MOX with multiple of the same module?


#1

Does the Mox support having multiple 4 port gigabit modules? So that if someone wanted to get 12 ports they could do so? Also would it support two or three of the 3x3 wifi modules at the same time? It would be nice to increase wifi bandwidth capacity by having multiple radios so that more clients could connect without sharing wifi link bandwidth.


#2

Short answer is no.
There will be probably better explanation from somebody involved, but it is not possible with the currently offered modules. There will (might) be in the future modules which will allow it. Also I think it is a plan to have LAN module with 8 ports.


#3

Its explained here https://doc.turris.cz/doc/en/howto/mox/mox-c-eth


#4

The new MOD E (8 port ethernet) will allow this. The example given is that the 4 port ethernet (MOD C) can be connected to the 8 port module (MOD E).

I suspect it uses an marvell switch 88E6390 chip which has 2x SGMII and using one for the uplink (e.g. to the CPU via moxtet) and one as downlink to the next module (e.g. SFP, 4 or 8 port gigE).

In general the CPU module supplies all the signals to the “bus” (moxtet) and each module “consumes” one signal (e.g. MOD C and D consume the SGMII signal and MOD B the PCIe). That means that no module using the same signal can be added unless the module closer to the CPU replicates the signal (e.g. MOD E seems to replicate the SGMII signal).
Replicating the signal is usually expensive in hardware and adds considerable software complexity as well as user understanding.
In the 2x MOD E example the 16 port switch the user sees is really 2x 8 port switch connected with a 2.5G (10G would be cool but I suspect to complex/expensive) trunk. This needs to be explained to the user for the user to understand that ports are not equal.


#5

Can someone explain how the new MOX G - mPCI-E pass through module works? It was said the CPU has only single PCI-E line so how can one use more mPCI-E cards with multiple G modules then?


#6

I suspect an PCIE switch is used. The can take an PCIE lane (or group) in and split it out into multiple PCIE lanes (groups).
This is very common on any “PC” motherboard because the normal Intel CPUs (like i* and E3-*) don’t provide enough PCIE lanes. Some of them are then switched to multiple PCIE slots.
It works the same as a network switch (or usb hub). You use one port as uplink to the cpu and have then another number of ports for your devices all sharing the capacity of that uplink.

An example of such PCIE switches.