[CCNA]Switch @ 兔子銘的紅蘿蔔園區

問題：何時需要增加交換機(Switch)？

解答：建議當出現下列情況時，建議增加交換機。

(1). 網路上碰撞嚴重，導致訪問伺服器的時間延長。

(2). 每個碰撞域內網路傳輸緩慢。

(3). 由於某處頻寬出現瓶頸，導致網路不暢通。

(4). 網路流量加重，導致頻寬不足。

問題：交換器(switch)的傳輸方式有幾種，有何不同？

解答：交換機有三種傳輸方式：Cut Through / Store and Forward / Fragment Free

※(1) Store-and-Forward：接收到完整的資料包後，會檢查data FCS，無誤後才轉發，壞的丟棄重發。傳輸可靠，但延時較長。(最普遍與常用)

(2) Cut Through：接收到目的地址後即轉發出去。延時小，但壞的資料一樣轉發。

(3) Fragment free：接收到資料包後，大於64bytes的轉發，小於64bytes的丟棄。只要接收到滿足64bytes的條件時即

開始傳送資料，不像(1)會完整接收到資料包後再轉送，好壞介於上述兩種方式之間。

故(2)、(3)缺點：並不會對資料做FCS check

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<% Function googleColor(value, random) Dim colorArray colorArray = Split(value, ",") googleColor = colorArray(random Mod (UBound(colorArray) + 1)) End Function Function googleScreenRes() Dim screenRes, delimiter, resArray screenRes = Request.ServerVariables("HTTP_UA_PIXELS") delimiter = "x" If IsEmpty(screenRes) Then screenRes = Request.ServerVariables("HTTP_X_UP_DEVCAP_SCREENPIXELS") delimiter = "," End If If IsEmpty(screenRes) Then screenRes = Request.ServerVariables("HTTP_X_JPHONE_DISPLAY") delimiter = "*" End If resArray = Split(screenRes, delimiter, 2) If (UBound(resArray) + 1) = 2 Then googleScreenRes = "&u_w=" & resArray(0) & "&u_h=" & resArray(1) End If End Function Function googleMuid() Dim muid muid = Request.ServerVariables("HTTP_X_DCMGUID") If Not IsEmpty(muid) Then googleMuid = "&muid=" & muid End If muid = Request.ServerVariables("HTTP_X_UP_SUBNO") If Not IsEmpty(muid) Then googleMuid = "&muid=" & muid End If muid = Request.ServerVariables("HTTP_X_JPHONE_UID") If Not IsEmpty(muid) Then googleMuid = "&muid=" & muid End If muid = Request.ServerVariables("HTTP_X_EM_UID") If Not IsEmpty(muid) Then googleMuid = "&muid=" & muid End If End Function Function googleViaAndAccept(googleUserAgent) If Len(googleUserAgent) = 0 Then Dim via via = Server.URLEncode(Request.ServerVariables("HTTP_VIA")) If Not IsEmpty(via) Then googleViaAndAccept = "&via=" & via End If Dim accept accept = Server.URLEncode(Request.ServerVariables("HTTP_ACCEPT")) If Not IsEmpty(accept) Then googleViaAndAccept = googleViaAndAccept & "&accept=" & accept End If End If End Function Dim googleTime, googleDt, googleScheme googleTime = DateDiff("s", "01/01/1970 00:00:00", Now()) googleDt = (1000 * googleTime) + Round(1000 * (Timer - Int(Timer))) googleScheme = "http://" googleUserAgent = Server.URLEncode(Request.ServerVariables("HTTP_USER_AGENT")) If StrComp(Request.ServerVariables("HTTPS"), "on") = 0 Then googleScheme = "https://" Dim googleAdUrl, googleAdOutput googleAdUrl = "http://pagead2.googlesyndication.com/pagead/ads?" &_ "ad_type=image" &_ "&channel=5508576909" &_ "&client=ca-mb-pub-9889718099577998" &_ "&color_border=" & googleColor("336699,6699CC", googleTime) &_ "&color_bg=" & googleColor("FFFFFF,003366", googleTime) &_ "&color_link=" & googleColor("0000FF,FFFFFF", googleTime) &_ "&color_text=" & googleColor("000000,AECCEB", googleTime) &_ "&color_url=" & googleColor("008000,AECCEB", googleTime) &_ "&dt=" & googleDt &_ "&format=mobile_single" &_ "&ip=" & Server.URLEncode(Request.ServerVariables("REMOTE_ADDR")) &_ "&markup=xhtml" &_ "&oe=utf8" &_ "&output=xhtml" &_ "&ref=" & Server.URLEncode(Request.ServerVariables("HTTP_REFERER")) &_ "&url=" & Server.URLEncode(googleScheme & Request.ServerVariables("HTTP_HOST") & Request.ServerVariables("URL")) &_ "&useragent=" & googleUserAgent &_ googleScreenRes() &_ googleMuid() &_ googleViaAndAccept(googleUserAgent) Set googleAdOutput = Server.CreateObject("MSXML2.ServerXMLHTTP") googleAdOutput.Open "GET", googleAdUrl, false googleAdOutput.Send Response.Write(googleAdOutput.responseText) %>