1. Cisco Academy – Chapter 5 Physical Layer

2. Physical Layer - 1 defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems Media Devices Topologies Collision Domains

3. Media STPShielded Twisted Pair UTPUnshielded Twisted Pair »10-100 Mbps, Inexpensive, 100 meters (333’), 4pairs CoaxialCoaxial Cable »10-100 Mbps, Inexpensive, 500 meters, Not used FiberGlass filament »>100 Mbps, Expensive, 2 km, single and multi-mode WirelessElectromagnetic waves

4. Standards Sets of rules or procedures that are either widely used, or officially specified, and that serve as the gauge or model of excellence ISO -International Standards Organization IEEEInstitute of Electrical & Electronic TIA/EIATelecommunications or Electrical Industry Association ULUnderwriters Laboratory

5. TIA/EIA Standards Horizontal cabling Telecommunications closets Backbone cabling Equipment rooms Work areas Entrance facilities

6. LAN Technologies Ethernet –10-Base T Patch Panels, Cables, Jacks, Wiring Closets, Plugs Transceivers, repeaters, hubs Token Ring FDDI

7. RJ-45 Jack and Connector Registered standard Reduces noise, reflection and stability problems Layer 1 component 8 conductor pins Punch down separates wires & forces into slots (Layer 1 component) –Rack mounted, 12 or 24 or 48 ports Wiring Standard 568A or 568B

8. Cat 5 Cable 4 Twisted Pairs (8 wires) –Reduces noise problems (crosstalk) Inexpensive Easy to install Layer 1 component –Carries the bits

9. Transceiver Combines transmitter and receiver Convert signals from one form to another –Converts AUI ports to RJ-45 ports Layer 1 devices Can be built into NICs –Called signaling components Encode signals onto the physical medium

10. Repeaters Retime and Regenerate Signals Deal with packets ONLY at bit level Layer 1 devices Extend length of network Extend collision domain Can’t filter traffic

11. Hubs Multi-port repeaters Amplify and retime signal Contain many ports Layer 1 Device Extend the collision domain Provides a central collection point for the network

12. Networks Shared –Many hosts have access to same medium Extended Shared –Extends environment for multiple access Point to Point (2 units, 1-1 connection) –Shared, connected to only other other device Indirectly connected –Circuit Switched

13. Collisions When two bits propagate (travel along the same media) at the same time Bits’ are actually packets containing many bits Result of too much network traffic (the more nodes the more work being done the more traffic) Domain – area within network where data packets originated and collided All of layer 1 connections are part of collision domain

14. Signals and Collisions Contention – managing competition for the system resources Collision results in destruction of data packets –Collision magnifies the signal strength A JAM Signal is sent to all nodes Algorithm takes over to determine when retransmission can occur (Back off algorithm) Segment is the collision domain

15. Collision Domain and Devices Layer 1 devices that extend the network result in larger collision domains –Includes repeaters and hubs A network segment includes all wires, repeaters, and hubs as part of one collision domain Too many collisions result in poor network performance

16. Four Repeater Rule A.K.A. as 5-4-3-2-1 rule 5 network segments 4 repeaters 3 network segments with hosts 2 link segments 1 collision domain

17. Segmentation At Layer 2 breaks up the collision domains Use Bridges and Switches (layer 2 devices) DECREASES the SIZE of the collision domains INCREASES the NUMBER of collision domains created Both filter the traffic –Keep local traffic on same segment –Allow traffic on other segments to pass through Segments are still part of the same broadcast domain

18. Segmentation cont. Try to design the LAN to keep 80% of the traffic local All nodes on a segment before, the bridge/switch will see and evaluate the datagram If the destination node is on the same segment the nodes processes the datagram The bridge/switch will evaluate the datagram but drop it Traffic on the LAN is isolated and reduced

19. Latency All devices add a latency component to the network It takes time for packets to travel through devices Bridges and switches have to take time to check MAC address to filter the frame Router has to take time to check IP address to route and switch the packet

20. Network Topology The study of location Two types - Physical and Logical Physical – describes the wiring schema Logical – describes how data flows through the network Network can have different physical and logical topologies

21. Network Types 10-Base T Ethernet –Logical Topology is a bus –Physical Topology is a star or extended star Token Ring –Logical Topology is a ring –Physical Topology is star FDDI –Logical and Physical Ring

22. Physical Topologies -1 Bus Star Extended Star Ring Hierarchical Mesh

23. Physical Topologies - 2 Bus –Logical – all devices can see all communications –Physical – each device is on the same wire Ring –Logical –each station passes data to adjacent station –Physical –devices wired in a daisy chain

24. Physical - 3 Star –Physical – all nodes connected to center node –Logical – all data passes through center node Extended Star –Physical – all center nodes from extensions connected to center node –Logical – hierarchical – information encouraged to stay local

25. Physical - 4 Tree –Logical – hierarchical –Physical – trunk has several layers or branches Mesh –Logical – depends on exact wiring –Physical – all nodes connected directly to each other

26. Physical - 5 Cellular –Physical – geographic cells; electromagnetic waves –Logical – communicate within cell or to adjacent cells