Advanced C3 comes in two forms: a firmware patch for existing C3 Systems, and new equipment that takes full advantage of the possibilities made by the patch.
Firmware Patch: Dynamic Linking
This firmware patch allows for dynamic battlefield linking of C3 systems in order to improve the network's resilience to having it links cuts. If for whatever reason a C3 Slave is cut off from its Master, it will automatically attempt to link up with any friendly C3 Master unit that has a free Slave port available. By the same token, if a Master loses contact with one of its sub-units (Slave or sub-Master), it's Slave port is now open and available for any free Slave/sub-Master to take.
The C3 Network is still limited to 12 units in the network however.
Dynamic Linking can be disabled or overridden if the user so chooses. However, if this is done on the battlefield, only the pilot using the C3 Master involved will be required to make a skill roll while doing nothing else in order to "fix" the network topology.
C3 Advanced
Based on studies made of C3i units captured during the Jihad, the C3 Advanced unit is basically a C3 Slave upgraded with extra functions. These functions are chosen and locked before combat begins. These functions are:
1) Link to Lower - The C3a links to a C3 unit lower on the C3 net. This can be a C3 Master, a C3 Slave, or a C3a set to Link to Higher.
2) Link to Higher - The C3a links a C3 unit highter on the C3 net. This can be a C3 Master, or a C3a set to Link to Lower. Also note that the Link to Higher function is what provides the unit's sensor data to the C3 network.
3) Network Management - The C3a manages multiple C3a units that are on the same platform it is. These units are required when using multiple C3a units on the same platform. A C3a manager can manage up to four units. C3a Network Managers can only manage C3a units. They do not manage standard C3 units.
A classic C3 Lance Master that is part of a company can be emulated by C3a by stacking together 5 C3a units: 1 Manager, 1 Link to Higher, and 3 Links to Lower.
Similarly, a classic Company Master can be emulated by using 1 Manager with 3 Links to Lower.
A Lance Master that is not part of a company net can dispense with the Link to Higher.
A C3a can act as a pure C3 Slave simply be setting it to Link to Higher.
C3a is compatible with standard C3 networks. As such, even in a C3 net composed purely of units with C3a, the net can only have 12 members.
Any network topology may be allowed so long as the units in it adhere to the above linking rules.
Even a C3i net can be emulated using 1 Link to Higher, 1 Link to Lower, and a Network Manager on each mech in a company, and then arranging the links into a "Ring" network. A Slight flaw in this design is that if a mech drops out of the network due to ECM, dynamic relinking will "close the gap" in the ring and prevent dropped mech from rejoining as there would be no open ports available. For the isolated mech to rejoin the network, it and the two mechs it would be "sliding in-between" need to make skill check rolls as described above in dynamic linking.
A C3a unit is 1 ton, and 1 crit. When carrying multiple C3a units on a single platform, the C3a units do NOT all have to be in the same location. Their functions must be designated before combat begins however.
Edit: In the event a C3a unit suffers a critical hit, only the hit C3a unit stops functioning. For Links to Lower and Links to Higher, the associated Link is destroyed until another C3a unit set to the same function can take it over. If the Network Manager suffers a critical hit, only one other onboard C3a (a Link to Higher by default) stays usable unless there is a backup Manager onboard. Changing this requires a Manual Topology Change roll.
While a mechwarrior can manually change what C3 units his C3a connects to, he cannot alter a C3a function mode on the battlefield. Altering function mode requires the services of a trained tech and 10 minutes of work.