LANs No. 1  Seattle Pacific University Small Local Area Networks: Single Collision-Domain Networks Kevin Bolding Electrical Engineering Seattle Pacific University

LANs No. 2  Seattle Pacific University Local Area Networks General Definition(s) of a LAN Small (<100 stations, single building) Trusted users Single ownership Fast Single Collision Domain networks All devices connected to the network share the network at the same time Only one device may send data on the network at a time Data is sent to all receivers; no routing occurs

LANs No. 3  Seattle Pacific University Network Topologies Network topology Describes the physical layout of a network How are the computers and devices connected? Basic shape of design Bus (line) Ring Star

LANs No. 4  Seattle Pacific University Bus Topology One cable connects all components Cable may be straight or “snake” through the building Individual devices are connected on branches of the backbone To: 37 Data:xxxx Each message is sent to all computers Only the addressed computer responds to the message  XX

LANs No. 5  Seattle Pacific University 10Base-2 Bus LANs Most Bus LANs are connected using 10Base-2 Coaxial Cable 10Mbps, baseband transmission, 200m max 50 , RG-58 A/U BNC-type connections Use a ‘T’ to make a spur to connect a workstation Terminators All cable ends must be terminated (50  ) to prevent reflections

LANs No. 6  Seattle Pacific University Bus Issues There’s only one cable system Any breaks will isolate part of the network It’s even worse! Unplugging a single workstation creates an un- terminated end in the network Communication in the whole network is stopped Like trying to talk in an echo chamber The Bus is a passive system Signals are simply sent through the wires No active components refresh the signals Repeaters can be used if necessary

LANs No. 7  Seattle Pacific University Bus Pros and Cons Simple “Plug and play” Many single-point failure modes Broken backbone Any unplugged computer that isn’t terminated Advantages Disadvantages Cheap Mostly all cables Cables are relatively inexpensive Linear arrangement Just run your backbone in a path that goes near the workstations Difficult to trace errors All one big “wire” Problem could be anywhere Limits on cable length seriously constrain size Repeaters needed

LANs No. 8  Seattle Pacific University Star (Hub) topologies A Hub is a multi-port repeater Reads input from any one of its ports Repeats it to all other ports Systems built around a hub usually have a star topology Usually use 10Base-T or 100Base-T 10/100Mbps, Baseband, UTP RJ-45 Connectors HP ProCurve Compact 10Base-T Hub 8 Standard Ports Crossover Port Logically, the same as a bus Medium is still shared by all stations at all times

LANs No. 9  Seattle Pacific University Star (Hub) Pros and Cons Termination is no longer an issue An un-terminated line only effects communication to one device Can’t bring the network down by unplugging your network connection Single-point failure If the hub goes down, all is lost Advantages Disadvantages Expansion is easier Active hubs reduce loading limitations Easier troubleshooting Isolated connections More cable needed All cables must reach from workstations to the hub

LANs No. 10  Seattle Pacific University Star-Star Multi-Hub LANs Connect multiple stars (hubs) together in a bus or star Isolates individual groups from each other Hierarchical Logically, still one single shared medium Star-Star A Star-Star hub network is logically the same as a bus network

LANs No. 11  Seattle Pacific University Connecting Hubs HP ProCurve Compact 10Base-T Hub 8 Crossover Port Rx Tx Tx Rx HubNIC Rx Tx Tx Rx Hub Tx Rx Connection from hub-to- hub requires a crossover port or crossover cable

LANs No. 12  Seattle Pacific University Ethernet Physical Media and Signals Most widely-accepted Ethernet standards use the same medium and connectors 4-pair UTP – Cat 5e is the most common today RJ-45 connectors Cable length of up to 100m

LANs No. 13  Seattle Pacific University Ethernet – 10BaseT 10BaseT Uses Manchester coding at 10Msps to send 10Mbps Uses only 2 of the 4 pairs – one for each direction

LANs No. 14  Seattle Pacific University Ethernet – 100BaseTX 100BaseTX For error correction, uses a 4B/5B code – sends 5 bits to represent 4 actual bits (80% efficient) Uses MLT-3 3-level coding (similar to AMI) at 125M symbols/s 125M symbols/s x 4/5 bits/symbol = 100Mbps Uses only 2 of the 4 pairs – one for each direction

LANs No. 15  Seattle Pacific University Ethernet – 1000BaseT 1000BaseT Each UTP pair uses a 5-level coding (2-bits per symbol) at 125M symbols/s to send 250Mbps Warning – this reduces the tolerable SNR by 6dB, which increases the error rate Uses all four pairs at the same time – 4 x 250Mbps = 1Gbps in one direction Uses simultaneous bi-directional signaling (echo cancellation) to send signals at the same time in both directions on the wire – 1Gbps in both directions Uses a complex coding scheme (Trellis coding) to decrease the error rate. This is equivalent to adding back 6dB to the SNR

LANs No. 16  Seattle Pacific University Ethernet – 10GBaseT 10GBaseT 10Gbps over twisted pair 55m over Cat-6 UTP 100m over Cat-6a UTP 16-level encoding (4 bits/symbol) * 800M symbols/s = 3.2 Gb/s per pair Encoding loses a few bits  2.5 Gb/s per pair 4 pairs, simultaneous bi-directional  10Gb/s in both directions Fiber – Several standards using single- or multi-mode fiber Up to 80 km!