AOSCX 101 - 1 - Network Fundamentals

Converting Binary to Hexadecimal. When you are going to convert a binary number to hexadecimal. Group 4 binary numbers (nibble), and assign column values of 8,4,2,1 to each group. Now look at example

1. In the most significant nibble, there are binary 1's in the 4's column and the 2's column. 4+2 = 6. In the least significant nibble, there are binary 1's in the 8's column and the 1's column, and 8+1 = 9. Therefore, 0110 1001 = 0x69 in hexadecimal. Now consider the second example. The high nibble has 1's in the 8's and 4's column. 8+4 = 12 in decimal, and 12 = 0xC in hex. The low nibble has 1's in the 4's and 1's column, and 4+1 = 5. Therefore, 1010 0101 in binary = 0xC5 in hex. In the third example, the high nibble is 4+2+1 = 7. The low nibble is 8+2+1 = 11 in decimal, which equals 0xB in hex. Thus, 0111 1011 = 0x7B in hex.

Consider this analogy: Alice meets Bob for first time, and starts the conversation by saying "Good morning, my name is Alice". Bob replies, "Good Morning Alice, my name is Bob," This brief conversation is actually a procedure. Notice that

Alice starts the communication with a greeting, and then she identifies herself. Bob's reply is also a procedure. He acknowledges Alice, and then he identifies himself by name. The implicit rules in this conversation help to establish and maintain a conversation. Likewise, computing devices exchange messages in a specific order, following specific rules.

Converting Binary to Hexadecimal. The conversion between Binary to Hexadecimal is simple. Just know that four binary digits represent a single hexadecimal number.

Based on this property, the conversion process is just a substitution, as shown in the figure. Let's look at this in another way.

Converting Hexadecimal to Decimal. There are several methods to convert a hexadecimal number into decimal, however the comparison method is the easiest to learn. This method simply uses the position value of each number (remember that in hexadecimal system each position is a power of 16) and then sum the values.

As an example, let's convert the hexadecimal number 0xC89A to decimal. Step 1. Create a table that includes the values of each position in power of 16 and the associate decimal value. Step 2. Write down the hexadecimal number below that, as shown in the figure.

Multicast: This traffic refers to one-to-many communication - one transmitter and multiple receivers. In our classroom analogy, suppose that lunch has been brought in for the learners.

Bob may call out, "All vegetarians can find their meals on the green table". The message came from one source - Bob. The message is destined for several people in the room - all of those with a vegetarian diet.

A Duplex communication system is a system composed by two or more connected parties that can communicate with one another in both directions. There are two types of duplex communication systems: Full duplex (FDX) and Half duplex (HDX) Full Duplex:

Both parties can communicate with each other simultaneously. An example of full-duplex is a telephone; parties in both ends can speak and can be heard by the other party simultaneously. Half Duplex: Both parties can communicate with each other but not simultaneously; the communication is one direction at the time. An example of half-duplex is a walkie-talkie; on this communication each person must press a "push-to-talk" button when they want to talk, when the button is pressed then the user cannot hear the remote person. To listen the button has to be released

Air (Radio Frequency). To transmit data, this media type modifies some aspects of an electromagnetic signal, such as amplitude, phase, or frequency. These modulated radio waves are then transmitted through the air. This wireless transmission technology liberates users from stationary, wired connections and allows them to roam around. Radio Frequency (RF) can be used to transmit radio, TV, and satellite signals. In the computer world, Wi-Fi is the technology that permits wireless endpoint communication. This technology works in two radio bands - 2.4GHz and 5GHz. Data rates using Wi-Fi can be up to 4.8 Gbps using the IEEE 802.11ax standard.

Compared to copper and fiber optic media standards-based Wi-Fi transmission supports the shortest distances. Depending on many factors, including device configuration, number and type of obstacles, required performance, and more - maximum distances between devices is typically between 15 and 30 meters (50 to 100 feet).

Layer 1: Physical Layer This layer dictates the physical aspects of how signals are transmitted and received across some media.

Computing devices convert logical data bits into the correct physical principle depending on the media in use, this process is known as modulation. The inverse process, converting signals into logical data bits is known as demodulation.

Layer 2: Data Link Layer. The Data Link provides three main functions: Media Access Control. In polite human conversation, only one person talks at a time. While Bob talks, Alice politely listens. She detects when Bob stops talking and knows that it is her turn to speak. Similarly, for most media, only one device may transmit at a time, so access to the media must be controlled. Likewise, many Media Access Control techniques leverage a "Carrier Sense" mechanism - before a station may transmit, it must sense the state of the carrier or media. If a transmission signal is detected, the station must wait to transmit, until the currently transmitting station is complete. Link Layer Addressing.

Consider this Analogy: In a crowded room, Bob may call out, "Hey, Alice can I buy you an ice cream?" Everyone hears these sounds waves, which travel over a shared media - the air in the room. However, only Alice responds - she was identified as the intended recipient. Likewise, each station on a LAN has a unique "name". Instead of an alphanumeric name like Alice or Bob, each station is identified by a 6-byte hexadecimal number called a MAC address. All stations on a shared media receive the message, but only the device identified as the intended recipient processes and responds. Like humans, the other stations realize, "This message is not for me" and simply ignore the message. This information is added to the data from the upper layers as so-called "header information", about which you will soon learn. Error Detection. For the receiver side, Layer 2 helps to detect errors that could occur during Layer 1 transmission. This avoids unnecessary processing of corrupted or incomplete messages. This is accomplished by adding a "Trailer" to the data.

Converting Decimal to Hexadecimal. The process relies on a repeated division-by-16 process. Start dividing the decimal number by 16. Keep track of the quotient and the remainder.

Continue dividing the quotient by 16 until you get a quotient of zero, then just write out the remainders in the reverse order. Consider the following example, where the number 89710 is converted to its Hexadecimal representation. Step 1. Divide the dividend 897 by the divisor 16. Step 2. Divide the quotient obtained in the previous step (56) by 16.

Layer 6: Presentation Layer. The Presentation Layer transforms data into the formats that the application accepts. Typical processes include: Compression/Decompression, Compression/Decompression, Code Translation (EBCDIC to ASCII)

For example, the figure shows how an application passes the clear-text message "Hello" to the Presentation Layer process, which encrypts this message before transmission. This provides confidentiality. If any bad actors or hackers intercept this data, they will not be able to read the message. Of course, upon receipt of an encrypted message, only the intended receiver has the correct digital keys to decrypt the data.

Layer 7: Application Layer. The Application Layer is the closest to the end user, which means that both the OSI Application Layer and the user interact directly with the software application. Application Layer functions include: Identifying Communication Partners. The application layer determines the identity and availability of communication partners for an application with data to transmit. Provide network resources. This layer provides network services to user applications, such as file transfer, email, video conferencing and many others. Some examples of application layer include:

Hypertext Transfer Protocol (HTTP), which relies on TCP for transport File Transfer Protocol (FTP), which also relies on TCP Domain Name System (DNS), which typically uses UDP, but sometimes also uses TCP Trivial File Transfer Protocol (TFTP), Which uses UDP as its transport mechanism

Converting Decimal to Binary - Patterns for Speed. Look at this left-most set of binary to decimal conversions. Notice that it goes from "all zeros" at the top example, to "all 1's" in the bottom example. Now look at the third example from the top: 00000011 = 3. Suppose you then add a 1 to the 128 column. You shouldn't need a lengthy process to convert this to decimal. You know that the one in the 128's column represents 128. Then add 3 to that and you get 131. With some practice, this begins to seem intuitive - you can do it in your head. Consider the next example: 00000111 = 7. Then suppose that say, the 32's column had a 1 instead of a 0. 32+7=39. Do you also notice that 3 is one number less than the next column to the right? The 4's column. And that 7 is one less than the next column to the right - the 8's column. Do you see the pattern? Once you understand this, you don't even have to memorize the chart shown in the figure.

If you see the binary sequence 00111111, you don't need to remember that this equals 63. You know that the sequence of binary 1's end right before the 64's column, and so this = 63. Now look at the right-hand column, which shows another set of sequential patterns. Look at the second example from the top: 11000000 = 192. Now suppose you saw another identical example, except that the 4's column was also set to 1. 192+4 = 196. With just 30 to 60 minutes of practice, this conversion process will continue to become ever-more intuitive. You will discover other useful patterns on your own, and quickly be able to convert from binary to decimal. Revisit and stay sharp with this skill. This ability to convert numbers is useful for passing Aruba exams. Perhaps more importantly, it will help you as you advance in your training, for things like complex subnet masking, advanced IP address assignment, advanced route filtering, and other concepts that you will learn about when you take more advanced courses. Now you know about decimal and binary, let's learn about another important numbering system for computers and networks - hexadecimal.

In the mid 1980's during the fast evolution of computing, every vendor wanted to implement their own, proprietary communication protocol. These proprietary protocols created interoperability challenges. The International Organization for Standardization (ISO) solved the problem by presenting a standard communication model for computing devices - The Open Systems Interconnection (OSI) model. The OSI model organizes computing communication in 7 layers. Each layer defines a phase of message processing. The OSI layers are shown in the figure, and described below:

Layer 7: Application Layer Layer 6: Presentation Layer Layer 5: Session Layer Layer 4: Transport Layer, which organizes data into segments, as you will soon learn. Layer 3: Network Layer, which organizes data into packets Layer 2: Data Link Layer, which organizes data into frames Layer 1: Physical Layer, which organizes the data into bits, and transmits those bits using physical hardware over wires, fiber optic cable, or RF Signals

Based on the geographical coverage a computing network can be categorized as a

Local Area Network (LAN) or a Wide Area Network (WAN).

Converting Decimal to Hexadecimal. Step 3. Divide the quotient obtained in the previous step (3) by 16. Step 4. Take all the Remainders and order them starting from the last Remainder (Remainder #3).

Note. On step 3 you know that the quotient of the division is actually a fraction number (0.1875). However, the process only focuses on the integer part of the quotient and the last remainder before the operation is actually done.

Binary Numerical System. Familiarization with the binary numerical systems is key to understand how computing systems process and communicate information. The binary system uses a base-2 numbering system, this means that there are only 2 possible symbols available to represent data: zero and one. In the binary system the position of a number represents a value of the power of 2. The table below shows the first 8 positions and the decimal number associated to each.

Note. To avoid any confusion this text will use an index after a number to indicate the base numerical system, for example 10010 will represent the number 100 (one hundred) on the decimal system. Counting in binary: The table shows the first eight decimal numbers and their representation in binary. The first two values only require one digit (2 & 0), and so zero and one are the same for both numerical systems. Please notice that for decimal number 2 in binary you must add a new binary number to the left indicating 1 and the number to the right 0. Let's make a quick comparison of binary and decimal numbering systems.

Fiber Optics are built from glass or plastic fiber. This media uses light signals to transmit and receive data. Light is guided down the center of the fiber cable, which is called the core. The core is surrounded by optical material called "cladding" that traps the light in the core using a technique called total internal reflection. Fiber optic cables can interconnect devices that are separated by much longer distances than Ethernet UTP's 100 meters, and with higher data rates. Distances and speeds depend on quality, type of fiber, and transceiver type. Common data rates are 1Gbps, 10Gbps, 25Gbps, 40Gbps, 50Gbps or even 100Gbps.

Note: A fiber optic transceiver is an optical module installed in the computing device. It is responsible for modulating and demodulating light signals. Fiber optic is categorized into two main groups - Multimode (MM) and Single mode (SM) fiber. MM is typically less expensive, for relatively shorter distances. SM is often more expensive but can often support very long distances. There are several standard fiber connectors. However the typical one that is used is LC connector. The image shows an example of this.

Layer Headers. In the OSI model each Layer has a specific responsibility during network communications. In the computing world, devices use headers to establish a communication exchange and to control information on a particular layer, or the layers above it.

Note: A header that is generated on a specific layer by the sender can only be read at the same level on the receiver side. Encapsulation. Is the process where each OSI Layer adds a header. This process is always done by the sender device. Decapsulation. Is the process to read and interpret the header information. This process is always done by the receiver device.

Hexadecimal Numerical System. The Hexadecimal system uses a base-16 numbering system, this means that there are 16 possible symbols available to represent data. In this case the hexadecimal system uses numbers (0-9) and the first six letters of the alphabet (A-F).

Note: It is common to represent hexadecimal numbers with a preceding 0x. This notation helps to differentiate hexadecimal numbers from decimal numbers. The hexadecimal number 0x29 is a very different value from the decimal number 29. In the hexadecimal system the position of a number represents a value of the power of 16.

The OSI model introduces the concept of a Protocol Data Unit (PDU). This is simply a structure that considers the header and payload or data for each Layer. The following table summarizes the PDUs from Layer 7 to Layer 2.

Note: PDU1 does not exist, remember that Layer 1 refers to signals that cross the media. There are three key terms related to PDUs that you should know: Segment. Refers to the encapsulation that is done in Layer 4. A segment is equivalent to PDU4. So, you might hear networking people speak about a TCP segment or a UDP segment. Packet. Refers to the encapsulation that is done in Layer 3. A packet is equivalent to PDU3. You might talk about Layer 3 IP packets. Frame. Refers to the encapsulation that is done in Layer 2. A frame is equivalent to PDU2. You might talk about Ethernet frames or Wi-Fi frames. You might notice that PDU2 - a Layer 2 Frame - not only includes a Header but also a Trailer that is appended after data, labeled "L2T" in the figure. The trailer is typically is used to detect errors during the transmission of the message. You recently learned about this during the discussion of Layer 2 of the OSI model. Layer 2 protocols like Ethernet and Wi-Fi add a Trailer, often labeled "Cyclic Redundancy Check" (CRC) or perhaps as a "Frame Check Sequence" (FCS).

Converting Decimal to Binary - Alternate method. As before, you wish to convert decimal 13 to binary. Look at the column values for the binary number system and compare. Is 13 greater than or less than 128? Less than, therefore you must place a 0 in the 128's column. 13 is also less than 64, 32, and 16, so those columns must all have a 0, as shown in the figure.

Now, 13 is obviously greater than 8, so you must place a 1 in the 8's column. We're still not to 13 yet, so keep going. Add the next lowest column: 8+4 = 12. You have not reached 13, so keep going. 12+2 = 14 and this value is greater than 13 then place a 0 on the 2's column. 12+1 = 13, which is equal to the number you are finding, then place a 1 on the 1's column. So 13 in decimal = 00001101 in binary. Let's try one more example.

Converting Decimal to Binary. The conversion from decimal to binary is not based on a sum but in a repeated divide-by-2 process. Start by dividing the decimal number by 2. Notice of the quotient and the remainder. Continue dividing the quotient by 2 until you get a quotient of zero, then just write out the remainders in the reverse order. Consider the following example, where the number 1310 is converted into its binary representation.

Step 1. Divide the dividend 13 by the divisor 2. This operation will have a result of 6 as the quotient and 1 as the remainder. Step 2. Take the quotient of the previous operation (6) and divided by 2. This operation will have a result of 3 as the quotient and 0 as the remainder. Step 3. Take the quotient of the previous operation (3) and divided by 2. This operation will have a result of 1 as the quotient and 1 as the remainder. Step 4. Take the quotient of the previous operation (1) and divided by 2. This operation will have a result of 0 as the quotient and 1 as the remainder. Note. On step 4 you know that the quotient of the division is, 0.5 and the Remainder 0, however the process only focus on the integer part of the quotient in this case is 0 and on the last Remainder before the operation is done, in this case the last Remainder is 1.

Converting Binary to Decimal. There are several methods to convert a binary number into decimal, however the comparison method is the easiest to learn. This method simply uses the position value of each number (remember that in binary system each position is a power of 2) and simply sums all the values where the binary number is set to 1. As an example, let's convert the binary number 100010102.

Step 1. Write down a table with all the positions values in terms of power of 2 and its value in decimal. This example has 8 binary characters, so you need to write down the first 8 values. Step 2. Write down the binary number below and verify which positions have the number 1.

Converting Hexadecimal to Decimal. Step 5.

Sum the values. 0xC89A = 4915210 + 204810 + 14410 + 1010 = 5135410

Layer 5: Session Layer. Layer 5 is responsible for setup, maintenance, and tear down of sessions between two computing devices. A session is a particular conversation between two computer devices. Suppose that some user opens a browser and connects to a web page like http://arubanetworks.com. A session is created. Then the same user opens a different browser to the same destination, since the application is different a new conversion or session is created. Thus, two separate sessions are maintained.

Suppose that some user opens a browser and connects to a web page like http://arubanetworks.com. A session is created. Then the same user opens a different browser to the same destination, since the application is different a new conversion or session is created. Thus, two separate sessions are maintained.

Layer 3: Network Layer. The main goal of the Network Layer is to establish device communications across multiple LANs or WANs, using the best available path. This is achieved using two fundamental techniques. Logical addressing. A unique Layer 3 identifier for the source and destination is maintained across the path. Path discovery and selection.

The Network Layer runs algorithms and protocols to find all possible paths, and then choose the best path. Later in this course, you will learn more about this, and things like the Routing Information Protocol (RIP) and Open Shortest Path First (OSPF). The communication between two computing devices can take a specific path but not necessary the same one will be used in the future. Protocols and algorithms used in this Layer could update the path any time depending of multiple factors. You will learn more about it in this training.

Layer 4: Transport Layer. The Transport Layer controls the reliability of a given link through segmentation, de-segmentation and error control. In this layer some protocols, like the Transmission Control Protocol (TCP) are connection-oriented. This means that the transport layer can keep track of the messages and retransmit those that fail. Other protocols, like the User Datagram Protocol (UDP), are stateless or connectionless. This means the transport layer does not keep track of the messages.

The advantage of this is that processing these connections is relatively fast and easy to compute. There are three main responsibilities of the transport layer, as described below: Segmentation. The sender's TCP or UDP process accepts files from the application and divides them into smaller pieces (typically 1500 bytes) called segments. Each piece is passed down to the lower layers and transmitted individually - over an Ethernet link in the example shown in the figure. De-segmentation. The receiver accepts each segment, puts them back in the correct order if need be, and reassembles the information. This then can be processed by the application. Error Control. Refers to the verification of the information received to avoid errors that could occur the lower Layers (1-3). Note. Error detection is a process that happens in different Layers: 2, 4 and sometimes in 7 of the OSI model.

The figure shows specifications for Multimode (MM) and Single mode (SM) fiber. Multimode (MM). The core size for this fiber is 50 or 62.5 micrometers (µm). This core size allows greater light-gathering capacity and facilitates the use of less expensive transceivers. Typical distances are up to 600 meters (2000 feet), With typical data rates of up to 10Gbps. Typically, fiber optic data sheets for Multimode Fiber include terms like 50/125 or 65.5/125, where the first number (50 or 62.5) is the diameter of the core and 125 represents the diameter of the cladding. Multi-mode fiber with 50µm has a faster light transmission but with shorter distance. Single Mode (SM). The core size is only 9µm and carries light directly down the fiber, as a result, light reflection created during light transmission decreases.

This lowers attenuation (loss of signal strength) and allows the signal to successfully travel over longer distances. Usually, this fiber is more suitable to be used to interconnect devices using higher data rates such as 40Gbps or even 400Gbps. As you might imagine 9/125 refers to the fact that the core is 9µm and the cladding is still 125µm.

Converting Hexadecimal to Binary. Now suppose you need to convert from hexadecimal to binary. Simply write the hexadecimal number down, leaving ample space for 4 bits underneath each hex number.

Then add the 8,4,2,1 column values if you like. Now simple convert each hex value to its binary equivalent. Reference the chart until you have the values memorized. You know that 8+4+2=1 = 15 in decimal, which equals 0xF in hex. Of course, 0 in hex = 0000 in binary, and so on. Thus, 0xF03BA in hex = 1111 0000 0011 1011 1010 in binary.

Computing communications can be classified in three types: Unicast:

This traffic refers to one-to-one communication. One transmitter and one receiver. Imagine that there are several learners in a classroom. Bob is the instructor. He calls out, "Alice, I have a message for you from the front desk". This message came from one source - Bob and is destined to a single destination - Alice.

A WAN in the other hand is a group of computer resources that can communicate over large geographical distances - typically a few kilometers or miles, and perhaps thousands of miles, such as the Internet. The Internet is considered a WAN since it permits communication across countries and continents,

Typically, WANs are deployed by Internet Service Providers (ISP) since those companies have the economic resources to interconnect long distances. Examples of WAN technologies include the following: • Internet • Multi-Protocol Label Switching (MPLS)204:18 PM • Asynchronous Transfer Mode (ATM)204:18 PM • Asynchronous Transfer Mode (ATM)204:18 PM • Frame Relay (largely obsolete)204:18 PM • Dark fiber

Converting Decimal to Binary - Compare and Add. Now you wish to convert decimal 187 to binary. Look at the column values for the binary number system and compare. Is 187 greater than or less than 128? Greater than, so that column gets a 1. Now add 128+64=192. That's too high, so the 64 column gets a 0. Go to the 32's column. 128+32 = 160. Lower than 187, so put a 1 in the 32's column. 160+16 = 176. Lower than 187, so put a 1 in the 16's column. 176+8 = 184. Lower than 187, so put a 1 in the 8's column. 184+4=188. Too high, so put a 0 in the 4's column. 184+2 = 186...a 1 in the 2's column. And 186+1 = 187...a 1 in the 1's column. So, 187 in decimal = 10111011 in binary.

With just a small bit of practice, you will soon have the columns memorized - 128, 64, 32, 16, 8, 4, 2, 1. With just a bit of experience, you will begin to learn certain patterns, and this will become more intuitive for you. Let's look at some common time-saving patterns that might give you an intuitive edge and speed your conversion efforts.

Binary Numerical System. Consider the decimal number 1,101 as shown in the figure. You know that the right-most digit (1) is in the "1's" column, then 0 is in the 10's column, the 1 is in the 100's column, and the 1 is in the 1,000 column. Therefore, the first 1 (left to right) does not merely represent a quantity of 9, it represents a quantity of one thousand - 1 X 1000 = 1,000. Similarly, 1 x 100 = 100. 0 x 10 = 0, and 1 x 1=1. You know this already, right? And 1000 + 100 + 0 + 1 = 1,101. Binary works exactly the same way.

Yes, the numbering system changed from base 10 to Base 2, but the fundamental rules never change. The only difference is that instead of 1000, 100, 10, and 1 - the columns are 8, 4, 2, and 1. For example, consider the binary number 1101. The left-most number is 1, and it is in the 8's column. 1 x 8 = 8. The next number to the right is1 and is under the 4 column; 1 x 4 = 4. The next number is 0, and 0 x 2 = 0. The right-most number is 1, and 1 x 1 = 1. Now add them up, just like before. 8 + 4 +1 =13. Let's take this a bit further, using a more methodical step-by-step process.

Physical Media - Copper. Computing devices might use different media to transmit information, and each media type has different characteristics. Recall that Fiber Optic media modulates light waves, Wi-Fi modulates Radio Waves, and Copper-based media modulates electrical properties like voltage. Copper cables You recently learned about how Layer 1 processes modulate or change some aspect of a signal, in order to represent binary data. In the example shown here, +5 volts represents a logical binary 1, while -5 volts represents a logical binary 0.

You recently learned about how Layer 1 processes modulate or change some aspect of a signal, in order to represent binary data. In the example shown here, +5 volts represents a logical binary 1, while -5 volts represents a logical binary 0. UTP cabling contains 8 color-coded wires, grouped into 4 pairs. Two wires are used for transmission (Tx) and two are used for reception (Rx). The remaining 4 lines are used to power some devices such as telephones or cameras, using a feature called Power over Ethernet (PoE). The typical connector used with UTP is an RJ-45 connector. To maintain a data rates of up to 1Gbps, the maximum length of UTP cable cannot be more than 100 meters (300 feet).

Converting Hexadecimal to Decimal. Step 3. Convert any existing letters into numbers. Please refer to the table presented previously.

You will soon have this memorized, with only a bit of practice. Step 4. Multiply the number obtained in the previous step times the value of the position.

A LAN is

a group of computer devices that are geographically in the same place. For example, a group of devices within a building can be considered a LAN. LANs are used in several settings: • Small Office/Home Office (SOHO) • Building LANs • Office LANs • Campus LANs

Communication is the main purpose of a computing network, and this communication is enabled using protocols. A protocol is

a group of rules or instructions that computer devices follow in order to properly establish and maintain communications.

Broadcast: This type of traffic refers to the communication one-to-all. In our classroom analogy, Bob calls out, "Attention everyone. It is break time, and there are free doughnuts in the lobby". The special word "everyone" means that

all people in the classroom are intended to receive this message. Similarly, there are special network addresses that all stations will receive and process. At layer 2, this is the MAC address FF:FF:FF:FF:FF:FF. At Layer 3, this is the IP address 255.255.255.255. This helps a particular computing device to discover others in a specific network.112:04 PM