計算機網(wǎng)絡(luò)(網(wǎng)絡(luò)學(xué)院)41

1、2345678lCaption: A Proxim RangeLAN wireless local area network interface card. Also shown is a table-top antenna which attaches to the interface card. 9lCaption: An AirLAN wireless local area network interface card. The white rectangular object is a wall or ceiling mount antenna which attaches to th

2、e interface. 10lCaption: A RangeLAN wireless local area network PCMCIA interface card. The black object attached to the left of the card is its antenna. 11lCaption: A RangeLAN wireless PCMCIA network interface card. Attached is its wireless tranceiver and antenna. 121314CT1NTCNNNCT)/()/(115站點模型：每個站點

3、是獨立的，并以統(tǒng)計固定的速率產(chǎn)生幀，一幀產(chǎn)生后到被發(fā)送走之前，站點被封鎖；單信道假設(shè)：所有的通信都是通過單一的信道來完成的，各個站點都可以從信道上收發(fā)信息；沖突假設(shè)：若兩幀同時發(fā)出，會相互重疊，結(jié)果使信號無法辨認，稱為沖突。所有的站點都能檢測到?jīng)_突，沖突幀必須重發(fā)；連續(xù)時間和時間分槽（確定何時發(fā)送）；載波監(jiān)聽和非載波監(jiān)聽（確定能否發(fā)送）。1617在純在純ALOHA中，完全任意地發(fā)送幀中，完全任意地發(fā)送幀18! keGGk19陰影幀的沖突危險區(qū)陰影幀的沖突危險區(qū)20 ALOHA系統(tǒng)中吞吐率和幀產(chǎn)生率之間的關(guān)系系統(tǒng)中吞吐率和幀產(chǎn)生率之間的關(guān)系2122232425各種隨機訪問協(xié)議的信道利用和載荷曲線的比較各種隨機訪問協(xié)議的信道利用和載荷曲線的比較五種多路訪問協(xié)議性能比較26272829303132333411/1Prkkkkp35對稱競爭信道獲取概率對稱競爭信道獲取概率36373839各站每小時18次，一萬個站，所以一秒鐘有180000/3600=50個請求，一個槽是一個槽是125 s，一秒鐘有，一秒鐘有8000個槽。所以平均每個時槽發(fā)送次數(shù)為：個槽。所以