Data communications and Networking Chapter 9 High Speed LANs and Wireless LANs References Book Chapters 16 and 17 Data and Computer Communications, 8th edition ByW∥ lam Stallings
Data Communications and Networking Chapter 9 High Speed LANs and Wireless LANs References: Book Chapters 16 and 17 Data and Computer Communications, 8th edition By William Stallings
Outline Fundamentals of ethernet -aloHA, slotted aloHA, csma -CSMA/CD Ethernet Examples 10-Mbps Ethernet -Fast ethernet -Gigabit Ethernet 10-Gbps Ethernet 802. 11 Wireless Lans
2 Outline • Fundamentals of Ethernet —ALOHA, slotted ALOHA, CSMA —CSMA/CD • Ethernet Examples —10-Mbps Ethernet —Fast Ethernet —Gigabit Ethernet —10-Gbps Ethernet • 802.11 Wireless LANs
Ethernet Most widely used high-speed LANs Ethernet(10Mbps, 100Mbps, 1Gbps 10Gbps) Fibre channel High-speed wireless LANs Ethernet protocol is developed by iEee 802.3 standards committee, consisting of Medium Access Control ( Mac) layer(CSMA/CD protocol) the key part of this chapter Physical Layer Earlier mac schemes ALOHA Slotted aloha CSMA
3 Ethernet • Most widely used high-speed LANs — Ethernet (10Mbps, 100Mbps, 1Gbps, 10Gbps) — Fibre channel — High-speed wireless LANs • Ethernet protocol is developed by IEEE 802.3 standards committee, consisting of — Medium Access Control (MAC) Layer (CSMA/CD protocol) • the key part of this chapter — Physical Layer • Earlier MAC schemes: — ALOHA — Slotted ALOHA — CSMA
ALOHA ALOHA protocol is developed for packet radio networks, but applicable to any shared transmission medium a number of stations share the transmission medium two or more simultaneous transmissions will cause a collision Sender When station has frame it sends Station listens for an amount of time If its hears an aCK, fine. If not, it retransmits the frame after a random time If no ACK after several transmissions, it gives up Frame check sequence can be used for error detection Receiver If frame is ok and address matches receiver, sends acK Otherwise, ignores this frame and does nothing Frame may be damaged by noise or by another station transmitting at the same time(collision). Overlap of frames also causes collision ALOHA is simple, but very inefficient Assuming random traffic, the maximum channel utilization is only about 18%
4 ALOHA • ALOHA protocol is developed for packet radio networks, but applicable to any shared transmission medium. — A number of stations share the transmission medium. Two or more simultaneous transmissions will cause a collision. • Sender — When station has frame, it sends — Station listens for an amount of time — If its hears an ACK, fine. If not, it retransmits the frame after a random time — If no ACK after several transmissions, it gives up — Frame check sequence can be used for error detection • Receiver — If frame is OK and address matches receiver, sends ACK — Otherwise, ignores this frame and does nothing • Frame may be damaged by noise or by another station transmitting at the same time (collision). Overlap of frames also causes collision. • ALOHA is simple, but very inefficient — Assuming random traffic, the maximum channel utilization is only about 18%
ALOHA Node 1 Packet Waiting a random time Node 2 Packet Retransmission Retransmission [2:3 Ime Collision Node 3 Packet 5
5 ALOHA