最近基于APRS（自动位置报告系统，Automatic Position Reporting System）的原理，在互联网上实现了一个类似的系统。系统的源码在这里。
A system, basing on principles similar to APRS(Automatic Position Reporting System, is implemented. This system runs in the Internet. Source code is here.
The idea is simple. APRS lets one broadcasts its position, and the signal is received by another DIGIPEATER and repeated. Then the signal is broadcast-ed more widely. Some receiver will put the received packet into Internet.
Existing Applications in Internet, such as Emails, IMs, or WeChat, can all be used to transmit short messages. But these applications have limited paths in transmitting such data. NPBS as here designed, is based on broadcasting at nodes. Although it have lower efficiency, and vulnerable to mass traffics, it is more robust, when the transmission of messages is concerned. But when referring to punctuality, it has disadvantage.
The NPBS System utilizes parameters in URL to transmit a packet, which is a string. The definition of the packet is in the source code(above). The max. length of a packet is 1655 bytes, constructed of characters which will not be encoded but case-sensitive. A packet consists of a HEAD(NPBS1, 1 for version), a LABEL(like a call-sign), a TTL(begin with 255 and reduced by 1 each time the packet is forwarded), a CHECKSUM using SHA1 of the data, to check the integrity of data and to drop duplicated packets.
The data is encoded in base64, thus allowing arbitrary data stored. The characters ‘+’, ‘/’, ‘=’ in Base64 are relatively replaced with ‘_’, ‘-’, ‘*’.
Currently a implementation in PHP is available, with a complex CAPTCHA(Chinese characters inputting expected, however one have a 10% possibility to get a mathematics CAPTCHA). This implementation does not rely on database, only on authorities of reading and writing local files.
The entrance to this system in this website is here: