Computer Networking From LANs to WANs Hardware Software

Computer Networking From LANs to WANs: Hardware, Software, and Security Chapter 4 Ethernet Technology CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 1

Objectives § Describe the format of an Ethernet frame and the interframe gap § Explain the basic operation of collision detection § Compare the features of the different 10 -Mbps Ethernet, Fast Ethernet, Gigabit Ethernet, and 10 Gigabit Ethernet technologies § Discuss the principles of wireless Ethernet CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 2

The Ethernet Frame Format Figure 4 -1 IEEE 802. 3 Ethernet frame § Comparison to Ethernet II • Identical preamble, no SFD, 2 -byte Type filed in place of Length field, Data field longer than 1500 bytes § Bits transmitted LSB to MSB (most significant byte) § Minimum, maximum sizes: 72 bytes, 1526 bytes • including the bytes used for Preamble and SFD (some book does not include preamble and SFD) • Any received frame not within this size will be considered as corrupted and will be discarded. CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 3

Ethernet Frame §All Ethernet standards use the same frame structure. • Ethernet has a header and a trailer. §There are three versions of Ethernet frame: • DIX • IEEE 802. 3 (Original) • IEEE 802. 3 (Revised 1997 CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 4

Interframe Gap Figure 4 -2 Interframe gap separates each Ethernet frame § Ethernet devices must allow a minimum idle period between transmission of Ethernet frames. • This idle period is call Interframe Gap § This idle time gives the network devices a chance to stabilize and give time for other network component to process the frame § 10 -Mbps Ethernet: 9. 6 microseconds interframe gap • Corresponds to 96 bit times CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 5

Interframe Gap § When frame size is larger: • More available bandwidth utilized • 96 -byte interframe gap becomes less significant Table 4 -2 Effect of frame size on bandwidth utilization CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 6

Carrier Sense Multiple Access with Collision Detection (CSMA/CD) § Technique used to share access to the available bandwidth § Refer figure: • The network consist of 5 segments connected by four repeaters • A and B is connected at the farthest end of the network. • There may be many stations connected to each segment and all competing for bandwidth using the same CMSA/CD method. • All this stations operate in a collision domain. Figure 4 -4 10 base 5 Ethernet network CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 7

CSMA/CD § Collision domain • Portion of LAN (or entire LAN) • Two or more transmitting stations interfere with each other § Refer figure: • If "Computer A" send a data signal to "Computer X" and "Computer B" send a data signal to "Computer Y", at same instance, a collision will happen. • The more the number of devices, the more the chances of collision • More collisions will result low quality of network • Switch – to divide a big collision domain to many small collision domains • Collision cannot happen between two devices which are connected to different ports of a Switch. CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 8

CSMA/CD – How it works? CSMA 1. If the medium is idle, transmit (immediately). 2. If the medium is busy, continue to listen until the channel is sensed idle. • If two or more stations are waiting to transmit, a collision is unavoidable. CD 3. If a collision is detected, transmit a jamming signal and then stop transmission. 1. Jam signal - to ensure all stations are notified the frame transmission failed due to a collision. 1. After sending jamming signal, wait a random amount of time (repeat from step 1) CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 9

CSMA/CD § No Collision During Frame • Station waits an idle period • Equal to (or longer than) the interframe gap • Station begins transmitting frame one bit at a time • Electronic signal represents each bit traveled • Limited speed within thickwire coax • 10. 8 microseconds worst case to travel 2500 meters from station A to B • Time based on cable speed coefficient • Signal absorbed at coaxial segment endpoint • By terminating resistor Cengage Learning: Computer Networking from LANs to WANs 10

CSMA/CD § A Collision Occurs During the Frame • Ethernet transceivers detect signal, energy distortions • Stations output a jam sequence • Begin random waiting period before retransmitting • Station must still be transmitting to detect collisions • Round-trip time • Important to collision detection Cengage Learning: Computer Networking from LANs to WANs 11

Figure 4 -5 Collision example CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 12

Ethernet Technologies § 10 Mbps Ethernet § 1000 Mbps Ethernet (Gigabit Ethernet) § 10 Gigabit Ethernet § Wireless Ethernet CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 13

Ethernet Technologies § The first Ethernet was developed back in 1970 s. • Started with 10 Mbps Ethernet. § Since then, it has evolved to meet the increased demand for high-speed LANs. • Today, the fastest Ethernet can achieve data rate up to 10 Gbps. • Also used in WANs (wide area networks) and MANs (metropolitan area networks). § There are various Ethernet standards to support different data rate, transmission media and connector specification. CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 14

Ethernet Technologies § To ensure compatibility between the various standards, Ethernet uses the same frame structure. • As a result, the different Ethernet standards can be used together in a single LAN. § Reasons for Ethernet success: • • Simplicity and ease of maintenance Ability to incorporate new technologies Reliability Low cost of installation and upgrade. CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 15

Historic Ethernet § The original Ethernet design uses a shared bus topology. § There were two standards: • 10 BASE 2 (Thinnet) – uses thin coaxial cable. • 10 BASE 5 (Thicknet) – uses thick coaxial cable. § These early Ethernet standards were deployed in low bandwidth (10 Mbps) LANs. § Due to the use of bus topology, collision may happen. • Therefore, access to the media was managed by CSMA, and later CSMA/CD. CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 16

Historic Ethernet CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 17

Legacy Ethernet §This generation of Ethernet is characterized by the use of UTP cable and physical star topology. • Hosts are connected to a hub using UTP cable. • This Ethernet standard is called 10 BASE-T. §However, the logical topology is still a bus. • A hub broadcast incoming frame to all outgoing ports. • Only one station can transmit at a time (half-duplex). • Collision may happen. • Access to the media is managed using CSMA/CD. §Later, the use of a hub is replaced with a switch. • This minimizes the possibility of collisions and increases the performance and reliability of Ethernet. CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 18

Legacy Ethernet CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 19

Current Ethernet § This Ethernet standard has a data rate of 100 Mbps. • The standard is called 100 BASE-T (Fast Ethernet). § The use of hubs has been replaced with switches. • This leads to point-to-point logical topology. § A switch can forward incoming frame only to the port that leads to the receiver. • This minimizes the possibility of collisions. • Eliminates the necessity to perform CSMA/CD. • It also enables the hosts to have the full bandwidth of the media. § Later switch implementation also support full-duplex communications. *NOTES : FULL DUPLEX = REFERS TO THE TRANSMISSION OF DATA IN TWO DIRECTIONS SIMULTANEOUSLY HALF DUPLEX = TRANSMISSION OF SEND AND RECEIVE, BUT ONLY ONE-WAY AT A TIME CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 20

Current Ethernet Topology physical: Star Logical: Point-to-point CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 21

Moving to 1 Gbps and Beyond § Ethernet nowadays can operate at the rate of 1 Gbps (1000 Mbps) or even 10 Gbps (10000 Mbps). • These are called Gigabit Ethernet and 10 -Gigabit Ethernet respectively. • This higher speed is necessary to properly support Voice over IP (Vo. IP) and multimedia applications. § Switch is still used as the connecting device. • However, the switch must have full-duplex capability. § In addition to UTP cable, fiber optic cable can also be used. • Fiber optic cable will allow for greater distance. • This enables Ethernet to be used in WANs and MANs. CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 22

Moving to 1 Gbps and Beyond CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 23

Wireless Ethernet § Ethernet over radio frequency (RF) or Infrared (IR) • Covered by IEEE 802. 11 standard § Wireless Ethernet network components • One or more fixed stations (base stations) • Service multiple mobile stations § Implementation details: • • Same frame formats for Ethernet and Token-ring CSMA/CA utilized 1 -Mbps, 2 -Mbps, 11 -Mbps, 54 Mbps supported Faster speeds becoming available CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 24

Wireless Ethernet § Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) • Differs from CSMA/CD • Wireless transceiver cannot listen for other transmissions while transmitting • Stations attempt to avoid collisions by using random backoff delays • Delay transmission when the network is busy • Handshaking sequence used between communicating stations *Notes: A random backoff - minimizes the probability that the same nodes will collide again CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 25

Wireless Ethernet § Two types of wireless LAN 1. RF-based • Signals propagate through objects (walls) • ISM band used for transmission • Uses spread spectrum technologies frequency hopping and direct sequence 2. IR-based • Diffused IR bounces signals off walls, ceilings, floors • Data rate limited by the multipath effect • Point-to-point IR • Uses line-of-sight IR lasers, faster data rate than diffused IR, works over larger distances (up to 1 mile) CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 26

Summary § Ethernet described by 802. 3 standard § Two Ethernet frame types: version 1 and version 2 § Interframe idle time helps regulate transmissions § Collision domain • Only one computer, station transmits data at a time • CSMA/CD: allows bandwidth sharing § Various Ethernet varieties exist • Ethernet media type has its own characteristics CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 28