IP Networks

1.1 INTRODUCTION

In last few decades the Internet has been transformed from a special purpose network to an omnipresent platform for a broad range of daily communication services. The demands on Internet availability and reliability have improved accordingly. An interruption of a link in central parts of a network has the ability to affect hundreds of thousands of phone conversations or TCP connections, with apparent adverse effects. The potential to recover from failures has always been a central design goal in the Internet ( Bhargav and Kartheek 2013).

IP networks are basically robust, since IGP routing protocols are designed to update the forwarding information based on the changed topology after failure has occurred in the network. This re-convergence believes full distribution of the new link state to all routers in the network area. When the new state information is circulated, each router individually computes new valid routing tables. The IGP convergence process is slow, as it is reactive i.e., it reacts to a failure after it has happened, and global i.e., it involves all the routers in the domain. This global IP re-convergence is a time consuming process, and a link/node failure is followed by a period of routing instability which results in packet drop. This phenomenon has been studied in both IGP and BGP context, and has an adverse effect on real-time applications ( Bhargav and Kartheek 2013). Though the different steps of the convergence of IP routing, i.e., detection, dissemination of information and shortest path calculation has been optimized, the convergence time is still too large for applications with real time demands ( Kvalbein, Hansen and ˇCiˇci´c,, et al. 2007). Since most network failures are short lived, too rapid triggering of the re-convergence process can cause route flapping. Later, the multiple routing configurations (MRC) method has been proposed for Fast Rerouting. The MRC method prepares backup configurations, which are precomputed and used for finding a detour route after a failure. In a backup configuration, some links are assigned a higher metric value. Such links are called isolated links. These isolated links can be regarded as protected links. They are not used to forward the traffic when a resource fails. An arbitrary link is an isolated link in at least one backup configuration. Therefore, we can achieve fast recovery against any single failure using backup configurations. But, it requires too many backup configurations consumes more network resources. It is necessary to recover more traffic flows with fewer backup configurations to ensure scalability. Along with these, MRC recovers network from single node/link failures, but does not support network from multiple node/link failures ( Anji Kumar and Prasad 2011).

This dissertation supports multiple node/link failures during data transmission in IP networks without frequent global re-convergence. EMRC is a threefold approach. First, a set of backup configurations are created, such that every network component is excluded from packet forwarding in one configuration. Second, for each configuration, a routing algorithm like OSPF is used to calculate configuration specific shortest paths and create forwarding tables in each router. Third, a forwarding process is designed which uses the backup configurations to provide fast recovery from a component failure. By recovering these failures, data transmission in network will become fast ( Bhargav and Kartheek 2013).

1.2 IP network recovery

IP networks are intrinsically robust. The IGP protocols like OSPF are design to update the forward information based on the topology which is changed after the failure, when the new information state is distributed to each router to calculate new routing tables. The IP re-convergence is the time —consuming process and a link is difficult to find the period of routing. During this packets can be dropped due to invalid routes. Both IGP and BGP context are studied and has the adverse effect on real-time application. Many efforts are optimize in different steps to convergence of IP routing as detection, dissemination of information and to calculate the shortest part ( Kvalbein, Hansen and ˇCiˇci´c,, et al. 2007).

1.3 IP Fast network failure recovery

In the IP level the routers of the network still should able to be deliver the packets in a long alternative path that exist. The perfect routing protocols are Open Shortest Path First (OSPF) and Intermediate System to Intermediate System (IS-IS). These routers are informed on network topology to change the update messages and re-calculate the routing path. The different approaches to handle the physical failures are Proactive Failure Recovery (PFR) were the routers compute and store the backup paths for potential failures and once the local link failure is detected. PFR has the shortest failure recovery time and can reduce both the update propagation and path re-calculation. The large portion of failures in IP network is short, transient failure and PFR should able to improve the quality of deliver packets. The goals for minimizing the failures of application performances use the post-failure load balance which is important. Weight-setting method is used for load balance in PFR. It gives the demand of the projected from previous measurements to find the weight set to avoid congestions. The links weights are re-assigned according to the load that carriers the large weights for heave loaded links and small weights for light loaded links and re-calculate the routing path based on the new link weights. PFR can has two design challenges of post failure load balancing that is first is how to select the multiple loop-free backup path with small and second is how to decide the amount of affected traffic that is to shed on each backup path in balanced manner (Kvalbein, Hansen and ˇCiˇci´, et al. 2009). By proposing the unique solutions can follow the four contributions as

i. Explore and identify other two additional types of loop-free alternative paths that is beside the Equal-Cost-Multiple-path that gives more path diversity to post-failure delivery

ii. Decides the traffic distribution over multiple paths that formulate it as LP problem that minimize the sum of links which are utilize. To solve the problem, assign the penalty factor to heavy loaded link to achieve the goal to maximize and minimize the utilized links in the network.

iii. Introduce the base factor into LP iteration to damp the oscillation.

iv. If the failure occurs, the LP problem can solve incrementally where the traffic affected by the failure is taken in consideration by objective function of LP. The result shows the simulation that the scheme has effectively balance to load the multiple paths which has small computation and fast converges.

1.4 Multiple Routing Configurations (MRC)

To assure fast recovery from link and node failures in IP networks, the new recovery scheme called Multiple Routing Configurations (MRC) is present. The proposed scheme guarantees recovery in all single failure scenarios, using a single mechanism to handle both link and node failures, and without knowing the root cause of the failure. MRC is strictly connectionless, and assumes only destination based hop-by-hop forwarding. The main idea of MRC is to use the network graph and the associated link weights to produce a small set of backup network configurations. The link weights in these backup Configurations are manipulated so that for each link and node failure, and regardless of whether it is a link or node failure, the node that detects the failure can safely forward the incoming packets towards the destination on an alternate link (Kvalbein, Hansen and ˇCiˇci´, et al. 2009). MRC assumes that the network uses shortest path routing and destination based hop-by-hop forwarding. MRC is a proactive and local protection mechanism that allows recovery in the range of milliseconds.

MRC has a range of attractive features:

1. It gives almost continuous forwarding of packets in the case of a failure. The router that detects the failure initiates a local rerouting immediately, without communicating with the surrounding neighbors.

2. MRC helps improve network availability through suppression of the re-convergence process. Delaying this process is useful to address transient failures, and pays off under many scenarios. Suppression of the re-convergence process is further actualized by the evidence that a large proportion of network failures is short-lived, often lasting less than a minute.

3. MRC uses a single mechanism to handle both link and node failures. Failures are handled locally by the detecting node, and MRC always finds a route to the destination (if operational).

4. MRC makes no assumptions with respect to the root cause of failure, e.g., whether the packet forwarding is disrupted due to a failed link or a failed router. Regardless of this, MRC guarantees that there exists a valid, preconfigured next-hop to the destination.

1.5 PARAMETERS FOR ANALYSIS

Node fault- When any router stops its functionalities in the network then it is called node fault. It causes packet drop in the network.

Link fault- When link L between two nodes u and v breaks, it is called link fault.

Preconfigured — It is predefined configuration for future point of view. IP recovery techniques use this configuration to send the data after detecting the failure in the network.

Connectionless- There is no physical link between two nodes is called connectionless. Two nodes connected logically. We assume that all recovery techniques are strictly connectionless.

Bi-connected- bi-connected means if any vertex remove from graph, the graph will remain connected. After removing any node from graph it would not split into two parts.

Links and nodes:

• An isolated link has infinite weight

A node is isolated when all attached links are either isolated or restricted

Traffic never goes through an isolated link or an isolated node!

1.6 TOPOLOGY CONSTRUCTION:

Topology is constructed by getting the names of the nodes and the connections among the nodes as input from the user. While getting each of the nodes, their associated port and IP address is also obtained. For successive nodes, the node to which it should be connected is also accepted from the user. While adding nodes, comparison will be done so that there would be no node duplication. Then we identify the source and the destinations (Meeravali, et al. 2013).

Figure 1.6: Topology Construction

1.7 MESSAGE TRANSMISSON:

Messages are transmit from source to destination. By choose a destination and select a shortest path for that destination. Shortest path is calculated by Dijkstra Algorithm. it will take minimum node cost an account to find the path between a source and destination. The shortest path is updated in the routing table. The source obtains the shortest path from the routing table itself. After receiving a message the destination will send an acknowledgement to the corresponding source and destination. The shortest path is updated in the routing table (Meeravali, et al. 2013). The source obtains the shortest path from the routing table itself. After receiving a message the destination will send an acknowledgement to the corresponding source.

Figure 1.7: Message Transmission

1.7.1 PREVENTING LINK FAILURE USING MRC:

MRC approach is best of threefold. First, create a set of backup configurations, so that every network component is excluded from packet forwarding in one configuration. Second, for each configuration, a standard routing algorithm like OSPF is used to calculate configuration specific shortest paths and create forwarding tables in each router, based on the configurations. The use of a standard routing algorithm guarantees loop-free forwarding within one configuration. Finally, design a forwarding process that takes advantage of the backup configurations to provide fast recovery from a component failure (Kvalbein, Hansen and ˇCiˇci´, et al. 2009).

Then construct the backup configurations so that for all links and nodes in the network, there is a configuration where that link or node is not used to forward traffic. Thus, for any single link or node failure, there will exist a configuration that will route the traffic to its destination on a path that avoids the failed element. Also, the backup configurations must be constructed so that all nodes are reachable in all configurations, i.e., there is a valid path with a finite cost between each node pair. And distinguish between the normal configuration and the backup configurations, Ci, i > 0. In the normal configuration, all links have ―normal‖ weights W0 (a) Д {1…Wmax}. We assume C0 that is given with finite integer weights.

MRC is agnostic to the setting of these weights. In the backup configurations, selected links and nodes must not carry any transit traffic. Still, traffic must be able to depart from and reach all operative nodes. Isolated links do not carry any traffic. Restricted links are used to isolate nodes from traffic forwarding (Meeravali, et al. 2013). The restricted link weight 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.

Figure 1.7.1: Preventing Link Failure Using MRC

1.8 OBJECTIVE

The main objective of Enhanced Multiple Routing Configuration (EMRC) is that. Each source to destination transmission maintains original route. First shortest path is taken as an original route. These shortest paths are calculated by using the OSPF algorithm. Initially, data packets will be transmitted using this original route. In this source to destination transmission, any sudden occurrence of node or link failure happens, total transmission is collapsed. At this time EMRC uses the timeslot mechanism. If a failure is occurred then will give the timeslot, means give some time to failure recovery before changing the 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 data is transmitted by using the backup route and send the probing for failure recovery. During the backup route transmission, if failure is recovered, then backup route transmission is stopped and again reuses the original route. By reusing the original route it can improve the fastness of routing, since the backup route is longer than the original route.

1.9 PROBLEM STATEMENT

Multiple Routing Configurations (MRC) provide an elegant and powerful hybrid routing framework, it doesn’t protect the network from multiple failures and MRC is expensive as it requires more number of backup configurations and consumes more network resources.

1.9.1 System Model

EMRC is designed to support multiple failures by utilizing time slot mechanism and less number of backup configurations. EMRC is a threefold approach. First, a set of backup configurations are created, such that every network component is excluded from packet forwarding in one configuration. Second, for each configuration, a routing algorithm like OSPF is used to calculate configuration specific shortest paths and create forwarding tables in each router. Third, a forwarding process is designed which uses the backup configurations to provide fast recovery from a component failure (PUJARI and PRASANNA n.d.).

Figure 1.9.1: System Model

1.9.2 Design Objectives

Our mechanism is allowed each source to destination transmission maintains original route. First shortest path is taken as an original route. These shortest paths are calculated by using the OSPF algorithm. Initially, data packets will be transmitted using this original route.

1.10 Dissertation Structure

The structure of this dissertation is organized: in section 2, presents the brief description of the Literature Review, section 3, present the implementation of SDTP, section 4, it shows the Result and finally conclude the paper in section 5.

Source: Essay UK - http://doghouse.net/essays/information-technology/ip-networks/


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