Make OTLP/gRPC a required and default transport

Resolves #1885

CHANGELOG.md

@@ -58,6 +58,7 @@ release.
 ### OpenTelemetry Protocol
 
 - Add environment variables for configuring the OTLP exporter protocol (`grpc`, `http/protobuf`, `http/json`) ([#1880](https://github.com/open-telemetry/opentelemetry-specification/pull/1880))
+- Make OTLP/gRPC a required and default transport.
 
 ### SDK Configuration
 

specification/protocol/exporter.md

@@ -17,7 +17,7 @@ The following configuration options MUST be available to configure the OTLP expo
 | Headers              | Key-value pairs to be used as headers associated with gRPC or HTTP requests. See [Specifying headers](./exporter.md#specifying-headers-via-environment-variables) for more details.                   | n/a               | `OTEL_EXPORTER_OTLP_HEADERS` `OTEL_EXPORTER_OTLP_TRACES_HEADERS` `OTEL_EXPORTER_OTLP_METRICS_HEADERS` |
 | Compression          | Compression key for supported compression types. Supported compression: `gzip`| No value              | `OTEL_EXPORTER_OTLP_COMPRESSION` `OTEL_EXPORTER_OTLP_TRACES_COMPRESSION` `OTEL_EXPORTER_OTLP_METRICS_COMPRESSION` |
 | Timeout              | Maximum time the OTLP exporter will wait for each batch export. | 10s               | `OTEL_EXPORTER_OTLP_TIMEOUT` `OTEL_EXPORTER_OTLP_TRACES_TIMEOUT` `OTEL_EXPORTER_OTLP_METRICS_TIMEOUT` |
-| Protocol             | The transport protocol. Options MAY include `grpc`, `http/protobuf`, and `http/json`. See [Specify Protocol](./exporter.md#specify-protocol) for more details. | n/a               | `OTEL_EXPORTER_OTLP_PROTOCOL` `OTEL_EXPORTER_OTLP_TRACES_PROTOCOL` `OTEL_EXPORTER_OTLP_METRICS_PROTOCOL` |
+| Protocol             | The transport protocol. Options MAY include `grpc`, `http/protobuf`, and `http/json`. See [Specify Protocol](./exporter.md#specify-protocol) for more details. | `grpc`               | `OTEL_EXPORTER_OTLP_PROTOCOL` `OTEL_EXPORTER_OTLP_TRACES_PROTOCOL` `OTEL_EXPORTER_OTLP_METRICS_PROTOCOL` |
 
 Supported values for `OTEL_EXPORTER_OTLP_*COMPRESSION` options:
 
@@ -50,9 +50,9 @@ The `OTEL_EXPORTER_OTLP_PROTOCOL`, `OTEL_EXPORTER_OTLP_TRACES_PROTOCOL`, and `OT
 - `http/protobuf` for protobuf-encoded data over HTTP connection
 - `http/json` for JSON-encoded data over HTTP connection
 
-SDKs MUST support either `grpc` or `http/protobuf` and SHOULD support both. They also MAY support `http/json`.
+SDKs MUST support `grpc` and SHOULD support `http/protobuf`. They also MAY support `http/json`.
 
-SDKs have an unspecified default, if no configuration is provided.
+The default transport is `grpc` if no configuration is provided.
 
 ### Specifying headers via environment variables