Internet Routing Architectures (CISCO):ISP Services and Characteristics

Router Collocation

Collocation is the act of placing one party's equipment on another party's premises. An example of collocation is putting the customer's router on the provider's site, as illustrated in figure 2-8. The customer motivation for such a collocation scheme would be to have the ISP provide local monitoring of the equipment. Usually ISPs do not like to put customer routers on their premises unless they really have to in order to satisfy the customer. Real estate is becoming a real issue, and the ISPs are having problems finding places for their own equipment at the POP.

Figure 2-8 Example: customer router located at ISP site.

The opposite of the situation described in figure 2-8 is for the ISP to collocate its own POP router at the customer's site. This is shown in figure 2-9. Usually in this case, the ISP would pay for the access line and the router and would charge the customer a monthly fee for the whole service. The ISP in this case would benefit from more real estate at his premises while providing a total package to the customer.

Figure 2-9 Example: ISP router located at customer site.

Looking Ahead

Technical characteristics of an ISP's network have significant repercussions for the customer's service, including the quality of routing architecture. Because the customer might not have direct control over some of these technical characteristics, it is critical that the customer at least evaluate them and make sure that they will deliver the required connectivity and quality.

If you are an ISP customer whose demarcation point and collocation agreements stipulate that you are running and maintaining equipment on your premises—even if you do not own it outright—you are likely to be taking a significant hands-on role in developing the routing policies and architecture for your network. Even if you are not running and maintaining the equipment, there are decisions you will need to make and understand with respect to routing architecture.

The next chapter completes the foundational part of this book by discussing addressing and address depletion. After that, all the groundwork will have been established for an in-depth discussion of routing protocols in subsequent chapters.

Frequently Asked Questions

Q—Is higher price an indication that I will receive faster, better connection service from an ISP?

A—Not neccessarily. Higher prices sometimes reflect the provider's having invested in fast connections, such as T3 or higher bandwidth links. The mere presence of such links, however, does not necessarily mean that your connections will be faster. A poorly designed combination of high-speed links and low-speed clouds, for example, might affect the overall performance of the provider negatively. The bottom line is that price is just one factor to consider; even more important is a sound network topology that offers enough redundancy and adequate bandwith to fit your needs.

Q—What causes bottlenecks in the ISP's backbone?

A—Bottlenecks are caused by oversubscription or overutilization of bandwidth on a physical link.

Q—When I connect to an ISP, should I buy my own equipment?

A—There are pros and cons to buying your own equipment; only you can decide whether this is the optimal approach for your organization's needs. First, find out whether your ISP insists on your using its equipment (some do). Even if the ISP will let you purchase your own, it probably will stipulate certain hardware and software that conform to its system. Cost issues are likely to factor significantly in your decision: Can your organization afford the capital investment, including upgrades and expansion as needed? By buying the equipment, you might also be committing yourself to maintaining it, although some ISPs will agree to maintain (for a fee) equipment owned by the customer.

Q—If my connection to an ISP goes down because of equipment failure, who is responsible for what?

A—It all depends on the service you are getting from the ISP. The preset demarcation point defines the line of responsibility between you and the provider.

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