Author: Martin

Wifi Tracing with an eeePC

About a year ago I figured out how to use a Linksys WRT54 Wifi router and Wireshark for Wifi packet tracing and reported about it here. Now I have found another inexpensive tool for the job, which is equally helpful.

Background: The problem with Wifi packet tracing and Windows is that the wireless card drivers do not report the Wifi specific headers and also can not be set into promiscuous mode, which required to pick up packets from other devices in the network. On Linux, things are a lot easier, as drivers forward the required information.

I recently bought a Linux based eeePC, for quite different purposes, but now stumbled over instructions how to make Wireshark work with it and how to set the Wifi chip into promiscuous mode. I gave it a try today and it works like a charm. I love Wikis!

Here are some additional hints I unfortunately can’t add to the Wiki as a login is required…:

  • Starting with Wireshark 0.99.5, WPA decryption is supported with manual key input. Very helpful for tracing real networks. Note: While I have this version on my Windows PC, the Debian packet manager only installed 0.99.4 on the eeePC. As a consequence, I have to wait with WPA decryption until I open the tracefile on the Windows PC.
     
  • For the WPA decryption to work (later on on the Windows PC), the eeePC’s network card needs to be set to a network without encryption before promiscuous mode is activated. Otherwise, the Wifi chip seems to reuse the previous encryption key and tries to decrypt the packets instead of delivering them as they are to higher layers.

I’ve already made some very interesting discoveries when tracing my N95 in idle mode with the SIP VoIP client active. Lots of power save, polling and other Wifi management messages going back and forth which can’t be seen when tracing the Ethernet layer only. More about that in a future post.

Network Vendors Supporting Evolved EDGE

Last week, Nokia Siemens Networks (NSN) press department did a good job announcing that they will support Evolved EDGE and double data speeds in GSM/EDGE based networks. Speculations started to go wild and the word iPhone was sometimes heard as well.

Well, by the time evolved EDGE hits the street the 2G iPhone will (hopefully) long be history. NSN says they will have it ready for operators by the end of this year. Which means that at best, we will see this available in some networks by mid- to end of 2009 at the earliest. Apple should have a 3G version of their phone by then, no? And besides, for those still having a 2G iPhone when evolved EDGE is available, they won’t benefit as it requires more than a simple software update in the mobile.

Anyway, it’s good to see that NSN is not the only vendor standing behind evolved EDGE. Others such as Ericsson and Nortel have announced their support (here and here) for about the same time frame long before.

Next, I am waiting for a word from mobile device vendors when they will support it. In the past they have supported features much earlier than they were available in life networks. DTM (Dual Transfer Mode, voice + packet data simultaneously) is a good example which Nokia already seems to support for ages now. I haven’t seen a network yet, however, that supports it.

The Good Side of Operator Diversity for Handset Manufacturers

Every now and then I just wonder why Nokia just can’t their feet on the ground in the U.S. I wonder if it has something to do with the fact that there is only T-Mobile and AT&T as GSM operators (plus a few small ones) and no direct sales channels or service providers like in many countries in Europe!? While the U.S. market is certainly big in terms of number of people, Nokia’s opportunities via only two carriers are rather small. Even if both worked with Nokia they can only address half the population, as the other half is with CDMA carriers. And if only one of those two doesn’t like Nokia (anymore), the opportunity is instantly cut in half. Compare that to markets such as Europe where there are at least 3 to 4 operators in each country. If Nokia falls out of favor with one of them, that’s not really a problem, there are so many more operators in so many more countries to do business with. O.k., it’s a lot of work to talk with so many operators but in the end it might greatly reduce their risk. And then there are the service providers in many countries or even laws that mobile phones must be sold independently from subscriptions. In countries where this is the case, Nokia depends even less on carriers.

Fixed my N95 SIP Problem in Paris

Every now and then I enjoy a break from book writing and other high level work and fix a problem at its base. In a previous post I reported about my joys with the N95 SIP VoIP client and the little quirk I have with it in my home network in Paris: Outgoing calls take 30 seconds before they start. Since the phone works fine in my home network in Germany I figured that there must be something wrong on the network side. However, without some tracing tools there is no telling why.

So when I returned to Paris this time, I brought along an extra Wifi access point and an Ethernet hub so I could trace the traffic between the N95 and the Internet with Wireshark to see why the outgoing call is always delayed by 30 seconds and to figure out if I can somehow fix it.

Pic1sip
The picture on the left shows what I saw at first. As per the standard, the Nokia SIP client sends a couple of DNS requests to get the IP address of the SIP server and the STUN server. As per the standards, the SIP client on the phone doesn’t use standard DNS requests but uses DNS SRV (service) requests which do not only resolve a domain to an IP address but a domain name + service (SIP + STUN) into an IP address. Looks like my brand new ADSL2+ D-Link modem/router can’t handle them because they simply remain unanswered. Eventually, the SIP client in the phone gives up and sends a standard DNS query to get the IP address of the SIP server. All well at this point, registration is successful and the SIP client goes into service state.

When making an outgoing call (packets marked in black in the picture), however, the SIP client suddenly remembers that the DNS SRV requests for SIP and STUN were not successful in the first place and sends them again. Once more, they are not answered. After 30 seconds (hello!) the SIP client gives up and places the call without pinging the STUN server first. Doesn’t seem to be a problem in practice as the router opens the UDP ports anyway.

Pic2sip
O.k., so the solution is to turn off DNS relaying on the router. The D-Link router might be stupid as far as DNS is concerned but at least one can turn off it’s stupidity and instruct the client devices to send DNS queries directly to the external DNS server. And voila, everything starts working as it should. The second picture on the left shows how the SIP client behaves once the external DNS server properly answers the DNS SRV requests. The client registers in a flash and for an outgoing call quickly pings the STUN server an then places the call. Wonderful!

So who’s to blame?

I guess 90% of the blame should go to D-Link for a crappy DNS implementation. Guys, how can it be that the latest generation ADSL2+ router can’t do DNS right!? I am speechless. 10% of the blame goes to Nokia. Why are you trying to contact the STUN server with fruitless DNS SRV requests when it is quite obvious they have not been answered in the past?  Being somewhat more flexible on the client side wouldn’t hurt 🙂

University of Oxford – Future Technologies Conference 2008

Last year, people said the University of Oxford’s Future Technology conference was THE wireless event to attend in 2007 and I was sad to have missed it. Not so this year, as my ticket is booked and I am looking forward very much to an exciting conference day on the 18th of April.

In case you haven’t heard of the event yet, take a look at the official web site here. At last, I will meet Dean Bubley, Ajit Jaokar, Tomi Ahonen and Christian Lindholm in person, all speakers at the conference. Topics on the agenda range from Mobile Social Networking, iPhone Applications, user-generated content and advertising, mobile web 2.0 applications, mobile browser extensions, mobile search, etc., etc. I know Tomi and Dean sometimes have different opinions on a topic so I am especially looking forward to their debate 🙂

If you are reading this and planning to go to Oxford for the event as well, I am looking forward very much to meet you there!

In case you have to miss this opportunity, there are also a number of interesting telecom courses at the beginning of summer at the university which you might be interested in. In case you are in the WiMAX business, have a closer look at the 2 day WiMAX course that I will present together with John Edwards of Picochip and Chris Beardsmore of Intel.

MIMO Explained

Multiple Input Multiple Output, or MIMO for short, seems to make it into every wireless radio technology today from Wifi to WiMAX, HSPA+ and LTE. Yes, we know that it requires multiple antennas at the transmitter and the receiver and offers to multiply throughput by sending an individual data stream over each antenna in the same frequency band. But just how can the receivers at the other end separate the two data streams again as they have combined in the air to something completely incomprehensible!? National Instruments has a great introduction to MIMO on their web page which describes this in simple terms with just the right amount of maths that it is still understandable for someone out of college for a decade or more and who hasn’t touched maths since  🙂

Nokia 6300i: WLAN and VoIP move to Mid-Range Phones

I just saw Nokia’s announcement of the 6300i and had to take a closer look. While I am more of a fan of their Nseries devices, the announcement nevertheless caught my eye since the 6300i includes WLAN for browsing and VoIP.

While Nokia’s website doesn’t (yet) confirm that VoIP equals a SIP client (and not UMA), it looks very much like it since the WLAN doesn’t seem to be inside for UMA and can be used as a standard Internet connection.

Interesting how fast those two high end features have moved to the mid-range sector and another sign VoIP over Wifi might soon become the norm rather the exception. I hope carriers are starting to think of a couple of alternatives to removing the VoIP functionality in their firmware version soon. Here are some suggestions.

Also on board of the S40 based phone is Nokia Maps as a Java application, another high end feature moving down to a mid-range phone at the lower end with a recommended retail price of around 200 euros (according to Teltarif).

Does anyone have experience with the S40 music player? If it’s good I can very well imagine this phone addressing a large audience.

HSPA+ Background Information

It looks like UMTS will not give way to LTE in the future just like that. The High Speed Packet Access (HSPA) extensions which are now used in most UMTS networks today might get another upgrade in the future with HSPA+. Features such as 64QAM modulation, MIMO and Continuous Packet Connectivity (CTC) are on the horizon. Here are some documents I found recently which go a bit deeper into the topics:

Enjoy!

Why IPv6 Will Be Good For Mobile Battery Life

The other day I ran a post on the behavior of the SIP VoIP implementation of my Nokia N95 and that I was quite surprised to see it sending keep-alives to the network every 30 seconds. While this is normal and necessary to keep the NAT firewall open, it does have an impact on battery life, especially if a cellular network is used for the connection. The impact of such keep-alives is also considerable on the network once the number of devices using such always-on applications rise. Each cell usually serves 2000 devices at a time. Now imagine 2000 devices sending a keep-alive every 30 seconds via the same cell…

Bob Hinden of Nokia recently gave a presentation on the issue at the recent Google IPv6 conference and you can find the video of his presentation on YouTube. He made two interesting points for me here:

  • With IPv4 and NAT, it’s not only SIP VoIP that sends keep-alives but also push eMail clients, VPN and Instant Messengers. So he’s right, the problem gets even worse.
  • With IPv6 the NAT problem goes away as there are plenty of addresses and NAT is no longer required. Hence, IPv6 capable always-on applications can live without the keep-alives and ‘silence returns’ to the idle time.

Good points! Until we arrive at this state, however, it’s not even a good idea in most scenarios to use a public IPv4 address while you are mobile. Take a look at this blog post I wrote some time ago on how peer to peer applications of others drain my battery because of IPv4 address reassignments. I don’t know a lot about IPv6 yet but this should not happen with IPv6 anymore because I will not be assigned an IP address that was previously used by someone else!? Comments as always welcome.

P.S. Thanks to afr who made me aware of the video in Jaiku who heard it from Constantine 🙂

Telecom Italia’s Plans To Upgrades Wireless Backhaul

This report on Telecom: Italy fits to my recent blog post on T-Mobile upgrading their wireless backhaul to meet the rising demand for higher data rates. The report says that Telecom Italia will connect about 1700 ‘antennas’ of their wireless base stations to new fiber infrastructure which will also be used to bring faster fixed line Internet connections to homes and businesses. The wording is a bit strange since base stations are connected to a backhaul fiber and not individual ‘antennas’. I wonder how many antennas they count per base station!? There are usually 3 sectors per base station, each having its own antenna. That would make it around 600 base stations. But that’s just a guess on my side.