Understanding ISP network terms
 
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After recent discussions with Web hosting companies and ISPs about how they exchange traffic, it seems worthwhile to spell out the different methods here.
While business users don't set up private peering connections with ISPs or buy wholesale services, in some cases it's important to know the types of connections your service provider has set up with ISPs. Here are the most common arrangements:
Public peering. Just about all ISPs have some dedicated connections at the metropolitan-area exchanges (MAE) or network access points (NAP) to exchange traffic with other ISPs. Even the smallest ISPs can swap traffic with the largest ISPs at these exchange points. The drawback to public peering is that more than 4,000 ISPs that offer Internet access service are connecting up to one or more of these exchange points to swap traffic. And that means that performance at the MAEs and NAPs suffer due to the sheer volume of traffic that ISPs try to exchange. That's why ISPs created private peering.
Private peering. This is a term that became more widely known to the rest of us around 1997, but ISPs actually started setting up private peering agreements in 1996, only a year after the public peering sites were created. Private peering generally comprises two dedicated connections between two ISPs. ISP "A" controls and manages one of the connections, and ISP "B" controls and manages the other connection. Each ISP only exchanges traffic destined for the other ISP's network. These connections improve performance, because the reduced number of router hops means that packets aren't getting dropped, as they often did at the MAEs and NAPs. The other plus about private peering is that the ISPs don't charge fees for setting up these connections, because they are beneficial to both ISPs - as long as both ISPs send almost the same amount of traffic (in other words, they're peers). But what happens if a small ISP wants to directly connect to UUNET? Well, the ISP has to buy a wholesale service.
Wholesale or interconnection services. This is when an ISP or a Web hosting service provider buys a direct connection to another ISP's network. Wholesale service usually means that the ISP is only buying access to the network of the ISP that's selling the wholesale service - meaning this service will not offer access to the rest of the Internet, only the wholesale ISP's network. ISPs or Web hosting service providers usually buy wholesale service to improve performance for their customers by offering direct access and eliminating hops. Now, if a service provider wants to buy access to the rest of the Internet or access to another ISP's network, it buys transit services.
Transit services. ISPs buy transit services to not only access another ISP's network, but also to route traffic through that ISP's network. So where private peering and interconnection links allow ISP "A" and ISP "B" to exchange traffic to and from their networks, transit services allow ISP "A" to buy access to ISP "B's" network and beyond. But if an ISP uses a lot of transit services, it may be adding several router hops between its customers and customers on other ISP networks if peering or interconnection services aren't used.
While most business users are not directly affected by their ISP's overall architectural setup, most should have an idea as to how their ISP is connecting with some of the largest backbone providers. It could affect the performance of the Internet access services you're buying if your ISP peers only at the MAEs and NAPs and buys only transit services.
RELATED LINKS
Denise Pappalardo is a senior editor for Network World, covering ISPs, VPNs and related topics. Reach her at denisep@nww.com.
Internet Services archive
Past newsletters.
Savvis Communications is on the move
Network World, 03/29/99.
New Internet Exchanges hit the street
Network World, 05/31/99.
