Key distribution is an important issue in wireless sensor network (WSN) design. It is a newly developing field due to the recent improvements in wireless communications.
Wireless sensor networks are networks of small, battery-powered, memory-constraint devices named sensor nodes, which have the capability of wireless communication over a restricted area [1]. Due to memory and power constraints, they need to be well arranged to build a fully functional network.
source:http://en.wikipedia.org/wiki/Key_distribution_in_wireless_sensor_networks
Key distribution schemes
Key predistribution is the method of distribution of keys onto nodes before deployment. Therefore, the nodes build up the network using their secret keys after deployment, that is, when they reach their target position.
Key predistribution schemes are various methods that have been developed by academicians for a better maintenance of key management in WSNs. Basically a key predistribution scheme has 3 phases:
1.Key distribution
2.Shared key discovery
3.Path-key establishment
During these phases, secret keys are generated, placed in sensor nodes, and each sensor node searches the area in its communication range to find another node to communicate. A secure link is established when two nodes discover one or more common keys (this differs in each scheme), and communication is done on that link between those two nodes. Afterwards, paths are established connecting these links, to create a connected graph. The result is a wireless communication network functioning in its own way, according to the key predistribution scheme used in creation.
There are a number of aspects of WSNs on which key predistribution schemes are competing to achieve a better result. The most critical ones are: local and global connectivity, and resiliency.
Local connectivity means the probability that any two sensor nodes have a common key with which they can establish a secure link to communicate.
Global connectivity is the fraction of nodes that are in the largest connected graph over the number of all nodes.
Resiliency is the number of links that cannot be compromised when a number of nodes(therefore keys in them) are compromised. So it is basically the quality of resistance against the attempts to hack the network. Apart from these, two other critical issues in WSN design are computational cost and hardware cost. Computational cost is the amount of computation done during these phases. Hardware cost is generally the cost of the memory and battery in each node.
There is a most-cited key predistribution scheme which is usually called "the main scheme" that introduced the ides of random key distribution, whereby the randomness factor drastically improves resiliency [2].
source:http://en.wikipedia.org/wiki/Key_distribution_in_wireless_sensor_networks
Key predistribution schemes are various methods that have been developed by academicians for a better maintenance of key management in WSNs. Basically a key predistribution scheme has 3 phases:
1.Key distribution
2.Shared key discovery
3.Path-key establishment
During these phases, secret keys are generated, placed in sensor nodes, and each sensor node searches the area in its communication range to find another node to communicate. A secure link is established when two nodes discover one or more common keys (this differs in each scheme), and communication is done on that link between those two nodes. Afterwards, paths are established connecting these links, to create a connected graph. The result is a wireless communication network functioning in its own way, according to the key predistribution scheme used in creation.
There are a number of aspects of WSNs on which key predistribution schemes are competing to achieve a better result. The most critical ones are: local and global connectivity, and resiliency.
Local connectivity means the probability that any two sensor nodes have a common key with which they can establish a secure link to communicate.
Global connectivity is the fraction of nodes that are in the largest connected graph over the number of all nodes.
Resiliency is the number of links that cannot be compromised when a number of nodes(therefore keys in them) are compromised. So it is basically the quality of resistance against the attempts to hack the network. Apart from these, two other critical issues in WSN design are computational cost and hardware cost. Computational cost is the amount of computation done during these phases. Hardware cost is generally the cost of the memory and battery in each node.
There is a most-cited key predistribution scheme which is usually called "the main scheme" that introduced the ides of random key distribution, whereby the randomness factor drastically improves resiliency [2].
source:http://en.wikipedia.org/wiki/Key_distribution_in_wireless_sensor_networks
What is shortest path routing
shortest path routing A form of ROUTING which attempts to send PACKETS of data over a network in such a way that the path taken from the sending computer to the recipient computer is minimized. The path can be measured in either physical distance or in the number of HOPS. This form of routing uses a NON-ADAPTIVE ROUTING ALGORITHM.
Refrence:http://www.encyclopedia.com/doc/1O12-shortestpathrouting.html
Refrence:http://www.encyclopedia.com/doc/1O12-shortestpathrouting.html
Open Shortest Path First
Open Shortest Path First (OSPF) is a dynamic routing protocol for use in Internet Protocol (IP) networks. Specifically, it is a link-state routing protocol and falls into the group of interior gateway protocols, operating within a single autonomous system (AS). It is defined as OSPF Version 2 in RFC 2328 (1998) for IPv4.[1] The updates for IPv6 are specified as OSPF Version 3 in RFC 5340 (2008).[2]
OSPF is perhaps the most widely-used interior gateway protocol (IGP) in large enterprise networks; IS-IS, another link-state routing protocol, is more common in large service provider networks. The most widely-used exterior gateway protocol is the Border Gateway Protocol (BGP), the principal routing protocol between autonomous systems on the Internet.
OSPF is perhaps the most widely-used interior gateway protocol (IGP) in large enterprise networks; IS-IS, another link-state routing protocol, is more common in large service provider networks. The most widely-used exterior gateway protocol is the Border Gateway Protocol (BGP), the principal routing protocol between autonomous systems on the Internet.
Neighbor relationships
Routers in the same broadcast domain or at each end of a point-to-point telecommunications link form adjacencies when they have detected each other. This detection occurs when a router identifies itself in a hello OSPF protocol packet. This is called a two way state and is the most basic relationship. The routers in an Ethernet or frame relay network select a designated router (DR) and a backup designated router (BDR) which act as a hub to reduce traffic between routers. OSPF uses both unicast and multicast to send "hello packets" and link state updates.
As a link state routing protocol, OSPF establishes and maintains neighbor relationships in order to exchange routing updates with other routers. The neighbor relationship table is called an adjacency database in OSPF. Provided that OSPF is configured correctly, OSPF forms neighbor relationships only with the routers directly connected to it. The routers that it forms a neighbor relationship with must be in the same area as the interface with which it is using to form a neighbor relationship. An interface can only belong to a single area.
As a link state routing protocol, OSPF establishes and maintains neighbor relationships in order to exchange routing updates with other routers. The neighbor relationship table is called an adjacency database in OSPF. Provided that OSPF is configured correctly, OSPF forms neighbor relationships only with the routers directly connected to it. The routers that it forms a neighbor relationship with must be in the same area as the interface with which it is using to form a neighbor relationship. An interface can only belong to a single area.
Area types
An OSPF network is divided into areas that are labeled with 32-bit area identifiers. The area identifiers are commonly, but not always, written in the dot-decimal notation of an IPv4 address. However, they are not IP addresses and may duplicate, without conflict, any IPv4 address. The area identifiers for IPv6 implementations of OSPF (OSPFv3) also use 32-bit identifiers written in the same notation. While most OSPF implementations will right-justify an area number written in other than dotted decimal format (e.g., area 1), it is wise to always use dotted-decimal formats. Most implementations expand area 1 to the area identifier 0.0.0.1, but some have been known to expand it as 1.0.0.0.
Areas are logical groupings of hosts and networks, including their routers having interfaces connected to any of the included networks. Each area maintains a separate link state database whose information may be summarized towards the rest of the network by the connecting router. Thus, the topology of an area is unknown outside of the area. This reduces the amount of routing traffic between parts of an autonomous system.
Several "special" area types are defined.
Areas are logical groupings of hosts and networks, including their routers having interfaces connected to any of the included networks. Each area maintains a separate link state database whose information may be summarized towards the rest of the network by the connecting router. Thus, the topology of an area is unknown outside of the area. This reduces the amount of routing traffic between parts of an autonomous system.
Several "special" area types are defined.
Backbone area
The backbone area (also known as area 0 or area 0.0.0.0) forms the core of an OSPF network. All other areas are connected to it, and inter-area routing happens via routers connected to the backbone area and to their own associated areas. It is the logical and physical structure for the 'OSPF domain' and is attached to all nonzero areas in the OSPF domain. Note that in OSPF the term Autonomous System Border Router (ASBR) is historic, in the sense that many OSPF domains can coexist in the same Internet-visible autonomous system, RFC1996 (ASGuidelines 1996, p. 25) [4].
The backbone area is responsible for distributing routing information between nonbackbone areas. The backbone must be contiguous, but it does not need to be physically contiguous; backbone connectivity can be established and maintained through the configuration of virtual links.
All OSPF areas must connect to the backbone area. This connection, however, can be through a virtual link. For example, assume area 0.0.0.1 has a physical connection to area 0.0.0.0. Further assume that area 0.0.0.2 has no direct connection to the backbone, but this area does have a connection to area 0.0.0.1. Area 0.0.0.2 can use a virtual link through the transit area 0.0.0.1 to reach the backbone. To be a transit area, an area has to have the transit attribute, so it cannot be stubby in any way.
The backbone area is responsible for distributing routing information between nonbackbone areas. The backbone must be contiguous, but it does not need to be physically contiguous; backbone connectivity can be established and maintained through the configuration of virtual links.
All OSPF areas must connect to the backbone area. This connection, however, can be through a virtual link. For example, assume area 0.0.0.1 has a physical connection to area 0.0.0.0. Further assume that area 0.0.0.2 has no direct connection to the backbone, but this area does have a connection to area 0.0.0.1. Area 0.0.0.2 can use a virtual link through the transit area 0.0.0.1 to reach the backbone. To be a transit area, an area has to have the transit attribute, so it cannot be stubby in any way.
Stub area
A stub area is an area which does not receive route advertisements external to the autonomous system (AS) and routing from within the area is based entirely on a default route. This reduces the size of the routing databases for the area's internal routers.
Modifications to the basic concept of stub areas exist in the not-so-stubby area (NSSA). In addition, several other proprietary variation have been implemented by systems vendors, such as the totally stubby area (TSA) and the NSSA totally stubby area, both an extension in Cisco Systems routing equipment.
Modifications to the basic concept of stub areas exist in the not-so-stubby area (NSSA). In addition, several other proprietary variation have been implemented by systems vendors, such as the totally stubby area (TSA) and the NSSA totally stubby area, both an extension in Cisco Systems routing equipment.
Not-so-stubby area
A not-so-stubby area (NSSA) is a type of stub area that can import autonomous system external routes and send them to other areas, but still cannot receive AS external routes from other areas. NSSA is an extension of the stub area feature that allows the injection of external routes in a limited fashion into the stub area.
Proprietary extensions
Totally stubby area
A totally stubby area in Cisco Systems routers,[5] is similar to a stub area. However, this area does not allow summary routes in addition to not having external routes, that is, inter-area (IA) routes are not summarized into totally stubby areas. The only way for traffic to get routed outside of the area is a default route which is the only Type-3 LSA advertised into the area. When there is only one route out of the area, fewer routing decisions have to be made by the route processor, which lowers system resource utilization. Occasionally, it is said that a TSA can have only one ABR.[citation needed] This is not true. If there are multiple ABRs, as might be required for high availability, routers interior to the TSA will send non-intra-area traffic to the ABR with the lowest intra-area metric (the "closest" ABR).
NSSA totally stubby area
Cisco Systems also implements a proprietary version of NSSA, called a NSSA totally stubby area. It takes on the attributes of a TSA, meaning that type 3 and type 4 summary routes are not flooded into this type of area. It is also possible to declare an area both totally stubby and not-so-stubby, which means that the area will receive only the default route from area 0.0.0.0, but can also contain an autonomous system border router (ASBR) that accepts external routing information and injects it into the local area, and from the local area into area 0.0.0.0.
Redistribution into an NSSA area creates a special type of LSA known as TYPE 7, which can exist only in an NSSA area. An NSSA ASBR generates this LSA, and an NSSA ABR router translates it into type 5 LSA which gets propagated into the OSPF domain.
An area can simultaneously be not-so-stubby and totally stubby. This is done when the practical place to put an ASBR, as, for example, with a newly acquired subsidiary, is on the edge of a totally stubby area. In such a case, the ASBR does send externals into the totally stubby area, and they are available to OSPF speakers within that area. In Cisco's implementation, the external routes can be summarized before injecting them into the totally stubby area. In general, the ASBR should not advertise default into the TSA-NSSA, although this can work with extremely careful design and operation, for the limited special cases in which such an advertisement makes sense.
By declaring the totally stubby area as NSSA, no external routes from the backbone, except the default route, enter the area being discussed. The externals do reach area 0.0.0.0 via the TSA-NSSA, but no routes other than the default route enter the TSA-NSSA. Routers in the TSA-NSSA send all traffic to the ABR, except to routes advertised by ASBR.
Cisco Systems also implements a proprietary version of NSSA, called a NSSA totally stubby area. It takes on the attributes of a TSA, meaning that type 3 and type 4 summary routes are not flooded into this type of area. It is also possible to declare an area both totally stubby and not-so-stubby, which means that the area will receive only the default route from area 0.0.0.0, but can also contain an autonomous system border router (ASBR) that accepts external routing information and injects it into the local area, and from the local area into area 0.0.0.0.
Redistribution into an NSSA area creates a special type of LSA known as TYPE 7, which can exist only in an NSSA area. An NSSA ASBR generates this LSA, and an NSSA ABR router translates it into type 5 LSA which gets propagated into the OSPF domain.
An area can simultaneously be not-so-stubby and totally stubby. This is done when the practical place to put an ASBR, as, for example, with a newly acquired subsidiary, is on the edge of a totally stubby area. In such a case, the ASBR does send externals into the totally stubby area, and they are available to OSPF speakers within that area. In Cisco's implementation, the external routes can be summarized before injecting them into the totally stubby area. In general, the ASBR should not advertise default into the TSA-NSSA, although this can work with extremely careful design and operation, for the limited special cases in which such an advertisement makes sense.
By declaring the totally stubby area as NSSA, no external routes from the backbone, except the default route, enter the area being discussed. The externals do reach area 0.0.0.0 via the TSA-NSSA, but no routes other than the default route enter the TSA-NSSA. Routers in the TSA-NSSA send all traffic to the ABR, except to routes advertised by ASBR.
Transit area
A transit area is an area with two or more OSPF border routers and is used to pass network traffic from one adjacent area to another. The transit area does not originate this traffic and is not the destination of such traffic.
Path preference
OSPF uses path cost as its basic routing metric, which was defined by the standard not to equate to any standard value such as speed, so the network designer could pick a metric important to the design. In practice, it is determined by the speed (bandwidth) of the interface addressing the given route, although that tends to need network-specific scaling factors now that links faster than 100 Mbit/s are common. Cisco uses a metric like 10^8/bandwidth (the base value, 10^8 by default, can be adjusted). So, a 100Mbit/s link will have a cost of 1, a 10Mbit/s a cost of 10 and so on. But for links faster than 100Mbit/s, the cost would be <1.
Metrics, however, are only directly comparable when of the same type. There are four types of metrics, with the most preferred type listed in order below. An intra-area route is always preferred to an inter-area route regardless of metric, and so on for the other types.
Metrics, however, are only directly comparable when of the same type. There are four types of metrics, with the most preferred type listed in order below. An intra-area route is always preferred to an inter-area route regardless of metric, and so on for the other types.
- Intra-area
- Inter-area
- External Type 1, which includes both the external path cost and the sum of internal path costs to the ASBR that advertises the route, 4.
- External Type 2, the value of which is solely that of the external path cost.
Refrence:http://en.wikipedia.org/wiki/Open_Shortest_Path_First
Traffic engineering
OSPF-TE is an extension to OSPF extending the expressivity to allow for traffic engineering and use on non-IP networks (RFC 3630)[6]. More information about the topology can be exchanged using opaque LSA carrying type-length-value elements. These extensions allow OSPF-TE to run completely out of band of the data plane network. This means that it can also be used on non-IP networks, such as optical networks.
OSPF-TE is mainly used within GMPLS networks, as a means to describe the topology over which GMPLS paths can be established. GMPLS then uses its own path setup and forwarding protocols, once it has the full network map.
OSPF-TE is mainly used within GMPLS networks, as a means to describe the topology over which GMPLS paths can be established. GMPLS then uses its own path setup and forwarding protocols, once it has the full network map.
OSPF router types
OSPF defines the following router types:
- Area border router (ABR)
- Autonomous system border router (ASBR)
- Internal router (IR)
- Backbone router (BR)
The router types are attributes of an OSPF process. A given physical router may have one or more OSPF processes. For example, a router that is connected to more than one area, and which receives routes from a BGP process connected to another AS, is both an ABR and an ASBR.
Each router has an identifier, customarily written in the dotted decimal format (e.g.: 1.2.3.4) of an IP address. This ID must be configured to an OSPF instance in order to be considered the ID. If not explicitly configured, the highest logical IP address will assume the router ID role. The router ID does not have to be a part of any routable subnet in the network and often isn't to avoid confusion.
Note: Do not confuse router types with designated router (DR), or backup designated router (BDR), which is an attribute of a router interface, not the router itself.
Area border router
An ABR is a router that connects one or more OSPF areas to the main backbone network. It is considered a member of all areas it is connected to. An ABR keeps multiple copies of the link-state database in memory, one for each area to which that router is connected.
Autonomous system boundary router
Autonomous system boundary router
An ASBR is a router that is connected to more than one AS and that exchanges routing information with routers in other ASs. ASBRs typically also run a non-IGP routing protocol (e.g., BGP), or use static routes, or both. An ASBR is used to distribute routes received from other ASs throughout its own AS.
Internal router
Internal router
An IR is a router that only has OSPF neighbor relationships with interfaces in the same area.
Backbone router
Backbone router
Backbone Routers: These are routers that are part of the OSPF backbone. By definition, this includes all area border routers, since those routers pass routing information between areas. However, a backbone router may also be a router that connects only to other backbone (or area border) routers, and is therefore not part of any area (other than Area 0).
Note that: an area border router is always a backbone router, but a backbone router is not necessarily an area border router.
Note that: an area border router is always a backbone router, but a backbone router is not necessarily an area border router.
Designated router
A designated router (DR) is the router interface elected among all routers on a particular multiaccess network segment, generally assumed to be broadcast multiaccess. Special techniques, often vendor-dependent, may be needed to support the DR function on nonbroadcast multiaccess (NBMA) media. It is usually wise to configure the individual virtual circuits of a NBMA subnet as individual point-to-point lines; the techniques used are implementation-dependent.
Do not confuse the DR with an OSPF router type. A given physical router can have some interfaces that are designated (DR), others that are backup designated (BDR), and others that are non-designated. If no router is DR or BDR on a given subnet, the DR is first elected, and then a second election is held if there is more than one BDR. [8] The DR is elected based on the following default criteria:
- If the priority setting on a OSPF router is set to 0, that means it can NEVER become a DR or BDR (Backup Designated Router).
- When a DR fails and the BDR takes over, there is another election to see who becomes the replacement BDR.
- The router sending the Hello packets with the highest priority wins the election.
- If two or more routers tie with the highest priority setting, the router sending the Hello with the highest RID (Router ID) wins. NOTE: a RID is the highest logical (loopback) IP address configured on a router, if no logical/loopback IP address is set then the Router uses the highest IP address configured on its active interfaces. (e.g. 192.168.0.1 would be higher than 10.1.1.2).
- Usually the router with the second highest priority number becomes the BDR.
- The priority values range between 0 - 254, with a higher value increasing its chances of becoming DR or BDR.
- IF a HIGHER priority OSPF router comes online AFTER the election has taken place, it will not become DR or BDR until (at least) the DR and BDR fail.
- If the current DR 'goes down' the current BDR becomes the new DR and a new election takes place to find another BDR. If the new DR then 'goes down' and the original DR is now available, it then becomes DR again, but no change is made to the current BDR.
DR's exist for the purpose of reducing network traffic by providing a source for routing updates, the DR maintains a complete topology table of the network and sends the updates to the other routers via multicast. All routers in an area will form a slave/master relationship with the DR. They will form adjacencies with the DR and BDR only. Every time a router sends an update, it sends it to the DR and BDR on the multicast address 224.0.0.6. The DR will then send the update out to all other routers in the area, to the multicast address 224.0.0.5. This way all the routers do not have to constantly update each other, and can rather get all their updates from a single source. The use of multicasting further reduces the network load. DRs and BDRs are always setup/elected on Broadcast networks (Ethernet). DR's can also be elected on NBMA (Non-Broadcast Multi-Access) networks such as Frame Relay or ATM. DRs or BDRs are not elected on point-to-point links (such as a point-to-point WAN connection) because the two routers on either sides of the link must become fully adjacent and the bandwidth between them cannot be further optimized.
source:http://en.wikipedia.org/wiki/Open_Shortest_Path_First
Distance-Vector Routing Protocols
This type of routing protocol requires that each router simply inform its neighbors of its routing table. For each network path, the receiving routers pick the neighbor advertising the lowest cost, then add this entry into its routing table for re-advertisement. Hello and RIP are common D-V routing protocols. Common enhancements to D-V algorithms include split horizon, poison reverse, triggered updates, and holddown. You will find a good discussion of D-V, or Bellman-Ford algorithms in RIP's protocol specification, RFC 1058.
source:http://www.freesoft.org/CIE/Topics/117.htm
source:http://www.freesoft.org/CIE/Topics/117.htm
Distance-vector routing protocol
A distance-vector routing protocol is one of the two major classes of routing protocols used in packet-switched networks for computer communications, the other major class being the link-state protocol. A distance-vector routing protocol uses the Bellman-Ford algorithm to calculate paths.
Distance Vector algorithm is routing algorithm that has information of the routers attached to it.
Examples of distance-vector routing protocols include RIPv1 and 2 and IGRP. EGP and BGP are not pure distance-vector routing protocols, because a distance-vector protocol calculates routes based only on link costs whereas in BGP, for example, the local route preference value takes priority over the link cost. In many cases, EGP and BGP are considered DV (distance-vector) routing protocols.
A distance-vector routing protocol requires that a router informs its neighbors of topology changes periodically and, in some cases, when a change is detected in the topology of a network. Compared to link-state protocols, which require a router to inform all the nodes in a network of topology changes, distance-vector routing protocols have less computational complexity and message overhead
Distance Vector algorithm is routing algorithm that has information of the routers attached to it.
Examples of distance-vector routing protocols include RIPv1 and 2 and IGRP. EGP and BGP are not pure distance-vector routing protocols, because a distance-vector protocol calculates routes based only on link costs whereas in BGP, for example, the local route preference value takes priority over the link cost. In many cases, EGP and BGP are considered DV (distance-vector) routing protocols.
A distance-vector routing protocol requires that a router informs its neighbors of topology changes periodically and, in some cases, when a change is detected in the topology of a network. Compared to link-state protocols, which require a router to inform all the nodes in a network of topology changes, distance-vector routing protocols have less computational complexity and message overhead
Method of Distance-vector routing protocol
The methods used to calculate the best path for a network are different between different routing protocols but the fundamental features of distance-vector algorithms are the same across all DV based protocols.
As the name suggests the DV protocol is based on calculating the direction and distance to any link in a network. The cost of reaching a destination is calculated using various route metrics. RIP uses the hop count of the destination whereas IGRP takes into account other information such as node delay and available bandwidth.
Updates are performed periodically in a distance-vector protocol where all or part of a router's routing table is sent to all its neighbors that are configured to use the same distance-vector routing protocol. RIP supports cross-platform distance vector routing whereas IGRP is a Cisco Systems proprietary distance vector routing protocol. Once a router has this information it is able to amend its own routing table to reflect the changes and then inform its neighbors of the changes. This process has been described as ‘routing by rumor’ because routers are relying on the information they receive from other routers and cannot determine if the information is actually valid and true. There are a number of features which can be used to help with instability and inaccurate routing information
As the name suggests the DV protocol is based on calculating the direction and distance to any link in a network. The cost of reaching a destination is calculated using various route metrics. RIP uses the hop count of the destination whereas IGRP takes into account other information such as node delay and available bandwidth.
Updates are performed periodically in a distance-vector protocol where all or part of a router's routing table is sent to all its neighbors that are configured to use the same distance-vector routing protocol. RIP supports cross-platform distance vector routing whereas IGRP is a Cisco Systems proprietary distance vector routing protocol. Once a router has this information it is able to amend its own routing table to reflect the changes and then inform its neighbors of the changes. This process has been described as ‘routing by rumor’ because routers are relying on the information they receive from other routers and cannot determine if the information is actually valid and true. There are a number of features which can be used to help with instability and inaccurate routing information
Limitations in Distance-vector routing protocol
The Bellman-Ford algorithm does not prevent routing loops from happening and suffers from the count-to-infinity problem. The core of the count-to-infinity problem is that if A tells B that it has a path somewhere, there is no way for B to know if the path has B as a part of it. To see the problem clearly, imagine a subnet connected like A-B-C-D-E-F, and let the metric between the routers be "number of jumps". Now suppose that A goes down (out of order). In the vector-update-process B notices that its once very short route of 1 to A is down - B does not receive the vector update from A. The problem is, B also gets an update from C, and C is still not aware of the fact that A is down - so it tells B that A is only two jumps from it, which is false. This slowly propagates through the network until it reaches infinity (in which case the algorithm corrects itself, due to the "Relax property" of Bellman Ford).
Partial solutions of Distance-vector routing protocol
RIP uses Split Horizon with Poison Reverse technique to reduce the chance of forming loops and use a maximum number of hops to counter the count-to-infinity problem. These measures avoid the formation of routing loops in some, but not all, cases. The addition of a hold time (refusing route updates for a few minutes after a route retraction) avoids loop formation in virtually all cases, but causes a significant increase in convergence times.
A number of loop-free distance vector protocols, such as EIGRP and DSDV, have been developed. These avoid loop formation in all cases, but suffer from increased complexity, and their deployment has been slowed down by the success of link-state protocols such as OSPF.
source:http://en.wikipedia.org/wiki/Distance-vector_routing_protocol
A number of loop-free distance vector protocols, such as EIGRP and DSDV, have been developed. These avoid loop formation in all cases, but suffer from increased complexity, and their deployment has been slowed down by the success of link-state protocols such as OSPF.
source:http://en.wikipedia.org/wiki/Distance-vector_routing_protocol
On-demand routing protocols
Another in the family of routing protocols for mobile ad-hoc network is on-demand routing protocols. With on-demand protocols, if a source node requires a route to the destination for which it does not have route information, it initiates a route discovery process which goes from one node to the other until it reaches to the destination or an intermediate node has a route to the destination.
It is the responsibility of the route request receiver node to reply back to the source node about the possible route to the destination. The source node uses this route for data transmission to the destination node. Some of the better known on-demand protocols are Ad-hoc On-demand Distance Vector routing (AODV), Dynamic Source Routing (DSR) and Temporary Ordered Routing Algorithm (TORA).
These protocols differ on storing the previously known route information and on how they use the established route data. Again, in a network with many participating nodes we may suffer with same sort of problems what we have seen in table-driven protocols.
ConclusionIn conclusion, routing is one of the core issues in mobile ad-hoc network. An effective routing mechanism will be helpful to extend the successful deployment of mobile ad-hoc networks. Current routing protocols provide routing solutions up to a certain level, but are lacking the ability to handle other related issues.
Moreover most of these protocols have designed and implemented on small scale. If these protocols could be extended further by taking into accounts other routing related factors we may come out with a standard routing solution for mobile ad-hoc network.
Dr. Humayun Bakht completed his Ph.D at the School of Computing and Mathematics in Liverpool at John Moores University. Prior to his current course of studies, he has successfully completed his MSc Software Engineering and BSc Electronics Engineering from University of Liverpool UK and Sir Syed University of Engineering and Technology in Karachi, Pakistan. Humayun's research interest is mobile ad-hoc networks, in particular, the development of a new routing algorithm for this type of networking. He can be reached at humayunbakht@yahoo.co.uk and you can visit his Web site at http://www.geocities.com/humayunbakht/.
It is the responsibility of the route request receiver node to reply back to the source node about the possible route to the destination. The source node uses this route for data transmission to the destination node. Some of the better known on-demand protocols are Ad-hoc On-demand Distance Vector routing (AODV), Dynamic Source Routing (DSR) and Temporary Ordered Routing Algorithm (TORA).
These protocols differ on storing the previously known route information and on how they use the established route data. Again, in a network with many participating nodes we may suffer with same sort of problems what we have seen in table-driven protocols.
ConclusionIn conclusion, routing is one of the core issues in mobile ad-hoc network. An effective routing mechanism will be helpful to extend the successful deployment of mobile ad-hoc networks. Current routing protocols provide routing solutions up to a certain level, but are lacking the ability to handle other related issues.
Moreover most of these protocols have designed and implemented on small scale. If these protocols could be extended further by taking into accounts other routing related factors we may come out with a standard routing solution for mobile ad-hoc network.
Dr. Humayun Bakht completed his Ph.D at the School of Computing and Mathematics in Liverpool at John Moores University. Prior to his current course of studies, he has successfully completed his MSc Software Engineering and BSc Electronics Engineering from University of Liverpool UK and Sir Syed University of Engineering and Technology in Karachi, Pakistan. Humayun's research interest is mobile ad-hoc networks, in particular, the development of a new routing algorithm for this type of networking. He can be reached at humayunbakht@yahoo.co.uk and you can visit his Web site at http://www.geocities.com/humayunbakht/.
Routing protocols for mobile ad-hoc networks
We continue our series on mobile ad-hoc networks with a discussion of routing protocols, or how the information is going to move throughout the network.
Mobile ad-hoc networks, also known as short-lived networks, are autonomous systems of mobile nodes forming network in the absence of any centralized support. This is a new form of network and might be able to provide services at places where it is not possible otherwise. Absence of fixed infrastructure poses several types of challenges for this type of networking. Among these challenges is routing.
By routing, we mean process of exchanging information from one station to the other stations of the network. Routing protocols of mobile ad-hoc network tend to need different approaches from existing Internet protocols, since most of the existing Internet protocols were designed to support routing in a network with fixed structure. In the academic and industrial world, those who think about such things have written quite a few papers proposing various routing solutions for mobile ad-hoc networks. Proposed solutions could be classified into six types: table-driven, on-demand, hierarchical, power-aware, geographical, and multicast protocols.
Table-driven protocolsTable-driven protocols are one of the old ways of acquiring routing in mobile ad-hoc networks. These protocols maintain consistent overview of the network. Each node uses routing tables to store the location information of other nodes in the network. This information is used to transfer data among various nodes of the network.
To ensure the freshness of the routing tables, these protocols adopts different sorts of mechanisms. One of the adopted methods is broadcasting "hello," a special message containing address information, at fixed intervals of time. On receiving this message, each node updates its routing tables with fresh locations information of other participating nodes. Destination Sequence Distance Vector routing protocol (DSDV), Wireless Routing Protocol (WRP) and Cluster-head Gateway Switch Routing (CGSR) are some of the popular table-driven protocols for mobile ad-hoc networks.
Table-driven protocols might not be considered an effective routing solution for mobile ad-hoc network. Nodes in mobile ad-hoc networks operate with low battery power and with limited bandwidth. Presence of high mobility, large routing tables and low scalability result in consumption of bandwidth and battery life of the nodes. Moreover continuous updates could create unnecessary network overhead.
source:http://www.computingunplugged.com/issues/issue200407/00001326001.html
Mobile ad-hoc networks, also known as short-lived networks, are autonomous systems of mobile nodes forming network in the absence of any centralized support. This is a new form of network and might be able to provide services at places where it is not possible otherwise. Absence of fixed infrastructure poses several types of challenges for this type of networking. Among these challenges is routing.
By routing, we mean process of exchanging information from one station to the other stations of the network. Routing protocols of mobile ad-hoc network tend to need different approaches from existing Internet protocols, since most of the existing Internet protocols were designed to support routing in a network with fixed structure. In the academic and industrial world, those who think about such things have written quite a few papers proposing various routing solutions for mobile ad-hoc networks. Proposed solutions could be classified into six types: table-driven, on-demand, hierarchical, power-aware, geographical, and multicast protocols.
Table-driven protocolsTable-driven protocols are one of the old ways of acquiring routing in mobile ad-hoc networks. These protocols maintain consistent overview of the network. Each node uses routing tables to store the location information of other nodes in the network. This information is used to transfer data among various nodes of the network.
To ensure the freshness of the routing tables, these protocols adopts different sorts of mechanisms. One of the adopted methods is broadcasting "hello," a special message containing address information, at fixed intervals of time. On receiving this message, each node updates its routing tables with fresh locations information of other participating nodes. Destination Sequence Distance Vector routing protocol (DSDV), Wireless Routing Protocol (WRP) and Cluster-head Gateway Switch Routing (CGSR) are some of the popular table-driven protocols for mobile ad-hoc networks.
Table-driven protocols might not be considered an effective routing solution for mobile ad-hoc network. Nodes in mobile ad-hoc networks operate with low battery power and with limited bandwidth. Presence of high mobility, large routing tables and low scalability result in consumption of bandwidth and battery life of the nodes. Moreover continuous updates could create unnecessary network overhead.
source:http://www.computingunplugged.com/issues/issue200407/00001326001.html
Mobile ad hoc network
A mobile ad hoc network (MANET), sometimes called a mobile mesh network, is a self-configuring network of mobile devices connected by wireless links.[1]
Each device in a MANET is free to move independently in any direction, and will therefore change its links to other devices frequently. Each must forward traffic unrelated to its own use, and therefore be a router. The primary challenge in building a MANET is equipping each device to continuously maintain the information required to properly route traffic.
Such networks may operate by themselves or may be connected to the larger Internet.
MANETs are a kind of wireless ad hoc networks that usually has a routeable networking environment on top of a Link Layer ad hoc network. They are also a type of mesh network, but many mesh networks are not mobile or not wireless.
The growth of laptops and 802.11/Wi-Fi wireless networking have made MANETs a popular research topic since the mid- to late 1990s. Many academic papers evaluate protocols and abilities assuming varying degrees of mobility within a bounded space, usually with all nodes within a few hops of each other and usually with nodes sending data at a constant rate. Different protocols are then evaluated based on the packet drop rate, the overhead introduced by the routing protocol, and other measures.
source:http://en.wikipedia.org/wiki/Mobile_ad-hoc_network
Each device in a MANET is free to move independently in any direction, and will therefore change its links to other devices frequently. Each must forward traffic unrelated to its own use, and therefore be a router. The primary challenge in building a MANET is equipping each device to continuously maintain the information required to properly route traffic.
Such networks may operate by themselves or may be connected to the larger Internet.
MANETs are a kind of wireless ad hoc networks that usually has a routeable networking environment on top of a Link Layer ad hoc network. They are also a type of mesh network, but many mesh networks are not mobile or not wireless.
The growth of laptops and 802.11/Wi-Fi wireless networking have made MANETs a popular research topic since the mid- to late 1990s. Many academic papers evaluate protocols and abilities assuming varying degrees of mobility within a bounded space, usually with all nodes within a few hops of each other and usually with nodes sending data at a constant rate. Different protocols are then evaluated based on the packet drop rate, the overhead introduced by the routing protocol, and other measures.
source:http://en.wikipedia.org/wiki/Mobile_ad-hoc_network
Types of MANET
- Vehicular Ad Hoc Networks (VANETs) are used for communication among vehicles and between vehicles and roadside equipment.
- Intelligent vehicular ad hoc networks (InVANETs) are a kind of artificial intelligence that helps vehicles to behave in intelligent manners during vehicle-to-vehicle collisions, accidents, drunken driving etc.
- Internet Based Mobile Ad-hoc Networks (iMANET) are ad-hoc networks that link mobile nodes and fixed Internet-gateway nodes. In such type of networks normal ad-hoc routing algorithms don't apply directly.
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