Tier 1 network

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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.


Relationship between the various tiers on Internet providers

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.[1]

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 most widely quoted source for identifying tier 1 networks 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 difficult to determine whether a network is paying settlements if the business agreements are not public information, or are covered under a non-disclosure agreement. The Internet "peering community" is roughly the set of peering coordinators present at Internet exchanges on more than one continent. The subset representing "tier 1" networks is collectively understood, but not published as such.

Strictly observing this definition of "tier 1" would exclude every network.[citation needed] For instance, many large telephone companies are tier 1 networks, but they buy, sell, or swap fiber amongst themselves. Payments between companies are not all known, nor whether they cover peering connections.

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.


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.[citation needed]

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


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 discontinue peering with each other, 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.[citation needed] 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.[original research?]

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.

Regional tier 1 networks[edit]

A common point of contention among people[who?] 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.[citation needed] 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.[original research?]

List of tier 1 networks[edit]

These networks appear to be tier 1 networks, in that they do not have overt settlements with any other network.

Name Headquarters AS number January 2011 degree[2][3] Peering policy
AT&T United States 7018 2365 AT&T Peering policy
CenturyLink (formerly Qwest and Savvis) United States 209 / 3561 1367 North America; International
Deutsche Telekom (now known as International Carrier Sales & Solutions (ICSS))[citation needed] Germany 3320 535 DTAG Peering Details
XO Communications[citation needed] United States 2828 2904 XO Peering Policy
GTT (formerly Tinet)[citation needed] United States 3257 886 AS3257 Peering Policy
Verizon Business (formerly UUNET) United States 701 / 702 / 703 1946 Verizon UUNET Peering policy 701, 702, 703
Sprint United States 1239 1183 Sprint Peering Policy
TeliaSonera International Carrier[citation needed] Sweden - Finland 1299 630 TeliaSonera International Carrier Global Peering Policy
NTT Communications (formerly Verio) Japan 2914 718 North America
Level 3 Communications (formerly Level 3 and Global Crossing) United States 3356 / 3549 / 1 4450 Level 3 Peering Policy
Tata Communications (Acquired Teleglobe) India 6453 569 Peering Policy
Zayo Group formerly AboveNet[citation needed] United States 6461 1066 AboveNet Peering Policy
Cogent formerly PSINet United States 174 6969 Cogent Peering Policy
Seabone (Telecom Italia Sparkle) Italy 6762 344

While most of these Tier-1 providers offer global coverage (based on the published network map on their respective public websites), there are some which are restricted to being geographically regional players in North America and do not have a global network footprint especially when it comes to IP Transit services like AT&T. However these do offer global coverage for mobiles and IP-VPN type services which are unrelated to being a Tier-1 provider.

A 2008 report shows Internet traffic relying less on U.S. networks than previously.[4]

Other major networks[edit]

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

Name Headquarters AS Number August 2012 degree[2][3] Settlement Peer
Cogent Communications United States 174 3537 Sprint/AS1239 and Level 3 Communications (L3)/AS3356
OpenTransit (Orange)[citation needed] France 5511 146 Possibly Verizon Business/AS701 & Sprint/AS1239
Telefónica[5] Spain 12956 160 Level 3 Communications (L3)/AS3356

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:[citation needed]

See also[edit]


  1. ^ "How the 'Net works: an introduction to peering and transit: Page 4". 2008-09-02. Retrieved 2008-11-04. "Tier 1 networks are those networks that don't pay any other network for transit yet still can reach all networks connected to the internet." 
  2. ^ a b CAIDA AS ranking
  3. ^ a b Visualizing Internet Topology at a Macroscopic Scale April 2005
  4. ^ Markoff, John (2008-08-30). "Internet Traffic Begins to Bypass the US". New York Times. 
  5. ^ Level 3's looking glass marks routes Level3_Customer and Suppress_to_Peers indicating paid peering.