Essay: METHODOLOGY & IMPLEMENTATION – Enhanced Multiple Routing Configurations (EMRC)

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  • METHODOLOGY & IMPLEMENTATION - Enhanced Multiple Routing Configurations (EMRC)
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3.1 Introduction
Enhanced Multiple Routing Configurations (EMRC) is designed to support multiple failures by utilizing time slot mechanism and less number of backup configurations. EMRC is a threefold approach. First, create a set of backup configurations, such that every network component is excluded from packet forwarding in one configuration. Secondly, each configuration, a routing algorithm such as OSPF is used to calculate configuration specific shortest paths and create forwarding tables in every router. Thirdly, a forwarding process is designed to uses the backup configurations to provide fast recovery from a component failure.
3.2 Generating Backup Configurations
For generating backup configurations, this shall adopt an algorithm proposed by Hansen( Anji Kumar and Prasad 2011). The algorithm takes as input the directed graph G and the number n of backup configurations that is intended created. Then also algorithm will typically be run once at the initial step of the network, and also each time a node or link is permanently added or removed. The notation shown in TABLE1 is used. Configuration of EMRC is defined by the network topology, and is the same in whole configurations, the associated link weights which differ among configurations ( Bhargav and Kartheek 2013)( Kumar, et al. 2013)(Kvalbein, Hansen and ˇCiˇci´, et al. 2009). The network topology represent as a graph G = (N, A), consist a set of nodes N and a set of links A. In order to guarantee any single-fault tolerance, then the topology graph G must be bi-connected. A configuration is defined by this topology graph and the associated link weight function: Definition: A configuration Ci is an ordered pair (G,Wi) by the graph G and function Wi : A â†'{1, .. . ,Wmax,Wr, ∞} that assigns an integer weight Wi(a) to each link a Д A.
And distinguish between the normal configuration C0 and the backup configurations Ci, i > 0. In the normal configuration C0, all links have normal weights W0 (a) Д {1, . . . ,Wmax}. Let assume that C0 is given with finite integer weights. EMRC is agnostic to the setting of link weights in C0. In the backup configurations, selected links and nodes must not carry any transited traffic. Still, the traffic must be able to depart from and reach all operative nodes( Anji Kumar and Prasad 2011)( Kvalbein, Hansen and ˇCiˇci´c,, et al. 2007)(Odom and Beasley 2012). These traffic regulations are imposed by assigning high weights to some links in the backup configurations.
Definition: A link a Д A is an isolated in Ci if Wi(a)=∞.
Definition: A link a Д A is an restricted in Ci if Wi(a) = Wr.
TABLE 3.2: Notation
G = (N,A) Graph comprising nodes N and directed links (arcs) A
Ci The graph with link weights as in configuration i
Si The set of isolated nodes in configuration Ci
Bi The backbone in configuration Ci
A(u) The set of links from node u
(u, v) The directed link from node u to node v
pi(u, v) A given shortest path between nodes u and v in Ci
N(p) The nodes on path p
A(p) The links on path p
wi(u, v) The weight of link (u, v) in configuration Ci
wi(p) The total weight of the links in path p in configuration Ci
Wr The weight of a restricted link
N The number of configurations to generate (algorithm
Isolated links do not carry any traffic. Restricted links are used to isolate nodes from traffic forwarding. The restricted link weight Wr must be set to a sufficiently high, finite value to achieve that. Nodes are isolated by assigning at least the restricted link weight to all their attached links. For a node to be reachable, we cannot isolate all links attached to the node in same configuration. Many nodes may be isolated in a configuration (Baranwal, Gupta and Srivastava 2012)( Anji Kumar and Prasad 2011). The set of isolated nodes in Ci is represent by Si, and the set of normal nodes Sn = N Si.
a b
Figure 3.2: isolated links and isolated nodes.
FIGURE 3.2.a. Node 5 is isolated (shaded color) by setting a high weight on its entire connected links. Only a traffic to and from the isolated node will use these restricted links. FIGURE 3.2.b. A configuration in which nodes 1, 4 and 5, and the links 1-2, 3-5 and also 4-5 are isolated (dotted).
The purpose of the restricted links is to isolate a node from routing in a specific backup configuration Ci. In many topologies, more than a single node can be isolated simultaneously. Restricted and isolated links are always given the same weight in both directions. EMRC guarantees single-fault tolerance by isolating each link and node in exactly one backup configuration. By which each configuration, all of the node pairs must be connected by a finite cost path that does not pass through an isolated node or isolated link. A configuration which satisfies this requirement is called valid ( Thakkar 2014)( Bhargav and Kartheek 2013)(Kvalbein, Hansen and ˇCiˇci´, et al. 2009).
Termination: The algorithm runs through all nodes trying to make them isolated in one of the backup configurations and will always terminate with or without success. If a node cannot be isolated in any of the configurations, then the algorithm terminates without success. However, algorithm is designed so that any bi-connected topology will result in a successfully termination, if the number of the configurations allowed is sufficient high.
Complexity: The complexity of the proposed algorithm is determined by the loops and the complexity of the connected method. This method performs a procedure similar to determining whether a node is an articulation point in the graph, bound to the worst case O (|N|+|A|). Additionally, for each node, we run through all adjacent links, whose number has an upper bound in the maximum node degree Δ. In the worst case, we must run through all n configurations to find a configuration where a node can be isolated. Then the worst case running time for the complete algorithm is bound by O (nΔ|N||A|).
3.3 Forwarding Procedure for EMRC
When we want to transmit any data from source to destination in the network, first identify the source node and destination node, after that they look at the shortest path in between them in the original routing table and the data packets are transmitted by using that shortest route. When a data packet reaches a failure, then the node adjacent to the failure, called the detecting node to stops the transmission of the data. At that time slot, detecting node gives the timeslot to failure recovery before shifting to the backup route. Within the timeslot, if the failure is recovered then data is transmitted by using the original route only and if the failure is not recovered, then the detecting node is responsible for finding a backup configuration where the failed component is isolated( Anji Kumar and Prasad 2011). The detecting node marks the packet as belonging to this configuration, and also forwards the packet. From that packet, all routers identify the packet with the selected backup configuration, and then forward it to the egress node to avoid the failed component. Packet marking is most easily done by using specific values in the DSCP field in IP header. If this is not be possible, all other packet marking strategies like IPv6 extension headers or using a private address space and tunneling could be used. During the backup route transmission, the detecting node sends the probing signals for failure recovery and if failure is recovered, then the backup route transmission is stopped and the data packets are transmitted by reusing the original route. By reusing the original route we can improve the fastness of routing, since the backup route is longer than the original route. If a failure lasts for more than a specified time interval, a normal re-convergence will be triggered ( Bhargav and Kartheek 2013)(Odom and Beasley 2012)( Pal and Devi 2013). EMRC does not interfere with this convergence process, or make it’s longer than normal. However, EMRC gives packet forwarding continuously during the convergence, and hence makes it easier to use mechanisms that prevent micro-loops during convergence, at the cost of longer convergence times. If a failure is deemed permanent, new configurations must be generated based on the altered topology( Anji Kumar and Prasad 2011).
Failed forwarding in node U towards node V
Figure 3.3Packet forwarding state diagram.
3.4 Comparison of MRC and EMRC
EMRC is developed from MRC. So, all the processes in EMRC such as backup route finding, shortest path finding and forwarding is same as the MRC. These all are explained and compared by using the following in FIGURE 3.4 and FIGURE 4.
FIGURE 3.4.1: Selection of routes in MRC and EMRC a) At the time of failure occurrence in MRC and EMRC a) After the failure recovery in MRC c) After the failure recovery in EMRC.
As shown in FIGURE 3.4.1, we want to transmit the data from node 1 to node 0 by using the shortest path. Hence, in FIGURE 3.4 the source node is 1 and destination node is 0 and the shortest route is 1-4-5-0. 1-4-5-0 route is taken as a original route. Another route i.e. 1-4-7-0 is a backup configuration, by which the node 5 is isolated. In original route, at middle of the transmission, any sudden failure occurrence in node 5, then data transmission is stopped at node 4. At that time MRC then use backup route which is. 1-4-7-0 transmits the data to destination. By using the backup route, total transmission time increases and fastness of the routing decreases.
Original Route 2 – 4 – 18 -17 – 6 – 3
Backup Route 2 – 14 – 18 – 11 – 19 – 3
Original Route 2 – 4 – 18 -17 – 6 – 3
Backup Route 2 – 14 – 18 – 11 – 19 – 3
Original Route 2 – 4 – 18 -17 – 6 – 3
Backup Route 2 – 14 – 18 – 11 – 19 – 3
FIGURE 3.4.2:Selection of routes in MRC and EMRC a) At the time of Failure occurrence in MRC and EMRC b) After the failure recovery in MRC c) After the failure recovery in EMRC.
By using EMRC, at the time of failure of node 4, it gives the timeslot for failure recovery before shifting to the backup route i.e. 2 – 14 – 18 – 11 – 19 – 3. Within the timeslot if the failure is recovered, then the data is transmitted by using the original route i.e. 2 – 4 – 18 – 17 – 6 – 3only. If the failure is not recovered, then the transmission is shifted to the backup route i.e. 2 – 14 – 18 – 11 – 19 – 3. During the time of backup route transmission we send the probes for failure recovery to the node 4. If at any time, failure is recovered, we again reuse the original route i.e. 2 – 4 – 18 – 17 – 6- 3and backup route transmission is stopped. In EMRC, by using the timeslot and reusing mechanism, we can improve both i.e. fastness of routing and as well as data transmission.
3.5 System Requirements
Software Specifications
OS : Linux(vmware)
Simulator : NS2
Language : Tcl/Tk
Graph : GNUplot
Hardware Specifications
Processor Type : Pentinum IV
Processor Speed : 2.7GHz
3.5.1 Simulation Tool
NS2 is an open-source event-driven simulator designed specifically for research in computer communication networks. Since its inception in 1989, NS2 has continuously gained tremendous interest from industry, academia, and government. Having been under constant investigation and enhancement for years,NS2 now contains modules for numerous network components such as routing, transport layer protocol, application, etc. To investigate network performance, researchers can simply use an easy-to-use scripting language to configure a network, and observe results generated by NS2. Undoubtedly, NS2 has become the most widely used open source network simulator, and one of the most widely used network simulators(Issariyakul and Hossain 2012)(Robbing 2015).
Figure-6 graphically shows an overall view of the layering concept used for communication between two computer hosts: a source host and a destination host.
Figure-3.5.1: Data flow in a layered network architecture.
3.5.2 Characteristics of NS – 2
• Is a discrete event simulator for networking research
• Work at packet level.
• Provide substantial support to simulate bunch of protocols like
• Simulate wired and wireless network.
• Is primarily Unix based.
• Use TCL as its scripting language.
• ns-2 is a standard experiment environment in research community.
3.5.3 Software Tools Used With Ns-2
In the simulation, there are the two tools are used
• NAM(Network Animator)
• XGraph
NAM provides a visual interpretation of the network topology created the application was developed as part of the VINT project. Its feature is as follows
• Provides a visual interpretation of the network created
• Can be executed directly from a Tcl script
• Controls include play stop fast forward,rewind ,pause,a display speed controller button and a packet monitor facility.
• Presented information such as throughput, number packets on each link
X-Graph is an x-window application that includes:
Interactive plotting and graphing Animated and derivatives to use graph in NS-2 the executable can be called with in a TCL Script .This will then load a graph displaying the information visually displaying the information of the file produced from the simulation.The output is a graph of size 800 x 400 displaying information on the traffic flow and time.
3.5.4 Time-Dependent Simulation
A main type of simulation is time dependent simulation which proceeds chronologically. This type of simulation maintains a simulation clock which keeps track of the current simulation time. In most cases, the simulation is run until the clock reaches a predefined threshold. Time-dependent simulation can be further divided into time-driven simulation and event-driven simulation. A time-driven simulation induces and executes events for every fixed time interval. In other words, the simulation advances from one time interval to another, and executes events (if any) until it reaches a certain limit. An event-driven simulation, on the other hand, induces events at arbitrary time(Robbing 2015).
The simulation moves from one event to another, and again executes the event (if any) until the simulation terminates. There is an important note for time-dependent simulation: The simulation must progress in a chronological order. While this note is fairly straight forward for a time-driven simulation, [7] specifies two important points for an implementation of event-driven simulation. First, every new event scheduled into the event list must be tagged with a timestamp equal to or greater than that of the current event.

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