Coaxial Cable - Bus Topology (Old Technology)

SEMESTER 1 Chapter 9 140 Points Ethernet V 4.0

9.1.1 Who originally published the published in 1980 by a consortium of Digital Ethernet standard and when Equipment Corporation, Intel, and Xerox (DIX). was that? Who and when published 1985, the Institute of Electrical and Electronics LAN standards? Engineers (IEEE) What is the number for the 802.3 Ethernet LAN standard? What layers of the OSI 1 and 2 model do Ethernet standards operate at? 9.1.2 What does Ethernet Layer 1 signals, bit streams that travel on the media, involve? physical components that put signals on media, and various topologies What are the Ethernet Layer Connects to the upper layers via the LLC 2 functions that overcome Uses addressing schemes to identify devices the limitations of Ethernet Uses frames to organize bits into groups Layer 1? Uses MAC to identify transmission sources 9.1.3 What are the two sublayers the Logical Link Control (LLC) sublayer and of the Data Link Layer? the Media Access Control (MAC) sublayer. What are the 4 functions of Makes connection with the upper layers the LLC? Frames the network layer packet Identifies the network layer protocol Remains relatively independent of the physical layer What type of environment is Software LLC implemented in? 9.1.4 Where is the MAC sublayer NIC implemented? What are the 2 primary Data Encapsulation functions of the MAC Media Access Control sublayer? What are the 3 primary Frame delimiting functions of data Addressing encapsulation? Error detection What are the two main Control of frame placement on and off the functions of the media media access control? Media recovery What is the underlying Mulit-access bus topology of Ethernet? What is the media access CSMA/CD Carrier Sense Multiple Access with control method for Collision Detection Ethernet? 9.1.5 What are the four factors Simplicity and ease of maintenance that have made Ethernet a Ability to incorporate new technologies success? Reliability Low cost of installation and upgrade What part of the Ethernet Frame structure standard remains consistent across all of its physical implementations? 9.2.1 What was the historic Alohanet network that Ethernet was based on called? 9.2.1.2 Describe the method of A frame received in one port is transmitted out transmission on a hub? all other ports 9.2.2 What is legacy Ethernet? 10Base-T network with a hub at its center What is the current standard 100Base-T network with switches for Ethernet? What is full duplex? a connection that can carry both transmitted and received signals at the same time What is the difference when Hub always send the signal out all ports and forwarding a frame from a switch sends directly to device if it’s address is switch vs. hub? known 9.2.3 What two new uses are Voice over IP (VoIP) and multimedia services requiring the move to Gigabit Ethernet? 9.2.3.2 Define a MAN? Ethernet connection across an entire city 9.3.1 What is the most significant the addition of a Start Frame Delimiter (SFD) difference between the and a small change to the Type field to include IEEE 802.3 (original) and the Length the revised IEEE 802.3? What were the minimum the minimum frame size as 64 bytes and the and maximum sizes of maximum as 1518 bytes Ethernet frames originally? What is the new maximum 1522 bytes size for a frame? What happens if the size of It is dropped a transmitted frame is less than the minimum or greater than the maximum? 9.3.1.2 What are the six portions of Preamble, start frame delimiter, destination an Ethernet frame address, source address, length/type, 802.2 discussed? header and data, frame check sequence 9.3.1.3 What is the Frame Check (4 bytes) used to detect errors in a frame Sequence (FCS)? What is the algorithm used Cyclical redundancy check in determining the value of the FCS? What happens if the FCS The frame is dropped values do not match? 9.3.2 What was created to assist Media Access Control (MAC) address in determining the source and destination address? How is an Ethernet MAC a 48-bit binary value expressed as 12 address represented? hexadecimal digits 9.3.2.2 Define the two parts of an All MAC addresses assigned to a NIC or other Ethernet MAC address? Ethernet device must use that vendor's assigned OUI as the first 3 bytes. All MAC addresses with the same OUI must be assigned a unique value (vendor code or serial number) in the last 3 bytes. What is another name for Burned-in address the MAC address? As an Ethernet frame the NIC passes the frame up the OSI layers, passes through a network where the decapsulation process take place what happens if that devices MAC address matches the destination MAC address? As an Ethernet frame The frame is discarded passes through a network what happens if that devices MAC address does not match the destination MAC address? 9.3.3.2 Where can you find your Ipconfig/all or ipconfig computer’s MAC address? 9.3.4 What is the problem with No meaning outside the local network physical addressing? What is the difference The Network layer address enables the packet between physical (Network to be forwarded toward its destination. Layer) and logical (Data The Data Link layer address enables the Link Layer) addressing? packet to be carried by the local media across each segment. 9.3.5 When a unicast when a frame is sent from a single transmitting transmission used? device to single destination device 9.3.5.2 When is a broadcast all hosts on that local network (broadcast transmission used? domain) will receive and process the packet How is a broadcast IP All 1’s in the host portion of the IP address address represented? How is a broadcast MAC FF-FF-FF-FF-FF-FF address represented? 9.3.5.3 When is a multicast When a frame is sent to a group of computers transmission used? How can a multicast packet as the destination of a packet only be used? What type of address does Unicast the source have? What is the multicast MAC Begins with 01-00-5E The value ends by address? converting the lower 23 bits of the IP multicast group address into the remaining 6 hexadecimal characters of the Ethernet address. The remaining bit in the MAC address is always a "0". 9.4.1 How does a shared media all devices have guaranteed access to the environment operate? medium, but they have no prioritized claim on it. If more than one device transmits simultaneously, the physical signals collide and the network must recover in order for communication to continue. When does a device on a When it detects that no other computer is shared environment sending a frame, or carrier signal transmit? 9.4.2 Define latency. The time delay between when a process is started and that same process is detected Define collision. When two stations transmit at the same time How does collision When a device is in listening mode it can detection occur? detect an increase in amplitude of the signal above the normal level What happens when all they send out a jamming signal devices on a shared medium detect a collision? What is invoked after a The backoff algorithm device receives a jamming signal? How does a backoff All devices stop transmitting for a random algorithm work? amount of time What mode does a device Listening return to after the backoff algorithm has expired? 9.4.2.2 What are the three reasons More devices are being connected to the given that the growth of the network. Internet has resulted in Devices access the network media more more collisions? frequently. Distances between devices are increasing. Define a collision domain? The media within a network where collsions can occur What does the connection They increase the collision domain size of hubs and repeaters do to collision domains? What happens when the reduces the network's efficiency and number of collisions effectiveness until the collisions become a increases significantly? nuisance to the user 9.4.3 Which devices extend the Hubs and repeaters latency in the medium? Why would an increased The other device may not hear the signal latency cause more before it begins to transmit collisions? 9.4.3.2 What is sent before an The preamble entire Ethernet frame is sent? What does asynchronous each receiving device will use the 8 bytes of communication mean? timing information to synchronize the receive circuit to the incoming data and then discard the 8 bytes What does synchronous the timing information is not required communication mean? 9.4.3.3 What is a bit time? a period of time is required for a bit to be placed and sensed on the media What is the slot time? The time it takes for an electronic pulse to travel the length of the maximum theoretical distance between two nodes. 9.4.4 What is interframe spacing? time measured from the last bit of the FCS field of one frame to the first bit of the Preamble of the next frame What happens to interframe The time reduces spacing as the network speed increases? 9.4.4.3 What happens when the it gives up and generates an error to the MAC layer is unable to send Network layer a frame after 16 attempts? 9.5.1 What are the four data rates 10 Mbps - 10Base-T Ethernet are currently defined for 100 Mbps - Fast Ethernet operation over optical fiber 1000 Mbps - Gigabit Ethernet and twisted-pair cables? 10 Gbps - 10 Gigabit Ethernet 9.5.2 What are the three principal 10BASE5 using Thicknet coaxial cable 10 Mbps implementations of 10BASE2 using Thinnet coaxial cable Ethernet? 10BASE-T using Cat3/Cat5 unshielded twisted-pair cable 9.5.2.2 What are the most popular 100BASE-TX using Cat5 or later UTP implementations of 100 100BASE-FX using fiber-optic cable Mbps Ethernet? 9.5.3 What is Gigabit Ethernet Noise more susceptible to because of its speed? What type of transmission the transmission and reception of data in both does 1000Base-T allow for? directions - on the same wire and at the same time What is the maximum 17 number of voltages used on the media at the same during transmission? What are the two main cable and termination problems causes of noise on the line? 9.5.4 What are the ways that Frame format is the same, allowing 10Gbps can be compared interoperability between all varieties of legacy, to other varieties of fast, gigabit, and 10 gigabit Ethernet, with no Ethernet? reframing or protocol conversions necessary. Bit time is now 0.1 nS. All other time variables scale accordingly. Because only full-duplex fiber connections are used, there is no media contention and CSMA/CD is not necessary. The IEEE 802.3 sublayers within OSI Layers 1 and 2 are mostly preserved, with a few additions to accommodate 40 km fiber links and interoperability with other fiber technologies. 9.6.1 What is the problem high levels of collisions on the LAN associate with the classic Ethernet implementation using hubs? List the four problems Scalability, Latency, Network Failure, and related to the Collisions implementation of classic Ethernet? 9.6.2 How do switches segment a Separate collision domains LAN? What does the separation of Full media bandwidth to each device collision domains mean for the bandwidth to the device? 9.6.2.2 What are the three reasons Dedicated bandwidth to each port that bandwidth increases Collision-free environment dramatically when each Full-duplex operation device is connected to a switch port? What are the three reasons Availability, Economics, and Requirements that hubs are still being used? 9.6.3 Describe selective establishing a momentary point-to-point forwarding? connection between the transmitting and receiving nodes What is the process called Store-and-forward when the switch holds the frame until the receiving node is available called? Describe the store-and- The switch receives the entire frame and forward operation mode of a checks the FCS before forwarding the frame switch? How does a switch use a The incoming frame destination MAC address MAC table? is compared to the MAC table to decide which port to forward the frame to 9.6.3.2 What are the five basic Learning operations of a switch? Aging Flooding Selective Forwarding Filtering How does a switch learn a The source address of the incoming frame MAC address? What happens when an The address is removed from the MAC table addresses countdown reaches 0? What happens when a The frame is flooded out all but the incoming switch does not know the port destination address? What type of frames will not A frame with a destination of the same port, a be forwarded? corrupt frame, and security reasons 9.7.1 What are the two basic Resolving IPv4 addresses to MAC addresses functions of ARP? Maintaining a cache of mappings What are the names of the ARP table or ARP Cache tables that store the list of MAC addresses with the network address? What are the two ways a From an incoming frame or using an ARP computer can gather MAC request addresses? What are the 2 destination Broadcast MAC address and the destination addresses in an ARP MAC address Request? 9.7.2 If the destination is on the The device MAC address local network segment, what MAC address is used? If the destination is on a The gateway MAC address remote network, what MAC address is used? If the MAC address of the ARP Request gateway is unknown, what process is used? 9.7.2.2 What is the most common When the device can not determine if the host reason for using a proxy is on the same network or not ARP? 9.7.3 How long are addresses 2 minutes unless used again in those 2 held in the ARP table? minutes and then 10 minutes 9.7.4 How could ARP requests Too many broadcasts at once that each host impact performance on a receives and processes therefore slowing network? down the network What is another problem Security- ARP spoofing which causes errors that may be associated with on the network ARP?

* 3 Ethernet media types: – Coaxial cable - bus topology (old technology) – Copper cable (UTP) - star topology – Optical fiber cable - star topology

* You need to be able to do Hexadecimal Number conversion.  For example, the binary value 0000 1010 is shown in hexadecimal as 0A. * Ethernet operates in the lower two layers of the OSI model: the Data Link layer and the Physical layer. • IEEE 802.2 standard describes the LLC sublayer • LLC handles the communication to the upper layers • LLC takes the network protocol data, and adds control information to help deliver the packet to the destination node. • IEEE 802.3 standard describes the MAC sublayer and the Physical layer functions. • Data Encapsulation • Frame delimiting • Addressing • Error detection • Media Access Control • The MAC sublayer controls the placement of frames on the media and the removal of frames from the media • CSMA/CD.

• Make sure you also remember the name mapping between OSI and TCP/IP model.

* The Frame – Encapsulating the Packet. – The Ethernet frame structure adds headers and trailers around the Layer 3 PDU.

* MAC address: . The MAC address is often referred to as a burned-in address (BIA) because it is burned into ROM (Read-Only Memory) on the NIC. . All MAC addresses assigned to a NIC must use that vendor's assigned OUI as the first 3 bytes. . All MAC addresses with the same OUI must be assigned a unique value in the last 3 bytes.

* Make sure you still remember this: – IP address global – Mac address local * What is the definition of “Interframe Spacing”? How does it work? . The Ethernet standards require a minimum spacing between two non-colliding frames. . This gives the media time to stabilize after the transmission of the previous frame and time for the devices to process the frame.

* What is the “random backoff” in CSMA/CD? How does it work? . 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. . The waiting period is intentionally designed to be random so that two stations do not delay for the same amount of time, which would result in more collisions. . Among the groups of devices that received the jam signals and starts the backoff timer, the station that will 1st try to resend the frame is the station whose timer expired first. (ADD this to the PPT)

* CSMA/CD: Collisions will occur in any shared media topology. – Collisions are the cost that Ethernet pays to get the low overhead associated with each transmission. – Every time a collision happens on a network, all transmission stops for a period of time. – Collisions are the cost that Ethernet pays to get the low overhead associated with each transmission. – Using hubs to provide network access to more users reduces the performance because the fixed capacity of the media has to be shared between more devices.

* These are all CSMA/CD LAN access protocols:

* Full Duplex (typically on a switch): – In a network that uses twisted-pair cabling, one pair is used to carry the transmitted signal. A separate pair is used for the return or received signal. It is possible for signals to pass through both pairs simultaneously. – In full duplex mode, there is no contention for the media (no collision). Thus, a collision domain no longer exists.

* Legacy Ethernet (Hub and half-duplex) – In 10BASE-T networks, typically the central point of the network segment was a hub. This created a shared media. – Because the media is shared, only one station could successfully transmit at a time. . – As more devices were added to an Ethernet network, the amount of frame collisions increased significantly.

* Using switch instead of hub: – Dedicated bandwidth to each port – Collision-free environment – Full-duplex operation – Increase throughput

* What is ARP? . For a frame to be placed on the LAN media, it must have a destination MAC address. The ARP protocol provides two basic functions: . Resolving IPv4 Addresses (known) to MAC Addresses (unknown) . Maintaining the ARP Table . When the destination device is on the same LAN (subnet) . ARP sends a Layer 2 broadcast to all devices on the Ethernet LAN. The frame contains an ARP request packet with the IP address of the destination host. . The node receiving the frame that identifies the IP address as its own responds by sending an ARP reply packet back to the sender as a unicast frame. This response is then used to make a new entry in the ARP table. . If the destination IPv4 host is not on the local network, . The source node will use the MAC address of the gateway as the destination address for frames containing an IPv4 packet addressed to hosts on other networks. . In the event that the gateway entry is not in the table, the normal ARP process will send an ARP request to retrieve the MAC address associated with the IP address of the router interface