Final Exam Summary PDF

[Data communications] What are data communications? -This is the exchange of data between two devices via some form of transmission medium such as via wire cable. How does data communication occur? -The communicating devices must be a part of a communication system made up of a combination of ha...

[Data communications] What are data communications? -This is the exchange of data between two devices via some form of transmission medium such as via wire cable. How does data communication occur? -The communicating devices must be a part of a communication system made up of a combination of hardware (physical equipment) and software (programs). What are the four fundamental characteristics that affect the effectiveness of data communication? 1. Delivery -- the system must deliver data to the correct destination. 2. Accuracy- the system must deliver data accurately. 3. Timeliness -- the system must deliver data in a timely manner. 4. Jitter -the variation in the time delay between data packets arriving over a network. What are the components of a data communication system? 1. **Message**. The message is the information (data) to be communicated. E.g. text, numbers, pictures, audio, and video. 2. **Sender**. The sender is the device that sends the data message. E.g. computer, workstation, telephone handset, video camera, and so on. 3. **Receiver**. The receiver is the device that receives the message. E.g. computer, workstation, telephone handset, television, and so on. 4. **Transmission medium**. the physical path by which a message travels from sender to receiver. E.g. twisted-pair wire, coaxial cable, fibre-optic cable, and radio waves. [DATA REPRESENTATION] How is data represented? ##### Text ##### Numbers ##### Images ##### Audio ##### Video DATA FLOW What are the different types of data flow? 1. Simplex- communication is unidirectional, as on a one-way street. Only one of the two devices on a link can transmit; the other can only receive. E.g. keyboards and monitors. 2. Half duplex- each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa. E.g. walkie talkies, citizens band radios. 3. Full duplex - both stations can transmit and receive simultaneously. In full-duplex mode, signals going in one direction share the capacity of the link with signals going in the other direction. E.g. telephone network. NETWORKS What is a network? -This is a set of nodes(devices) connected by communication links. E.g. computer, printer What is distributed processing? -This is when a task is divided among multiple computers. Most networks use it. What are the criteria a network must meet? 1. Performance- is measured in: What are the factors that affect the performance of a network? - number of users - type of transmission medium - capabilities of the connected hardware, and - efficiency of the software. 2. Reliability - network reliability is measured by the frequency of failure, the time it takes to recover from failure, and the network\'s robustness in a catastrophe. 3. Security -- network security issues include: - protecting data from unauthorized access - protecting data from damage and development - implementing policies and procedures for recovery from breaches and data losses. Physical Structures What is a link? -This is a communications pathway that transfers data from one device to another. What are the two types of connections in networks? 1. Point to point -- this provides a dedicated link between two devices. 1. Mesh Topology - every device has a point-to-point link that carries traffic only between the two devices it connects. #### n (n - 1) / 2 1. A mesh topology is robust. 2. privacy or security. 3. Point-to-point links make fault identification and fault isolation easy. 4. It has no traffic problems due to the fact that the links can carry their own data load. 1. Installation and reconnection are difficult. 2. The bulk of the wiring is greater than the available space. 3. The hardware that connects I/O ports and cable is expensive. 2. Star topology -each device has a dedicated point-to-point link only to a central controller, usually called a [hub.] \- Nodes are connected to the bus cable by [drop lines] and [taps.] A diagram of a station Description automatically generated \*[A drop line] is a connection running between the device and the main cable. \* [A tap] is a connector that either splices into the main cable or punctures the sheathing of a cable to create a contact with the metallic core. [Advantages] -It is easy to install. -Redundancy is eliminated. [Disadvantages] -Difficult reconnection and fault isolation because it is difficult to add new devices. -Signal reflection at the taps can cause degradation in quality. -A fault or break in the bus cable stops all transmission. 4.Ring topology - each device has a dedicated point-to-point connection with only the two devices on either side of it. \- A signal is passed along the ring in one direction, from device to device, until it reaches its destination.  Advantages -Easy to install and reconfigure. -To add or delete a device requires changing only two connections. -Fault isolation is simplified. [Disadvantages] -Unidirectional traffic can be a disadvantage. 4. Tree topology -- integrates multiple star topologies into a bus. -point to point writing for individual segments. -supported by several hardware & software venders. 5. Hybrid topology -- a star backbone with three bus networks. 1. Local Area Network (LAN) - is usually privately owned and links the devices in a single office, building, or campus. 2. Metropolitan Area Networks (MAN) -- is a network with a size between LAN and WAN. - Network address - Host address What are the current private IP ranges? 1. IPV4 -- internet protocol version 4 -- 4 billion available addresses 2. IPV6- internet protocol version 6 -- 128-bit addresses **Name** **First octet** **Number of subnets** **Number of hosts** **Description** ---------- ----------------- --------------------------- ---------------------------- --------------------------------------------- Class A 1 to 126 126 Approximately 16.7 million Many hosts per network. Class B 128 to 191 16,384 65,536 Many hosts per network. Class C 192 to 223 Approximately 2.1 million 254 Many networks with fewer hosts per network. Class D 224 to 239 n/a n/a Multicasting. Class E 240 to 254 n/a n/a Experimental. What is a subnet? - These are isolated network segments, which is a piece of a network that an administrator divides off. What is a subnet mask? -Determines which part of a host IP address is the network ID and which is the host ID. -It helps devices determine the network area which they belong. [How to convert an IP address from decimal into binary] 1. International service providers (ISPS) -- are at the top of the hierarchy that connects nations together. 2. National service providers -- provide connectivity between end users by using complex switch stations run by a third party known as NAPS (network access points). -Some are connected to one another by private switching stations known as peeing points. -Operate at a high data rate. 3. Regional service providers -- connected to one or more national ISPs. - Smaller data rate. 4. Local service providers -- provide direct service to the end users. (Used by most users) -Can be connected to regional ISPs or national ISPs.  [Protocols and Standards] What is an entity? -This is anything capable of sending or receiving information. -For communication to occur entities must agree on a protocol. What is a protocol? **-**A protocol is a set of rules that govern data communications. What are the key elements of a protocol? - **Syntax → format of the data** - **Semantics → meaning of each section.** - **Timing → when data should be sent and how fast.** What are standards? -This are agreed upon specification's that guarantee compatibility and interoperability between devices, applications and vendors on a network. What are the two categories of standards? - **De facto → by fact (not approved as a standard)** - **De jure → by Law (approved)** [Standards organizations] - **International Organization for Standardization (ISO)** - **International Telecommunication Union - Telecommunication Standards (ITU-T)** - **American National Standards Institute (ANSI)** - **Institute of Electrical and Electronics Engineers (IEEE)** - **Electronic Industries Association (EIA)** - **Forums** - **Regulatory agencies** **What is an internet standard?** **-** is a thoroughly tested specification that is useful to and adhered to by those who work with the Internet. [Network Models] What is a network model? -This is a layered architecture that has: - Task broken into subtasks. - Implemented separately in layers in stack. - Functions needed in both systems. - Peer layers communicate. What are some types of network models? -OSI model -open system interconnections model -TCP/ IP model - Transmission Control Protocol/Internet Protocol What are the tasks involved in sending a letter?  [OSI MODEL] What is the OSI model? -The Open Systems Interconnection model is the standard that covers all aspects of network communications from International Standards Organization (ISO). What is the layered architecture of the OSI model. A screen shot of a computer Description automatically generated with medium confidence 1. Physical layer - **responsible for movements of individual bits from one node(hop) to the next.** **Function:** - Physical characteristics of interfaces and media - Representation of bits - Data rate - Synchronization of bits - Line configuration (point-to-point or multipoint) - Physical topology (mesh, star, ring or bus) - Transmission mode (simplex, half-duplex or duplex) 2. Data link layer -- moves frames from one node to the next. Function: - Framing - Physical addressing - Flow control - Error control - Access control 3. Network layer - **responsible for the delivery of individual packets from the source host to the destination host.** **-Source to destination delivery.** - Logical addressing - routing 4. Transport layer - **responsible for the delivery of a message from one process to another.** **-Process to process delivery** **Functions:** - Port addressing - Segmentation and reassembly - Connection control (Connection-oriented or connection-less) - Flow control - Error control 5. Session layer - **It establishes, maintains and synchronize the interaction between communicating system** Function: - **Dialog control** - **Synchronization (checkpoints)** 6. Presentation layer - **responsible for translation, compression, and encryption.** - **Translation** (EBCDIC-coded text file  ASCII-coded file) - **Encryption and Decryption** - **Compression** 7. application layer - **is responsible for providing services to the user.** - Network virtual terminal (Remote log-in) - File transfer and access. - Mail services - Directory services (Distributed Database) - Accessing the World Wide Web -- -- -- -- -- -- -- -- -- -- What are the principles of an OSI model? - A layered model - Each layer performs a subset of the required communication functions. - Each layer relies on the next lower layer to perform more primitive functions. - Each layer provides services to the next higher layer. - Changes in one layer should not require changes in other layers. - The processes on each machine at a given layer are called peer-to-peer processes. How does the peer-to-peer process work? - Communication moves downwards through the layers on the sending device, over the communication channel and upward the receiving device. - Each layer in the sending device adds it own information to the message it receives from the layer just above it and passes it to the layer below it. - At the receiving device, the message is unwrapped layer by layer with each process receiving and removing the data meant for it. - The passing of data and network information down and up through the layers is made possible by an interface between each layer. [TCP/IP MODEL] What is the TCP/IP (Transmission Control Protocol/Internet Protocol) model? \- It is a hierarchical protocol made up of interactive modules, each of which provides a specific functionality. What are the layers of the TCP/IP Model? - Physical layer - Data link layer - Network layer - Transport layer - Application layer What is the internet layer (network layer)? -IP is a host-to-host protocol. -It supports protocols such as: - Address Resolution Protocol (ARP) - Reverse Address Resolution Protocol (RARP) - Internet Control Massage Protocol (ICMP) - Internet Group Massage Protocol (IGMP) What is the transport layer? -It is a process-to-process protocol. -It supports protocols such as: - User Datagram Protocol (UDP) - Transmission Control Protocol (TCP) - Stream Control Transmission Protocol (SCTP) [ADRESSES IN TCP/IP PROTOCOLS] -Four levels of addresses are used in an internet employing the TCP/IP protocols: 1\. physical 2\. logical 3\. port 4\. specific  RELATIONSHIP OF LAYERS AND ADDRESSES IN TCP/IP A diagram of a computer Description automatically generated What is a physical address (MAC)? -Is the address of a node as defined by its LAN or WAN -It is included in the frame used by data link layer -They may change from hop to hop. -Most local areas uses a 6-byte physical address written as 12 hexadecimal digit. -every byte (2 hexadecimal digits) is separated by a colon. e.g. **07:01:02: 01:2C:4B** **What is a logical address (IP)?** **-They are 32-bit addresses that uniquely define a host.** **-Necessary for universal communication that are independent of physical network.** - **Header- has information where the data is going.** - **Tailer- has extra bit for error correction and control.** **-No two host addresses on the internet can have the same IP address** **-They do not change.** **What is a port address?** **-It is a 16-bit address represented by one decimal number that ranged from (0-65535) to choose a process among multiple processes on the destination host.** **-[destination port] number is needed for delivery.** **-[source port] number is needed for receiving a reply as an acknowledgement.** **-They do not change.** e.g. **753** **What is a Specific address?** **-An email address, URL, or Universal Resource Address is a specific address in the Internet\'s TCP/IP protocol suite.** **[NETWORKING DEVICES]** What are some examples of networking devices? 1. Repeaters 2. Hubs 3. Switches 4. Bridges 5. Routers What are internetworking devices? -These are products used to connect networks. -As a network gets bigger so do the networking devices used to connect them. What is the purpose of networking devices? - Allow a greater number of nodes to be connected to the network. - They extend the distance over which a network can extend - They localise traffic on the network - They merge existing networks - They isolate network problems so they can be diagnosed more easily. [Local area networks and devices]  D:\\dco3310\\still4-14b.gif What internetworking devices operate at the physical layer of the OSI model? 1. A repeater -- to receive a signal and retransmit it, extending the signal\'s reach or enabling it to be received past an obstruction.  2. Hub -- [multi-port repeaters] are known as hubs -serves as the center of a star topology network. What is the disadvantage of using a repeater? -It can't filter network traffic. -Data passes through a repeater to other LAN segments of a network whether it needs to go there or not. What problems could occur because of too much traffic on a network? - If segments of a network are only connected to repeaters, this can result in more than one user trying to send data on the network at the same time. - If more than one node attempts to transmit at the same time, a collision will occur. - When a collision occurs, the data from each device impact and are damaged. What internetworking device can be used to filter traffic on the network? -[A bridge] - eliminates unnecessary traffic and minimizes the chances of collisions occurring on a network by dividing it into segments. -It is more intelligent than a hub because it analyses incoming packets and forwards (or drops) based on addressing information. What are the functions of a bridge? -Controls broadcast to the network -Maintains address tables  What are some types of bridges? D:\\dco3310\\still6-6d.gif -Transparent -Source route (Used in token ring LANs) At what layer of the OSI model do bridges operate? -The data link layer. How do bridges filter network traffic? - **Read the destination address**: The bridge reads the destination address of a packet. - **Determine if it should forward or filter**: The bridge decides whether to forward the packet or filter it out. - **Forward or filter**: If the destination is on a different segment, the bridge forwards the packet to that segment. If the destination is on the same segment as the source, the bridge filters the packet.  How are bridge data- forwarding decisions limited? -Although bridges use tables to determine whether or not to forward data to other segments, the types of comparisons and decisions they make are low level. What type of network problems is a bridge incapable of solving? \- When traffic between network segments becomes too heavy, the bridge can become a bottleneck and actually slow down communication. [SPANNING TREE PROTOCOL] -STP is a layer 2 network protocol used to prevent looping within a network topology. -It was created to combat problems that arise when computers exchange data on a LAN that contains redundant paths. What is a redundant path? \- This is a backup route that ensures data can continue to flow if the primary path fails but it can lead to a bridge looping. What is a loop? -It occurs when data travels from a source to a destination along redundant paths and the data begins to circle around the same paths resulting in a broadcast storm. How does a spanning tree protocol work? **1. Switches** will share messages known as **Bridge Protocol Data Units** to establish a connection between one another. 2\. A **Root Bridge** is chosen which will be the main reference point for the network. In this case, **it is Switch A**. 3\. Then the switches decide the **best paths to connect to the root bridge**, while the other paths are put on hold. Which is the path between **switch B and C?** 4\. The paths that are not being used are temporarily "**Turned Off**" to prevent loops. This is known as a **blocking port**. 5\. If the active paths **stop working**, the backup path is then turned on to keep the network running. What are some real-world applications of a spanning tree protocol? 1. Telecommunications 2. Campus networks 3. Public infrastructure 4. Internet service providers (ISP) 5. Retail sector What is the importance of a spanning tree protocol? \- prevents loops in a local area network (LAN) by selecting the most efficient paths between switches. What are the advantages and disadvantages of a spanning tree protocol? [ADV] 1. Higher network stability 2. Topology management 3. Automatic fall over [DIS] 1. Danger of misconfiguration 2. Increased network delays [NETWORK ADDRESSING SCHEMES] How many addressing schemes are there in networking? 1. MAC address 2. IP address How do IP addresses differ from MAC addresses? -Both MAC and IP addresses are unique. \- Mac addresses are physical addresses hard coded into the NIC card IP addresses are implemented in software. -MAC addresses occur at the data link layer while IP addresses occur on the network layer of the OSI model. What is a router? \- These devices pass data packets between networks based on network protocol or layer 3 information. -They have the ability to make intelligent decisions as to the best path for delivery of data on the network. How do routers work? \- Routers are used to connect two or more networks. For routing to be successful, each network must have a unique network number. How is a path determined in the network layer? -Layer 3 functions to find the best path through the internetwork. How do the paths communicate with one another? -Addresses represent the path of media connections. -Routing helps contain broadcasts. What is the difference between a network and a node in addressing? -A network address -- is a path part used by the router. -A node address -- is a specific port or device on the network. What network problems can routers help resolve? - Excessive broadcast traffic - they do not forward broadcast frames unless specifically told to do so. What is the difference between a router and a bridge? 1. Bridging occurs at the data link layer or layer 2, while routing occurs at the network layer or layer 3 of the OSI model. 2. Bridges use physical (MAC addresses) to make data forwarding decisions while Routers use a different addressing scheme that occurs at layer three. [TRANSMISSION MEDIA] What is transmission media? -It is a physical medium through which data is transmitted from one device to another within a network.  What are the classes of transmission media? - **Conducted or guided media use a conductor.** such as a wire or a fiber optic cable to move the signal from sender to receiver. - **Wireless or unguided media** use radio waves of different frequencies and do not need a wire or cable conductor to transmit signals. What are the design factors for transmission media? - Bandwidth - All other factors remain constant, the greater the bandwidth of a signal, the higher the data rate that can be achieved. - Transmission impairments - Limit the distance a signal can travel. - Interference - Competing signals in overlapping frequency bands can distort or wipe out a signal. - Number of receivers- Each attachment introduces some attenuation and distortion, limiting distance and/or data rate. What is Guided transmission media? -Its transmission capacity depends on the distance and on whether the medium is point-to-point or multipoint. Examples: - twisted pair wires. - coaxial cables - optical fiber What are twisted pair wires? \- Consists of two insulated copper wires arranged in a regular spiral pattern to minimize the electromagnetic interference between adjacent pairs. \- Often used at customer facilities and also over distances to carry voice as well as data communications -Low frequency transmission medium What are the types of twisted pair wires? - STP (shielded twisted pair) -the pair is wrapped with metallic foil or braid to insulate the pair from electromagnetic interference - UTP (unshielded twisted pair) -each wire is insulated with plastic wrap, but the pair is encased in an outer covering What are the ratings of twisted pairs? - Category 3 UTP -data rates of up to 16mbps are achievable - Category 5 UTP -data rates of up to 100mbps are achievable -more tightly twisted than Category 3 cables -more expensive, but better performance - STP -More expensive, harder to work with. What are the advantages and disadvantages of twisted pair wires? [ADV] - Inexpensive and readily available - Flexible and light weight - Easy to work with and install. [DIS] - Susceptibility to interference and noise - Attenuation problem - For analog, repeaters needed every 5-6km. - For digital, repeaters are needed every 2-3km. - Relatively low bandwidth (3000Hz) What are coaxial cables (COAX) - Used for cable television, LANs, telephone. - Has an inner conductor surrounded by a braided mesh. - Both conductors share a common center axial, hence the term "co-axial." What are the layers of a COAX?  What are the advantages and disadvantages of COAX? [ADV] - Higher bandwidth - 400 to 600Mhz - up to 10,800 voice conversations - Can be tapped easily (pros and cons) - Much less susceptible to interference than twisted pair [DIS] - High attenuation rates make it expensive over long distances. - Bulky What is a Fiber optic cable? - Relatively new transmission medium used by telephone companies in place of long-distance trunk lines. - Also used by private companies in implementing local data communications networks - Require a light source with injection laser diode (ILD) or light-emitting diodes (LED) What are the layers of a Fiber optic cable? What are the types of Fiber optic cables? - multimode step-index fiber -the reflective walls of the fiber move the light pulses to the receiver - multimode graded-index fiber -acts to refract the light toward the center of the fiber by variations in the density - single mode fiber -the light is guided down the center of an extremely narrow core What are Fiber optic signals?  What are the advantages and disadvantages of Fiber optic signals? [ADV] - greater capacity (bandwidth of up to 2 Gbps) - smaller size and lighter weight - lower attenuation - immunity to environmental interference - highly secure due to tap difficulty and lack of signal radiation. [DIS] - expensive over short distance - requires highly skilled installers. - Adding additional nodes is difficult. What is wireless (Unguided media) transmission? - Transmission and reception are achieved by means of an antenna. - directional -transmitting antenna puts out focused beam -transmitter and receiver must be aligned - omnidirectional -signal spreads out in all directions -can be received by many antennas What are some examples of wireless transmission? - terrestrial microwave - satellite microwave - broadcast radio - infrared What is a terrestrial microwave? - used for a long-distance telephone service. - uses radio frequency spectrum, from 2 to 40 Ghz. - parabolic dish transmitter, mounted high. - used by common carriers as well as private networks. - requires an unobstructed line of sight between source and receiver. - Curvature of the earth requires stations (repeaters) \~30 miles apart. What are some applications of terrestrial microwave? - Television distribution - Long-distance telephone transmission - Private business networks What are some disadvantages of microwave transmission? - line of sight requirement - expensive towers and repeaters - subject to interference such as airplanes and rain. What is satellite microwave transmission? - A microwave relay station in space - can relay signals over long distances. - geostationary satellites -remain above the equator at a height of 22,300 miles (geosynchronous orbit) -travel around the earth in exactly the time the earth takes to rotate What are satellite transmission links? - earth stations communicate by sending signals to the satellite on an uplink. - The satellite then repeats those signals on a downlink. - The broadcast nature of the downlink makes it attractive for services such as the distribution of television programming. What are the applications of satellite transmission? - television distribution - long-distance telephone transmission - private business networks What are some principal satellite transmission bands? - C band: 4(downlink) - 6(uplink) GHz -the first to be designated - Ku band: 12(downlink) -14(uplink) GHz -rain interference is the major problem - Ka band: 19(downlink) - 29(uplink) GHz -Equipment needed to use the band is still very expensive What is the difference between Optical Fiber and Satellite Transmission? **Satellite Communication** **Optical Communication** ------------------------------------------------------------------------------------------------------------ ----------------------------------------------------------------------------- Satellite communication uses electromagnetic waves as a medium for propagation. Optical communication uses light rays as a medium of propagation. In satellite communication, satellites as a relay stations are used for communication. In optical communication, communication happens via optical fiber. In satellite communication, for transmission and reception of signals special type of antennas are needed. In optical communication, no special antennas are needed for communication. It supports mobility. It does not support mobility because of the working within fixed locations. Satellite communication has less bandwidth and transmission rates compared to optical communication. Optical communication offers greater bandwidth and transmission rates. What is radio? - radio is omnidirectional and microwave is directional. - Radio is a general term often used to encompass frequencies in the range 3 kHz to 300 GHz. - Mobile telephone occupies several frequency bands just under 1 GHz. What is infrared? - Uses transmitters/receivers (transceivers) that modulate noncoherent infrared light. - Transceivers must be within line of sight of each other (directly or via reflection). - Unlike microwaves, infrared does not penetrate walls. [ERROR DETECTION AND CORRECTION] What is an error? \- This is a condition when the receiver's information does not match the senders.  -Data may get scrambled by noise in the data link or transport layer of the OSI model. -To prevent such errors, error-detection codes are added as extra data to digital messages.  What are the types of errors? 1. Single bit error - when one bit in a transmitted data unit is altered during transmission, leading to incorrect or corrupted data. A blue arrow pointing to the right Description automatically generated 2. Multiple bits error -arises when more than one bit in a data transmission is affected.   3. Burst error-a Frame contains more than1 consecutive bits corrupted. How to control errors in an OSI model? 1. Error detection 2. Error correction What are some error detection methods? 1. Parity check -One extra bit is sent along with the original bits to make number of 1s either even in case of even parity, or odd in case of odd parity. 2. Checksum -The process involves dividing the data into equally sized segments and using a [1's complement](https://www.geeksforgeeks.org/ones-complement/) to calculate the sum of these segments. 3\. Cyclic Redundancy Check (CRC) - a sequence of redundant bits, called cyclic redundancy check bits, are appended to the end of the data unit so that the resulting data unit becomes exactly divisible by a second, predetermined binary number. What are the advantages of error detection? 1. Increased data reliability 2. Improved network performance 3. Enhanced data security 1. Backward error correction - When the receiver detects an error in the data received, it requests back the sender to retransmit the data unit. - It is simple and inexpensive 2. Forward error correction - When the receiver detects some error in the data received, it executes error-correcting code, which helps it to auto-recover and to correct some kinds of errors.