# Q1(c) · SCTP services

Subject: Computer Networks

Exam: TEE

Reader: https://deep-learning-study-room.vercel.app/cn/#tee/papers/paper-2025-feb-reexam/q1c

Canonical: https://deep-learning-study-room.vercel.app/read/cn/tee/papers/paper-2025-feb-reexam--q1c/

Actual paper; 100 marks attempted. Current-syllabus alignment is stated per question.

### Q1(c). Explain any 5 services of SCTP. [5 marks]

### Answer

**Stream Control Transmission Protocol (SCTP)** is a reliable message-oriented transport. A relationship between endpoints is an **association**. Its packets contain a common header followed by chunks, which carry data or control information.

Swipe across the diagram to read its labels ↔

![SCTP association setup](https://deep-learning-study-room.vercel.app/cn/fig/tee-sctp.55048562bb.svg)

Diagram: SCTP association setup. Labels: SCTP association setup | SCTP association setup | Endpoint A | Endpoint B | INIT | INIT ACK + state cookie | COOKIE ECHO | COOKIE ACK | Stream 0 ordered messages; stream 1 separately ordered messages. | Multihoming supplies alternate paths, not automatic rate addition.

SCTP four-message association setup and independent ordered streams.

1. INIT → INIT ACK → COOKIE ECHO → COOKIE ACK is the normal setup. The state cookie helps avoid committing full association resources solely on an initial request.
2. Data is organized into messages on streams. Transmission Sequence Numbers track reliable chunk delivery across the association; ordering information identifies order within an ordered stream.
3. Multiple streams allow a missing message in one stream to avoid forcing every other stream to wait for that stream’s ordering. They still share association/network resources, so this does not guarantee total independence.
4. Multihoming lets endpoints advertise multiple addresses, supporting alternate paths and failover. Standard multihoming does not automatically mean all paths’ bandwidth is aggregated.
5. SCTP supplies retransmission, selective acknowledgements, receiver flow control and congestion control. Its common header is 12 bytes; chunks add their own headers and data.

#### Practical example

A signalling application can use separate streams for independent dialogues. If a primary network path fails, an available alternate address/path can maintain the association.

**Yaad rakho:** SCTP association: streams separate order, addresses provide failover.

### Five SCTP services

| Service | Explanation |
| --- | --- |
| Process-to-process delivery | Port numbers identify the sending and receiving applications |
| Reliable message delivery | Checks, sequence tracking, acknowledgements and retransmission recover missing chunks while preserving messages |
| Multistreaming | Separate ordering within streams reduces cross-stream ordering blockage |
| Multihoming | Multiple endpoint addresses permit an alternate path if the primary fails |
| Flow and congestion control | Receiver flow control limits receiver overload; congestion control adapts traffic to network conditions |