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Ethernet
Fundamentals
Semester 1 – Module 6
Module Objectives: Describe the basics of Ethernet technology Explain naming rules of Ethernet technology Explain how Ethernet relates to the OSI model Describe the Ethernet framing process and frame structure List Ethernet frame field names and purposes Identify the characteristics of CSMA/CD Describe Ethernet timing, interframe spacing, and backoff time after a collision Define Ethernet errors and collisions Explain the concept of auto-negotiation in relation to speed and duplex
IEEE Ethernet Naming Rules
Ethernet and the OSI Model
Ethernet and the OSI Model
Naming
Layer 2 Framing
- Framing is the Layer 2 encapsulation process
- A frame is the Layer 2 protocol data unit
Ethernet Frame Structures
Ethernet II Frame Structures
Media Access Control (MAC)
The specific technologies for each are as follows:
- Ethernet – uses a logical bus topology to control information flow on a linear bus and a physical star or extended star topology for the cables
- Token Ring – uses a logical ring topology to control information flow and a physical star topology
- FDDI – uses a logical ring topology to control information flow and a physical dual-ring topology
MAC Rules and Collision Detection/Backoff
- Carrier Sense Multiple Access/Collision Detection (CSMA/CD)
Interframe Spacing and Backoff
- Asynchronous
- 10Mbps and slower
- each receiving station will use the eight octets of timing information to synchronize the receive circuit to the incoming data, and then discard it
- Synchronous
- 100Mbps and higher
- timing information is not required
- for compatibility reasons the Preamble and Start Frame Delimiter (SFD) are present
- Interframe Spacing
- 10Mbps = 9.6 bit-times or 9.6 microseconds
- 100Mpbs = 9.6 bit-times or .96 microseconds
Error Handling
Note: Jam signal can be any binary data with an invalid Checksum
Ethernet Auto-Negotiation
- Auto-Negotiation is accomplished by transmitting a burst of 10BASE-T Link Pulses from each of the two link partners
- The burst communicates the capabilities of the transmitting station to its link partner
- After both stations have interpreted what the other partner is offering, both switch to the highest performance common configuration and establish a link at that speed
Transmission Priority Rank
