Change network.transport from recommended to opt-in in the HTTP semconv

CHANGELOG.md

@@ -13,6 +13,8 @@ release.
   ([#374](https://github.com/open-telemetry/semantic-conventions/pull/374))
 - BREAKING: Define url.scheme in terms of logical operation in HTTP server semconv.
   ([#376](https://github.com/open-telemetry/semantic-conventions/pull/376))
+- BREAKING: Change `network.transport` from recommended to opt-in in HTTP semconv.
+  ([#402](https://github.com/open-telemetry/semantic-conventions/pull/402))
 
 ### Features
 

docs/http/http-spans.md

@@ -125,8 +125,8 @@ sections below.
 | [`http.response.status_code`](../attributes-registry/http.md) | int | [HTTP response status code](https://tools.ietf.org/html/rfc7231#section-6). | `200` | Conditionally Required: If and only if one was received/sent. |
 | [`network.protocol.name`](../general/attributes.md) | string | [OSI application layer](https://osi-model.com/application-layer/) or non-OSI equivalent. [6] | `http`; `spdy` | Recommended: if not default (`http`). |
 | [`network.protocol.version`](../general/attributes.md) | string | Version of the protocol specified in `network.protocol.name`. [7] | `1.0`; `1.1`; `2`; `3` | Recommended |
-| [`network.transport`](../general/attributes.md) | string | [OSI transport layer](https://osi-model.com/transport-layer/) or [inter-process communication method](https://en.wikipedia.org/wiki/Inter-process_communication). [8] | `tcp`; `udp` | Conditionally Required: [9] |
-| [`network.type`](../general/attributes.md) | string | [OSI network layer](https://osi-model.com/network-layer/) or non-OSI equivalent. [10] | `ipv4`; `ipv6` | Recommended |
+| [`network.transport`](../general/attributes.md) | string | [OSI transport layer](https://osi-model.com/transport-layer/) or [inter-process communication method](https://en.wikipedia.org/wiki/Inter-process_communication). [8] | `tcp`; `udp` | Opt-In |
+| [`network.type`](../general/attributes.md) | string | [OSI network layer](https://osi-model.com/network-layer/) or non-OSI equivalent. [9] | `ipv4`; `ipv6` | Recommended |
 | `user_agent.original` | string | Value of the [HTTP User-Agent](https://www.rfc-editor.org/rfc/rfc9110.html#field.user-agent) header sent by the client. | `CERN-LineMode/2.15 libwww/2.17b3` | Recommended |
 
 **[1]:** If the request fails with an error before response status code was sent or received,
@@ -175,15 +175,9 @@ The attribute value MUST consist of either multiple header values as an array of
 
 **[7]:** `network.protocol.version` refers to the version of the protocol used and might be different from the protocol client's version. If the HTTP client used has a version of `0.27.2`, but sends HTTP version `1.1`, this attribute should be set to `1.1`.
 
-**[8]:** The value SHOULD be normalized to lowercase.
+**[8]:** Generally `tcp` for `HTTP/1.0`, `HTTP/1.1`, and `HTTP/2`. Generally `udp` for `HTTP/3`. Other obscure implementations are possible.
 
-Consider always setting the transport when setting a port number, since
-a port number is ambiguous without knowing the transport, for example
-different processes could be listening on TCP port 12345 and UDP port 12345.
-
-**[9]:** If not default (`tcp` for `HTTP/1.1` and `HTTP/2`, `udp` for `HTTP/3`).
-
-**[10]:** The value SHOULD be normalized to lowercase.
+**[9]:** The value SHOULD be normalized to lowercase.
 
 Following attributes MUST be provided **at span creation time** (when provided at all), so they can be considered for sampling decisions:
 

model/trace/http.yaml

@@ -20,8 +20,10 @@ groups:
         sampling_relevant: true
         requirement_level: required
       - ref: network.transport
-        requirement_level:
-          conditionally_required: If not default (`tcp` for `HTTP/1.1` and `HTTP/2`, `udp` for `HTTP/3`).
+        requirement_level: opt_in
+        note: >
+          Generally `tcp` for `HTTP/1.0`, `HTTP/1.1`, and `HTTP/2`. Generally `udp` for `HTTP/3`.
+          Other obscure implementations are possible.
       - ref: network.type
       - ref: user_agent.original