SOME/IP--协议英文原文讲解8

前言
SOME/IP协议越来越多的用于汽车电子行业中，关于协议详细完全的中文资料却没有，所以我将结合工作经验并对照英文原版协议做一系列的文章。基本分三大块：

1. SOME/IP协议讲解

2. SOME/IP-SD协议讲解

3. python/C++举例调试讲解

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4.2 Specification of SOME/IP Protocol
This chapter describes the Remote Procedure Call(RPC), Event Notifications and Error
Handling of SOME/IP.

4.2.1 Transport Protocol Bindings
In order to transport SOME/IP messages different transport protocols may be used.
SOME/IP currently supports UDP and TCP. Their bindings are explained in the following sections,
while Chapter 6 discusses which transport protocol to choose.

SOME/IP支持TCP/UDP传输 第6章讲怎么选择

[PRS_SOMEIP_00138]
Upstream requirements: RS_SOMEIP_00015
If a server runs different instances of the same service, messages belonging to different
service instances shall be mapped to the service instance by the transport protocol
port on the server side.
For details of see Chapter 4.2.1.3

不同的服务实例在不同的server上要用port区分

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什么是 服务实例？

 服务 是给一组或一种功能 编的号码。如果多个设备同时都提供这个服务，那怎么区分呢？
就在服务ID的基础上 再进一步区分实例ID，实例就是实现这个服务的不同设备。给这些设备编上不同ID，这个ID就是实例ID。

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[PRS_SOMEIP_00535]
Upstream requirements: RS_SOMEIP_00010
All Transport Protocol Bindings shall support transporting more than one SOME/IP
message in a Transport Layer PDU (i.e. UDP packet or TCP segment).
TCP UDP 都应支持SOME/IP的聚包发送 -- 单条UDP/TCP消息中有多条SOME/IP消息组合在一起
[PRS_SOMEIP_00142]
Upstream requirements: RS_SOMEIP_00010
The receiving SOME/IP implementation shall be capable of receiving unaligned
SOME/IP messages transported by UDP or TCP.
传输层过来的多条消息长度不同的SOMEIP消息 要能够拆分解析
Rationale:
When transporting multiple SOME/IP payloads in UDP or TCP the alignment of the
payloads can be only guaranteed, if the length of every payloads is a multiple of the
alignment size (e.g. 32 bits).

[PRS_SOMEIP_00140]
Upstream requirements: RS_SOMEIP_00010
The header format allows transporting more than one SOME/IP message in a single
packet. The SOME/IP implementation shall identify the end of a SOME/IP message by
means of the SOME/IP length field.