Ethernet LAN 1 1

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

Standards Setting LANs are Subnets (single networks) Subnet technology is Dominated by OSI Standards (true for LANs) IEEE Creates most LAN Standards Institute for Electrical and Electronic Engineers Submits its standards to ISO and ITU-T for ratification 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 3

LANs and OSI Architecture OSI is a 7-layer architecture LAN transmission only uses Layers 1 and 2 Layer 1: Physical Layer Connectors, Media, Electrical signaling 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 Station B Transmission Medium (telephone wire, etc.) Connector Plug Connector Plug F4-1 5 5

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

Data Link Layer 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 First function: Packaging of Data (1s and 0s) PDU at Data Link Layer is called a frame 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

Logical Link Control Layer Media Access Control (MAC) Layer Data Link Layer Logical Link Control Layer OSI Data Link Layer (Layer 2) Media Access Control (MAC) Layer OSI Physical Layer (Layer 1) 802.3 10Base-T 802.3 10Base-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 9

Media Access Control (MAC) Layer OSI Physical (Layer 1) 802.3 10Base-T 802.3 10Base-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 10

Logical Link Control Layer LLC 802.2 Logical Link Control Layer 802.3 Media Access Control (MAC Layer) 802.5 MAC 4 Mbps 802.5 MAC 16 Mbps Other MAC OSI Physical (Layer 1) 802.3 10Base-T 802.3 10Base-5 802.3 Other Physical Layer 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 11

Simple LAN Using Ethernet 10Base-T RJ-45 jacks 10Base-T Hub (Multiport Repeater) 10Base-T UTP Wiring Bundles: 4 Pairs EIA Category 3, 4, or 5 Unshielded Twisted Pair (UTP) Wiring (4-Pair Bundle) PC Network Interface Card RJ-45 Jack NIC 12 14 12

NICs Network Interface Cards Implement Physical Layer Plug and Electrical Signaling Implements the Data Link Layer (data packaging, access control, etc.) LLC (802.2) MAC (802.3 MAC) 13

Wiring Unshielded Twisted Pair (UTP) Categories of UTP Wiring Twisted several times per foot to reduce interference, T in 10Base- and Unshielded 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 Wiring Plugs: RJ-45 Standard Similar to home (RJ-11) jacks, but wider 14

Layering in 802 Networks Internet Layer TCP/IP Internet Layer Standards (IP, ARP, etc.) Other Internet Layer Standards (IPX, etc.) Data Link Layer Logical Link Control Layer 802.2 Media Access Control Layer Ethernet 802.3 MAC Layer Standard Non-Ethernet MAC Standards (802.5, 802.11, etc.) <Read the box near the top.> Physical Layer 100BASE- TX 1000 BASE- SX … Non-Ethernet Physical Layer Standards (802.11, etc.) 15 15

Ethernet Physical Layer Standards UTP Physical Layer Standards Speed Maximum Run Length Medium Required 10BASE-T 10 Mbps 100 meters 4-pair Category 3 or higher 100BASE-TX 100 Mbps 100 meters 4-pair Category 5 or higher 1000BASE-T (Gigabit Ethernet) 1,000 Mbps 100 meters 4-pair Category 5 or higher Let’s look first at Ethernet physical layer standards. We will begin with standards that use 4-pair UTP copper wiring. -T in the names indicates twisted-pair wire. <Go through the rows.> 100BASE-TX dominates access links today, Although 1000BASE-T is growing in access links today [Note the TX in 100BASE-TX. The 802.3 Working Group actually created two 100 Mbps UTP standards. Only 100BASE-TX was produced and used.] 100BASE-TX dominates access links today, Although 1000BASE-T is growing in access links today 16 16

Ethernet Physical Layer Standards Fiber Physical Layer Standards Speed Maximum Run Length Medium 850 nm light (inexpensive) Multimode fiber 1000BASE-SX 1 Gbps 220 m 62.5 microns 160 MHz-km 1000BASE-SX 1 Gbps 275 m 62.5 200 1000BASE-SX 1 Gbps 500 m 50 400 At 1 Gbps and higher speeds, Ethernet offers the option of using optical fiber. 1000BASE-SX dominates switch-to-switch trunk lines for gigabit Ethernet. Ethernet normally uses 850 nm light. This is short wavelength, so the standard is called 1000BASE-SX. Note that maximum distance depends on both core diameter (50 or 62.5 microns) and modal bandwidth. 1000BASE-SX 1 Gbps 550 m 50 500 The 1000BASE-SX optical fiber standard dominates trunk links today S means that the standard uses short wavelength light (850 nm) 17 . 17

Shared media LANs Limits to Shared Media LANs FDDI, 100Base-X, 1000Base-SX are all shared media LANs Only one station can transmit at a time, causing latency Every station hears every message, so as the number of stations grow, the LAN saturates 100, 1000 Mbps speed only delays saturation 18 21

Switched LANs 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 21

Switch With a switch, multiple stations may transmit simultaneously: no congestion as traffic grows. Switch Station C Station A Connection 1 A-C Connection 1 A-C Station D Station B Connection 2 B-D Connection 2 B-D 20 22

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

Hierarchical Ethernet LAN In Ethernet, hosts connect to workgroup switches. Core switches connect switches together. The group of all core switches is called the network’s core. Ethernet switches MUST be organized in a hierarchy. If you create a loop, bad things happen. <Trace the single path between Client PC1 and Server X.> <Trace the single possible path between Client PC1 and Server Y.> Ethernet switches must be arranged in a hierarchical topology In a hierarchical LAN, there is only one possible path between any hosts 22 22

Routed LAN with Ethernet Subnets <Read the text box.> [Even the largest LANs can be completely switched. However, if routers are used, this gives the network manager better control over transmission because routers are very sophisticated.] When a routed LAN links multiple Ethernet switched networks, individual switched networks are called subnets 23 23