transmission concepts and media part 1 of 2_v401/course/... · transmission concepts and media part...

Transmission Concepts and Media Part 1 of 2

Table of Contents

Transmission Concepts – Signaling ................................................................................................. 2

Transmission Concepts – Formatting ............................................................................................. 4

Transmission Media ........................................................................................................................ 6

Transmission Media – Standards .................................................................................................... 9

Transmission Media – Coaxial Cable ............................................................................................. 12

Transmission Media – Twisted Pair .............................................................................................. 14

Notices .......................................................................................................................................... 18

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Transmission Concepts – Signaling

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Transmission Concepts – Signaling

Analog

Digital

Frequency Modulation

Amplitude Modulation

1

0

1

0

1

0

1

0

**050 So let's dig into these concepts here. First, we need to talk about the way we actually transmit signal. There's two ways to do this: analog and digital. When we deal with analog we can increase the frequency at which the waves come-- that's the frequency modulation, that's how many different- different squiggles we see on the line-- or the amplitude modulation, how high and low the peaks are.

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In analog we use both of those concepts to actually pass data across the wire. When we go from analog physical signal as far as the wire is concerned over to a digital signature- a digital signal, then what we do is we tend to smooth this out and have a square wave. Today we primarily use digital. Very few people are using modulation/demodulation tools; modems these days. Even though they'll call it a DSL modem, it's not really a DSL modem. It happens to be some sort of router; and it is digital at that point.

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Transmission Concepts – Formatting

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Transmission Concepts – Formatting

Synchronous formatting• Clocked data control, or embedded in data stream• Reduced overhead – better for large data transmissions

Asynchronous formatting• 1 bit start, stop, and parity (error checking) for every 8 bytes• 3 bits of overhead for every 8 bits of data

Start Data Parity Stop

1 1 18

Control Data ErrorCheck

**051 When we look and compare the two transmission concepts from a formatting standpoint, synchronous formatting uses one thing that asynchronous doesn't; and that is a clocking mechanism. That means that the clocking mechanism on your side and the clocking mechanism on my side, they have to be in perfect sync; not at the one second level that you see here but at the millisecond level. And I can't wave my arms that fast. That's expensive. And what was realized in a lot of synchronous communications was it was too

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expensive and there was another way. So what we did was we decided to convert to more of an asynchronous format; which signals the beginning and the end of a particular transmission using a stop and start bit. The problem is is that that stop and start bit happen on every single transmission, even if we transmit no data whatsoever. So it increases the overall overhead when we're using an asynchronous format versus a synchronous format. The signaling methodology in synchronous with the timing says: At the beginning of this transmission synchronize your clock to this and I'll synchronize my clock to this. And we go, go, go, go, go; and the only thing that we have to fix at this point is the error checking between us to make sure that it actually went correctly. And that can be reduced calculation. A synchronous bit, you've got a stop and a start bit; and there's three bits of overhead for the entire thing because we also have to calculate the parity, which is error checking again.

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Transmission Media

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Transmission Media

Move signals from one point to another• Various cables and wireless methods exist• Selection criteria

— Throughput – how quickly a media moves data (bits per second)— Distance – the maximum distance between devices— Data sensitivity – how susceptible data is to interception on this media— Environment – layout, interference, and climate

**052 Let's look at the transmission media. I mean, the idea here is that we want to move a signal from one point to another; and we've got all these different possible ways to do that, physical ways to do that, of transmitting that. So when we set our cabling or wireless plant in place, we make some business decisions and we make some security decisions. How much data is being transmitted? How would you know that? Well you'd take a sampling of what your communications are and you'd see how much utilization you have over a

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particular pipe. You wouldn't do this unless there was actually some sort of form of networking in place. Usually what happens is is people decide that they're going to use 100 megabit, and they realize that 100 megabit isn't fast enough; so they need to go to gigabit because the utilization on the network is at 99 percent and we every once in awhile- - by the way, when we hit the upper limits we gets lots and lots and of collisions, and no communication happens. If anybody's been around for awhile, there used to be the hubs that we'll talk about, the devices that we talked about, have what's called a collision meter on them; I called it a collision- o-meter at that point. And what you would see is when you have a certain number of hosts on the network everything would be fine; and you'd plug in or turn on that last host and the collision meter would go all the way to the top and pin itself and then knock everybody off the network because of the collisions that were actually occurring. So the amount of throughput can get to a critical level whereby you can't do any communication whatsoever. Also how long is it from me to you? How- what's that distance there? And there are requirements on when we're transmitting over copper that we have a limited distance or a limited run.

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Next is the data sensitivity. If this is more sensitive information, maybe we make it go faster or maybe we encrypt it as it goes across the wire; or maybe we don't use wireless. So we start making those choices. And then finally: What does the environment look like? I've talked to some engineers that do wiring in some of the Asia Pacific countries, and they have a very big problem with- in their- in their places where they actually put their copper. They have a big problem with rodents coming in and chewing on the wire; because the rodents are sensitive to this vibration in the wire and they think that it's good in some way, shape or form. So in their environment they can't use any copper whatsoever. So what they do to deal with that issue is they run fiber; even though it's much more expensive for them. It's either that or tear out the wires every couple of months because you've lost a particular signal across there.

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Transmission Media – Standards

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Transmission Media – Standards

Exist to ensure working implementations• Cable must be assembled correctly• Shielding or wire twisting used to counteract interference• Test cables and certify them before use• Do not exceed maximum lengths

**053 Okay so Transmission Media Standards. When we put those out, we're all going to follow that same standard. So when you wire yours one way and I wire mine another way, we're never going to communicate. But if we say: Okay we'll wire to this standard and we'll follow that standard across everything that we implement, then that becomes also a purchasing choice. We do bulk purchasing. We also look at the connectors on the end that we're using; also the physical plant and actually putting in the network cards themselves.

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Today for end-users' workstations, since we're using so much wireless out there we've really stopped wiring the room with ports all over the place. I mean, we used to do that all the time. And now what we do is we say: Okay you're in this room. There's a port for this room, there's a wireless access point on the ceiling right about there; or maybe there's even two if it's a large room. And that's kind of the end of it. Sometimes you need a physical wire because of the sensitivity of the network. Also when you're dealing wiring those locations, now you also have to deal with interference. So you might put in shielding. If there's lots and lots of power being run there, you don't want to run the power and the Ethernet cable next to each other because you'll get lots and lots of crosstalk as they go down a line. All the cables have to be tested and certified before they're actually put in place. In a business environment you may be changing continually. So therefore you need somebody who is qualified to make those cables, do those cable runs, actually has all the testers, and will certify it. And actually they'll do a printout on the more complex certifiers out there. There's a million machines out there.

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I always use the yellow ones; everybody knows who makes the yellow ones. And it actually gives you a printout to say that this cable at this run, at this location, at this time was valid and correct. And then you put those into your change management operations, so that everybody knows that the cables have been tested and validated across the- for all your wiring schemes. Normally what you do is in your first implementation you call in cabling specialists that will actually wire the building for you; and you kind of stop it at that point. But if you've got a constant churn there, you want to make sure from a business standpoint that you've got somebody on staff that's qualified to do that. That person might be you; you know, you might have to learn how to do that. So you have to do that, not only for Ethernet-- because that's the predominant one-- but you've got to be ready for all the other possibilities that are out there.

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Transmission Media – Coaxial Cable

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Transmission Media – Coaxial Cable

Thinnet – “lite” version of the original Ethernet specification• RG-58 coaxial cable• Bus topology, inherent weaknesses in single points of failure• aka 10Base2 (10Mbps, up to 200 meters cable length)

Thicknet – the original Ethernet specification• RG-5 coaxial cable• Same bus topology and weaknesses• aka 10Base5 (10Mbps, up to 500 meters cable length)

**054 So let's talk about some of the other possibilities. Okay coax. They've got those lines either buried or running up the telephone poles behind your house; unless you happen to be- unless you're lucky enough to be in a fiber network or a fiber neighborhood. So we have two different kinds of media at the coax level that we pay the most attention to. There are others out there. But these are part of the networking standard of Thinnet and Thicknet. You can know

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this by its cabling standard of RJ-58 or RJ-5. We tend not to use these in networking today; because of one reason: proliferation of Ethernet. And also the proliferation of Ethernet cards in all of our devices. If they're going to have a network port on it, it's going to be an Ethernet port and not Thinnet or Thicknet. They don't come standard anymore. So because of the force in the market and everybody purchasing this, they've kind of let these things fall by the wayside. Thinnet and Thicknet have their purpose. They are rigid and they last a very long time when exposed to the elements; especially Thicknet. Now it goes at a relatively slow speed. So that's not very elegant for our internal networking at this point. So these are the kind have kind of fallen by the wayside at this point.

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Transmission Media – Twisted Pair

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Transmission Media – Twisted Pair

Copper wires are twisted together to reduce interference

Cat5e is de facto standard for Ethernet implementations

Maximum length for Cat5 is 100mCategory 1, < 1 Mbps, ISDNCategory 2, < 4 Mbps, Token RingCategory 3, < 16 Mbps, 10Base-T EthernetCategory 4, < 20 Mbps, 16 Mbps Token RingCategory 5, 100 Mbps, 100Base-TX Ethernet and ATMCategory 5e, 1000 Mbps, 1000Base-T (Gigabit Ethernet)Category 6, 1000 Mbps, 1000Base-T (Gigabit Ethernet)

— Difference between cat 5e and cat 6 is transmission performance and extension of the available bandwidth from 100 MHz for cat 5e to 200 MHz for cat 6

Cable will support speed IF the device attached to it supports it

**055 Let's talk about twisted pair. This is where we live today. And by the way, we live somewhere around between CAT 5E and Category 6; that's where most physical wiring occurs. When we look at this copper that's twisted together, we actually take pairs of wires-- and in the case of Ethernet we have eight wires, which are in four pairs; and each one of the pairs is twisted by themselves and then all of those are twisted together. That reduces the interference because we actually create a shielding type mechanism there.

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We can also add- additionally to that we can add shielding to it if we're in- if we're in an environment where that's a requirement. Now think about this from the attacker standpoint. Okay there's that cable, I see it there. I splice that cable and listen into what's going on. I could get ahold of that twisted pair and actually intercept the signal and listen in. There are some evil-doers today that are so good at it that they don't even have to splice the cable. They can pull the signal off the outside of the cable. That's fairly sophisticated and fairly amazing. That doesn't happen that often. It's much easier, by the way, to splice it and put a little what I call a throwing start tap in the middle. You can actually get these online from a whole bunch of places. It looks like- it looks like a little box with four Ethernet- female Ethernet connectors on it; and you can set it up so that you splice the cable, put the two ends on and put this in- put this in between, and then actually tap coming off of that. Today in heavy duty penetration testing we will not only put that tap in place but we'll bury it under the floor or put it up in the ceiling, and we'll put a little tiny computer next to it that will actually capture all those signals.

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And then instead of trying to transmit across the wire where everybody else is trying to transmit, what we'll do is we'll transmit cellularily so that there's no communication going across your network that you know anything about. This means from a physical standpoint you must control- from a security standpoint you must control your physical environment. You must actually use something like a time domain reflect-o-meter, a TDR, or that yellow handheld device, to actually see that the cable run is complete from end to end. That means that you had to certify it beforehand. That means you had to know that this cable run is- all these cable runs are this number of feet; and in fact when you go back and test them again, they're that same number of feet and there's not something inside of the- something in there causing a problem, like an evil- doer tapping into your network. And by the way, it's much easier for adversaries to do this wirelessly in your network; because typically we have a wireless access point that they can tap into and then they go back into the network that way. Depending on the security mechanisms that are in place. But at twisted pair-- as we look at the older categories less throughput. As we look at the newer categories higher throughput.

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We are getting to a point right now where there's this question about how much is the possible throughput when we get-- what's the theoretical limit? And at this point what we're finding out is that it may be in our best interest that when we go above one gigabit of Ethernet-- even though there is a theory that says we're going to go to 10 gigabit Ethernet-- it may be better to switch over to fiber at this point; because the fiber is actually coming down in cost, and that might be a reasonable tool in our network. But I have to ask you, if you look at the hosts that are out there, other than the ones that are in your mail servers or in your DMZ or your servers themselves, other than those how many clients really need more than gigabit Ethernet to actually get their job done? Are they truly utilizing that? So as utilization has crept up over time, then the need for speed has crept up over time. But I think for this future-- you know, for the next five or 10 years, however long this conversation is good-- I would say that we're probably-- the clients aren't out- aren't maxing out the capabilities of their workstations. Remember, the cables may support a speed. But the nodes also have to support that speed, all along the way from the source and destination.

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If I attach to a really slow website, and they only have one or two or 10 megabits' worth of communication there, and my connection on my side is gigabit Ethernet, I can only go as fast as the slowest link or as the slowest node on this network will allow at that point. So we have to make sure that we're in a- we're in an area where we actually can utilize that bandwidth.

Notices

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Notices© 2015 Carnegie Mellon University

This material is distributed by the Software Engineering Institute (SEI) only to course attendees for their own individual study.

Except for the U.S. government purposes described below, this material SHALL NOT be reproduced or used in any other manner without requesting formal permission from the Software Engineering Institute at [email protected].

This material was created in the performance of Federal Government Contract Number FA8721-05-C-0003 with Carnegie Mellon University for the operation of the Software Engineering Institute, a federally funded research and development center. The U.S. government's rights to use, modify, reproduce, release, perform, display, or disclose this material are restricted by the Rights in Technical Data-Noncommercial Items clauses (DFAR 252-227.7013 and DFAR 252-227.7013 Alternate I) contained in the above identified contract. Any reproduction of this material or portions thereof marked with this legend must also reproduce the disclaimers contained on this slide.

Although the rights granted by contract do not require course attendance to use this material for U.S. government purposes, the SEI recommends attendance to ensure proper understanding.

THE MATERIAL IS PROVIDED ON AN “AS IS” BASIS, AND CARNEGIE MELLON DISCLAIMS ANY AND ALL WARRANTIES, IMPLIED OR OTHERWISE (INCLUDING, BUT NOT LIMITED TO, WARRANTY OF FITNESS FOR A PARTICULAR PURPOSE, RESULTS OBTAINED FROM USE OF THE MATERIAL, MERCHANTABILITY, AND/OR NON-INFRINGEMENT).

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