[HLD] DSCP/TC remapping for tunnel traffic

doc/qos/tunnel_dscp_remapping.md

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+# DSCP remapping for tunnel traffic
+
+## 1 Table of Content ###
+
+- [Revision](#11-revision)
+- [Scope](#2-scope)
+- [Definitions/Abbreviations](#3-definitionsabbreviations)
+- [Overview](#4-overview)
+- [Design](#5-design)
+    - [SWSS Schema](#51-swss-schema)
+        - [Define new table for mapping](#511-define-new-table-for-mapping)
+        - [Update existing TUNNEL table](#512-update-existing-tunnel-table)
+        - [Define new field for extra lossless queues](#513-define-new-field-for-extra-lossless-queues)
+    - [SAI attribute](#52-sai-attribute)
+    - [orchagent](#53-orchagent)
+- [Test requirement](#6-test-requirement)
+- [Open Questions](#7-open-questions)
+
+### 1.1 Revision ###
+| Rev |     Date    |       Author       | Change Description                |
+|:---:|:-----------:|:------------------:|-----------------------------------|
+| 0.1 |             | Bing Wang   | Initial version                   |
+
+
+## 2 Scope ##
+
+This document covers high level design of DSCP and TC remapping for tunnel traffic in SONiC.
+
+## 3 Definitions/Abbreviations ##
+
+
+| Term | Meaning |
+|:--------:|:---------------------------------------------:|
+| PFC | Priority-based Flow Control  |
+| TC | Traffic class|
+| DSCP| Differentiated Services Code Point |
+
+## 4 Overview
+
+The current QoS map architecture allows for port-based selection of each QoS map. However, we are not able to override the port-based QoS map for tunnel traffic. 
+This design proposes a method to remapping DSCP and TC for IPinIP tunnel. 
+
+
+## 5 Design ##
+
+### 5.1 SWSS Schema
+#### 5.1.1 Define new table for mapping
+Please be noted that below config is to remap traffic in queue 3 to queue 2, and traffic in queue 4 to queue 6.
+* Table for decap
+
+    DSCP_TO_TC_MAP for mapping DSCP to TC
+    ```json
+    "DSCP_TO_TC_MAP": {
+        "AZURE_TUNNEL": {
+            "0": "1",
+            "1": "1",
+            "2": "2",
+            "3": "3",
+            "4": "4",
+            "5": "1",
+            "6": "6",
+            "7": "1",
+            "8": "0",
+            "9": "1"
+    }
+    ```
+    TC_TO_PRIORITY_GROUP_MAP for mappping TC to PG
+    ```json
+    "TC_TO_PRIORITY_GROUP_MAP": {
+        "AZURE_TUNNEL": {
+            "0": "0",
+            "1": "0",
+            "2": "0",
+            "3": "2",
+            "4": "6",
+            "5": "0",
+            "6": "0",
+            "7": "7"
+    }
+    ```
+* Table for encap
+
+    TC_TO_QUEUE_MAP for remapping queue
+    ```json
+    "TC_TO_QUEUE_MAP": {
+        "AZURE_TUNNEL": {
+            "0": "0",
+            "1": "1",
+            "2": "1",
+            "3": "2",
+            "4": "6",
+            "5": "5",
+            "6": "1",
+            "7": "7"
+    }
+    ``` 
+    TC_TO_DSCP_MAP for rewriting DSCP
+    ```json
+    "TC_TO_DSCP_MAP": {
+        "AZURE_TUNNEL": {
+            "0": "8",
+            "1": "0",
+            "2": "0",
+            "3": "2",
+            "4": "6",
+            "5": "46",
+            "6": "0",
+            "7": "48"
+    }
+    ```
+
+#### 5.1.2 Update existing TUNNEL table
+1. Change `dscp_mode` from `uniform` to `pipe` for TC remapping
+2. Add TC remapping config if TC remapping is enabled
+
+```json
+    "TUNNEL": {
+        "MuxTunnel0": {
+            "dscp_mode": "pipe",
+            "dst_ip": "10.1.0.32",
+            "ecn_mode": "copy_from_outer",
+            "encap_ecn_mode": "standard",
+            "ttl_mode": "pipe",
+            "tunnel_type": "IPINIP",
+            "decap_dscp_to_tc_map": "[DSCP_TO_TC_MAP|AZURE_TUNNEL]",
+            "decap_tc_to_pg_map": "[TC_TO_PRIORITY_GROUP_MAP|AZURE_TUNNEL]",
+            "encap_tc_to_queue_map": "[TC_TO_QUEUE_MAP|AZURE_TUNNEL]",
+            "encap_tc_color_to_dscp_map": "[TC_TO_DSCP_MAP|AZURE_TUNNEL]"
+        }
+    }
+```
+
+#### 5.1.3 Define new field for extra lossless queues
+Two new fields are added to specify software or hardward PFC watchdog.
+
+* `pfc_wd_sw_enable` Specify the queue(s) to enable software PFC watchdog
+* `pfc_wd_hw_enable` Specify the queue(s) to enable hardware PFC watchdog.
+
+In current version, software PFC watchdog will read field `pfc_enable` to determine PFCWD is enabled on which queue(s). To maintain compatible with current logic, `db_migrator` script is required to be updated.
+
+```json
+"PORT_QOS_MAP": {
+        "Ethernet0": {
+            "dscp_to_tc_map": "[DSCP_TO_TC_MAP|AZURE]",
+            "pfc_enable": "3,4,2,6",
+            "pfc_wd_sw_enable": "3,4",
+            "pfc_wd_hw_enable": "2,6",
+            "pfc_to_queue_map": "[MAP_PFC_PRIORITY_TO_QUEUE|AZURE]",
+            "tc_to_pg_map": "[TC_TO_PRIORITY_GROUP_MAP|AZURE]",
+            "tc_to_queue_map": "[TC_TO_QUEUE_MAP|AZURE]"
+        }
+}
+```
+### 5.2 SAI attribute
+TC remapping requires below SAI attributes change.
+```cpp
+    /**
+     * @brief Enable TC AND COLOR -> DSCP MAP on tunnel at encapsulation (access-to-network) node to remark the DSCP in tunnel header
+     */
+    SAI_TUNNEL_ATTR_ENCAP_QOS_TC_AND_COLOR_TO_DSCP_MAP,
+
+    /**
+     * @brief Enable TC -> Queue MAP on tunnel encap
+     */
+    SAI_TUNNEL_ATTR_ENCAP_QOS_TC_TO_QUEUE_MAP,
+
+    /**
+     * @brief Enable DSCP -> TC MAP on tunnel at termination (Network-to-access) node. This map if configured overrides the port MAP
+     */
+    SAI_TUNNEL_ATTR_DECAP_QOS_DSCP_TO_TC_MAP,
+
+    /**
+     * @brief Enable TC -> Priority Group MAP. TC is derived from the tunnel MAP
+     */
+    SAI_TUNNEL_ATTR_DECAP_QOS_TC_TO_PRIORITY_GROUP_MAP,
+```
+### 5.3 orchagent
+
+Code change in orchagent
+
+1. Update `tunneldecaporch` to read and set new tunnel attributes when creating decap tunnel.
+2. Update `create_tunnel` defined in `muxorch.cpp` to read and set new tunnel attributes when creating tunnel.
+
+## 6 Test requirement
+All changes are to be covered by system test.
+* Encap at standby side
+
+    * Test case 1 Verify DSCP re-writing
+    * test case 2 Verify traffic is egressed at expected queue
+    * Test case 3 Verify PFC frame generation at expected queue
+
+* Decap at active side
+
+    * Test case 1 Verify packets egressed to server at expected queue
+    * Test case 2 Verify PFC pause frame block expected queue
+    * Test case 3 Verify PFC frame generation at expected queue
+
+
+## 7 Open Questions
+
+
+