IXP

(1) (Internet EXchange Processor) See IXA.

(2) (Internet eXchange Point) A public junction point on the Internet that provides an on-ramp to the Internet as well as a location for carriers to exchange traffic. There are approximately 300 IXPs around the world, with more than 100 in the U.S.

An IXP is physically some combination of switches and routers. The organization connects to the IXP from a port on its router to a port on the IXP's switch. The attachment is at the data link level (layer 2) and is typically Ethernet, but can also be ATM.

Public Peering
At these exchange points, major carriers accept traffic from each other and agree to carry the other's packets to their downstream destination point without charge. Peering arrangements are made with bilateral and multilateral agreements between the carriers.

If a carrier with less traffic wants to exchange packets, or a smaller, regional ISP needs an on-ramp to the Internet, a transit agreement is struck, wherein the backbone carrier charges the smaller operator a fee for transmitting its packets.

Private Peering
Major carriers also have private peering agreements between each other in locations where two or more carriers have switching points in close proximity. In late 1995, UUNET, MCI and GTE were the first to begin private arrangements. Thus, the Internet backbones are managed by a combination of public peering at the IXPs, also called "network access points" (see NAP) and private peering at their own locations. See Tier 1 network.