Creepily letting myself into this topic again … only to throw another wrench …
(because clearly this topic isn’t convoluted enough yet):
Your broker actually doesn’t have to be your custodian. It often is not. I am guessing the larger and the more volatile your order, the more often your custodian/broker is not your broker for the deal given.
In this thread so far, the two - broker and custodian - seem to be joined at the hip, or at least married, which is probably the perspective of most retail investors: they conflate their custodian with being their broker. Let’s call this conflated entity CusBr (CustodianBroker).
What happens in reality (or should happen - I personally am not so sure at least with Swissquote) is, AFAIK:*
- You place an order for security S on exchange(s) E with your CusBr.
- Your CusBr is supposed to find the best conditions for your order, regardless of the dealers (brokers) permitted as traders on the exchange(s) E for your security S. The CusBr where you placed the order might offer you the best conditions, e.g. executing your trade on their own book, but if another broker (a not-CusBr, or another different CusBr) offers a better deal (for you and your conditions), then your CusBr is supposed to hand the deal to the other (non-)CusBr (taking into account all your order instructions, e.g. Limit, Market, etc, etc).
- The best deal for your order closes, with your CusBr or another (non-)CusBr.
- Settlement time!
- an independent 3rd party settlement agency matches your order instructions with the order actually executed at your CusBr or another (not-)Cusbr.
- the settlement agency also adds and substracts any “small misunderstandings” from both parties making the deal at the said broker (your CusBr or someone else), e.g. differences in misunderstandings about executions fees, etc. These things can be arcane, and they can change at the whim of the broker involved, the market / exhange you’re trading in, regulations that just changed, corporate actions that were announced around your time of trading, you name it. Most of the time it goes through very smoothly – no surprises – but every now and then, guaranteed, settlement requires manual intervention to make things go through. For a retail investor, this all takes place behind the curtains.
- the money and the security change their hand at the will of the settlement agency with T+2.***
Ok, rookie time is over now.

Here’s how it works for professional investors. Note that they typically have multiple custodians (and lots more brokers via their intermediary order brokers).
- They place their order at an intermediary independent order broker for placing their order with all the brokers allowed to participate for trading the security S at exchange E.
- The intermediary independent order broker selects the broker with the best conditions. Steps 3 and 4 from above ensue.
Independent order brokers include Bloomberg. Their “exchange” for equity orders is EMSX; the one for bonds is TSOX. They have others for FX and possibly for other types of securities. At any rate, Bloomberg offers these exchanges of exchanges (and of course takes a cut, too). Other independant order brokers probably exist, but I am not aware of them.
Getting back on topic:
Theoretically, if you were to work with the safest custodian ever (for some of you apparently Switzerland only), you’d still be dealing with many many brokers for getting your orders executed.
For those safeguarding against your custodian going belly up and you taking possession of your assets ASAP, I would recomment to doing your research.
If I made things less clear to some of you, I apologize.
Good luck.
(To be clear: I believe that in the end, things work out just fine for the asset holder, regardless of custodian, broker, you name it, it might just take a few more days depending on whether it’s IBKR or SwissQuote or someone else … but you will be in possession of your securities eventually, relatively quickly, and you won’t have an advantage from you CusBr being Swiss or not.)
I’ll see myself out again.
* I’m not an expert on the mechanics of this, but this is what I learned as a noob at a small asset management company in the past couple of years.
** BTW, mechanically, this is done through the Message Transfer (MT) Protocol on the SWIFT network.
The latter — SWIFT — is heavily regulated and has a God-Emperor (the US) and the former — MT — is as ancient as it gets. The MT protocol wasn’t formulated yet on Moses’ tables of stone (at least not on the front side, but probably shortly after on the back side of those tables).
*** Soon changing to T+1 for some US markets. Search the forum for ‘T+2’ if you are interested in learning more.