Mobile Broadband for Techies

What is NAT? Why is IPv6 important?

When you are using the Internet, your computer has an "IP Address" which identifies it on the Internet. The IP address is a bit like your phone number and means that when you visit a web page, the computer on which that web site is hosted knows where to send the page back to (i.e. your computer). You can find out your current IP address here.

When the Internet was started, it was envisaged that the 4,294,967,296 IP addresses would be enough, but due to the global expansion of the Internet, we're almost out of IPv4 (IP version 4) addresses. It's a bit like running out of phone numbers, when we have to start adding digits, but on a far larger scale.

To deal with this problem, the technical community came up with IPv6, a new version of the IP protocol which has many more addresses and should last for a long time. Also, address conservation technologies were developed including Network Address Translation (NAT).

NAT is a bit like telephone extensions. When you're in an office, you can get an 'outside line' by dialling '9' before the phone number and you have an internal extension number such as 1234. Those who see your call coming in on their mobile screen will probably see your company's main switchboard number. In the same way when you visit a web page, the web server might see your company's primary IP address as your computer will be 'behind NAT'.

The problem is that on the public Internet, you can't duplicate IP addresses. If you don't have a unique phone number, then routing phone calls becomes impossible. However, there are some IPv4 addresses known as 'private address space' blocks defined in Internet standard RFC1918 which anyone can use without getting permission. These are the private 'extensions'. NAT allows you to for example have several hundred, thousand or even more users on these private IP addresses and only use up one public IP address, a valuable resource.

Mobile phone networks have tended to use NAT because many users login and logout quickly, and there has been very little demand for 'real' IP addresses from most users. Generally speaking, users use the network for applications which don't suffer from the problems NAT can cause in some cases. 

Why do the images on web pages look so awful?

Mobile broadband providers have been compressing the images they serve to mobile users in an attempt to save on bandwidth, and therefore deliver a faster service (and keep costs down too). You can compress an image in various ways, but generally speaking it degrades the quality. Consider for example the following text:


You could represent the above in less space by saying "type 'A' 50 times" which is shorter than spelling out the letter 'A' 50 times as shown above. This is an example of lossless compression as you don't lose any quality. Now, let's consider:


This is slightly different as there is one 'B' in the middle. You could still compress this by saying "type 'A' 50 times, replace 21s 'A' with 'B'" which would retain the accuracy of the text. Alternatively, you could just decide that "type 'A' 50 times" is close enough that you will accept a small loss in quality.

This is essentially how image compression works, although mobile phone networks take it a bit further, hence the noticeable loss in quality.

Can I turn image compression off?

Some networks allow you to turn off image compression by changing a setting in their software.

O2 Mobile Broadband users can use the following settings to turn off image compression. These would be entered in the software used to dial-up to the O2 network:


Vodafone users have a software option in older versions of Vodafone Mobile Connect (VMC). Newer versions provide this option at install-time. It is not possible to disable this in VMC for Apple software. You may find that depending on the IP address you get, compression will be enabled. At present the only sure way to do this, is to tunnel your web connections through some kind of VPN or SSH connection. You may find that if you 'refresh' a page twice, the images clear up.

You may find that on many networks you can use a Firefox plug-in which forces no-cache header to be applied bypassing the compression activity that takes place.  

Mobile data, GPRS, and 9600bps/baud modems..

Mobile broadband is a natural evolution from earlier mobile data services such as WAP which provided simple web browsing using very cut down web pages programmed in an XML based language known as WML (Wireless Markup Language). These earlier data services used GPRS (General Packet Radio Service) which provided low speed data at speeds of 9.6Kbps using packet switching on the existing 2G GSM network.

GPRS became common and the network, known as "2.5G", could support speeds similar to that of a standard dial-up connection- around 56Kbps. Speeds gradually evolved, and now with EDGE (Enhanced Data Rates for GSM Evolution) have a maximum speed of around 230Kbps. Orange and O2 in the UK have EDGE deployments (O2 notably deploying it when they won the rights to be the sole distributor of the iPhone in the UK as the original version of the phone did not support the then popular 3G).

3G, 3.5G and the "mobile broadband" revolution

Following 2.5G and EDGE, 3G became the technology to give the mobile world a good shake up. The first 3G network was operated by Three and launched in March 2003 with bulky handsets and limited data access. However, the technology quickly evolved and other networks started to offer data cards giving access at speeds of up to 384Kbps. A real step forward from GPRS speeds, as EDGE hadn't caught on by this point.

Late came HSPA (High Speed Packet Access), a collection of two mobile protocols HSDPA (High Speed Downlink Packet Access) and HSUPA, the uplink variant. The UK sees most deployments offering speeds up to 7.2Mbps with Vodafone also touting 14.4Mbps in some cities, although this is a theoretical maximum. These speeds are only really approachable if you have exceptional mobile coverage and no other users nearby vying for the same network access. The technology allows for speeds up to 42Mbps however this is only possible by the use of MIMO (multiple-input multiple-output), i.e. using multiple antenna. HSUPA allows for an uplink speed of 11.5Mbps. Generally, mobile broadband speeds vary a lot and speeds below 2Mbps are commonplace.

The definition of where to draw the line as broadband is always obscure, with marketing often clouding the actual service that is available. Whilst today's HSPA technologies do rival fixed-line based services, the future does allow for much greater speeds.

Long Term Evolution (LTE), today's current standard, often known as 4G is capable of 100Mbps over the air with fields tests of 300Mbps also taking place. The latency of 4G is also reduced, in theory capable of 5ms but in pratice it's more like the 60-70ms in the real world. The technology is strong, however it's main drawback over its fibre competitors is attaining and maintaining this speed with interference and contention from other users.


Mobile broadband connections generally experience higher latency than on most fixed line broadband. 4G comes in at around 60-70ms. If you are on a 3.5G connection, a typical latency is around 110 ms. This makes use of interactive applications such as SSH far easier which can be very sluggish on GPRS connections where latency ranges from 300ms upwards, rising sharply if you are using the connection. 3G connections are somewhere in between GPRS and 3.5G from our experience.

Do the allowances include upload as well as download bandwidth?

Yes. Mobile broadband packages generally include both upload and download traffic in your traffic allowance whilst many fixed line broadband packages only measure download for fair usage policy purposes.