4The Big JobWhenever you have a big job to do, it helps to break it down into discrete chunks or functionsFor example, moving your family from one city to another could be broken down into:What to moveHow to packHow to load the vanHow to unload the vanThe job of moving data from one place to another is also a big job
5OSI Seven-Layer ModelThe big job of moving data from one place to another is broken down into functions defined by the OSI Seven-Layer Model
6Case Study ExampleLet’s look at the process of networking from a conceptual viewpointAssume we are just trying to move a file from one PC to another in a small officeOne of the workers has just completed a new employee handbookShe needs to transfer the Word document to the other worker for review
7Case Study ExampleThe file could be copied to a diskette, USB, or CD/DVD and handed over to the other worker – called Sneakernet – but that’s not necessary todayThe document may be transferred using the networkThe next section examines the various hardware required
14Network Interface Cards Since all the networked systems are connected to the same hub, each system must have a unique identifierMedia Access Control (MAC) addressA unique address burned into a ROM chip on the network cardEach MAC address is 12 hex characters or 48 bits in lengthMAC address printed on surface of chip – it’s burned inside the chip.
15MAC Addresses MAC addresses are 48 bits long Usually represented using hexadecimal characters (12 hex digits = 48 bits)Here’s a typical MAC address:D49Identifies the manufacturerUnique serial number determined by the manufacturerNo two MAC addresses are ever the same!
16WINIPCFG Used on Windows 98/Me systems to view network configuration MAC address
17ipconfig /allUsed on Windows NT/2000/XP systems to view network configurationDetermine your own MAC address using either WINIPCFG or ipconfig/all.MAC address
18Bits A MAC address is a series of ones and zeros called bits Data is sent using pulses of electricity, light, or radio waves
19Frames Data is sent across the network in frames Frames are discrete chunks of dataThere are a number of different frame types used in different networks. All NICs on the same network must use the same frame type or they will not be able to communicate with other NICs.
20Fields Frames are made up of fields that contain information Frames typically contain the recipient’s MAC address, the sender’s MAC address, the data itself, and a cyclic redundancy check (CRC) for error checkingCRCs (Cyclic Redundancy Check) are used to check the frame for accuracyFrames are sometimes corrupted while in transit from one device to anotherThe data in the frame is divided by a number called the key, producing a four byte CRC value that is placed in the frame at the sending stationThe receiving station does the same calculation on the received frameIf the value matches the CRC, the frame is good
21Data What is inside the data part of the frame? It could be part of a file, a print job, a web page, anythingNICs do not care what the data, or payload, is
22Frame Size Different networks use different sizes of frames Many frames hold about 1500 bytes of dataThe sending software breaks up large amounts of data into smaller chunksThe receiving station must then put the chunks back together in the proper order
23Processing FramesqAll devices on the network see the frame, but only the device that it is addressed to will process itEvery frame is received by every NICThe MAC address is used to decide if the frame belongs to a given device
24Getting Data on the Cable Only one system may speak at a time since the cable is sharedProcesses are used to keep two NICs from talking at the same time
25Getting To Know YouHow does the sending NIC know the MAC address of the NIC to which it is sending data?Most of the time the two devices have talked before, so the destination MAC address is already knownIf the MAC address is not known, then a broadcast message is sent over the networkThe destination device will respond by sending its MAC addressA broadcast MAC address is FF-FF-FF-FF-FF-FFHow does the destination device know that it is the intended destination device? Remember, the MAC address is still unknown. On most networks today, another address called an IP address is used to identify the destination device.
26Moving Frames – Step 1The sending system’s network software hands some data to the NICThe NIC begins building a frame
27Moving Frames – Step 2After the NIC creates the frame, it adds the CRC and data to itIt also puts its MAC address and the destination’s MAC address in the frame
28Moving Frames – Step 3When no other NIC is using the cable, it sends the frame through the cable
29Moving Frames – Step 4 The frame propagates down the wire to the hub The hub creates a copy of the frame to send to every other systemThe receiving device processes the frame
30Moving Frames – Step 5The receiving station checks the CRC value in the frameIf the value matches what it should, then the NIC sends the data portion to the network operating system for processingIf the value does not match, the frame has errors and must be resent
32Beyond the Single WireWhat if one system is using a modem to dial into the network?What if one of the systems is a Macintosh?
33RoutersA single network with single hub can only support up to 1,024 computers before the network becomes too slowRouters are used to chop large networks up into smaller ones
34Network ProtocolsNetwork protocols define rules for how systems are addressed, how to chop data up into chunks, how to deal with routers, and so onAs a network grows a more universal addressing method than MAC addresses is neededTCP/IP are the most popular universal addressing protocols
35TCP/IP Transmission Control Protocol (TCP) Internet Protocol (IP) Gives each device on the network a unique numeric identifierIP addresses consist of four 8-bit numbersEach 8-bit number ranges from 0 to 255No two systems on the same network share the same IP address
36DHCP IP addresses must be manually configured on each device Or they may be automatically configured using Dynamic Host Configuration Protocol (DHCP)Each system in a network has two addressesMAC address burned into a chip on the NICIP address configured through software
38IP packet with frame added PacketsThe network software creates a packet that contains the sending and receiving IP addresses along with the dataThe packet is enclosed within a frame that contains the sending and receiving MAC addressesIP packet in a frameThe diagram above does not include all the fields in an IP packet – it is a highly simplified IP packet.IP packetIP packet with frame added
39Connecting to the Internet To connect the local network to the Internet a router is neededThe local hub is connected to the routerThe router is connected to the Internet through a phone lineThe phone line uses a different kind of frame, so the router strips the frame and creates a new one
40Connecting to the Internet Router removing network frame and adding one for telephone lineAdding a router to the network
41Moving through the Internet The router strips off the MAC addresses and uses the type of addressing the phone company uses insteadThe frame uses the IP address to guide it to the receiving systemThe receiving router strips off the telephone frame and adds the MAC address for the receiving systemThe NIC strips off the MAC header and hands the frame off to the NOS
42Assembly and Disassembly Most data is much larger than a single frameNetwork protocols chop up the data into smaller packets and gives each one a sequence numberThe sequence numbers are used by the receiving system to put the packets back in order and to assemble themTransmission Control Protocol (TCP) is one such protocol
43SessionsIf the receiving system also has a printer to share on the network, then it may receive packets for print jobs as well as packets for filesThe sending system must also contact the receiving system to make sure it is ready to handle a print job as wellThe software that handles these processes is called session software
44Multiple Sessions Single session Multiple sessions How many sessions does a PC have running at a time? If your network uses TCP/IP, use the following command to list each session line by line:Netstat –a
45Standardized Formats Macintoshes and PCs use very different formats Standardized formats have been created that allow very different operating systems to exchange data
46VPNsVirtual Private Networks (VPNs) enable a user away from the office to connect to the corporate network via the Internet
47Encryption Many networks encrypt data to prevent unauthorized access Both the sending and receiving system must know the encryption method used
48Network ApplicationsUsers use network applications to exchange data on a networkMy Network Places in Windows for filesInternet Explorer or Netscape Navigator for web pagesOutlook Express for
49Copy a File Across a Network The next few slides illustrate a typical process that takes place to copy a file from one machine to another over the network
50My Network PlacesThe receiving station finds the remote file using My Network Places
51Moving the Word Document Drag and drop the Word document from My Network Places to the Desktop
52DisassemblyThe sending system chops the packet into segments and assigns sequence numbers
60Early NetworkingIn the early days of networking each company designed the networking process from the ground upThese proprietary systems could not talk to each otherFor networking to grow a model needed to be created to standardize the process
61OSI ModelThe International Organization for Standardization (ISO) proposed the Open System Interconnection (OSI) ModelThe OSI Model is a seven-layer model that describes the networking processISO is derived from the Greek word isos, which means equal.
62OSI’s Seven Layers Layer 7 Application Layer 6 Presentation Layer 5 SessionLayer 4TransportLayer 3NetworkLayer 2Data LinkLayer 1PhysicalExam TipMemorize both the layer number and the name of each OSI layer.
63Modular Design Each protocol is designed to deal with a specific layer Each protocol needs to know how to interface with the layer immediately above and below itThese layers are not laws of physics – anybody that designs a network can do it any way they want. While many protocols fit neatly into one of the seven layers, others do not.
64Layer 7 - ApplicationDefines a set of tools that programs may use to access the networkHTTPFTPMicrosoft APIs
65Layer 6 - PresentationPresents data from the sending system in a form that applications on the receiving system can understandASCII and Unicode text formatsEncryptionCompressionTranslates between different machine languages
66Layer 5 - SessionManages the connections between machines on the networkConnections may be for file transfers, for print jobs, for , or many other possibilitiesAllows machines to keep track of who they are talking to
67Layer 4 - TransportBreaks up data it receives from the upper layers into smaller pieces for transportOn the receiving side the packets are reassembled from lower layersProvides for error checkingLayer 4 is a pivotal layer in the processLower layers are concerned with moving data from point A to point BUpper layers deal with the data
68Layer 3 - NetworkHelps to get packets from network to network by adding unique identifiers (like IP addresses) to the packets
69Layer 2 – Data LinkDefines the rules for accessing and using the Physical layerSpecifies the rules for identifying devicesDetermines which machine may use the network at a given timeChecks for errorsThe Data Link layer is divided into two sub-layers:Media Access Control (MAC)Logical Link Control (LLC)The LLC layer sits above the MAC layer and under the Network layer.The MAC sub-layer controls access to the Physical layer. It encapsulates frames, adds source and destination MAC addresses and error checking, and decapsulates data at the receiving station.The LLC sub-layer provides an interface with Network layer protocols. It provides for flow control and retransmission of corrupt packets.
70Layer 1 - PhysicalDefines the physical form taken by data when it travels across a cableDefines how ones and zeros are turned into actual electrical signals on a wire, light pulses on a fiber optic cable, or radio waves in a wireless network
71NICs and LayersNetwork Interface Cards work at both layer 2 and layer 1When it is said that a NIC is a layer 2 device, keep in mind that it also functions as a layer 1 device