The LTE Diaries: SCTP Support, Because Every Bit Counts

NOTE: This is one post in a long series, catch up on the most recent LTE development updates, or check out our recent LTE webcast.

CORRECTION: Blog post updated to accurately communicate the distribution of our SCTP support through a BreakingPoint firmware update.

As you know from Dennis’ earlier blog post, BreakingPoint is deep into our development of LTE support and reporting our progress right here for all of you. The first element for LTE we are implementing is SCTP support and I’m happy to say that I’m the one working on this part of the project. I wanted to take a moment to update you on our rapid progress.

To quickly recap, SCTP stands for Stream Control Transmission Protocol and is a Transport Layer protocol, similar to TCP and UDP. SCTP is used in LTE to ensure reliable, in-sequence transport of messages.

SCTP does differ though from TCP and UDP in some important areas:

• SCTP uses what are called “associations”, which are similar to the “connections”, with which we are all familiar in TCP. However, a SCTP association can actually include multiple connections.
• It is not uncommon to see hundreds of point-to-point connections under one SCTP association. In fact this is a requirement for a telecommunications network.
• SCTP provides multi-homing support where one (or both) endpoints of a connection can support more than one IP address. This capability provides transparent fail-over between redundant network paths.

Why SCTP for LTE?

Now we all know that TCP is great for what it does over the Internet, but in a telecom environment SCTP is necessary. Why? SCTP handles the communications between the eNodeB and the MME (check out Dennis’ post for a primer on these). This communication connection is very important and fragile since it must be able to detect dropouts very quickly. TCP does not do this, whereas SCTP has “watchdogs” that immediately recognize when a packet is dropped or a link goes down. LTE providers specifically and telecom networks in general need this ability to insure a high quality of service.

Additionally SCTP has, as a default, “selective ACK”, which is optional in TCP. What this means is that a packet will NEVER be resent if it has already been acknowledged as sent. In the LTE world, where every bit counts, using SCTP means no wasted data.

SCTP Development Plans

The unique architecture of the BreakingPoint product, specifically our use of network processors, makes the development of SCTP support fairly straightforward. The network processor, of course, provides four key functions: Transmit (sends the packet out), Receive (takes the packet in), State Machine (which transition you’re going in) and Timer (for updates of protocols). And since SCTP is similar to TCP I’ll be using that as a foundation during development. Additionally, and current BreakingPoint customers already know this, the network processor is the key to our enormous performance numbers. That means that any simulation using SCTP will have the same high-performance benefits, which will be critical for LTE carriers.

So far I’m happy to say that it HAS been a fairly straightforward process. I started by compiling and moved quickly onto the portions of the NP: Transmit, Receive, State Machine and Timers. After I get through each of those, we’ll do clean up and push it over to QA. Realistically, I should be done with the development side of things in less than a month.

When it is ready for use, all of our customers will get support for SCTP through a firmware update. And although we’ve been talking about SCTP under the umbrella of LTE, it is very useful for many of our current customers in the telecom industry. Our SCTP support will allow each of these organizations to transport any of our 130+ applications over SCTP. That means realistic simulation of a telecom network and proper measurement of the performance and security of any of their network gear. And when every bit counts anything less is unacceptable.

Related Content:

• LTE Performance and Security Testing
• Webcast: Testing LTE/4G Infrastructure Easily and Economically at Massive Scale

Posted by Scott Canion

Printer Friendly Create PDF

2 comments
Tags: 4G Testing // Tech Talk //