Author: Martin

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.

Carlo Longino Starts Blogging For Nortel

Carlo Longino, probably known by many from his musings at Mobhappy, has recently started blogging for Nortel on the Hyperconnectivity blog. His topics are WiMAX and 40G optical. I just stumbled over it by accident and quite like what I have seen. Seems like a good move from Nortel to find some bloggers from outside the company to push their ideas in addition to blogs such as those from Nortel’s CTO John Roese and Phil Edholm.

Interesting also to see and to compare the approaches of different companies. Nokia’s S60, for example, is also doing lots of different blogs to reach out. Their approach is not from the top level or from the outside but from the people actually working on the products.

If you have recommendations of good blogs from people of other wireless companies please leave a comment.

Tracing the N95’s VoIP Implementation

Sip_nokia
A couple of days ago I posted an entry on my experiences with the N95’s SIP VoIP implementation. While the overall result was very positive, I continue to see the strange 30 seconds dial out delay with my Wifi/DSL setup in Paris. To get to the bottom of this I have started a little tracing session to see at which point things go wrong.

To have a positive example for a comparison, I traced the SIP behavior of the N95 in my Wifi network in Germany where everything works fine. For the purpose I have put a hub in between the DSL modem and the Wifi access point to trace the messages going back and forth between the SIP server, the voice gateway and the N95. Here are some interesting results which I didn’t expect:

STUN Implementation

Once the SIP client on the phone is registered, it communicates once every 30 seconds with the STUN (Simple Traversal of UDP over NAT) server on the Internet. This is required due to the Network Address Translation feature of DSL and cable modems that allow using many devices in the local network despite only having a single IP address. While I knew that the SIP client has to ping the STUN server every now and then to keep the UDP ports open on the NAT firewall in the DSL router, I didn’t expect to see it every 30 seconds. Seems to be a normal behavior as a Windows XP SIP Client behaves the same.

Registration Interval And Impact Of Signaling on the Network

To keep the UDP session with the SIP Registar and Proxy alive, the
SIP client on the N95 registers with the service every 5 minutes. This
is probably also a precaution or necessity to keep the UDP port open
for incoming signaling messages in the NAT firewall. In Wifi/DSL/cable
networks, this frequent communication together with the 30 seconds STUN
updates is not a problem. It also doesn’t seem to have a big impact on
battery performance as I discovered already in my earlier blog entry.
For cellular networks however, such behavior is quite problematic. Just
imagine 2000 VoIP capable devices hanging on each cell and sending SIP
and STUN signaling messages over it every 30 seconds… Thats over 66
uplink resource requests per second just for SIP and STUN signaling.
Bye bye Idle state… Looks like the combination of NAT and SIP over cellular networks on a large scale is a no go!

STUN Before The Invite

When dialing out or before accepting an incoming call, the Nokia SIP implementation also pings the STUN server once before proceeding with the call. The Windows XP SIP client doesn’t do that so it seems to be a precaution on Nokia’s side.

One RTP Packet Opens the NAT

When dialing out, the Nokia SIP implementation sends an RTP packet to open the NAT firewall for incoming RTP speech packets. Further outgoing RTP packets are only sent when the other side picks up. So that first (and only packet) is definitely sent for this purpose.

Supported Speech Codecs

According to the Session Description in the Invite message the Nokia VoIP client supports the following speech codecs: G.711 PCM a-law and my-law, Adaptive Multirate (AMR), iLBC and G729. With the SipGate voice gate to the standard phone network, the G.711 PCM codec is selected so no speech transcoding is required at the gateway. Good for the gateway and good for speech quality but this requires 10 kbyte/s bandwidth in the uplink or downlink. Not very resource efficient 🙂

Summary

Some of the things I have described here can also be seen in the screenshot at the top of this blog entry. Click on the image to get the full sized version. Next week, I’ll be in Paris again and will check out things there. More news then.

The 8-10 Year Interval in Mobile Repeats with LTE

I just realized that new cellular network technologies seem to be launched every 8-10 years. Analog cellular networks such as the C-Netz started operation back in 1984, GSM went on air in 1992 and UMTS became operational in 2002. Now it’s 2008 and LTE and mobile WiMAX are at the doorstep. While WiMAX is a bit ahead and will be used by newcomers, most incumbent operators will probably opt for LTE which in my opinion won’t go live before 2010, i.e. 8 years after UMTS was generally available. And from there it will take another year or two before we see LTE devices beyond PC cards and a network coverage beyond a few major cities.

Mobile 2.0 Slidepack Update

I almost made it to the Plug.eu conference in Brussels last week but had to change my plans on short notice. Too bad, hopefully next year. One of the reasons I wanted to go was because Rudy de Waele of m-trends was talking about Mobile 2.0. He was already giving a similar presentation a couple of months ago at another conference and I found it very interesting and inspiring. Looks like he continued to keep his eyes and ears open in the meantime since his latest presentation contains a full update. Lots has happened in the past months! For all who are interested, here’s a link to the presentation. Don’t be afraid by the number of pages, it’s definitely worth the time!

The Packet Call Becomes History with LTE

This week I’ve been taking a closer look at how LTE networks will be used in practice. One of the big differences to current 3G and 3.5G networks is that LTE is fully based on IP, i.e. there is no longer a circuit switched core network for voice telephony. Today, it makes sense for 3G/3.5G devices to attach to the network without requesting an IP address since they are (still) mostly used for voice telephony. In LTE networks, however, a device without an IP address is completely useless. Hence, the LTE network attach procedure already includes the assignment of an IP address. Consequently, an LTE device will always have an IP address. For people coming from the LAN/WLAN world this is nothing new. For people in the cellular industry, however, this is revolutionary. The 3G/3.5G  procedure of ‘establishing a packet call’, a term coined with the old thinking of establishing a circuit switched connection for a voice call in mind, will thus become history with 4G. Many people in the industry will have to change their picture of the mobile world to accommodate for this.

Is Spell Checking Only A Nice To Have Feature On Mobiles?

Quite often I am using my N95 and a Bluetooth keyboard to respond to eMails and to write a blog entry such as this one. While it works quite well, I am really missing a good spell checking feature. I don’t think that’s to difficult since the dictionary for it is already in the phone for the T-9 functionality. Is this only a nice to have feature desired by few? What do you think?

Early Bearer Aware Applications

In the future, we might see cellular networks tightly integrated into an overall fixed/wireless network concept and it won’t matter anymore whether a device uses Wifi or cellular network access. But this is definitely not the case today so bearer awareness in applications is a concept that remains neccessary for the foreseeable future. While I have already speculated about this concept in the past it is good to see that it is becoming reality. Let’s take some very data hungry applications I usually only use via Wifi on my Nokia N95 as an example. When I come home the phone automatically detects that my Wifi network is available which triggers a number of applications to jump into action. The SIP VoIP client automatically connects to the Internet and my phone becomes a Wireless/Cordless phone. Shozu connects to the Internet to upload the pictures I have taken to Flickr. And the podcasting application also detects that contact to the network has been reestablished and automatically checks for new podcasts in my favourite streams and downloads them automatically so I can listen to them next time I am out and about. And it all happens automatically. Depending on the country where I am at a particular time, I allow some of these applications to use the cellular network as well. That really depends on how far mobile network operators allow prepaid users to venture out into the Internet, both in terms of price and access restrictions.

A TDD/FDD Question for LTE Radio Designers

Here’s a question for LTE Radio designers both on the network and the terminal side that I can’t find a good answer for in the documents I have read on LTE so far: In the 3GPP E-UTRAN standards documents, both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) is defined. It is often said that the implementation of the two different modes is very similar. Other sources point out that LTE will first be deployed in bands assigned for use with FDD. So I wonder if TDD will have a similar fate as UMTS TDD, which was specified, but never used on a large scale!? From my point of view, LTE TDD will only get a real chance if it is part of the first release of base stations and terminals. So here is my question: Does anyone know if TDD mode is part of mobile devices from day 1 and if so which market TDD mode addresses?