计算机英语课件-p6.1

?2 What is VPN and why do we need VPN ?
2. What Does a VPN Do?
A virtual private network is a way to simulate a private network over a public network, s同u位c语h as the
原因状语从句
Internet. It is called "virtual" because it depends on the use of virtual connections-t同h位at语is从,句temporary
定语从句
connections that have no real physical presence, but
email system, and even its own favorite network
同位语从句
protocol-none of which might be compatible with other
时间状语从句
offices’ setups. As more company resources moved to
ISP (Internet Service Provider) 因特网服务提供商
POP (Point-Of-Presence)
接入点
roaming user
漫游用户
Intranet
因特网内部网
Extranet
因特网外部网
Web server
万维网服务器
laptop
膝上（电脑）
1. Why Build a Virtual Private Network? Until now there has always been a clear division between public and private networks. A public network, like the public telephone system and the Internet, is a
定语从句
may be cases, however, where you’ll want far-flung offices to share data or remote users to connect to your Intranet, and these users may be using the Internet as their means of connection.
原因状语从句
reach of an intranets. Since Intranets are typically used to communicate proprietary information, you don’t want them accessible from the Internet. There
?1 Who can have and use private network ? There also was a time, not too long ago, 定w语he从n句 companies could allow their LANs to operate as separate, isolated islands. Each branch office might have its own LAN, with its own naming scheme,
Even many of the smaller ISPs have toll-free numbers
for their roaming users. At the time of this writing,
unlimited access dial-up PPP accounts, suitable for business use, are around $25 per month per user.[6] At any rate, well-chosen ISP accounts should be c比h较eaper
?3 Dose VPN have a real physical connection ?
Using the Internet for remote access saves a lot of money. You’ll be able to dial i介n词w宾h语er从e句ver your Internet service provider (ISP) has a point-ofpresence (POP). If you choose an ISP with nationwide POPs, there’s a good chance y定o语u从r L句AN will be a local phone call away. Some ISPs have expanded internationally as well, or have alliances with ISPs overseas.
based upon a flat monthly fee, plus mileage expenses.
条件状语从句
If a company has offices across the country, this cost
can be prohibitive. Private networks also have trouble handling moving users, 同su位c语h as traveling salespeople.
extremely expensive proposition.
定语从句
The virtual private network (VPN) is a concept that
blurs the line between a public and private network.
VPNs allow you to create a secure, private network over a public network such as the Internet. They can be created using software, hardware, or a combination of the two that creates a secure link between peers over a public network. This is done through encryption, authentication, packet tunneling, and firewalls.[4]
条件状语从句
If the salesperson doesn’t happen to be near one of
the corporate computers, he or she has to dial into a
非限定性定语从句
corporation’s modem long-distance, which is an
purchase hours in bulk from the long-distance
companies.
?4 What is the major benefit of using VPN ? 3. How VPNs relate to Intranets Virtual private networks can be used to expand the
are going to be the only ones using the network, and
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that information sent between them will (at worst) only be seen by others in the group.[2] The typical
KEYWORDS
VPN (Virtual Private Network) 虚拟专用网
public network
公用网
gateway
网关
router
路由器
firewall
防火墙
protocol
协议
link
链路，链接
encryption
加密
authentication
验证
tunneling
隧道技术
consist of packets routed over various machines on the Internet on an ad hoc basic.[5] Secure virtual
connections are created between two machines, a
machine and a network, or two networks.
corporate Local Area Network (LAN) or Wide Area
Network (WAN) is an Example of a private network.
The line between a private and public network has
always been drawn at the gateway router,
computers, however, there came a need for these
offices to interconnect. This was traditionally done using
leased phone lines of varying speeds. By using leased
w非h限e定r性e 定a语c从om句pany will erect a firewall to keep intruders from the public network out of their private network, or to keep their own internal users from perusing the public network.[3]