16．下列哪項不屬于虛擬局域網(wǎng)的功能（　　�。�

A．控制廣播數(shù)據(jù)                                    B．增強網(wǎng)絡(luò)安全性

C．實現(xiàn)第三層交換                                 D．減少站點移動和改變的開銷

17．為帶寬并不確定的突發(fā)式通信設(shè)計的ATM高層服務(wù)是（　　　）

A．ABR                                                   B．CBR

C．UBR                                                   D．VBR

18．為保證一定的業(yè)務(wù)質(zhì)量，ATM層用于實現(xiàn)阻塞控制的字段是（　　�。�

A．VPI                                                    B．VCI

C．PTI                                                    D．CLP

19．常用的簡單網(wǎng)絡(luò)管理協(xié)議是（　　�。�

A．SMTP                                                B．RMON

C．RMON Ⅱ                                          D．SNMP

20．HTTP協(xié)議實現(xiàn)的Internet應(yīng)用是（　　�。�

A．網(wǎng)上聊天                                           B．web瀏覽

C．代理服務(wù)                                           D．遠程登錄