Internet transit
Encyclopedia
Internet transit is the service of allowing network traffic to cross or "transit" a computer network, usually used to connect a smaller Internet service provider
(ISP) to the larger Internet. Technically, it consists of two bundled services:
In the 1970s and early 1980s-era Internet, the assumption was made that all networks would provide full transit for one another, since all were ultimately publicly funded by the United States government's National Science Foundation
. In the modern private-sector Internet, two forms of interconnect agreement
s exist between Internet networks: transit, and peering
. Transit is distinct from peering, in which only traffic between the two ISPs and their downstream customers is exchanged and neither ISP can see upstream
routes over the peering connection. A transit free network uses only peering; a network that uses only unpaid peering and connects to the whole Internet is considered a Tier 1 network
The transit service is typically priced per megabit per second per month, and customers are often required to commit to a minimum volume of bandwidth
, and usually to a minimum term of service as well. Some transit agreements provide "service-level agreements" which purport to offer money-back guarantees of performance between the customer's Internet connection and specific points on the Internet, typically major Internet exchange point
s within a continental geography such as North America
. These service level agreements still provide only best-effort delivery since they do not guarantee service the other half of the way, from the Internet Exchange Point to the final destination.
Internet service provider
An Internet service provider is a company that provides access to the Internet. Access ISPs directly connect customers to the Internet using copper wires, wireless or fiber-optic connections. Hosting ISPs lease server space for smaller businesses and host other people servers...
(ISP) to the larger Internet. Technically, it consists of two bundled services:
- The advertisement of customer routesRoutingRouting is the process of selecting paths in a network along which to send network traffic. Routing is performed for many kinds of networks, including the telephone network , electronic data networks , and transportation networks...
to other ISPs, thereby soliciting inbound traffic toward the customer from them - The advertisement of others ISPs routes (usually but not necessarily in the form of a default routeDefault routeA default route, also known as the gateway of last resort, is the network route used by a router when no other known route exists for a given IP packet's destination address. All the packets for destinations not known by the router's routing table are sent to the default route...
or a full set of routes to all of the destinations on the Internet) to the ISP's customer, thereby soliciting outbound traffic from the customer towards these networks.
In the 1970s and early 1980s-era Internet, the assumption was made that all networks would provide full transit for one another, since all were ultimately publicly funded by the United States government's National Science Foundation
National Science Foundation
The National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health...
. In the modern private-sector Internet, two forms of interconnect agreement
Interconnect agreement
An interconnect agreement is a business contract between telecommunications organizations for the purpose of interconnecting their networks and exchanging telecommunications traffic...
s exist between Internet networks: transit, and peering
Peering
In computer networking, peering is a voluntary interconnection of administratively separate Internet networks for the purpose of exchanging traffic between the customers of each network. The pure definition of peering is settlement-free or "sender keeps all," meaning that neither party pays the...
. Transit is distinct from peering, in which only traffic between the two ISPs and their downstream customers is exchanged and neither ISP can see upstream
Upstream (networking)
In computer networking, upstream refers to the direction in which data can be transferred from the client to the server . This differs greatly from downstream not only in theory and usage, but also in that upstream speeds are usually at a premium...
routes over the peering connection. A transit free network uses only peering; a network that uses only unpaid peering and connects to the whole Internet is considered a Tier 1 network
Tier 1 network
A tier 1 network is an Internet Protocol network that participates in the Internet solely via settlement-free interconnection, also known as settlement-free peering.-Definition:...
The transit service is typically priced per megabit per second per month, and customers are often required to commit to a minimum volume of bandwidth
Bandwidth (computing)
In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
, and usually to a minimum term of service as well. Some transit agreements provide "service-level agreements" which purport to offer money-back guarantees of performance between the customer's Internet connection and specific points on the Internet, typically major Internet exchange point
Internet Exchange Point
An Internet exchange point is a physical infrastructure through which Internet service providers exchange Internet traffic between their networks . IXPs reduce the portion of an ISP's traffic which must be delivered via their upstream transit providers, thereby reducing the average per-bit...
s within a continental geography such as North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. These service level agreements still provide only best-effort delivery since they do not guarantee service the other half of the way, from the Internet Exchange Point to the final destination.