16 x 4 on cisco ubr10k and mc20x20

some 20x20 card options
----------------------------

Option 1 :
5 x mac domains,
4 x primary DS per mac domain,
4 way DS bonding,
typically 4 x US per mac domain

Option 2 :
4 x mac domains,
4 x primary DS per mac domain,
"span" the remaining 4 DS as non primary across the 4 mac domains,
4 and 8 way DS bonding
4 to 6 x US per mac domain

Option 3 :
2 x mac domains,
8 x primary DS per mac domain,
span the remaining 4 DS as non primary across the 2 mac domains
4 and 8 and 12 way bonding
8 US per mac domain, 4 US stranded

Unless you have SPA/DTI/Edgeqam, the 20x20 card isn't really suitable for 16 way bonding (unless you are happy to strand most of your upstreams).
If you do have access to this gear then it gives you some further options :

Option 4 :
As per option 3, but add a SPA-24XDS-SFP card, plus DTI server and EdgeQAM
This gives you another 24 DS channels which can be attached to your 20x20 card
So you can use 12 SPA channels to make mac-domain 3, and other 12 SPA channels to make mac-domain 4
Reconfigure the US channels to have 4 to 6 US per mac domain
No need for every DS to be primary (wastes too much bandwidth). Instead make every 4th or 8th DS primary.

Option 5:
with SPA and DTI and EdgeQAM
2 x mac domains,
mac domain 1 is 20 DS from the MC20x20, with 8 x US
mac domain 2 is 24 DS from the SPA, with 8 x US
4 x US are stranded
No need for every DS to be primary (wastes too much bandwidth). Instead make every 4th or 8th DS primary.

I'll attach a couple of screenshots to try and make it clearer

---
(Such a shame that you cant create a bonding group that comprises of 20x20-DS AND SPA-DS. If this was possible you could easily use these SPAs to boost your 20x20 cards to 24 or 32 way bonding groups. Perhaps an intended ploy by Cisco to force people to upgrade to 3G60?)

[edited Jun 2018 to add option 5]