Peering
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Peering is the practice of exchanging Internet traffic with peers. It involves three elements:
- the physical interconnection of the networks,
- technical liaison between the networks to allow exchange of routes, and
- the commercial and contractual peering agreements.
Internet service providers (ISPs) set up peering points, the physical locations where exchanges happen and negotiate peering agreements (which are essentially legal contracts setting out the exact details of how traffic is to be exchanged). Most peering points are located in colocation centres, where the different network operators 'co-locate' their Points of Presence.
History of peering
In the early days of the Internet, a single backbone network existed in the form of first the ARPANET and later the NSFNET. All other networks connected with one another via the Internet backbone, and routing information was conveyed between the backbone and the other networks via the Exterior Gateway Protocol (EGP).
The modern Internet no longer has a single backbone in the traditional sense. Rather, it has many backbones, consisting of the individual backbones of various commercial ISPs and private networks. These networks are interconnected either at an Internet Exchange Point or through private interconnections between two or more networks. Their operations all rely upon the Border gateway protocol (BGP) which allows them to coordinate the operation of the Internet without the need for any central authority.
Types of peering agreements
The act of peering can be done as:
- a private peering,
- a peering via an Internet Exchange Point (ones that are independent of any single provider), or
- as a customer-provider relationship.
Providers with large traffic volumes, often known as Tier 1 carriers, tend to peer without charge with other large providers, and charge for peering with smaller ISPs.
Providers with smaller traffic tend to converge at Internet exchange points, which provides them with a commercially neutral venue for peering.
Peering as a customer-provider relationship is most common at the bottom tiers of the Internet business. The latter is not a true peering relationship; rather, the customer pays for transit via their upstream ISP.