What is Phantom?

Phantom is a loosely-coupled set of servers and communications protocols designed to supercede SPIRIT. The goal is not to produce a commercial/finalised offering but rather to deliberately leave things open-ended in order to facilitate research.

To this end, the design philosophy is such that you should be able to use phantom proided you have can use unicast and multicast on your network and machine. That is the only requirement: no client side libraries are required (although some may be produced). This allows embedded devices access to everything so integrating, say, an iPaq, should be very easy.

Persistent storage is through a postgres database which is attached to a server that, initially, executes SQL commands on belhalf of a client and returns the results (thereby allowing clients to execute SQL without needing any libraries). Users can access the database and change contents directly: all changes are multicast to a particular channel using database triggers.

The Database

The database presently resides wholly on firestoker. There is a documented multicast group where clients can ask for a database that knows about a certain table. Such a database respondes on the same channel with its contact details (IP address and TCP port ). The client may then connect to this server and send the SQL query as a string, receiving the results in a binary format as follows:

Byte 1            Number of fields in result (unsigned char), c
Byte 2            Number of tuples (rows) in result (unsigned char), r
Bytes 3 -- (3+r)  Phantom type of each field (each an unsigned char -- see below)
Varies            Field names (concatenated and delimited by '\0')
<Then each element of each row concatenated in binary format (strings null-terminated)>            

The postgres data types are as follows:

Type     Data (size in bytes)
1        bool (i)
2        char (1)
3        int2 (2)
4        int4 (4)
5        int8 (8)
6        float4 (4)
7        float8 (8)
8        abstime (8)

20       ALL string types (null-terminated char array)

Multicast Groups

Phantom uses the multicast groups 225.0.1.0 to 225.0.1.255

Unfortunately multicast groups have to be attached to a port so Phantom adopts a convention based on the group address 225.0.A.B, such that the port is 10000+A*256+B. Note that the database server uses a TCP channel for result delivery, and the IP address/port is available on a set multicast channel.

The allocated spaces are as follows:

225.0.0.* : System comms

225.0.0.0      Database request channel
225.0.0.1      Database change broadcast channel
225.0.0.2      Error channel

225.0.1.* : Sensor system (raw) events

225.0.1.0      Bat system events

225.0.2.* : Aggregated events

225.0.2.1      Location events
225.0.2.2      Spatial Indexer events

Phantom Message Structure

Multicast messages have a set header. We have allowed for future versions of the message header by including versioning data in the header. At present only version 1 exists and is 16 bytes in length:

Bytes   C++ Type        Description
1       unsigned char   Message Version (1 at present)
2	short	        Phantom event id
1       unsigned char   Sequence Number for Bat messages
4	long            UNIX time (seconds)
4       long            UNIX time (microseconds)
4       n/a             Reserved

This format is to allow easy filtering of events that are not wanted.