Big Blog

Tens of thousands of SMS messages have been sent through the new Skype for Windows 2.5 BETA. But there have been some minor teething problems.

After reading comments on the SMS forum I thought it would be useful to give some background on how the system works and the kinds of issues you can expect to come across…

]]>### Here’s how SMS works…

After you type in your message and click send, Skype sends the message to one of several aggregators.

An aggregator is a company that routes messages to one or more local mobile operators or (more often the case) other aggregators who are responsible for finding the most reliable route to the handset.

So if you’re sending an SMS from the US to someone on a Vodafone mobile in the UK, that message may pass through several aggregator networks before arriving on Vodafone’s doorstep (called the SMSC or Short Message Service Centre). This happens in much the same way packets of data travel over the Internet and assemble as an email at your ISP’s or employer’s email server.

The local operator (in this example, Vodafone) is then responsible for delivering the message from the SMSC to the mobile handset. If the handset is switched off, or out of range then the message sits in the SMSC until Vodafone can deliver it – in the same way an email will sit on your email server until you download.

After the message is sent to an aggregator, Skype has no control over it. So the message will appear Pending (on Skype) until we receive a delivery notification – either that the message has been delivered successfully or not. There can be a short delay between when the message appears on the handset, and when we receive a delivery notification.

Not all mobile operators send a confirmation when the message appears on the handset. In some countries, and on some networks, we can only report a message as Sent when it hits the operator’s SMSC (and trust the operator to deliver to the handset). In some countries where we know to expect confirmation of delivery to the handset that is what we wait for. This is how traditional mobile operators work; eg in the example above if you sent the message from your US mobile, it would most likely be treated as sent and billed when it hits the SMSC in the UK.

### Where can it go wrong?

If the local mobile operator fails to deliver to the handset, or (more often the case) the handset does not confirm receipt the message will stay pending. We have no way of checking this and rely on our BETA testers to report any cases to support. This is the same service available to traditional mobile operators.

If there is a delay, failed delivery (to a valid number), if the message is corrupted or sent twice then this is a failing of our aggregator partner, their partners or the local mobile operator. Somewhere along the network the message has gone astray. By the time of public release our goal is to deliver messages with the speed and quality of a traditional mobile operator but at a fraction of the cost. Unfortunately when it comes to transmitting the message in many countries you get what you pay for so there is a trade-off required.

Failures can be caused by network congestion, mobile operators failing to deliver to the handset and incorrect numbers which are not picked up immediately.

### How can we control quality?

In theory, one or more of our aggregator partners can deliver to each country listed on the website.

In practise, some routes will work better than others. Once we know where the message is going, we will pass the message to the aggregator who has

* the highest success rate,
* the quickest response time for delivery notifications, and
* cheapest rates

for that destination (in that order of priority).

Even though collectively our aggregator partners carry a huge share of the international SMS traffic worldwide there are literally dozens of routes into a country and networks can be subtly different. With failure rates statistically quite small, we need to collect plenty of data in BETA in order to optimize and deliver the best possible guarantee of service at the lowest price worldwide.

### How can I help?

Submit a support request through http://support.skype.com/

The Subject should be SMS and it should be sent to the “Technical Problems” Department.

The more detail you provide the better. If possible please include:

* the mobile number you tried to send to
* what network it was one (ie the local mobile operator)
* time/date sent
* time/date received at handset (if applicable)
* time/date reported as sent/failed/pending on Skype
* whether the mobile was roaming; ie in another country
* whether the number had been ported from another operator and if so, when
* whether you successfully re-sent the message

You can also share your experiences with other users and Skype staff on the SMS discussion forum:

### Sender ID

In all countries except the US, Taiwan and China, the SenderID function works as follows:

* The default is that the sender will appear as your Skype username
* If the receiver tries to reply they will see an error message saying something like “invalid number” (actual text may vary from handset to handset)
* If you set your SenderID (Tools -> Options -> SMS Messages) to your personal mobile, replies will be sent to that mobile.

In the US the SenderID will be overridden by the local network. This is a regulatory requirement unique to the US, because you need to be able to reply with the word ‘STOP’ to block future texts. This number will vary from network to network and will usually be a local number. In future releases we intend to standardize this number to avoid confusion and also to allow for you to be able to reply to the Skype user.

In Taiwan and China the SenderID will also be overridden by a local reply address.

### Why does it cost more to text than to talk?

Our fees are set by our aggregators and their fees are set by local mobile operators. Laws of supply and demand apply here – there are simply more voice minutes sold than texts so they will generally be cheaper. Rates will vary from country to country as well for the same reason.

### Why not make Skype SMS free/cheaper?

Some users have, quite passionately, argued that Skype should provide this service for free. After all, it is free to talk to people on Skype – why should it cost to text?

With Skype to Skype calls, we were able to develop software once and then it didn’t matter whether 1 million or 100 million users were on it, our costs were the same. Well not quite because there are servers, updates and customer service costs but our costs do not increase in direct proportion to the number of users, making it possible to offer the free service.

The difference with SMS is that somewhere along the line it costs money to convert the text typed in over the Internet into an SMS. It is not possible to offer the service on the scale of Skype without funding it somehow.

A smaller company might be able to offer free SMS through its website but they are hoping to make money somewhere along the line. For example from advertising; perhaps by sending you SMS spam – check the fine print in the terms of use!

Similarly, anyone who signs up to a bundle with their local mobile operator is paying for something. You might get 1,000 free texts each month but you have to pay for 400 minutes of talking, whether you use them or not. Some mobile operators charge less for texts within their network than to other networks (who charge them to receive the message).

To keep things simple and fair we have gone for the cheapest rate per text we can. As we progress with BETA testing we hope to drive some of these costs down as cheaper routes stand up to the test of time.

As a general rule, the prices are competitive to average rates for mobile operators in our major markets. You may find some operators who are cheaper and some who offer plans that work out better for you based on the convenience of the service, reliability etc. But on average, we are generally cheaper. In future we plan to be the cheapest of everyone.

Remember, the only reason we are charging for SMS is that mobile operators charge us to deliver the SMS. This cost needs to be passed along the line. If they received SMS for free we wouldn’t need to charge – so hopefully that is the way things will go in the future!

### Can you only send SMS mobile phones?

You can send an SMS to any service that is set up to receive SMS.

So if you have a landline service that can receive SMS it will work. If not, the message will fail (it might take 24 hours for us to report the message as failed).

For example, try sending an SMS to your UK SkypeIn number! (the local operator there captures the SMS and converts it to digitized speech and will call you)

### What’s next for Skype SMS?

First priority during BETA phase is to guarantee quality of service for the lowest possible price.

Then we plan to allow your friends to reply to your texts … but one step at a time.

In the meantime, please remember this is a BETA release so any feedback to customer service will be much appreciated.

Who is this guy?

I recently joined the Skype carrier team in London and am product manager for SMS as well as being involved with SkypeIn market expansion in Europe. I was one of the first to sign up for an Aussie SkypeIn number because I haven’t been home for a few years. Jaanus has asked me for a flattering picture to add to my profile which I think is going to prove a tougher challenge than landing a job at Skype, but I’ll see what I can find.