Hey guys, I just started a networking course and I'm pretty bogged down with information that I'm trying to put into a rational context.

From my understanding, networking first began with the telephone line, which is pretty straightforward. You have the sender and the receiver. Then there was the problem of sending text information, so from that demand, came the modem, which worked on the telephone line, and so that was also straightforward.

What I can't quite wrap my head around yet is hubs, switches and routers.

I think my difficulty stems from not having a clear understanding of the problem that hubs, switches and routers solve. What exactly was the limitation of merely a modem based network? Why was there a demand for further technologies like hubs, switches and routers?

My understanding is that hubs are a simpler and less intelligent technology.

The next step up would be switches

And then the next step in evolution was routers.

But I'm not clear on the difference between hubs, switches and routers. I did google this info, and I found the explanations difficult because like I've been emphasizing, none of the explanations focus on the problems that these technologies solve.

So that's where I need you guys.

 

Old modem tecnologies only allowed 2 computers to be linked.
By using routers, you can link many computers together and have them share a connection to the internet.

Think of it this way:

You bought a 5 bedroom house. You rent out the other rooms to help pay for the mortgage.

Now everyone wants internet access in their room.

SO, You can call BIGCo (The internet company) and have them run and install 5 modems, (One for each roomate) or you can have them install 1 modem.

I would rather pay $40 a month for 1 modem opposed to $200 a month for 5 modems.

Ok. Now you have the modem in your room. GREAT! you have internet.

But how do the roommates get online?

Thats where switches and routers come in to play.

The router ACTUALLY ROUTES the other computers requests for internet.

Only one can talk at a time, so the switch SWITCHES between computers at a fast rate to allow access to all.

http://en.wikipedia.org/wiki/Router

 

Ok. Now you have the modem in your room. GREAT! you have internet.

But how do the roommates get online?

Thats where switches and routers come in to play.

The router ACTUALLY ROUTES the other computers requests for internet.

A good analogy then might be to imagine a single plug outlet that can provide power to merely one appliance. A router is like a power bar that you plug into the single plug outlet, creating 5+ outlets.

Is that a good analogy?

Only one can talk at a time, so the switch SWITCHES between computers at a fast rate to allow access to all.

http://en.wikipedia.org/wiki/Router

I realize this is where my plug analogy breaks down. Routers cannot supply incoming information to all computers simultaneously, so the router segments the incoming information, categorizing each segment according to the computers making the page requests. How does that sound?

 

Are you studying electronics or computing or.....?

You should realise that when you have several machines connected together, they cannot be allowed to all 'talk at once' and there has to be a way of identifying which machine is the target for a particular message. There is also one machine in overall charge or control of the network.

Older ways to achieve this use extra connections called control lines. Very often such a network is called a BUS.

Modern data networks usually use serial communication, without control lines. This means that the control information is contained within the signal.

Routers are one way to control a network to achieve the above. They contain the necessary controller for an ethernet type network. It is also possible to use a computer for this function.

Other serial networks can be established on USB or Firewire with controllers in USB or Firewire hubs.

 

Traffic lights are the best analogy. The intersections with the sensors in the ground.

If there is no traffic at light 2, 3 and 4 then light 1 stays green.

As soon as traffic appears at more or all of the lights, the system "routes" the cars along their way without any car having to wait more than others.

 

Routers solved the IP address interconnect problem....
The internet is vast...
And so vast that no one knows all the available connections...
Routers are smart boxes - but they only know the IP addresses of the boxes/routers they are connected to (normally not the IP addresses of routers connected to other routers). They do this by maintaining a Router IP Index database (in the router itself). Yes they can be configured to add IP addresses of destinations not directly connected to them - this is a discussion for a higher level of understanding).
This is the exact technical reason why the internet works. No one router has all the IPs and no one router is actually connected directly to everything. But - the IP address itself is an actual digital address. Kinda like a phone number. Each tier in the network is associated with an IP tag group, put all the tag groups together and then add the final device IP and you have a direct connection (so to speak).
...
In the early days we had hubs - which allowed multiple computers to share the same network. HUBs were just hard wired IP Splitters. a network can have 256 avalable IP's with one being the device, and another being the Server/source.
..
They also occupied available IP addresses (not a problem in the early days)..
Then came LAN Switches - which basically allowed an almost limitless address scheme. The switches basically added additional subnet IPs to the mix.
...
No one person actually knows the "whole" Internet. they may comprehend and understand how it all meshes together - but really. I was in the ARPA NET and DDN NET working groups when we wrestled with the delimmas of Net Architecture and how they would inter operate.
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The CISCO Systems recommendation of distributed Routers with interconnect IP tables that store the Other routers connected to each router directly was the scheme that actually survived and performed in the early stages. And we were only dealing with 255,000,000,000 possible addresses. All these were grouped into 99 regions and 252 Tiers. the 252 subnets and 252 destinations gave us a seemingly unlimited address schemes. But to keep it all working - each router had to deal with only the "other IPs directly connected to it. This way when the packet headers are stripped and decoded they would continue on to the router closest to the match set in the router table.
..
Web pages are a whole different scheme - but they still require IP addresses to work. They get the IP from a DNS (Domain Name Search) database. When a Domain Name is registered it is associated with a destination IP address and an Alternate Destination IP address. The domain is also associated and indexed to a region tag, and a subnet tag (oops we don't call them subnet anymore - they call them Tier IP links). The search engine takes the Domain <snip> and pulls the IP scheme fron the DNS. The DNS server provides an IP address for the web host server and the requested web page. Then the search engine on the requesting computer assembles a Packet Interchange Request Group (called a PING) and sends it to the provided IP address. During this wait state you get a "searching" message in the browser - because the routers in the system are routing to all the other routers trying to resolve the IP address into a packet address stream.
..
Once the packet address scheme is assembled --- Because when the PIG gets to the Hosts Web Server it contains all the Router IPs of all the routers it went through to get there - hence a road map back to the requesting computer. It even contains the misdirected IPs (in fact each IP jump has a "latency" score attached so the Host Server can rate and cull all the long paths and configure the shortest path back to the originator.
..
All this is done in the TCP/IP Software. The TCP/IP Stack assembles the IP Interchange Request, and once ank Acknowlegement is received - prepares the Message IP header and packets for transmission.
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Once the Web Site Host acknowledges the IP PIG your browser Search engine shows the message "connecting" Now your requested page is being sent back down the pipe to the computer that requested it. Since some of the packets will be redirected (routers also do traffic balancing a redirect some packets by alternate routes to keep the system from getting over loaded) the in coming packets are stored until they have them in a reasonable order to be displayed.
..
Now for the magic - there is a neat little trick in HTML that allows one to fragment a page into multiple layers. This allows the page to be transmitted in layers. In the transport process the reliability increases and the page will load quicker. The page will load fuzzy and get clearer as the final packets are received. Usually the images will load last. In the early days the smaller images loaded before the larger images.
..
This was desirable because no one wants to sit for say 3-5 minutes watching that stupid scanner bar going back and forth. But a fuzzy page that gets progressively clearer is intriguing. And time goes by faster when something is actually happening.
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Routers actually solved the problem of interconnectivity without overly complicated address schemes. Without the router scheme - the internet would crash. Instead of only a two lane road - they provide a 252 x 252 lane electronic highway with road signs at every intersection and automatic toll gates to speed the through traffic on to the next interchange and allowing packets arriving to be directed to the intranet connected to the local network for local delivery.
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Without the routers - one would have to make a request for a web page and wait about two-five days, or even a week for a reply.
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The internet is dynamic, and as such IP addresses and IP links routinely come and go. Having a router based system that allows for each router to monitor the links directly connected to them - allows a router to re direct packets around a link that is inoperative or overloaded and keep the packets flowing.
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Yes I would say that the development of routers is one of the most critical developments of Global Internet Connectivity.
...
Dave R. Mason
Phoenix Computer Labs
dataman19

 

A good analogy then might be to imagine a single plug outlet that can provide power to merely one appliance. A router is like a power bar that you plug into the single plug outlet, creating 5+ outlets.

[image removed]

Is that a good analogy?

This is actually a pretty good analogy for a hub, but misses the point of switches and routers completely.

In this analogy, a switch would be more like your houses circuit-breaker panel, and a router would be the electrical substation somewhere down the street from you house.

A hub just connects everybody to the same thing. Everybody gets all the network traffic that everyone else does, whether it is for them or not.

A switch somewhat separates traffic meant for each user to only go to that user.

A router also separates traffic, but does it at a higher level, usually at a level where each port would then go to the input of a switch. Each output from a switch may (or may not) go to a hub before connecting to a user.

As you might guess, on a hub, the speed is limited to the total of all the traffic attached, meaning that each user may get substantially less than the max "speed" of the connection. Switches can get past that limit and are easy enough to implement that they have largely replaced hubs.

Each level of hub/switch/router operates at a higher level of abstraction. These correspond to different levels in the multilevel protocol stack that you should be learning about.

 

One of the most important features that routers provide is that they can talk to each other and work out the best path for data. The TCP/IP protocol set, along with routers, was designed by the military. If a line was blown-up, the router would work-out another way of reaching the destination. Nowadays, instead of bombs, the problems are likely to be maintenance on lines, and too much traffic. If the connection between two places is bogged-down, the router can find a quicker way that goes through other routers.

 

Message routing predates modern computer networking technology. In a old school navy message center "Inrouter, Outrouter" were people that manually sorted incoming/outgoing messages to the correct destination.

Working as a router was know to cause excessive drinking.

http://www.google.com/url?sa=t&sour...sg=AFQjCNGXd934wL08plgubb2vLAIvmRdIvg&cad=rja