- Designs may be decomposed hierarchically.
- Each Design element has both a well-defined interface (for connecting it to other elements) and a precise behavioral specification (for simulating it).
- Behavioral specifications can use either an algorithm or an actual hardware structure to define an element’s operation. For example, an element can be defined initially by an algorithm, to allow design verification of higher level elements that use it; later, the algorithmic definition can be replaced by a hardware structure.
- Concurrency, timing, and clocking can all be modeled. VHDL handles asynchronous as well as synchronous sequential-circuit structures.
- The logical operation and timing behavior of a design can be simulated.
CSMA/CD shared medium Ethernet
- Frame ready for transmission.
- Is medium idle? If not, wait until it becomes ready and wait the interframe gap period (9.6 µs in 10 Mbit/s Ethernet).
- Start transmitting.
- Did a collision occur? If so, go to collision detected procedure.
- Reset retransmission counters and end frame transmission.
Collision detected procedure
- Continue transmission until minimum packet time is reached (jam signal) to ensure that all receivers detect the collision.
- Increment retransmission counter.
- Was the maximum number of transmission attempts reached? If so, abort transmission.
- Calculate and wait random back off period based on number of collision
- Re-enter main procedure at stage 1.
3.4. Repeaters and hubs
3.5. Bridging and switching
3.6. Fast Ethernet
- 100BASE-T: A term for any of the three standard for 100 Mbit/s Ethernet over twisted pair cable. Includes 100BASE-TX, 100BASE-T4 and 100BASE-T2.
- 100BASE-TX: Uses two pairs, but requires Category 5 cable. Similar star-shaped configuration to 10BASE-T. 100 Mbit/s.
- 100BASE-T4: 100 Mbit/s Ethernet over Category 3 cabling (as used for 10BASE-T installations). Uses all four pairs in the cable. Now obsolete, as Category 5 cabling is the norm. Limited to half-duplex.
- 100BASE-T2: No products exist. 100 Mbit/s Ethernet over Category 3 cabling. Supports full-duplex, and uses only two pairs. It is functionally equivalent to 100BASE-TX, but supports old cable.
- 100BASE-FX: 100 Mbit/s Ethernet over fibre.
- 1000BASE-T: 1 Gbit/s over Category 5e copper cabling.
- 1000BASE-SX: 1 Gbit/s over fiber.
- 1000BASE-LX: 1 Gbit/s over fiber. Optimized for longer distances over single-mode fiber.
- 1000BASE-CX: A short-haul solution (up to 25 m) for running 1 Gbit/s Ethernet over special copper cable. Predates 1000BASE-T, and now obsolete.
- 10GBASE-SR: designed to support short distances over deployed multi-mode fiber cabling, it has a range of between 26 m and 82 m depending on cable type. It also supports 300 m operation over a new 2000 MHz·km multi-mode fiber.
- 10GBASE-LX4: uses wavelength division multiplexing to support ranges of between 240 m and 300 m over deployed multi-mode cabling. Also supports 10 km over single-mode fiber.
- 10GBASE-LR and 10GBASE-ER: these standards support 10 km and 40 km respectively over single-mode fiber.
- 10GBASE-SW, 10GBASE-LW and 10GBASE-EW. These varieties use the WAN PHY, designed to interoperate with OC-192 / STM-64 SONET/SDH equipment. They correspond at the physical layer to 10GBASE-SR, 10GBASE-LR and 10GBASE-ER respectively, and hence use the same types of fiber and support the same distances. (There is no WAN PHY standard corresponding to 10GBASE-LX4.)
- 10GBASE-T: designed to support copper twisted pair was specified by the IEEE Std 802.3an-2006 which has been incorporated into the IEEE Std 802.3-2008.