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43 Cards in this Set
- Front
- Back
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What does IEEE stand for?
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Institute of Electrical and Electronics Engineers
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What are the IEEE standards for Lans?
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802 for LANs. 802.3 for Ethernet, from physical up to MAC. 802.2 for LLC, but isn't Ethernet.
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In Ethernet, what are the Layer One limitations?
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Cannot communicate with upper layers,
cannot identify devices, can only recognise streams of bits, cannot determine the source of a transition when multiple devices are transmitting. |
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In Ethernet, how does the Layer Two functions address layer one limitations?
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Connects to upper layers via LLC,
uses addressing schemes to identify devices, uses frames to organise bits into groups, uses MAC to identify transmission sources |
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What are some functions of LLC?
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Makes the connection with upper layers,
frames the Network layer packet, identifies the Network layer protocol, remains relatively independent of the physical equipment. |
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In a computer, the LLC is the driver for?
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the NIC
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What are the Ethernet MAC sublayer's two primary functions?
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Data encapsulation and media access control
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What are the three primary functions of Data Encapsulation?
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Frame delimiting, addressing, and error detection
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What are the two primary functions of Media Access Control?
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Control of frame placement on and off the media, media recovery
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What is the media access control method for classice Ethernet?
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CSMA/CD
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What is the topology of classice Ethernet?
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Shared Bus
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What were the early versions of Ethernet known as?
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Thicknet (10BASE5) - 500m
Thinnet (10BASE2) - 185m coaxial cable |
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What topology did early Ethernet evolve into?
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Physical: Star
Logical: Bus |
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What sort of communication style did 10BASE-T Ethernet employ?
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Half-Duplex with a hub as the centre point
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What sort of communication style does 100BASE-TX Ethernet employ?
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Full-Duplex with a switch as the centre point
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What are the two styles of Ethernet framing?
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DIX (Ethernet II) and IEEE 802.3 standard
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What are the differences between the two styles of Ethernet framing?
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802.3 as a Start Frame Delimiter (SFD), and a Length field instead of a Type field.
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What is the minimum and maximum Ethernet frame size?
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64-1518 bytes, 802.3ac increased to 1522 to accommodate vLAN
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What are frame fields with 802.3?
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preamble
start frame destination MAC address source MAC address length/type 802.2 header and data (pads) FCS |
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Explain the function of the first two fields with 802.3
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preamble (7bytes) and SFD (1 byte) are used to synchronise sending and receiving devices
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Explain the function of the Length field in 802.3
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Length of Data frame plus what higher level protocol is being used
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Explain the function of the last feild in 802.3
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FCS (4 bytes) detects errors in the frame using CRC
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What characterises a MAC address?
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An Ethernet MAC address is a 48-bit binary value expressed as 12 hexadecimal digits
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What standards does a vendor have to comply with in regards to MAC addresses?
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assigned code, called Organisationally Unique Identifier (OUI) for first 3 bytes, then must have a unique last three bytes
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What is a MAC address often referred to, and why?
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a burned in address (BIA) because it is burned into the ROM of the NIC
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What does the NIC when a computer boots up?
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copies MAC address into RAM
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What is the special multicast MAC address?
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Starts with 01-00-5E
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What is the broadcast MAC address?
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All Fs
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In CSMA/CD, what does Carrier sense do?
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Listens for other traffic on the media, and if the coast is clear, it fires off it's data
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In CSMA/CD, what is the problem of Multi-Access?
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Latency can mean that one host doesn't detect data on the media, and fires off, causing collisions.
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In CSMA/CD, what happens when a collision occurs?
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Once detected, every device transmitting will continue to transmit to ensure that all devices on the network detect the collision. Then the transmitting devices transmit a jamming signal which causes all devices to not transmit for a random backoff time
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What is bit time?
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Period of time it takes for one bit to be placed and sensed on the media
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What is slot time?
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The time for an electrical pulse to travel the maximum theoretical distance between two nodes.
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What are the slot times of the different speeds of Ethernet?
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10 mbps - 512
100 mbps - 512 1000 mbps - 4096 10 gbps - not applicable |
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What is the role of interframe spacing, and what is it's time value?
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is a minimum spacing between two frames that gives the media time to stabilise, and the device to process the frame. 96 bit time
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What are the four data rates for Ethernet over fibre or copper twisted pair?
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10 Mbps - 10Base-T Ethernet
100 Mbps - Fast Ethernet 1000 Mbps - Gigabit Ethernet 10 Gbps - 10 Gigabit Ethernet |
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What are some of the problems with using hubs?
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Scalability, Latency, Network Failure, Collisions
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Switches increase thoughput for three primary reasons:
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Dedicated bandwidth to each port
Collision-free environment Full-duplex operation |
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In switching, what is selective forwarding?
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Establishes a momentary connection between two nodes to transfer frame
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In switching, what is store and forward?
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buffers frame, and waits until destination port is idle before sending it there
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What basic operations do Ethernet LAN switches employ?
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Learning
Aging Flooding Selective Forwarding Filtering |
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What are the two basic functions of the ARP protocol?
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Resolving IPv4 addresses to MAC addresses
Maintaining a cache of mappings |
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What is the ARP table stored?
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In the RAM of the device
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