understanding two addresses in the simpel_desc_req

From the code, I can see there are two addresses of the interest, and the second one is what I want to get the simple descriptor of. What about the first one? should I just use the same address, as the second one? 

void MT_ZdoSimpleDescRequest(uint8 *pBuf)
{
  uint8 cmdId;
  uint8 retValue;
  uint8 epInt;
  zAddrType_t destAddr;
  uint16 shortAddr;

  /* parse header */
  cmdId = pBuf[MT_RPC_POS_CMD1];
  pBuf += MT_RPC_FRAME_HDR_SZ;

  /* Dev address */
  destAddr.addrMode = Addr16Bit;
  destAddr.addr.shortAddr = BUILD_UINT16( pBuf[0], pBuf[1] );
  pBuf += 2;

  /* Network address of interest */
  shortAddr = BUILD_UINT16( pBuf[0], pBuf[1] );
  pBuf += 2;

  /* endpoint/interface */
  epInt = *pBuf++;

  retValue = (uint8)ZDP_SimpleDescReq( &destAddr, shortAddr, epInt, 0);

  MT_BuildAndSendZToolResponse(((uint8)MT_RPC_CMD_SRSP | (uint8)MT_RPC_SYS_ZDO), cmdId, 1, &retValue);
}