2nd/10_Wiki/Topics/Architecture/System_Protocol_Standard.md

---
id: wiki-2026-0508-system-protocol-standard
title: System Protocol Standard
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [Protocol Standardization, Wire Protocol Design, Interface Standards]
duplicate_of: none
source_trust_level: A
confidence_score: 0.85
verification_status: applied
tags: [protocol, standard, interoperability, design]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: multi
  framework: protobuf-grpc
---

# System Protocol Standard

## 매 한 줄
> **"매 system 간 wire-level contract 의 versioned, versionable specification"**. 매 protocol standard 의 — message format + transport + semantics + evolution rules. 2026 의 modern stack 의 protobuf + gRPC + OpenAPI + AsyncAPI 의 dominant.

## 매 핵심

### 매 components of protocol spec
- **Syntax**: 매 wire format (binary, JSON, XML).
- **Semantics**: 매 message meaning + state machine.
- **Transport**: TCP, UDP, HTTP/2, QUIC, WebSocket.
- **Versioning**: 매 backward / forward compat rules.
- **Error model**: 매 status codes, retry semantics.

### 매 design 원칙
- **Forward compat**: 매 old client 의 new server 의 read.
- **Backward compat**: 매 new client 의 old server 의 read (graceful).
- **Self-describing**: 매 schema 의 embed (JSON-Schema, protobuf descriptor).
- **Idempotency**: 매 retry 의 safe.
- **Explicit versioning**: 매 URL `/v1/`, header, or schema `apiVersion`.

### 매 standard families
- **RPC**: gRPC, Thrift, Cap'n Proto, JSON-RPC.
- **REST**: HTTP + OpenAPI 3.1.
- **Message**: AMQP, MQTT, Kafka wire, NATS, AsyncAPI 3.0.
- **Streaming**: WebRTC, RTSP, HLS, WebTransport.

### 매 응용
1. Microservice contracts.
2. IoT device protocols.
3. Inter-org B2B (EDI → modern API).
4. Embedded → cloud telemetry.

## 💻 패턴

### Protobuf — versionable schema
```protobuf
syntax = "proto3";
package order.v1;

message Order {
  string id = 1;
  string customer_id = 2;
  repeated LineItem items = 3;
  google.protobuf.Timestamp created_at = 4;
  reserved 5, 6;            // burned fields — never reuse
  reserved "deprecated_field";
}

message LineItem {
  string sku = 1;
  int32 qty = 2;
  Money price = 3;
}
```

### gRPC service contract
```protobuf
service OrderService {
  rpc Create(CreateOrderRequest) returns (Order);
  rpc Get(GetOrderRequest) returns (Order);
  rpc Stream(StreamOrdersRequest) returns (stream Order);
}
```

### OpenAPI 3.1 — REST contract
```yaml
openapi: 3.1.0
info:
  title: Order API
  version: 1.4.0
paths:
  /v1/orders/{id}:
    get:
      operationId: getOrder
      parameters:
        - name: id
          in: path
          required: true
          schema: { type: string }
      responses:
        '200':
          content:
            application/json:
              schema: { $ref: '#/components/schemas/Order' }
```

### Versioning — semver + deprecation
```http
GET /v1/orders/123
Sunset: Wed, 01 Jan 2027 00:00:00 GMT
Deprecation: true
Link: </v2/orders/123>; rel="successor-version"
```

### Schema evolution rules (protobuf)
```
ALLOWED:
  - Add new optional field (new tag #)
  - Rename field name (tag # is contract)
  - Add new RPC

FORBIDDEN:
  - Change tag #
  - Change field type (int32 → string)
  - Make optional → required
  - Reuse reserved tag
```

### Error model — gRPC + RFC 7807
```protobuf
message Error {
  string code = 1;       // RESOURCE_NOT_FOUND
  string message = 2;
  string trace_id = 3;
  google.protobuf.Any details = 4;
}
```

```json
// REST RFC 7807
{
  "type": "https://api.example.com/errors/insufficient-funds",
  "title": "Insufficient funds",
  "status": 422,
  "detail": "Account balance is $5; tried to withdraw $100",
  "instance": "/accounts/12345/withdraw"
}
```

### AsyncAPI — event protocol
```yaml
asyncapi: 3.0.0
info: { title: Order Events, version: 1.0.0 }
channels:
  order.created:
    address: order.v1.created
    messages:
      OrderCreated:
        payload:
          $ref: '#/components/schemas/Order'
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Internal microservice, polyglot | gRPC + protobuf |
| Public API | REST + OpenAPI 3.1 |
| Browser real-time | WebSocket / WebTransport |
| Event-driven | AsyncAPI + Kafka/NATS |
| Embedded / IoT | MQTT + protobuf |

**기본값**: 매 protobuf + gRPC (internal), 매 OpenAPI + JSON (external).

## 🔗 Graph
- 부모: [[API Design]] · [[Distributed Systems]]
- 변형: [[gRPC]] · [[REST]]
- 응용: [[Microservices]]
- Adjacent: [[Backward Compatibility]] · [[Idempotency]]

## 🤖 LLM 활용
**언제**: schema generation, migration plan (v1 → v2), client SDK scaffolding.
**언제 X**: final wire format approval (security/perf review 의 human).

## ❌ 안티패턴
- **No versioning**: 매 v1 의 미래 의 painful breaking change.
- **Reuse reserved tags**: 매 silent data corruption.
- **Required fields in proto3**: 매 forward-compat 의 break.
- **Stringly-typed enums**: 매 typo + drift — 매 enum 의 사용.
- **"Dump it all"**: 매 message 의 too-fat — 매 Single Responsibility 의.

## 🧪 검증 / 중복
- Verified (Google API Design Guide; gRPC docs; OpenAPI 3.1; RFC 7807).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — protobuf, OpenAPI, AsyncAPI, versioning rules |