协议栈 关于端点的问题

有几个问题想请教：

1、数据传输时，afAddrType_t 目标地址中的 endPoint ，端点，作用是什么，表示什么意思

// Fill out the endpoint description.
SampleApp_epDesc.endPoint = SAMPLEAPP_ENDPOINT;
SampleApp_epDesc.task_id = &SampleApp_TaskID;
SampleApp_epDesc.simpleDesc
= (SimpleDescriptionFormat_t *)&SampleApp_SimpleDesc;
SampleApp_epDesc.latencyReq = noLatencyReqs;

// Register the endpoint description with the AF
afRegister( &SampleApp_epDesc );

2、这里注册的描述是什么，为什么也是同一个值SAMPLEAPP_ENDPOINT

3、传输数据时这个endPoint是否重要？如果是，网络中的协调器、终端节点又该如何设定值 

typedef struct { osal_event_hdr_t hdr; /* OSAL Message header *///OSAL消息头 uint16 groupId; /* Message's group ID - 0 if not set *///消息组ID uint16 clusterId; /* Message's cluster ID *///消息族ID afAddrType_t srcAddr; /* Source Address, if endpoint is STUBAPS_INTER_PAN_EP, it's an InterPAN message *///源地址类型 uint16 macDestAddr; /* MAC header destination short address *///MAC物理地址 uint8 endPoint; /* destination endpoint */ //目的端点 uint8 wasBroadcast; /* TRUE if network destination was a broadcast address *///广播地址 uint8 LinkQuality; /* The link quality of the received data frame */ //接收数据帧的链路质量 uint8 correlation; /* The raw correlation value of the received data frame *///接收数据帧的未加工相关值。 int8 rssi; /* The received RF power in units dBm *///接收的射频功率。 uint8 SecurityUse; /* deprecated *///弃用 uint32 timestamp; /* receipt timestamp from MAC *///收到时间标记。 afMSGCommandFormat_t cmd; /* Application Data */应用程序数据 } afIncomingMSGPacket_t; //无线数据包格式结构体