I was recently asked by a potential customer if we supported Gx over Gy. I’d never heard of this before, so I gave my standard “If it’s in the spec we should support it, but I’ll check” answer, and got them to send me a PCAP, which I’ve got. This is weird. So for starers, … Continue reading Tales from the Trenches – Gx over Gy? →

There’s a cool feature in PFCP that allows you to redirect traffic, which I’ve written about before. But there’s a funky thing that’s left me scratching my head, in the Redirect information IE, you can set a SIP URI. That’d be great and all, but PFCP is all about packets not about calls. So what’s … Continue reading PFCP and SIP Redirect →

PFCP includes a “Redirect Information” IE, which if set, allows you to change the forwarding action in PFCP to Redirect traffic. We use this for walled garden redirects, when the OCS reports credit exhausted to the PGW-C, the PGW-C can tell the UPF (PGW-U) that all the traffic from a given subscriber should be redirected … Continue reading Walled Gardens & Redirection in 4G/5G…

I rooted my WebOS TV. I’m trying to shift away from all the garbage that comes with so many Android app, the LG app that acts as a TV remote in particular caught my ire – You need to sign in and give it location permission just to control the TV, and stream the audio … Continue reading WebOS remote without the bloat →

This is an idea I’ve been kicking around for a little while – A single GSM TRX being broadcast across multiple cell sites. Generally in GSM land, a “TRX” is a cell or a sector – but it doesn’t need to be. Later in GSM features like antenna diversity allow the same signal to be … Continue reading GSM SuperCell →

I was recently in Sydney for a GSMA event with a few extra days in town after. So I reached out to our Nokia account manager and asked if I could “The pointy room”. It did not disappoint. As well as all the fancy RAN kit and pointy room, they’ve got the kind of machine … Continue reading Field Trip – UTS Nokia Lab →

One of our customers is an MVNE and they reached out the other day with an issue. They were turning up a new PGW and they’d see Create Session Request, everything looked OK, it’d get a response, but then in the GUI of the PGW-C they’d see the session drop. The logs showed the newly … Continue reading Tales from the Trenches – PGW-C Deleting Sessions →

I do a lot of protocol testing, writing Diameter/PFCP/GTP-C etc, and spend a lot of time referencing the standards. So I built this – Inspired by a 1990s video game / TV / Playing card franchise online reference tool, but rather than identifying pocket monsters, it’s identifying AVPs and stuff You can punch in the … Continue reading Protocoldex – A quick reference guide for AVPs / IEs / Commands…

Preface: I build cellular networks for a job. We support a network in Alaska, and one of the guys we work with there – John – has a story (which I’ll steal here) where he gets a phone call late at night from someone saying they’re in the US Air Force, and uh, they’ve, uh, … Continue reading Somebody’s watching me – Adventures in Cellular Locating →

One of my favorite things about Ansible and network automation as a whole is that I can do things in a repeatable manner, super quickly. One of the worst things about network automation is I can uniformly break things super quickly. Recently I was working on spinning up a core for a customer, who had … Continue reading Ansible & SSH – Screwing up en mass →

I was recently looking for a field I could use in PFCP to denote the VRF / Network Segment to be used, and initially thought Network Instance would be perfect for this. It’s not. Network Instance is kinda preferred over the APN/DNN for decisions, for example a Packet Detection Rule (PDR) does not give a … Continue reading Network Instance in PFCP →

Over a decade ago, Dan McKinley published a blog post titled “Choose Boring Technology” which advocates that software developers and engineers design systems using “boring” technology. One of the most worthwhile exercises I recommend here is to consider how you would solve your immediate problem without adding anything new. First, posing this question should detect the … Continue reading Telco to…

When a UE enters Idle mode, the network releases radio resources and the UE enters power saving mode. When the UE wants to send data (Uplink) the UE just tells the network “hey I want to send something” and away it goes, nice and simple. But when the network wants to send data to the … Continue reading Packet Buffering in the UPF →

I have run AMPS (1G) in my lab. I’ve run 2G (GSM) networks in production. There’s a few dozen production LTE/5G networks out there I’ve put my stamp on, but… Never, have I ever, run UMTS. And that feels like a blind spot. Sure, core wise 3G it reuses the 2G core (MSC / SGSN … Continue reading Adventures not building 3G UMTS RNCs →