传统蓝牙服务问询协议SDP概念
零.概述
本文主要介绍传统蓝牙SDP的概念，SDP在整个协议栈中的架构,SDP的UUID，服务类，以及服务类属性介绍。
服务发现协议(SDP)为应用程序提供了一种方法来发现哪些服务可用，并确定这些可用服务的特征。比如主动问询对方支持哪些蓝牙协议，或者单独问询对方蓝牙电话HFP
一. 声明
本专栏文章我们会以连载的方式持续更新，本专栏计划更新内容如下：
第一篇:蓝牙综合介绍 ，主要介绍蓝牙的一些概念，产生背景，发展轨迹，市面蓝牙介绍，以及蓝牙开发板介绍。
第二篇:Transport层介绍,主要介绍蓝牙协议栈跟蓝牙芯片之前的硬件传输协议,比如基于UART的H4,H5,BCSP，基于USB的H2等
第三篇:传统蓝牙controller介绍，主要介绍传统蓝牙芯片的介绍，包括射频层（RF），基带层（baseband），链路管理层（LMP）等
第四篇:传统蓝牙host介绍，主要介绍传统蓝牙的协议栈，比如HCI,L2CAP,SDP,RFCOMM,HFP,SPP,HID,AVDTP,AVCTP,A2DP,AVRCP,OBEX,PBAP,MAP等等一系列的协议吧。
第五篇：低功耗蓝牙controller介绍，主要介绍低功耗蓝牙芯片，包括物理层（PHY），链路层（LL）
第六篇：低功耗蓝牙host介绍，低功耗蓝牙协议栈的介绍，包括HCI,L2CAP,ATT,GATT,SM等
第七篇：蓝牙芯片介绍，主要介绍一些蓝牙芯片的初始化流程，基于HCI vendor command的扩展
第八篇：附录，主要介绍以上常用名词的介绍以及一些特殊流程的介绍等。
另外，开发板如下所示，对于想学习蓝牙协议栈的最好人手一套。以便更好的学习蓝牙协议栈，相信我，学完这一套视频你将拥有修改任何协议栈的能力（比如Linux下的bluez，Android下的bluedroid）。
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CSDN学院链接（进入选择你想要学习的课程）：https://edu.csdn.net/lecturer/5352?spm=1002.2001.3001.4144
蓝牙交流扣扣群：970324688
Github代码：https://github.com/sj15712795029/bluetooth_stack
入手开发板：https://item.taobao.com/item.htm?spm=a1z10.1-c-s.w4004-22329603896.18.5aeb41f973iStr&id=622836061708
蓝牙学习目录：http://www.noobyard.com/article/p-wkbgqcxj-nt.html
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二. SDP概念
服务发现协议(SDP)为应用程序提供了一种方法来发现哪些服务可用，并确定这些可用服务的特征。比如主动问询对方支持哪些蓝牙协议，或者单独问询对方蓝牙电话HFP，在整个蓝牙中的架构如红框内：
整个SDP是基于C/S架构，主要是client发起request,server回送response,如下图：
三. SDP常用术语
1. 服务记录
服务是任何一个能够提供信息、执行动作、或代表另一实体控制资源的实体 。服务可以以软件、硬件、或硬软件混合的形式来实现。由 SDP 服务器所维护服务的所有信息都包含于一条服务记录中。该服务记录全部由一张服务属性表组成。如下图所示：
其中服务记录包括服务句柄+服务属性服务句柄是一个32位无符号整形的数字，整个sdp server中必须唯一服务属性如下小节。
2. 服务属性
服务属性用于描述某一服务的一个特征。服务属性的实例如下：
其中服务属性的格式如下：
其中属性ID是1个16位无符号整形的数字，属性值要看ID，来决定是什么格式，属性在后面介绍
总结起来，整个服务器应该包含如下结构（0条或者多条记录）：
3.UUID
UUID 是经授权可在所有时空中保持唯一的通用定位符。UUID 可以分布的方式独立创建，而且不需要指定 UUID 的中心注册机构。UUID 值长度为 128 位。
为了减少存储压力，并便于 128 位 UUID 值的转换,UUID 值域已经为了常用和注册的目的进行预先分配。在该已分配域的第一个 UUID 作为蓝牙基 UUID，具有来自蓝牙号码分配文件的值 00000000-0000-1000-7007- 00805F9B34FB。在该已分配域的 UUID 值都具有 16 位或 32 位的别名。这些别名常被称为 16 位或 32位 UUID。但每一别名实际上都代表一个 128 位 UUID 。可以通过一个简单的数学运算计算 16 位或 32 位 UUID 的全部 128 位值。
128 位值 = 16 位值 × 2^96+ 蓝牙基 UUID
128 位值 = 32 位值 × 2^96+ 蓝牙基 UUID
通过对 16 位值进行零扩展，将 16 位 UUID 转换成为 32 位 UUID 格式。另外
一个转换方法是将 16 位值加到所有位都为零的 32 位 UUID 。
注 ：可以直接对两个 16 位 UUID 或 32 位 UUID 或 128 位 UUID 进行比较,如果要对不同大小的 UUID 进行比较，短 UUID 必须在比较前转换成为长 UUID 格式。
具体协议的UUID如下，参考：https://www.bluetooth.com/specifications/assigned-numbers/service-discovery/
Base Universally Unique Identifier (UUID)
The Base UUID is used for calculating 128-bit UUIDs from “short UUIDs” (uuid16 and uuid32) as described in the SDP Specification. See Service Discovery Protocol (SDP) in the Bluetooth Core Specification.
NOTE: Currently all assigned short UUIDs are uuid16 types.
| UUID Name | UUID |
|---|---|
| BASE_UUID | 00000000-0000-1000-8000-00805F9B34FB |
| Protocol Name | UUID | Protocol Specification |
|---|---|---|
| SDP | 0x0001 | Bluetooth Core Specification |
| UDP | 0x0002 | [NO USE BY PROFILES] |
| RFCOMM | 0x0003 | RFCOMM with TS 07.10 |
| TCP | 0x0004 | [NO USE BY PROFILES] |
| TCS-BIN | 0x0005 | Telephony Control Specification / TCS Binary [DEPRECATED] |
| TCS-AT | 0x0006 | [NO USE BY PROFILES] |
| ATT | 0x0007 | Attribute Protocol |
| OBEX | 0x0008 | IrDA Interoperability |
| IP | 0x0009 | [NO USE BY PROFILES] |
| FTP | 0x000A | [NO USE BY PROFILES] |
| HTTP | 0x000C | [NO USE BY PROFILES] |
| WSP | 0x000E | [NO USE BY PROFILES] |
| BNEP | 0x000F | Bluetooth Network Encapsulation Protocol (BNEP) |
| UPNP | 0x0010 | Extended Service Discovery Profile (ESDP) [DEPRECATED] |
| HIDP | 0x0011 | Human Interface Device Profile (HID) |
| HardcopyControlChannel | 0x0012 | Hardcopy Cable Replacement Profile (HCRP) |
| HardcopyDataChannel | 0x0014 | See Hardcopy Cable Replacement Profile (HCRP) |
| HardcopyNotification | 0x0016 | Hardcopy Cable Replacement Profile (HCRP) |
| AVCTP | 0x0017 | Audio/Video Control Transport Protocol (AVCTP) |
| AVDTP | 0x0019 | Audio/Video Distribution Transport Protocol (AVDTP) |
| CMTP | 0x001B | Common ISDN Access Profile (CIP) [DEPRECATED] |
| MCAPControlChannel | 0x001E | Multi-Channel Adaptation Protocol (MCAP) |
| MCAPDataChannel | 0x001F | Multi-Channel Adaptation Protocol (MCAP) |
| L2CAP | 0x0100 | Bluetooth Core Specification |
4. 服务类
每一服务都是服务类的一个实例。服务类定义提供对所有包含于服务记录中属性的定义，而这些服务记录就代表一个类实例。每一属性定义将给出该属性 ID的数字值、该属性值的用法及其格式。服务记录包含服务类的专用属性，以及用于所有服务的通用属性。
每一服务类将指定一个唯一标识符 。 该服务类标识符包含于ServiceClassIDList 属性的属性值，并表示为 UUID。由于服务记录中的某些属性的格式和含义依赖于服务记录的服务类,因此 ServiceClassIDList 属性非常重要。在使用任一类指定属性之前，应检查或验证它们的值。由于服务记录的所有属性必须遵循所有的服务类,包含于 ServiceClassIDList 属性中的服务类标识符也与此有关。特别要说明的是,每一服务类都是另外一类的子类，该父类的标识符包含在 ServiceClassIDList 列表中。服务子类定义与其父类不同，子类中包含该其它子类特定的属性定义。ServiceClassIDList 属性中的服务类标识符，按照从底层类到高层类的顺序一一列出。
在定义本身是另一服务类子类的新服务类时，该新类将保留父类定义的所有属性。同时，也将定义专用于新服务类的其它属性。换句话说, 向已有服务类的某些实例添加新属性的机制将创建一个新的服务类，该服务类是已有服务类的子类。
有以下服务类，如excel
| Service Class Name | UUID | Specification | Allowed Usage |
|---|---|---|---|
| ServiceDiscoveryServerServiceClassID | 0x1000 | Bluetooth Core Specification | Service Class |
| BrowseGroupDescriptorServiceClassID | 0x1001 | Bluetooth Core Specification | Service Class |
| SerialPort | 0x1101 | Serial Port Profile (SPP) NOTE: The example SDP record in SPP v1.0 does not include a BluetoothProfileDescriptorList attribute, but some implementations may also use this UUID for the Profile Identifier. |
Service Class/ Profile |
| LANAccessUsingPPP | 0x1102 | LAN Access Profile [DEPRECATED] NOTE: Used as both Service Class Identifier and Profile Identifier. |
Service Class/ Profile |
| DialupNetworking | 0x1103 | Dial-up Networking Profile (DUN) NOTE: Used as both Service Class Identifier and Profile Identifier. |
Service Class/ Profile |
| IrMCSync | 0x1104 | Synchronization Profile (SYNC) NOTE: Used as both Service Class Identifier and Profile Identifier. |
Service Class/ Profile |
| OBEXObjectPush | 0x1105 | Object Push Profile (OPP) NOTE: Used as both Service Class Identifier and Profile. |
Service Class/ Profile |
| OBEXFileTransfer | 0x1106 | File Transfer Profile (FTP) NOTE: Used as both Service Class Identifier and Profile Identifier. |
Service Class/ Profile |
| IrMCSyncCommand | 0x1107 | Synchronization Profile (SYNC) | |
| Headset | 0x1108 | Headset Profile (HSP) NOTE: Used as both Service Class Identifier and Profile Identifier. |
Service Class/ Profile |
| CordlessTelephony | 0x1109 | Cordless Telephony Profile (CTP) NOTE: Used as both Service Class Identifier and Profile Identifier. [DEPRECATED] |
Service Class/ Profile |
| AudioSource | 0x110A | Advanced Audio Distribution Profile (A2DP) | Service Class |
| AudioSink | 0x110B | Advanced Audio Distribution Profile (A2DP) | Service Class |
| A/V_RemoteControlTarget | 0x110C | Audio/Video Remote Control Profile (AVRCP) | Service Class |
| AdvancedAudioDistribution | 0x110D | Advanced Audio Distribution Profile (A2DP) | Profile |
| A/V_RemoteControl | 0x110E | Audio/Video Remote Control Profile (AVRCP) NOTE: Used as both Service Class Identifier and Profile Identifier. |
Service Class/ Profile |
| A/V_RemoteControlController | 0x110F | Audio/Video Remote Control Profile (AVRCP) NOTE: The AVRCP specification v1.3 and later require that 0x110E also be included in the ServiceClassIDList before 0x110F for backwards compatibility. |
Service Class |
| Intercom | 0x1110 | Intercom Profile (ICP) NOTE: Used as both Service Class Identifier and Profile Identifier. [DEPRECATED] |
Service Class |
| Fax | 0x1111 | Fax Profile (FAX) NOTE: Used as both Service Class Identifier and Profile Identifier. [DEPRECATED] |
Service Class |
| Headset – Audio Gateway (AG) | 0x1112 | Headset Profile (HSP) | Service Class |
| WAP | 0x1113 | Interoperability Requirements for Bluetooth technology as a WAP, Bluetooth SIG [DEPRECATED] | Service Class |
| WAP_CLIENT | 0x1114 | Interoperability Requirements for Bluetooth technology as a WAP, Bluetooth SIG [DEPRECATED] | Service Class |
| PANU | 0x1115 | Personal Area Networking Profile (PAN) NOTE: Used as both Service Class Identifier and Profile Identifier for PANU role. |
Service Class / Profile |
| NAP | 0x1116 | Personal Area Networking Profile (PAN) NOTE: Used as both Service Class Identifier and Profile Identifier for NAP role. |
Service Class / Profile |
| GN | 0x1117 | Personal Area Networking Profile (PAN) NOTE: Used as both Service Class Identifier and Profile Identifier for GN role. |
Service Class / Profile |
| DirectPrinting | 0x1118 | Basic Printing Profile (BPP) | Service Class |
| ReferencePrinting | 0x1119 | See Basic Printing Profile (BPP) | Service Class |
| Basic Imaging Profile | 0x111A | Basic Imaging Profile (BIP) | Profile |
| ImagingResponder | 0x111B | Basic Imaging Profile (BIP) | Service Class |
| ImagingAutomaticArchive | 0x111C | Basic Imaging Profile (BIP) | Service Class |
| ImagingReferencedObjects | 0x111D | Basic Imaging Profile (BIP) | Service Class |
| Handsfree | 0x111E | Hands-Free Profile (HFP) NOTE: Used as both Service Class Identifier and Profile Identifier. |
Service Class / Profile |
| HandsfreeAudioGateway | 0x111F | Hands-free Profile (HFP) | Service Class |
| DirectPrintingReferenceObjectsService | 0x1120 | Basic Printing Profile (BPP) | Service Class |
| ReflectedUI | 0x1121 | Basic Printing Profile (BPP) | Service Class |
| BasicPrinting | 0x1122 | Basic Printing Profile (BPP) | Profile |
| PrintingStatus | 0x1123 | Basic Printing Profile (BPP) | Service Class |
| HumanInterfaceDeviceService | 0x1124 | Human Interface Device (HID) NOTE: Used as both Service Class Identifier and Profile Identifier. |
Service Class / Profile |
| HardcopyCableReplacement | 0x1125 | Hardcopy Cable Replacement Profile (HCRP) | Profile |
| HCR_Print | 0x1126 | Hardcopy Cable Replacement Profile (HCRP) | Service Class |
| HCR_Scan | 0x1127 | Hardcopy Cable Replacement Profile (HCRP) | Service Class |
| Common_ISDN_Access | 0x1128 | Common ISDN Access Profile (CIP) NOTE: Used as both Service Class Identifier and Profile Identifier. [DEPRECATED] |
Service Class / Profile |
| SIM_Access | 0x112D | SIM Access Profile (SAP) NOTE: Used as both Service Class Identifier and Profile Identifier. |
Service Class / Profile |
| Phonebook Access – PCE | 0x112E | Phonebook Access Profile (PBAP) | Service Class |
| Phonebook Access – PSE | 0x112F | Phonebook Access Profile (PBAP) | Service Class |
| Phonebook Access | 0x1130 | Phonebook Access Profile (PBAP) | Profile |
| Headset – HS | 0x1131 | Headset Profile (HSP) NOTE: See erratum #3507. 0x1108 and 0x1203 should also be included in the ServiceClassIDList before 0x1131 for backwards compatibility. |
Service Class |
| Message Access Server | 0x1132 | Message Access Profile (MAP) | Service Class |
| Message Notification Server | 0x1133 | Message Access Profile (MAP) | Service Class |
| Message Access Profile | 0x1134 | Message Access Profile (MAP) | Profile |
| GNSS | 0x1135 | Global Navigation Satellite System Profile (GNSS) | Profile |
| GNSS_Server | 0x1136 | Global Navigation Satellite System Profile (GNSS) | Service Class |
| 3D Display | 0x1137 | 3D Synchronization Profile (3DSP) | Service Class |
| 3D Glasses | 0x1138 | 3D Synchronization Profile (3DSP) | Service Class |
| 3D Synchronization | 0x1139 | 3D Synchronization Profile (3DSP) | Profile |
| MPS Profile UUID | 0x113A | Multi-Profile Specification (MPS) | Profile |
| MPS SC UUID | 0x113B | Multi-Profile Specification (MPS) | Service Class |
| CTN Access Service | 0x113C | Calendar, Task, and Notes (CTN) Profile | Service Class |
| CTN Notification Service | 0x113D | Calendar Tasks and Notes (CTN) Profile | Service Class |
| CTN Profile | 0x113E | Calendar Tasks and Notes (CTN) Profile | Profile |
| PnPInformation | 0x1200 | Device Identification (DID) NOTE: Used as both Service Class Identifier and Profile Identifier. |
Service Class / Profile |
| GenericNetworking | 0x1201 | N/A | Service Class |
| GenericFileTransfer | 0x1202 | N/A | Service Class |
| GenericAudio | 0x1203 | N/A | Service Class |
| GenericTelephony | 0x1204 | N/A | Service Class |
| UPNP_Service | 0x1205 | Enhanced Service Discovery Profile (ESDP) [DEPRECATED] | Service Class |
| UPNP_IP_Service | 0x1206 | Enhanced Service Discovery Profile (ESDP) [DEPRECATED] | Service Class |
| ESDP_UPNP_IP_PAN | 0x1300 | Enhanced Service Discovery Profile (ESDP) [DEPRECATED] | Service Class |
| ESDP_UPNP_IP_LAP | 0x1301 | Enhanced Service Discovery Profile (ESDP)[DEPRECATED] | Service Class |
| ESDP_UPNP_L2CAP | 0x1302 | Enhanced Service Discovery Profile (ESDP)[DEPRECATED] | Service Class |
| VideoSource | 0x1303 | Video Distribution Profile (VDP) | Service Class |
| VideoSink | 0x1304 | Video Distribution Profile (VDP) | Service Class |
| VideoDistribution | 0x1305 | Video Distribution Profile (VDP) | Profile |
| HDP | 0x1400 | Health Device Profile | Profile |
| HDP Source | 0x1401 | Health Device Profile (HDP) | Service Class |
| HDP Sink | 0x1402 | Health Device Profile (HDP) | Service Class |
| (Max value 0xFFFF) |
五.特定类属性
具体参照,如图：
我们以截图的方式给出：