【導(dǎo)讀】的路徑傳送就是能依靠網(wǎng)絡(luò)的條件了。包交換技術(shù)比線路交換技術(shù)更能容錯。事實(shí)上，這也是它被發(fā)明的理由！此時(shí)如果在進(jìn)行包交換，包將在已選擇的路徑上停止交換。預(yù)先建立一條路徑也開創(chuàng)預(yù)先保留帶寬的可能性。一個(gè)包到達(dá)時(shí)，通過保留的帶寬它可以被立即發(fā)送出去。于包交換，那么所有的包將不得不等待著被轉(zhuǎn)發(fā)。留下來的帶寬將被浪費(fèi)而不能用于其它用戶的傳輸。包交換是利用存儲器并向前發(fā)送的。送到下一個(gè)路由器的。都是透明的它允許聲音，數(shù)據(jù)和傳真共同存在于電話系統(tǒng)里。比如移動電話除打國際電話外距離是不列入計(jì)算的，而時(shí)間。絡(luò)中心的收費(fèi)是基于它們的流量的。美國政府決定不把標(biāo)準(zhǔn)商業(yè)化因而它失去了數(shù)字市場。即使美國擁有移動電話的所有權(quán)，但是在應(yīng)用上歐洲要遠(yuǎn)遠(yuǎn)超過美國的。因之一就是整個(gè)歐洲擁有相同的簡單系統(tǒng)。移動電話充分體現(xiàn)了政治和市場的特征。

　　

【正文】 ub Form_Load () 39。 Establishes DataGrid controls the data pool = AdScore 39。 Establishes ADO controls the connection character string and the initial record source, namely demonstration content = Provider=。 Persist_Security Info=False。 Data Source= student information = selet * from student result order by result 39。 Supposes in advance withdraws the SQL sentence which the recording uses Rs (1) = select * from the student result where result = + Chr (34) + is superior + _Chr (34) + order the by result Rs (2) = select * from the student result where result = + Chr (34) + is good + _Chr (34) + order the by result Rs (3) = select * from student result where result = + Chr (34) + center + _Chr 16 (34) + order by result Rs (4) = select * from student result where result = + Chr (34) + difference _Chr (34) + order by result End Sub Private Sub MC$score_SeriesSelected (Series as Integer, MouseFlags as _Integer, Cancel as Integer) SelectedSeries=Series End Sub Private Sub MC$score_PointSelected (Series as Integer, DataPoint as_Integer, MouseFlags as Integer, Cancel as Integer) SelectedSeries=Series End Sub Private Sub MC$score_Db1Click () 39。 Changes ADO controls the record source and renovates =Rs (SeletedSeries) End Sub VB does for the rapid application development (RAD) the tool more and more obtains the development personnel39。s approval and accepts. It to many API (for example ODBC API, SOCKET API and so on) the seal causes the programming to change is simple. At the same time, it supports under the integrated development environment visible, the event actuates, to be objectoriented and so on the programming characteristic. Under, we chat in VB transfer the memory process the realization method and its the matters needing attention. We know, the VB database programming has permits the many kinds of method, for instance straight takes over the use of ODBC the API programming, this method is flexible, is highly effective, the programmer may realize to the database plex control。 Also may use in VB the data object, like RDO (longdistance data object), 17 DAO (data visit object), ADO (ActiveX data object), this method realizes conveniently, quickly, but flexible worse somewhat. As a result of memory process in realization data merit and so on seal, hideaway as well as code pre translation, reduced work load, maintenance convenience, therefore does by many RDBMS and the programming tool the support. In VB each 類數(shù) also provides to saves the process according to the object the support. We as regularly explain its realization take ADO the step 1. Foundation, debugging memory process. You may also be allowed to hang the procedure in the database outside other under the support carry on the memory process the foundation and the debugging work. In this example memory process code is as follows (uses in PUBS MS SQL the example storehouse): CREATE PROCEDURE myprocedure @job_id smallint, @job_lvl tinyint AS SELECT * FROM employee WHERE job_id @job_id AND job_lvl @job_lvl 2. Produces one new project in VB, the project has one window, one COMMAND (NAME: COMMAND1) button, one MSFlexGrid (NAME: MSFlexGrid1) controls. 3. The foundation connects ADO connection。 4. The foundation orders ADO mand。 18 5. The foundation parameter and establishes each parameter the attribute。 6. Carries out ADO mand。 7. The logarithm according to carries on processing。 MSFlexGrid demonstrates inquires data 8. The release connects, withdrawal procedure. Code as follows: States below the variable in the window: Dim n1 As 39。 connects Dim mymand As 39。 orders Dim parm_jobid As 39。 parameter 1 Dim parm_joblvl As 39。 parameter 2 Dim rstByQuery As 39。 result collection Dim strCnn As String 39。 connection character string Joins the following code in the window LOAD event: Set n1 = New 39。 Produces one connects strCnn = \ DSN=MYDSN。 uid=sa。 pwd=\ 39。 Foundation system data pool MYDSN aims at the PUBS database strCnn 39。 opens connects Joins the code as follows in window UNLOAD: 39。 the closure connects Set n1 = Nothing 39。 the release connects In button code as follows: 19 Dim i As integer Dim j as integer Set parm_jobid = New Set mymand = New \39。 = \ name1\ this line can be ommited = adInteger 39。