Ad-Hoc Networks


An Ad-Hoc network is any subset of Peer-to-peer ( P2P ) networks spontaneously created upon the connection of multiple devices, all without the need of a central base (such as a router or an access point). Contrasting drastically from the more complex infrastructure networks( PAN WAN , LAN , CAN , MAN ), Ad-Hoc networks function entirely without the use of a central hub to relay information from one device to another and so each node in the network can serve both as host and/or router. Each node participates in routing by forwarding data for other nodes, and so the determination of which nodes forward data is made dynamically based on the network connectivity(and thus, the topology of the network fits the needs of the devices and constantly shifts), and not on whim of the central device. (2)

Common Types and Their Implementations


Some of the more common Ad-Hoc networks are the ones created between Bluetooth devices, Internet Service Sharing over Wi-Fi , and proprietary connections for smaller devices. (3)
Basic Piconet
Basic Piconet


Piconets


Piconets are Ad-Hoc networks, with a range of about 200 meters and a transfer rate between about 200 and 2100 kbit/s, created by the connection of two Bluetooth-enabled devices using a 3-bit Logical Transport Address, thereby effectively limiting the max number of connected devices to eight and the parked to 255 (9). In a Piconet, each device is a peer and thus are each implemented the same, with one exception: The master. One of the issues with creating a Piconet is that bluetooth devices often oscillate between frequencies to avoid interference from other devices. The Piconet fixes this issue by instituting the master/slave relationship:

"We've seen how devices can avoid one another's transmissions by constantly changing channels, but how do they know which channel to be on at any particular time? The answer comes from the master: When Bluetooth devices first connect, the master's clock and the Bluetooth device address (BD_ADDR) are passed to the slaves in a special packet called a frequency-hop synchronization packet (FHS packet). The master's Bluetooth device address is used to calculate the sequence of frequency hops that all devices in a piconet will follow, and the master's clock decides which is the current hop in the sequence (the phase). All the devices in a piconet keep a track of the difference between their own native clock and the master's clock, so they know exactly which frequency to transmit or receive on at any moment. " (5)

Scatternet

Scatternet
Scatternet

Scatternets are an Ad-Hoc network wherein two or more Piconets are connected to each other. A Scatternet is formed when a member of a current Piconet (either the master or a slave) becomes the slave in another Piconet. This allows for seamless transfer of data from any device in any Piconet to another device using the shared slave(acts similar to the master, but for inter-network communication).Through scatternets, Bluetooth devices are able to transcend the Bluetooth limitations and have a theoretically infinite range. Unfortunately, due to current limitations, Scatternets are seldom used and are not yet reliable nor efficient enough for wide implementation, but much research is being done to expand their capabilities. (10)

Wi-Fi
Basic Wi-Fi Ad-Hoc Network
Basic Wi-Fi Ad-Hoc Network


Unlike Bluetooth, the Wi-Fi implementation (currently) is designed for the more complex and permanent infrastructure networks. Despite this, Wi-Fi is often used to setup Ad-Hoc networks between several devices (usually wireless enabled computers). While the malleability and ease of use is lacking from Wi-Fi based Ad-Hoc networks, the connections are often much more power and are ideal for transfer of large chunks of data between devices.

Proprietary Implementations


While the two above types are the only true widely used implementations, there are several lesser Ad-Hoc types. Some of the more popular implementations are used in many handheld gaming devices such as Nintendo DS and Sony Playstation Portable. (3)

Some companies such as Nintendo and Sony have implemented the use of Ad-Hoc networks in their portable gaming devices such as in the Sony Playstation Portable and the Nintendo DS to create private networks between several of these devices for multiplayer gaming. If several Playstation Portables are nearby or several Nintendo DS are nearby then one could create a private network between the devices without the use of a central hub or connection to the internet. This does not grant the devices connection to the internet but it is a way of connecting the devices together for a limited play in the same network without using an actual WAP (Wireless Access Point), this allows up to 16 Playstation Portable users to be connected together to play the same games together and send messages and images between each other. (12)

How to do it



An ad-hoc network is easy to set up, one just needs to know how. Since there are some differences between Windows XP and Vista/Windows 7, both methods will be explained:

Windows 7

Step 1:
Click on start and in the search bar on the bottom of the menu that pops up, type wireless. Click on manage wireless networks. Note: this option can also be accessed through control panel -> Network and Sharing Center -> Manage wireless networks .

Step 2:
Click on add a network.

Step 3:
This will then give you a bunch of options. Select " Create an Ad-Hoc Network ".

Step 4:
Enter a name for the network you wish to create. Next, select the security options. If you want to set a password, you may do so. Also, you can add encryption to your connection here if you so desire. Hit ok.

The Ad-Hoc network should now work.


Windows XP

For XP, the steps differ greatly than from its Vista/Windows 7 counterpart. To make this work, you first need to assign a static IP to each computer on the network. Next, you need to configure a computer to host the network. Finally, you need to configure each computer to connect to the host computer.

A) Setting up a static IP

Step 1

Go to start -> Control panel -> Network connections

step 2
Right click on Local Area Connections (LAN) and click on properties.

Step 3
A window with the title network connections will appear. There should be a list of connections with check marks next to them. Click on Internet Protocol (TCP/IP) and click the properties button.

Step 4
There should now be a window with the following lines: IP Address, Subnet mask and default gateway. Note: There are more lines to enter data in, but for the purposes of this discussion, these three options are what we will be what we are focusing on.You first want to click the bubble that says user configured. This will allow you to type inside the text boxes. In the first box, the one that says IP address, you want to enter 192.168.1.X, with x being any number between 0 and 255. Note that you do not want two computers with the same IP address, as this will screw up the network connection, with both of those computers kicking each other off the network.You also want to set the subnet mask to 255.255.255.0 (this will automatically be filled in for you).

B ) Configuring the host computer

Step 1
Go back to your network settings window. Right click on the wireless network connection and click properties.

Step 2
Click on the wireless networks tab. Then click on the check box next to Use Windows to configure my wireless network settings. Click on the advanced button.

Step 3
Select Computer-to-computer (Ad-Hoc) networks only option in the advanced tab and click close.

Step 4
Click add to add a new Ad-Hoc network to the list.

Step 5
Name your network. You can now add a password and encryption if you want.


C) Setting up the client computers (the connecting computers)

Step 1
Follow steps 1-3 in the host setup.

Step 2
The Ad-Hoc network should show up just like any other wireless network. Connect to it the same way.

You are now done. If this was slightly confusing, watch the video below for further information and clarity (it is an explanation for the XP method).





Ad-Hoc Networking considerations


Pros

1) Fast setup time -Just as the name implies, an Ad-Hoc network is a temporary and quick way to create a network. All one must do is to hit a few buttons and the ad-hoc mode will be activated (1) .

2) Cost - With the reduced cost of personal wireless routers, making a network with a router really isn't as much of a problem as it was a few years ago. Today, one can get a wireless router as cheap as about $30. However, to some people, this is a signifigant investment and may play a role in their wireless decisions. So, using an ad-hoc network may be a better choice (1) .


Cons

1) Access to the internet is limited- keep in mind that ad-hoc networking works in the fashion of one computer managing the wireless internet and allowing other computers to connect to it. Thus, if that computer goes down, the whole network goes down. That means that if that main computer freezes, sleeps, hibernates or shuts down, the connection is gone. Also, The effective range of a network such as this is about 30 feet, meaning that all computers must be within a 30 foot radius of the host computer to receive a connection (1) .


2)Difficult network management . Network management becomes a headache with ad hoc networks because of the fluidity of the network topology and lack of a centralized device. Without an access point, network managers can't easily monitor performance, perform security audits, etc. Effective network management with ad hoc wireless LANs requires network management at the user device level, which requires a significant amount of overhead packet transmission over the wireless LAN. This again leans ad hoc mode away from larger, enterprise wireless LAN applications. (1)

Future of Ad-Hoc Networks


It is estimated that in the future ad-hoc networks will use mobile routers to provide Internet connectivity to mobile ad-hoc users and allow mobility of an ad-hoc network where mobile users may use an Internet access within an ad-hoc network domain. Mobile ad-hoc networks of this type have recently captured the interest of several companies, as far as applications such as distributed collaborative computing, distributed sensing networks, potential fourth generation wireless systems, and response to incidents that destroyed the existing communication structure go.The emerging field of mobile computing, with its current focus on mobile IP operation, illustrates that there is a real need for dynamic ad-hoc networking technology. Of course, if mobile computing expects to manage multi-hop clusters that can operate autonomously and possibly be able to attach at some point to the bigger network, it will require highly-adaptive networking technology. (11)

Already mobile telecommunication technology found in most cellphone companies are starting to use that for Wi-Fi connection for more devices than just smartphones. Products such as the Sprint Overdrive are using these technologies to create a Wi-Fi network anywhere in the United States. Anywhere where you can receive a 3G or 4G connection from Sprint, you can connect your Sprint Overdrive and connect up to 5 different devices via Wi-Fi network. This already seems like a faster and more effective way of connecting devices together. The cons about such product are pricing and the fact that you would have to subscribe to Sprint for the use of their 3G and 4G network. Ad-Hoc still remains a cheaper solution for connecting devices together. (13)


References and Links

  1. http://www.wi-fiplanet.com/tutorials/article.php/1451421
  2. http://ntrg.cs.tcd.ie/undergrad/4ba2.05/group11/index.html
  3. http://www.wisegeek.com/what-is-an-ad-hoc-network.htm
  4. http://ntrg.cs.tcd.ie/undergrad/4ba2.05/group3/index.html
  5. http://www.informit.com/articles/article.aspx?p=21324
  6. http://www.home-network-help.com/ad-hoc-wireless-network.html (XP)
  7. http://www.kombitz.com/2009/02/09/windows-7-how-to-create-an-ad-hoc-network/ (win7)
  8. http://searchmobilecomputing.techtarget.com/sDefinition/0,,sid40_gci213462,00.html
  9. Halsall, F., 2005, Computer Networking and the Internet, 5thEdition
  10. http://users.ece.gatech.edu/tommaso/papers/jsac_bluetooth.pdf
  11. http://www.computingunplugged.com/issues/issue200410/00001395001.html
  12. http://computersavvy.wordpress.com/2009/04/19/qa-what-does-ad-hoc-mode-mean-in-psp-terms/
  13. http://mobilebusiness.sprint.com/broadband/index.html?pid=4&id9=vanity:overdrive?id9=SEM_Google_C_Sprint_Mobile_Broadband


Kyle Soper, Michael Lindo, Carl Pierre, Beth Pramschufer, Jeffrey Sullivan