The OSI Model: Layers, Protocols, and Communication Fundamentals, Exams of Advanced Education

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CNIT 344 Exam 1 Answered 2024

1st Layer of the OSI Model - ANSWER-Physical Layer 2nd Layer of the OSI Model - ANSWER-Data Link Layer 3rd Layer of the OSI Model - ANSWER-Network Layer 4th Layer of the OSI Model - ANSWER-Transport Layer 5th Layer of the OSI Model - ANSWER-Session Layer 6th Layer of the OSI Model - ANSWER-Presentation Layer 7th Layer of the OSI Model - ANSWER-Application Layer At what clock rate does Ethernet operate? - ANSWER-20 MHz Components of Communication - ANSWER-Message Source -> Encoder -> Transmitter -> Transmission Medium "The Channel" -> Receiver -> Decoder -> Message Destination Describe a parallel connection. - ANSWER-Able to send data over short distances. Limited by electrical signal interference and degradation by EMI. Describe a serial connection. - ANSWER-Able to send data over long distances. Nearly all LAN/WAN technologies utilize serial communications. Describe a synchronous transmission mode. - ANSWER-It is time-based. An internal or external clock provides the synchronization to handle this communication. Timing is maintained regardless of presence of data. Describe an asynchronous transmission mode. - ANSWER-There is no timing source to control when data is sent. It utilizes start and stop bits to indicate the beginning and end of communication (it may have 1, 1.5, or 2 stop bits for simple RS systems). The synchronization must be re-established for every communication cycle. Example of full duplex - ANSWER-Telephone network in which communication is occurring between two persons who can talk and listen at the same time. Example of half-duplex - ANSWER-A walkie-talkie sends one message at a time in both directions.

Example of simplex - ANSWER-Keyboard can only input, monitor can only output. Examples of parallel and asynchronous - ANSWER-Not many communications protocols and standards, reviewed for HPC Examples of parallel and synchronous - ANSWER-Internal buses, printers and scanners Examples of serial and asynchronous - ANSWER-Most "terminal" applications, keyboard, mice, ATM, Firewire Examples of serial and synchronous - ANSWER-T-Carrier system, SONET, frame relay, xDSL, ISDN, USB, Firewire Full duplex - ANSWER-Can transmit and receive simultaneously. It is used when communication in both directions is required all the time. The capacity of the channel must be divided in two directions, however. Half-duplex - ANSWER-Can transmit and receive, but not at the same time. It is used for when there is no need to communicate in both directions at the same time. How are VLAN memberships assigned? - ANSWER-- by port

• by MAC addresses
• by network protocols
• by IP subnets (L3)
• by higher layers, such as network services (L4-L7) How do re-transmit requests work? - ANSWER-By sequence # and ACK. How does addressing the frame work? - ANSWER-It allows data to be sent to an appropriate destination and responses are returned. How does continuous ARQ work? - ANSWER-It requires the retransmission of everything in the window from the error forward. It slides the window and sequence numbers. How does CSMA/CA work? - ANSWER-The devices on a WLAN must sense the medium for energy and wait until the medium is free before sending. How does discrete ARQ work? - ANSWER-Stop and wait How does selective ARQ work? - ANSWER-It requires the retransmission of only the error frame. It slides the window and sequence numbers. How many byte is the size of the frame check sequence? - ANSWER-4 bytes How many bytes in size is the data/pad? - ANSWER-46 - 1500 bytes

How many bytes is the preamble of an Ethernet frame? - ANSWER-7 bytes How many bytes is the size of the destination MAC address? - ANSWER-6 bytes How many bytes is the size of the length/type? - ANSWER-2 bytes How many bytes is the size of the source MAC address? - ANSWER-6 bytes How many bytes is the size of the start of frame delimiter? - ANSWER-1 byte Is circuit switching connection-oriented or connectionless? - ANSWER-Connection- oriented. List all 7 layers of the OSI Model - ANSWER-7. Application

6. Presentation
7. Session
8. Transport
9. Network
10. Data Link
11. Physical Name the two error correction approaches. - ANSWER-- Forward Error Correction (FEC) This adds additional information.

• Automatic Repeat reQuest (ARQ) The sender and receiver exchange the message to ensure all data arrives correctly. Simplex - ANSWER-Only unidirectional communication. One device can only transmit and one device can only receive. What are common implementations of a parallel transmission mode? - ANSWER-PCI, memory bus, many HDD interfaces, older printers, and some scanners. What are common implementations of a serial transmission mode? - ANSWER-Telco/ISP Links, Ethernet, SATA What are some application protocols that exist at the application layer? - ANSWER- HTTP, SIP, Telnet/SSH, SMTP, and Routing Protocols. What are some benefits to the OSI Model? - ANSWER-1. Breaks network communication into smaller, more manageable parts. Prevents changes in one layer from affecting other layers.

2. Standardizes network components to allow multiple vendor development and support.
3. Allows different types of network hardware and software to communicate with each other. What are some code conversions/translations? - ANSWER-ASCII, EBCDIC, Unicode What are some Ethernet operations? - ANSWER-- Data rates vs signaling rates

• Auto-Negotiation
• Auto-MDIX
• Power over Ethernet (PoE) What are some routable protocols for the network layer of the OSI model? - ANSWER- IP, IPX, Appletalk What are some routing protocols for the network layer of the OSI model? - ANSWER- RIP, OSPF, BGP What are some sources of transmissions errors? - ANSWER-Interference, distortion, and attenuation What are the benefits of VLANs? - ANSWER-Traffic isolation, cost reduction, higher performance, broadcast storm mitigation, and improved IT staff efficiency What are the DSSS standards? - ANSWER-802.11b and 802.11g What are the OFDM standards? - ANSWER-802.11a, 802.11g, 802.11n What are the primary components of wireless association? - ANSWER-Beacons, probes, authentication, and association. What are the Rules for Communication for the OSI Model? - ANSWER-1. The communication between layers is handled in a specified (defined) manner.

2. Each layer is only able to communicate with its adjacent layers.
3. Each layer relies on the layers below it to perform their specified function.
4. Each layer relies on the layers above it to perform their specified function. What are the two sub-layers in the data link layer? - ANSWER-- MAC

• LLC

What are the types of VLANs? - ANSWER-- Data VLAN

• Default VLAN
• Native VLAN
• Management VLAN
• Voice VLAN What can a bridge, layer 1-2 device break? - ANSWER-It can break contention domains, but not broadcast domains. What can a hub, multiport repeater, layer 1 device break? - ANSWER-It cannot break contention domains or broadcast domains. What can a repeater, layer 1 device break? - ANSWER-It cannot break contention domains or broadcast domains. What can a router, layer 1-3 device break? - ANSWER-It can break contention domains and broadcast domains. What can a switch, typically layer 1-2 device, multiport bridge device break? - ANSWER-It can break contention domains, but not broadcast domains (unless a VLAN is used). What do switches use MAC addresses for? - ANSWER-To direct network traffic to the appropriate port. What do VLANs do? - ANSWER-They allow for multiple VLANs on a switch, and allow the same VLAN to cross multiple switches through trunking. What does a modem do? - ANSWER-A modulator/demodulator performs both modulation and demodulation. What does a wireless router do? - ANSWER-It performs the role of access point, Ethernet switch, and router. What does an SSID do? - ANSWER-It is a unique identifier that client devices use to distinguish between multiple wireless networks in the same vicinity. What does CRC stand for? - ANSWER-Cyclic Redundancy Check What does CSMA/CA stand for? - ANSWER-Carrier Sense Multiple Access with Collision Avoidance. What does CSMA/CD stand for? - ANSWER-Carrier Sense Multiple Access with Collision Detection.

What does duplex mode auto-negotiation do? - ANSWER-It sets Link Speed and Duplex mode. What does OSI stand for? - ANSWER-Open System Interconnection. What does SSID stand for? - ANSWER-Shared service set identifier. What does the data link layer convert? - ANSWER-It converts data into frames. What does the LLC sub-layer of the data link layer do? - ANSWER-It is used for framing (addressing), multiplexing, flow control, and error control. What does the MAC sub-layer of the data link layer do? - ANSWER-It is used for accessing shared media. What does the network layer convert? - ANSWER-It converts data to packets. Packets = reliable. Datagrams = unreliable. What does the OSI Model do? - ANSWER-It defines 7 layers that describe the complete application-based communications between any two systems. It provides open interconnections between layers, such that multi-vendor environments can be supported. What does the transport layer convert? - ANSWER-It converts data into messages or segments. What does VLAN stand for? - ANSWER-Virtual Local Area Network What is a Basic Service Sets (BSS) wireless topology? - ANSWER-It has access points that provide an infrastructure. What is a beacon? - ANSWER-Frames used by the WLAN network to advertise its presence. What is a broadcast? - ANSWER-An address that is used to send information to all hosts. What is a domain? - ANSWER-The scope at which a given communication can be received and processed by other hosts. What is a MAC broadcast domain? - ANSWER-The scope a MAC broadcast can reach. What is a media access domain? - ANSWER-The scope of multiple devices competing for the same access media.

What is a multicast? - ANSWER-An address that is recognized by a specific group of hosts. What is a probe? - ANSWER-Frames used by WLAN clients to find their networks. What is a socket? - ANSWER-Port + Layer 3 (Network) Address What is a trunk? - ANSWER-A physical and logical connection between two switches across which network traffic travels. What is a unicast? - ANSWER-A unique address that identifies a specific host. What is a wireless LAN? - ANSWER-An extension of the Ethernet LAN. What is a wireless NIC? - ANSWER-The device that makes a client station capable of sending and receiving RF signals. It is most often associated with mobile devices, like laptops. What is an Ad Hoc wireless topology? - ANSWER-It is a wireless network that can operate without access points. What is an Extended Service Sets (ESS) wireless topology? - ANSWER-It is used when BSS provides insufficient RF coverage. What is association? - ANSWER-Establishing the data link between an access point and a WLAN client. What is Carrier Sense? - ANSWER-A process required to test the medium for current activity. What is circuit switching? - ANSWER-It has a dedicated channel that is defined from source to destination prior to data forwarding. It has guaranteed resources for duration connection, and no other data is forwarded along the channel. What is code division multiplexing? - ANSWER-Each source data stream is assigned a unique orthogonal code for use in the entire channel. Any overlapping data streams are seen as noise in the system and ignored. What is Collision Detection? - ANSWER-It has a sample carrier and received signals to identify dissimilarities. What is demodulation? - ANSWER-The process of converting an analog signal into a digital bit stream.

What is Direct Sequence Spread Spectrum (DSSS)? - ANSWER-It is the simpler of the modulation techniques and less expensive to implement. What is flow control? - ANSWER-The process of managing the amount of data in transit to a specific destination. The two major approaches are stop and wait, and sliding window. What is frequency division multiplexing? - ANSWER-Each source data stream is assigned to a specific sub-frequency of the channel. A guard band is required to minimize adjacent channel interference. What is frequency modulation referred to as in the industry and publications? - ANSWER-FSK What is frequency modulation? - ANSWER-It manipulates the frequency of the carrier wave in order to indicate data. In true FM, only the frequency changes. What is Gigabit Ethernet? - ANSWER-It is intended to further extend the capabilities of LANs through faster data rates while still maintaining backwards compatibility. What is Inter-Switch Link, Cisco Proprietary (ISL)? - ANSWER-All received packets are expected to be encapsulated with an ISL header. All transmitted packets are sent with an ISL header. Untagged frames received from an ISL trunk port are dropped. What is LAN segmentation? - ANSWER-LANs are segmented into a number of smaller collision and broadcast domains using routers and switches. What is logical adjacency? - ANSWER-The apparent capability of peer-layer protocols to communicate directly. It is made possible through encapsulation and decapsulation. What is modulation? - ANSWER-The process of converting digital bits into an analog signal that can be sent over an analog medium. What is Multiple Access? - ANSWER-It is based on the sensing methods, the access to the medium can be seized by any number of hosts. What is Orthogonal Frequency Division Multiplexing (OFDM)? - ANSWER-It has faster data rates compared to DSSS. What is packet switching? - ANSWER-It does not have a dedicated channel defined prior to data forwarding. It has no guarantee of resources, and other data is forwarded along portions of the same channel.

What is phase modulation referred to as in industry and publications? - ANSWER-PSK What is phase modulation? - ANSWER-It manipulates the phase of the carrier wave in order to indicate data. In true PM, only the phase changes. What is shift keying? - ANSWER-The term used when the signal is digital. What is the 802.11 wireless LAN? - ANSWER-An IEEE standard that defines how radio frequency (RF) in the unlicensed industrial, scientific, and medical (ISM) frequency bands is used for the Physical layer and the MAC sub-layer of wireless links. What is the application layer of the OSI model responsible for? - ANSWER-It provides the interface between user applications and network's services (usually through network-capable APIs). This does NOT include actual user applications. What is the data link layer of the OSI model responsible for? - ANSWER-It is responsible for providing point-to-point validity of the data via point-to-point checking/correction, and it is responsible for the procedures and protocols for reliably operating the communication links. It has an independent address architecture from other layers. What is the data/pad? - ANSWER-It is the encapsulated data from Layer 3. It is most commonly an IPv4 packet. If the total frame length is less than 64 bytes, the field is padded to the right with enough null characters to meet the minimum frame length. What is the destination MAC address? - ANSWER-It identifies the node that is to receive the frame. A receiving device compares its MAC address to the contents of this field. If the addresses match, the frame is accepted. What is the equation for analog bandwidth? - ANSWER-𝑓𝑚𝑎𝑥 - 𝑓𝑚𝑖𝑛 What is the extended range of VLAN IDs? - ANSWER-1006 - 4094. What is the frame check sequence? - ANSWER-It is used to detect errors in a frame that may have occurred during transmission along the media. What is the ideal correlation between layers for logical adjacency? - ANSWER-1- What is the IEEE cable modem standard? - ANSWER-802. What is the IEEE Ethernet standard? - ANSWER-802.

What is the IEEE Token Ring standard? - ANSWER-802. What is the IEEE Wireless LAN (Wi-Fi) standard? - ANSWER-802. What is the IEEE Wireless PAN standard? - ANSWER-802. What is the maximum size for an Ethernet frame? - ANSWER-1518 bytes What is the minimum size for an Ethernet frame? - ANSWER-64 bytes What is the MTU? - ANSWER-The Maximum Transmission Unit. It usually refers to the size of the payload. What is the network layer of the OSI model responsible for? - ANSWER-It enables internetworking, it provides globally-unique addressing for every node in the network, and it determines routes between source and destination networks (end-to-end with analysis at each hop). It relies on higher layer protocols for error detection and correction (this is UNRELIABLE). What is the normal range of VLAN IDs? - ANSWER-1 - 1005. 1, 1002-1005 are automatically created. What is the payload? - ANSWER-It refers to the "data" portion of the frame (frame body) or service data unit (SDU). What is the physical layer of the OSI model responsible for? - ANSWER-It is responsible for the transmission and receipt of the bit stream to/from nodes. It is solely concerned with signaling techniques (such as activating, maintaining, and terminating the physical circuit). What is the preamble and start of frame delimiter? - ANSWER-It is used to synchronize the NIC with the media in preparation for receiving a frame. It is NOT considered the part of the frame length. It will not appear in any capture of the frame. What is the presentation layer of the OSI model responsible for? - ANSWER-It is responsible for managing the way data is presented. It is NOT the GUI. What is the responsibility of a trunk link? - ANSWER-To act as a conduit for VLANs.

What is the session layer of the OSI model responsible for? - ANSWER-It establishes, maintains, and terminates host-to-host interactive sessions. It is used to uniquely identify a service, application, or function on a host via ports. What is the source MAC address? - ANSWER-It identifies the node that originated the frame. What is the transport layer of the OSI model responsible for? - ANSWER-It is responsible for host-to-host integrity of transmission. It detects damaged or lost packets and generates re-transmit requests. It re-sequences packets. What is time division multiplexing? - ANSWER-Each source data stream is assigned to a timeslot in the channel. Data can only be sent during an assigned timeslot. What ISO Standard is the OSI Model? - ANSWER-ISO Standard 7498. (ITU-T specifies X.200-X.299 Recommendations). What reliable communications does the data link layer provide? - ANSWER-Error detection, error correction, error control What transmission mode transmits multiple bits at a time? - ANSWER-Parallel What transmission mode transmits one bit at a time? - ANSWER-Serial What transmission mode transmits signal-based? - ANSWER-Asynchronous What transmission mode transmits time-based (clock-based) but with a fixed gap between the transmission of data items? - ANSWER-Isochronous What transmission mode transmits time-based (clock-based) with no gaps between data items? - ANSWER-Synchronous What year was the first Ethernet standard published? - ANSWER- When did IEEE modify the Ethernet standard? - ANSWER- Where is the application layer of the OSI model defined? - ANSWER-X. Where is the data link layer of the OSI model defined? - ANSWER-X. Where is the network layer of the OSI model defined? - ANSWER-X. Where is the physical layer of the OSI model defined? - ANSWER-X. Where is the presentation layer of the OSI model defined? - ANSWER-X.

Where is the session layer of the OSI model defined? - ANSWER-X. Where is the transport layer of the OSI model defined? - ANSWER-X. Where was Ethernet designed at? - ANSWER-Xerox Which layer has "true" adjacency? - ANSWER-Physical layer