09 - An introduction to networks

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The net is vast and infinite

– Motoko Kusanagi

Communication service providers

A communication service provider can offer one or many of the following services:

As you already know, the future is all-IP (convergence between all kinds of networks and TCP/IP1 networks). As a consequence, all these services come from an ISP (Internet Services Provider)

ISPs typically own both a fixed and a mobile (4G) network. The other services (voice, TV) tend to become data traffic:

So ISPs concentrate all these services in what is referred as “Triple play”: voice, data, TV.

How to guarantee that the quality of the phone calls is always good? Thanks to QoS (Quality of Service) rules that reserve a part of the bandwith.

The word “Carrier” can refer to a part of an electric signal, but in English it also means a “wireless communication service provider” (Movistar, Pepephone…).

Own vs. hired network

Both fixed and mobile communications providers can have their own network or hire an existing one thanks to the spanish Law NEBA “Nueva Ethernet de Banda Ancha” (for fixed networks) or OMV “Operadores Móviles Virtuales” (for mobile networks).

OSI model

The Open Systems Interconnect tries to standard the communications. It consists on seven layers. The most important ones:

  1. PHY (physical layer). It represents the voltages, the frequencies…
  2. MAC. It represents the physical addressing. You should not change your MAC address (but you can).
  3. In TCP/IP, this is the IP address. It depends on the network.
  4. In TCP/IP, this is the port number. It depends on the application.
  5. , 6 and 7. Not important for this course.

TCP/IP basic concepts

This theory is necessary for networking subjects, but also for understanding VoIP telephony (Voice over IP).

Definition: A host is any device connected to a network. A host can have one or many IP address(es).

These fields are necessary for the network configuration of any host:

Difference between switch and router

<<This is a quick and dirty explanation>>

Switch
Switch

Basically, a switch connects many hosts that belong to the same network (192.168.0.1/24, 192.168.0.2/24…). It doesn’t have to have an IP address.

…while a router connects to two or more different networks.

Router
Router

For example, your home modem-router connects on one side to the WAN network of your ISP (83.213.53.12) and on the other side to your home network (192.168.0.1). It must have one address on each network.

Example network:

Difference between router and modem-router

A router connects two or more networks of the same standard (typically ethernet).

A modem-router also connects two or more networks, but one of them is not ethernet. It can be DSL, DOCSIS, GPON.

Network types according to their topology

Otras variantes son Estrella extendida y malla parcial.

Mira el siguiente cómic sobre Paul Baran y la historia de las telecomunicaciones: Historia de las redes: guión ilustrado

Lectura larga: How the Internet works: Submarine fiber, brains in jars, and coaxial cables.

Networks according to their size

Some of them can be partially wireless: WLAN, WMAN. Example: Guifinet:

Guifinet in Sarria
Guifinet in Sarria

What is Ethernet?

According to Wikipedia: Ethernet /ˈiːθərnɛt/ is a family of computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 1983 as IEEE 802.3.

Ethernet standards according to their media and speed

Como norma general el primer número indica la velocidad de transmisión en Mbps, la palabra BASE indica que los datos se transmiten sin modular, directamente “1” equivale a un voltaje y “0” a otro (en par trenzado se usa Manchester2).

Fuente.

Ejemplo: 100BASE-T indica 100Mbps sobre par trenzado (la “T” indica “twisted pair”).

Tradicionalmente, las velocidades han aumentado en múltiplos de 10, pero ahora ya no se avanza tan rápido. Así, los estándares más típicos son:

Categorías en Wikipedia.

Más información en el podcast de Eduardo Collado.

Imagen de https://www.telecocable.com/blog/diferencias-entre-categorias-de-cables-de-par-trenzados/563
Imagen de https://www.telecocable.com/blog/diferencias-entre-categorias-de-cables-de-par-trenzados/563

Existen tecnologías de Link aggregation que permiten sumar el ancho de banda de varios canales .

Kinds of twisted pair cables

We have…

…for telephony/DSL:

…for data networks but also telephony/DSL we use twisted pair:

Remember to use RJ-49 plugs when shielding is present.

Categories of twisted pair cabling

Newer categories (7a, 8.1, 8.2…) will support above 1 GHz.

Number of wires/pairs used

As you know, UDP/FTP/STP/FTP cabling has four pairs (8 wires). The number of wires used depends on the bitrate (speed):

This is no standard UTP CAT5e cable. This is some shitty cable.
This is no standard UTP CAT5e cable. This is some shitty cable.

When you use UDP cables for ICT distribution networks, they transport DSL signals (NOT ethernet), so they just use one single pair (the other three act as a reserve).

NOT INTERESTING ANYMORE: You could use the same cabling for telephone and ethernet ≤100Mbps. You just have to use the blue pair for telephone, and the green and orange pairs for ethernet.

The PoE standard

The Power over Ethernet standard allows to transport the DC necessary to power the devices. It eliminates the necessity of power supplies in certain areas.

More info.

 About fiber optics

…more info later.

What is Wi-Fi?

It is the standard IEEE 802.11. It is used in WLAN and WMAN networks

…more info later.

What is LMDS/WiMAX?

It is the standard IEEE 802.16. It is used in WMAN networks.

…more info later.


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  1. TCP/IP usually refers to “data networks”, but any data network can serve many purposes (voice, TV, sound…) ↩︎
  2. Ojo porque en DSL, DOCSIS y GPON los datos si están modulados (no sería “BASE”, sino “ANCHA”/“WIDE”). ↩︎
  3. This leads to some confusion since 100 Mbps is no longer “fast”. ↩︎