How to parse traffic to your mobile site

and avoid duplicate content penalties

[Musicarl]

So we have mobile version of our site built and ready to go on a subdomain:
mobile.example.com

Now the challenge is sending the mobile traffic to this subdomain without harming the main site in any way. Also of concern: since the mobile site is just reformating content from the main site, how can we protect from duplicate content penalties?

One option appears to be WURFL, which parses the user agent and sends the traffic in the right direction.

[Musicarl]

I'm still baffled by the duplicate content issue with mobile sites, and I'm not convinced Google knows how to handle it either. From their guidelines:

Duplicate content generally refers to substantive blocks of content within or across domains that either completely match other content or are appreciably similar. Most of the time when we see this, it's unintentional or at least not malicious in origin: forums that generate both regular and stripped-down mobile-targeted pages, store items shown (and -- worse yet -- linked) via multiple distinct URLs, and so on.

It's scary to think that by trying to enhance the user experience by providing quality content in mobile format can trash the results for the main site.

As for parsing user agents, I've come across 2 schools of thought:

1) Something called WURFL, which uses an XML file to sort through the user agent of every mobile device type to determine which content to send. This seems to be the most comprehensive method, but in my testing is slowed down the site.

2 Use something like this, which will check most phones, but some will slip through:

$user_agent = $_SERVER['HTTP_USER_AGENT'];
$is_mobile = preg_match('/(up-browser)¦(blackberry)¦(windows ce)¦(playstation portable)¦(opera mini)¦up.browser¦elaine¦blazer¦semc-browser¦reqwirelessweb¦avantgo¦xiino¦netfront¦symbian¦palm¦lynx¦nokia/i', $user_agent);
if ($is_mobile) {
header("Location: [website.mobi...]
}

I'll try to post here as we learn more about setting up our mobile site.

[sugarrae]

Why wouldn't you simply block the mobile subdomain from being indexed by the engines? Also, as someone who is a very frequent mobile surfer, I prefer m.domain.com instead of mobile.domain.com - easier and faster to type. ;-)

[Musicarl]

Sugarrae-

I agree that m.domain.com is better, and I've made that change. The problem with blocking the search engines from the mobile pages is that I want them to know about our mobile content so that users can find our pages from their mobile phones. It seems like google.com/m would give preference to mobile sites, but they may also slam us for duplicate content.

[nomis5]

Interesting post. I'm considering a mobile version for one of my sites. Reading these posts though, I'm not clear why you would use mobile.domain.com.

Why not just have "mobile version" in the top left of each standard page. Clicking on "mobile version" would send the user to a mobile version of that page. Links from the mobile version would go to other mobile versions of pages.

From the, admittedly little, I've seen of mobile pages, they are significantly different from the full version. Different enough to avoid the duplicate content issues.

What are the pros and cons of this (from a complete amateur).

As an aside, I can't understand the lack of interest in pages for mobiles / PDAs, aren't they on the brink of becoming THE thing?