RFC 2960 Stream Control Transmission Protocol

1
RFC 2960Stream Control Transmission Protocol

• R. Stewart and Q. Xie Motorola
• K. Morneault and C. Sharp Cisco
• H. Schwarzbauer Siemens
• T. Taylor Nortel Networks
• I. Rytina Ericsson
• M. Kalla Telcordia
• L. Zhang UCLA
• V. Paxson ACIRI
• Presented by Ming-Yen Lai

2
Outline

• Motivation
• Functional View of SCTP
• Features of SCTP
• SCTP Packet Format
• SCTP Association State Diagram

3
Motivation

• Problems with TCP
• TCP is vulnerable to denial of service attacks,
  such as SYN attacks.
• Some applications need reliable transfer without
  sequence maintenance or they need only partial
  ordering.
• The stream-oriented nature of TCP is often an
  inconvenience.
• TCP doesnt support multiple interfaces.
• Transport of PSTN signaling across the IP network
  is an application for which all of these
  limitations of TCP are relevant.

4
Functional View of SCTP (cont.)
SCTP User Application
Association startup and Takedown
Sequenced deliverywithin streams
User Data Fragmentation
Acknowledgement andCongestion Avoidance
Chunk Bundling
Packet Validation
Path Management
5
Functional View of SCTP (cont.)

• Association Startup and Takedown
• Four-way handshake
• Graceful close (shutdown) and ungraceful close
  (abort)
• Sequenced Delivery within Streams
• The term stream is used in SCTP to refer to a
  sequence of user messages that are to be
  delivered to the upper-layer protocol in order
  with respect to other messages within the same
  stream.
• This is in contrast to its usage in TCP, where it
  refers to a sequence of bytes.
• User Data Fragmentation
• Ensure that the SCTP packet conforms to the path
  MTU.

6
Functional View of SCTP (cont.)

• Acknowledgement and Congestion Avoidance
• Packet retransmission and congestion control
• Chunk Bundling
• SCTP packet is composed of a common header
  followed by one or more chunks.
• Each chunk may contain either user data or SCTP
  control information.
• The SCTP user has the option to request bundling
  of more than one user messages into a single SCTP
  packet.
• The chunk bundling function of SCTP is
  responsible for assembly of the complete SCTP
  packet and its disassembly at the receiving end.

7
Functional View of SCTP

• Packet Validation
• Adler-32 checksum algorithm
• Path Management
• Choose the destination transport address for each
  outgoing SCTP packet based on the SCTP users
  instructions and the currently perceived
  reachability status of the eligible destination
  set.
• Monitor reachability through heartbeats when
  other packet traffic is inadequate to provide
  this information and advises the SCTP user when
  reachability of any far-end transport address
  changes.
• Be responsible for reporting the eligible set of
  local transport addresses to the far end during
  association startup, and for reporting the
  transport addresses returned from the far end to
  the SCTP user.

8
Features of SCTP

• Multi-homing
• Multi-streaming

9
SCTP Packet Format (cont.)

• A SCTP packet is composed of a common header and
  chunks.
• A chunk contains either control information or
  user data.
• Multiple chunks can be bundled into one SCTP
  packet up to the MTU size, except for the INIT,
  INIT ACK, and SHUTDOWN COMPLETE chunks.

• SCTP packet format

10
SCTP Packet Format (cont.)

• SCTP Common Header Field Descriptions
• Source and destination ports. Together with the
  IP addresses in the IP header, the port numbers
  identify the association to which an SCTP packet
  belongs.
• Verification tags. Vtags ensure that the packet
  belongs to the current incarnation of an
  association.
• Checksum. This computed value maintains the
  entire packets data integrity.

11
SCTP Packet Format (cont.)

• Chunk Field Descriptions
• Chunk Type. This field identifies the type of
  information contained in the Chunk Value field.
• Chunk Flags. The usage of these bits depends on
  the chunk type as given by the Chunk Type.
• Chunk Length. This value represents the size of
  the chunk in bytes including the Chunk Type,
  Chunk Flags, Chunk Length, and Chunk Value
  fields.
• Chunk Value. The Chunk Value field contains the
  actual information to be transferred in the chunk.

12
SCTP Packet Format (cont.)

• Main Chunk Type

ID Value Chunk Type
0 Payload Data (DATA)
1 Initiation (INIT)
2 Initiation Acknowledgement (INIT ACK)
3 Selective Acknowledgement (SACK)
4 Heartbeat Request (HEARTBEAT)
5 Heartbeat Acknowledgement (HEARTBEAT ACK)
6 Abort (ABORT)
7 Shutdown (SHUTDOWN)
13
SCTP Packet Format (cont.)

• Main Chunk Type

ID Value Chunk Type
8 Shutdown Acknowledgement (SHUTDOWN ACK)
9 Operation Error (ERROR)
10 State Cookie (COOKIE ECHO)
11 Cookie Acknowledgement (COOKIE ACK)
12 Reserved for Explicit Congestion Notification Echo (ECNE)
13 Reserved for Congestion Window Reduced (CWR)
14 Shutdown Complete (SHUTDOWN COMPLETE)
14
SCTP Association State Diagram (cont.)
(frm any state)
rcv ABORT
ABORT
rcv INIT
or
delete TCB
snd ABORT delete TCB
CLOSED
generate Cookie snd INIT ACK
ASSOCIATE
create TCBsnd INIT strt init timer
rcv valid COOKIE ECHO
COOKIE-WAIT
rcv INIT ACK
create TCB snd COOKIE ACK
snd COOKIE ECHO stop init timer strt cookie timer
COOKIE-ECHOED
rcv COOKIE ACK
stop cookie timer
ESTABLISHED
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SCTP Association State Diagram (cont.)
(From the ESTABLISHED state only)
SHUTDOWN
check outstanding DATA chunks
rcv SHUTDOWN / check outstanding DATA chunks
SHUTDOWN- PENDING
No more outstanding
snd SHUTDOWN strt shutdown timer
SHUTDOWN- RECEIVED
SHUTDOWN- RECEIVED
(A) rcv SHUTDOWN ACK
No more outstanding
(B) rcv SHUTDOWN
stop shutdown timer Send SHUTDOWN COMPLETE Delete
TCB
send SHUTDOWN ACK strt shutdown timer
SHUTDOWN-ACK-SENT
(B) rcv SHUTDOWN
Send SHUTDOWN ACK start shutdown timer move to
SHUTDOWN- ACK-SENT
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SCTP Association State Diagram (cont.)
(C) rcv SHUTDOWN COMPLETE
stop shutdown timer Delete TCB
(D) rcv SHUTDOWN ACK
stop shutdown timer send SHUTDOWN COMPLETE delete
TCB
CLOSED