Communications

Skype - MySpace integration falls short

In a recent article over at Skype Journal, I lamented the fact that Skype had not built it's subscriber base as rapidly as I'd hoped or as rapidly as QQ in China or even (perhaps) Windows Live Messenger.  Shortly after I wrote those words a friend pointed out the MySpace-Skype announcement from last October.  It sounded like just what I'd been adovocating, i.e., Skype cuts deals so they interoperate with as many communities as possible thus growing the range of people I can connect with.

I immediately went to my (otherwise little used) MySpace account to check it out.  Unfortunately, the integration between MySpace IM and Skype only applies to voice!  You can't chat between the two services.  What good is that?

One of the significant features that Skype introduced was the idea of combining presence, text chat and voice conversation in a single user interface.  That value is lost when the MySpace - Skype integration is restricted to voice calling only.

Why the Danes text while the US talks

Recently I can by some interesting data on monthly voice and SMS usage in Denmark.  But first let me set the stage.  It's well known that people are price sensitive ― as per minute prices fall, telephony usage goes up.  It's also true that people prefer flat rate pricing as it reduces their mental transaction costs.  This graph (from Andrew Odlyzko) shows what happened to mobile minutes of use when flat rates were introduced in the US.

AT&T launched their Digital One-Rate plan in 1998 offering a block of minutes for one monthly fee with no long distance or roaming complications.  This plan was so popular that all operators were forced to respond, with the results visible in the graph above.

Today US mobile voice usage is approaching 800 minutes per month and that's average.  Leap Wireless and MetroPCS subscribers use 1500-2000 minutes per month.  One wonders how much time people can spend on the phone...

So here's the new (to me) data from Denmark.

The Danish regulator has a wonderful set of statistics available in half-year increments.  Those above are from 2H02 thru 2H07.  Voice minutes are out-going traffic in millions of minutes per period (6 months).  The population of Denmark is 5.5 million (82% are over the age of 14) so this represents ~330 voice minutes and ~225 messages per person per month.

Wireless minutes of use continue to rise, but fixed line minutes are falling faster so total voice minutes are falling.  But total person-to-person communications is still increasing because SMS and E-Mail usage has soared, growing to roughly 40% of all communications.

This is very interesting as flat rate pricing for monthly bundles of SMS messages was introduced in Denmark in 2002.  Meanwhile, Danish mobile voice calls are mostly charged per minute (very typical in Europe) and are expensive compared to the US.

So price matters, but flat rate monthly bundles (rather than per minute or per message charges) is even more important in driving usage.

Gold bits and brown bits ― When you need QoS, two classes will do it!

Quality of Service is a contentious subject.  Every now and again, I look at Wikipedia's QoS page.  (Here are my comments 18 months ago).  While the Wikipedia content continues to evolve, it always downplays anything that questions the value of sophisticated QoS.  As of today, the section titled "QoS Problems" has been cut back to a single sentence (which does reference a classic anti-QoS paper):  "Internet2's QoS Working Group concluded that increasing bandwidth is probably more practical than implementing QoS."

Rather than directly debunk QoS yet again, let me investigate where QoS is actually useful by looking real life situations and the deployed solutions that allow for robust services despite congestion.  Identifying common elements in successful deployed solutions is much more realistic than theorizing about NGNs that still await deployment.

The first thing to notice: the only problem is on access links.  As I've written before:

Once you get beyond the access network, every link in the Internet — local, regional, national or international — is carrying multiplexed traffic from many users. Multiplexing many, many, bursty flows results in relatively predictable volume. Traffic volumes vary by time of day, but these links don’t saturate, except as a result of poor engineering or forecasting on the part of an ISP, or failures in other parts of the network causing rerouted traffic. Either case generates a rapid response from any ISP that expects to remain in business. So “best efforts” in the Internet core means sub-millisecond delay variations and near zero lost packets.

Net, net:  you never need QoS priority schemes in the core, all traffic gets excellent service. 

Access links are another story for two reasons.  First it can be very expensive to add more bandwidth.  This may be a byproduct of political/ regulatory issues, but we won't go there, at least in this post. :-)  Second, an access link may saturate due to an outgoing email with large Powerpoint attachment (the home case) or an equivalent event in the corporate environment, for example, transfer of a large CAD file.

But these are solved problems with multiple commercial products on the market for residential and corporate use.  It's worth looking at what these products do in order to understand exactly what kind of QoS is really required, when you can't just provision more bandwidth.

In the corporate market, there are two approaches.  The brute force approach splits voice and video telephony traffic from data traffic using two separate Internet connections with the VoIP connection sized to preclude any potential congestions.  When a single access link is shared, the typical solution employs a QoS router at the customer’s end. The QoS router gives absolute priority to outbound VoIP packets and protects inbound VoIP packets by active traffic shaping; i.e., by signaling remote TCP hosts to throttle inbound TCP data flows so there’s enough capacity for inbound VoIP packets.

Elsewhere within corporate LANs, there is either no QoS or simple priorities. Since VoIP traffic is a tiny percentage of all traffic, it can be given absolute priority without noticeably impacting other applications.  Thus some enterprise VoIP installations use QoS based on DiffServ or Ethernet 802.11p/q.  Typically there are just two classes assigned, with absolute priority for VoIP and video telephony.

I've written about equivalent solutions for residential situations that support VoIP and interactive gaming.  The solution?  Consumer VoIP phone adapters incorporate simple priority and have the ability to fragment large packets (so as to reduce serialization delays).  Because it's so useful for VoIP and also for interactive gaming, this functionality is showing up in popular residential routers from Linksys, Netgear, etc.

Two classes and simple priority is what it takes ― Gold bits for voice (and video and interactive gaming); Brown bits for everything else.

And that's only when you can't get more bandwidth.  On your own premises, it's likely cheaper and easier to upgrade to Fast Ethernet or Gigabit Ethernet.

WiMAX will be successful, as a fringe technology

A recent Infonetics press release says “WiMAX has gained such momentum across so many regions that it is no longer sensible to suggest that WiMAX growth will be flattened by the emergence of LTE in the next few years."

Probably true, but it's also clear WiMAX will never reach the scale of either mainstream wireless family, i.e., WiFi or GSM/3GSM.  By comparison with these giants, WiMAX will be a fringe operation.  The critical issue is volume, and what counts is the wireless technology brand, not the technology itself.

Both WiFi and GSM/3GSM have already evolved through multiple generations of technology while maintaining backwards compatibility and thus interoperability.  Within the GSM community, there may be no commercial LTE subscribers as yet and relatively few HSPA subscribers, but more than a billion GSM/3GSM devices are manufactured each year with individual chip set product lines running multi-hundred million units per year.  WiFi chipsets also run at hundred-million units per year rates.  These volumes (and the guarantee of interoperability) mean GSM/3GSM and WiFi devices will always be substantially lower cost than anything WiMAX aspires to.  [Note:  today there are slightly less the 2 million WiMAX subscribers while optimistic projections suggest there will be more than 100 million in 2012.]  WiMAX may have technology leadership, but it can't catch up.  WiFi and GSM are the wireless families that will prosper, each in it's sphere – WiFi for unlicensed, GSM for licensed spectrum.

WiMAX will benefit from technology specific licensing in some emerging markets, i.e., valuable spectrum tied to specific technologies,  So WiMAX will survive, even while it's more expensive than LTE or WiFi.  As for market share, the optimistic parallel is "CDMA cellular", i.e. IS-95/ CDMA One/ CDMA 2000.  CDMA had technology leadership and it managed to capture nearly 20% of the 2G cellular market at it's peak, but it could never overtake GSM and, today, major operators are jumping ship to join the 3GSM crowd.

There may be a decade of contention, but in the end, WiMAX will die or be absorbed into the GSM brand.

Asian innovation in mobile social networking

I'm continually amazed at the East-West cultural gap (that's between Asia and the US/EU, not between Boston and Silicon Valley).  It goes both ways, but as an American Internet and mobile enthusiast with Asian connections, I'm usually struck by US ignorance of Asian Internet and mobile services.

Today, China has the worlds largest mobile population and the worlds largest Internet population.  Korea is a leader in high speed broadband, as is Japan.  Japan is also the #2 economy in the world and arguably the world's leading mobile society.  Surely it's worth the time to understand what's happening in their markets!

For a change, over the weekend, I stumbled on an excellent presentation, What Asia can tell us about mobile social networks, from O'Reilly's conference, Graphing Social Patterns East, held in June in Washington DC.  The presenter was Benjamin Joffe who resides in Beijing where, among other things, he's the founder of Mobile Monday Beijing.

Some of his numbers may be a year old, but the impact is clear.  Asian services like QQ (740M registered users), CyWorld (used by 90% of young Koreans) and Mixi (10M mobile users in Japan) typically started before Facebook, have many more features, and are profitable!
Here's Benjamin's features list:

Check out the entire presentation.  Well worth the effort!

Fascinating potential increment in WiFi & WiFi mesh performance

I just stumbled on an interesting paper by Shyamnath Gollakota and Dina Katabi at MIT describing ZigZag decoding.  They will be talking about their work at SIGCOMM later this month.

The problem they've addressed is that of hidden terminals competing in a shared medium, in this case 802.11 WiFi.  This diagram shows the problem:

Alice's radio can "hear" the base station (the access point of AP above) and can transmit to it, but her radio can't hear Bob's radio so, while Bob is transmitting, Alice starts transmitting.  Their transmissions interfere, neither is acknowledged, both retry and even though they each delay a random interval, it's highly likely that at least part of their retransmissions again interfere.  Alice's and Bob's radios are said to be hidden from each other.  The critical issue is, since they can't hear each other the normal "listen before transmit" algorithm doesn't help.

ZigZag allows the base station to decode both of the colliding packets with an efficiency as good as if they had been sent in separate timeslots.  What's more ZigZag is compatible with all the various WiFi modulations and works with existing terminals, i.e., only the base station (the AP) requires an upgrade.

So far they've only implemented a prototype in software using GNU radio, so we're unlikely to see this in commercial products for a year or two.  But their results are impressive:

We have implemented a ZigZag prototype in GNU Radio, and evaluated it in a 14-node testbed, where 12% of the sender-receiver pairs are hidden terminals, 8% sense each other partially, and 80% sense each other perfectly. Our results reveal the following findings.

• The loss rate averaged over scenarios with partial or perfect hidden terminals decreases from 82.3% to less than 0.7%, with some severe cases where the loss rate goes down from 100% to zero.
• Averaging over all sender-receiver pairs, including those that do not suffer from hidden terminals, we find that ZigZag improves the average throughput by 31% when compared to current 802.11.
• At all SNRs, ZigZag’s bit error rate (BER) is lower than if the colliding packets were scheduled in separate time slots. The average reduction in bit error in comparison to scheduling packets separately is 1.4x.

They've invented a straight forward approach to decoding colliding packets.  It seems obvious now that I read it and yet I've been interested in this subject for 25 years and their approach never occurred to me.  :(   If you are at all interested, read just the introduction to their paper.

Why does it matter?

First, it's another increment in the continuing exponential improvement in radio performance

Second, it helps IT directors get more capacity on wireless LANs.

But most important for the long term, it improves the prospects for mesh networks.  While I can't predict specifics for how it will happen, mesh networks have the potential to create capacity from the edge!  No operators, just individuals and enterprises purchasing devices for other reasons.  Now that will be significant!