How Computer Network Works and Topoly in Network Design.pptx

How Computer Network Works

Network Topology, Topology in Network Design, COLOR-CODE STANDARDS, Color Coding

1. How Computer Network Works In the world of computers, networking is the practice of linking two or more computing devices together for the purpose of sharing data. Networks are built with a mix of computer hardware and computer software. Introduction to Network Types Networks can be categorized in several different ways. One approach defines the type of network according to the geographic area it spans. Local area networks (LANs) , for example, typically reach across a single home, whereas wide area networks (WANs) , reach across cities, states, or even across the world. The Internet is the world's largest public WAN. One way to categorize the different types of computer network designs is by their scope or scale. For historical reasons, the networking industry refers to nearly every type of design as some kind of area network . Common examples of area network types are:

2. LAN - Local Area Network WLAN - Wireless Local Area Network WAN - Wide Area Network MAN - Metropolitan Area Network SAN - Storage Area Network, System Area Network, Server Area Network, or sometimes Small Area Network CAN - Campus Area Network, Controller Area Network, or sometimes Cluster Area Network PAN - Personal Area Network DAN - Desk Area Network LAN and WAN were the original categories of area networks, while the others have gradually emerged over many years of technology evolution. Note that these network types are a separate concept from network topologies such as bus, ring and star. A local area network (LAN) supplies networking capability to a group of computers in close proximity to each other such as in an office building, a school, or a home. A LAN is useful for sharing resources like files, printers, games or other applications. A LAN in turn often connects to other LANs, and to the Internet or other WAN . Most local area networks are built with relatively inexpensive hardware such as Ethernet cables, network adapters, and hubs. Wireless LAN and other more advanced LAN hardware options also exist. Wireless Local Area Network (WAN) - A wireless LAN (or WLAN, for wireless local area network, sometimes referred to as LAWN, for local area wireless network) is one in which a mobile user can connect to a local area network ( LAN ) through a wireless (radio) connection.

3. Wide Area Network ( WAN ) is a geographically dispersed telecommunications network . The term distinguishes a broader telecommunication structure from a local area network ( LAN ). A wide area network may be privately owned or rented, but the term usually connotes the inclusion of public (shared user) networks. An intermediate form of network in terms of geography is a metropolitan area network ( MAN ). - Covers a broad area (i.e., any network whose communications links cross metropolitan, regional, or national boundaries [1] ). Or, less formally, a network that uses routers and public communications links [1] . Contrast with personal area networks (PANs), local area networks (LANs), campus area networks (CANs), or metropolitan area networks (MANs) which are usually limited to a room, building, campus or specific metropolitan area (e.g., a city) respectively. The largest and most well-known example of a WAN is the Internet . Wide Area Networks (WANs) span broad geographical distances - entire regions, states, continents, or the entire globe. The most universal and powerful WAN is the Internet. Computers connect to a WAN through public networks such as the telephone system or private cable systems, or through leased lines or satellites. A Metropolitan Area Network (MAN) is a large computer network that spans a metopolitan area or campus. Its geographic scope falls between a WAN and LAN. MAns provide Internet connectivity for LANs in a metropolitan region, and connect them to wider area networks like the Internet .

4. Network Topology - In computer networking, topology refers to the layout of connected devices. This article introduces the standard topologies of networking.   - Represents its layout or structure from the point of view of data flow.

5. Topology in Network Design   Think of a topology as a network's virtual shape or structure. This shape does not necessarily correspond to the actual physical layout of the devices on the network. For example, the computers on a home LAN may be arranged in a circle in a family room, but it would be highly unlikely to find a ring topology there. Network topologies are categorized into the following basic types: Bus Ring Star Tree Mesh More complex networks can be built as hybrids of two or more of the above basic topologies.

6. Bus Topology Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message. Ethernet bus topologies are relatively easy to install and don't require much cabling compared to the alternatives. 10Base-2 (" ThinNet ") and 10Base-5 (" ThickNet ") both were popular Ethernet cabling options many years ago for bus topologies. However, bus networks work best with a limited number of devices. If more than a few dozen computers are added to a network bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.

7. Bus Topology Diagram

8. Ring Topology In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network.   To implement a ring network, one typically uses FDDI, SONET , or Token Ring technology. Ring topologies are found in some office buildings or school campuses.

9. Ring Topology Diagram

10. This diagram illustrates the ring network topology. A ring topology such as FDDI or SONET sends messages clockwise or counterclockwise through the shared link.

11. Star Topology Many home networks use the star topology. A star network features a central connection point called a "hub" that may be a hub , switch or router . Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.   Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire LAN. (If the hub fails, however, the entire network also fails.)

12. Star Network Topology Diagram

13. This diagram illustrates the star network topology. A star topology typically uses a network hub or switch and is common in home networks.  

14. Tree Topology Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.

15. Tree Network Topology

16. This diagram illustrates the tree network topology. A tree topology integrates the star and bus topologies in a hybrid approach to improve network scalability.

17. Mesh Topology   Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs , most notably the Internet, employ mesh routing. A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others.

18. Mesh Network Topology

19. This diagram illustrates the mesh network topology. A mesh topology provides redundant communication paths between some or all devices (partial or full mesh).   Summary Topologies remain an important part of network design theory. You can probably build a home or small business computer network without understanding the difference between a bus design and a star design, but becoming familiar with the standard topologies gives you a better understanding of important networking concepts like hubs, broadcasts, and routes.

20. COLOR-CODE STANDARDS Again, please bear with me...  Let's start with simple pin-out diagrams of the two types of UTP Ethernet cables and watch how committees can make a can of worms out of them.  Here are the diagrams: Note that the TX (transmitter) pins are connected to corresponding RX (receiver) pins, plus to plus and minus to minus.  And that  you must use a crossover cable to connect units with identical

21. interfaces.  If you use a straight-through cable, one of the two units must, in effect, perform the cross-over function. Two wire color-code standards apply: EIA/TIA 568A and EIA/TIA 568B. The codes are commonly depicted with RJ-45 jacks as follows (the view is from the front of the jacks):

22. If we apply the 568A color code and show all eight wires, our pin-out looks like this:

23. Note that pins 4, 5, 7, and 8 and the blue and brown pairs are not used in either standard.  Quite contrary to what you may read elsewhere, these pins and wires are not used or required to implement 100BASE-TX duplexing--they are just plain wasted. However, the actual cables are not physically that simple.  In the diagrams, the orange pair of wires are not adjacent.  The blue pair is upside-down.  The right ends match RJ-45 jacks and the left ends do not.  If, for example, we invert the left side of the 568A "straight"-thru cable to match a 568A jack--put one 180° twist in the entire cable from end-to-end--and twist together and rearrange the appropriate pairs, we get the following can-of-worms: This further emphasizes, I hope,  the importance of the word "twist" in making network cables which will work.  You cannot use an flat-untwisted telephone cable for a network cable.  Furthermore, you must use a pair of twisted wires to connect a set of transmitter pins to their corresponding receiver pins.  You cannot use a wire from one pair and another wire from a different pair. Keeping the above principles in mind, we can simplify the diagram for a 568A straight-thru cable by untwisting  the wires, except the 180° twist in the entire cable, and bending the ends upward.  Likewise, if we exchange the green and orange pairs in the 568A diagram we will get a simplified diagram for a 568B straight-thru cable.  If we cross the green and orange pairs in the 568A diagram we will arrive at a simplified diagram for a crossover cable.  All three are shown below .

24. LET'S MAKE IT SIMPLE There are only two unique cable ends in the preceding diagrams. They correspond to the 568A and 568B RJ-45 jacks and are shown to the right.  Again,  the wires with colored backgrounds may have white stripes and may be denoted that way in diagrams found elsewhere.  For example, the green wire may be labeled Green-White--I don't bother.  The background color is always specified first. Now, all you need to remember, to properly configure the cables, are the diagrams for the two cable ends and the following rules:

25. A straight-thru cable has identical ends. A crossover cable has different ends. It makes no functional difference which standard you use for a straight-thru cable.   You can start a crossover cable with either standard as long as the other end is the other standard.  It makes no functional difference which end is which.  Despite what you may have read elsewhere, a 568A patch cable will work in a network with 568B wiring and 568B patch cable will work in a 568A network.  The electrons couldn't care less. My preference is to use the 568A standard for straight-thru cables and to start crossover cables with a 568A end.  That way all I have to remember is the diagram for the 568A end, that a straight-thru cable has two of them, and that the green and orange pairs are swapped at the other end of a crossover cable .

26. LET'S MAKE SOME CABLES 1.  Pull the cable off the reel to the desired length and cut.  I have a box of cable at one end of my shop and a mark on the floor 10' away.  For cable lengths which are a fraction of  ten feet, I eye-ball the length as  I  pull the cable out of the box (also, my feet are about one foot long).  For longer cables, I pull it out to the ten foot mark and go back to the box and pull the remaining fraction or another ten feet.  If you are pulling cables through walls, a hole in the floor, etc., it easier to attach the RJ-45 plugs after the cable is pulled.  The total length of wire segments between a PC and a hub or between two PC's cannot exceed 100 Meters (328 feet or about the length of a football field) for 100BASE-TX (and 10BASE-T).

27. 2.  Strip one end of the cable with the stripper or a knife and diags .  If you are using the stripper, place the cable in the groove on the blade (left) side of the stripper and align the end of the cable with the right side of the stripper.  This is about right to strip a little over 1/2" of the jacket off the cable.  Turn the stripper about one turn or so.  If you turn it much more, you will probably nick the wires.  The idea is to score the outer jacket, but not go all the way through.  Once scored, you should be able to twist the end of the jacket loose and pull it off with one hand while holding the rest of the cable with the other.  If you are using a knife and diags , carefully slit the cable for about an inch or so and neatly trim around the circumference of the cable with the diags to remove the jacket.

28. 3.  Inspect the wires for nicks.   Cut off the end and start over if you see any.  You may have to adjust the blade with the screw at the front stripper.  Cable diameters and jacket thicknesses vary. 4.  Spread and arrange the pairs roughly in the order of the desired cable end .

29. 5.  Untwist the pairs and arrange the wires in the order of the desired cable end.  Flatten the end between your thumb and forefinger. Trim the ends of the wires so they are even with one another.  It is very important that the unstripped (untwisted) end be slightly less than 1/2" long.    If  it is longer than 1/2" it will be out-of-spec and susceptible to crosstalk.  If it less than slightly less than 1/2" it will not be properly clinched when RJ-45 plug is crimped on..  Flatten again.  There should be little or no space between the wires.

30. .6. Hold the RJ-45 plug with the clip facing down or away from you.  Push the wire firmly into the plug.  Now , inspect the darn thing... before crimping and wasting the plug!   Looking through the bottom of the plug, the wire on the far left side will have a white background.  The wires should alternate light and dark from left to right.  The furthest right wire is brown.  The wires should all end evenly at the front of the plug.  The jacket should end just about where you see it in the diagram--right on the line.  Aren't you glad you didn't crimp the plug

31. Color Coding In the cabling industry color coding is used to identify a pair of conductors by its unique number, corresponding to the combination of tip and ring colors. Copper and fiber color coding are somewhat different, so the tables are split onto copper and fiber sections. Please follow the links below to see the color code tables, depending on the pair (fiber) count of the cable. 4 pair cable's color code table. Every pair uses white as a tip color and one of four (blue, orange, green, brown) ring colors.

32. pair figure tip ring 1 white blue 2 white orange 3 white green 4 white brown pair figure tip ring