Almost exactly 2 years ago, I've first seen a demonstration of a cat Cat 7/8 HSDPA device and went away very impressed after seeing downlink speeds of 4.2 MBit/s. Now I've finally gotten my hands on one myself and tested it in Vodafone's network in Germany. On the 6th floor of a building, the base station pretty close by (I assume) and my download speeds easily exceeded 5 MBit/s (= 700 kbyte/s) consistently over several days and at different times of the day. Wow, that's twice as fast as my ADSL line. But that's not the end of the line, a few operators have already rolled out HSPA+ with 21 MBit/s. Examples are Mobilkom Austria in Vienna and Telstra in Australia.
Author: Martin
Base Station Throttling Revisited
A couple of weeks ago I posted my thoughts around doing throttling of heavy users directly at the base station so the current load can be taken into account as well. No need to throttle heavy users if nobody else is using the cell. While it was just a "Gedankenexperiment" a reader pointed my to this paper in which Ericsson actually describes just such an approach and says it has already implemented it in their RAN. Very interesting! The paper unfortunately doesn't contain a lot of information of how this is done from a technical point of view, i.e. how is the base station informed which users to prefer over others. If you know more, if this is not a state secret and some information about the feature is publicly available, please let me know!
Mobile Notification for Parcel Deliveries from DHL
Here's an innovative mobile service from the German Postal Service (Deutsche Post, DHL) I think I will use more often from now on: My big problem when getting things via mail is that I am usually not at home when the parcels are delivered. That leaves me with guessing when the parcels arrive, go home early to pick up the delivery failure notice and then drop by the post office before it closes in the evening. But now there's a better solution for it: Close to my office there's a so called "Packstation" to which my parcel can be delivered. Once it's there I automatically get an e-mail or SMS to inform me that I can pick it up. Great, I just have to walk over, insert my customer card, type in the PIN and the parcel is mine. Great mobile service, that's how I like it!
Web Browsing over DSL and 3G Compared Side by Side
Web surfing over 3G must be slower than over DSL, right? To see if this statement is correct, I used two computers side by side, one connected to to Internet over a 3 Mbit/s DSL line and the other one over a 3G dongle. The 3G network of choice was that of Vodafone Germany in Cologne with the base station at least supporting HSDPA category 8 (7.2 Mbit/s) devices.
For the first web browsing test I used a Huawei E220 3G dongle with a somewhat older but very reliable HSDPA category 6 software load. Computer screens side side by side I simultaneously clicked on links to load web pages, both visited and never visited before, to see on which computer the pages displayed first. The result: In this test, the web pages took around one second longer to be first displayed on the 3G connected computer but the difference was quite minor. Definitely less than what I expected.
In a second test, I used an HSDPA category 8 + HSUPA capable E176 which has been available on the market already for a little while. Definitely not the latest and greatest anymore but still good hardware. With this setup the side by side comparison showed no difference anymore, pages on both computers showed up almost instantly. Sometimes, the page would show on the DSL connected computer a fraction of a second earlier, sometimes it would be loaded a bit quicker over the 3G connection. Fantastic!
A little caveat: At the time of the test the network was only slightly loaded so one of these days I have to find a time at which it is a bit busier and repeat the test to see if that makes a big difference.
Current State of Data Roaming Charges in the EU
This September the EU mandated a maximum price wireless network operators could charge each other for GPRS and UMTS data roaming. The cap imposed was one euro per megabyte and the hope was that as a result, end user prices would fall as well. So has it happened yet?
Taking my German prepaid SIM from MVNO Congstar to France recently, I was greeted with an SMS message informing me that data roaming charges were 99 cents per 50 kb and in addition a daily service charge of 49 cents would apply. That's a whoppin 20 euros per megabyte! Orange France is not much cheaper. Their prepaid roaming charges for data in Belgium is 9 cents per 10 kb or 9 euros per megabyte.
Well, Ms. Redding, I guess the plan hasn't quite worked so far and I still have to rely on local SIM cards.
HSPA and TCP Window Auto-Scaling
Back in 2006 I noticed that my Windows XP machine could not fully use the bandwidth of my ADSL line and also throughput over HSDPA to some servers was less than I expected. As I found out at the time, the fixed and small TCP window size was responsible for the behavior. In Windows XP, things could be tweaked by changing the window size in the registry as I described here. When running some throughput tests with Ubuntu Linux this week with an HSPA 7.2 MBit/s 3G stick, I noticed that no tweaking was necessary to get the full speed.
A quick look with Wireshark revealed why: Unlike Windows XP that has a static window size that is set somewhere around 17 kbytes, Ubuntu sets the TCP window size dynamically. It starts with a modest 5k window and steadily increases it during the file download to over 1 megabyte. Looks like Vista has a similar algorithm as well. Very nice, no more worries about throughput limitations in the future!
The Baby and the Mobile
Another mobile Internet story today taken from real life: A friend of mine has recently become a father and has since then discovered the power of mobile web browsing. It looks like his son really enjoys being carried around and seems to be quite persuasive to get what he wants. So during endless hours carrying his newborn son around, my friend now really understands the power of mobile (slight grin on my face). With one hand free, browsing the web using Opera Mini and replying to my e-mails seems to make his "walks" in the early and late hours of the day a bit more enjoyable and interesting.
The 14.4 Psychology
A little anecdote today: In the "old" days I had a 14.4 kbit/s fixed line modem for quite a number of years. Even though new and shiny 28.8 kbit/s modems came on the market, I was stuck with my '14.4' because the new modems were expensive and as a student my monetary resources forbade an upgrade. So for me, the number '14.4' has a bit of a negative touch attached to it ever since.
Fast forward to today to the "megabit" era. In wireless, HSPA 7.2 Mbit/s downlink is currently pretty much state of the art. Some network operators have announced further upgrades and in due time, top speeds of 21 MBit/s and beyond will be reached. On the way to double digit speeds, there's also a 14.4 step. No, not kbit/s, but Mbit/s. Still it kind of reminds me of my 14.4 kbit/s days and has a negative "psychological" touch to it to me.
Strange strange, because I'd really like to have this 14.4 this time around 🙂 Any numbers in telecoms that have a psychological edge for you?
The HSUPA RTD Delight
When discussing High Speed Pack Uplink Access (HSUPA), or E-DCH, to use the correct term, the major focus usually lies on the improved uplink speeds. Seldom is it mentioned, however, that E-DCH also improves the latency, i.e. the time it takes for an IP packet to be sent to a server and a response packet to arrive back to the source. But is this relevant in practice?
So far, I used an HSDPA 3.6 non E-DCH capable 3G stick and my round trip delay times (RTD) to a number of web sites I visit most were around 110 milliseconds. Over a DSL link, the same sites can be reached with an RTD of around 45 ms. In other words, a difference of 55 ms. In practice this can be felt especially during web browsing, as web sites take a bit longer to load over 3G compared to a DSL link with a similar bandwidth. Not that this is a showstopper but it can definitely be felt.
A few days ago, I ran some tests with a Cat 8 HSDPA + HSUPA 3G stick and was quite surprised that the RTD times to those web sites were just around 65 ms. In other words, that's only 20 ms more compared to DSL. The difference to the HSDPA only 3G stick are quite remarkable. I compared backwards and forwards with my DSL line but I couldn't "feel" the difference anymore. Stunning!
The one thing E-DCH does not do away with, however, are the delays incurred when radio states are switched. The 300 ms or so delay when switching between a full DCH and the less power and resource intensive FACH are still there. In practice, however, background traffic from applications such as my Instant Messengers usually keep the link in DCH state so I rarely come into contact with it anyway.
Google Books and the Hardcopy on the Table
There are lots of political discussions around Google books these days but this short blog just focuses on a cool feature I just found. I've got lots of good books on wireless topics at home but when searching for a specific piece of information it often takes a long time to find it, even if I know in which book I could find the answer. So I usually turn to Google first to see what the search engine can come up with before I start flipping through and index or the table of contents of a book.
So one of these days I wanted to find out what the A1 event in LTE is all about. So I typed "LTE A1 event" into the Google search engine and one of the first entries in the result list was a book on Google books which had the answer. Google books gives me a page number and a preview of the page. In this particular case I had the book on the bookshelf already so I could go directly to the page and read the whole subsection on the topic. Excellent!