When I get on a new mobile network I usually give it a thorough check for my research and to discuss results with interested operators. Most already do application testing on their own such as how many videos are viewed without interruption or how fast web pages load, etc. However, some do overlook some other important parameters.
One of the first things I noticed in Vodafone’s 3G network here in Spain at the Mobile World Congress is that sometimes when I log into the network with my mobile phone and remain connected, the battery runs flat within only 2 hours. A bit of research revealed that the reason for this is that they are assigning public IP addresses for transparent Internet connections (via the APN airtelnet.es).
So you might wonder what the battery drain has to do with a public IP address assignment!? Well in theory, not much, but in practice, quite a lot. When getting assinged a public IP address, all IP packets to this address get routed to the mobile device no matter whether they are wanted or not. Since IP addresses are dynamically assigned the new holder of an IP address potentially gets the ‘leftover’ from a previous user and all the junk emitted from viruses and other malware on the Internet. While the mobile device doesn’t really care and discards those incoming packets, the radio link is constantly active instead of falling back to a power conserving state while no user data is exchanged.
In my case I noticed that in some cases when I attached to the network the air interface link was constantly kept up as every couple of seconds an unsolicited IP packet was received. Most operators use network address translation (NAT), which assings a private IP address to the mobile and thus fixes this issue.
A somewhat crude fix for this problem from the user side short of hooking up the mobile to a power source once an hour is to fall back on the 2G GPRS network. The unwanted IP packets still come in but the power consumption in 2G mode is significantly less as the air interface link is kept for a much shorter time than in 3G mode after the last IP packet has been received and also requires less power.
So Vodafone, while I appreciate a public IP address for my 3G notebook dongle I think it’s a particularly bad idea for battery driven devices and user statisfaction. Also from a network point of view this is far from ideal as it wastes significant ressources on the radio link that would better be used for real traffic.
PS: I’ve noticed that there is also an APN with private IP addresses but that seems to be only good for web surfing as all my other applications are blocked.
A firewall on the Gi that will block all the unsolicited packets will solve this issue.
NATing many users to one address or to a small pool will cause difficulties to load balance traffic in the BGP links to the PDN.
Hi Dudi,
most network operators are using NAT today (e.g. 10.x.x.x) addresses. Difficult to tell how many external addresses they are mapping users to.
Cheers,
Martin
Ok, I’ll weigh in here. It is certainly interesting to see the real-world impact. If you’re not on flat rate that traffic is probably costing eurocents too…
1. Public IPs are good for some applications, notably things that don’t always work properly though NAT (VoIP, some VPN applications, etc).
2. Firewalled Public IPs are good for some other applications and keep the customer “safe”. Depends on the firewall rules and mode of operation.
3. NAT’d IPs are reasonable for everything, except the apps that fail when they are unexpectedly NAT’d(as per 1).
Everyone just expects their apps (phone or laptop) to work. Public IPs help this happen without a call to the helpdesk, reprogramming the APN, and the real $$ cost of that in image and person time. The big Corporates that pay the $$$ expect their apps to work, or they’ll pull out another SIM…
On the other hand we’re running out of IPv4 addresses, and IANA might not be so keen on giving everyone IPv4 addresses (and so therefore will deny your request for more of them).
I think it depends what expectation a user (and application has): should operators default to NAT’d, firewalled IPs just like you might have at home or work, or public IPs that allow anything to come in or go out?
With the amount of NATing increasing hugely due to IPv4 scarcity most applications are NAT aware and have workarounds, so I’d agree that the default should be NAT’d. I think there should be two more APNs though: Public with a permissive firewall, and thirdly completely open with all the risks that implies.
PS I’ve heard some operators, possibly cable ones, are *forced* to give IPv6 addresses internally due to a shortage of IPv4’s (10.0.0.0/8 only gives 16M addresses…)
martin, i have to agree with dudi, a firewall can fix this issue. it seems the vodafone spain network is completely open on the Gi.. this is a bit weird… could it not be they have tuned the parameters so that people get better speeds in the area of the conference…
ajay