Device Characterization - Define Cached Content

Device Characterization (DC) provides additional ways to accelerate and optimize your content based on the requesting device's features and capabilities. Property Manager provides two behaviors for controlling these functions: Device Characterization - Forward in Header and Device Characterization - Define Cached Content.
With DC, you can:

  • identify the characteristics of each device that requests data from your site,

  • use this information to serve content optimized for each device class,

  • fine-tune content caching.

How it works

The Device Characterization algorithm identifies many key characteristics of the requesting device by cross-referencing multiple resources: the device's user-agent string, an industry-standard database (WURFL), and internal device monitoring capabilities. With DC enabled, you select which device characteristics are used to cache content. DC creates cache keys based on the values of the characteristics you select. This way, the cached content is optimized for devices with different characteristics.

Definitions

  • Forwarding. In this context, sending information about the requesting end-user device from the edge server to the origin.

  • Caching. Storing content on the edge server so that subsequent requests for the same content don't have to go to the origin.

Why you need it

Imagine you want to cache content optimized for devices with a resolution width of 640 pixels. Set DC to cache content based on the resolution_width characteristic. When a first user with a 640-pixel-wide screen requests an object, DC caches content optimized for that resolution. The cache entry is labeled with a cache key that contains both the original request and the resolution width. The content will subsequently be available for other devices with the same resolution. DC creates a new cache entry for every request from a device with a different resolution width.

Typical characteristics available for caching

โ€‹Akamaiโ€‹ continuously improves the database behind DC, so the list of available characteristics changes over time. Typical characteristics include:

CharacteristicData TypeDescription
resolution_height resolution_width integerThe screen height/width, measured in pixels.
physical_screen_height physical_screen_width integerThe height/width of the screen, in millimeters.
max_image_height max_image_width integerThe maximum height/width, in pixels, for an image to be viewable when the page renders in a mobile-optimized format.
device_os stringThe requesting device's operating system (for example, Android, iOS, Windows 10).
device_os_version stringThe request device's operating system version.
mobile_browser stringThe requesting device's browser.
mobile_browser_version stringThe version of the requesting device's current mobile browser.
brand_name stringDevice maker (for example, Samsung, Apple).
model_name stringRequest device's model (for example, SCH-I110).
marketing_name stringThe device model's commercial name (for example, Samsung Illusion).
pdf_support true/falseIndicates if the requesting device can read PDF files.
dual_orientation true/falseIndicates if the requesting device can rotate displayed content, which swaps the height and width dimensions.
ajax_support_javascript true/falseIndicates if the requesting device supports JavaScript.
cookie_support true/falseIndicates if the requesting device's browser supports cookies. However, please note that cookie support doesn't indicate that the cookies exist. Also, even if the native browser doesn't support cookies, they might be supported via other methods.
is_mobile true/falseIndicates if the requesting device is a mobile device.
is_tablet true/falseIndicates if the device is a tablet; this is a subcategory of mobile device.

Special considerations for Apple devices

Most manufacturers of mobile devices include information in the device's user-agent string that identifies the hardware revision of the device. However, Apple has a policy of not including this information. For Apple devices, DC can identify the iOS version and the browser version, but it cannot distinguish between different models of the same product.

In contrast, consider this user-agent string:

Samsung Galaxy S3: Mozilla/5.0 (Linux; U; Android 4.1.1; en-us; SGH-T999 Build/JRO03L) AppleWebKit/534.30 (KHTML, like Gecko) Version/4.0 Mobile Safari/534.30

Unlike the Apple products, this Samsung user-agent string includes the model number.

Implementation

Before the edge servers can forward and cache device characteristics, you'll need to create one or more rules that include the DC behaviors. These are the high-level steps for getting started:

  1. Create a rule, and determine match criteria.

  2. Add the Device Characterization - Forward in Header behavior, and then select which characteristics to forward.

  3. Add the Device Characterization - Define Cached Content behavior, and then select which characteristics to use to create the cache keys.

Step 1: Create a rule and set its match criteria

As with other Property Manager rules, DC rules consist of two parts: match criteria and behaviors. To optimize content and/or cache content by device type, include one or more match criteria that use the device characteristics options.

To create a rule for your DC configuration, perform the following steps.

How to

  1. In the โ€‹Akamai Control Centerโ€‹, go to the property page.

  2. Under Manage Versions and Activations, go to the Version History tab and select a version link.

  3. At the top of the Rules list, click Add.

  4. Select a rule template (for example, the Blank Rule Template).

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To narrow down the All Templates list, select a category in the left column.

  1. Click Insert Rule.

  2. In the Criteria section, click the Add Match button, and indicate the conditions that will trigger Device Characterization. Create additional match criteria as needed.

Select which device characteristics to forward to the origin. The more characteristics you select, the bigger your forward header will be, which may adversely affect performance between the edge server and the origin. Aim to maximize device-specific content delivery and minimize the number of characteristics you forward to do so.

How to

  1. In the Behaviors section, click Add Behavior.

  2. Scroll through the behavior menu on the left, and select the Device Characterization - Forward in Header option.

  3. Click Insert Behavior.

A new DC behavior appears in your rule.

  1. Click the Send These Characteristics field to select what to include in the forward header. You can use the mouse to select from the drop-down menu, or start typing in the box to search the options. Click the X to remove a selection.

  2. Click Save.

Step 3: Configure characteristic-based caching (optional)

Select which characteristics are added to the cache key. Every unique combination of values of the characteristics you select will produce a separate cache entry. Therefore, it is recommended that you include only characteristics that request different content for different values.

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Consider how characteristics selected in this behavior relate to the device characteristics in the match criteria. You will probably find that the characteristics with boolean values (like is_mobileand is_tablet) are the most effective.

How to

  1. In the Behaviors section, click Add Behavior.

  2. Scroll through the behavior menu on the left, and select the Device Characterization - Define Cached Content option.

  3. Click Insert Behavior.

A new DC behavior appears in your rule.

  1. Click the Cache Based on These field to select what to include in the cache key. You can use the mouse to select from the drop-down menu, or start typing in the box to search the options. Click the X to remove a selection.

  2. Click Save.

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Adding a greater number of characteristics to the cache key (especially if you select characteristics that have many values) can negatively affect performance and offload.

Tips and best practices

โ€‹Akamaiโ€‹ recommends that any characteristic you add to your cache key you also add to your list of characteristics to forward. Then, you can use the X-Akamai-Device-Characteristics header to monitor what is being added to your cache key. Likewise, the characteristics in the rule's match criteria should align with the characteristics used in the behaviors. Also, your servers should provide different content based on the values of the characteristics in your cache key.

A good way to approach DC configuration is to begin by describing how you want to classify devices. For example, you might simply divide them by device type: desktop, mobile device, or tablet. Or you might also want to distinguish high-end mobile devices from low-end devices. Create a rule for each class, and use the match criteria to identify all the devices that belong in that class.