transmission concepts and media part 2 of 2 - usalearning_v401/course/... · transmission concepts...

Transmission Concepts and Media Part 2 of 2

Table of Contents

Transmission Media – Fiber Optics ................................................................................................. 2

Transmission Media – Wireless ...................................................................................................... 6

Transmission Media – Radio Wave ................................................................................................. 9

Transmission Media – Patch Panels .............................................................................................. 10

Communication Closets and Wiring Points .................................................................................. 12

Notices .......................................................................................................................................... 14

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Transmission Media – Fiber Optics

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Transmission Media – Fiber Optics

Light, not electricity, carries information

Not susceptible to interference, difficult to tap

Suitable for long cable runs

Fiber Types• Single-mode, laser light

— Glass core supports longer distances— More expensive than multi-mode

• Multi-mode, LED light— Plastic core— Less expensive than single-mode

**056 Let's switch over and go from copper to fiber. Now this is light, it's not electricity, and there may be instances where you could potentially cause a shock or a problem. So when we do it with light, no electrical transmissions. It's not susceptible to interference; except for when we start what I call monkeying around with the cable. When we start bending and flexing that cable-- I mean, it is glass after all; and if we keep on playing with it and trying to play-- even if it's flexible stuff-- when we keep on playing with it eventually what we will do is we will break and shatter

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the little pieces of glass in there. Over a period of time if you keep on doing that, you'll actually decrease your transmission across that- across that particular- that particular media. So how we deal with this in a lot of cases is we create these looping structures. You'll see them on cabling racks where there'll be a big U at the top. If you're doing data runs up and down a building in vertical shafts, what you actually have is something that looks like a little tiny hula-hoop with the edges cut of it; so that you actually wrap the cable around that once before you send it up to the next floor, so that you reduce the overall tension. There's an ISP in Baltimore, Maryland that their headquarters actually sits at the top of a 20-storey building; and they have fiber runs that go all the way to the top and they have this looping structure in there. And when they were calculating how much fiber to actually do for the runs, they miscalculated because they didn't realize that they had to take the tension in slack; and they had to reorder all of their fiber. Because once we put the fiber in place, it's not like it's very easy to put the splice on the end. At this point the splicer to actually make this all work out, that splicer was around $50,000.00 to actually terminate the ends.

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Today those splicers have come down in price. But that means that it is difficult for individuals to do. It also may be-- as adversaries it may be difficult for them to tap. It's not impossible to tap. But here's what happens. When we tap fiber, one of the key things that happens in the communication between you and I in fiber is a separate methodology for testing the effectiveness of that- of that communication between us; and what we do is we measure the signal loss over time between us. If we were to actually splice a piece of fiber and put in a prism to actually refract some of that light, what we would be doing at that point is-- we would be able to tap. We could do it for around $5000.00. But between you and I, the signal would drop off. We would-- there would be an error- a higher error rate in the signal that is very detectable. So it's not difficult to tap. It's difficult to tap undetected. And that's really the trick with fiber optics. There are two kinds of fiber optics. There's single-mode and multi-mode. When we talk about single-mode, sometimes people call that the dark fiber; which basically means that there's a piece run underground and we only use it for this one purpose. When we talk about multi-mode we're actually doing LED light. It is

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less expensive than single-mode fiber, and more readily used. I can't speak to the effectiveness of one over the other. Now fiber, by the way, is not just a single pulse of light over a single- over a single color. It's not just white light being pumped across there flicking on and off at this point; also it's going very, very fast. What we can do now is we can transmit across that media. Since light is a frequency also, we can actually do about a hundred different frequencies of light being passed over that particular fiber.

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Transmission Media – Wireless

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Transmission Media – Wireless

Not constrained by a physical wire – useful where cables are too expensive or not otherwise feasible to run

More susceptible to interference and interception than cables

Antenna Types• Omni-directional – wireless signal extends 360 degrees• Directional – wireless signal travels in a path; line of sight

Line of sight concept• Transmitter and receiver must be able to “see” each other• Lasers can be blocked by fog• Satellites can be blocked by mountains• Wi-Fi can be blocked by thick walls

**057 Now we've talked about the wired media. But wireless's proliferation is amazing at this point. Now the problem is that there's no physical constrained wire. So when I told you before you want to put that in conduit to protect it, or you want to know what your physical wiring plant is so that you can run a TDR against that particular wire, well how do we do that for wireless? And the answer is well we don't; unless we've gotten certain vendor specifications. There are some vendors that have figured out how to protect the wireless. But that's

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specific to the vendors and that's not something for us to discuss here. So what we have to do is we have to shape that signal as best for us. But remember, somebody who can intercept that signal does not need to be on your physical property anymore. In this room right here I'm sure I have a couple of wireless access points that I can use. But if I was just standing outside that wall out there in the street where I was on public property, I could probably pick up that signal. Now we would shape that traffic, either Omni-directional or directional. And in fact one of the things that I do to pick up a wireless signal using 3g and 4g is actually I have two antennas on the outside of my house at this point. I have one that's a conical shape which points at the tower so I capture the signal and it all flows into this cone that I have; and I also have a directional antenna which points directly at the tower for when I send. So when I receive, I want to collect; because the signal over time fades away. So this is my collector. And then when I transmit I want to transmit in a perfect- a perfect path to that tower. And you can tune those devices so that they're perfectly in alignment.

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That's my wireless signal for 3g and 4g. The same thing can be done with wireless signal when we're talking about wireless that we use: 802.11a, b, g and ac. The trick with a lot of wireless technologies that are not based on 802.11 is there's a requirement of line of sight. So when we shoot lasers at each other and signal and communicate through those lasers, it could be that fog could block our communication between the two of us. Satellites also can be blocked by mountains. We have to have line of sight when we're pointing up at the satellite. Wi-Fi can be blocked by two things: Thick walls-- usually and we talk about metal interference there-- but also a high amount of water content between us. So line of sight concept, it's not perfect line of sight, especially with Wi-Fi; but you want as best line of sight as you possibly can get. And that means that your signal strength will be relatively good.

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Transmission Media – Radio Wave

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Transmission Media – Radio Wave

Fixed frequency – data sent on a single frequency or channel• Simple implementation

Spread-spectrum – data sent over several channels• Resistant to interference• Requires transmitter and receiver to be in sync with the other

**058 When we talk about the radio waves themselves, we're talking about one of two possibilities here: Fixed frequency or spread-spectrum. Today we don't do as much fixed frequency because it sends the signal over- the single frequency over a channel; and then we divide up the channels that way. We tend to do a lot of spread-spectrum so that we have more usage of the media itself.

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Transmission Media – Patch Panels

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Transmission Media – Patch PanelsProvide central point for interconnecting cables and devices

Configuration management solution instead of direct connections

Allows easy rewiring of devices without running new cable

From D

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**059 Let's talk about some transmission media here. One of the things- one of the words that you run into in a lot of cases is called a concentrator. And a concentrator is nothing more than a concentration of transmission signal; like and when we talk about a concentrator for Ethernet we would talk about a hub. At its very lowest form a hub, or even a patch panel is a concentrator of wires. When we talk about the patch panels themselves, remember we're centrally connecting all of this service at one location.

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So that we don't have to have hubs, switches and routers spread out throughout the entire company, what we'll say is: Okay for these pieces of the building right here, the distance, the furthest distance away for this wiring closet, we can't have a client that's more than 300 feet away. So what we'll do is we'll lay out the wiring so that it covers these three floors, and all runs back to a central location where there sits a whole bunch of patch panels that will then connect into devices like hubs and switches. What's nice is when we have those patch panels there and we want to rewire things and we want to reconnect things, we can do that relatively easily because we've organized ourselves. What you'll normally see in a lot of organizations is that they'll have-- this is a Cisco term-- they'll have an access switch that will be dedicated to one floor where they'll run all the wiring back to a patch panel; and then from that patch panel they'll just connect them into the switch with little jumpers. In theory what you could do is have no patch panel whatsoever and you could run the cable from that desk port there all the way up through; and then eventually you could terminate it with an Ethernet connector on the other end and just plug it straight into the switch.

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But if something goes wrong with the switch or something goes wrong with a particular port, how do you know which one's which? So be very organized about it. That's your first tool that you use is-- from devices to devices usually what we say is from the end nodes to a switch, or from switch to switch in most cases. This could be a router also.

Communication Closets and Wiring Points

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Communication Closets and Wiring Points

Physical security of cables, patch panels, and devices• Security vulnerabilities usually require physical access to exploit• Locations where cables come together are prime targets• Use physical access controls for protection

**060 This communications closet and wiring point needs to respect the fact

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that there is a limited distance as to how far away our nodes can be. These locations where all the wires descend and aggregate becomes that security problem. So the wiring closet now needs to be managed by the Access Control Department, where we might use badging, locks, keys; anything to protect that particular location. This is also a great place, if I could actually get in here, if I have a switch there. A lot of switches have this concept of mirroring or spanning all the communication that comes out of each one of the switch ports. I could aggregate all that information and I could suck down all the packets from all the hosts communicating in that particular area. By the way, those span ports or those uplink ports are relatively expensive to install on a machine- on a switch. So normally what happens is is they're in use. So the communication closet and the wiring points-- whether that's your telephone company bringing in access to you or whether you're pulling all your local area network data together to actually connect up to the telephone closet-- now we've got this closet where there's sensitivity there; and we also have shared use because the telephone company is going to want to get into that particular location.

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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).

CERT ® is a registered mark owned by Carnegie Mellon University.

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