Peering: The inner workings of service providers

As a corporate network manager, how much do you need to know about the inner workings of the Internet - or about the business plans of the service providers that connect your corporate LAN or Web site to the rest of the world?

With the rapid evolution of the Internet's technical and business infrastructure, the answer is "plenty." How your Internet bandwidth provider or Web site outsourcing service connects to the Internet will affect the performance and availability you're paying for.

As the Internet becomes increasingly popular, two trends are working in opposition to each other. Corporations are deploying more Internet-based business-critical applications, but this increased Internet usage is placing more strain on the Internet infrastructure. The effect of this strain can be seen clearly at the public Internet exchange points (IXP), where most providers exchange traffic, but where no provider has control over quality.

Historically, Internet providers exchanged traffic at IXPs - the network access points (NAP) and the metropolitan-area exchanges (MAE) - through a free exchange relationship called bilateral public peering. Today, these public exchange points are plagued with congestion problems.

Two connectivity alternatives are emerging: private peering among the largest backbone providers and, more recently, private transit connections to multiple backbone providers, which are favored by specialized ISPs.

Public peering
Public peering is the oldest and most problematic strategy for exchanging Internet traffic. The number of ISPs that connected to IXPs with a DS-3 link and acquired many peering agreements grew rapidly in the mid-1990s. This growth brought capacity problems to many IXPs.

Specifically, packet loss is increasing at the IXPs for the following reasons:

The shared media - giga-switches, Ethernet LANs or FDDI rings - are subject to degradation in performance as they approach saturation.

The circuits connecting to the major providers, the destination of most of the traffic, frequently run at or near capacity. As more routers announce more destinations to each other, the constant chatter causes routing instability.

In addition to these growing technical problems, the viability of a public peering strategy is under threat due to the withdrawal of free peering agreements by the Big Five backbone providers - MCI Communications Corp.; WorldCom, Inc.'s UUNET Technologies, Inc. and ANS Communications Corp.; Sprint Corp.'s SprintLink and GTE Corp.'s BBN.

Private peering
In a vote of no confidence for public peering, the Big Five providers implemented private peering among themselves in 1995 and 1996. No longer exchanging traffic among themselves at the IXPs, each has implemented four or more private interconnections with each of the others.

These private peering sessions are direct connections from one peer to the other, in contrast to public peering over a shared medium at the IXPs. Private peering has solved the packet loss problem for the top Internet backbone providers.

Private transit
So with the largest providers peering privately among themselves and with no end in sight to the problems at the public exchanges, where does that leave the rest of the providers? Some, such as companies that provide specialized Web hosting services, have high connectivity requirements for their customized services.

Many of these providers are adopting a new technology, called private transit, with the goal of keeping customer traffic from traversing the public IXPs.

Private transit is achieved by direct connections to multiple major backbone providers. These are contractual, commercial transit connections.

In addition to eliminating packet loss, private transit has two additional benefits. A transit provider accepts traffic for every destination on the Internet, while peers only accept traffic destined for their own network. And providers with multiple private transit connections still have connectivity even when there's an outage at a major backbone provider.

Another alternative
Using technology similar to private transit, a group of service providers - Savvis Communications Corp., Williams Communications, Exodus Communications, Inc. and Electric Lightwave, Inc. - have founded the Brokered Private Peering Group. The group wants to establish six ATM-based peering points around the U.S. The group's main goal, like other private peering plans, is to revamp the way providers exchange traffic and provide more reliable Internet services.

Winkleman is the chief technology officer at NaviSite Corp., an ISP. He can reached at (888) 298-8222.

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