Assume there are N nodes connected to a wireless access point (AP) operating on
ID: 3553688 • Letter: A
Question
Assume there are N nodes connected to a wireless access point (AP) operating on IEEE 802.11b, and every node has at least one packet to send at a given time. The nodes continuously transmit data to the AP, and also download data from it. Is the channel access opportunity among all the nodes of the network fair? Is there any reason for a node to preferentially grab the channel over the others in such a network? If so, describe some ways that this forced unfairness can be achieved and their pros and cons using the typical parameters of the IEEE 802.11b standard.
Explanation / Answer
Command Line Interface Tools Traceroute - A command-line troubleshooting tool that enables you to view the route to a specified host. This will show how many hops the packets have to travel and how long it takes. In Windows operating systems, the command used is "tracert". traceroute IPCONFIG - This command is used to view network settings from a Windows computer command line. Below are the ipconfig switches that can be used at a command prompt. ipconfig /all will display all of your IP settings. ipconfig /renew forces the DHCP server, if available to renew a lease. ipconfig /release forces the release of a lease. IFCONFIG - IFCONFIG is a Linux/Unix command line tool that is similar to IPCONFIG in Windows. Common uses for ifconfig include setting an interface's IP address and netmask, and disabling or enabling a given interface. At boot time, many UNIX-like operating systems initialize their network interfaces with shell-scripts that call ifconfig. As an interactive tool, system administrators routinely use the utility to display and analyze network interface parameters. PING - PING (Packet InterNet Groper) is a command-line utility used to verify connections between networked devices. PING uses ICMP echo requests that behave similarly to SONAR pings. The standard format for the command is ping ip_address/hostname. If successful, the ping command will return replies from the remote host with the time it took to receive the reply. If unsuccessful, you will likely recieve and error message. This is one of the most important tools for determining network connectivity between hosts. ARP (Address Resolution Protocol) - A host PC must have the MAC and IP addresses of a remote host in order to send data to that remote host, and it's ARP that allows the local host to request the remost host to send the local host its MAC address through an ARP Request. Guide To ARP, IARP, RARP, and Proxy ARP ARP ARP PING (ARPING) - ARPING is a computer software tool that is used to discover hosts on a computer network. The program tests whether a given IP address is in use on the local network, and can get additional information about the device using that address. The arping tool is similar in function to ping, which probes hosts using the Internet Control Message Protocol at the Internet Layer (OSI Layer 3). Arping operates at the Link Layer (OSI Layer 2) using the Address Resolution Protocol (ARP) for probing hosts on the local network (link) only, as ARP cannot be routed across gateways (routers). However, in networks employing repeaters that use proxy ARP, the arping response may be coming from such proxy hosts and not from the probed target. NSLOOKUP - This is a command that queries a DNS server for machine name and address information. Originally written for Unix operating systems, this command is now available on Windows and other operating systems. To use nslookup, type "nslookup" followed by an IP address, a computer name, or a domain name. NSLOOKUP will return the name, all known IP addresses and all known aliases (which are just alternate names) for the identified machine. NSLOOKUP is a useful tool for troubleshooting DNS problems. nslookup Hostname - The hostname command is used to show or set a computer's host name and domain name. It is one of the most basic of the network administrative utilities. A host name is a name that is assigned to a host (i.e., a computer connected to the network) that uniquely identifies it on a network and thus allows it to be addressed without using its full IP address. Domain names are user-friendly substitutes for numeric IP addresses. Dig (domain information groper) - Dig is a Linux/Unix tool for interrogating DNS name servers. It performs DNS lookups and displays the answers that are returned from the name server(s) that were queried. Mtr - Mtr is a Linux command line tool that combines the functionality of the traceroute and ping programs in a single network diagnostic tool. Route - The route command is used to display and manipulate a local routing table. Examples of its use include adding and deleting a static route. This tool is available in Unix, Linux and Windows. NBTSTAT - Is a Windows utility used to troubleshoot connectivity problems between 2 computers communicating via NetBT, by displaying protocol statistics and current connections. NBTSTAT examines the contents of the NetBIOS name cache and gives MAC address. NETSTAT - Is a Windows, Linux, and Unix command-line tool that displays network connections (both incoming and outgoing), routing tables, and a number of network interface statistics. It is used for finding problems in the network and to determine the amount of traffic on the network as a performance measurement. Domain 5.2: Network Scanners Packet Sniffers - A packet sniffer is a device or software used to capture packets traveling over a network connection. The packets are logged and can be decoded in order to provide information and statistics about the traffic on the network or network segment. These tools are used for troubleshooting difficult network problems, monitoring network traffic, and detecting intrusion attempts. Also known as Packet Analyzers. Intrusion Detection Software - This was covered earlier in domain 3.1. Intrusion Prevention Software - This was covered earlier in domain 3.1. Port Scanners - A port scanner is a program designed to probe network hosts for open ports. This is often used by administrators to verify security policies of their networks and by attackers to identify running services on a host that can be exploited to gain access. Domain 5.3: Hardware Tools Cable Testers - Cable testers are electronic devices used to test a cable's integrity by checking for opens and shorts which can cause connectivity problems. Protocol Analyzers - This tool is used to monitor network traffic and display packet and protocol statistics and information. As far as we're concerned, it is pretty much the same thing as a packet sniffer. Most tools sold today combine the functions of the listening device (packet sniffer) and the analytical device (packet analyzer). Certifiers - Certifiers are a tool that tests cables in order to ensure that they will perform the job intended. This includes checking the speed loads that it can handle. TDR (Time Domain Reflectometer) - Sends a signal down a cable and measures the distance that the signal travelled before bouncing back (like sonar). Used to find opens and shorts in cables. OTDR (Optical Time Domain Reflectometer) - Similar to the TDR above, however, this is used to test fiber optic cables with light. Multimeter - A multimeter, also known as a volt/ohm meter, is an electronic measuring instrument used to measure voltage, current and resistance. Toner Probe - Most will detect opens and shorts like a cable tester, but this tool is mainly used to locate the termination points of cables. Butt Set - A portable telephone that connects to a line using alligator clips and is used to test telephone circuits. Punch Down Tool - A punch down tool is used to connect cabling such as telephone and ethernet to wall jacks. Cable Stripper - Fairly self explanatory. A tool used to strip the jackets off of cables in order to expose the wire that can be connected to connectors or wall jacks. Snips - Special scissors used for cutting cable. Voltage Event Recorder - Captures and logs electrical current information for devices which can then be accessed on a PC. Mostly used for mission critical devices such as those found in a hospital. Temperature Monitor - We aren't entirely sure what CompTIA is referring to with this. There are all kinds of temperature monitors from CPU temperature monitoring software to devices that monitor the temperature of a server room. Domain 6.0: Network Security Domain 6.1: Hardware and Software Security Devices The topics covered in this section are already covered elsewhere in this guide. Domain 6.2: Firewalls Application Layer vs. Network Layer