In this series we have discussed the basics of RF Theory, Fresnel Zones, Channel Bandwidths and Antennas. Now, we want to use this foundation to make up an outdoor wireless link.
First, a couple of basics that we need to understand is where a PtP (Point to Point) link and a PtMP (Point-to-Multipoint) link will be used.
In this network overview we aim to provide internet access to our subscribers. We have internet being provided by a Tier 1 service provider in the form of Fibre, and we now need to distribute this down towards our customers. Our first obstacle is that our Sector Antenna base station is too far away from our Fibre connection. To overcome this, we put up a base station close to where our Fibre terminates and use a PtP link with high gain antennas to our sector base station. In this PtP link, we use radios that operates in FDD or Frequency Division Duplexing. This means that the radio uses one frequency to Transmit and another to Receive and they have a large enough offset between them that they do not interfere with each other. This allows your PtP link to Send and Receive at the same time (High capacity throughput).
So now that we have the Internet access via a wireless link to the sector base station, we can use a 90° or 120° sector antenna with a wide beam width to distribute the internet access down to our subscribers. This is also what is known as a Point to Multipoint network and this portion of the network operates on TDMA or Time Division Multiple Access, where one frequency is used both for sending and receiving, however not at the same time, but on separate dedicated time slots. Throughput of the TDMA protocol is slightly less when compared to the FDD protocol, but equipment that operates on TDMA is generaly more cost effective.
Understanding the outdoor wireless equipment to make PtP links and even PtMP links is fundamental, however there are various other components that form part of the entire network operations, such as Routers and Switches.
A network switch, also referred to as a layer 2 device, is a constituent of computer networks that connects two network devices together. A switch can also be termed a network bridge with multiple ports which helps to process and route packets and data link layer of the OSI reference model.
A network router, also referred to as a layer 3 device, is a networking device that forwards data packets between computer networks. Routers perform the traffic direction functions on the internet. A data packet is typically forwarded from one router to another router through the networks that constitute the internetwork until it reaches its destination node.
Most outdoor wireless networks do support layer 2 functionality, i.e. acts as a network switch, so switches can be located on both your base stations and your Point of Presence along with routers that allows for firewall functionality.
This however, brings the introduction to wireless communication series to an end, but also introduces us to the next part, namely introduction to networking fundamentals.
Our next series will aim to provide you with the same fundamental information based on networking from IP Address assignment, subnetting all the way to BGP and OSPF.