電路交換網與vb調用數據庫[外文翻譯]


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中文：4100字
英文：13000字



電路交換網與vb調用數據庫

切換電路的連接設置的結果是保留了從發(fā)送端到接收端的包所通過的線路帶寬。其它的特性這一就是所有的包都沿同一個線路意味著如果包傳輸超過了時序那它將不能到達接收端.由于沒有路徑用來進行包交換，所以要想不同的包沿不同的路徑傳送就是能依靠網絡的條件了。這樣包即便是超過了時序它們也有可能到達的。
包交換技術比線路交換技術更能容錯。事實上，這也是它被發(fā)明的理由！當一個交換開頭被拉下，則所有使用它的線路將被切斷并且其余的包將不能再被傳送。此時如果在進行包交換，包將在已選擇的路徑上停止交換。
預先建立一條路徑也開創(chuàng)預先保留帶寬的可能性。如果帶寬被保留，那么當一個包到達時，通過保留的帶寬它可以被立即發(fā)送出去。假如沒有帶寬被保留用于包交換，那么所有的包將不得不等待著被轉發(fā)。
預先保留帶寬意味著當一個包出現時不會發(fā)生擁塞(除非出現的包比預期的還多)。在另一方面,當嘗試建立一條電路時，由于擁塞，嘗試將會失敗。因此，在線路交換(在設置時)和包交換(在包發(fā)送時)的不同時間擁塞都可能發(fā)生。





Electric circuit exchange network
and vb transfer database

The result of the connection setup with circuit switching is the reservation of bandwidth all the way from the sender to the receiver. All packets follow this path. Among other properties, having all packets follow the same path means that they cannot arrive out of order. With packet switching there is no path , so different packets can follow different paths, depending on network conditions at the time they are sent. They may arrive out of order.
Packet switching is more fault tolerant than circuit switching. In fact, that is why it was invented. If a switch goes down, all of the circuits using it are terminated and no more traffic can be sent on any of them. With Packet switching, packets can be routed around dead switches.
Setting up a path in advance also opens up the possibility of reserving bandwidth in advance. If bandwidth is reserved, then when a packet arrives, it can be sent out immediately over the reserved bandwidth. With packet switching, no bandwidth is reserved, so packets may have to wait their turn to be forwarded.