Monday, December 31, 2007
Wednesday, December 26, 2007
Bluetooth for Ad-Hoc Networking
Bluetooth
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Ericsson as a method to replace cables in networks created Bluetooth in 1994. In 1998 the Bluetooth SIG was founded and it currently has over 3000 members. The principle aims of the technology were to replace wire and form short-range ad-hoc networks. Since then the bluetooth standard has blossomed so much so that it takes up over 1500 pages!!!
An ad-hoc network is one that consists of independent wireless nodes that have the ability to dynamically form connections with each other to create a network. An ad-hoc network does not require any central infrastructure and it can grow, shrink and fragment without having to make any requests or reports to a central authority. Ina bluetooth network there are two types of node: a slave and a master. Each node has the ability to be either or both at the same time.
How Bluetooth Works
Now a bluetooth network actually consists of small subnets or piconets. A piconet consists of two or more connected nodes sharing the same channel. Every piconet have one master and up to 7 slaves. There is never a direct transmission between slaves. Rather all communication goes through the master.
Two or more connected piconets form a scatternet. To connect piconets simply let them have a node in common. A node may be a slave in one piconet and a master in another. This is the basis for forming ad-hoc networks in bluetooth.
The core bluetooth protocol stack contains 5 layers. The radio and baseband layers describe the physical implementation of bluetooth. It operates on the 2.4GHz frequency. There are 79 1MHz channels and upper and lower guard bands. The technology uses frequency hopping spread spectrum for information transmission with 1600 hops per second. Each channel is occupied for 0.625ms, called a slot and the slots are number sequentially. The master in the piconet determines the frequency hopping sequence and it is a function of the master’s address. Bluetooth uses time division multiple access. There are three power classes in bluetooth:
| Class | Power Consumption | Range |
|---|---|---|
| One | 100mW | 100m |
| Two | 10mW | 10m |
| Three | 1mW | ~10cm |
Bluetooth Links
There are two types of link between bluetooth nodes. The first is a synchronous connection orientated (SRO) link and the second is an asynchronous connectionless (ACL) link. An SRO link is a fixed bandwidth point-to-point link between master and slave nodes. The master maintains the connection by reserving slots at regular intervals. It is suitable for time bound transmissions like audio. Packets are not resent in an SRO link. A master can maintain up to 3 SRO links, while a slave can maintain 2 or 3. The maximum data rate is 64Kbps. An ACL link is a point to multi-point link between in the master and all the slaves in a piconet. Packets are transmitted in the unreserved slots and a master can transmit to a slave even if its already part of (SRO) link. Only one ACL link can exist in a piconet. Packets are retransmitted in most cases. The maximum data transmission rate is 720Kbps.
Forming PicoNets
When forming bluetooth nodes form a piconet they goes through a series of states. The two major states are STANDBY- not part of a piconet and CONNECTION – device is part of a piconet. To form a piconet the master transmits an ID packet over 32 of the 79 channels. Devices in the STANDBY state periodically scan for this packet. If it hears it, the device sends its address and timing info to the master. The device then waits for the master to page it. When the master is satisfied that it has identified all the devices in its range it starts to form the piconet. It pages each device with its own device access code (DAC) using a frequency hopping sequence based on the slaves address. When the slave hears this it sends a confirmation packet. On the next slot the master sends the slave the master DAC. The slave then enters the CONNECTION state. The master does this for all the slaves in the piconet then it enters the CONNECTION state itself.
What Bluetooth Ad Hoc Networks are used for
Some of the uses for Bluetooth Ad Hoc networks include: inter-vehicle communication, BEDD ∓ the Bluetooth Umbrella Project.
BEDD uses Bluetooth wireless communications "to scan strangers' phones for their personal profiles. Once the software is downloaded into a compatible phone, it automatically starts searches for and exchanges profiles with other phones that come within a 20-meter radius." [1] The system launched in Singapore last year allows you to send buy-and-sell ads, dating ads, instant messages and more through your mobile phone. The application runs in the background on your phone and exchanges your profile with other phones in range. Profiles can contain info about who you would like to meet, your buy-and-sell ads, etc. If BEDD finds that a profile in range has information matching your profile, it alerts you. It also "enables free Bluetooth chat and instant messaging or regular mobile contact via SMS, MMS, Call, IM or Email". [2] The creators say that "BEDD is like internet matching sites, on-line chat and newspaper classifieds, only all inside your mobile phone, doing all the work for you, allowing you to meet that someone special or find that cool thing to buy or sell, all as you go throughout your day." [2]
Sussex University Communications Research Group have used Bluetooth Ad Hoc networks to create a system of inter-vehicle communication. Bluetooth is a good choice for inter-vehicle communication because the nodes (vehicles) are constantly moving in and out of range of the master node and local piconets. "If Vehicle A is travelling at 97 Km/h and Vehicle B is travelling at 113 km/h. The difference of 16 km/h equates to approximately 4.5 m/s. After coming into range, Vehicle B would need to travel 200m more than Vehicle A for it to exceed the Bluetooth range. Using these speed values the two vehicles would be in range for a period of approximately 44 seconds. During this time period vital information can be exchanged between the vehicles depending on the envisaged application." [3] Some of the applications suggested by Sussex University Communications Research Group are "real time safety critical systems as well as entertainment, and wireless communication for remote user application in the local and wide area." [3]
In Trinity College, the Networks and Telecommunications Research Group are running a project called Umbrella.net which "is exploring the idea of ad-hoc networks to connect people in urban space" [4]. The idea is that temporary networks would be created when people in close proximity open their bluetooth equipped umbrellas. The umbrellas – which house the routers - are linked via bluetooth to PDAs. NTRG have written PDA applications to detect people in the ad hoc range and also those within a number of ‘hops’ away. The transitory network could be used for anything from instant messaging to filtering weather reports through the network of umbrellas. Particularly in the city, the dense canopy of umbrellas would allow information to travel large distances across the network. "We believe these transitory networks can add surprise and beauty to our currently fixed communication channels." [5]
Advantages and Disadvantages of Bluetooth for Ad-Hoc Networks
Ad-hoc networks can be formed using many different wireless technologies, but Bluetooth has become almost a household name in the ad-hoc networking world for the numerous advantages it offers over competing technologies.
The main reason Bluetooth is so popular for ad-hoc networks is that it was specifically designed for use in this fashion; while the likes of the 802.11 (WiFi) standard were designed to provide a replacement for wired infrastructure networks. While other networks can be configured to operate in an ad-hoc fashion, without any central "controlling" device, Bluetooth offers automatic network configuration, authentication and service discovery; thereby making setting up an ad-hoc network much simpler for the average user, who is unlikely to be familiar with networking protocols and router configuration.
Bluetooth was designed to require as little power as possible, to be implemented in the smallest possible design, and to be cheap to produce. As wireless technologies imply no fixed wired connections at all, it can be taken for granted that any devices using any wireless technology, be it WiFi, Bluetooth, GSM, etc., will be supplied by an on-board battery. WiFi and other technologies are extremely power-hungry, relative to Bluetooth – Bluetooth operates using just 2.5mW of power, compared to 100mW for WiFi [6]! Small, low-power, cheap devices meant that they could be integrated into just about every device under the sun allowing them to communicate with one another using a common standard.
Users of Bluetooth technologies are not faced with legal obstacles when using the radio frequencies utilised by Bluetooth devices as Bluetooth uses the unlicensed 2.4GHz ISM (Industrial, Scientific, and Medical) band. This offers users the advantage of not having to obtain licences etc from their local communications authority.
Unfortunately, Bluetooth does have some limitations. Primarily, these are to do with range and bandwidth. Bluetooth offers a range of typically 10m. While some versions of Bluetooth support much greater ranges (up to 100m), these consume far more power (up to 100mW). 10 metres was chosen, however, with some care, as it was decided that for the purposes of cable-replacement and ad-hoc networks, such a great distance between nodes was unlikely to be necessary in practice. It should be noted, however, that it is possible to communicate between distant devices if there are other Bluetooth devices in between to relay the messages.
The second downfall is the lack of bandwidth. Bluetooth is capable of transmitting and receiving data at a mere 720kbps. This compares rather poorly with the 11 and now 54mbps offered by WiFi networks [6]. Quite often it is sufficient for the required communication, such as streaming audio and transfer of reasonably sized files (several hundred kilobytes can be transferred in a matter of seconds); but should the transfer of extremely large files be necessary, the user might be better off opting for the faster 802.11 standard.
The Future of Bluetooth Ad-Hoc Networks
Today 802.11b and g are the only real alternatives to Bluetooth. However they do not compete for the same markets as they provide much higher data rates than Bluetooth. They will provide internet hot spots to businesses and others whereas Bluetooth will be used to connect devices in a small area. The 802.11b and g peer to peer ad hoc networking is very cumbersome and Bluetooth is technically superior to them and is much cheaper which leads us to believe that Bluetooth is best suited to PANs – Personal Area Networks. The future of Bluetooth networks depends largely on more and more consumers getting interested in PANs.
The chances that Bluetooth will be a real force in the future are quite real. Bluetooth is supported by Mac OS X, Windows XP and Linux which has lead to a lot of consumers buying Bluetooth enabled products. As all the main operating systems support Bluetooth this means that manufacturers are going to be able to introduce it into their devices without any problems. This will mean that virtually any handheld electronic devices would have the ability to communicate to others near or beside them. Examples of these would be mobile phones, USB keys, PDAs, laptops etc and these would all be part of the PAN.
The PAN or Personal Area Network will be the key to the success of Bluetooth. PANs can be constantly online. This would be due to either access via a 2.5 G cellular phone and/or a wireless LAN access point. This means that there would be no restrictions to using such a network. Communication between different PAN’s is also possible and in the future the likes of participants at a meeting been able to share documents and presentations through Bluetooth will be the norm.
There is a future for Bluetooth in the Smartphones industry also. These new Smartphones that are very powerful and are beginning to appear on the market nowadays will be much more widespread in the near future. These phones implement J2ME and JSR-82 enabling MIDlets to communicate over Bluetooth links. The likes of multi-party games and other such programs on these phones are likely to become popular and Bluetooth is the perfect tool for them to communicate to each other.
The IEEE 802.15 working group is dedicated to PANs. This is essential to the existence of Bluetooth in the future. In fact the work of this task group has led IEEE to accept parts of the Bluetooth 1.1 standard as an IEEE standard which is denoted by 802.15.1. If Bluetooth is to be a force to be reckoned with in the future there are some current limitations that musty be corrected. These are things like the standard does not address routing in piconets and scatternets. It does not support multi hop multicasting and it does not fully address how to cope with mobility. Once these can be fixed the future looks promising. Bluetooth will provide many people who understand the underlying technology with opportunities in fields like education, consulting and software development and I think the future is very promising for the technology.
Download Bibliography
- http://www.computingunplugged.com/issues/issue200411/00001397001.html
- http://www.bedd.com/
- http://www.comms.scitech.susx.ac.uk/research/bluetooth.php
- http://www.theregister.co.uk/2004/09/02/bluetooth_umbrella/
- http://www.undertheumbrella.net/
- http://www.cs.tcd.ie/courses/baict/bass/4ict9/Section2/Adhoc-Four2003.pdf
Basic Hardware Components
All networks are made up of basic hardware building blocks to interconnect network nodes, such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and Routers. In addition, some method of connecting these building blocks is required, usually in the form of galvanic cable (most commonly Category 5 cable). Less common are microwave links (as in IEEE 802.11) or optical cable ("optical fiber").
Network Interface Cards
A network card, network adapter or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It provides physical access to a networking medium and often provides a low-level addressing system through the use of MAC addresses. It allows users to connect to each other either by using cables or wirelessly.
Repeaters
A repeater is an electronic device that receives a signal and retransmits it at a higher level or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances without degradation.
Because repeaters work with the actual physical signal, and do not attempt to interpret the data being transmitted, they operate on the Physical layer, the first layer of the OSI model.
Hubs
A hub contains multiple ports. When a packet arrives at one port, it is copied to all the ports of the hub. When the packets are copied, the destination address in the frame does not change to a broadcast address. It does this in a rudimentary way, it simply copies the data to all of the Nodes connected to the hub. [4]
Bridges
A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. Bridges do not promiscuously copy traffic to all ports, as hubs do. but learns which MAC addresses are reachable through specific ports. Once the bridge associates a port and an address, it will send traffic for that address only to that port. Bridges do send broadcasts to all ports except the one on which the broadcast was received.
Bridges learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge assumes that MAC address is associated with that port. The first time that a previously unknown destination address is seen, the bridge will forward the frame to all ports other than the one on which the frame arrived.
Bridges come in three basic types:
- Local bridges: Directly connect local area networks (LANs)
- Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced by routers.
- Wireless bridges: Can be used to join LANs or connect remote stations to LANs.
Switches
Switches are a marketing term that encompasses routers and bridges, as well as devices that may distribute traffic on load or by application content (e.g., a Web URL identifier). Switches may operate at one or more OSI layers, including physical, data link, network, or transport (i.e., end-to-end). A device that operates simultaneously at more than one of these layers is called a multilayer switch.
Overemphasizing the ill-defined term "switch" often leads to confusion when first trying to understand networking. Many experienced network designers and operators recommend starting with the logic of devices dealing with only one protocol level, not all of which are covered by OSI. Multilayer device selection is an advanced topic that may lead to selecting particular implementations, but multilayer switching is simply not a real-world design concept.
Routers
Routers are the networking device that forward data packets along networks by using headers and forwarding tables to determine the best path to forward the packets. Routers work at the network layer of the TCP/IP model or layer 3 of the OSI model. Routers also provide interconnectivity between like and unlike media (RFC 1812) This is accomplished by examining the Header of a data packet, and making a decision on the next hop to which it should be sent (RFC 1812) They use preconfigured static routes, status of their hardware interfaces, and routing protocols to select the best route between any two subnets. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP's network. Some DSL and cable modems, for home use, have been integrated with routers to allow multiple home computers to access the Internet.
Internetwork
Two or more networks or network segments connected using devices that operate at layer 3 (the 'network' layer) of the OSI Basic Reference Model, such as a router. Any interconnection among or between public, private, commercial, industrial, or governmental networks may also be defined as an internetwork.
In modern practice, the interconnected networks use the Internet Protocol. There are at least three variants of internetwork, depending on who administers and who participates in them:
- Intranet
- Extranet
- "The" Internet
Intranets and extranets may or may not have connections to the Internet. If connected to the Internet, the intranet or extranet is normally protected from being accessed from the Internet without proper authorization. The Internet itself is not considered to be a part of the intranet or extranet, although the Internet may serve as a portal for access to portions of an extranet.
Intranet
An intranet is a set of interconnected networks, using the Internet Protocol and uses IP-based tools such as web browsers, that is under the control of a single administrative entity. That administrative entity closes the intranet to the rest of the world, and allows only specific users. Most commonly, an intranet is the internal network of a company or other enterprise.
Extranet
An extranet is a network or internetwork that is limited in scope to a single organization or entity but which also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities (e.g. a company's customers may be given access to some part of its intranet creating in this way an extranet, while at the same time the customers may not be considered 'trusted' from a security standpoint). Technically, an extranet may also be categorized as a CAN, MAN, WAN, or other type of network, although, by definition, an extranet cannot consist of a single LAN; it must have at least one connection with an external network.
Internet
A specific internetwork , consisting of a worldwide interconnection of governmental, academic, public, and private networks based upon the Advanced Research Projects Agency Network (ARPANET) developed by ARPA of the U.S. Department of Defense – also home to the World Wide Web (WWW) and referred to as the 'Internet' with a capital 'I' to distinguish it from other generic internetworks.
Participants in the Internet, or their service providers, use IP Addresses obtained from address registries that control assignments. Service providers and large enterprises also exchange information on the reachability of their address ranges through the BGP Border Gateway Protocol.
Types of networks
Personal Area Network (PAN)
A personal area network (PAN) is a computer network used for communication among computer devices close to one person. Some examples of devices that may be used in a PAN are printers, fax machines, telephones, PDAs, or scanners. The reach of a PAN is typically within about 20-30 feet (approximately 4-6 Meters). PANs can be used for communication among the individual devices (intrapersonal communication), or for connecting to a higher level network and the Internet (an uplink).
Personal area networks may be wired with computer buses such as USB and FireWire. A wireless personal area network (WPAN) can also be made possible with network technologies such as IrDA and Bluetooth.
Local Area Network (LAN)
A network covering a small geographic area, like a home, office, or building. Current LANs are most likely to be based on Ethernet technology. For example, a library will have a wired or wireless LAN for users to interconnect local devices (e.g., printers and servers) connect to the internet. All of the PCs in the library are connected by category 5 (Cat5) cable, running the IEEE 802.3 protocol through a system of interconnection devices and eventually connect to the internet. The cables to the servers are on Cat 5e enhanced cable, which will support IEEE 802.3 at 1 Gbps.
The staff computers (bright green) can get to the color printer, checkout records, and the academic network and the Internet. All user computers can get to the Internet and the card catalog. Each workgroup can get to its local printer. Note that the printers are not accessible from outside their workgroup.
network, in a branching tree topology and controlled access to resourcesAll interconnect devices must understand the network layer (layer 3), because they are handling multiple subnets (the different colors). Those inside the library, which have only 10/100 Mbps Ethernet connections to the user device and a Gigabit Ethernet connection to the central router, could be called "layer 3 switches" because they only have Ethernet interfaces and must understand IP. It would be more correct to call them access routers, where the router at the top is a distribution router that connects to the Internet and academic networks' customer access routers.
The staff have a VoIP network that also connects to both the Internet and the academic network. They could have paths to the central library system telephone switch, via the academic network. Since voice must have the highest priority, it is on the pink network. The VoIP protocols used, such as RSVP, are virtual circuits rather than connectionless forwarding paths.
Depending on the circumstance, the computers in the network might be connected using cables and hubs. Other networks might be connected strictly wirelessly. It depends on the number of PCs that you are trying to connect, the physical layout of your workspace, and the various needs of network. Not shown in this diagram, for example, is a wireless workstation used when shelving books.
The defining characteristics of LANs, in contrast to WANs (wide area networks), include their much higher data transfer rates, smaller geographic range, and lack of a need for leased telecommunication lines. Current Ethernet or other IEEE 802.3 LAN technologies operate at speeds up to 10 Gbit/s. This is the data transfer rate. IEEE has projects investigating the standardization of 100 Gbit/s, and possibly 40 Gbit/s. Inverse multiplexing is commonly used to build a faster aggregate from slower physical streams, such as bringing 4 Gbit/s aggregate stream into a computer or network element with four 1 Gbit/s interfaces.
Campus Area Network (CAN)
A network that connects two or more LANs but that is limited to a specific and contiguous geographical area such as a college campus, industrial complex, or a military base. A CAN, may be considered a type of MAN (metropolitan area network), but is generally limited to an area that is smaller than a typical MAN.
This term is most often used to discuss the implementation of networks for a contiguous area. For Ethernet based networks in the past, when layer 2 switching (i.e., bridging (networking) was cheaper than routing, campuses were good candidates for layer 2 networks, until they grew to very large size. Today, a campus may use a mixture of routing and bridging. The network elements used, called "campus switches", tend to be optimized to have many Ethernet-family (i.e., IEEE 802.3) interfaces rather than an arbitrary mixture of Ethernet and WAN interfaces.
Metropolitan Area Network (MAN)
A Metropolitan Area Network is a network that connects two or more Local Area Networks or Campus Area Networks together but does not extend beyond the boundaries of the immediate town, city, or metropolitan area. Multiple routers, switches & hubs are connected to create a MAN.
Wide Area Network (WAN)
A WAN is a data communications network that covers a relatively broad geographic area (i.e. one city to another and one country to another country) and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.
Global Area Network (GAN)
Global area networks (GAN) specifications are in development by several groups, and there is no common definition. In general, however, a GAN is a model for supporting mobile communications across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key challenge in mobile communications is "handing off" the user communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrial Wireless local area networks (WLAN) [3]. INMARSAT has defined a satellite-based Broadband Global Area Network (BGAN).
IEEE mobility efforts focus on the data link layer and make assumptions about the media. Mobile IP is a network layer technique, developed by the IETF, which is independent of the media type and can run over different media while still keeping the connection.
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