Megaco/H.248 is a protocol for control of elements in a physically decomposed multimedia gateway, enabling separation of call control from media conversion. A Media Gateway Controller (MGC) controls one or more Media Gateways (MG).

Megaco有非常清晰的日誌和診斷供我們參考, 精細到幾行程式碼一個診斷資訊, 非常好的風格. 有了這些資訊對系統的執行完全瞭如指掌.

有3種方式:
1. 大量的除錯日誌, 在DEBUG方式下, 會有大量的系統允許期間的軌跡和訊息

%%%----------------------------------------------------------------------                                                                                                                         %%% Debug                                                                                                                                                                                                      
%%%----------------------------------------------------------------------  
-ifdef(megaco_debug).                                                                               
-define(d(F,A), io:format("~w: " ++ F ++ "~n",[?MODULE|A])). 
-else.
-define(d(F,A), ok).
-endif.

用起來很方便, 摘抄一段如下

?d("encode(~p) -> entry with"
"~n   PackageItem: ~p"
"~n   SubItem:     ~p", [Scope, PackageItem, SubItem]),

2. 異常日誌, 用於記錄程式允許中間產生的各種各樣的異常, 便於事後調查.

%%%----------------------------------------------------------------------                                                                                                                         %%% Error/warning/info message macro(s)                                                                                                                                                                        
%%%----------------------------------------------------------------------                                                                                                                         -define(megaco_info(F, A),                                                                                                                                                                                     
        (catch error_logger:info_msg("[ ~w : ~w : ~p ] ~n" ++ F ++ "~n", [?APPLICATION, ?MODULE, self()|A]))).
                                                                                                                                                                                                               
-define(megaco_warning(F, A),                                                                                                                                                                                  
        (catch error_logger:warning_msg("[ ~w : ~w : ~p ] ~n" ++ F ++ "~n", [?APPLICATION, ?MODULE, self()|A]))).
                                                                                                                                                                                                               
-define(megaco_error(F, A),                                                                                                                                                                                    
        (catch error_logger:error_msg("[ ~w : ~w : ~p ] ~n" ++ F ++ "~n",[?APPLICATION, ?MODULE, self()|A]))). 

使用, 摘抄一段如下

warning_msg(F, A) ->                                                                                
   ?megaco_warning("Transaction sender: " ++ F, A). 
error_msg(F, A) ->                                       
   ?megaco_error("Transaction sender: " ++ F, A).

3. Event Trace機制
先進的trace能夠讓系統的訊息互動,執行軌跡以可視的方式體現在使用者面前.

%%%----------------------------------------------------------------------                                                                                                                         
%%% Event Trace                                                                                                                                                                                                
%%%----------------------------------------------------------------------                                                                                                                         -ifdef(megaco_trace_io).
-define(report(Level, C, Label, Contents),
        io:format("*** [~s] ~p ~p *** "
                  "~n   ~p[~p] " ++ Label ++
                  "~n   ~p"
                  "~n   ~p"
                  "~n",
                  [megaco:format_timestamp(now()),
                   self(), Level, ?MODULE, ?LINE, C, Contents])).
-else.
-define(report(Level, C, Label, Contents),
        megaco:report_event(Level, ?APPLICATION, Label,
                            [{line, ?MODULE, ?LINE}, C | Contents])).
-endif.

-define(report_important(C, Label, Contents), ?report(20, C, Label, Contents)).
-define(report_verbose(  C, Label, Contents), ?report(40, C, Label, Contents)).
-define(report_debug(    C, Label, Contents), ?report(60, C, Label, Contents)).
-define(report_trace(    C, Label, Contents), ?report(80, C, Label, Contents)).

使用, 摘抄一段如下

?report_trace(ReceiveHandle, "callback: syntax error", [ErrorDesc, Error]), 

實際效果圖(點選放大):

總結: ET很強大, 而且是專門為Megaco開發的, 目的就是能夠視覺化看到Megaco系統元件見的訊息流程互動.

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