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🤝 Article 55 · SGP.22 v3.x

🤝 The Secret Handshake

How eSIM Devices Agree on What They Can Do Together

A story of feature menus, compatibility checks, and why asking first makes everything work better

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Server Can do: ✓ MEP supported ✓ Push Service ✓ Device Change ✗ Chip Updates v3.2 Chip Can do: ✓ MEP supported ✓ Push Service ✗ Device Change ✗ Chip Updates v3.0 ? Can they work together? Different versions, different features!

🤔 Before We Work Together

Not all eSIM devices are created equal. A server might be running v3.2 with all the latest features, while your phone's chip only supports v3.0 basics. If the server tries to use a feature the chip doesn't understand, things break! They need a way to check compatibility first.

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Server "Can you do MEP?" "Push Service?" Chip "MEP? Yes! ✅" "Push? Yes! ✅" MEP ✅ Push ✅ Dev Chg ✗ Updates ✗ Only use what both can handle!

❓ "Can You Do This?" "Yes!"

Before any work begins, the server and the chip perform a feature check. The server asks: "Can you do MEP? Push Service? Device Change?" The chip answers honestly with what it supports. Based on the answers, they agree on a common set of features: only using what both sides understand.

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🏷️ The Feature Tag Menu MEP Two profiles at once PushService Doorbell notifications DeviceChange Move keys to new phone PCM Chip software updates RemoteMgmt Remote profile control BPP Protected profile packages Each tag = one feature the chip can "speak" Server checks the menu before ordering!

🏷️ The Feature Tag Menu

Every v3.x chip comes with a menu of feature tags: like a restaurant menu listing what dishes are available. Tags include: MEP (multiple profiles), PushService (doorbell), DeviceChange (key moving), PCM (chip updates), and more. The server reads this menu before placing any "order"!

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❌ Without Handshake "Do MEP!" Chip: "What's MEP?" 💥 ERROR! CRASH! Broken session, confused devices ✅ With Handshake "What can you do?" "MEP: no. Push: yes." "OK, Push only!" Smooth session, happy devices 💡 Asking first = everything works! Graceful degradation beats crashing every time

🛡️ Asking First Avoids Problems

Without feature negotiation, the server might ask the chip to do something it doesn't understand: causing errors, crashes, or broken sessions. With the secret handshake, they agree on exactly what's supported before any real work starts. Even if a chip is older, it can still work: just with fewer features. This is called graceful degradation!

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1. Connect Secure link established 🔒 → 2. Ask "What features do you support?" → 3. Answer Chip sends feature list 🏷️ → 4. Agree Use common features only 🤝 ✨ Locked in! 🤝 Handshake complete: let's work!

🤝 The Handshake, Step by Step

1. Connect: Encrypted link established. 2. Ask: Server queries the chip's feature menu. 3. Answer: Chip sends back its tags: honestly! 4. Agree: Both sides lock in the common subset of features. Now the real work begins, using only commands the chip understands. No surprises, no crashes!

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Old Chip v2.x (limited) New Server v3.5 (full) 🤝 "We'll use basic features: and that's OK!" 🧠 Old + New still work together!

Feature Support is the glue that makes v3.x backwards-compatible. A brand-new server (v3.5) can still talk to an older chip (v2.x) because they negotiate shared capabilities first. The server simply uses fewer features. This means the entire ecosystem can evolve gradually: no need for everyone to upgrade at once!

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