Some phones have old magic, some have new: but everyone still gets to play together!
There are billions of older eSIM chips out there running v2.x magic. When SGP.22 v3.x arrived with all its shiny new spells, it had a crucial question to answer: can a brand-new v3.1 phone still talk to a 5-year-old v2.x Key Maker? The answer had to be yes!
Not everyone upgrades at the same time. You could have old phone + old server (easy!), new phone + old server (phone adapts!), old phone + new server (server adapts!), or new + new (full v3.x party!). v3.x was designed for all four scenarios from day one.
The secret is beautifully simple. A v3.x phone shares its capability card saying "I can do v3.1." A v2.x server sends no capability card at all. The phone sees the missing card and instantly knows: "Old magic! I'll speak v2.x." The negotiation takes one exchange, and everything just works.
When a new v3.x phone calls an old v2.x server, the phone becomes a v2.x phone for that conversation: using only the spells the old server knows. The server never even realises it's talking to a newer device! It's like being fluent in both modern slang and old-fashioned language.
The bridge between old and new magic is remarkably simple: a missing capability card. When a server doesn't send rspCapability, it means "I'm pre-v3." That's it: one simple rule bridges billions of old devices with all the new ones. No complex version tables, no negotiation protocols, just a missing card that says everything!
The v3.x rulebook includes politeness rules every server must follow: always include your capability card, never crash on old requests, never reject extra fields you don't understand, and always pick the right profile package version. These rules ensure that old and new devices play together harmoniously, no matter what combinations arise!
This backwards-compatibility means you could take a brand-new v3.1 phone to a mobile company running a 5-year-old v2.x Key Maker: and everything would work perfectly. The phone simply becomes a well-behaved v2.x phone for that conversation. It's like being fluent in both modern slang and old-fashioned language, switching effortlessly!
🎮 Next: The Magic Remote Control →