81 lines
3.5 KiB
Markdown
81 lines
3.5 KiB
Markdown
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# Eddystone-URL
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The Eddystone-URL frame broadcasts a URL using a compressed encoding format in order to fit more within the limited advertisement packet.
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Once decoded, the URL can be used by any client with access to the internet. For example, if an Eddystone-URL beacon were to broadcast the URL `https://goo.gl/Aq18zF`, then any client that received this packet could choose to [visit that url](https://goo.gl/Aq18zF).
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The Eddystone-URL frame forms the backbone of the [Physical Web](http://physical-web.org), an effort to enable frictionless discovery of web content relating to one’s surroundings. Eddystone-URL incorporates all of the learnings from the [UriBeacon](http://uribeacon.org) format from which it evolved.
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## Frame Specification
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Byte offset | Field | Description
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------------|-------|------------
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0 | Frame Type | Value = `0x10`
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1 | TX Power | Calibrated Tx power at 0 m
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2 | URL Scheme | Encoded Scheme Prefix
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3+ | Encoded URL | Length 1-17
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### Tx Power Level
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Tx power is the received power at 0 meters, in dBm, and the value ranges from -100 dBm to +20 dBm to a resolution of 1 dBm.
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Note to developers: the best way to determine the precise value to put into this field is to measure the actual output of your beacon from 1 meter away and then add 41dBm to that. 41dBm is the signal loss that occurs over 1 meter.
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The value is a signed 8 bit integer as specified by
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[TX Power Level Bluetooth Characteristic](https://developer.bluetooth.org/gatt/characteristics/Pages/CharacteristicViewer.aspx?u=org.bluetooth.characteristic.tx_power_level.xml).
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#### Examples
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* The value 0x12 is interpreted as +18dBm
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* The value 0xEE is interpreted as -18dBm
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### URL Scheme Prefix
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The URL Scheme Prefix byte defines the identifier scheme, an optional prefix and how the remainder of the URL is encoded.
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|Decimal | Hex | Expansion
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|:------- | :--------- | :--------
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|0 | 0x00 | `http://www.`
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|1 | 0x01 | `https://www.`
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|2 | 0x02 | `http://`
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|3 | 0x03 | `https://`
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### Eddystone-URL HTTP URL encoding
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The HTTP URL scheme is defined by RFC 1738, for example
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`https://goo.gl/S6zT6P`, and is used to designate Internet resources
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accessible using HTTP (HyperText Transfer Protocol).
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The encoding consists of a sequence of characters. Character codes
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excluded from the URL encoding are used as text expansion codes. When
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a user agent receives the Eddystone-URL the byte codes in the URL
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identifier are replaced by the expansion text according to the table
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below.
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|Decimal | Hex | Expansion
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|:------- | :--------- | :--------
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|0 | 0x00 | .com/
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|1 | 0x01 | .org/
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|2 | 0x02 | .edu/
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|3 | 0x03 | .net/
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|4 | 0x04 | .info/
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|5 | 0x05 | .biz/
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|6 | 0x06 | .gov/
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|7 | 0x07 | .com
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|8 | 0x08 | .org
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|9 | 0x09 | .edu
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|10 | 0x0a | .net
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|11 | 0x0b | .info
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|12 | 0x0c | .biz
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|13 | 0x0d | .gov
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|14..32 | 0x0e..0x20 | Reserved for Future Use
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|127..255 | 0x7F..0xFF | Reserved for Future Use
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Note:
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* URLs are written only with the graphic printable characters of the US-ASCII coded character set. The octets **00-20** and **7F-FF** hexadecimal are not used. See “Excluded US-ASCII Characters” in RFC 2936.
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* Range **07-13** define the same top level domains as **00-06** without a /.
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## See Also
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* **[Configuration Service Specification](docs/config-service-spec.md)** — An optional GATT service for configuring the Eddystone-URL output of your beacon
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