Tier 1 network
Encyclopedia
A tier 1 network is an Internet Protocol
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...

 (IP) network that participates in the Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...

 solely via settlement-free interconnection, also known as settlement-free 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...

.

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
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...

 without purchasing IP transit
Internet transit
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 to the larger Internet...

 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 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
Route views
Route Views is a project founded by the University of Oregon to allow Internet users to view global BGP routing information from the perspective of other locations around the internet...

 servers, the Packet Clearing House
Packet Clearing House
Packet Clearing House or PCH is a non-profit research institute formed in 1994. It supports operations and analysis in the areas of Internet traffic exchange, routing economics, and global network development.-Overview:...

, and others.

It is difficult to determine whether a network is paying settlements if the business agreements are not public information, or covered under a non-disclosure agreement
Non-disclosure agreement
A non-disclosure agreement , also known as a confidentiality agreement , confidential disclosure agreement , proprietary information agreement , or secrecy agreement, is a legal contract between at least two parties that outlines confidential material, knowledge, or information that the parties...

. 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. 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
    Tier 2 network
    A Tier 2 Network is an Internet service provider who engages in the practice of peering with other networks, but who still purchases IP transit to reach some portion of the Internet....

    : 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
Internet backbone
The Internet backbone refers to the principal data routes between large, strategically interconnected networks and core routers in the Internet...

 was the ARPANET
ARPANET
The Advanced Research Projects Agency Network , was the world's first operational packet switching network and the core network of a set that came to compose the global Internet...

 when it provided the routing between most participating networks. It was replaced in 1989 with the NSFNet
NSFNet
The National Science Foundation Network was a program of coordinated, evolving projects sponsored by the National Science Foundation beginning in 1985 to promote advanced research and education networking in the United States...

 backbone. The Internet could be defined as the collection of all networks connected and able to interchange Internet Protocol
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...

 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
Border Gateway Protocol
The Border Gateway Protocol is the protocol backing the core routing decisions on the Internet. It maintains a table of IP networks or 'prefixes' which designate network reachability among autonomous systems . It is described as a path vector 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
Multihoming
Multihoming is a technique used to increase the reliability of the Internet connection for an IP network. As an adjective, it is typically used to describe a customer, rather than an Internet service provider network...

 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
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...

.

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 tier 2 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 agreement
Non-disclosure agreement
A non-disclosure agreement , also known as a confidentiality agreement , confidential disclosure agreement , proprietary information agreement , or secrecy agreement, is a legal contract between at least two parties that outlines confidential material, knowledge, or information that the parties...

s 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

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

These networks are believed to be tier 1 networks, in that they do not have overt settlements with any other network.
Name AS number
Autonomous system (Internet)
Within the Internet, an Autonomous System is a collection of connected Internet Protocol routing prefixes under the control of one or more network operators that presents a common, clearly defined routing policy to the Internet....

September, 2007 degree
Degree (graph theory)
In graph theory, the degree of a vertex of a graph is the number of edges incident to the vertex, with loops counted twice. The degree of a vertex v is denoted \deg. The maximum degree of a graph G, denoted by Δ, and the minimum degree of a graph, denoted by δ, are the maximum and minimum degree...

Peering policy
Centurylink (formerly Qwest and Savvis)
CenturyLink
CenturyLink, Inc. is a United States telecommunications firm, headquartered in Monroe, Louisiana. The company, founded as Central Telephone & Electronics Corporation in 1968, later changed its name to Century Telephone Enterprises, Inc. in 1971, and then was called CenturyTel, Inc. from 1999 to 2010...

209 / 3561 828 North America; International
Telecom Italia Sparkle (Seabone)
Telecom Italia
Telecom Italia is the largest Italian telecommunications company, also active in the media and manufacturing industries. Now a private concern listed on the Borsa Italiana, it was founded in 1994 by the merger of several state-owned telecommunications companies, the most important of which was...

6762
Verizon Business
Verizon Business
Verizon Business is one of three operating units of Verizon Communications It was created in 2006 when Verizon Communications closed on its merger with MCI, Inc..Verizon Business has over 30,000 employees with 321 offices in 75 countries...

 (formerly UUNET
UUNET
UUNET founded in 1987, was one of the largest Internet service providers and one of the nine Tier 1 networks. It was based in Northern Virginia and was the first commercial Internet service provider...

)
701 1452 Verizon UUNET Peering policy 701, 702, 703
Sprint
Sprint Nextel
Sprint Nextel Corporation is an American telecommunications company based in Overland Park, Kansas. The company owns and operates Sprint, the third largest wireless telecommunications network in the United States, with 53.4 million customers, behind Verizon Wireless and AT&T Mobility...

1239 880
TeliaSonera International Carrier
TeliaSonera International Carrier
TeliaSonera International Carrier is a global provider of cross-border and domestic communication services. It is wholly owned by the TeliaSonera Group, the largest telecommunications group in the Nordic and Baltic regions...

1299 TeliaSonera International Carrier Global Peering Policy
NTT Communications 2914
Deutsche Telekom AG (DTAG) 3320 501 DTAG Peering Details
Level 3 Communications
Level 3 Communications
Level 3 Communications is a telecommunications and Internet service provider headquartered in Broomfield, Colorado.It operates a Tier 1 network. The company provides core transport, IP, voice, video and content delivery for most of the medium to large Internet carriers in North America and Europe...

 (formerly Global Crossing
Global Crossing
Global Crossing Limited was a telecommunications company that provides computer networking services worldwide. It maintained a large backbone and offered transit and peering links, VPN, leased lines, audio and video conferencing, long distance telephone, managed services, dialup, colocation and...

)
3356 / 3549 499 Global Crossing Peering policy (2003)
Tata Communications
Tata Communications
Tata Communications Limited ) is a telecommunications company located in Mumbai. They own a submarine cable network, a Tier-1 IP network, and also rent data center and colocation space. They operate India's largest data center in Pune...

6453 Peering Policy
AT&T
AT&T
AT&T Inc. is an American multinational telecommunications corporation headquartered in Whitacre Tower, Dallas, Texas, United States. It is the largest provider of mobile telephony and fixed telephony in the United States, and is also a provider of broadband and subscription television services...

7018 1382 AT&T Peering policy


Out of these tier-1 networks, some are located in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 and others are not. Global Crossing is headquartered in Bermuda
Bermuda
Bermuda is a British overseas territory in the North Atlantic Ocean. Located off the east coast of the United States, its nearest landmass is Cape Hatteras, North Carolina, about to the west-northwest. It is about south of Halifax, Nova Scotia, Canada, and northeast of Miami, Florida...

, Telecom Italia in Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

. On Monday April 11, 2011, it was announced that Level 3 Communications intended to acquire Global Crossing.

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

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
Autonomous system (Internet)
Within the Internet, an Autonomous System is a collection of connected Internet Protocol routing prefixes under the control of one or more network operators that presents a common, clearly defined routing policy to the Internet....

September, 2007 degree
Degree (graph theory)
In graph theory, the degree of a vertex of a graph is the number of edges incident to the vertex, with loops counted twice. The degree of a vertex v is denoted \deg. The maximum degree of a graph G, denoted by Δ, and the minimum degree of a graph, denoted by δ, are the maximum and minimum degree...

Peering policy
AOL
AOL
AOL Inc. is an American global Internet services and media company. AOL is headquartered at 770 Broadway in New York. Founded in 1983 as Control Video Corporation, it has franchised its services to companies in several nations around the world or set up international versions of its services...

 Transit Data Network (ATDN)
1668 ATDN Peering Policy

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
Autonomous system (Internet)
Within the Internet, an Autonomous System is a collection of connected Internet Protocol routing prefixes under the control of one or more network operators that presents a common, clearly defined routing policy to the Internet....

September, 2007 degree
Degree (graph theory)
In graph theory, the degree of a vertex of a graph is the number of edges incident to the vertex, with loops counted twice. The degree of a vertex v is denoted \deg. The maximum degree of a graph G, denoted by Δ, and the minimum degree of a graph, denoted by δ, are the maximum and minimum degree...

Settlement Peer
Cogent Communications
Cogent Communications
Cogent Communications is a multinational internet service provider whose network spans more than 53,300 intercity fiber route miles and 15,800 metro fiber miles. Cogent provides service in over 165 markets across 31 countries in North America and Europe...

174 Sprint
Sprint Nextel
Sprint Nextel Corporation is an American telecommunications company based in Overland Park, Kansas. The company owns and operates Sprint, the third largest wireless telecommunications network in the United States, with 53.4 million customers, behind Verizon Wireless and AT&T Mobility...

/AS1239 and Level 3 Communications (L3)
Level 3 Communications
Level 3 Communications is a telecommunications and Internet service provider headquartered in Broomfield, Colorado.It operates a Tier 1 network. The company provides core transport, IP, voice, video and content delivery for most of the medium to large Internet carriers in North America and Europe...

/AS3356
XO Communications
XO Communications
XO Communications is a telecommunications company owned by XO Holdings, Inc...

2828 Level 3 Communications (L3)
Level 3 Communications
Level 3 Communications is a telecommunications and Internet service provider headquartered in Broomfield, Colorado.It operates a Tier 1 network. The company provides core transport, IP, voice, video and content delivery for most of the medium to large Internet carriers in North America and Europe...

/AS3356
AboveNet
AboveNet
AboveNet, Inc. , provides high bandwidth connectivity primarily for large corporate enterprises and communications carriers. AboveNet operates private metro area and long haul optical networks, and offers services including high bandwidth metro access to WDM, Metro Ethernet, VPN and IP networks,...

6461 Level 3 Communications (L3)
Level 3 Communications
Level 3 Communications is a telecommunications and Internet service provider headquartered in Broomfield, Colorado.It operates a Tier 1 network. The company provides core transport, IP, voice, video and content delivery for most of the medium to large Internet carriers in North America and Europe...

/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:
  • Allstream/AS15290 (Verizon Business
    Verizon Business
    Verizon Business is one of three operating units of Verizon Communications It was created in 2006 when Verizon Communications closed on its merger with MCI, Inc..Verizon Business has over 30,000 employees with 321 offices in 75 countries...

    /AS701 transit, AT&T
    AT&T
    AT&T Inc. is an American multinational telecommunications corporation headquartered in Whitacre Tower, Dallas, Texas, United States. It is the largest provider of mobile telephony and fixed telephony in the United States, and is also a provider of broadband and subscription television services...

    /AS7018 transit, Level 3 Communications (L3)
    Level 3 Communications
    Level 3 Communications is a telecommunications and Internet service provider headquartered in Broomfield, Colorado.It operates a Tier 1 network. The company provides core transport, IP, voice, video and content delivery for most of the medium to large Internet carriers in North America and Europe...

    /AS3356 transit)
  • British Telecom/AS5400 (Global Crossing (GBLX)
    Global Crossing
    Global Crossing Limited was a telecommunications company that provides computer networking services worldwide. It maintained a large backbone and offered transit and peering links, VPN, leased lines, audio and video conferencing, long distance telephone, managed services, dialup, colocation and...

    /AS3549 transit, Level 3 Communications (L3)
    Level 3 Communications
    Level 3 Communications is a telecommunications and Internet service provider headquartered in Broomfield, Colorado.It operates a Tier 1 network. The company provides core transport, IP, voice, video and content delivery for most of the medium to large Internet carriers in North America and Europe...

    /AS3356 transit, Sprint Nextel Corporation/AS1239 transit)
  • Cable and Wireless/AS1273 (Level 3 Communications (L3)
    Level 3 Communications
    Level 3 Communications is a telecommunications and Internet service provider headquartered in Broomfield, Colorado.It operates a Tier 1 network. The company provides core transport, IP, voice, video and content delivery for most of the medium to large Internet carriers in North America and Europe...

    /AS3356, SAVVIS
    SAVVIS
    Savvis – A CenturyLink Company is a subsidiary of CenturyLink, a company headquartered in Monroe, Louisiana. Savvis provides information technology solutions for enterprises and government agencies...

    /AS3561 transit)
  • France Telecom
    France Télécom
    France Telecom S.A. is the main telecommunications company in France, the third-largest in Europe and one of the largest in the world. It currently employs about 180,000 people and has 192.7 million customers worldwide . In 2010 the group had revenue of €45.5 billion...

    /AS5511 aka OpenTransit (Verizon Business
    Verizon Business
    Verizon Business is one of three operating units of Verizon Communications It was created in 2006 when Verizon Communications closed on its merger with MCI, Inc..Verizon Business has over 30,000 employees with 321 offices in 75 countries...

    /AS701 transit, possibly paid peering with Sprint Nextel Corporation/AS1239)
  • Hurricane Electric
    Hurricane Electric
    Hurricane Electric is a global Internet backbone , with a specific focus on IPv6. Hurricane Electric operates datacenters in the San Francisco Bay Area, primarily within the city of Fremont...

    /AS6939 (Global Crossing (GBLX)
    Global Crossing
    Global Crossing Limited was a telecommunications company that provides computer networking services worldwide. It maintained a large backbone and offered transit and peering links, VPN, leased lines, audio and video conferencing, long distance telephone, managed services, dialup, colocation and...

    /AS3549 transit, TeliaSonera
    TeliaSonera
    TeliaSonera AB is the dominant telephone company and mobile network operator in Sweden and Finland. The company has operations in other countries in Northern, Eastern Europe, Central Asia and Spain, with a total of 150 million mobile customers...

    /AS1299 transit)
  • PCCWGlobal/AS3491 (Global Crossing (GBLX)
    Global Crossing
    Global Crossing Limited was a telecommunications company that provides computer networking services worldwide. It maintained a large backbone and offered transit and peering links, VPN, leased lines, audio and video conferencing, long distance telephone, managed services, dialup, colocation and...

    /AS3549 transit)
  • tw telecom/AS4323 (Sprint Nextel Corporation/AS1239 transit, paid peering with Level 3 Communications (L3)
    Level 3 Communications
    Level 3 Communications is a telecommunications and Internet service provider headquartered in Broomfield, Colorado.It operates a Tier 1 network. The company provides core transport, IP, voice, video and content delivery for most of the medium to large Internet carriers in North America and Europe...

    /AS3356)
  • L2Networks/AS40911 (Hurricane Electric
    Hurricane Electric
    Hurricane Electric is a global Internet backbone , with a specific focus on IPv6. Hurricane Electric operates datacenters in the San Francisco Bay Area, primarily within the city of Fremont...

    /AS6939 transit)

See also

  • Tier 2 network
    Tier 2 network
    A Tier 2 Network is an Internet service provider who engages in the practice of peering with other networks, but who still purchases IP transit to reach some portion of the Internet....

  • 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...

  • Internet transit
    Internet transit
    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 to the larger Internet...

  • 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...

  • Network access point
    Network access point
    A Network Access Point was a public network exchange facility where Internet Service Providers connected with one another in peering arrangements. The NAPs were a key component in the transition from the NSFNET era when many networks were government sponsored and commercial traffic was prohibited...

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