1. 1 Media, Connections, and Collisions Honolulu Community College Cisco Academy Training Center Semester 1 Version 2.1.1

2. 2 Overview n Network foundation is the physical layer, Layer 1 of the OSI Reference Model. n Physical layer defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems. n Different types of networking media. n How network devices, cable specifications, network topologies, collisions and collision domains affect how much data can travel across the network and how fast.

3. 3 F Speed and throughput: 10-100 Mbps F Average $ per node: Moderately Expensive F Media and connector size: Medium to Large F Maximum cable length: 100m (short)

4. 4 Shielded Twisted Pair - STP n Combines the techniques of shielding, cancellation, and twisting of wires. n STP gives greater protection from all types of external interference, but is more expensive than UTP (unshielded twisted-pair cable). n Shielding must be properly grounded. u If improperly grounded, shielding to act like an antenna (noise pickup).

5. 5 F Speed and throughput: 10-100 Mbps F Average $ per node: Least Expensive F Media and connector size: Small F Maximum cable length: 100m (short)

6. 6 UTP - Unshielded Twisted Pair n Least expensive networking media, and most common. u Small size (.43 cm diameter) u easy to install, and more cables in wiring ducts. n Relies on cancellation to minimize interference. u prone to electrical noise and interference n To reduce crosstalk, the number of twists in the wire pairs varies. n Uses solid RJ-45 connection. n Fastest copper media. n Disadvantage is short unboosted runs - 100m.

7. 7 Coaxial Cable (coax) n Longer unboosted distances than other copper media. n Two sizes: u Thinnet -10Base2 - 185m. u Thicknet -10Base5 - 500m. F Speed and throughput: 10-100 Mbps F Average $ per node: Inexpensive F Media and connector size: Medium F Maximum cable length: 500m (medium)

8. 8 Problems with Coax n Difficult to work with - thicker diameter. n Requires proper grounding at both ends. n Improper grounding can give more interference.

9. 9 Fiber Optic Cable F Speed and throughput: 100+ Mbps F Average $ per node: Most Expensive F Media and connector size: Small F Maximum cable length: Up to 2km F Single mode: One stream of laser-generated light F Multimode: Multiple streams of LED-generated light

10. 10 Fiber Optic Cable n Uses modulated light transmissions. n Most expensive networking media, in materials and installation. n Not susceptible to EMI and RFI. n Does not conduct electricity (advantage for use between buildings, floors, etc). n Fastest speeds of all networking media. n Long unboosted distances - up to 2 km. n Used primarily for backbone cabling.

11. 11 Wireless Communications n Wireless signals are electromagnetic waves, which can travel through a vacuum or air. u no physical medium is necessary.

12. 12 Purpose of LAN Media Specifications n Mid-1980s, no standards, networking media were largely proprietary, networks used different specs and implementations. n OSI model was created; provided a set of standards. u Standards are sets of rules or procedures that are either widely used, or officially specified. u Ensured compatibility and interoperability between various types of network technologies.

13. 13 Standards n Many groups joined the movement to specify the types of cable that could be used for specific purposes or functions. u IEEE - Institute of Electrical and Electronics Engineers u UL - Underwriters Laboratories u EIA - Electrical Industries Association u TIA - Telecommunications Industry Association

14. 14 Standards (cont.) n IEEE u cabling requirements in 802.3 (Ethernet) and 802.5 (Token Ring) specifications. n UL u identification program that lists markings for shielded and unshielded twisted-pair media. n TIA/EIA u 568-A cabling standards, 569 wiring closets. u greatest impact on networking media standards.

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16. 16 TIA/EIA 568-A n Focuses on standards for horizontal cabling. u horizontal cabling includes the networking media that extends from wiring closet to workstation. n Maximum distance for cable runs in horizontal cabling is 90 m (CAT 5 UTP ). n Patch cords or cross-connect jumpers located at the horizontal cross-connect cannot exceed 6 m. n Patch cords to connect equipment at the work area - 3m.

17. 17 UTP - Category Ratings n Cat 1 - not rated for data. n Cat 2 - for voice/PBX (private branch exchange). u Low performance UTP, for voice, low speed data. n Cat 3 - use for 10BaseT networks. n Cat 4 - low loss, 10baseT, up to 16 Mbps. n Cat 5 - low-loss extended frequency, for 100baseX systems - Fast Ethernet.

18. 18 Ethernet 10BaseT n Layer 1 Components and Devices u Passive (no energy to operate) components: F patch panels, plugs, cabling, jacks. u Active devices: F transceivers, repeaters, hubs. n Connectors & Jacks: RJ-45 u 8 wire connector, terminates UTP. u Jacks require punch-down tool. n Cabling: standard is Cat 5 UTP.

19. 19 Ethernet Layer 1 Components n Patch panel: convenient groupings of RJ-45 jacks. u 8 wire jacks, require punch-down tool. n Transceiver: a combination of transmitter and receiver. u Connects to AUI port to give a particular type of connection. u Transmit from one pin configuration and/or media to another.

20. 20 Ethernet Layer 1 Components (2) n Repeaters: regenerate, and retime signals, which enables cables to reach longer distances. u cannot filter network traffic. n Hubs: multiport repeaters. u serve as the center of a star topology. n Layer 1 components create or act on the bits. u They recognize no information patterns in the bits, no addresses, and no data. u Their function is simply to move bits around.

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22. 22 Types of Networks n Shared media - occurs when multiple hosts have access to the same medium. u Ethernet is a shared media environment. n Point-to-point - one device is connected to only one other device via a link.

23. 23 Circuit vs Packet Switched n Circuit-switched - indirectly-connected network in which actual electrical connection is ‘switched on’ for the duration of the communication. u Telephone service is circuit-switched. u ISDN. n Packet-switched - link connection between two communicating hosts, where the source sends messages in packets. u Advantage: many hosts can share same link. u Frame Relay is an example of packet-switched.

24. 24 Collisions & Collision Domains n Ethernet allows only one data packet to access the media at any one time. u If two or more nodes transmits at the same time, a collision occurs, and the data is damaged. n Collision domain - area in the network, where the data packets originate and collide. n When a collision occurs, the data packets that collide are destroyed, bit by bit. n CSMA/CD is the method Ethernet uses to handle media contention. u Developed at the University of Hawaii in 1960s.

25. 25 Repeaters and Collision Domain n Repeater extends the collision domain, therefore, the network on both sides of the repeater is one larger collision domain. One Large Collision Domain

26. 26 Hubs and Collision Domain n Hubs, like repeaters, extend the collision domain. One Large Collision Domain

27. 27 5-4-3-2-1 Rule of Thumb u Five sections of the network, u Four repeaters or hubs, u Three sections of the network have hosts, u Two sections are link segments (for link purposes), u One large collision domain. One Collision Domain

28. 28 Segmentation n Purpose is to reduce size of collision domains. n Can segment with bridges, switches or routers. One Collision Domain

29. 29 Physical Topology n Topology defines the structure of the network. n Physical topology is the actual layout of the wire (media).

30. 30 Logical Topology n Logical topology is how information flows through a network. n A network’s physical topology may be completely different from its logical topology. u Ethernet 10Base-T uses an extended-star physical topology, but acts like a logical bus topology. u Token Ring uses a physical star, and a logical ring. u FDDI uses a physical and a logical ring.

31. 31 Linear Bus Topology n Bus topology has all nodes connected directly to one link. n Physical perspective: u all hosts are connected to each other, and can communicate directly. u a break in the cable disconnects hosts from each other. n Logical perspective: u enables all devices to see all signals from all other devices.

32. 32 Ring Topology n Ring topology has each node connected directly to only the two adjacent nodes. n Physical perspective: u all devices are directly connected to two adjacent devices in a daisy-chain. n Logical perspective: u each station passes the data to its adjacent station.

33. 33 Dual Ring Topology n Dual ring topology has two concentric rings. n Physical perspective: u same as a ring topology, except there is a second, redundant ring, that connects the same devices. u each device is part of two independent ring topologies. n Logical perspective: u acts like two independent rings, of which, only one at a time is used.

34. 34 Star Topology n Star topology has a central node with all links to other nodes radiating from it. n Physical perspective: u all nodes communicate with each other, through central node. u central node is a single point of failure. n Logical perspective: u all information goes through one device. u desirable for security or restricted access reasons. u but network is susceptible to any problems in the star's central node.

35. 35 Extended Star Topology n Each node that links to center node is also the center of another star. n Physical perspective: u a core star topology, with each of the end nodes acting as the center of its own star topology. u advantage is shorter wiring runs. u limits number of devices that interconnect to any one central node. n Logical perspective: u extended star topology is very hierarchical.

36. 36 Tree Topology n Tree topology uses a trunk node from which it branches to other nodes. n Physical perspective: u trunk is a wire that has several layers of branches. n Logical perspective: u flow of information is hierarchical.

37. 37 Irregular Topology n Irregular network topology has no obvious pattern to the links and nodes. n Physical perspective: u wiring is inconsistent; the nodes have varying numbers of wires leading from them. n Logical perspective: u no obvious pattern.

38. 38 Mesh Topology n In a mesh topology every node is linked directly to every other node. n Physical perspective: u every node is physically connected to every other node, creating a redundant connection. u requires large amount of media and connections. n Logical perspective: u behavior of a mesh topology depends greatly on the devices used.

39. 39 Cellular Topology n Cellular topology consists of circular or hexagonal areas, each of which has an individual node at its center. n Physical perspective: u a geographic area that’s divided into regions (cells) for the purposes of wireless technology. n Logical perspective: u communication is directly between nodes or only with adjacent cells (distance limitations and interference affect operations).

40. 40 Summary n Function of the physical layer is to transmit data. n Networking media: u Coax, STP, UTP, fiber. n TIA/EIA-568-A & TIA/EIA-569 - most widely used standards for networking media. n Collisions and collision domains. n Physical topology vs logical topology.