Ethernet LAN 1 LANs u Local Area Networks

Ethernet LAN 1

LANs u Local Area Networks u Limited Geographical Area – Single office – Single building – University campus or industrial park u Generally, high speeds – Now, most operate at around 10 Mbps – 100 Mbps is emerging as the new “base speed” u Most Data Traffic is Local 2

Standards Setting u LANs are Subnets (single networks) u Subnet technology is Dominated by OSI Standards (true for LANs) u IEEE Creates most LAN Standards – Institute for Electrical and Electronic Engineers – Submits standards to ISO and ITU-T for ratification u IEEE 802 Committee – – LAN standards are set by the IEEE 802 Standards Committee. 802. 3 for Ethernet Standards 802. 5 for Token-Ring LAN Standards 802. 11 for Radio and Infrared Wireless LANs 3

LANs and OSI Architecture u OSI is a 7 -layer architecture u LAN transmission only uses Layers 1 and 2 u Layer 1: Physical Layer – Connectors, Media, Electrical signaling u Layer 2: Data Link Layer – Packaging data into frames – Managing transmission over link (error handling, etc. ) – Access control: when each station may transmit 4

OSI Physical and Data Link Layers Physical Layer (OSI Layer 1) Physical (plugs, media, etc. ); Electrical (voltages, timing, etc. ) Electrical Signal Station A Connector Plug F 4 -1 Station B Transmission Medium (telephone wire, etc. ) Connector Plug 5

OSI Physical and Data Link Layers Data Link Layer (OSI Layer 2) Frame 2 Station A Frame 1 Station B 6

Data Link Layer u For point-to-point transmission – A point-to-point connection is a data link – So is a transmission system shared by multiple devices, only one of which can transmit at a time because of collisions Transmission 7

Data Link Layer u First function: Packaging of Data (1 s and 0 s) – PDU at Data Link Layer is called a frame u Second Function: Access Control – Only one station can transmit at any time – If another transmitted, their signals would scramble one another – Must control access to (transmission into) the transmission medium 8

Data Link Layer OSI Data Link Layer (Layer 2) OSI Physical Layer (Layer 1) Logical Link Control Layer Media Access Control (MAC) Layer 802. 3 10 Base-T 10 Base-5 802. 3 Other Physical Layer 802. 5 Physical Layer 4 Mbps 802. 5 Physical Layer 16 Mbps Other Physical Layer OSI Data Link Layer is subdivided into two layers Media access control Logical link control 9

MAC Layer Media Access Control OSI Physical (Layer 1) Media Access Control (MAC) Layer 802. 3 10 Base-T 10 Base-5 802. 3 Other Physical Layer 802. 5 Physical Layer 4 Mbps 802. 5 Physical Layer 16 Mbps Other Physical Layer MAC layer implements media access control: When a station may transmit Controls the framing of data along the wire 10

Logical Link Control Layer LLC 802. 2 Logical Link Control Layer 802. 3 Media Access Control (MAC Layer) OSI Physical (Layer 1) 802. 3 10 Base-T 10 Base-5 802. 3 Other Physical Layer 802. 5 MAC 4 Mbps 802. 5 MAC 16 Mbps Other MAC 802. 5 Physical Layer 4 Mbps 802. 5 Physical Layer 16 Mbps Other Physical Layer Provides Control Function Begin/end connections between stations Error correction (optional) 11

Simple LAN Using Ethernet 10 Base-T Hub (Multiport Repeater) Unshielded Twisted Pair (UTP) Wiring (4 -Pair Bundle) PC NIC RJ-45 Jack RJ-45 jacks 10 Base-T UTP Wiring Bundles: 4 Pairs EIA Category 3, 4, or 5 Network Interface Card 12

NICs u Network Interface Cards – Implement Physical Layer t Plug and Electrical Signaling – Implements the Data Link Layer (data packaging, access control, etc. ) t LLC (802. 2) t MAC (802. 3 MAC) 13

Wiring u Unshielded Twisted Pair (UTP) – Twisted several times per foot to reduce interference, T in 10 Base- and Unshielded t t u No protection except for plastic coating Distance limitation: 100 meters (attenuation, distortion, noise and interference, crosstalk) -- propagation Categories of UTP Wiring – Category 5, 6: The best. Good for 100 Mbps – Category 3 and 4: lower. May be OK for 100 Mbps u Wiring Plugs: RJ-45 Standard – Similar to home (RJ-11) jacks, but wider 14

Layering in 802 Networks Internet Layer Data Link Layer TCP/IP Internet Layer Standards (IP, ARP, etc. ) Logical Link Control Layer Media Access Control Layer Physical Layer Other Internet Layer Standards (IPX, etc. ) 802. 2 Ethernet 802. 3 MAC Layer Standard 100 BASETX 1000 BASESX … Non-Ethernet MAC Standards (802. 5, 802. 11, etc. ) Non-Ethernet Physical Layer Standards (802. 11, etc. ) 15

Ethernet Physical Layer Standards UTP Physical Layer Standards 10 BASE-T Speed Maximum Medium Run Required Length 10 Mbps 100 meters 4 -pair Category 3 or higher 100 BASE-TX 100 Mbps 100 meters 4 -pair Category 5 or higher 1000 BASE-T (Gigabit Ethernet) 1, 000 Mbps 100 meters 4 -pair Category 5 or higher 100 BASE-TX dominates access links today, Although 1000 BASE-T is growing in access links today 16

Ethernet Physical Layer Standards Fiber Physical Layer Standards Speed Maximum Medium Run 850 nm light (inexpensive) Length Multimode fiber 1000 BASE-SX 1 Gbps 220 m 62. 5 microns 160 MHz-km 1000 BASE-SX 1 Gbps 275 m 62. 5 200 1000 BASE-SX 1 Gbps 500 m 50 400 1000 BASE-SX 1 Gbps 550 m 50 500 The 1000 BASE-SX optical fiber standard dominates trunk links today S means that the standard uses short wavelength light (850 nm) 17

Shared media LANs u Limits to Shared Media LANs – FDDI, 100 Base-X, 1000 Base-SX are all shared media LANs t Only one station can transmit at a time, causing latency t Every station hears every message, so as the number of stations grow, the LAN saturates – 100, 1000 Mbps speed only delays saturation 18

Switched LANs u In a switched network – Incoming frame arrives on a single port – Frame sent out again only on a single port--the one leading to the receiver – No congestion on other ports Switch 19

Switch With a switch, multiple stations may transmit simultaneously: no congestion as traffic grows. Station A Station B Switch Station C Connection 1 A-C Connection 2 B-D Station D Connection 2 B-D 20

Switch connections u paths called connections must be pre-defined between stations u a fixed logical data link (logical connection) is established between stations before transmission even begins u during the transmission, all traffic between the stations must pass over that data link u unless a data link has been pre-established, two stations may not communicate at all u only OSI Layer 2 (Data Link Layer) protocols are needed 21

Hierarchical Ethernet LAN Ethernet switches must be arranged in a hierarchical topology In a hierarchical LAN, there is only one possible path between any hosts 22

Routed LAN with Ethernet Subnets When a routed LAN links multiple Ethernet switched networks, individual switched networks are called subnets 23