Tier 1 network

A tier 1 network is an Internet Protocol (IP) network that participates in the Internet solely via settlement-free interconnection, also known as settlement-free peering.

Definition

Although there is no authority that defines tiers of networks participating in the Internet, the most common definition of a tier 1 network is one that can reach every other network on the Internet without purchasing IP transit or paying settlements.

By this definition, a tier 1 network is a transit-free network that peers with every other tier-1 network. But not all transit-free networks are tier 1 networks. It is possible to become transit-free by paying for peering or agreeing to settlements.

The networks listed below are thought to be the only transit free (as of July 2008). The most widely quoted source is Renesys Corporation, but the base information to prove the claim is publicly accessible from many locations, such as the RIPE RIS database, the Oregon Route Views servers, the Packet Clearing House, and others.

It is impossible for an outside authority to confirm that a network is not paying settlements of any type because such business agreements are frequently not public information, or even covered under a non-disclosure agreement. The information presented here is the best collective knowledge of the Internet peering community. There is little disagreement amongst the community itself, even though there is no quotable source for the information. For clarity, here we will define the "peering community" as the set of peering coordinators for networks which are present at Internet exchanges on at least two continents.

It is commonly believed that observing this definition strictly would result in every network being disqualified. For instance, many large telephone companies who are also tier 1 networks buy, sell, or swap fiber amongst themselves. Even if it were possible to list every transaction, it is not possible to know if some of those transactions were required for or in payment of a peering connection.

As a result, the term tier 1 network is used in the industry to mean a network with no overt settlements. An overt settlement would be a monetary charge for the amount, direction, or type of traffic sent between networks.

Common definitions of tier 2 and tier 3 networks:

• Tier 2: A network that peers with some networks, but still purchases IP transit or pays settlements to reach at least some portion of the Internet.
• Tier 3: A network that solely purchases transit from other networks to reach the Internet.

History

The original Internet backbone was the ARPANET when it provided the routing between most participating networks. It was replaced in 1989 with the NSFNet backbone. The Internet could be defined as the collection of all networks connected and able to interchange Internet Protocol datagrams with this backbone.

When the Internet was opened to the commercial markets, and for-profit Internet backbone and access providers emerged, the network routing architecture was decentralized with new exterior routing protocols, in particular the Border Gateway Protocol. New tier 1 ISPs and their peering agreements supplanted the government-sponsored NSFNet, a program that was officially terminated on April 30, 1995.

Routing

Internet traffic between any two tier 1 networks is critically dependent on the peering relationship of the partners, because a tier 1 network does not have any alternate transit paths. If two tier 1 networks arrive at an impasse and discontinue peering with each other (usually in a unilateral decision), single-homed customers of each network will not be able to reach the customers of other networks. This effectively partitions the Internet and traffic between certain parts of the Internet is interrupted. This has happened several times during the history of the Internet. Those portions of the Internet typically remain partitioned until one side purchases transit, or until the collective pain of the outage or threat of litigation motivates the two networks to resume voluntary peering.

Lower tier ISPs and their customers may be unaffected by these partitions because they may have redundant interconnections with more than one tier-1 provider.

Marketing

The term tier 1 is often misused as a marketing slogan, rather than being an accurate technical description of a network, because there is no formal definition or authoritative body which determines who is and is not a tier 1 network. Frequent misconceptions of the tier hierarchy include:

• Tier 1 networks are closer to the backbone of the Internet.
  • In reality, tier 1 networks usually have only a small number of peers (typically only other tier 1 networks and very large tier 2 networks), while tier 2 networks are motivated to peer with many other tier 2 and end-user networks. Thus a tier2 network with good peering is frequently much closer to most end users than a tier 1.
• Tier 1 networks by definition offer better quality Internet connectivity.
  • By definition, there are networks which tier 1 networks have only one path to, and if they lose that path, they have no backup transit which preserves their continuous connectivity.
  • Some tier 2 networks are significantly larger than some tier 1 networks, and are often able to provide more or better connectivity.
• Tier 2 networks are resellers of services from tier 1 networks.
  • Only tier 3 networks (who provide Internet access) are true resellers, while many large tier 2 networks peer with the majority or even vast majority of the Internet directly except for a small portion of the Internet which is reached via a transit provider.

Because the tier-based ranking system is used in marketing and sales, a long-held though generally misguided view among customers is that they should "only purchase from a tier 1". Because of this, many networks claim to be tier 1 even though they are not, while honest networks may lose business to those who only wish to purchase from a tier 1. The frequent misuse of the term has led to a corruption of the meaning, whereby almost every network claims to be a tier 1 even though it is not. The issue is further complicated by the almost universal use of non-disclosure agreements among tier 1 networks, which prevent the disclosure of details regarding their settlement-free interconnections.

Some of the incorrect measurements which are commonly cited include numbers of routers, route miles of fiber optic cable, or number of customers using a particular network. These are all valid ways to measure the size, scope, capacity, and importance of a network, but they have no direct relationship to tier 1 status.

Another common area of debate is whether it is possible to become a tier 1 through the purchase of paid peering, or settlement-based interconnections, whereby a network "buys" the status of tier 1 rather than achieving it through settlement-free agreements. While this may simulate the routing behaviors of a tier 1 network, it does not simulate the financial or political peering motivations, and is thus considered by most Peering Coordinators to not be a true tier 1 for most discussions.

Regional tier 1 networks

See also: Internet Exchange Point

A common point of contention among people discussing tier 1 networks is the concept of a regional tier 1 network. A regional tier 1 network is a network which is not transit free globally, but which maintains many of the classic behaviors and motivations of a tier 1 network within a specific region.

A typical scenario for this characteristic involves a network that was the incumbent telecommunications company in a specific country or region, usually tied to some level of government-supported monopoly. Within their specific countries or regions of origin, these networks maintain peering policies which mimic those of tier 1 networks (such as lack of openness to new peering relationships and having existing peering with every other major network in that region). However, this network may then extend to another country, region, or continent outside of its core region of operations, where it may purchase transit or peer openly like a tier 2 network.

A commonly cited example of these behaviors involves the incumbent carriers within Australia, who will not peer with new networks in Australia under any circumstances, but who will extend their networks to the United States and peer openly with many networks. Less extreme examples of much less restrictive peering requirements being set for regions in which a network peers, but does not sell services or have a significant market share, are relatively common among many networks, not just regional tier 1 networks.

While the classification regional tier 1 holds some merit for understanding the peering motivations of such a network within different regions, these networks do not meet the requirements of a true global tier 1 because they are not transit free globally.

List of tier 1 networks

The following networks are believed to be tier 1 networks; they do not have overt settlements with any other network:

Name	AS number	September, 2007 degree	Peering policy
Qwest	209	828	North America; International
Verizon Business UUNet	701	1452	Verizon UUNET Peering policy 701, 702, 703
Sprint	1239	880
TeliaSonera International Carrier	1299
NTT Communications	2914
Tinet	3257
Global Crossing (GBLX)	3549	499	Global Crossing Peering policy (2003)
Savvis	3561
AT&T	7018	1382	AT&T Peering policy
Tata Communications	6453		Peering Policy

Out of these tier-1 networks, only 6 are located in the United States and others are international. Global Crossing is headquartered in Hamilton, Bermuda, TeliaSonera is headquartered in Sweden and Tinet which has its operational headquarters in Italy. This demonstrates a shift in the way Internet traffic is being carried with lower reliance on U.S. networks.

The following networks were tier 1 networks and may still be, but there is some question in the community as to whether they are now paying settlements to one or more of their peers:

Name	AS number	September, 2007 degree	Peering policy
AOL Transit Data Network (ATDN)	1668		ATDN Peering Policy
Level 3 Communications (L3)	3356

Some have suggested that Level 3 no longer qualifies for Tier 1 status based on an temporary agreement with Comcast to pay to serve content to Comcast's users. Others consider this not to be a transit agreement and that Level 3 still qualifies as Tier 1 as they reach Comcast's network for free, and are paying to reach the users of Comcast's closed network and not the network itself.

Other major networks

The following networks are transit-free networks, even though they have settlement based or paid peering with one or more other networks:

Name	AS Number	September, 2007 degree	Settlement Peer
Cogent Communications	174		Sprint/AS1239 and Level 3 Communications (L3)/AS3356
XO Communications	2828		Level 3 Communications (L3)/AS3356
AboveNet	6461		Level 3 Communications (L3)/AS3356
Telecom Italia Sparkle (Seabone)	6762		Sprint/AS1239

Due to the marketing considerations mentioned above, many people mistakenly believe that other networks are tier 1 when they are not. Because of this, many online resources and forums incorrectly list several non-qualifying networks as tier 1. Below is a list of some of these tier 2 networks which are often listed as tier 1, along with their upstream providers:

• Allstream/AS15290 (Verizon Business/AS701 transit, AT&T/AS7018 transit, Level 3 Communications (L3)/AS3356 transit)
• British Telecom/AS5400 (Global Crossing (GBLX)/AS3549 transit, Level 3 Communications (L3)/AS3356 transit, Sprint Nextel Corporation/AS1239 transit)
• Cable and Wireless/AS1273 (Level 3 Communications (L3)/AS3356, SAVVIS/AS3561 transit)
• Deutsche Telekom/AS3320 (Sprint Nextel Corporation/AS1239 transit)
• France Telecom/AS5511 aka OpenTransit (Verizon Business/AS701 transit, possibly paid peering with Sprint Nextel Corporation/AS1239)
• Hurricane Electric/AS6939 (Global Crossing (GBLX)/AS3549 transit, TeliaSonera/AS1299 transit)
• PCCWGlobal/AS3491 (Global Crossing (GBLX)/AS3549 transit)
• tw telecom/AS4323 (Sprint Nextel Corporation/AS1239 transit, paid peering with Level 3 Communications (L3)/AS3356)
• L2Networks/AS40911 (Hurricane Electric/AS6939 transit)

See also

• Tier 2 network
• Peering
• Internet transit
• Interconnect agreement
• Network access point