We have a CIX 670 with 4 cabinets. All the documentation says there is a max of 80 extensions per cabinet. But it also implies that this is due to power requirements and seems to allow other types of cards in the same cabinet with the 80 extensions such as SIP trunks, PRI, CO, etc.

If the 80 extension restriction is really due to power then it seems you should be able to max out a cabinet with 10 MIPU cards and have 160 ip phones on a single cabinet.

Has anyone done this? Is it legal to do this?

Also, are all the slots in a cabinet treated equally? For example should the MIPU that our SIP trunk is on be in a low numbered slot?
We have occasion where we lose our SIP trunk and have to physically reset the card to get it working again. It is in slot 7 of cabinet 4.

Toshiba doesn't recommend putting an mipu in any slot past the 5th in an expansion cabinet. which puts you at 80 or you could put a mipu24 in 5th slot to get 88

of course we have many of them out there with mipu in higher slots without issue but we did have one customer where it was a problem and we had to re-configure

Thanks for the info.
If we put MIPU's in slots 1 - 5, then what could we put in the remaining slots?
We are going to have to add a 5th cabinet and need to pack as much as we can into every cabinet.
Is there a max number of MIPU cards that the CIX can handle without having issues ?

An MIPU can go into all 8 slots in the base cabinet. Per the install guide an MIPU should only be in slots 1-6 in the expansion (assuming an MIPU 16), and you are also limited to 5 MIPU card per expansion cabinet.

Slots 7-10 in the expansion cabinets only support 8 port cards, such as a BDKU, RCOU, RSTU, or BIOU. If someone put an MIPU in slot 7 of the expansion then this is technically incorrect. It will probably work if slot 8 is open, but it is usually best to follow Toshiba's guidelines if you want to avoid problems.

Max MIPU cards per a 7 cabinet system is 36 MIPU cards, or until you reach 560 maximum extensions.