CCENT 3 S01 E08 – LANS: Welcome to the Ethernet

  CCENT, LANs, Networking

The Evolution of Ethernet

1973: Xerox invents Ethernet (3 Mbps)
1982: Ethernet Standardized Between Vendors (10 Mbps) – Prior to this everything was proprietory, so would have to purchase everything from the same vendor.
1995: Fast Ethernet Emerges (100 Mbps)
2000: Gigabit Ethernet (1000 Mbps)
2002: 10 Gigabit Ethernet (10,000 Mbps)
2007: 100 Gigabit Ethernet (100,000 Mbps)

* Study shows average actual usage 5% of 100 Mbps (5 Mbps)!

Understanding Speed and Size in Networks

Byte – 1 Character. ‘e’ = 1 Byte
Kilobyte = 1024 Characters. 1 Page of data
Megabyte = 1024 Kilobytes
Gigabyte = 1024 Megabytes
Terabytes = 1024 Gigabytes

When talking networks, we use “bits”, 1/8 of a Byte.
‘0’ or ‘1’, on or off.
‘e’ = ‘01100101’
5 = 00000101

Fabric of Networks: Ethernet

Ethernet matches up to bottom 2 layers of the OSI Model, Data Link and Physical

Data Link

  • Divided into 2 sublayers
  • Logical Link Control (LLC) Layer (Picks direction to go into the Network Layer – good for TCP/IP alt. protocols)
  • Media Access Control (MAC) Layer

Physical Standards

  • CAT 5, Wireless, Fiber, Etc.

CSMA/CD – MEMORIZE!!

Carrier Sense, Multiple Access / Collision Detection

  • CSMA/CD is a set of rules (standard) for governing how you talk on an Ethernet Network.
  • Carrier: The Network Signal
  • Sense: The ability to detect if there is a signal occurring: Will listen before sending.
  • Multiple Access: All devices have equal access
  • Collision: What happens if two devices send at once
  • Detection: How the computers handle collisions when they happen.

Token Ring used SCMA/CA (Collision Avoidance)

  • Only device with token could send a signal
  • Token could only go so fast (33 Mbps?)

Methods of Communicating in the LAN

There are 3 types of communication methods

Unicast

  • One to One:  Computer communicates only with another Computer.

Broadcast

  • One to All:  Message goes out to all devices EXCEPT the one sending the signal.
  • ARP is an example of a broadcast message

Multicast

  • One Message to a Group: Think Radio!
  1. Unicast would require unique connection for all listeners.  Huge load on source server.
  2. Broadcast would send to EVERYBODY, so non-listening servers would have to drop it.  Especially bad if only a small group of listeners exist.
  3. Multicast sends only 1 stream, but only the listeners receive it.

The Official Explanation of a MAC Address

12 Hexidecimal characters.  0-9 and A-F

Generally written 2 ways xx:xx:xx:xx:xx:xx:xx OR XXXX:XXXX:XXXX

  • 1st. 6 characters are the Organizer ID.  The company assigned to that ID must use their identifier for their devices.
  • 2nd 6 characters are vendor assigned.  (Think serial number)

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