Internet Service Providers
An Internet service provider (ISP) is a company that provides Internet access to business and residential customers on a commercial basis. ISPs offer a range of connection types, including dial-up, DSL or cable, and most provide email services inclusive of multiple mailboxes, and personal Web space on their Internet servers. ISPs usually (though not always) have their own regional (Tier 2) network that connects to one of the Internet backbone (or Tier 1) networks via a point of presence (PoP), either directly or via other Tier 2 networks. Often, an ISP will have multiple points of presence, giving it a number of routing alternatives for Internet traffic.
A Tier 1 network is one of the networks that together constitute the backbone of the modern global internet. In the early days of the Internet, NSFNet replaced ARPANET as the Internet backbone network, but has since been superceded by the Tier 1 networks. By definition, a Tier 1 network has connectivity with the entire Internet thanks to peering arrangements with each of the other backbone networks. Peering is essentially an agreement between two or more networks to carry each other's traffic without levying charges for the services they provide to each other. Such an agreement is known as transit free peering, because traffic from each network may transit the other networks that are party to the agreement free of charge.
In some cases, one of the networks may feel that it is making a larger contribution in terms of the services provided than its partner (or partners) in the peering agreement, and may require a settlement of some kind, which usually involves a sum of money changing hands. Under the strictest definition of what constitutes a Tier 1 network, any network that pays a settlement to another would lose its Tier 1 status. In reality, many of the larger networks enter into such arrangements with each other. Thanks to the almost universal use of non-disclosure agreements, however, very little information is available about these settlements. A looser, but generally accepted definition of a Tier 1 network is one that can reach every other network on the Internet without paying for transit or making overt settlements.
The eight networks listed below are generally believed to meet the accepted definition of a Tier 1 network (i.e. they do not pay for transit, and have not made any an overt peering settlement to any other network):
- AT&T
- Global Crossing
- Level 3 Communications
- NTT Communications (Verio)
- Qwest
- Sprint
- Verizon Business (formerly UUNET)
- SAVVIS
A Tier 2 network is defined as a network that has peering agreements with some networks, but must purchase transit, or pay an overt settlement, in order to reach certain parts of the Internet. By far the majority of Internet ISPs operate Tier 2 networks. Some Tier 2 networks claim the status of "regional Tier 1" because they operate on a transit-free basis within a particular country or region. British Telecom, for example, claim Tier 1 status within the UK, although in order to implement connectivity with the global Internet they purchase transit with Global Crossing, Level 3 Communications, and Sprint Nextel Corporation. The term Tier 3 is sometimes used to describe organisations that buy internet access in bulk from a Tier 1 or Tier 2 network, and resell it to their customers. The diagram below illustrates the typical transit and peering relationships between various networks. Note that networks owned and run by a single organisations are sometimes referred to as autonomous systems, hence the networks shown are labelled AS1 ... AS6.
Typical transit and peering relationships between networks
Interconnectivity between networks requires the presence of physical interconnection points, and an exchange of routing information. The latter is managed on the Internet using the Border Gateway Protocol (BGP), which allows routers to periodically send each other information about the networks to which they are directly connected (more about BGP later, in the page entitled "Internet Protocols") The physical interconnections between the various major networks that form the bulk of the internet fall into two categories:
- Private peering - a direct point-to-point link between two networks
- Public peering - a shared switch, typically a Gigabit or 10Gigabit Ethernet switch, is used to interconnect multiple networks
The switches employed for the purpose of providing public peering interconnections are usually referred to as Internet exchange points (IXPs). Some of the largest IXPs can connect hundreds of networks, and often occupy quite large colocation facilities. Some of these facilities are operated by commercial, carrier-neutral third parties, who promote inter-network co-operation and encourage new peering relationships. The largest individual Internet exchange points in the world are AMS-IX in Amsterdam, DE-CIX in Frankfurt, and LINX in London.
Tier 1 networks usually have only a small number of peers (typically the other Tier 1 networks and very large Tier 2 networks). Tier 1 networks interconnect with each other directly, and do not have an alternative transit path to any of their Tier 1 peers, so a major dispute between Tier 1 networks can potentially partition the Internet if the peering agreement is discontinued, and this has indeed happened in the past. Fortunately, such disputes are not frequent, and are usually resolved quickly. In any case, most major Tier2 networks have transit (or peering) agreements with more than one Tier 1 network, so their Internet connectivity is not usually too badly affected.
When choosing an Internet service provider, the factors that will affect your decision will be the cost, the nominal connection speed, and the terms of the contract (for example, how long are you tied in to a particular ISP once you have signed up?). Depending on the sort of thing you intend to do with your Internet connection, you may also want to know whether there is any limit on the amount of data you can download in any one month, whether or not the ISP provides email services (most do), and whether they give you any personal Web space (and if so, what you are allowed to do with it). Bear in mind when choosing an ISP that the availability of some types of broadband service is currently limited to certain areas. You will need to check with the ISP whether your area can receive the services they offer. Most areas of Britain can now get ADSL broadband, which operates over standard telephone lines. The following table compares some of the currently available services offered by ISPs in the UK.
| ISP | Service description | Speed | Downloads | Contract | Price/month |
|---|---|---|---|---|---|
| AOL | Broadband Wireless Flexi Off-Peak Free wireless router & off-peak calls. No minimum contract. | <= 8Mb | 10Gb | 1 month | £4.99 (first 3 months - can vary with area) |
| AOL | Broadband Wireless Flexi Anytime Free wireless router & anytime calls. No minimum contract. | <= 8Mb | 10Gb | 1 month | £4.99 (first 3 months - can vary with area) |
| AOL | Broadband Wireless Off-Peak Free wireless router & off-peak calls. | <= 8Mb | 10Gb | 18 months | £4.99 (first 3 months - can vary with area) |
| AOL | Broadband Wireless Anytime Free wireless router & unlimited calls. | <= 8Mb | 10Gb | 18 months | £4.99 (first 3 months - can vary with area) |
| Be | Be Value One month free subscription, free wireless modem & no connection fee | <= 8Mb | Unlimited | 12 months | £8.00 (free until 1 February) |
| Be | Be Unlimited Free wireless modem, static IP & technical support | <= 24Mb | Unlimited | 3 months | £17.50 |
| Be | Be Pro Free wireless modem, static IP & technical support. Up to 2.5Mb upload | <= 24Mb | Unlimited | 3 months | £21.50 |
| BT | Option 1 Free wireless Home Hub & UK calls. Optional BT Vision. | <= 8Mb | 10Gb | 18 months | £7.78 (first 3 months) |
| BT | Option 2 Free wireless Home Hub & off-peak UK calls. Optional BT Vision. | <= 8Mb | 15Gb | 18 months | £13.69 (for 3 months) |
| BT | Option 3 Free wireless Home Hub, phone & UK calls. Optional BT Vision. | <= 8Mb | Unlimited | 18 months | £18.59 (for 3 months) |
| O2 | Broadband Standard Free wireless router. Discounted for existing customers. | <= 8Mb | Unlimited | 12 months | £7.34 (£12.23 for non-O2 customers) |
| O2 | Broadband Premium Free wireless router. Discounted for existing customers. 3 months free | <= 20Mb | Unlimited | 12 months | £9.79 (£14.68 for non-O2 customers) |
| O2 | Broadband Pro Free enhanced wireless router. Discounted for all existing customers. Prioritised customer service. 3 months free | <= 20Mb | Unlimited | 12 months | £17.13 (£22.02 for non-O2 customers) |
| Orange | Home Starter Free off-peak landline calls & wireless modem | <= 8Mb | 10Gb | 18 months | £10.00 (price can vary on area) |
| Orange | Home Max Free line rental, free calls, VoIP & wireless LiveBox modem | <= 8Mb | Unlimited | 18 months | £25.00 (price can vary on area) |
| PlusNet | Option 1 Free modem, VoIP calls & overnight usage | <= 8Mb | 2Gb | 1 month | £9.75 |
| PlusNet | Option 2 Free wireless router, 120 minutes VoIP calls & overnight usage | <= 8Mb | 15Gb | 1 month | £14.65 |
| PlusNet | Option 3 Free wireless router, 240 minutes anytime VoIP talk & overnight use | <= 8Mb | 30Gb | 1 month | £19.55 |
| Post Office | Broadband Standard Free modem and evening & weekend calls, line rental included | <= 8Mb | 5Gb | 12 months | £19.53 (incl line rental) |
| Post Office | Broadband Extra Free wireless router, evening & weekend calls and PC security suite, line rental included | <= 8Mb | Unlimited | 12 months | £24.42 (incl line rental) |
| Sky | Broadband & TV [1] Free wireless router, 1 TV pack, UK evening & weekend calls. £15 online credit & £50 M&S vouchers | <= 2Mb | 2Gb | 12 months | £17.00 |
| Sky | Broadband & TV [2] Free wireless router, 6 TV packs, UK evening & weekend calls. £15 online credit & £50 M&S vouchers | <= 2Mb | 2Gb | 12 months | £22.00 |
| Sky | Broadband & TV [3] Free wireless router, 4 Entertainment & 1 Premium TV packs, UK evening & weekend calls. £15 online credit & £50 M&S vouchers | <= 2Mb | 2Gb | 12 months | £36.00 |
| Sky | Broadband & TV [4] Free wireless router, 6 TV packs, sports mix & movies pack, free off-peak calls. £15 online credit & £50 M&S vouchers | <= 2Mb | 2Gb | 12 months | £47.00 |
| Talk Talk | Essentials Free wireless router, off-peak calls & inclusive broadband. | <= 8Mb | 40Gb | 18 months | £6.49 (line rental £10.50) |
| Tiscali | Option 1 Free wireless router, connection & weekend calls | <= 8Mb | Unlimited | 12 months | £6.49 (first 3 months) |
| Tiscali | Talk 1 Free line rental, wireless router & weekend calls | <= 8Mb | Unlimited | 12 months | £9.99 (first 3 months) |
| Tiscali | Talk 2 Free line rental, wireless router & anytime calls | <= 8Mb | Unlimited | 12 months | £14.99 |
| Virgin Media | M Phone (Cable) Fibre optic broadband with free weekend calls, modem & PCguard. Order online for £25 credit | <= 2Mb | Unlimited | 12 months | £4.50 (landline £11) |
| Virgin Media | L Phone (Cable) Fibre optic broadband with free wireless router & weekend calls. Order online for £25 credit | <= 10Mb | Unlimited | 12 months | £8.00 (first 6 months, £11 line rental) |
| Virgin Media | M (Cable) Fibre optic broadband with a free modem & PCGuard. Landline not required | <= 2Mb | Unlimited | 12 months | £10.00 (first 6 months) |
| Virgin Media | XL Phone (Cable) Fibre optic broadband with free wireless router & weekend calls. Order online for £25 credit | <= 20Mb | Unlimited | 12 months | £10.00 (first 6 months, £11 line rental) |
| Virgin Media | 3 for £16 (TV) Fibre optic broadband, 40+ TV channels (including Sky), calls & wireless router. Order online & save £50 | <= 10Mb | Unlimited | 12 months | £16.00 (landline £11) |
| Virgin Media | L (Cable) Fibre optic broadband with free wireless router. Landline not required | <= 10Mb | Unlimited | 12 months | £17.00 (first 6 months) |
| Virgin Media | Virgin Media 2 for £25 (TV) Over 83 TV channels (including Sky), free modem & PCGuard | <= 2Mb | Unlimited | 12 months | £25.00 |
| Virgin Media | XL (Cable) Fibre optic broadband wit free wireless router. Landline not required | <= 20Mb | Unlimited | 12 months | £29.00 |
| Virgin Media | 3 for £30 (TV) Fibre optic broadband, calls, 90+ TV channels (including Sky) & wireless router. | <= 2Mb | Unlimited | 12 months | £30.00 |
| Virgin Media | 4 for £40 (TV) Fibre optic broadband, 90+ TV channels (including Sky), mobile & home phone. | <= 2Mb | Unlimited | 12 months | £40.00 |