我正在尝试从sharepoint读取excel文件的范围，所以我使用了microsoft graph。但随机它会引发以下问题。
{"readyState":4,"responseText":"{\r\n \"error\": {\r\n \"code\": \"MaxRequestDurationExceeded\",\r\n \"message\": \"Service Unavailable.\",\r\n \"innerError\": {\r\n \"request-id\": \"ddd-9a30-eee-927a-fff\",\r\n \"date\": \"2018-04-24T10:37:29\"\r\n }\r\n }\r\n}","responseJSON":{"error":{"code":"MaxRequestDurationExceeded","message":"Service Unavailable.","innerError":{"request-id":"5ef4e30d-9a30-48a0-927a-8a540e96f495","date":"2018-04-24T10:37:29"}}},"status":504,"statusText":"Gateway Timeout"} collection https://graph.microsoft.com/v1.0/sites/xxx.sharepoint.com,aaa,bbb/drives/ccc/items/dddN/workbook/worksheets('Toc-Master')/usedRange?$select=values
如何解决此问题。