A SIM that connects but performs badly is a different problem from one that won't connect, and it has a different set of causes. Some are worth investigating, some are fixed by a setting, and some are outside anyone's control. This article separates the three.

Slow and high latency are not the same thing

Worth establishing before you start, because they point at different causes.

• Throughput is how much data moves per second. It is limited mostly by the radio technology in use, the signal, and how busy the local cell is

• Latency is how long a round trip takes. It is affected by the radio technology, but also by how far your traffic travels before reaching the internet

A connection can have perfectly good throughput and poor latency, or the reverse. If your application is timing out rather than transferring slowly, latency is the one to look at.

1. Is the SIM being throttled?

Run Diagnostics on the SIM. It reports whether throttling is applied, which is the one cause on this list that produces a hard ceiling rather than variable performance. See Diagnostics.

Throttling is set through the API, and only on Black, Red and Green profiles. If one of your SIMs is throttled, it was configured that way through your own API access, so check your integrations. It is removed the same way.

On Blue, Yellow and Cyan profiles, throttling cannot be applied at all, so you can rule it out and move on.

2. What radio technology is the device using?

A device attached on 2G will be slow no matter what else is correct, and no configuration will change that. Check what the device is actually connected on rather than what it supports.

If it is falling back to an older technology in a place with LTE coverage, that usually points at the device: band support, antenna, or a network mode setting restricting it. See Radio access technology and Compatibility check.

3. Is the breakout location far from the device?

This is the main cause of high latency, and the one most worth fixing.

Traffic on a Simbase SIM leaves the mobile network at a breakout point, and that point is not always near the device. A device in Australia breaking out in Europe adds the round trip to every request, which shows up as latency even when throughput looks fine.

On Black, Red and Green profiles you can force the breakout with the APN:

Set the APN that matches where the device is deployed, then reboot the device or use Reset connection so it opens a new session. See Set up the APN.

Blue, Yellow and Cyan profiles use a single breakout, so there is no APN to change. Distance to that breakout can still add latency if the device is deployed a long way from it, but it is not something you can adjust. If that looks like your situation, contact support.

If you are deploying in the Asia-Pacific region, the Singapore breakout is selected automatically and there is no APN to set. Leave the APN as simbase, since forcing a US or European breakout would add latency rather than remove it. If you are unsure which breakout applies, contact support with the deployment country.

4. Is the MTU set correctly?

An MTU that is too high causes packets to be fragmented, which shows up as slow transfers or connections that stall part way rather than failing outright. It is an easy thing to rule out.

Many IoT deployments run an MTU of 1200 on the cellular interface. If you are seeing stalls rather than uniformly slow speeds, this is worth trying before anything else.

5. What does the signal strength look like?

Weak or marginal signal reduces throughput and increases retransmissions, which raises latency as well. A device at the edge of coverage, inside a metal enclosure, or with a poorly sited antenna will underperform regardless of everything above.

Before concluding the connection is slow, check the signal the device reports and, where possible, test the same SIM in a known-good location.

What Simbase cannot change

Being straight about this saves time on both sides. Simbase cannot raise the speed of your connection, because the speed is set by things outside the SIM:

• The device hardware and its modem

• The firmware it runs

• Distance to the cell tower, and how many other devices are on it

• The radio technology available where the device sits

• Physical conditions, including buildings, terrain and weather

What can be changed is the breakout location, the APN, throttling, and anything misconfigured on the device. Those are the levers, and they are all covered above.

Still slow

Contact support with:

• The SIM's ICCID

• The deployment country, and the APN currently set

• Whether the problem is throughput, latency, or connections stalling

• Measurements rather than impressions, a speed test or ping result if you can get one

• Whether it is one SIM or several, and whether it has always been this way

Common questions

Related

• Diagnostics, check for throttling on a single SIM

• Set up the APN, forcing a breakout location

• Radio access technology, what each technology delivers

• Quality of service (QCI), how traffic is prioritized

• Optimizing device configuration, connection logic for your own hardware

• Connectivity issues, if the SIM drops rather than slows