Locality of networks

An underlying concept, locality of networks, underlies a great many terms ranging from "personal area network" to "interplanetary network". Many physical, and some logical, networking technologies make an assumption of what area they serve, or, in other terms, what is local to them.

Range	Generic type of network	Representative technologies
First meter	Personal area network, RFID	Bluetooth
First 10 meters	Line-of-sight wireless	Infrared wireless
First 100 meters	LAN star cabling, femtocell	10BaseT, 100BaseT
First kilometer	Local loop	Digital subscriber loop, intracell cellular telephony, T1 carrier, E1 carrier
Second kilometer	Drop from metropolitan area network, interoffice trunk, pair gain	SONET, SDH, T3 carrier, short-haul optical, CWDM
First Tens of kilometers	Metropolitan area network	SONET, SDH, DWDM
Planetary	Internet, Public Switched Telephone Network	Logical packet switching, HF radio, very long haul optical
Interplanetary	Interplanetary Internet project	http://www.ipnsig.org/aboutstudy.htm

Scope of information

In dealing with networking technologies of different locality, the idea of scope or locality of reference applies to addresses and other identifiers. The levels of locality listed below are general concepts and have a variety of protocol- and implementation-specific variants.

• link-local information is unique only on a shared transmission medium
• area-local information is unique only to a certain part of the hierarchy of a logical addressing structure
• domain-local information is unique only to the local logical structure. For example, if the logical structure used Internet Protocol version 4 in the private address space and used Network Address Translation (NAT) to communicate with the public Internet, the private address space used on the "inside" of the NAT would be domain-local.
• global information is unique to all reachable points of the logical or physical network.

User perspectives

From the end user perspective, locality starts from the person, and moves outward. It may even begin inside the person, as with a cardiac pacemaker that electromagnetically couples to an interrogation probe connected to a monitoring control computer.

Perceptions of the network

While much of this article deals with transmission technology, evolution of human interfaces should not be forgotten. Ubiquitous computing creates an environment where the computer interfaces are everywhere, but taking actions invisibly to a user. A very basic use of ubiquitous computing, for example, turns on a room light when it senses a person has entered. A much more advanced version, demonstrated at Xerox Palo Alto Research Center, when a room was occupied by one person, it would sense the direction in which the person is looking, and turn lights on and off so the light was never in the occupant's eyes. When the system detected an additional person or persons in the room, it would change to diffuse lighting.

The other extreme of human interface is virtual reality, where, rather than the ubiquitous computing paradigm that senses a human in the real environment, the alternate paradigm creates the reality.

Both of these technologies will involve short-range, high-speed communications, for functions such as detecting a human in a room, or, in a virtual reality system, detecting body movement and changing the generated visual perspective to match.

Carrier perspectives

Some writers treat these in reverse, as, for example, the "last mile" problem, but there is little question that one of the most challenging, capital- and labor-intensive problems in communications is reaching the individual user, or small office.

FTTX

Carrier perspectives indeed often focus on the "last" increment of media, the subscriber end of fiber optic networks, generically Fiber to the X (FTTX), where:

• Fiber to the home (FTTH) describes installation where optical fiber physically enters the subscriber premises and connects to a router or other end equipment there;
• Fiber to the curb (FTTC) can refer to telephone installations where the fiber terminates in a curbside weatherproof pedestal, from which copper pairs connect to the subscriber locations. This is also seen in cable television networks where the main distribution is optical, but, at each telephone pole from which a customer will receive service, there is a converter box that picks off the appropriate signal and enters the premises via coaxial cable or, rarely, high-grade copper pair using Very High Speed Digital Subscriber Loop (VHDSL) technology.
• Fiber to the building (FTTB) uses fiber to deliver a high-speed connection from the provider's point of presence to a multi-unit office or apartment building, where it is distributed using LAN technology. Depending on the speeds and distances involved, the in-building distribution may use fiber or high-grade (Cat5 or better) twisted pair. Coaxial cable LANs essentially are obsolete.