 330
elements in 37-38
flags 38
forming SCTP packets from 127-128
general rules in dealing with 41-42
header 330
INIT 44-47
INIT-ACK 50-53
length 38
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
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


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