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To picture it, there are just a few players involved that makes the whole DC (Data Center) shebang easy to understand:
The datacenter itself provides space — whole 19" racks, cages and private rooms. A datacenter usually does not sell space less than a whole 19" rack. It also provides power and cooling.
The building containing the datacenter looks/feels pretty much like a fortress (barred windows, every inch inside and outside is covered by CCTV, etc.). The datacenter operator itself does not care about fibre backbones nor about the provision for hardware e.g. random 1U server.
Carriers are those who own a fibre backbone. They do not care about the air-conditioning in the datacenter or a particular 19" rack and stuff like that. The only thing most carriers care about is extending their global net of fibre cables and monitoring it. For the most part, carriers are telcos e.g. the British Telecom is, amongst other things, what is considered a carrier in datacenter terms.
Internet Service Provider
Those are connected to n carriers (with
In datacenter terms, ISPs must not necessarily be what most of us think — an ISP provides Internet connection to end-users. An ISP can simply provide connectivity to customers which house their equipment within the datacenter. However, an ISP can do both — provide Internet to end-users and provide connectivity for datacenter customers.
This is what most of us are. A company can rent space from the datacenter, put its own equipment on this space and buy connectivity from an ISP. The space bought from the datacenter usually starts with whole 19" racks, then cages and at the upper end we have private rooms.
In case one just needs one or two servers colocated in a datacenter, then he should rather ask an ISP for an all-in-one package — space for 5Us plus connectivity. There is no need to become a dedicated datacenter customer for as little as 5Us.
As of now (February 2008), the minimum costs for a 19" rack plus 10Mbit/sec committed bandwidth (95% rule) come for around 2000 euros per month (rack rented from the datacenter, 800x800x2000 mm with doors and lock).
The connectivity for this case is mostly single-homed i.e. the datacenter customer is connected to an ISP which is then connected to several carriers for redundancy reasons. However, a datacenter customer may directly connect to one or more carriers and use dynamic routing (BGP (Border Gateway Protocol)). However, that increases costs and complexity dramatically and is mostly not recommended if the need for bandwidth is less than 100Mbit/sec (again, 95% rule).
Open Systems Interconnection
Packet vs Circuit switched
Two major packet switching modes exist; connectionless packet switching, also known as datagram switching, and connection-oriented packet switching, also known as virtual circuit switching. In the first case each packet includes complete addressing or routing information. The packets are routed individually, sometimes resulting in different paths and out-of-order delivery. In the second case a connection is defined and preallocated in each involved node before any packet is transferred. The packets include a connection identifier rather than address information, and are delivered in order.
Switching / Routing
Ein autonomes System (AS) ist eine Ansammlung von IP-Netzen, welche als Einheit verwaltet werden und über ein gemeinsames (oder auch mehrere) internes Routing-Protokoll (IGP) verbunden sind. Dieses Netz wiederum kann sich aus Teilnetzen zusammensetzen. Ein AS steht unter einer gemeinsamen Verwaltung, typischerweise von einem Internet Service Provider (ISP), einer internationalen Firma oder einer Universität. Autonome Systeme sind untereinander verbunden und bilden so das Internet.
Point of Presence
IP Address Space