Ch-4: Ethernet Communications

Ch-4: Ethernet Communications

1. Networking Basics

   • uses MAC address to communicate on a LAN from host to host
   • Uses name resolution
     • broadcasts asking for info (all f's for MAC)

2. Ethernet Basics

   • def=contention based media access method that allows all host on a network to share the same bandwith of a link
   • collision domain=area of network where collision events are possible-where every host must pay attention
   • broadcast domain=area of network where a broadcast would reach-normally delineated by switches, hubs, etc.
   • CSMA/CD=carrier sense multiple access collision detection=a protocol for avoiding packet collisions=
     • monitor segment, if collision event, then all hosts stop transmitting for a while, then free-for-all to transmit
   • half-duplex=one pair of wires for transmitting or receiving. 30-40% efficient
   • full-duplex=two pairs of wire, supposed to be 100% efficient, uses point-to-point communication, requires dedicated switch port
     • switch to host, switch to switch, host to host (using crossover)

3. Physical Layer

   • EIA/TIA required ethernet use RJ-45 connection
   • inherent attenuation measured in decibals
   • crosstalk
   • 802.3=ethernet LAN
     • 802.3u=FastEthernet
       • 802.3ab=Gigabit Ethernet on Cat 5+
         • 802.3ae=Gigabit over fiber/coax
   • 10Base2=10Mbps, coax, thinnet, 185m, BNC connector
     • 10Base5=10Mbps, coax, thicknet, 500m
       • 10BaseT=10Mbps, Cat3, 100m, phys star logic bus
         • 100BaseTX=FastEthernet, 100Mbps, Cat3+, 100m
           • 100BaseFX=mm fiber, 100Mbps,
             • 1000BaseCX=twinax (double coax), 1Gbps, 25m
               • 1000BaseT=Cat 5 UTP, 4 pair, 100m, 1Gbps
                 • 1000BaseSX=mm fiber, 1Gbps, max 550m
                   • 1000BaseLX=sm fiber, max 10km, 1Gbps
                     • 10GBaseT=10Gbps, Cat 5e+, economical
                       • 10GBaseSR=mmfiber, 300m, 10Gbps
                         • 10GBaseLR=smfiber, 10km, 10Gbps
                           • 10GBaseER=smfiber, 40km, 10Gbps
                             • 10GBaseSW=mmfiber, used with SONET, 300m
                               • 10GBaseLW=smfiber, 10km, SONET
                                 • 10GBaseEW=40km, smfiber, SONET

4. Data Link Layer

   • responsible for hardware addressing and framing packets in prep for transmission
   • binary number=byte of 1's and 0's. values are 128,64,32,16,8,4,2,1 with value being adding all of the enabled spots.. decimal=regular numbers. hex=0-9 are regular, a=10, b=11,c=12,d=13,e=14,f=15, hex number is 0x or h then two values. convert from binary to hex by dividing into nibbles and changing value of nibble to hex value
   • MAC address=burned into NIC
     • first 24 bits are OUI (organizationally unique id) second 24 bits are vendor specific
       • of OUI,1st bit=I/G(individual group), if 0 it's a device, if 1 it's an ethernet broadcast. 2nd bit=G/L(global/local), if 0 it's globally admin'd, if 1 it's locally admin'd.
   • Ethernet stations pass data frames between each other using a group of bits known as a MAC FRAME FORMAT. This provides error detection from a cyclic redundancy check (CRC)
   • Channel bonding is a computer-networking arrangement where two or more network interfaces on a host are combined for redundancy and/or increased throughput
     • aka Link Aggregation or Cisco=EtherChannel
     • switch to server, switch to switch, or switch/router to ISP