1 / 43

Multiple Access

Multiple Access. Multiple-access protocols. Random Access. MA. CSMA. CSMA/CD. CSMA/CA. Evolution of random-access methods. The earliest random-access method Developed at the University of Hawaii in early 1970’s Used on a wireless LAN with a data rate 9600 bits/sec

mada
Download Presentation

Multiple Access

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. MultipleAccess

  2. Multiple-access protocols

  3. Random Access MA CSMA CSMA/CD CSMA/CA

  4. Evolution of random-access methods

  5. The earliest random-access method Developed at the University of Hawaii in early 1970’s Used on a wireless LAN with a data rate 9600 bits/sec A base station is the central controller The base station receives the frame and relays it to the intended destination The uploading transmission uses carrier frequency of 407 MHz The downloading uses carrier freq of 413 MHz ALOHA

  6. ALOHA network

  7. Procedure for ALOHA protocol

  8. The station waits an amount of time b/w 0 and 2N *(maximum_propagation_time) For the first time between: 0 and 21 *(max_propg_time) For the second time between: 0 and 22 (max_propag_time), and so on N is the number of attempted transmissions Back off time

  9. Carrier Sense Multiple Access To minimize the chance of collision Based on the principle “sense before transmit” Can reduce the possibility of collision, but can not eliminate it Collision because of the propagation delay CSMA

  10. Collision in CSMA

  11. The procedure for a station that senses a busy medium Two substrategies Nonpersistent Persistent Persistent Strategy

  12. Persistence strategies

  13. In 1-persistent, the station sends its frame immediately, when finds the line idle It increase the chance of collision due to same time sending In P-persistent, the station may or may not send, when finds the line idle The system generates a random number b/w 1 and 100 If the number is less than 20, then sends, otherwise not Persistence strategies cont…

  14. Carrier Sense Multiple Access with collision detection The station monitors the medium after sending a frame If successful, the station is finished If collision, the frame is resent Used in Ethernet CSMA/CD

  15. CSMA/CD procedure

  16. Carrier Sense Multiple Access with collision avoidance No chance of collision Used in Wireless LANs CSMA/CA

  17. CSMA/CA procedure

  18. Control Access Reservation Polling Token Passing

  19. Reservation access method

  20. One primary station, other devices are secondary stations All data transmission must be made through the primary device The secondary devices follow its instructions In case of receiving the data, the primary device does polling In case of sending the data, the primary device does selection Polling

  21. Select

  22. Poll

  23. A station is authorized to send data when it receives a special frame called token When no data are being sent, a token is circulating around the ring. If a station needs to send data, it waits for the token Token passing

  24. Token-passing network

  25. Token-passing procedure

  26. Local Area Networks:Ethernet

  27. Developed by Xerox’s Palo Alto Research Center (PARC) in 1976 IEEE 802.3 standard History of Ethernet

  28. TraditionalEthernet • Designed to operate at 10 Mbps • Access Method CSMA/CD • Ethernet frame contains 7 fields

  29. 802.3 MAC frame

  30. Preamble 7 bytes (56 bits) alternating 0’s and 1’s alert the receiver to the coming frame SFD 1 byte (10101011) Shows beginning of the frame Last 2 bits 11 alert the receiver that the next field is the DA DA 6 bytes Contains the physical address of the receiver SA 6 bytes Contains the physical address of the sender 802.3 MAC frame cont…

  31. Length/type Defines the length of the Data field Data Caries the data, min of 46 and max 1500 bytes CRC Contains error detection information 802.3 MAC frame cont…

  32. Minimum and maximum length

  33. Ethernet addresses in hexadecimal notation

  34. Categories of traditional Ethernet

  35. Physical layer

  36. PLS

  37. Fast Ethernet Operates at 100 Mbps • Physical Layer Implementation • RS (Reconciliation Sublayer) • responsible for passing of 4 bit data to MII • MII (Medium Independent Interface) • AUI was replaced with MII • PHY (Transceiver) • Responsible for encoding and decoding

  38. Fast Ethernet implementations

  39. Fast Ethernet physical layer

  40. Gigabit Ethernet Operates at 1000 Mbps • Physical Layer Implementation • RS • responsible for passing of 8 bit data to GMII • GMII • Connects RS to the PHY • PHY (Transceiver) • Encodes and decodes the data

  41. Gigabit Ethernet implementations

  42. Physical layer in Gigabit Ethernet

  43. Thank you!

More Related