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Fritz!Fon 7150 woes (and how they were solved) July 8, 2008

Posted by CK in IT, Networking.
Tags: , , ,

After having my DSL connection activated, I went for a router and a phone. I wanted to use a VoIP provider who would allow some cheap calls to Greece, so SIP capabilities on the router were absolutely necessary. WiFi was also a requirement. I was familiar with AVM‘s Fritz!Box, a really cool box which included by default lots of useful functionality. For those who are not aware of AVM, they have something like 50% of the DSL router market in Germany, and they really are pioneers in the domain.

Looking around, I stumbled across Fritz!Fon: A real gem, unfortunately only sold in Germany. Less ports, but a great added feature: Integrated DECT phone. Not only was I saving money (well, it is quite expensive so I needed an excuse), but I was also saving space and wires (more excuses). Anyway, I bought it, brought it home and happily connected. 1st shock: The interface was German only. Thankfully, with some online translation and my experience with their administrative interface, it was ok and I was online in no time. Then I registered with my SIP service, and tried to make a phone call. 2nd shock: Sound quality was really poor unacceptable. I switched on the laptop, fired up SJPhone, sound was great. I wasn’t downloading anything, so it couldn’t be congestion (plus, on the other end they could hear me perfectly). I fiddled through all settings I could possibly think off: Codecs, traffic shaping, you name it. The only interesting diagnostic was jitter ~= 10ms, and some evident packet drops (although the box doesn’t account for them).

Yesterday, I was going through the settings I can modify on my SIP account, on the provider’s side. I noted this setting with 4 levels on RTP packet size. It was on “level 1”, and the provider recommended increasing it if there were audio problems/gaps. I increased it, no changes. Then it hit me: What if the packets are too big? What if they are fragmented somewhere along the path, and Fritz!Fon doesn’t have big enough buffers for that? Changing it to the lowest level, I immediately enjoyed perfect audio quality for my VoIP-based phone calls. I’ll try to decode this further if I can in the next days, and get back with updates to this post.

So now if you experience interrupts and breaking sound on your Fritz!* product, you know what to try first!



1. Vodafone service in Germany « Logos of Crafts - August 19, 2008

[…] telling me that delivering the service takes a long time, was really great. I had already bought a different router which I attached and had Internet available immediately. […]

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