SCTPStream Control Transmission Protocol

CH 23

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

2

SCTP

Stream Control Transmission Protocol (SCTP) is a new reliable, message-oriented transport layer protocol. SCTP, however, is mostly designed for Internet applications that have recently been introduced. These new applications need a more sophisticated service than TCP can provide.

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

3

SCTP

SCTP is a message-oriented, reliable protocol that combines the best

features of UDP and TCP.

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

4

SCTP Services

1. Process-to-process Communication

Table 23.4 Some SCTP applications

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

5

SCTP Services (Cont..)

2. Multiple Streams

Figure 23.27 Multiple-stream concept

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

6

SCTP Services (Cont..)

An association in SCTP can involve multiple streams.

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

7

SCTP Services (Cont..)

3. Multihoming

Figure 23.28 Multihoming concept

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

8

SCTP Services (Cont..)

4. Full-Duplex Communication

5. Connection-Oriented Service

6. Reliable Service

SCTP association allows multiple IP addresses for each end.

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

9

SCTP Features

1. Transmission Sequence Number

In SCTP, a data chunk is numbered using a TSN.

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

10

SCTP Features (Cont..)

2. Stream Identifier

To distinguish between different streams, SCTP uses an SI.

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

11

SCTP Features (Cont..)

3. Stream Sequence Number

To distinguish between different data chunks belonging to the same stream,

SCTP uses SSNs.

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

12

SCTP Features (Cont..)

4. Packets

TCP has segments; SCTP has packets.

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

13

SCTP Features (Cont..)

Figure 23.29 Comparison between a TCP segment and an SCTP packet

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

14

SCTP Features (Cont..)

In SCTP, control information and data information are carried in separate

chunks.

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

15

SCTP Features (Cont..)

Figure 23.30 Packet, data chunks, and streams

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

16

SCTP Features (Cont..)

Data chunks are identified by three items: TSN, SI, and SSN.

TSN is a cumulative number identifying the association; SI defines the stream; SSN defines the chunk in

a stream.

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

17

SCTP Features (Cont..)

5. Acknowledgment Number

6. Flow Control

7. Error Control

8. Congestion Control

In SCTP, acknowledgment numbers are used to acknowledge only data

chunks;control chunks are acknowledged by

other control chunks if necessary.

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

18

Packets Format

Figure 23.31 SCTP packet format

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

19

Packets Format (Cont..)

In an SCTP packet, control chunks come before data chunks.

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

20

Packets Format (Cont..)

1. General Header

Figure 23.32 General header

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

21

Packets Format (Cont..)

2. Chunks

Table 23.5 Chunks

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

22

An SCTP Association

A connection in SCTP is called an association (to emphasize

multihoming).

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

23

An SCTP Association (Cont..)

1. Association Establishment

Figure 23.33 Four-way handshaking

• Cookie: To solve SYN flooding kind of attacks.

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

24

An SCTP Association (Cont..)

No other chunk is allowed in a packet carrying an INIT or INIT ACK chunk.A COOKIE ECHO or a COOKIE ACK

chunk can carry data chunks.

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

25

An SCTP Association (Cont..)

2. Data Transfer

In SCTP, only DATA chunks consume TSNs;

DATA chunks are the only chunks that are acknowledged.

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

26

An SCTP Association (Cont..)

Figure 23.34 Simple data transfer

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

27

An SCTP Association (Cont..)

• Multihoming Data Tranfer

• Multistream Delivery

• Fragmentation

The acknowledgment in SCTP defines the cumulative TSN, the TSN of the last data chunk received in order.

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

28

An SCTP Association (Cont..)

3. Association Termination

Figure 23.35 Association termination

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

29

Flow Control

In SCTP, we need to handle to units of data, the byte and the chunk. The values of rwnd and cwnd are expressed in bytes; The values of TSN and acknowledgments are expressed in chunks.

Some assumptions to ease understanding:• There is never congestion in the network

• The network is error-free

• Data transfer is unidirectional

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

30

Flow Control (Cont..)

Figure 23.36 Flow control, receiver site

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

31

Flow Control (Cont..)

Figure 23.37 Flow control, sender site (Assumption: each chunk is 100 bytes long)

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

32

Flow Control (Cont..)

Figure 23.38

Flow control

scenario

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

33

Error Control

SCTP uses a SACK chunk to report the state of the receiver buffer to the sender.

Aseel Alturki

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

34

Error Control (Cont..)

Figure 23.39 Error control, receiver site

Aseel Alturki

35

Error Control (Cont..)

Figure 23.40 Error control, sender site (Assumption: each chunk is 100 bytes long)

Aseel AlturkiBased on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

Based on Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007

36

Error Control (Cont..)

1. Sending Data Chunks

The total size of the data chunk or chunks included in the packet must not exceed rwnd – inTransit

AND

The total size of the frame must not exceed the MTU (Maximum Transmission Unit) size

• Retransmission

2. Generation SACK Chunks

Aseel Alturki