It’s time to go under the hood. Network devices send data down the cable by converting the data into a signal. But how do they do this? And what else might be hiding in the signal? Just like a doctor needs to look at blood cells to identify blood-borne diseases, a network pro needs to look at what’s in the network signal to detect network intrusions, perform audits, and generally diagnose problems. And the key to all of this is packet analysis.

1. Packet Sequence Number For Macro

Keep reading while we put your network signal under the microscope. Manchester Phase Encoding: Non-Return to Zero: Welcome, Non-Return to Zero. Is there something I can call you for short? I prefer NRZ, but some folks call me NRZ-L for Non-Return to Zero Level. My name’s nice and transparent.

When I encode a signal, it starts at zero voltage, but it never gets to go back to zero voltage. So you give a positive voltage a one and a negative voltage a zero?

I can do it that way or vice versa, depending on how I’m implemented, but I always stick to the rules of that implementation. I am a slim encoding technique. After all, I require only half the bandwidth you require. A little extra bandwidth is worth the price. I have built-in clocking.

I make sure the data gets there, and I can spot errors. Can you do that? I like to keep the encoding process simple. Clocking is overrated. What happens when you have a whole bunch of bits in a row?

Say you’re trying to send a whole bunch of zeroes? What sort of crazy standard would allow for a bunch of bits in a row? Ethernet, for one. If you have a bunch of bits in a row. The signal sits there at the same voltage level for a long time. Without a clock, the sending device and the receiving device will get out of sync. I don’t get caught up in all that high-falutin’ stuff.

Economy and simplicity is the name of my game. I use self-clocking.

I give a network more bang for the buck. You’d be good for writing data to a hard drive, but you just don’t cut it on a network, do you? Data should stay home.

All that crazy travel over cables is unnecessary and fraught with problems. That’s what I thought you might say. Q: Q: Why do we need to encode and decode signals? A: A: If we don’t encode and decode signals, they come in as raw waveforms, i.e. 1’s & 0’s represented by voltages. We can’t do much with such waveforms.

We encode and decode signals so that we have a way to carry data on the signal. Networking is all about sending messages, so encoding and decoding are crucial to networking. Q: Q: Why don’t we just encode data in one way and stick to that?

A: A: Different encoding methods have different advantages. Some encoding methods are more efficient. Some methods have better error correction. Over time, better and better encoding methods come about. These methods offer different advantages and disadvantages over others.

Q: Q: What is error correction? A: A: Any time you send data on a network, you can run into problems with that data. Different encoding methods allow for detection and correction of those problems.

Error correction helps maintain the integrity of your data. Q: Q: How many different kinds of data encoding are there? A: A: Data encoding comes in many flavors: American Standard Code for Information Interchange (ASCII), Binary Coded Decimal (BCD), Differential Manchester Encoding (DME), Extended Binary Coded Decimal Interchange Code (EBCDIC), Feedback Shift Register (FSR), Manchester Phase Encoding (MPE), Non Return to Zero (NRZ), Non Return to Zero Invertive (NRZ-I), Return to Zero (RZ), and Unicode. Some older encoding schemes in networking are Manchester, NRZ, and NRZ-I. Q: Q: Older schemes?

What is being used now in networking? A: A: 4B/5B and 8B/10B are used for Fast Ethernet and Gigabit Ethernet. The 4B/5B scheme uses 5 bits to represent the 4 bit numbers and 10 bits to represent 8 bit numbers.

This is done to assure that there is a transition at some point. Q: Q: As a network professional, I just need to know how to connect stuff.

Why should I learn all of this math and physics? A: A: Networking is all about sending messages (data) over a carrier (signals). To diagnose problems, a good mechanic needs to know all the aspects of how an engine works. Similarly, a networking professional needs to know how data is packaged to understand how to completely troubleshoot a network. Q: Q: Where do I go if I want to find out more about the Ethernet protocol? A: A: The Ethernet protocol was written by the Institute of Electrical and Electronics Engineers (IEEE).

Packet Sequence Number For Macro

You can find a whole lot more about the IEEE Ethernet working group and its publications at the following sites. The Scholar’s Corner Manchester Encoding a method used in networking, which turns electric signals into data formats that a computer can read.

The difference between Manchester and other binary encoding methods is that Manchester encodes data based on a change in the signal. The direction of the change in the signal determines whether the bit is a “0” or a “1.” A more formal definition appears in Federal Standard 1037C, Glossary of Telecommunications Terms. You can find this document at the following url. Q: Q: Why don’t computers just use decimals like humans do? A: A: Computers use binary because it’s more convenient to implement with electronics. Electricity is easier to deal with when it’s in two states, like on-off, high-low, positive-negative.

If we had to represent ten numbers at the signal level, we’d have to represent ten states. To do so, we’d need expensive, highly-sensitive electronics. We’d also have to account for errors in state and spend huge chunks of time error-correcting and troubleshooting.

Binary is way easier and way cheaper to use. Q: Q: Where will I use binary in a day-to-day networking job? A: A: The most common place you’ll use binary as a network professional is in subnetting (which we cover in a later chapter). Subnetting can seem like magic if you don’t understand the binary behind it.

If you want to monitor packets on a network, binary can help you understand the data more completely. In the end, understanding binary makes you a better networking professional.

Q: Q: Can you add, subtract, multiply, and divide binary numbers? A: A: You can do all of the same operations we do with decimal numbers. You just need to learn some special rules to do so.

Q: Q: Can’t I just do binary on some sort of calculator? A: A: On a Macintosh computer, you can use the Calculator app. When you open the app, choose “View Programmer” and you’ve got a calculator that will do binary. For other operating systems, you can find and download a good programmer’s calculator. You can also search the Internet for web-based binary converters. Don’t add the two numbers! Just put them side-by-side, and you have the hexadecimal conversion.

Convert each half into its hexadecimal equivalent. Because the binary number is broken into halves, the highest number you can get is 15 (which is “F” in hex). Concatenate the two numbers.

Concatenate is a programmer’s word that simply means “put them beside each other from left to right.”. Look the number up in an ASCII table.

The table to the right is just a sample. To find common ASCII codes, use the handy ASCII conversion table we’ve provided in. Sharpen your pencil The messages below are written in binary, decimal, and hexadecimal. Practice your decoding skills by deciphering the message.

Binary 010111 011010 011001 001000 011001 001001 011000 011001 011010 011110 011101 011110 001111 011011 011100 011001 011111 000110 Decimal 69 118 101 110 32 100 101 99 105 109 97 108 115 32 99 97 110 32 98 101 32 101 110 99 111 100 101 100 32 97 115 32 65 83 67 73 73 46. Note Hint: Use the ASCII table in to lookup the ASCII code. Sharpen your pencil The messages below are written in binary, decimal, and hexadecimal. Practice your decoding skills by deciphering the message.

Binary 010111 011010 011001 001000 011001 001001 011000 011001 011010 011110 011101 011110 001111 011011 011100 011001 011111 000110 Computers speak binary and so should network pros. Decimal 69 118 101 110 32 100 101 99 105 109 97 108 115 32 99 97 110 32 98 101 32 101 110 99 111 100 101 100 32 97 115 32 65 83 67 73 73 46. Note Hint: Use the ASCII table in to lookup the ASCII code. Even decimals can be encoded as ASCII. Hexadecimal 48 65 78 61 64 65 63 69 6d 61 6c 20 70 61 63 6b 73 20 61 20 6c 6f 74 20 6f 66 20 76 61 6c 75 65 20 69 6e 74 6f 20 61 20 6c 69 74 74 6c 65 20 73 70 61 63 65 2e Hexadecimal packs a lot of value into a little space. Q: Q: Does it take a long time to encode Manchester, hex, and ASCII data? A: A: Computers encode data at high speeds (like faster than we can blink), but it is dependent on hardware and how it’s engineered.

Obviously, the newest network gear is faster than the old stuff. The transmission media has a big impact on speed, too. For instance, fiber-optic cable allows for x speed. Whereas Ethernet cable allows for X speed depending on whether we’re dealing with 10 mbps, 100 mbps, or 1000 mbps. Q: Q: Ethernet goes at different speeds?

A: A: Yes, the original Ethernet was 10Mbps, but engineers quickly figured out how to get more speed, and that quest has never ended. You can purchase Ethernet equipment right now that can go as fast as 10Gbps. Q: Q: So do all speeds of Ethernet use Manchester Encoding?

A: A: Good Question. No, they don’t. 100 Mbps, or Fast Ethernet, uses the 4B5B encoding scheme.

The simplest way to think about this encoding scheme is that 5 bits are used to transmit 4 bits of data. Gigabit Ethernet, 1000Mbps or 1Gbps, uses an 8B10B encoding scheme. Gigabit Ethernet also uses all 4 pairs of wire in a cable. Q: Q: So how do these encoding schemes help the various devices stay in sync? A: A: By using an encoding scheme, a device sending data on a network “embeds” its clock into the signal. The clock is what determines the 1’s & 0’s. Imagine if there was just a string of 0’s using the NRZ encoding scheme.

This means that there is just a low voltage. A device receiving this signal would not know if this was really the signal or if there was a break in the line. A signal with the clock embedded in the signal allows the receiver to properly decode the signal because the data is in the transitions of voltages and not in just the voltage level. Q: Q: Doesn’t a computer have to do all this encoding and decoding?

A: A: You might think that, but the engineers that designed this stuff are really smart people. They figured out how to create hardware that can do this encoding/decoding very fast. This is built into the network cards. Protocols define the structure of a message In order to effectively communicate, network devices use protocols, a set of guidelines, or rules, for the network conversation. These procotols cover such things as how fast data can be sent and how data will be structured when it’s sent. Most protocols define a size limit for messages, which means that the messages need to be broken into separate packages and labeled with information about where the message came from and where it’s headed. Network messages come in two kinds of packages: frames and packets.

Q: Q: How can I find the MAC address on my computer? A: A: On a Macintosh, go to “System Preferences.” In the search entry box in the upper right, type Ethernet ID and hit “Return.” The next window you see will show your Ethernet ID, which is really just another name for your MAC address.

On a Windows machine, go to “Start. Network frames have lots of layers Encoding and decoding signals allows us to ship data efficiently.

Frames give that data structure, but does a frame give us enough structure to package our data? A network frame contains nested structures that allow us to pack and unpack the data efficiently. Like a series of nested dolls, each smaller structure is enclosed by the next largest structure. The payload of a frame is actually a structure nested within the frame.

We call it a packet, and the EtherType field lets us know what type of packet the payload contains. Q: Q: Why are there so many different IP packet types? A: A: The main reason is that there are many different types of communication that happens via IP.

For example, routers exchanging route information or other protocol type such as IPX encapsulated inside of an IP packet. Q: Q: How many are there? A: A: The current size of the protocol field in an IP header is 8 bits, which gives us 2 8 or 256 possible types of IP packets.

There are currently about 139 registered IP protocols. Q: Q: Aren’t packets and frames really the same thing? We call data transmitting over Ethernet frames. Inside those frames, in the data field, are packets. Generally frames have to due with the transmission protocol, i.e., Ethernet, ATM, Token Ring, etc.

But, as you read more about networking, you will see that there is some confusion on this. Q: Q: A guy in my office calls packets datagrams. Are they the same? A: A: Not really. Packets refer to any data sent in as packets.

Whereas datagrams are used to refer to data sent in packets by an unreliable protocol such as UDP or ICMP. Q: Q: So packets are inside frames; is there some type of data structure inside the packet? A: A: Great question. This is usually an application specific protocol. Remember protocol simply means a set way of structuring information that is agreed upon by the parties involved. So when a web browser request a web page from a web server, it uses the http protocol to request that page, and the server responds with the data using the http protocol. When a server sends email, it uses the smtp protocol.

There are many different application type protocols. TCP Packet: UDP Packet: Well hello UDP. How are you doing? Not bad, how you doing? I heard you had some dropped packets the other day. What is that all about? What do you mean “dropped packets”?

I mean packets that did not get from point A to point B. How would I know if packets get anywhere?

Exactly my point. You see I can tell when a packet does not get from one point to another. The packets sent using me as a protocol have information in them that the sender enters which lets the receiver know if there are any lost packets. Well why is it that most of the streaming stuff on the Internet, such as music or movies, is sent using me as a protocol? What do you have to say to that? I guess lost packets don’t mean much for that type of information then.

But a lost packet with a database search or server command could be devastating. It could ruin the entire data set sent. So I protect it. I will tell you the cost: performance.

I can send data much faster than you because I have much lower overhead. I guess the choice is one of reliability versus performance. It is never an easy decision. The entire message may need more than one frame.

Sometimes messages are spread across frames. So why’s that? An Ethernet frame can hold about 1500 bytes of data.

So any data that is larger than that will have to be broken apart. There’s another reason too. In order to have a reliable transfer of data, the sender and receiver communicate using the TCP protocol on how the transfer is going. If there are errors in the packets, the sender will notify the receiver and it will resend the packets that had errors. Imagine if there was one large packet with all the data.

If the connection is poor it might never get sent. Askey wifi driver for mac download. To reassemble the entire message, we need to collect together all the frames, making sure they’re in the right order. So what do we mean by the right order?

Why should they be out of order? Let’s take a look. Across Down 2. Which Ethernet uses 8B10B encoding? American Standard Code for Information 4.

Protocols are. Hello written in ASCII hex code. Packets are inside. 1011 X-NOR 1010 equals 1110. 101001 in ASCII 16.

Connection Oriented Connection Protocol 17. 1010 base 2 in decimal equals A 18. Used by computers to connect to a network 19. Encoding used for Ethernet 10Mbs 5. Manchester Encoding uses this boolean operation 6. Simple packet type used to test network connections 7. 1010 OR 0000 equals 1000 9.

Hex is base 15 11. 1001 AND 1111 equals 1001 13.

Connectionless Protocol Type 15. What is embedded with data in a Manchester signal? You can do math such as adding and subtracting with binary numbers. Across Down 2.

Which Ethernet uses 8B10B encoding? American Standard Code for Information ASCII 4. Protocols are RULES 8. Hello written in ASCII hex code. 48656C6C6F 10.

Packets are inside FRAMES 12. 1011 X-NOR 1010 equals 1110 TRUE 14. 101001 in ASCII HI 16. Connection Oriented Connection Protocol TCP 17. 1010 base 2 in decimal equals A TRUE 18. Used by computers to connect to a network NIC 19.

NRZ NONRETURNTOZERO 1. Encoding used for Ethernet 10Mbs MANCHESTER 5. Manchester Encoding uses this boolean operation EXCLUSIVENOR 6. Simple packet type used to test network connections ICMP 7. 1010 OR 0000 equals 1000 FALSE 9. Hex is base 15 FALSE 11. 1001 AND 1111 equals 1001 TRUE 13.

Connectionless Protocol Type UDP 15. What is embedded with data in a Manchester signal? You can do math such as adding and subtracting with binary numbers. TRUE With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, interactive tutorials, and more.