21 - TEORÍA y EJERCICIOS - Redes VoIP y repaso (operadores cables, categorías)

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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:

The switch inside VoIP phones

Los teléfonos tienen 2 puertos:

Así que los teléfonos tienen internamente un switch de tres puertos:

El conector LAN soporta en muchos casos alimentación PoE. Cuando sea así (y el switch del aula lo soporte), no necesitarás fuente de alimentación.

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 Manchester1).

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.


Ejercicios redes VoIP

  1. VoIP. Dibuja el esquema lógico de la siguiente red local (192.168.0.0/24) que consta de:

Indica todas las configuraciones. Después, responde a las preguntas:

  1. Una empresa alquila una ventana de 1 Gbps en una fibra óptica DWDM comunicar sus dos sucursales. Pretenden cursar llamadas ToIP entre las dos zonas usando el protocolo más típico de VoIP: señalización SIP, códec de audio G.711 alaw (64 kbps a 8 kHz de frecuencia de muestreo) streaming UDP. Los equipos de red no han sido configurados para QoS (calidad de servicio), así que se procede a hacer una llamada de prueba con captura de paquetes durante 5 segundos en uno de los sentidos. Estos son los resultados obtenidos:

Datos de referencia: latencia ≤ 150 ms; jitter ≤ 30 ms, pérdida de paquetes ≤ 1%; Bitrate típico VoIP: 30 - 128 kbps. (Datos extraidos de Cisco CCNAv6, módulo 4, diapositiva 6.1.2.3)

Análisis de latencia y jitter en una conversación VoIP:

Tests de ancho de banda


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  1. Ojo porque en DSL, DOCSIS y GPON los datos si están modulados (no sería “BASE”, sino “ANCHA”/“WIDE”). ↩︎
  2. This leads to some confusion since 100 Mbps is no longer “fast”. ↩︎