Network Communication – Overview
One of the challenges in learning the Cisco CCNA is learning how to navigate the massive amounts of jargon or lingo. Like the word services which can also be worded as applications, or programs, and can also be called processes. Many processes and services run behind the scenes in an operating system, if it is a Linux OS we call them daemons. Now the test writers when they make up their multiple choice tests have to make it hard somehow, so you get the picture.
A great place to start learning networking is a discussion of network communication basics. Many texts compare computer communication to regular verbal communication where two people have a conversation and they take turns, one speaking and the other listening. This is analogous to computers sending and receiving information. When computers exchange information there is a sender (the source) and a receiver (the destination) over the medium or media. The media is name give to the copper wire, the fiber optic cable, or the radio waves if it is wireless. The sender and the receiver and the media make a channel for communication. The message or data is what travels over that channel. The message is divided into smaller pieces or segments. Commonly we refer to these as packets. Later in the curriculum the word ‘packet’ will receive a more specific meaning as a single part of the overall data segment. Phew!
Multiplexing is when different types of data can travel over the wire at the same time by interleaving the individual packets. This is multiple conversations going over the channel.
We can also distinguish between end devices on a network like a computer, an ip-phone, or a network printer and intermediary devices that connect the end devices. Like a switch, hub, router, firewall or wireless access point. On a network end devices are also called hosts or clients. Another type of host is a server. A server is a host that is running server software or server programs. This means that a server is listening for requests on specific ports and is able to respond or serve data when a request comes in. A computer can be a client a server or both at the same time.
Intermediary devices have a number of functions like regenerating and resending the data signals. For instance, data signals can only travel so far on a copper wire without having to be regenerated and resent. If the signals travel too far beyond specifications, without being regenerated, then the signal, in this case voltage will weaken and the end device will not be able to correctly decode the binary 1s and 0s. Intermediary devices also maintain information about paths through the network. For example routers know paths to different networks and switches know which end devices are connected to which ports on the switch. Intermediary devices can also report errors close or route data to other paths when there is failure on a link, prioritize messages according to QoS, and filter data according to access lists which can permit or deny the flow of data.
In class the question was asked, “What is the difference between a router and a switch?” A router interconnects and routes users to different networks and a switch connects users to a single network or LAN (unless it is configured with vlans).
A LAN or local area network is a network that spans a specific area like a business, or a school. A lan is usually controlled and maintained by a single organization. The college where we have class is an example of a lan. At the college there are a lot of separate networks or subnets, many switches and routers but the entire college is in one location and under one administration so it is an example of a lan. Simply speaking if you have a bunch of computers and you network them together by connecting them to a switch and give them a common addressing or network protocol scheme then you have a lan. This could also be called an intranet or interior network in that it is interior to that organization only.
A WAN or wide are network is a network that connects lans across wide geographical distances. It is also the network that is formed between you and your lan and your ISP or internet service provider. If you have a Linksys wireless router at home or another brand you may notice that the physical ports on the back of the router are sometimes labelled LAN ports and WAN port. The lan ports connect to your home devices like computers and a network printer and the wan port connects to your modem or your ISP. In layman’s terms the wan port is what connects you to the internet.