modems, routers, gateways, ethernet, token ring..uughhh...

[nothingman02]

Hi,
I am a newbie to the field of computer science. Ive recently made a career change from Mech. Engg. to computers. Im studying linux and the basics of h/w, OS, N/W etc and am planning to take up the RHCT and CCNA exams soon.
Im right now studying the n/w part and am stuck with this doubt and cant figure out despite all the google searches and would really appreciate some help.

THe doubt is about n/w hardware. What are the DIFFERENCES and SIMILARITIES between a modem and a router and a gateway. I mean if they all can transmit digital data, waht is the need for a modem? Cant a router connect to the ISP by itself? And what exactly is a gateway?

Secondly, are routers, hubs, switches, bridges and finally modems indepedent of the cabling media and physical layer topologies and technologies? I mean, does it matter if I have ethernet, token ring, and externally - telephone wires, cables, satellite, fiber optic etc to;
1) a Modem
2) a Router
3) a bridge

For instance, if I have network of PCs with ethernet NICs and cabling and another network of PCs with token ring NICs and cabling, can I simply connect these two with a hub? Or a switch or a router? Can I connect directly to the modem?
CCan the router communicate directly with the ISP irrespective of the media (fiber optics, DSL, cable, T1, Satellite etc) or do I have to have a modem?

I am new and am working very hard right now to catch up and learn and give the tests. Any help would be greatly appreciated. Thanks for your patience and your time.

 

[office politics]

i suggest studying the OSI model and focus on a good understanding of what each device does at each layer.

Routers, Switches & Firewalls ? Learn how they are different

http://pages.prodigy.net/dscribner/pub/osi_layers.pdf

Webopedia: The 7 Layers of the OSI Model

 

[nothingman02]

Hi and thanks for the reply.
I have been studing the OSI layers for a while now. I have a good idea about what happens in each layer but im getting stuck when it comes to selection.

Simply put, if one is designing and installing a small network, how is the physical media selected? I mean on what basis is the specific type of cable, hub, router and modem selected?
What I am trying to understand is that, can I just pick any kind of cabling for my network and is it going to work with any kind of router and any modem?
Are these routers and modems indepedent of the cabling?
Thanks for the help.

 

[office politics]

different devices have different requirements. different devices have different functionality. you'll want to use different devices in different situations.

As I type this, I'm thinking of phrases like "From my personal experience" and "In the real world". With this known, the only time I'll ask for a hub is for when i need to capture packets off the line. The hub broadcasts any packet received to all ports on the devices. This allows you to the traffic from other computers. Good for monitoring web traffic and troubleshooting network issues.

Typically, people will use a switch in a star network. ... Typically, everybody uses ethernet or wireless. I consider token ring a legacy technology. I'll prollly never interact on a token ring network.

Anyways, star network with a switch. You use a switch because it breaks up collision domains. Switches operate as either store-and-forward or cut-through switching. VLans & QoS are commonplace in corporate networking.

I've mainly used bridges to move data from one physical medium to another. Most commonly, wireless to ethernet.

Router allows you to communicate with other networks. Modems are similar but i can't explain the difference.

 

[oldskool]

Token ring: This is a technology not as prevalent as it once was, but is still in use today. It is made up of two rings, where data follows one ring, and if there is a break in the ring for any reason, the other ring can take over. It works on the principle of a "token" which is data that is seen by the ring as like a traffic cop, for lack of a better analogy.

Ethernet has different forms (10/100, Gigabit, etc.) , but usually runs over either Cat 5, Cat5e, or less often, Cat6 cable. It is eight-wire, which is 4 pairs of two. Cat6 differs from Cat5 in the respect that each pair is isolated from the others in the cable, which allows for better data transmission and less "crosstalk" and EMI.

Gateways can be routers, but usually are a dedicated machine that includes routing technology with other things, so they are like a router on steroids. You can google any of this stuff by the way...

Modem = modulator/demodulator. It is what turns the analgous waveforms over cable into digital data that the system can use.

EDIT: to continue, a router differs from a modem in the sense that a router operates at Layer 3, which routes packets (data packages) to various devices. A modem turns analgous waveforms (electrical energy pulses) into digital messages (on / off, or "1"/ "0").

By the way, computers don't read 1's and 0's, they read On and Off. The ones and zeroes are humans' way of recognizing the On and Off. The machine only knows two things - ON and OFF messages.

 

[bob442]

Hi and thanks for the reply.
I have been studing the OSI layers for a while now. I have a good idea about what happens in each layer but im getting stuck when it comes to selection.

Simply put, if one is designing and installing a small network, how is the physical media selected? I mean on what basis is the specific type of cable, hub, router and modem selected?
What I am trying to understand is that, can I just pick any kind of cabling for my network and is it going to work with any kind of router and any modem?
Are these routers and modems indepedent of the cabling?
Thanks for the help.

well routers switch's hubs can all use diffrent types of cable like fiber, cat 5, coax, wireless, ect. the diffrence between the devices are jobs they do and are capable of.

hub are used for small networks, they transmit al data that it recives too all ports on the hub. They can be good for certin apps in a large network, but if not used for that ertin app the would cause excess network traffic on a large network.

Switchs have evolved quite a bit scince they became a mainstreem networking device. A basic switch is similer to a hub but is smarter, it will do a little bit of packet inspection to send data it recives to a certing port on the switch witch is connected to its destination, witch could be any network device.... Switchs have become vary advanced network devices, in some cases they can serve as both a switch and router using things like VLAN's and QoS. They seperate network devices and nodes into seprate networks but are still connected to the same switch, it helps with network utilization to put is basicly. these would be a layer 3 switch because they are capable of routing, but are not a router.

Routers are are basicly what their name is, they route traffic to diffrent networks. They are mostly used for WAN connections but somtimes used to seperate portions of a LAN aswell, similer to a layer 3 switch but is more of a physical seperation because of how much it inspects the packets of data that hits it. Routers can also be considered Gateways as well.

Gateways are basicly router that are on the perimiter of the network, they uslaly run some sort of application like a firewall or AV protection for email, ect.

hope this helps...

 

[nothingman02]

Hi everybody and thanks for the replies...
Im afraid im still not in the clear. Here goes...Hope Id get some more clarification.
-----------------------------------------

Lets consider a few technologies in LAN and WAN.
Ethernet
Token ring
-----
Frame relay
ATM
X.25
T1
ISDN
----------------------------------------------------

Now, my doubt is, how does it all work and how do I pick my equipment?

I mean, if I want to have ethernet and token ring networks in my LAN and then connect to the WAN (ISP) using;
DSL or
Cable or
Satellite,
How do I pick my cabling and hubs, switches, routers etc? Are they indepedent of the technologies used? I came across that since ethernet and token ring use different frames, I would need different hubs, switches, cabling etc and I would need a translation bridge to join those two n/ws in my LAN. What about selecting a router and whats the need for a modem?

Essentially, im trying to understand if I can simply get some wires and connect every piece of equipment and connect everything to the Router and connect the router to the telephone line or cable or fiber optic etc....I mean is it as simple as that? If not, what are the determining rules for selecting cables and equipment?

Wy would I need a modem at the border between LAN and WAN when all the data is digital and there is no conversion between and analog and digital required.

Please excuse my lack of knowledge. Again, I am from a mech, engg background and making a career change into linux/sys admin and am starting off with learning the fundamentals of everything (H/W, OS, N/W, Scripting etc)
THanks for all the help again.

EDIT to ADD: If routers can not operate at layers 1 and 2 and if ne would need a switch, how is that all I have is a router in my home DSL (AT&T) network. I dont have anything else. NO modem either. Just a router to which I connect my notebook and which connects to the telephone jac. (Or could it be that all I have is a modem and no router?? I am confused! )

 

[oldskool]

EDIT to ADD: If routers can not operate at layers 1 and 2 and if ne would need a switch, how is that all I have is a router in my home DSL (AT&T) network. I dont have anything else. NO modem either. Just a router to which I connect my notebook and which connects to the telephone jac. (Or could it be that all I have is a modem and no router?? I am confused! )

I have to go to work so I will answer this part quickly ^ ^ ^

Routers operate at Layer 3, and pass on Layers 1 & 2. It isn't designed to "read" those packets. Rather, it looks in the source and destination "fields" of the packet (among other things) and relays it or not, depending if it is destined for the local subnet or another subnet. You have heard of a MAC address ? That is the number created at the factory and stamped in the firmware of the NIC or other device. That is why there is a unique number, each is given its very own hardware number. Routers just look at IP addresses and other information, and could care less about the MAC address, it just passes that along, and encapsulates it with IP address information as it is being sent from the source, or relayed if sent from another router, for example.

I can tell you more, but gotta head out the door.

 

[CntdwnToExtn]

Hi everybody and thanks for the replies...
Im afraid im still not in the clear. Here goes...Hope Id get some more clarification.
-----------------------------------------

Lets consider a few technologies in LAN and WAN.
Ethernet
Token ring
-----
Frame relay
ATM
X.25
T1
ISDN
----------------------------------------------------

Now, my doubt is, how does it all work and how do I pick my equipment?

Well, you would determine what your needs are and then find the technology that can provide it.
If you're LAN needs to be large with people accessing data simultaneously then Ethernet would be your best bet (faster, no waiting for the Token to come around to you to send/receive data).
FYI, Token Ring is basically dead. If you see it...run!

The WAN technologies, once again, dependent on what you need.
You'd use ISDN for faxing were as T1/T3 would be your workhorse WAN connection for download/upload.
Frame Relay, x25 and ATM are types of ways to transmit data like TCP is.

I mean, if I want to have ethernet and token ring networks in my LAN and then connect to the WAN (ISP) using;
DSL or
Cable or
Satellite,
How do I pick my cabling and hubs, switches, routers etc? Are they indepedent of the technologies used?
I came across that since ethernet and token ring use different frames, I would need different hubs, switches, cabling etc and I would need a translation bridge to join those two n/ws in my LAN.

Once again, you would pick your equipment for what your needs are.
If you need both networks and they needed to talk to each other, you would need a multi protocol adapter between the two.
Ethernet best runs off of switches were I believe Token ran off of Hubs.

DSL and Cable compete directly against each other most of the time, but Cable can offer speeds much faster than DSL.
DSL runs over phones lines and you need to be a certain distance from the provider to achieve maximum bandwidth. However your speed should never slow down as it is a dedicated line directly to you.
Cable runs over the cable lines (TV) and you can be any distance from the provider. However, the more people on the same segment and total usage of that segment you connection could slow down since you "share" the bandwidth.

What about selecting a router and whats the need for a modem?

A modem is a Modulator demodulator - it changes digital to analog and vice versa.
Selecting a router, once again...what you need it to do.
There are simple onces like D-Link and Linksys that are used for home networks. Very simple allowing port forwarding, logging, some parental controls.
There are complex ones like Cisco that allow multiple types of connections like Serial, RJ11, Ethernet, etc. You can set up Access Control Lists, Telnet Access, etc. These are usually a heck of a lot more robust and offer many more features.

Essentially, im trying to understand if I can simply get some wires and connect every piece of equipment and connect everything to the Router and connect the router to the telephone line or cable or fiber optic etc....I mean is it as simple as that? If not, what are the determining rules for selecting cables and equipment?

Yes, you can connect many different types of communications to each other as long as you have the appropriate hardware.

I'm not sure if you are misinterpreting what a router actually does. It segments different networks from each other.
192.168.0.0 cannot communicate to a 172.16.0.0 directly. It needs routers to connect those 2 networks.
The reason why households use a Modem to Router to PC is the fact that a router acts as a hardware firewall as well.
You can bypass your router and connect directly to the Modem with your PC (Cable, DSL) so long as you create the right connection.

Wy would I need a modem at the border between LAN and WAN when all the data is digital and there is no conversion between and analog and digital required.

If you were running Frame Relay then you wouldn't need a Modem, but a DTE and DCE switch.
If you had DSL, then yes a modem would be required since telephone lines are analog.

Please excuse my lack of knowledge. Again, I am from a mech, engg background and making a career change into linux/sys admin and am starting off with learning the fundamentals of everything (H/W, OS, N/W, Scripting etc)
THanks for all the help again.

We were all once there. Heck, I'm still learning and I've been into computers for 15 years.
Forums are great to ask questions, Wiki is great to learn in depth about the technology.

 

[moshkid213]

Going to try and break this down

Hi,
I am a newbie to the field of computer science. Ive recently made a career change from Mech. Engg. to computers. Im studying linux and the basics of h/w, OS, N/W etc and am planning to take up the RHCT and CCNA exams soon.
Im right now studying the n/w part and am stuck with this doubt and cant figure out despite all the google searches and would really appreciate some help.

THe doubt is about n/w hardware. What are the DIFFERENCES and SIMILARITIES between a modem and a router and a gateway. I mean if they all can transmit digital data, waht is the need for a modem? Cant a router connect to the ISP by itself? And what exactly is a gateway?

-------A modem converts signal "modulator-demodulator" Its part of an encapsulation process (If your taking a CCNA soon, you should know the encapsulation process for TCP and UDP along with your OSI model by heart)

-------A router, does exactly that. It routes to other networks, a router also has an IOS with software to help you out, Call Manager Express, transcoding software for codecs in use with Cisco Call Manager servers, the ability to create VLAN's by using subinterfacing and saving ports in a physical sense. MUCH MUCH more, Routers are the key to networking. IMO.

--------A gateway, is well, virtual and physical at the same time. A gateway is your key to the ouside world. You have a computer, connected to a switch which is connected to your router, the routers interface that that switch is connected to, would be your gateway, or "Default Gateway". That IP scheme also has a Net ID and Broadcast IP to go along with that.

Secondly, are routers, hubs, switches, bridges and finally modems indepedent of the cabling media and physical layer topologies and technologies? I mean, does it matter if I have ethernet, token ring, and externally - telephone wires, cables, satellite, fiber optic etc to;
1) a Modem
2) a Router
3) a bridge

-------Your wording on this confuses me. So I'm not going to try and input on it. A token ring is a network topology.

For instance, if I have network of PCs with ethernet NICs and cabling and another network of PCs with token ring NICs and cabling, can I simply connect these two with a hub? Or a switch or a router? Can I connect directly to the modem?

----Depends, you can have 2 different topologys but still be on the same network, If Im correct. You can have a network span over a switch.

CCan the router communicate directly with the ISP irrespective of the media (fiber optics, DSL, cable, T1, Satellite etc) or do I have to have a modem?



I am new and am working very hard right now to catch up and learn and give the tests. Any help would be greatly appreciated. Thanks for your patience and your time.