What Is SCTP in LTE?

Long-Term Evolution or LTE is one of the standards in mobile communications. There are others, such as CDMA, GSM, WiMax, to name a few. It is closely related to 4th Generation mobile data transfer or what most people know as “4G.” LTE is not really a standard per se, it’s more of a technical philosophy to achieve 4G speeds. At the moment, LTE (as a philosophy) is moving towards reaching 4G speeds. Because it is designed to be ten times faster than 3G, LTE also currently shows substantial improvements from it. However, Stream Control Transmission Protocol (SCTP) is a relatively new transport layer to improve LTE and data transfer as a whole. It is designed to increase messaging reliability over the network.

How is SCTP improving LTE Networks?

SCTP is used to carry telecom signaling over IP. However, unlike TCP which uses a byte stream interface (hence a byte limit), SCTP works as a data stream and can even work with multiple streams sending multiple messages called chunks. 

Because SCTP operates in streams instead of bytes, it offers more flexibility in certain applications that require continuous data exchange such as VoIP. 

The following table from IBM highlights the differences between SCTP and other transfer protocols such as TCP and UDP.

One of the most important differences in SCTP is it provides additional security features in protecting against Denial of Service (DoS) and Man-in-the-Middle (MIM) attacks. It waits until a client’s identity is verified before sending data over the network.

Looking at the table overall, the differences between existing protocols are not overwhelming, but the improvement in security alone makes SCTP superior compared to the other existing protocols.

Why is SCTP better for LTE?

Most networking professionals are aware of the pros and cons of using TCP or UDP over IP. They all work well for their purpose, but the exponential increase of data loads on mobile phones is slowing them from reaching the designed limit. Adding hardware infrastructure solves the problem, but that requires a significant investment and is not infinitely scalable (There’s a physical limit on how many data towers a company can build in a specific space). On the software end, SCTP can handle multiple simultaneous and multiplexed streams as opposed to TCP, which can handle only one stream of data per end-to-end connection. 

Modern data is transferred using the OSI reference model consisting of the four layers.

1. Application Layer
2. Transport Layer
3. Internet Layer
4. Network Access Layer

The transport layer protocols do the actual transfer and move data across the network. Transmission Control Protocol (TCP), for example, delivers the data in an ordered manner. User Datagram Protocol (UDP), on the other hand simply transfers the data and lets the application layer sort it out afterwards. SCTP, because of its multi-streaming capabilities and its reliable ordered packet, can deliver data over the IP (v4 or v6) to mobile hardware, and it’s more complicated applications.

In fact, a paper in the Journal of Network and Computer Applications claims that LTE has congestion avoidance mechanisms that negatively affect its performance. Using SCTP in the transport layer mitigates this problem and improves overall performance in the network.

Using SCTP as the standard protocol as opposed to TCP and UDP makes more sense in LTE as it’s more flexible, secure, and faster. As more and more users rely on mobile data and use high bandwidth applications such as video conferencing, it is necessary to make all the necessary improvements at the telecommunications provider level to fulfill that demand.