icnd1 ch3
Terms
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- 4 common types of ethernet:
- ethernet: 10mbps, \"10BASE-T\", copper, 100m fast ethernet: 100mbps, \"100BASE-TX\", copper, 100m gigabit (GE): 1000mbps, \"1000BASE-SX\", fiber, 550m \" \" \" \" \"1000BASE-LX\", fiber, 5000m GE: 1000mbps, \"1000BASE-T\", copper, 100m (FE and GE (1000BASE-T) use utp cabling
- what is the CSMA-CD algorithm?
- carrier sense-multiple action with collision detection. Cabling creates an electrical bus. If 2+ signals were sent at the same time, they would ovelap/collide. Ethernet defines specs on how to ensure that 1 device sends traffic at a time. A device that wants to send a frame waits until the LAN is silent before sending electrical signal. If collision occurs, the devices that caused the collision wait a random amt. of time then try again. Avoid collisions. If collision occurs, take action to correct it.
- Straight-through cable: what pins? connect what to what?
- pin 1 to pin 1, 2 to 2, etc. For connecting pc to switch. cabling uses pins 1,2,3,6.
- Crossover cable: what pins? for what?
- pins 1 to 3, 2 to 6.
- Devices that transmit on 1,2; receive on 3,6:
- pc NICs, routers, WAPs, network printers
- Devices that transmit on 3,6; receive on 1,2:
- hubs, switches
- which ethernet types require 4 pairs of wires, used simultaneously?
- 1000BASE-T (GE copper) and 1000BASE-SX/LX (fiber)
- What is half-duplex?
- using hubs; a device sends OR receives at any moment, but never both at the same time. CSMA-CD is used. Performace is affected: as load on LAN increases, chance for collison increases.
- 6 steps of CDMA/CD algorithm:
- 1. device that will send a frame listens to the ethernet to check when it\'s not busy. 2. when ethernet\'s not busy, the sender sends the frame. 3. the sender listens to make sure no collisions occur. 4. if collision occurs, sending device sends jamming signal to let others know of the collision. 5. After jamming is complete, each sender waits a random amt. of time before resending the collided frame. 6. after random amt. of time expires, process starts again with step 1.
- 4 differences of switches vs. hubs
- 1. do not create a single shared electrical bus, so LAN switches reduce/eliminate collisions. 2. Switches interpret the bits in received frame (layer 2 device: looks at the header); hubs do not, they act as repeaters(layer 1 device). 3. switches send frame out to the one required port rather than all ports. 4. If more than one frame needs sending, the switch buffers other frames in memory and sends one at a time.
- what is Full duplex?
- used by switches; devices can send/receive simultaneously, so CSMA/CD is disabled; collisions don\'t occur.
- shared ethernet vs. switched ethernet:
- shared: hubs. uses CSMA/CD algorithm; bandwidth has to be shared. switched ethernet: switches. doesn\'t use CSMA/CD, bandwidth doesn\'t have to be shared.
- A valid ethernet address looks like:
- 6 bytes long, in hex. 4 hex digits with periods in between: 0000.0C12.3456
- what is a unicast address?
- ID\'s a single LAN card.
- First 1/2 of MAC address on a LAN card is: (also known as:)
- the manufacturer\'s ID. Assigned to each mfg. by IEEE. Also known as: OUI (organizationally unique identifier).
- size of unicast address, in bits (and bytes):
- 24 bits (6 bytes)
- Size of unicast address in hex digits: (example:)
- 6 hex digits; 6 hex digits. Example: 00 60 2F. 3A 07 BC.
- What is a BIA? What are other names for this?
- A burned-in address on teh rom chip on the LAN card. Sometimes called UAA (universally administered address). AKA: LAN address, ethernet address, hardware address, physical address, MAC address.
- LAN MAC address term/feature: MAC:
- media access control. 802.3 (ethernet) defines the MAC sublayer of IEEE ethernet.
- LAN MAC address term/feature: Ethernet address, NIC address, LAN address:
- other names used insead of MAC address. These terms describe the 6 byte address of teh LAN interface card.
- Burned-in address:
- the 6 byte address assigned by the vendor making the LAN card.
- broadcast address:
- an address that means (all devices that reside on the LAN right now.\"
- multicast address:
- on ethernet, this implies some subset of all devices currently on the LAN.
- ethernet \"framing\":
- the meaning of bits transmitted and received over a network.
- The _________ layer gets bits from one device to another.
- physical
- If the header of a frame has \"length\" field instead of \"type\" field, 2 more headers are added before the data field in the frame:
- LLC (logical link control) and SNAP (sub-network access protocol)
- The last field in the trailer of the frame is:___________. Describe.
- FCS (frame check sequence). A complex math function is done on the sending end. the solution is the same on the receiving end, the frame has no errors. If error occurs, it could be electrical interference. The frame is discarded. FCS is an error check, not a recovery check.
- LAN: describe:
- local area network. Allows local computers to connect with each other.
- WAN: describe:
- wide area network. Router connects to LAN and WAN, provides connection between various sites.
- UTP
- unshielded twisted pair. common ethernet standard of cabling.
- IEEE
- Institute of Electrical and Electronic Engineers; define ethernet standards.