Grayhill EZCOMWL24IP Wireless LAN Router User Manual EZCom IP Users Manual A6

Grayhill Inc Wireless LAN Router EZCom IP Users Manual A6

User manual for product

IP Users ManualRevision A6Friday, January 26, 2001

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 2 Of 54Table Of ContentsGetting Started.....................................................................................................................4Initialization ..................................................................................................................... 4EZCom-IP Explorer Introduction ................................................................................. 4Point-to-Point Link Example........................................................................................ 6Windows TCP/IP Set Up ...................................................................................................13Multipoint Store-&-Forward Example ........................................................................ 14Technical Reference..........................................................................................................18Introduction ................................................................................................................... 18Protocols And Protocol Architecture............................................................................. 19A Simple Model ......................................................................................................... 20The TCP/IP Protocol Architecture ............................................................................. 21TCP/IP Communications............................................................................................... 23The TCP/IP Protocol Stack ....................................................................................... 23Application Layer....................................................................................................... 23Transport Layer ......................................................................................................... 23User Datagram Protocol............................................................................................ 25Network Layer ........................................................................................................... 26Overview of TCP/IP Addresses................................................................................. 26Internet Protocol Routing........................................................................................... 28The ROUTE Utility Program...................................................................................... 31Finding Another Machine’s Address ......................................................................... 32Ethernet Physical Layer ................................................................................................ 34MAC Frame............................................................................................................... 34Routing, Putting All of the Pieces Together .............................................................. 34Subnetting..................................................................................................................... 35How Do You Subnet?................................................................................................ 35Determining Your Addressing Needs .................................................................... 35Remembering Binary................................................................................................. 35Defining Your Subnet Mask................................................................................... 36Finding Out How Many Networks, How Many Hosts............................................. 37Subnet IDS............................................................................................................. 37EZCom IP Routing ........................................................................................................ 40Introduction................................................................................................................ 40Indicators and Connectors ........................................................................................ 43Grayhill EZCom-IP Explorer Program ...............................................................................44Introduction................................................................................................................ 44Views ......................................................................................................................... 44Menus & Tool Bar...................................................................................................... 45Control Tabs.............................................................................................................. 46Troubleshooting Guide ......................................................................................................50LED Activity B ............................................................................................................... 50No Ethernet Link indicator............................................................................................. 50Link Test Failed ......................................................................................................... 50Ping Failed to Respond............................................................................................. 51Ethernet (CSMA/CD) .........................................................................................................52Precursors ................................................................................................................. 52Description of CSMA/CD........................................................................................... 53

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 3 Of 54List Of Tables & FiguresTable 1, Factory Default Settings ....................................................................................... 4Table 2, Point-To-Point Setup Parameters ........................................................................ 6Table 3, Example II, EZCom-IP Radio Settings ............................................................... 14Table 4, Example II Device IP Addresses ........................................................................ 15Table 5, Routing Table for 192.168.1.2 (EZCom-IP radio)............................................... 16Table 6, Routing Table for 192.168.1.1 (PC) ................................................................... 16Table 7 Store & Forward Example Routing Summary ..................................................... 16Table 8, Bit Position Values.............................................................................................. 27Table 9, TCP/IP Address Classes—First Octet................................................................ 27Table 10, Address Class Summary.................................................................................. 28Table 11, Active Routes: .................................................................................................. 30Table 12, Extracting a Network ID Using a Standard Subnet Mask................................. 36Table 13, Extracting a Network ID Using a Custom Subnet Mask................................... 36Table 14, Extracting the Target Network ID Using Standard and Custom Masks ........... 36Table 15, Creating a Custom Subnet Mask by Adding Subnetting Bits........................... 37Table 16, Valid Subnet Numbers...................................................................................... 37Table 17 Calculating the Subnet IDs Using Binary .......................................................... 38Table 18, Subnet IDs for a Three-Bit Subnet Mask.......................................................... 38Table 19, Table for Calculating Subnet Mask, IDs, and Number of Subnets................... 38Table 20 Finding the Last Host ID by Subtraction............................................................ 39Table 21 Host IDs for a Subnetted (lP) Address .............................................................. 39Table 22, Finding the Last Host ID by Subtraction........................................................... 39Table 23, Host IDs for a Subnetted Class C Address ...................................................... 39Table 24, Typical EZCom-IP Radio Routing Table .......................................................... 41Figure 1, Local Connection................................................................................................. 4Figure 2, EZCom Explorer Window.................................................................................... 5Figure 3, Point-to-Point Link ............................................................................................... 6Figure 4, EZCom-IP Explorer After Finding a Radio .......................................................... 8Figure 5, IP Address Tab.................................................................................................... 8Figure 6, Radio Settings Tab.............................................................................................. 9Figure 7, EZCom-IP Routing Table .................................................................................... 9Figure 8, Diagnostics Tab................................................................................................. 10Figure 9, Link Test Dialog................................................................................................. 11Figure 10, Ping Utility Program......................................................................................... 11Figure 11, Example II Network layout............................................................................... 14Figure 12, TCP/IP Protocol Stack..................................................................................... 22Figure 13, IP Address Formats......................................................................................... 28Figure 14, IP Routing Logic .............................................................................................. 29Figure 15, ARP Packet..................................................................................................... 32Figure 16, IEEE 802.3 frame format................................................................................. 34Figure 17, More Networks Mean Fewer Hosts Per Network & Vice Versa...................... 36Figure 18, EZCom-IP Routing Mechanism....................................................................... 40Figure 19, EZCom processing done at IP layer ............................................................... 40Figure 20, EZCom-IP Indicators....................................................................................... 43Figure 21, EZCom Explorer Window................................................................................ 44Figure 22, Control Tabs.................................................................................................... 46

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 4 Of 54Section1. Getting StartedInitializationWhen you first remove an EZCom IP radio from it’s carton and apply power to it, the radiowill boot-up and go through a series of self-tests. After completing the boot process theradio will be ready to receive configuration information. Before the radio can be used totransmit or receive application specific information (network traffic) it must first beconfigured for the network that it will be used on. All necessary configurations can bedone using the Grayhill EZCom-IP Explorer program.A listing of all the EZCom-IP parameters along with the factory default settings for eachparameter is given in Table 1, below. In this first section “Getting Started” we will practiceconfiguring some EZCom-IP radios for specific examples. First we will setup a point-to-point link typical of what you may want to institute for a bench test and then we will moveon to a more involved example that will demonstrate some of the more advancedfeatures of you EZCom-IP radio. For readers that are looking for a more detailedexplanation of specific settings please refer to the Technical Reference section of thismanual.Table 1, Factory Default SettingsParameter Factory Default CommentsRadio IP Address 192.168.1.1Network Subnet mask 255.255.255.0Radio Mac Address ******-****** Factory set unique valueRouting Table NoneCenter Frequency 2.442 GHz Approximately Center of BandConfiguration can be accomplished through a local connection or remotely over the air. Alocal or direct connection is when an EZCom-IP radio is connected to the local areanetwork where you have the Grayhill EZCom-IP Explorer program running as illustratedin Figure 1. Remote configuration can be accomplished over the air provided that theremote EZCom-IP radio is already set to operate at the same center frequency as thelocal radio. Remote configuration is discussed in detail in the Technical Referencesection of this manual.Figure 1, Local ConnectionEZComEZCom-IP Explorer IntroductionBefore we start on the examples in this section let’s take a few minutes to familiarizeourselves with the EZCom-IP Explorer program. If you have not loaded the GH EZCom-IP Explorer program please do so now. The Explorer is a client side program that can berun on any 32 bit Windows based PC. It is designed to communicate configuration anddiagnostic information with the EZCom-IP radios either directly attached or via the localarea network. The program offers the user a verity of configuration and diagnostic tools.Figure 2, below illustrates the initial screen of the Explorer program. The screen isdivided into three main parts;

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 5 Of 541. The Network View, which graphically displays the EZCom-IP, radios in thenetwork.2. The Control Tabs that can be used to change configuration settings and initiatediagnostic functions.3. The Monitor, which can be used to observe specific communication events.When you first start the Grayhill EZCom-IP Explorer your will see a single icon in theNetwork View. This icon represents the computer that is running the GH Explorerprogram. No other icons appear at this time because the Explorer program must beprompted to go out and find any radios in the network first. If you click on the Tools menuand then pick Find Links the Explorer will go out and find any EZCom-IP radios on thelocal network.Figure 2, EZCom Explorer WindowGH Explorer will then add a radio icon to the Network View for each radio it finds on thelocal network (see Figure 4).The information in the Control Tab window is associated with the icon selected in theNetwork View. As you click on different icons in the Network View the information in theControl Tab View is updated with the setup values from the object represented by theicon selected. If you select the GH Explorer icon at the top of the window (which isselected by default when you start the program) only the IP address tab is accessible.This is because the GH Explorer icon points to the PC that the program is running on andnot to a radio. When you select a radio icon in the Network View the information in theControl Tab will be downloaded from the radio and displayed in the appropriate tab. If youchanging any of the information in the Control Tab and click the update button the setupinformation in the radio pointed to by the icon in the Network View will be changedaccordingly.As you can see changing the setup information in a radio is as simple as selecting whichradio you want to modify from the Network View and then entering the appropriateinformation in the Control Tab view.NetworkViewControlTabsMonitor

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 6 Of 54Point-to-Point Link ExampleIn this first example we will set up a point-to-point link between two Ethernet networks.For simplicity we have represented both networks as consisting of one PC and oneEZCom-IP radio (router). In reality a point-to-point configuration could be used to connectanything from a single PC and router to a fully developed enterprise network. After wehave set up the example we will uses some of the built-in EZCom diagnostic tools to testour setup. After we complete our testing we will try a few simple client server applicationsthat are part of the windows operating system to demonstrate the functionality of thenetwork.You will need 2 PCs and 2 EZCom-IP radios to fully implement this first example. Youmay also need to have your operating system CD handy in the event that Windows wantsto copy additional files. If you don’t have 2 PCs you can still set up the example with onlyone PC but you will only be able to run the built in diagnostic functions of the EZCom-IPradio you will not be able to run the applications.Figure 3, Point-to-Point LinkEthernet192.168.1.0Ethernet192.168.2.0192.168.1.2 192.168.2.2192.168.1.1 192.168.2.1There are 3 basic steps involved in setting up this example: setting the IP addresses onthe two PCs, configuring the radios, and setting file share permissions on one of the PCsto allow file access across the network. Table 2 shows each step along with theparameters that need to be setup and the appropriate values.Table 2, Point-To-Point Setup ParametersStep Parameter Value For PC (A) &Radio (A) Value For PC (B) &Radio (B)IP Address 192.168.1.2 192.168.2.2Subnet Mask 255.255.255.0 255.255.255.01. Set PC IPAddressesDefault Gateway 192.168.1.1 192.168.2.1IP Address 192.168.1.1 192.168.2.1Subnet Mask 255.255.255.0 255.255.255.0Default Gateway 192.168.2.1 192.168.1.12. Set RadioParametersRouting Table Default Default3. Set File SharePermissions File and Print sharingfor MicrosoftNetworks installedBoth PCs must have an Ethernet network interface card or equivalent PCMCIA cardinstalled and both PCs must also have the TCP/IP protocol installed. For information oninstalling your network interface card see the card manufactures installation instructions.For help installing the TCP/IP protocol, please see the sidebar Windows TCP/IP Set Upon page 13 of this manual.To get started with this example take a RJ45 Category 5 patch cable and connect oneend of it to the Ethernet port on your EZCom-IP radio and connect the other end to anopen port on your network hub. If you do not have an existing network you can connectdirectly to the PC’s NIC card or PCMCIA card. Now apply power to the EZCom-IP radio

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 7 Of 54and the PC. After the PC and radio have gone through their normal boot process youshould see a green link indicator (see Figure 20, on page 43). If you do not see the greenlink indicator please follow the steps in the troubleshooting guide for “No Ethernet Link”.Now that we have a physical connection between the client PC that will be running theEZCom-IP Explorer and an EZCom-IP radio we can begin to setup our first example.Setting-up The PC’s IP Address1. Click the Start button. Choose Settings, ThenControl Panel.2. Double-click the Network icon. Your Networkwindow should pop up as shown on the right.3. Select the Configuration tab.4. Highlight TCP/IP (for your network adaptor)under the list of components installed.5. Click the Properties Button. You should nowsee the TCP/IP properties window below.6. Select the IP Address tab.7. Make sure the Specify IP Address option isselected.8. Enter the appropriate IP Address and Subnet Mask (from the setup table on page 6)in the spaces provided.9. Now select the Gateway tab10. Enter the Default Gateway (again from the setuptable) and make sure you click the ADD button.11. Click the OK button on the TCP/IP PropertiesWindow.12. Click the OK buttonon the NetworkWindow.After clicking the OKbutton on the TCP/IPproperties tab you willbe prompted to rebootyour computer beforetheses changes will take effect. Click OK. The IP Address, Subnet Mask and Default Gateway arenow set up on your PC. Repeat these steps using theappropriate setup values for the second PC in thenetwork. You may wish to reopen either one of theproperties windows to verify the values match those listed in the example’s setup table.In the next step we will setup the radio parameters for the EZCom-IP radios that will beused in this example.Setting-up The Radio ParametersStart the Grayhill EZCom-IP Explorer by selecting “EZCom-IP Explorer” from your PC’sStart/Programs menu. After the program loads select Find Links from the Tools menu atthe top of the explorer main screen. The Searching for Radios dialog box will appear.

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 8 Of 54Once the searching process is complete press OK to return to the EZCom-IP Explorermain window.Figure 4, EZCom-IP Explorer After Finding a RadioThe Explorer should now look like the one shown in Figure 4, above. Don’t worry if the IPaddresses and other data on your screen are not exactly as shown. What is important isthat there is an EZCom-IP radio icon below the GH Explorer icon in the Network View.Click on the radio icon. The data in the Control Tab window will update to reflect thecurrent settings for the radio you just selected. If the radio you are using is new thesettings should look like those listed in Table 1, Factory Default Settings on page 4.The first Control Tab is the IP Address Tab, which is shown in Figure 5. On this tab wewill set the radio’s IP Address, Subnet Mask and Default Gateway. In each of therespective text boxes please enter the appropriate setting from Table 2, Point-To-PointSetup Parameters on page 6. When you are done your IP Address tab should look likethe one shown in Figure 5 below.Figure 5, IP Address TabEZCom-IPRadioExplorerIcon

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 9 Of 54Don’t worry if you do not fully understand each of the settings that you are about to enter,we will cover each of the settings in more detail in the technical reference section latter inthis manual.Now click the Radio Tab. You should not have to change any settings on this tab. All ofthe factory defaults settings should be fine. You may just want to look over the valuesand verify that they match those shown if Figure 6. If any of your values are differentplease change them to match.Figure 6, Radio Settings TabNow click the Routing Tab. The routing table should contain two entries, which werecreated automatically by the Explorer program. For our example all routing is actuallyhandled by the Default Gateway setting that we established on the IP Address Tab. Ifthere is any other entries in your routing table select them by clicking any where on therow and then click the Delete button. Repeat this step for all extra entries. Your routingtable should look like the one shown in Figure 7 below.Figure 7, EZCom-IP Routing Table

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 10 Of 54Setting Up The Second PC & RadioNow that we have completed setting up our first PC and an EZCom-IP radio we will needto repeat the steps we followed with the second PC and radio. For the second PC andradio use the setup information listed in the last column of Table 2 on page 6.Testing The Radio LinkWith both PCs and both radios setup we can now run a few diagnostic test to verify thatwe first have a link between the radios and then a network connection from one PC to theother. First connect the radios and PCs as shown in Figure 3. Make sure that youconnect the radios to the PC with the same subnet ID.The first test that we will conduct will be a link test. This is to verify that the radios cancommunicate. This is strictly a radio communications test and none of the networksettings are used. Select the Diagnostics Tab then click on the Link Test button. The linktest dialog box will appear. Enter the Mac Address of the radio you want to link to andclick on the Run Test button.Figure 8, Diagnostics TabIn the Test Results window you will see an announcement that the test is in progress.During a link test packets are transmitted every 50 milliseconds. If you multiply theNumber of packets by this interval you can get an idea of how long the test will take.Using the default number of packets the test should take 100*0.05 or just over a halfsecond.

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 11 Of 54Figure 9, Link Test DialogWhen the Link test is complete you should see the test results in the Link Test dialogsimilar to the results shown in Figure 9. If your Link Test fails, that is you don’t get a largenumber of Successful packets (typically 90% to 100%), please follow the steps listed inthe Troubleshooting guide on page 50.After successfully running a link test we will now verify that we have a logical networkconnection from one PC to the other. To accomplish this we will use one of the Windowsbuilt in network utilities known as “Ping”. Actually ping is a member of the TCP/IP protocolsuite.Ping is a simple but very useful utility program, ping sends a special (ICMP) test packetto a designated IP address and then listens for the packet to be echoed back. Figure 10 shows the output of a ping request. To run the Ping utility program click Startthen select Programs and click on the MS-DOS Prompt. When the DOS Window openstype the word ping along with the IP address of the host that you want to ping and pressenter. Ping will then transmit 4 test packets and output the round trip time it takes foreach packet to traverse the network. If you are unable to successfully ping the remote PCin this example please follow the trouble shooting procedures on page 51 for “Ping Failedto Respond”. Figure 10, Ping Utility ProgramIf you have successfully run the link test and ping test you are ready to setup yourapplication to run across the wireless network.Running our example applicationBefore we can run an application across the wireless link we must first install the File andPint sharing for Microsoft Networks service. This service is built in to the Microsoft

$Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 12 Of 54Windows operating system and in essence enables the PC it’s running on to act as a fileand/or print server.To enable file and printer sharing on your computer1. Click on the Start Button and select Settings and Control Panel.2. After the Control Panel dialog box opens double-click the Network icon.3. Click File and Print Sharing.4. Select the check box for the “I want to give others access to my files”, sharingoption. A check mark indicates the feature is activated.5. Click OK.6. Windows will now install the File & Print Sharing service on your PC. You will beprompted that you must restart your computer before these changes will takeeffect. Click OK,After your computer reboots you will need to tell windows which files or folders you wantto share on the network. For this example we are going to simply share the entire C drive.To share The C Drive1. In Windows Explorer or My Computer, click the C drive root folder.2. On the File menu, click Properties.3. Click the Sharing tab, and then click Shared As. Enter the share name “ServerDrive”. Note: The Sharing tab is not visible if you don’t have file and print sharingservices enabled.4. Click the Access Type you want, and, if necessary, enter a password.Running Our Example ApplicationNow that we have File and Print sharing setup on our 192.168.2.2 PC we will access thefiles on this machine from our 192.168.1.2 PC, which is at the other end of our wirelesslink. The first thing we need to do is to make the Windows operating system on192.168.1.2 aware of the network connection to 192.168.2.2. Start by:1. Double clicking the My Computer icon on your windows desktop.2. After the My Computer dialog opens, in the Address Bar type \\192.168.2.2\.3. Just below the address bar you will see a dropdown list with the share name“Server Drive”. This is the share name we gave to the c drive on 192.168.1.2.Select the Server Drive share name by clicking on it.4. The My Computer window should now be a listing of the files and folders on the192.168.2.2 c drive. Now click on the Favorites menu and select Add toFavorites.You can now use the Server Drive just as though it was a hard drive in your 192.168.1.2PC. Try by copying or accessing any of your data files just as you would if there were onyou c drive.$

$Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 13 Of 54Windows TCP/IP Set UpFollow these instructions to install the TCP/IP protocol on your PC only after a networkcard has been successfully installed. These instructions are for Windows 95 andWindows 98. For TCP/IP setup under Windows NT or Windows 2000, please refer toyour operating system manual.1. Click the Start button. Choose Settings, then Control Panel.2. Double-click the Network icon. Your Network window should pop up. Select theConfiguration tab.3. Click the Add button.4. Double-click Protocol.5. Highlight Microsoft under the list of manufactures.6. Find and double-click TCP/IP in the list to the right.7. After a few seconds you should be brought back to the main Network window. TheTCP/IP Protocol should now be listed.8. Click OK. Windows may ask for the original Windows installation files. Supply themas needed (i.e.: D:\win98, D:\win95, C:\windows\options\abs.)9. Windows will ask you to restart the PC. Click Yes.The TCP/IP Installation is complete.$

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 14 Of 54Multipoint Store-&-Forward ExampleThis second example is designed to demonstrate in detail how to setup and utilize therouting functions available within a TCP/IP network using the EZCom-IP radio. It may notbe practical to setup this example because it requires at least 4 EZCom-IP radios, 4 PCs,and a WAND router. Even if you do not setup the example it is beneficial to follow alongto develop an understanding of how to setup the different routing aspects of the network.In our first example we relied on the default Gateway settings for both the PCs and theEZCom-IP radio to handle all of the routing decisions. No routing table entries weremade. In this example we will endeavor to more fully illustrate the routing capabilities ofthe EZCom-IP radio.Figure 11, Example II Network layoutEthernet192.168. 1. 0Ethernet192.168. 4. 0Ethernet192.168. 3. 0Ethernet192.168. 2. 0RouterInternetThe first step in setting up this example is to program the IP address and other settings inthe EZCom-IP radios. Probably the easiest way to handle this task is to take one PC,which has the EZCom-IP Explorer program installed on it and directly connecting it toeach of the radios one after the other. For information and instructions on how to performthe setup tasks from a single point in the network please refer to EZCom-IP Exploredocumentation on page 44. Table 3, below is a listing of all the settings for both the IPAddress Tab and the Radio Tab that need to be set up. Most of these settings are thefactory default settings and should already be set.Table 3, Example II, EZCom-IP Radio SettingsTab Setting Radio A Radio B Radio C Radio DIP Address 192.168.1.2 192.168.2.2 192.168.3.2 192.168.4.2Default Gateway 192.168.1.3 192.168.1.2 192.168.1.2 192.168.3.2IP AddressSubnet Mask 255.255.255.0 25.255.255.0 255.255.255.0 255.255.255.0* TX & RX Center Frequency 2.441-GHz 2.441-GHz 2.441-GHz 2.441-GHz* PN Code (Hex) 05B8 05B8 05B8 05B8* Modulation BPSK BPSK BPSK BPSKRadio* Transmit Att. level 0 dB 0 dB 0 dB 0 dB* Indicates Factory Default SettingsOnce we have the radio settings complete we will need to setup the TCP/IP proprietiesfor the remaining devices on the four separate subnets. For this example all four subnets

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 15 Of 54are part of the same network. The IP style network ID is 192.168.0.0 with a subnet maskof 255.255.255.0. Therefore the third byte of the IP address is the subnet ID. Theindividual subnets are simply identified as (.1), (.2), (.3) & (.4). All of the devices on allfour subnets have the same subnet mask 255.255.255.0.The IP addresses for each of the devices in the network are listed in Table 4 below. If youneed help setting the IP addresses on the PCs please refer to Setting-up The PC’s IPAddress in the first example on page 4. If you need help setting up the IP address of yourrouter please refer to the manufactures instructions.Table 4, Example II Device IP AddressesSubnet PC EZCom-IPRadio Router(.1) 192.168.1.1 192.168.1.2 192.168.1.3(.2) 192.168.2.1 192.168.2.2 NA(.3) 192.168.3.1 192.168.3.2 NA(.4) 192.168.4.1 192.168.4.2 NANext we need to establish the routing tables for each of the devices in the network.Before we jump into entering routing table information lets take a moment or two anddiscuss the routing requirements. If you are uncertain as to what we mean when we aretalking about routing tables and default gateways you can refer to EZCom IP Routing onpage 40 of this manual.Subnet (.1) consists of three devices: a PC, a router and an EZCom-IP radio. One port onthe router is connected to our subnet and another is connected to the Internet. Theprimary purpose of the router is to allow Internet access to all of the PCs in our network.Therefore all of the other subnets need to be able to communicate with subnet (.1).Subnet (.4) as shown in Figure 11, is only able to communicate with subnet (.3) thereforewe will need to route subnet (.4) traffic through subnet (.3).Subnet (.2) can only communicate with subnet (.1) therefore we will have to route anytraffic from subnet (.2) to either subnet (.3) or subnet (.4) through subnet (.1).Since subnet (.2) can only communicate with subnet (.1) we can set the default gatewayon subnet (.2)’s EZCom-IP radio to 192.168.1.2. This will cause the radio to forward allpackets that are not specifically targeted for devices on subnet (.2) to subnet (.1). Inaddition to setting the radio’s default gateway we also need to set subnet (2)’s PC defaultgateway to 192.168.2.2. This will direct all datagrams that are not destine for a subnet(.2) device to the radio.The setup for devices on subnet (.4) are similar to what we just described for subnet (.2).First we need to set the default gateway on the PC to 192.168.4.2 this will direct all datatraffic not intended for a device on subnet (.4) to the radio for transmission. Next we needto set the default gateway of the radio to 192.168.3.2. This indicates to the radio that alldatagrams arriving from the network should be transmitted to the radio on subnet (.3).The settings for subnet (.3) are slightly different than subnets (.2) & (.4) because theradio on subnet (.3) can communicate with both subnet (.1) and (.4). First we will set thedefault gateway on the PC to 192.168.3.2 thus all datagrams not intended for subnet (.3)will be forwarded to the radio for transmission. Next we will have to set the defaultgateway on the radio to 192.168.1.2 this will handle the bulk of the traffic assuming thereis a lot of Internet activity. In addition to the default gateway setting we will also need toadd a route to the routing table in the radio to forward subnet (.4) packets to the radio on(.4). Add the following route: (Destination 192.168.4.0, Subnet Mask 255.255.255.0, NextHop 192.168.4.2). Please refer to the Routing Tab section on page 47 of this manual forspecific instructions on how to enter a route in the radios routing table.

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 16 Of 54Now for subnet (.1), first we will need to set both the PC’s and radio’s default gateways to192.168.1.3. This will insure that all packets not specifically addressed to one of oursubnets be forwarded to the Internet router. Next we need to add routes to the radio’srouting table for all packets destined for one of our subnets. This will entail entering threeseparate routes as shown in Table 5 below.Table 5, Routing Table for 192.168.1.2 (EZCom-IP radio)Destination Subnet Mask Next Hope Interface Origin192.168.2.0 255.255.255.0 192.168.2.2 Radio EZCom192.168.3.0 255.255.255.0 192.168.3.2 Radio EZCom192.168.4.0 255.255.255.0 192.168.3.2 Radio EZComWe will also need to add the following routes to the subnet (.1) PC’s routing table and tothe Internet routers routing table as well. If you are not familiar with the adding a route toyour PC’s routing table please refer to the sidebar “The ROUTE Utility Program” on page 31 of this manual. For adding routes to your routerplease refer to the manufactures instructions.Table 6, Routing Table for 192.168.1.1 (PC)Destination Subnet Mask Next Hope Interface192.168.2.0 255.255.255.0 192.168.1.2192.168.3.0 255.255.255.0 192.168.1.2192.168.4.0 255.255.255.0 192.168.1.2These PC routes were added to direct any datagrams generated by the PC destine forone of our subnets to the radio for transmission. This is necessary because we havealready set the default gateway at the PC to 192.168.1.3, which is the Internet router. Onall of our other subnets we did not need to make individual route entries because anydatagrams that needed to be routed outside the local subnet where handled by thedefault gateway entry. Subnet (.1) on the other hand has two routers, the Internet routerand the EZCom-IP radio.In summary to setup the network illustrated in Figure 11 on page 14 you would first needto set each device IP address as listed in Table 4 and then you would have to establishthe routing tables which are summarized in Table 7.Table 7 Store & Forward Example Routing SummarySubnet Device Device IPAddress Route Type Target Next HopDefault Gateway 0.0.0.0 192.168.1.3Add Route 192.168.2.0 192.168.1.2Add Route 192.168.3.0 192.168.1.2PC 192.168.1.1Add Route 192.168.4.0 192.168.1.2Default Gateway 0.0.0.0 192.168.1.3Add Route 192.168.2.0 192.168.2.2Add Route 192.168.3.0 192.168.3.2Radio 192.168.1.2Add Route 192.168.4.0 193.168.3.2Add Route 192.168.2.0 192.168.1.2Add Route 192.168.3.0 192.168.1.2(.1)Router 192.168.1.3Add Route 192.168.4.0 192.168.1.2PC 192.168.2.1 Default Gateway 0.0.0.0 192.168.2.2(.2) Radio 192.168.2.2 Default Gateway 0.0.0.0 192.168.1.2PC 192.168.3.1 Default Gateway 0.0.0.0 192.168.1.2Default Gateway 0.0.0.0 192.168.1.2(.3) Radio 192.168.3.2Add Route 192.168.4.0 192.168.4.2PC 192.168.4.1 Default Gateway 0.0.0.0 192.168.4.2(.4) Radio 192.168.4.2 Default Gateway 0.0.0.0 192.168.3.2

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Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 18 Of 54Section2. Technical ReferenceIntroductionThe technical reference section of this manual is intended to develop a basic overview onthe subject of network technology, sufficient in detail to explain the routing function of theEZCom-IP radio. It is not intended to be an exhaustive coverage of the subject but it doseburrow in to some detail of the lower level protocols. Although much of what is presentedis germane to all forms of network communications, the examples and illustrations arebiased toward Ethernet IP applications because it is the underling technology of theEZCom-IP radio.Many of the subsections that follow are relatively generic in nature and may seemremedial to some readers. The following list describes each section and presentsrecommendations as to who should read those sections and who can feel free to skipthem to focus on the EZCom-IP specific information.1. Protocols And Protocol Architecture starts off with a basic introduction to theconcept of a protocol stack it then moves on to a general description of theInternet Protocol. If you are already familiar with the idea of a protocol stack youcan skip right to the descriptions of the IP protocol. If you are already familiar withthe IP protocol also. please feel free to skip this section entirely.2. TCP/IP Communications presents an overview of the TCP/IP protocol stackwith a detailed description of the IP protocol. The section is divided into foursubsections: The Application Layer, The Transport Layer, The Network Layerand The Physical Layer. Having a through understanding of the TCP/IP protocolis not necessary for the application of the EZCom-IP radio. This section ispresented for the advanced user. If you are in a hurry you may want to just readthe network layer subsection.3. Subnetting. This is a fairly lengthy section that goes into some detail regardingwhy and how to subnet. Subnetting is one of the more important topics dealt within this manual. A good understanding of the subject matter will greatly improveyour ability to establish large distributed wide area networks. Any one not alreadyfamiliar with Subnetting and considering using the EZCom-IP radio in a large-scale distributed network should read this material.4. EZCom IP Routing - This section briefly goes through the EZCom-IP routingmechanism. Its brevity is primarily due to the simplistic nature of the routingscheme. Anybody who wants to gain even an intuitive understanding of theEZCom-IP radio should read this section. It will help you maximize thefunctionality of an EZCom-IP extended network.5. Connectors and Indicators. Briefly introduces you to the indicators on the faceof the radio.6. EZCom-IP Explorer program This section goes through all if the menu picksand program dialogs explaining where specific information is entered and whereappropriate also offers some guidance as to what should be entered.

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 19 Of 54Protocols And Protocol ArchitectureWhen computers and/or other data processing devices such as PLC’s exchange data,there must be a data path between the two computers, via a communication network.Although, a data path alone is not sufficient to establish communications, more isneeded. Typically the following tasks also need to be performed:1. The source system must inform the communication network of the identity of thedesired destination system.2. The source system must ascertain that the destination system is prepared toreceive data.3. The application on the source system must ascertain that an application on thedestination system is prepared to accept the data for a particular use.4. If the data formats used on the two systems are incompatible, one or the othersystem must perform a format translation function.It is clear that there must be a high degree of cooperation between the two computersystems. The exchange of information between computers for the purpose of cooperativeaction is generally referred to as data communications. Similarly, when two or morecomputers are interconnected via a communication network, the set of computer stationsare referred to as a computer network.In this discussion of computer networks, two concepts are paramount, Protocols andProtocol Architectures.A protocol is used for communication between entities in different systems. The terms"entity" and "system" are used in a very general sense. Examples of entities are userapplication programs, file transfer packages, database management systems, electronicmail facilities, etc. Examples of systems are computers, PLCs, and remote sensors.In general, an entity is anything capable of sending or receiving information, and asystem is a physically distinct object that contains one or more entities. For two entities tocommunicate successfully, they must "speak the same language." What iscommunicated, how it is communicated, and when it is communicated must conform tosome mutually acceptable conventions between the entities involved. The conventionsare referred to as a protocol, which may be defined as a set of rules governing theexchange of data between two entities. The key elements of a protocol are• Syntax, which includes such things as data format and signal levels.• Semantics, which includes control information for coordination and errorhandling.• Timing, which includes speed matching, and sequencing.Having introduced the concept of a protocol, we can now introduce the concept ofprotocol architecture. It is clear that there must be a high degree of cooperation betweenthe two computers. Instead of implementing the logic for this as a single module, the taskis broken up into subtasks, each of which is implemented separately. Thus, instead of asingle module for performing communications, there is a structured set of modules thatimplements the communications function. That structure is referred to as a protocolarchitecture or protocol stack. In the remainder of this section, we will present a simplifiedprotocol architecture. Followed by an introduction to the more complex TCP/IP protocolstack.

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 20 Of 54A Simple ModelIn very general terms, data communications can be said to involve three agents:applications, computers, and networks. The applications execute on computers that canoften support multiple simultaneous applications. The computers are connected to thenetwork, and the data to be exchanged is transferred by the network from one computerto another. Thus, the transfer of data from one application to another involves first gettingthe data to the computer in which the application resides and then getting it to theintended application within the computer.With this concept in mind, it appears natural to organize the communication task intothree relatively independent layers:• Application layer• Transport layer• Network access layerThe network access layer is concerned with the exchange of data between a computerand the network to which it is attached. The sending computer must provide the networkwith the address of the destination computer, so that the network may route the data tothe appropriate destination. Thus, it makes sense to separate those functions having todo with network access into a separate layer.Regardless of the nature of the applications that are exchanging data, there is usually arequirement that data be exchanged reliably. That is, we would like to be assured that allof the data arrive at the destination application and that the data arrive in the same orderin which they were sent. As we shall see, the mechanisms for providing reliability areessentially independent of the nature of the applications. Thus, it makes sense to collectthose mechanisms in a common layer shared by all applications; this is referred to as thetransport layer.Finally, the application layer contains the logic needed to support the variousapplications. For each different type of application, such as file transfer program, aseparate module is needed that is peculiar to that application.To demonstrate this concept let us trace a simple operation. Suppose that an application,on computer A, wishes to send amessage to another application, oncomputer B. The application on Ahands the message over to itstransport layer with instructions to sendit to a specific application on computerB. The transport layer hands themessage over to the network accesslayer, which instructs the network tosend the message to computer B. Notethat the network need not be told theidentity of the destination application.All that it needs to know is that the datais intended for computer B.To control this operation, control information, as well as the original user data, must betransmitted. Let us say that the sending application generates a block of data and passesthis to the transport layer. The transport layer may break this block into two smallerpieces to make it more manageable. To each of these pieces the transport layer appendsa transport header, containing protocol control information. The combination of data andcontrol information is known as a protocol data unit (PDU); in this case, it is referred to asa transport protocol data unit. The header in each transport PDU contains controlApplicationTransportNetworkApplicationTransportNetworkPhyical LayerComputerBComputerA

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 21 Of 54information to be used by the peer transport protocol at computer B. Examples of itemsthat may be stored in this header include• Destination application. When the destination transport layer receives thetransport protocol data unit, it must know to whom the data are to be delivered.• Sequence number. Because the transport protocol is sending a sequence ofprotocol data units, it numbers them sequentially so that if they arrive out oforder, the destination transport entity may reorder them.• Error-detection code. The sending transport entity may include a code that is afunction of the contents of the remainder of the PDU. The receiving transportprotocol performs the same calculation and compares the result with theincoming code. A discrepancy results if there has been some error intransmission. In that case, the receiver can discard the PDU and take correctiveaction.The next step is for the transport layer to hand each protocol data unit over to thenetwork layer, with instructions to transmit it to the destination computer. To satisfy thisrequest, the network access protocol must present the data to the network with a requestfor transmission. Once again, this operation requires the use of control information. In thiscase, the network access protocol appends a network access header to the data itreceives from the transport layer, creating a network access PDU. Examples of the itemsthat may be stored in the header include• Destination computer address. The network must know to whom (whichcomputer on the network) the data are to be delivered.• Facilities requests. The network access protocol might want the network to makeuse of certain facilities, such as priority.With the concept of protocol architecture still fresh in our minds let jump right into theTCP/IP protocol stack because it is this architecture that the EZCom-IP radio supports.The TCP/IP Protocol ArchitectureTCP/IP is the most widely used interoperable network communications architecture inuse today. TCP/IP is a result of protocol research and development conducted on theexperimental packet-switched network, ARPANET, funded by the Defense AdvancedResearch Projects Agency (DARPA), and is generally referred to as the TCP/IP protocolsuite. This protocol suite consists of a large collection of protocols that have been issuedas Internet standards by the Internet Activities Board (IAB).There is no official TCP/IP protocol model, however, based on the protocol standards thathave been developed, we can organize the communication task for TCP/IP into fiverelatively independent layers:1. Application layer2. Host-to-host, or Transport layer3. Internet layer4. Network access layer5. Physical layerThe physical layer covers the physical interface between a data transmission device(e.g., computer or PLC) and a transmission medium or network. This layer is concernedwith specifying the characteristics of the transmission medium, the nature of the signals,the data rate, and related matters.The network access layer is concerned with the exchange of data between an endsystem and the network to which it is attached. The sending computer must provide the

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 22 Of 54network with the address of the destination computer, so that the network may route thedata to the appropriate destination.The network access layer is concerned with access to and routing data across a networkfor two end systems attached to the same network. In those cases where two devices areattached to different networks, procedures are needed to allow data to traverse multipleinterconnected networks. This is the function of the Internet layer. The Internet protocol(IP) is used at this layer to provide the routing function across multiple networks. Thisprotocol is implemented not only in the end systems but also in routers. A router is aprocessor that connects two networks and whose primary function is to relay data fromone network to the other on its route from the source to the destination end system. Thisis essentially what the EZCom IP radio dose.Regardless of the nature of the applications that are exchanging data, there is usually arequirement that data be exchanged reliably. That is, we would like to be assured that allof the data arrive at the destination application and that the data arrive in the same orderin which they were sent. The mechanism for providing this reliability is referred to as thehost-to-host layer, or transport layer. The Transmission Control Protocol (TCP) is themost commonly used protocol to provide this functionality.Finally, the application layer contains the logic needed to support the various userapplications. For each different type of application, such as file transfer program, aseparate module is needed that is peculiar to that application.Figure 12, TCP/IP Protocol StackMac headerLLC headerI P headerApplication DataTCP headerMAC trailerIP DatagramMAC FrameApplication layerTCP LayerIP LayerLLC LayerMAC LayerPhysical LayerFigure 12, shows how the TCP/IP protocols are implemented in end systems. Note thatthe physical and network access layers provide interaction between the end systems andthe network, whereas the transport and application layers are what is known as end-to-end protocols; they support interaction between two end systems. The Internet layer hasthe flavor of both. At this layer, the end system communicates routing information to thenetwork but also must provide some common functions between the two end systems.

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 23 Of 54TCP/IP CommunicationsThe TCP/IP Protocol StackIn the previous section we introduced the concept of Protocol Architecture and wedescribed the basic structure of the TCP/IP protocol stack. In this section will take acloser look at some of the individual protocols associated with the TCP/IP protocol stack.Most of our attention will be focused on the Internet Protocol (IP) because it isresponsible for routing of information on a TCP/IP network. Essentially an EZCom-IPradio is an IP router and as such relies on the IP protocol to implement routing function.Application LayerThe top layer of the stack is the Application layer. This is not where you find applicationssuch as Word or Excel, but rather where you find NetBIOS and Winsock (the two mainnetworking APIs in the Microsoft network architecture). These components provideservices to the actual applications that can call on the network by using these networkAPIs. As stated, the APIs provide a standard method for programmers to call on theservices of the underlying network without having to know anything about it.Sitting at this layer, you might also add an NCP (Netware Core Protocol) component toenable you to talk with or provide services to the Novell world, or maybe add an NFScomponent to enable you to work with the Network File System that is popular on theUnix platforms.Transport LayerOverview of TCPTCP is used to provide a connection-oriented delivery service for the higher-levelprotocols. To do this, TCP must first establish a session with the remote communicatinghost. It does this by means of a three-way handshake. First the host initiating thecommunications sends a packet to the other host that contains information about itselfand a SYN (or synchronize flag) telling the other host that a session is requested. Theother host receives this packet and responds with information about itself—the SYN flagand an ACK (acknowledgment) of the information that it received. Finally the first hostACKs the information it received from the other, and a session now exists between thetwo systems.At the end of the communication session, a similar three-way handshake is used to dropthe session with the remote host. This ensures that both of the hosts are throughtransmitting. It closes the session cleanly.Transmission Control Protocol (TCP)TCP provides reliable communication between processes that run on interconnectedhosts. This Transport layer functions independently of the network structure. TCP is notconcerned with routing data through the internetwork; the network infrastructure is theresponsibility of the IP layer. TCP on one host communicates directly with TCP onanother host, regardless of whether the hosts are on the same network or remote fromeach other.In fact, TCP is oblivious to the network. A wide variety of network technologies can beaccommodated, including circuit switching and packet switching on local and wide areanetworks. TCP identifies hosts by using IP addresses and does not concern itself withphysical addresses.

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 24 Of 54The main functions of TCP are:• Session establishment• Byte stream communications• Sliding windowsSession EstablishmentApplications using the TCP protocol must be able to open, close, and check the status ofsessions to allow them to communicate. To perform this function, TCP uses a three-wayhandshake. The handshake is important not only to create the session, but also inallowing the hosts to exchange data about their capabilities.The handshake starts when one host is asked by Winsock to open a connection (orsession). A TCP segment is generated to start the session, and the SYN control bit isturned on. This tells the other host that a session is requested. The host also includes inthe TCP header the starting Sequence number for this connection and the currentwindow size.The TCP segment is now sent to the other host, who acknowledges the segment,including its window size. The segment sent to acknowledge the first host also includesthe SYN control bit. Finally, the process ends when the first host acknowledges thereceipt of the other’s segment.After the hosts have completed their communications, the connection is closed in asimilar manner, the difference being that the FIN control bit is set rather than the SYN bit.Byte Stream CommunicationsWhen a connection (session) is established, the upper-layer protocol uses thisconnection to send data to the other host. The upper-layer protocols do not concernthemselves with formatting data to fit the underlying topology, but send the data as acontinuous stream.This process, called byte stream communications, means that TCP must have somemethod for dealing with a large volume of data that has no boundaries. Every byte in astream is assigned a Sequence number, enabling every byte sent, to be acknowledged. IfTCP sent each byte as a single package, this would be unmanageable. TCP thereforebundles the data stream it sends into segments; a segment contains chunks of data.The TCP header specifies the segment Sequence number for the first byte in the datafield, and each segment also incorporates an Acknowledgment number. Because you donot know which byte will be the first in a given segment, you must give each byte aSequence number. When TCP sends a segment, it retains a copy of the segment in aqueue (transmit window), where it remains until an acknowledgment is received.Segments not acknowledged are retransmitted.When TCP acknowledges receipt of a segment, it relieves the sending TCP ofresponsibility for all data in that segment. The receiving TCP then becomes responsiblefor delivering the data in the segment to the appropriate upper-layer process.Sliding WindowsThis is all necessary because of the way the Internet (or your intranet) works. Thesegments that you send could each take a different route. This might happen becauserouters can become busy or links could fail. Data must be buffered on the sending hostuntil the remote host has acknowledged it.The Sliding Window is the buffer that enables byte stream communications, and enablesTCP to guarantee the delivery of segments of data. During the session establishment, thetwo hosts exchange the current size of the receive window. This information is also

$Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 25 Of 54included in the TCP header of each and every segment sent. A host that iscommunicating sets the size of its send window to match the other host’s receivewindow.If you look at the data being transmitted, you would see a series of bytes. If you overlay awindow at the start of the data, you can see that a portion of the data falls into thewindow. This is the only data with which the TCP layer can work. The window cannotslide (move to cover more data) until all the data currently in the window is sent andacknowledged.As the data in the window is transmitted to the remote host, the retransmit timer is set foreach segment sent. The receiving host acknowledges the segments when its receivewindow fills to a predetermined amount (in Windows 98 & NT this is two consecutivesegments). When the sender receives the acknowledgment, it’s transmit window slidespast the acknowledged data and the next segments are transmitted.In the process of moving the data from point A to point B, many things might happen tothe segments being transmitted. They could be lost due to congestion at the routers, orcould be received out of sequence.If a packet is lost, the retransmit timer expires on the sending host, the segment isretransmitted, and the retransmit timer is set to two times the original value. Thiscontinues until the segment is acknowledged or the maximum number of retries has beenmade (about 16 seconds). If the data cannot be transmitted, TCP reports the conditionand you get an error message.In a case where the segments are received out of order, the receiving host sets thedelayed acknowledgment timer for the segment it did receive, and waits for othersegments to arrive. If the delayed acknowledgment timer (hard-coded to 200 ms) expires,TCP on the receiving host sends an acknowledgment for the segment it did receive.TCP Window SizeYou can adjust the size of the sliding window. Great care should be taken in adjusting thewindow size. If the window size is set too small, only a few packets can be sent at a time.This means that the system transmits the packets and then must wait foracknowledgments. If the size is set too large, network traffic delays the transmission.You can adjust the TCP window size under:HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\TCPIP\Paramters.The default is 8760, which is tuned for Ethernet. This setting affects only TCP, becauseUDP does not use a sliding window.User Datagram ProtocolTCP is a connection- or session-oriented protocol that requires hosts to establish asession, which is maintained for the duration of a transfer, after which the session isclosed. The overhead required to maintain connections is justified when reliability isrequired but often proves to be misspent effort.User Datagram Protocol provides an alternative transport for processes that do notrequire reliable delivery. UDP is a datagram protocol that does not guarantee datadelivery or duplicate protection. As a datagram protocol, UDP need not be concernedwith receiving streams of data and developing segments suitable for IP. Consequently,UDP is an uncomplicated protocol that functions with far less over-head than TCP.In the following several situations, UDP might be preferred over TCP as a host-to-hostprotocol:$

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 26 Of 54• Messages that require no acknowledgment. Using UDP can reduce networkoverhead. Simple Network Management Protocol (SNMP) alerts fall into thiscategory. On a large network, considerable SNMP alerts are generated becauseevery SNMP device transmits status updates. Seldom, however, is loss of anSNMP message critical. Running SNMP over UDP, therefore, reduces networkoverhead.• Messages between hosts are sporadic. SNMP again serves as a goodexample. SNMP messages are sent at irregular intervals. The overhead requiredto open and close a TCP connection for each message would delay messagesand bog down performance.• Reliability is implemented at the process level. Network File System (NFS) isan example of a process that performs its own reliability function and runs overUDP to enhance network performance.Network LayerBoth TCP and UDP pass information to the IP layer. This layer is responsible for actuallymoving the data from one machine on the network (or internet work) to another. The IPlayer handles a number of different communication tasks. The IP layer, however, doesnot guarantee delivery; this is dealt with by TCP. Some of the functions handled at thislayer include the following:• Routing of datagrams• Resolution of IP addresses to MAC addresses• Fragmentation and re-assembly of datagrams• Error detection and reportingWith respect to the EZCom-IP radio this is the most important part of the TCP/IP stackbecause this is where routing takes place. The EZCom-IP radio processes IP packetsjust like a PC or other device on the network.Before we can have a truly meaningful discussion regarding how the Network layerperforms it’s tasks we need to first develop an understanding of the IP addressingscheme.Overview of TCP/IP AddressesTo make TCP/IP work, each and every device on a TCP/IP network requires a uniqueaddress. An IP address identifies the device to all the other devices on the network. IPaddresses are made up of two parts. The first identifies the network ID. This ID is used toroute the information being sent to the correct network. The other part of the IP addressis the host ID, a unique number that identifies each computer and device on your TCP/IPnetwork.An IP address is very similar to your street address. If your address is 110 Main Street,the address identifies which street you are on, Main Street. It also identifies your houseon that street, number 110. The only difference between a street address and a TCP/IPaddress is that the street addresses are reversed. If this were a TCP/IP address, it wouldlook like this: Main Street, 110.How much of the address describes the network ID depends on the type of address youhave. Three main classes of addresses exist: Class A, B, and C. A TCP/IP address is,simply put, a 32-bit binary number. Looking at an address as 32 zeros or ones is difficultfor humans, so the address is viewed as a dotted decimal address in the following format:198.53.147.153. In this case, you are on network 198.53.147, and you are host number153. Each of the four numbers represents 8 bits of the address and is referred to as an

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 27 Of 54octet or byte. To understand TCP/IP and some of the concepts that make it work, it isimportant to be familiar with the binary form of the address.Understanding binary is relatively easy. Look at the number 238, for example. Inconventional math, this is two hundred and thirty-eight. Automatically, you see the 2 astwo groups of one hundred, the 3 as three groups of ten, and there are eight groups ofone. Each of the digits is multiplied by a positional value to make the total. That value isalways ten times the value to the right because there are ten different numbers: 0 1 2 3 45 6 7 8 9.Normally, you need only to work with binary numbers that are 8 digits long. Table 8,shows the values for those first 8 positions:Table 8, Bit Position Values128 64 32 16 8 4 2 1In binary, there are only two numbers, 1 and 0. Where the decimal system is a base tensystem, the binary system is a base two system. Like the decimal system, the positionalvalues increase. Here, however, they increase by two times the previous value(exponentially). Using Table 8, you should be able to figure out that the binary code110110 does not represent one hundred and ten thousand, one hundred and ten.Instead, it represents one group of thirty-two, one group of sixteen, no groups of eight,one group of four, one group of two, and no groups of one. That is, 110110 representsthe number 54 if you express it in decimal form.If you were to take the 198 from the example address 198.53.147.153, you could expressthis number as 128+64+4+2 (or 11000110). Remember that each of the 4 numbersrepresents 8 bits of the address, making up the total of 32 bits.The most obvious difference between the three main types of addresses is the number ofoctets used to identify the network ID. Class A uses the first octet only; this leaves 24 bits(or three octets) to identify the host. Class B uses the first two octets to identify thenetwork, leaving 16 bits (two octets) for the host. Class C uses three octets for thenetwork ID, leaving 8 bits (one octet) for the host.Table 9, TCP/IP Address Classes—First OctetClass Start(Binary) Finish(Binary) Start(Decimal) Finish(Decimal)A00000001 01111111 1 127B10000000 10111111 128 191C11000000 11011111 192 223A couple of rules determine what you can and cannot use for addresses. Neither thenetwork ID nor the host ID can be represented by all 0’s or by all 1’s, because each ofthese conditions has a special meaning. As well, the network with the first octet 127 isused solely for loop back tests.The classes of networks also differ in how their addresses start in binary. Class Aaddresses start with 0. Class B addresses start with 10. Class C addresses start with110. You can tell which class of address a host has by the first octet of its TCP/IPaddress. Knowing that the first octet represents the first 8 bits of the address, and byknowing the starting bits for the classes of addresses, you can see the first octet rangesfor the respective classes in Table 9

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 28 Of 54Figure 13, IP Address Formats0Network (7 bits)Host (16 bits)Host (24 bits)Network (14 bits)Network (21 bits)Format undefined11111010Host (16 bits)Class AClass BClass CExtendedAddressing ClassBecause the Class A addresses use only the first octet to identify the network ID, thereare a limited number of them (126, to be exact; 127 is reserved). Each of these 126networks, however, can have many hosts on it: 2 24 (the remaining 24 bits) hosts minustwo (the host IDs that are all 0’s and all 1’s) equals 16,777,214 hosts on a single network(albeit impossible).Class B addresses use the first two octets. The first 2 bits, however, are set to binary 10.This leaves 14 bits that can be used to identify the network: 2 14 possible combinations (6bits in the first octet and 8 from the second)—16,384 network IDs (because the first twodigits are 10, you don’t have to worry about an all 0’s or all 1’s host ID.) Each of thosenetwork IDs has 16 bits left to identify the host or 65,534 hosts (2 16 – 2).Class C networks use three octets (or 24 bits) to identify the network. The first three bits,however, are always 110. This means that there are five bits in the first octet and eight inthe other two that can be used to uniquely identify the network ID or 2 21 possiblenetworks (2,097,152)—each of which has 8 bits for hosts or 254 (2 8 –2).Table 10 summarizes all the possible TCP/IP addresses.Table 10, Address Class SummaryAddressClass FirstOctetStartFinish Number ofNetworks HostsEachA1 126 126 16,777,214B128 191 16,384 65,534C192 223 2,097,152 254Internet Protocol RoutingWhen a packet arrives at the IP layer the subnet mask can be used to determine whetherthe destination host is a local or remote host. First the devices own IP address is ANDedwith the subnet mask to extract the network ID for the local network on which the hostresides. Then the IP address that IP receives in the pseudo header is ANDed with thesubnet mask to determine the designation’s network ID. It is important to note that thenetwork ID generated from the ANDing with the local host’s subnet mask might beincorrect. If the local host attempting to send the datagram is a Class C host using255.255.255.0 as the subnet mask, ANDing generates an incorrect address if the remotehost is a Class B. This does not matter, however, because the network IDs will not match(remember the first octet differs, depending on the class of network). As you can see,therefore, the subnet mask enables you to extract the network ID. This information isused to see whether the datagram is for the local network. If it is not, the system needs tolook at the remote IP address and use the routing table to figure out where to send it.After the network IDs are known, they can be compared. The only case where theyshould match is if the two hosts are on the same network. If the host that you are trying toreach is on the same network, the IP layer finds that host and transmits the data to it. If

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 29 Of 54not, it needs to look for a route to the host. This will be done in the routing table. We willtake a closer look at the routing table in just a minute. For now lets look at the logic usedto find a route in the routing table first.Figure 14, IP Routing LogicExtract destination IPaddress D and determinedestination Network NReceive Datagram fromUpper LayerDose Nmatch anattached networkID?Report a routing ErrorDeliver the datagram tothe attached networkSend the datagram tothe default routerSend the datagram tothe next hop specifiedin the routing tableStopDose routingtable have aroute to NDose routingtable specify adefault route?Dose routingtable have aroute to DSend the datagram tothe next hop specifiedin the routing tableAs you can see from Figure 14, the IP layer has a very specific logic it uses indetermining how a datagram should be routed. This is referred to as the routingmechanism and all IP based devices use this same mechanism. The simplicity of therouting mechanism is part of what makes the IP protocol so attractive and also varyrobust. You are probably thinking how can such a simple mechanism be used to routeinformation all over the world as it dose in the Internet. The simplicity comes from the factthat any device on the network only has to know the next hop in the overall routing of anydatagram. The strength and complexity of routing datagrams all over the world isattributed to what is referred to as the routing policy. Routing policy is responsible forwhat is in the individual routing tables. In the case of the EZCom-IP radio the routingpolicy is completely up to you. All entries in the routing table are entered via the EZCom-IP explore program. This type of routing policy is referred to as static routing. There is averity of dynamic routing protocols in use today on routers that are part of the Internet butdynamic routing is not currently an option on the EZCom-IP radio.

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 30 Of 54Routing TableAll devices that use the IP protocol have a routing table, which includes the EZCom-IPradio. In some cases a host’s, routing table does not contain much routing information,except for the default gateway (router) address. In this case any packet not on the localnetwork is normally sent to the default gateway. IP on the gateway then looks in itsrouting table for a route to the remote network. In most cases you will need to haveentries in the local host’s routing table. In those cases, the table is consulted to find thefirst hop in the route. The following is an example of a routing table.Table 11, Active Routes:NetworkAddress Subnet mask Gateway Address Interface Metric0.0.0.0 0.0.0.0 206.51.250.69 206.51.250.69 1127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1206.51.250.0 255.255.255.0 206.51.250.69 206.51.250.69 1206.51.250.69 255.255.255.255 127.0.0.1 127.0.0.1 1206.51.250.255 255.255.255.255 206.51.250.69 206.51.250.69 1224.0.0.0 224.0.0.0 206.51.250.69 206.51.250.69 1255.255.255.255 255.255.255.255 206.51.250.69 206.51.250.69 1A routing table contains the following five pieces of information:• Network Address. The actual network ID to which the entry describes a route.This is the real network ID, not the one generated earlier when checking, if thehost is local or remote.• ?Netmask. The subnet mask that can be used to generate the network ID. Thesystem runs through the table and ANDs the IP address you are trying to reachwith each of the netmasks. Then it can compare the result to the NetworkAddress to see whether they match. If they match, a route has been found.• Gateway Address. Where to send the packet if it is a remote network ID towhich the computer is sending.• Interface. Which network interface to send the packet from. Normally you onlyhave one network card, and this is the same for all entries. (The exception hereis the loopback and multicasting addresses.) In the case of the EZCom-IP radiothere are 2 interfaces one that attaches the radio to the local subnet and theother is the radio link to other EZCom-IP radios. You can learn more about this inthe EZCom IP Routing section on page 40.• Metric. How far away this network is. This is the number of routers (gateways)that the packet must travel through to get to the remote.There will often be an entry for network 0.0.0.0 with a netmask of 0.0.0.0. This is theentry for the default gateway and is checked last. If you work it out in binary, you will seethat all addresses match this one. Figure 14 summarizes the process that IP uses todetermine where it should send the packet.You can add routes or modify the routing table in your EZCom-IP radio using the EZCom-IP Explorer program. If you need to setup a route or modify one on you PC you need touse the ROUTE utility program included with the windows operating system.

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 31 Of 54The ROUTE Utility ProgramSyntax for the ROUTE command is as follows:Manipulates network routing tables.ROUTE [-f] [command [destination] [MASK netmask] [gateway] [METRIC metric]]-f Clears the routing tables of all gateway entries. If this is used in conjunction withone of the commands, the tables are cleared prior to running the command.-p When used with the ADD command, makes a route persistent across boots ofthe system. By default, routes are not preserved when the system is restarted.When used with the PRINT command, displays the list of registered persistentroutes. Ignored for all other commands, which always affect the appropriatepersistent routes.command Specifies one of four commandsPRINT Prints a routeADD Adds a routeDELETE Deletes a routeCHANGE Modifies an existing routedestination Specifies the host.MASK If the MASK keyword is present, the next parameter is interpreted as thenetmask parameter.netmask If provided, specifies a sub-net mask value to be associated with thisroute entry. If not specified, it defaults to 255.255.255.255.gateway Specifies gateway.METRIC specifies the metric/cost for the destinationAll symbolic names used for destination are looked up in the network database fileNETWORKS. The symbolic names for gateway are looked up in the host name databasefile HOSTS.If the command is print or delete, wildcards may be used for the destination and gateway,or the gateway argument may be omitted.

Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 32 Of 54Finding Another Machine’s AddressWhether a packet that you are sending is going to a host on your network or to a host ona remote network, the packet is always sent to a MAC address (the hardware address ofthe network card). The only difference in sending to the local or the remote network isthat the address used for a remote network is the address of the router on the localnetwork. Remember that a router is a simple device that connects two (or more)networks; it has a network interface on each network (with an IP address on each subnet)and the IP layer to enable it to route packets between different networks based on therouting table. In the case of a packet going to a remote system, the system finds the MACaddress of the default gateway’s IP address on the local subnet (see Figure 14).The resolution of hardware addresses, as previously mentioned, is the responsibility ofARP (Address Resolution Protocol). ARP first checks the ARP cache to see whether ithas recently resolved the address. If it has, it can pass that to IP so that the packet canbe sent. Otherwise, ARP creates a broadcast packet that is sent on the network (seeFigure 15). The packet contains the IP address your system wants to resolve. It alsocontains the IP address and MAC address of your machine.Figure 15, ARP PacketHardware type Protocol Type HardwaeAddressLengthProtocolAddressLength Operation CodeTarget's IP AddressSender's MAC AddressTarget's MAC AddressSender's IP AddressThe parts of the ARP packet are as follows:• Hardware type, references which type of hardware is being used to access thenetwork (for example, token ring).• Protocol type. The protocol being used to perform the address resolution.Normally set to 0800 (hex), which is IP.• Hardware address length. Size of the hardware address in bytes. For TokenRing and Ethernet, this is 06 (hex).• Protocol address length. Size in bytes of the address being sought. This is 04(hex) for IP.• Operation code. Determines what this packet is. Operations include Query andReply.• Sender’s addresses. Both the MAC and IP address. This is added to the targetmachine’s ARP cache, and is used to reply.• Target’s addresses. The information being sought. The IP address is known,and the MAC address is returned.When the ARP packet is broadcast on the network, all the systems receive the packetand pass it up to their own IP layer. ARP sees whether the IP address being sought is itsown IP address. If it is, it takes the IP address and MAC address of the other host andadds it to its own table. Then it creates an ARP reply to tell the other system its MACaddress. Both systems now know each other’s IP and MAC addresses. You should,however, remember a couple of things about the ARP cache: Entries in the ARP cacheexpire after a short period of time; if the address is not used again, the entry lasts for twominutes; if it is used, it is kept for ten minutes. An entry could also be removed if thecache is getting full—in this case, ARP removes the oldest entries first. You can also adda static entry in the ARP cache. It remains, however, only until the system is restarted.

$Grayhill EZCom IP Users Manual Rev A6 1/26/2001Page 33 Of 54This might seem a little severe. Entries in the ARP cache, however, are the hardwareaddresses of the network cards in other hosts. This could very possibly change for agiven host, and would (if your entries were permanent) require all the hosts to beupdated.ARP Utility ProgramTo work with your ARP cache, you can use the ARP command. You can use ARP todisplays and modify the IP-to-Physical address translation tables used by the addressresolution protocol (ARP).The following is the help text for the ARP command:C:\users\default>arp /? ARP -s inet_addr eth_addr [if_addr] ARP -d inet_addr [if_addr] ARP -a [inet_addr] [-N if_addr]-a Displays current ARP entries by interrogating the current protocol data. Ifinet_addr is specified, the IP and Physical addresses for only the specifiedcomputer are displayed. If more than one network interface uses ARP, entries foreach ARP table are displayed.-g Same as -a.inet_addr Specifies an internet address.-N if_addr Displays the ARP entries for the network interface specified by if_addr.-d Deletes the host specified by inet_addr.-s Adds the host and associates the Internet address inet_addr with the Physicaladdress eth_addr. The Physical address is given as 6 hexadecimal bytesseparated by hyphens. The entry is permanent.eth_addr Specifies a physical address.if_addr If present, this specifies the Internet address of theinterface whose address translation table should be modified.If not present, the first applicable interface will be used.$