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Another savings that can be considered when the Internet is used to connect corporate locations concerns the use of router ports. In Exhibit 1 only three serial router ports are required to provide three locations with the ability to communicate with each other. Now assume the number of corporate locations increased to four. Then four routers with one serial port per router would be required to enable communications between any location via the Internet. In comparison, you could connect four locations on a private network with four leased lines as shown in the top portion of Exhibit 2. In doing so each router would require two serial ports. Since router ports can easily cost $1000 or more, the use of a private router based network to interconnect a large number of geographically separated organizational locations can result in the cost of routers considerably exceeding the cost of routers used to provide a similar networking capability via the Internet.
Another benefit that can be obtained from the use of the Internet is reliability. Once data reaches an ISP it is transferred onto a mesh structured backbone which contains redundant circuits that provide alternate paths between ISPs. Thus, the failure of a circuit on the Internet backbone is normally transparent to user operations as routers used by ISPs have the ability to select alternate routers. In comparison, additional circuits and router ports would be required to provide a mesh structured private network facility. Exhibit 2B illustrates how four routers would each require three serial ports to support a mesh structure topology that could be used to easily route data around circuit failures. However, this level of reliability would be extremely costly as it would require the installation of additional circuits and additional router ports for each router in the network. Now that we have an appreciation for the advantages associated with the use of the Internet as a virtual network to interconnect geographically separated organizational locations, lets turn our attention to two key issues that may restrict the ability of your organization to use this method of virtual networking network predictability and security.
Currently the Internet can be classified as an unpredictable network. That is, there is currently no assurance that data transmitted from one location will not be adversely affected by network traffic in such a manner that packets are received at the destination with variable time delays between packets. This means that the Internet is better suited for transporting certain types of data streams than other types of data streams. For example, time dependent applications such as SNA logical link control (LLC) type 2 data could be adversely affected by variable time delays, possibly resulting in session timeouts occurring even though a workstation on one LAN accessing a mainframe connected to a distant LAN responded in a timely manner to a mainframe query. Similarly, an attempt to route digitized voice via the use of a specialized gateway that converts voice into a sequence of IP packets would be more suitable for use on an internal private network than for transmission over the Internet. In this example an organization could install ReSerVation Protocol (RSVP) compatible equipment to allocate portions of bandwidth through their internal network for time delay sensitive applications, such as the transport of digitized voice. In comparison, the deployment of RSVP compatible equipment by Internet Service Providers is probably several years away as several key issues remain to be resolved to include how to bill subscribers for reserved bandwidth established between several ISPs.
When considering network predictability as an issue, there are several applications that are very suitable for transport via the Internet. Those applications include electronic mail, file transfer, and Web browsing into a corporate database. Thus, if your organization is considering the use of the Internet as a mechanism to replace a costly leased line based private network and your applications fall into the previously mentioned types of time dependent data transfers that are not adversely affected by the unpredictable nature of Internet transmission, an economic comparison becomes warranted. However, if your organization currently uses a private network for transporting digitized voice conversations or for accessing one or more mainframes using a time dependent protocol such as LLC2, you should probably defer a decision on the use of the Internet as a virtual network until RSVP becomes available and is priced. At that time you would then perform an economic analysis to determine if the potential savings afforded from replacing a private line based network by the use of the Internet is worth the effort. Concerning that effort, another issue that requires careful attention when you move from a private leased line based network to the use of the Internet is security.
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