Chapter 4ver2

Click to edit Master subtitle style Todd Lammle’s CompTIA Network+ Chapter 4: Ethernet Instructor:

Chapter 4 Objectives 2.6 Categorize LAN technology types and properties Types: Ethernet 10BaseT 100BaseTX 100BaseFX 1000BaseT 1000BaseX 10GBaseSR 10GBaseLR 10GBaseER 10GBaseSW 10GBaseLW 10GBaseEW 10GBaseT Properties CSMA/CD Broadcast Collision Bonding Speed Distance

Binary to Decimal to Hex Each digit used is limited to either a 1 (one) or a 0 (zero), and each digit is called 1 bit (short for bi nary digi t ). Typically, you count either 4 or 8 bits together, with these being referred to as a nibble and a byte , respectively.

Binary to Decimal What all this means is that if a one digit (1) is placed in a value spot, then the nibble or byte takes on that decimal value and adds it to any other value spots that have a 1. And if a zero (0) is placed in a bit spot, you don’t count that value. Let’s work through an example: 10010110 Which bits are on? The 128, 16, 4, and 2 bits are on, so we’ll just add them up: 128 + 16 + 4 + 2 = 150.

Ethernet – Standard and Implementation Robert Metcalfe and his coworkers at Xerox designed the 1 st Ethernet LAN more than thirty years ago. The first Ethernet standard was published in 1980 by a consortium of Digital Equipment Corporation, Intel, and Xerox (DIX). In 1985, the Institute of Electrical and Electronics Engineers (IEEE) standards committee for Local and Metropolitan Networks published standards for LANs. These standards start with the number 802. The standard for Ethernet is 802.3. The IEEE wanted to make sure that its standards were compatible with those of the International Standards Organization (ISO) and OSI model. The IEEE 802.3 standards address the needs of Layer 1 and the lower portion of Layer 2 of the OSI model.

Ethernet – Layer 1 and Layer 2 Ethernet operates across 2 layers of the OSI model. The Physical layer. Ethernet at Layer 1 involves signals, bit streams that travel on the media, physical components that put signals on media, and various topologies. Ethernet Layer 1 performs a key role in the communication that takes place between devices.

Logical Link Control – Connecting to the Upper Layer Ethernet separates the functions of the Data Link layer into two distinct sublayers: the Logical Link Control (LLC) sublayer IEEE 802.2 standard describes the LLC sublayer LLC handles the communication between the upper layers and the networking software, The LLC takes the network protocol data, and adds control information to help deliver the packet to the destination node. LLC is implemented in software , and it is independent of the physical equipment. In a computer, the LLC can be considered the driver software for the NIC. the Media Access Control (MAC) sublayer. IEEE 802.3 standard describes the MAC sublayer and the Physical layer functions. MAC is implemented in hardware , typically in the NIC. MAC handles the communication to the lower layers, typically the hardware.

MAC – Getting Data to the Media The Ethernet MAC sublayer has two responsibilities: Data Encapsulation Frame delimiting The MAC layer adds a header and trailer to the Layer 3 PDU. It aids the grouping of bits at the receiving node. It provides synchronization between the transmitting and receiving nodes. Addressing Each header contains the physical address (MAC address) that enables a frame to be delivered to a destination node. Error detection Each trailer contains a CRC. After reception of a frame, the receiving node creates a CRC to compare to the one in the frame. If these two CRC calculations match, the frame can be trusted to have been received without error. Media Access Control The MAC sublayer controls the placement of frames on the media and the removal of frames from the media. This includes the initiation of frame transmission and recovery from transmission failure due to collisions. The media access control method for Ethernet is CSMA/CD. All the nodes in that network segment share the medium. All the nodes in that segment receive all the frames transmitted by any node on that segment.

Early Ethernet Media The first versions of Ethernet used coaxial cable to connect computers in a bus topology . Each computer was directly connected to the backbone. This topology became problematic as LANs grew larger. This versions of Ethernet were known as Thicknet, (10BASE5) and Thinnet (10BASE2). 10BASE5, used a thick coaxial that allowed for distances up to 500 meters before the signal required a repeater. 10BASE2, used a thin coaxial cable and more flexible than Thicknet and allowed for cabling distances of 185 meters. The original thick coaxial and thin coaxial physical media were replaced by early categories of UTP cables. Compared to the coaxial cables, the UTP cables were easier to work with, lightweight, and less expensive. The physical topology was also changed to a star topology using hubs . Hubs concentrate connections. When a frame arrives at one port, it is copied to the other ports so that all the segments on the LAN receive the frame. Using the hub in this bus topology increased network reliability by allowing any single cable to fail without disrupting the entire network.

Ethernet Collision Management Legacy Ethernet (Hub and half-duplex) In 10BASE-T networks, typically the central point of the network segment was a hub . This created a shared media. Because the media is shared, only one station could successfully transmit at a time. This type of connection is described as a half-duplex . As more devices were added to an Ethernet network, the amount of frame collisions increased significantly.

CSMA/CD (Carrier Sense Multiple Access with Collision Detection) Network access method Controls how nodes access communications channel Necessary to share finite bandwidth Carrier sense Ethernet NICs listen, wait until free channel detected Multiple access Ethernet nodes simultaneously monitor traffic, access media

CSMA/CD (cont’d.) Collision Two nodes simultaneously: Check channel, determine it is free, begin transmission Collision detection Manner nodes respond to collision Requires collision detection routine Enacted if node detects collision Jamming NIC issues 32-bit sequence Indicates previous message faulty

CSMA/CD (cont’d.) Figure 5-12 CSMA/CD process

CSMA/CD (cont’d.) Collision domain Portion of network where collisions occur Ethernet network design Repeaters repeat collisions Result in larger collision domain Switches and routers Separate collision domains Collision domains differ from broadcast domains

Ethernet Collision Management Current Ethernet (switch and full-duplex) To enhanced LAN performance, switch was introduced to replace hubs in Ethernet-based networks. This corresponded with the development of 100BASE-TX . Switches can isolate each port and sending a frame only to its proper destination (if the destination is known), rather than send frame to every device. This, and the later introduction of full-duplex communications (having a connection that can carry both transmitted and received signals at the same time), has enabled the development of 1Gbps Ethernet and beyond.

Switch operation Full Duplex In a network that uses twisted-pair cabling, one pair is used to carry the transmitted signal. A separate pair is used for the return or received signal. It is possible for signals to pass through both pairs simultaneously. The capability of communication in both directions at once is known as full duplex. Most switches are capable of supporting full duplex, as are most network interface cards (NICs). In full duplex mode, there is no contention for the media. Thus, a collision domain no longer exists . Theoretically, the bandwidth is doubled when using full duplex. A switch uses full-duplex mode to provide full bandwidth between two nodes on a network.

Switch operation Microsegments When only one node is connected to a switch port, the collision domain on the shared media contains only two nodes. These small physical segments are called microsegments . A bridge or switch increase the number of collision domains but have no impact on broadcast domains

Collision and Broadcast Domains The term collision domain is an Ethernet term that refers to a particular network scenario wherein one device sends a packet out on a network segment, thereby forcing every other device on that same physical network segment to pay attention to it. Ethernet uses both Data Link and Physical layer specifications. A broadcast domain refers to the set of all devices on a network segment that hear all the broadcasts sent on that segment. Even though a broadcast domain is typically a boundary delimited by physical media like switches and repeaters, it can also reference a logical division of a network segment where all hosts can reach each other via a Data Link layer (hardware address) broadcast. Broadcast domains are made smaller by routers.

CSMA/CD (cont’d.) Ethernet cabling distance limitations Effected by collision domains Data propagation delay Time for data to travel From one segment point to another point Too long Cannot identify collisions accurately 100 Mbps networks Three segment maximum connected with two hubs 10 Mbps buses Five segment maximum connected with four hubs

Ethernet Standards for Copper Cable IEEE Physical layer standards Specify how signals transmit to media Differ significantly in signal encoding Affect maximum throughput, segment length, wiring requirements

Ethernet Standards for Copper Cable (cont’d.) 10Base-T 10 represents maximum throughput: 10 Mbps Base indicates baseband transmission T stands for twisted pair Two pairs of wires: transmit and receive Full-duplex transmission Follows 5-4-3 rule of networking Five network segments Four repeating devices Three populated segments maximum

Ethernet Standards for Copper Cable (cont’d.) Figure 5-13 A 10Base-T network

Ethernet Standards for Copper Cable (cont’d.) 100Base-T (Fast Ethernet) IEEE 802.3u standard Similarities with 10Base-T Baseband transmission, star topology, RJ-45 connectors Supports three network segments maximum Connected with two repeating devices 100 meter segment length limit between nodes 100Base-TX 100-Mbps throughput over twisted pair Full-duplex transmission: doubles effective bandwidth

Ethernet Standards for Copper Cable (cont’d.) Figure 5-14 A 100Base-T network

Ethernet Standards for Copper Cable (cont’d.) 1000Base-T (Gigabit Ethernet) IEEE 802.3ab standard 1000 represents 1000 Mbps Base indicates baseband transmission T indicates twisted pair wiring Four pairs of wires in Cat 5 or higher cable Transmit and receive signals Data encoding scheme: different from 100Base-T Standards can be combined Maximum segment length: 100 meters, one repeater

Ethernet Standards for Copper Cable (cont’d.) 10GBase-T IEEE 802.3an Pushing limits of twisted pair Requires Cat 6 or Cat 7 cabling Maximum segment length: 100 meters Benefit Very fast data transmission, lower cost than fiber-optic Use Connect network devices Connect servers, workstations to LAN

Ethernet Standards for Fiber-Optic Cable 100Base-FX (Fast Ethernet) IEEE 802.3u standard 100-Mbps throughput, broadband, fiber-optic cabling Multimode fiber containing: at least two strands Half-duplex mode One strand receives, one strand transmits 412 meters segment length Full duplex-mode Both strands send and receive 2000 meters segment length One repeater maximum

Ethernet Standards for Fiber-Optic Cable (cont’d.) 1000Base-LX (1-Gigabit Ethernet) IEEE 802.3z standard 1000: 1000-Mbps throughput Base: baseband transmission LX: reliance on 1300 nanometers wavelengths Longer reach than any other 1-gigabit technology Single-mode fiber: 5000 meters maximum segment Multimode fiber: 550 meters maximum segment One repeater between segments Excellent choice for long backbones

Ethernet Standards for Fiber-Optic Cable (cont’d.) 1000Base-SX (1-Gigabit Ethernet) IEEE 802.3z standard Differences over 1000Base-LX Multimode fiber-optic cable (installation less expensive) Uses short wavelengths (850 nanometers) Maximum segment length dependencies Fiber diameter, modal bandwidth used to transmit signals 50 micron fibers: 550 meter maximum length 62.5 micron fibers: 225 meter maximum length One repeater between segments Best suited for shorter network runs

10-Gigabit Fiber-Optic Standards Extraordinary potential for fiber-optic cable 802.3ae standard Fiber-optic Ethernet networks Transmitting data at 10 Gbps Several variations Common characteristics Star topology, allow one repeater, full-duplex mode Differences Signal’s light wavelength, maximum allowable segment length

IEEE Standards (cont.) 10GBase-SR An implementation of 10 Gigabit Ethernet that uses short-wavelength lasers at 850 nm over multimode fiber. It has a maximum transmission distance of between 2 and 300 meters, depending on the size and quality of the fiber. 10GBase-LR An implementation of 10 Gigabit Ethernet that uses long-wavelength lasers at 1,310 nm over single-mode fiber. It also has a maximum transmission distance between 2 meters and 10 km, depending on the size and quality of the fiber. 10GBase-ER An implementation of 10 Gigabit Ethernet running over single-mode fiber. It uses extra-long-wavelength lasers at 1,550 nm. It has the longest transmission distances possible of the 10-Gigabit technologies: anywhere from 2 meters up to 40 km, depending on the size and quality of the fiber used.

802.3 Standards (cont.) 10GBase-SW 10GBase-SW, as defined by IEEE 802.3ae, is a mode of 10GBase-S for MMF with a 850 nm laser transceiver with a bandwidth of 10Gbps. It can support up to 300 meters of cable length. This media type is designed to connect to SONET equipment. 10GBase-LW 10GBase-LW is a mode of 10GBase-L supporting a link length of 10 km on standard single-mode fiber (SMF) (G.652). This media type is designed to connect to SONET equipment. 10GBase-EW 10GBase-EW is a mode of 10GBase-E supporting a link length of up to 40 km on SMF based on G.652 using optical-wavelength 1550 nm. This media type is designed to connect to SONET equipment.

Summary of Common Ethernet Standards Table 5-1 Common Ethernet standards

Ethernet Frames Four types Ethernet_802.2 (Raw) Ethernet_802.3 (Novell proprietary) Ethernet_II (DIX) Ethernet_SNAP Frame types differ slightly No relation to topology, cabling characteristics Framing Independent of higher-level layers

Ethernet frames Ethernet 802.3 (Raw) This is the original (and default) frame type used by NetWare. IT CAN ONLY SUPPORT NOVELL IPX/SPX TRAFFIC! The frame is similar to that described in 802.3 except that it does not contain the Logical Link Control (LLC) information in the packet Ethernet 802.2 This frame includes fields from 802.3 and 802.2 (Logical Link Control) and can support the Novell IPX/SPX and FTAM (File Transfer, Access, and Management) protocols. Ethernet SNAP Sub-Network Access Protocol (SNAP) is similar to 802.2, with LLC parameters, but with expanded LLC capabilities Ethernet_II (DIX) Developed by DEC, Intel, Xerox (abbreviated DIX) Before IEEE Contains 2-byte type field Identifies the Network layer protocol

Ethernet Frames (cont’d.) Frame Fields Common fields 7-byte preamble, 1-byte start-of-frame delimiter SFD (start-of-frame delimiter) identifies where data field begins 14-byte header 4-byte FCS (Frame Check Sequence) Frame size range: 64 to 1518 total bytes Larger frame sizes result in faster throughput Improve network performance Properly manage frames

PoE (Power over Ethernet) IEEE 802.3af standard Supplying electrical power over Ethernet connections Two device types PSE (power sourcing equipment) PDs (powered devices) Requires Cat 5 or better copper cable Connectivity devices must support PoE Compatible with current 802.3 installations

PoE (cont’d.) Figure 5-16 PoE-capable switch Figure 5-17 PoE adapters

Summary Summary Exam Essentials Section Written Labs Review Questions

Chapter 4ver2

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Chapter 4ver2

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