Internet Routing Architectures (CISCO):ISP Services and Characteristics



























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This chapter covers the following key topics:

•  ISP Services
A basic categorization of Internet service providers in terms of physical access methods, basic services, and security options.
•  ISP Service Pricing
Survey of price ranges for different physical access methods.
•  ISP Backbone Selection Criteria
Criteria for evaluating ISPs in terms of their network topology and traffic exchange agreements.
•  Demarcation Point
Distinguishing the provider's network, equipment, and responsibilities from those of the customer.

Chapter 2ISP Services and Characteristics

Before going deeper into the technical subject of interdomain routing, it is important to be familiar with some of the basic provider services and characteristics that affect the quality of Internet connections. Anybody who can offer Internet connectivity could claim to be a service provider; this description covers everything from a provider with a multimillion dollar backbone and infrastructure to a provider with a couple of routers and access servers in his garage.

Price should not be the main factor on which you base your decision. What really matters are factors such as the provider's services, backbone design, fault tolerance, redundancy, stability, bottlenecks, provider/customer equipment arrangement, and so on.
Routing behaviors on the Internet are affected by how routing protocols and data traffic behave over an already established physical connectivity. A good physical infrastructure design and maintenance is one of the main factors in achieving healthy routing on the Internet.
ISP Services
Different ISPs offer different services depending on how big they are and the infrastructure of their networks. Mainly, providers can be categorized by their method of physical Internet access, the applications they provide, and the security services they provide.

The following physical access methods are the most commonly deployed throughout the Internet:

•  Leased lines—Leased lines could be provided at 19.2 Kbps or 56 Kbps, with increments of 56 Kbps or 64 Kbps up to T1/E1 lines on the lower-end, and T3 and fractional T3 (in multiple T1s) on the higher-end of the bandwidth scale. Leased lines are usually used when traffic bandwidth is predictable and the frequency of network access is high enough to justify a line being up 24 hours a day. Of course, the trade-off is the cost, which is higher than any other connection type.
•  Frame relay—Frame relay connections are one of the most economical ways for corporations to hook up to the Internet. Purchasing sufficient point-to-point leased line connections can be prohibitively expensive for some companies, in which case they may want to consider connecting to existing frame relay backbones on a per-need basis. With frame relay, corporations can buy enough bandwidth to meet their existing needs and to easily expand as traffic requirements increase. The trade-off is that you are limited by the bandwidth offered by your provider. Other wide area network services such as ATM are starting to be used and recognized, but do not have the success that frame relay has experienced.
•  Dialup services—This includes Asynchronous dialup at 9.6, 14.4, and 28.8 Kbps, ISDN Basic Rate Interface (BRI), or Primary Rate Interface (PRI). Dialup services range from serving individual users to serving corporations that are subcontracting with providers to obtain all their remote login needs. ISDN BRI and PRI services have experienced great growth lately due to their on-demand nature and their capability to carry digital signaling essential for multimedia services.

Prices for ISP services are often predicated on physical access methods, as discussed further in the next section. Customers need to weigh costs and benefits of the different options against their needs.

Almost every single provider offers the following basic services: electronic mail, Usenet newsgroups, ftp, Gopher retrieval, and Wide Area Information Servers (WAIS) resource discovery tool. In addition, due to the phenomenal popularity of the World Wide Web, most ISPs provide this service in one form or another. Customers who do not want to maintain an in-house WWW server can buy space from a shared server on the ISP's premises. Some ISPs are even offering total Web solutions for companies that need a total package, such as advertising, enabling customers to order online, updating inventory, billing, and shipping.
ISPs can offer consulting for different security services. The easiest service would be providing packet filtering on the router level. More security measures involve firewalls and, usually, additional fees. ISPs can integrate their own firewalls or help you configure firewalls that you buy from outside vendors.
ISP Pricing and Technical Characteristics
Besides evaluating services, customers should consider pricing and technical characteristics of an ISP before choosing one. Although technical characteristics in particular may seem intimidating, they have enormous implications for the reliability and ease-of-use of the provider you eventually select. Technical issues that this section addresses include backbone issues and demarcation.




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