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

CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 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

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

CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 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

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

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

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 10base5 Ethernet network CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS

CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 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

CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS CSMA/CD – How it works? CSMA If the medium is idle, transmit (immediately). 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 If a collision is detected, transmit a jamming signal and then stop transmission. Jam signal - to ensure all stations are notified the frame transmission failed due to a collision. After sending jamming signal, wait a random amount of time (repeat from step 1) CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS

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

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

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

Ethernet Technologies 10 Mbps Ethernet 100 Mbps Ethernet 1000 Mbps Ethernet (Gigabit Ethernet) 10 Gigabit Ethernet Wireless Ethernet CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS

Ethernet Technologies The first Ethernet was developed back in 1970s. 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

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

CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS Historic Ethernet The original Ethernet design uses a shared bus topology. There were two standards: 10BASE2 (Thinnet) – uses thin coaxial cable. 10BASE5 (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

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

CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 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 10BASE-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

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

CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS Current Ethernet This Ethernet standard has a data rate of 100 Mbps. The standard is called 100BASE-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

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

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 (VoIP) 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

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

CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 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, 54Mbps supported Faster speeds becoming available CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS

CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 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

CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS Wireless Ethernet Two types of wireless LAN RF-based Signals propagate through objects (walls) ISM band used for transmission Uses spread spectrum technologies frequency hopping and direct sequence 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

CENGAGE LEARNING: COMPUTER NETWORKING FROM LANS TO WANS 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