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Unit Eight Project Running Head: UNIT Eight PROJECT Unit Eight Project Dale Henderson Kaplan University IT283-02 Networking with TCP/IP Anthony Stabile 1 Unit Eight Project 2 Unit Eight Project Table 9-1, match the function on the right with the correct IEEE sublayer of the data link layer. Sublayer A. LLC B. MAC Function A Provides an interface to upper layer B Controls the placement of frame on the medium A Remains relatively independent of the physical equipment B Adds a frame delimiter B Provides a unique source and destination address Concept Questions 1. Why has Ethernet been so successful? Simplicity and ease of maintenance Ability to incorporate new technologies Reliability Low cost of installation and upgrade 2. What functions does data encapsulation provide? Frame delimiting Addressing Error detection 3. How does Ethernet handle error detection? The sending node calculates a Cyclic Redundancy Check (CRC) of the bits in the frame. The node places the CRC result in the Frame Check Sequence (FCS) field in the trailer part of the Ethernet frame. After receiving a frame, a receiving node calculates its own CRC to compare to the one in the frame. If the two CRC results match, the recipient assumes that the frame arrived without error. Unit Eight Project 3 Vocabulary Exercising: Matching Term Description a. 10BASE5 b. 10BASE2 c. Hub d. Half duplex e. Full duplex f. Switch D Only one station at a time can transmit C Concentrates connections, allowing the network to see a group of nodes as a single unit B Uses 185 meters of thin coaxial cable F Isolates each port and sends a frame only to its proper destination (if the destination is known) E Both ends of connection can send at the same time A Uses 500 meters of thick coaxial cable Concept Questions 1. Compare and contrast half duplex and full duplex Half-duplex – Only one station could successfully transmit at a time. Full-duplex – having a connection that can carry both transmitted and received signals at the same time, have enabled the development of 1-Gbps Ethernet beyond. 2. What aspects of Ethernet has remained relativity unchanged over the years, and what aspects have changed? The ability to migrate the original implementation of Ethernet to current and future Ethernet implementation is based on the practically unchanged structure of the Layer 2 frame. Physical media and MAC continually evolved, but the Ethernet frame header and trailer have essentially remained constant through the many Unit Eight Project 4 generations of Ethernet. Ethernet’s simplicity and ease of use and installation have remained unchanged. The Ethernet frame has remained relatively unchanged. Ethernet is still usually connected in a star topology, but the center of the star is a switch rather than a hub these days. The cabling for Ethernet has evolved from coaxial to unshielded twisted pair to fiber-optic. Unshielded twisted pair is still widely used. Fiberoptic is reserved mostly for data centers, links between switches, and high-end devices. Vocabulary Exercise: Matching Field A. Preamble B. Start of frame delimiter C. Destination address D. Source address E. Length/type F. Data G. Frame check sequence Definition G. Used for error detection A. Used for synchronization B. Specifies the number of bytes in the data part of the frame or specifies the type of data (the upper-layer protocol) F. Carries the upper-layer data E. Tells other devices on the network that a frame is coming along the medium D. Specifies the frame’s sender C. Specifies the frame’s intended recipient Multiple- Choice Questions 1. What is the maximum size of an Ethernet frame according to the IEEE 802.3ac standard? A. 1522 bytes 2. What is the minimum size of an Ethernet frame? D. 64 bytes Unit Eight Project 5 3. What does a receiving device do if it receives a frame that is less than the allowed minimum size or greater than the allowed maximum size? B. The receiving device drops the frame 4. How does a recipient device know if the sender used the Length/Type field to specify a length or a type? D. The recipient bases the decision on whether it’s been configured for Ethernet II or IEEE 802.3 5. Why is padding sometimes added to the data part of an Ethernet frame? B. To ensure the frame is at least 64 bytes. 6. What happens if a frame arrives damaged? A. The recipient calculates a CRC that differs from the CRC in the FCS field and drops the frame. 7. How long is a MAC address? C. 48 bits Concept Questions 1. Compare and Contrast MAC addresses with IP addresses MAC addresses operate at the OSI data link layer (Layer 2). Layer 2 addresses are used only for local delivery when transporting a frame across a local medium. These Unit Eight Project 6 addresses use a flat addressing scheme and do not indicate on what network a device is located. If a device is moved to another network, its Layer 2 address does not need to change. IP addresses operate at the OSI network layer (Layer 3). Layer 3 addresses are carried from source to destination host across an internetwork. Layer 3 addresses use a hierarchical addressing scheme and indicate a network number and host identifier. 2. Compare and contrast unicast, broadcast, and multicast communications at the MAC sublayer Unicast – the unique address used when a frame is sent from a single transmitting device to a single destination device Broadcast – uses a special address that allows all nodes to accept and process the frame Multicast – allows a source device to send a packet to a group of devices. Vocabulary Exercise: Completion 1. Because devices using coaxial or hub-based Ethernet send their messages on a shared medium, a carrier sense multiple access collision detect (CSMA/CD) is used to determine if the medium is already in use before a sender transmits. Unit Eight Project 7 2. When a device detects that no other computer is sending a frame, the device waits if it has something to send. All devices that have messages to send must listen before transmitting. 3. If a device detects a signal from another device, it waits before attempting to transmit. 4. When no traffic is detected, a device transmits its message. While transmitting, the device continues to listen for traffic from another device. If another device is sending at the same time, a collision has occurred. 5. If a collision happens, the sending devices continues to send for the time it takes to send a jam signal and then jamming signal sending. The devices invoke a backoff algorithm that causes them to wait a random amount of time before trying to send again. Concept Questions 1. What is interframe spacing, and why does Ethernet use it? It is the time measured from the last bit of the FCS field of one frame to the first bit of the Preamble of the next frame. After a frame has been sent, all devices on a 10-Mbps Ethernet network are required to Unit Eight Project wait a minimum of 96 bit times (9.6 microseconds) before any device can transmit its next frame. 2. Why is the backoff timing random when an Ethernet collision occurs? After a collision occurs and all devices allow the cable to become idle (each waits the full interframe spacing), the devices whose transmissions collided must wait an additional and potentially progressively longer period of time before attempting to retransmit the collided frame. Vocabulary Exercise: Completion 1. 10BASE-T uses two pairs of a four-pair cable and is terminated at each end with an eight-pin RJ-45 connector. The pair connected to pins 1 and 2 is used for transmitting, and the pair connected to pins 3 and 6 is used for receiving. 2. Replacing hubs with switches in 10BASE-T networks has greatly increased the throughout available to these networks and has helped Ethernet maintain its longevity in the LAN market. The 10BASE-T links connected to a switch can support either half-duplex or full-duplex operation. 3. The most popular implementations of 100 Mbps Ethernet are 100BASE-TX, which uses Category 5 or later UTP cable, and 100BASE-FX, which uses fiber-optic cable. 8 Unit Eight Project 9 4. 1000BASE-T Ethernet provides full-duplex transmission using all four pairs in Category 5 or later UTP cable. 5. The two fiber versions of Gigabit Ethernet are 1000BASE-SX and 1000BASE-LX. Fiber-optic cabling offers better noise immunity than UTP, a smaller physical size, and higher distances and bandwidth. 6. A difference between 1000BASE-SX and 1000BASE-LX is the link media, connectors, and wavelength of the optical signal. 7. The IEEE 802.3ae standard was adapted to include 10-Gbps, full-duplex transmission over fiber-optic cable, 10-Gigabit Ethernet is evolving for use not only in LANs, but also in MANs and WANs. 8. Although Gigabit Ethernet is now widely available and 10Gigabit products are becoming more available, the IEEE and the 10-Gigabit Ethernet Alliance are working on 40-, 100-, and even 160-Gbps standards. Vocabulary Exercise: Matching Term a. Hub b. Switch Characteristic B. Divides collision domains A Forwards received bits out every port B Supports full-duplex communication A Simplifies network cabling but doesn’t have any performance benefits A When many nodes that transmits frequently are connected to the device, latency increases, because Unit Eight Project 10 each node must wait for an opportunity to transmit B Provides an alternative to contention-based Ethernet B Maintains a table that maps each MAC address to a port Vocabulary Exercise: Completion 1. A switch selectively forwards an individual frame that it receives on a port to the port where the destination node is connected. 2. Switches use store-and-forward switching, whereby the switch receives an entire frame, checks the FCS for errors, and forwards the frame to the appropriate port. 3. A switch maintains a table, called the MAC table, which matches a MAC address with the port used to connect the node with that address. Concept Question List and describe the five basic operations of an Ethernet LAN switch. Learning. A switch populates the MAC table by learning which port it should use to reach each MAC address. As a frame enters the switch, the switch examines the MAC source address. If no entry exists in the table for this address, the switch creates a new entry that Unit Eight Project 11 pairs the source address with the port on which the frame arrived. The switch can now use this mapping to forward frames to the node with the MAC address in the table entry. Aging. A switch tracks how long an entry has been in the MAC table. If the entry reaches a certain age without being refreshed by a new frame from the same node on the same port, the entry is removed. Flooding. If a switch has not yet learned which port it should use to forward a frame to a destination, the switch sends the frame to all ports, except the port on which the frame arrived. Selective forwarding. A switch examines the destination MAC address in a frame and forwards the frame out the appropriate port. Filtering. After a switch has learned the address or addresses that map to a port, it filters frames from going out that port that include a destination address that is not mapped to the port. Multiple-Choice Questions 1. What is a basic job of ARP? A. Resolve IPv4 addresses to MAC addresses Unit Eight Project 12 2. If a node has recently sent a frame to another node, where is the mapping of IPv4 address to MAC address stored? B. ARP cache 3. When a node has not recently sent a frame to another node, how does the node discover the correct MAC address to use for the IPv4 address of the destination node? C. The sender monitors traffic until it discovers the correct MAC address to use. 4. What type of header does an ARP frame contain? A. IP 5. When an Ethernet transmitter sends to a destination not on its local network, what MAC destination address does it use, and how does it discover this address? A. The transmitter uses the MAC address of the destination, which it discovers with an ARP request. 6. What is the destination address in the frame when a node sends an ARP request to find the MAC address associated with a known IP address? B. The address of the local router interface Unit Eight Project References Dean, Tamara. (2009). Network+ Guide to Networks. Boston: Course Technology, Cengage Learning. Dye, McDonald, Rufi. (2010). Network Fundamentals: CCNA Exploration Companion Guide. Indianapolis: Cisco Press. 13