TAPI Set Information Requests 的问题！

9.2 TAPI Set Information Requests
OID_TAPI_ANSWER
这个结构中有一个hdCall IN参数，其描述如下：
1）Specifies the miniport's handle to the call to be answered. The driver set this handle up when it called NdisMIndicateStatus with the LINE_EVENT_NEWCALL indication.

2）NdisMIndicateStatus ： indicates changes in the status of a NIC to higher-level NDIS drivers.

3）WAN miniports return no information for set requests other than the completion status. All OID-specific structures are provided by the protocol driver, and their members are read-only to the underlying WAN NIC miniport.

问题在于3）说OID-TAPI -ANSWER的结构由协议驱动设置，结构成员对NIC只读，从1）2）的说法推断，hdCall是由小端口驱动设置的 啊？

这是为什么呀？

“只读”是指在该OID_TAPI_XXX的set infomation操作中只读，不是指在整个过程中都不能被小端口改变。hdCall是在最初该呼叫事件(newCall)到来时被小端口设置的。
见：
The driver set this handle up when it called NdisMIndicateStatus with the LINE_EVENT_NEWCALL indication