What Is SCTP Used For?

Stream Control Transmission Protocol (SCTP) is one of the few transport layer protocols used as a logical sender and receiver over the Internet. 

In layman’s terms, it is one of the protocols that determine how data is transferred over the World Wide Web and who will receive that data. Every device connected to the internet can send and/or receive data (including sending data to itself). 

The Open System Interconnection (OSI) is a conceptual model that shows the functional interconnection of the systems. It is composed of seven layers, and SCTP can be one of a few logical protocols in the transport layer.

What role does SCTP play in the OSI Model?

To understand SCTP and SCTP End Points, one must first understand the OSI layer model. Like a carburetor or fuel injector, it is a cog in the machine. 

Layer 1 – Physical

They are the hardware from your endpoint devices, such as a PC or Mobile phone, which functions as a connector to the internet backbone. Examples can be NIC’s and hubs.

Layer 2 – Data Link 

It handles the node-to-node data transfer between two connected nodes. Layer 2 manages physical addressing schemes similar to the way that MAC addresses controlling access of any various network devices to the physical medium. 

Layer 3 – Network Layer

Layer 3 handles addressing and routing of data — sending it in the right direction to the right destination on outgoing transmissions and receiving incoming transmissions at the packet level.

Layer 4 – Transport Layer

This layer determines the connection through which data will be sent over the network.It tells the network how much data to send, at what rate, where it goes, how that data is sent (through chunks, packets, or streams), among other functions.

UDP is the simplest protocol used. It only knows the IP address of the receiver and what port to use. Because it has no error check, it is regarded as unreliable and “connectionless.” However, it is the fastest of the three protocols.

TCP is the most commonly used protocol over the internet. The data is tracked and acknowledged by both endpoints and transferred using a continuous segmented data stream. Data packets sent using TCP are transferred in sequence to increase reliability, compared with UDP.

SCTP is a newer protocol designed to be message-oriented to combine the best features of UDP and TCP. Like the UDP and TCP, it can send multiple packets to an IP address destination, but reassembled through Stream Identifier and Transmission sequence number for checking before passed on to higher layers.

Layers 5-7 Session, Presentation, and Application Layers

These three other layers determine (step-by-step) what happens to the data once the receiving machine obtains it from the sender.

Now we have a clear technical understanding of how the internet works by passing a byte of data from one endpoint to another machine. It’s easier to understand what SCTP does, and what role it plays in the entire system.

The efficiency of STCP can probably be seen more clearly if we use the analogy of a fleet of trucks sent by a logistics company to various destinations. Some truck drivers have more equipment, get more briefing, or are probably more knowledgeable in what they do than others. 

UDP:

UDP can be likened to truck drivers who are pretty much left on their own, and are not given the support that they need to execute their jobs. Truck drivers are given the “IP” address of the destination and they are left to their own devices on how to get there. 

Some drivers can get lost, along with their cargo. This particular group in the fleet will get known as the unreliable bunch.

TCP:

TCP can be likened to a group of truck drivers who travel in a convoy, which in this case is the data stream. This group is given solid instructions and the destination or the IP address. They also know how to get to the destination even if they get separated from the group. However, these truck drivers have been mandated to follow each other — or the one in front of them — in front of a single line. They all arrive at the destination at the same time, with remote chances of any one of them getting lost. Upon arrival, they check if each truck arrived in sequence, and that all the trucks arrived safely.

SCTP:

SCTP can be likened to a group of trucks who are further divided into small groups in order to arrive at the destination faster. It’s like a convoy broken down into several mini-convoys. Each mini-convoy takes a different route to arrive at the destination. 

One convoy may take an interstate highway, while another will opt for a shortcut through the woods. But all of them are estimated to arrive at the destination at the same time. In a sense, they can beat the TCP group when it comes to speed. Upon arrival, the truck drivers do check if everyone arrived safely.

In using this splintered approach, SCTP has an advantage over the others:  it prevents congestion in the network as different convoys use different routes to get to the same destination. They arrive faster and perform the same checks as TCP. It is also easier to protect the data from hijacking because they are not in a single data stream.