De-peering

Cogent and TeliaSonera's Peering Dispute

On 14 March 2008, Cogent Communications depeered TeliaSonera, a European carrier with a primary customer base in the Nordic region and a significant Internet bandwidth business. In this context, "peering" refers to the settlement-free direct exchange of Internet traffic between two Internet service providers (ISPs).

Cogent, which sells aggressively priced Internet connectivity to businesses, including large content providers, has been involved in high-profile peering disputes in the past. The most notable of these was in 2005, when Level 3 depeered Cogent; pressure from its own customers was significant in forcing Level 3 to restore the peer and negotiate an agreement with Cogent. More recently, Cogent has been depeering other networks, most notably content delivery network (CDN) provider Limelight Networks.

Peering disputes are almost always over traffic imbalances. Ideally, when two ISPs peer with each other, the bilateral flow of traffic across the peer is approximately equal - each ISP sends the other about as much traffic as it receives from the other. If this ratio becomes overly imbalanced, one provider is likely to feel that the other should be purchasing connectivity, not obtaining it for free.

However, it seems likely that Cogent's recent depeering moves are not about traffic imbalances with the network that is being depeered. Rather, these are more likely attempts to balance its traffic ratios with other network service providers, and thus make it more attractive as a peering partner. Cogent has far more outbound traffic than it does inbound traffic, so moves that concentrate inbound traffic over valued peers are beneficial to it. For instance, when Cogent stopped peering directly with Limelight Networks, Limelight's traffic ended up flowing to Cogent via other service providers. This likely helped Cogent's traffic ratios with some of its other peered networks.

The situation with TeliaSonera, however, is exceptional because Cogent has reportedly been trying to get more effective peering in Europe. While Cogent's extensive peers include many European providers, the peering locations are primarily in the United States. We speculate that this move may be Cogent's heavy-handed attempt to negotiate European peering with TeliaSonera.

This kind of dispute is not good for either Cogent's customers or TeliaSonera's. TeliaSonera is advising its customers to purchase Internet access from an additional ISP that does have connectivity to Cogent. In general, Gartner strongly advises multihomed (multi-ISP) connectivity for reliability, and disputes such as this, which make networks unreachable for days at a time, are a particularly clear instance of the benefits of such. Cogent customers in particular are strongly encouraged to have a backup ISP, because we anticipate that Cogent's peering disputes are likely to continue, as it rationalizes its peering arrangements.