Network Topology
================

CSP uses a network oriented terminology similar to what is known from the Internet and the TCP/IP model. A CSP network can be configured for several different topologies. The most common topology is to create two segments, one for the Satellite and one for the Ground-Station. 

.. code-block:: none

                 I2C BUS
     _______________________________
    /       |       |       |       \
   +---+   +---+   +---+   +---+   +---+
   |OBC|   |COM|   |EPS|   |PL1|   |PL2|       Nodes 0 - 7 (Space segment)
   +---+   +---+   +---+   +---+   +---+
             ^
             |  Radio
             v
           +---+           +----+
           |TNC|  -------  | PC |              Nodes 8 - 15 (Ground segment)
           +---+    USB    +----+
   
           Node 9          Node 10

The address range, from 0 to 15, has been segmented into two equal size segments. This allows for easy routing in the network. All addresses starting with binary 1 is on the ground-segment, and all addresses starting with 0 is on the space segment. From CSP v1.0 the address space has been increased to 32 addresses, 0 to 31. But for legacy purposes, the old 0 to 15 is still used in most products.

The network is configured using static routes initialised at boot-up of each sub-system. This means that the basic routing table must be assigned compile-time of each subsystem. However each node supports assigning an individual route to every single node in the network and can be changed run-time. This means that the network topology can be easily reconfigured after startup.