Security - What are the principal ways to secure a wireless network?

Securing a wireless network is as important as securing wired networks, and in many cases even more since it can be easier to tap into a wireless network. One or the other time all of us might have used a WiFi network which might be unsecure (highly unsecure, or may have recent holes that are not yet patched). But this would not do much harm if you are just honestly looking for connecting to the internet. If you own an unsecure wireless network, you should know that everyone is not honest as you are. Attackers with bad intentions can know what activities are taking place in your network and how your network resources can be exploited.  This problem can be fixed by following some basic principles of securing your wireless network:
- WEP and WPA encryption: Encryption is the first line of defense that you can call up for the security of your network. The data that your PC transmits to the wireless router is encoded. But usually what happens is that in most of the routers this option is disabled. You first need to check if it is enabled or not. If you keep it disabled, it will expose your network to several vulnerabilities. You should keep the encryption in enable mode and use the strongest form that is supported by your computer. WPA2 is more sophisticated when compared to WPA. WEP can be easily cracked and so it has been replaced by the most recent version of WPA i.e., the WPA2. One thing to be taken care of is that all the devices should have either WEP or WPA if you are using either of them. These two protocols cannot be mixed and used. The WEP uses the same key every time but this is not the case with the WPA. Here the keys keep on changing dynamically. This makes it almost impossible to hack. The encryption key must have a strong password like a combination of numbers and letters of more than 14 characters. If your computer has an old router that supports only WEP, use the 128-bit WEP key as it is the safest. But you should continuously keep checking for a firmware update at the manufacturer’s website. This update will provide WPA support to WEP. If no update is available, you can replace the old routers and the adapters with their new models that provide support for WPA. It’s better to go with hybrid version of the routers that support both WPA and WPA2. This will provide stronger encryption at the same time while maintaining compatibility with the other adapters.
It should be made sure that the default network name as well as the password have been changed. Doing so will make it difficult for the hackers to break int o the system and change its configuration. Even if you do have a firewall in the router, additional security measures have to be taken. The firewall does not lets the hackers break in to the system. But it does not stop people that lie in to the geographical range of wi-fi from accessing the network. There are readily available tools that can be used for sniffing the traffic through your wireless networks. To supplement the security, the software firewall should also be installed on the computer. Public hotspots are typically very unsecure.  If there are no precautions it should be assumed internet traffic whether incoming or outgoing is visible to the attackers. Before connecting to the network always make sure that is a legitimate one, make sure that the firewall is enabled. And keep the file sharing option to off. You can check whether you have selected the appropriate security options in the firewall settings. These are some tips to increase your security level when dealing with WiFi.

Differentiate between transparent and nontransparent fragmentation?

A number of problems are encountered because of the size of the data packets. There is no ability in the data link layer by means of which it could handle these problems and so the bridges also don’t work here. 

The Ethernet also experiences a number of problems because of the following:

Ø  Different way in which the maximum packet size is defined.

Ø  Maximum packet size that can be handled by a router.

Ø  The maximum length slot that are used for transmission

Ø  Errors due to the packet length

Ø  Standards

The data packets can be fragmented in two ways namely:

1. Transparent and
2. Non – transparent

Both these ways can be followed based on a network by network basis. We can also say that no such end – to – end agreement exists based up on which it can be decided which process is to be used.

Transparent Fragmentation: 

- This type of fragmentation is followed when a packet is split in to smaller fragments by a router.

- These fragments are sent to the next router which does just the opposite i.e., it reassembles the fragments and combine them to form original packet. 

- Here, the next network does not come to know whether any fragmentation has taken place. 

- Transparency is maintained between the small packet networks when compared to the other subsequent networks.

- For example, transparent fragmentation is used by the ATM networks by means of some special hardware. 

- There are some issues with this type of fragmentation. 

- It puts some burden on the performance of the network since all the fragments have to be transmitted through the same gateway. 

- Also, sometimes the repeated fragmentation and reassembling has to be done for small packet network in series. 

- Whenever an over-sized packet reaches a router, it is broken up in to small fragments. 

- These fragments are transported to the next exit router. 

- The fragments are assembled by this exit router which then forwards them to the next router.

- Awareness regarding this fragmentation is not maintained for the subsequent networks. 

- For a single packet fragmentation is done many times before the destination is finally reached. 

- This of course consumes a lot of time because the repeated fragmentation and assembling has to be carried out. 

- Sometimes, it also presents the reason of corrupting the packet’s integrity.

Non-Transparent Fragmentation: 

- In this type, the packet is split in to fragments by one router. 

- But the difference is that these fragments are not reassembled until the fragments reach their destination. 

- They remain split till then. 

- Since in this type of fragmentation the fragments are assembled only at the destination host, the fragments can be routed independent of each other. 

- This type of fragmentation also experiences some problems such as header has to be carried by each of the fragments till they reach their destination. 

- Numbering has to be done for all the fragments so that no problem is experienced in reconstructing the data stream.

Whichever type of fragmentation we use, one thing has to be made sure which is that later we should be able to form the original packets using the fragments. This insists on having some type of labeling for the fragments. 

Segmentation is another name for the fragmentation. A packet is injected in to the data link layer by the IP layer but it is not responsible for reliable transmission of the packets. Some maximum value on the size of the packets is imposed by each layer for their reasons. For a large packet that travels through the network for which the MTU is small, fragmentation is very much needed. 

What is fragmentation?

- The fragmentation technique is implemented in the IP (internet protocol) for breaking down the datagrams into smaller pieces. 

- This is done so that it becomes easy for the data packets to be passed through the link with a datagram size smaller than that of the original MTU or the maximum transmission unit. 

- The procedure for the IP fragmentation along with the procedures for reassembling and transmitting the datagrams is given in the RFC 791. 

- For determining the optimal MTU path, the IPv6 hosts are needed so that the packets can be sent. 

- If in case the PDU i.e., the protocol data unit received by the router is larger than the MTU of the next hop, then there are two options are available if IPv4 transport is being used:

Ø Dropping the PDU and sending an ICMP (internet control message protocol) message indicating that the condition packet is quite big.

Ø  Fragmenting the IP packet and then transmitting it over the link whose MTU is smaller. Any IPv6 packet with a size less than or equal to 1280 bytes can be delivered without having the need for using the IPv6 fragmentation.

- If a fragmented IP packet is received by the recipient host, its job is to reassemble the datagram and then send it over to the protocols at the higher layers. 

- The purpose of reassembling is expected to take place at the recipient’s host side but for some practical reasons it might be done by some intermediate router. 

- For example, the fragments might be reassembled by the NAT (network address translation) for translating the data streams. 

- Excessive re-transmission can result as a consequence of the IP fragmentation whenever packet loss might be encountered by the fragments. 

- It is required for all the reliable protocols (example, TCP) for re-transmitting the fragments in their correct order for recovering from the single fragment loss. 

Thus, typically two approaches are used by the senders for determining datagrams of what size should be transmitted over the network:

1. First approach: The sender must transmit an IP datagram of size as same as that of the first hop’s MTU.
2. Second approach: Running the path MTU discovery algorithm.

- Fragmentation does leave an impact on the network forwarding. 

- When there are multiple parallel paths for the internet router the traffic is split by the technologies such as the CEF and LAG throughout the links via some hash algorithms. 

- The major goal of this algorithm is to make sure that all the packets with the same flow are transmitted out on the same path for the minimization of the not so required packet reordering. 

- If the TCP or UDP port numbers are used by the hash algorithm, the fragmented packets might be forwarded through different paths. 

- This is so because the layer 4 information is contained only in the first fragment of the packet. 

- As a result of this, usually the initial fragment arrives after the non-initial fragments. 

- This condition is often treated as an error by most of the security devices in the hosts.  

- Therefore, they drop these packets.

- The fragmentation mechanism differs in IPv4 and IPv6. 

- In the former, the fragmentation is performed by the router. 

- On the other hand, in IPv6 fragments that are larger than MTU are dropped by the routers.

- Also, in both the cases there is a variation in the header format. 

- Since fragmentation is carried out using analogous fields, therefore the algorithm can be used again and again for the purpose of fragmentation and reassembling. 

- A best effort should be made by the IPv4 hosts for reassembling the datagram fragments. 

What are the advantages and disadvantages of datagram approach?

- Today’s packet switching networks make use of a basic transfer unit commonly known as the datagram. 

- In such packet switched networks, the order of the data packets arrival, time of arrival and delivery comes with no guarantee. 

- The first packet switching network to use the datagrams was CYCLADES. 

- Datagrams are known by different names at different levels of the OSI model. 

- For example, at layer 1 we call it Chip, at layer 2 it is called Frame or cell, data packet at layer 3 and data segment at layer 4. 

- The major characteristic of a datagram is that it is independent i.e., it does not rely on any other thing for the information required for exchange.

- The duration of a connection between any two points is not fixed such as in telephone conversations. 

- Virtual circuits are just the opposite of the datagrams. 

- Thus, a datagram can be called as a self containing entity. 

- It consists of information sufficient for routing it from the source to the destination without depending up on the exchanges made earlier. 

- Often, a comparison is drawn between the mail delivery service and the datagram service. 

- The user’s work is to just provide the address of the destination. 

- But he/she is not guaranteed the delivery of the datagram and if the datagram is successfully delivered, no confirmation is sent to the user. 

- The data gram are routed to some destination without help of a predetermined path. 

- The order in which the data has to be sent or received is given no consideration. 

- It is because of this that the datagrams belonging to a single group might travel over different routes before they reach their common destination. 

Advantages of Datagram Approach

1. Datagrams can contain the full destination address rather than using some number.
2. There is no set up phase required for the datagram circuits. This means that no resources are consumed.
3. If it happens during a transmission that one router goes down, the datagrams that will suffer will include only those routers which would have been queued up in that specific router. The other datagrams will not suffer.
4. If any fault or loss occurs on a communication line, the datagrams circuits are capable of compensating for it.
5. Datagrams play an important role in the balancing of the traffic in the subnet. This is so because halfway the router can be changed.

Disadvantages of Datagram Approach

1. Since the datagrams consist of the full destination address, they generate more overhead and thus lead to wastage of the bandwidth. This in turn makes using datagram approach quite costly.
2. A complicated procedure has to be followed for datagram circuits for determining the destination of the packet.
3. In a subnet using the datagram approach, it is very difficult to keep congestion problems at bay.
4. The any-to-any communication is one of the key disadvantages of the datagram subnets. This means that if a system can communicate with any device, any of the devices can communicate with this system. This can lead to various security issues.
5. Datagram subnets are prone to losing or re - sequencing the data packets during the transition. This puts a great burden on the end systems for monitoring, recovering, and reordering the packets as they were originally.
6. Datagram subnets have less capability of dealing with congestion control as well as flow control. This happens because the direction of the incoming traffic is not specified. In the virtual circuit subnets, the flow of the packets is directed only along the virtual circuits thus making it comparatively easy for controlling it.
7. The unpredictable nature of the flow of the traffic makes it difficult to design the datagram networks. 

What are the differences between inter-network routing and intra-network routing?

- The individual networks when combined together form the inter-network. 

- Intermediate inter networking devices are used for making connections between them. 

- All these networking elements combine to work as single large unit. 

- The creation of the internetworking has been made possible because of the packet switching technology. 

- The router is the most common and important device used for performing inter-network routing and intranetwork routing.

- Routing across various networks in the inter network is termed as internetwork routing and routing within the same network is termed intranetwork routing. 

In this article we discuss about the differences between internetwork routing and intranetwork routing. 

- Just like inter-network, intranetwork also uses IP (internet protocol) technology for computing services and sharing information. 

- But what makes it different from internetworking is that it is limited to some organization whereas internetwork extends beyond all i.e., it is not limited.

- Or we can put it in other words: Internetwork is spread across organizations and Intranetwork lies within an organization. 

- In some cases, the term intranetwork might mean only the internal website of the organization, but in other cases it might be a larger part of the IT infrastructure of the organization. 

- Sometimes, it may span over a number of LANs (local area networks). 

- The intranetwork is driven by the goal of minimizing the time, effort and cost of the individual’s desktop in order to make it more competitive, cost efficient, timely as well as productive.

- An intranetwork is capable of hosting multiple websites that are private to organizations and may even constitute an important part of the collaboration and communication between the members of the organization. 

- Intranetwork also makes use of various well known protocols such as the FTP, SMTP and HTTP. 

- The intranets are often incorporated with the technologies for lending a modern interface to the systems that host the corporate data. 

- These systems are known as the legacy systems. 

- We can see intranetwork to be a private analog of the internetwork. 

- It means the internetwork has been simply extended to an organization for its private use. 

- Extranetworks are a modified version of the intranetworks.

- Here, the website might be accessed by the non-members i.e., the suppliers, customers or some other approved third parties and so on. 

- Intranetworks are well equipped with a special protocol called the AAA protocol. 

- The 3 As stand for authentication, authorization and accounting. 

- There are a number of organizations who are concerned about the security of their intranetworks. 

- They have deployed a firewall and a network gateway for controlling the access to their services. 

- The intermediate systems when connect together form the internetwork whereas they may bound together a part of the internetwork which might be an intranetwork. 

- The intranetwork routing involves routing between two routers which lie in the same network whereas in internetwork routing, routing is done between routers which reside across different networks. 

- Intranetwork routing is quite easy when compared to the internetwork routing. 

- Protocols used in both the types of routing are different.

- Interior gateway protocol is responsible for routing in the intranetworks whereas the exterior gateway protocol takes the responsibility of routing across the internetwork. 

- Most common example of interior gateway protocol is the OSPF or the open shortest path first protocol. 

- And most common example of exterior gateway protocol is the border gateway protocol or BGP. 

- Also, the routing graphs for both the types are different. 

- In the intranetwork’s graph, all the routers are simply linked to one another in the same network. 

- There is less mess.

- On the other hand, the inter network’s graph is quite tedious. 

- This is so because routers of different networks have to be inter-linked with one another. 

Explain the concept of inter-networking?

- The practice in which one computer network is connected with the other networks is called inter-networking. 

- The networks are connected with the help of gateways. 

- These gateways are used since they offer a common method for routing the data packets across the networks.

- The resulting system in which a number of networks are connected is called the inter-network or more commonly as the internet. 

- The terms “inter” and “networking” combine together to form the term “internet working”.  

- Internet is the best and the most popular example of the inter networking. 

- Internet has formed as a result of many networks connected with the help of numerous technologies. 

- Many types of hardware technologies underlie the internet. 

- The internet protocol suite (IP suite) is the inter networking protocol standard responsible for unifying the diverse networks. 

- This protocol is more commonly known as the TCP/ IP. 

- Two computer local area networks (LANs) connected to one another by means of a router form the smallest internet but not the inter network. 

- Inter networking is not formed by simply connecting two LANs together via a hub or a switch. 

- This is called expansion of the original local area network. 

- Inter networking was started as a means for connecting the disparate networking technologies. 

- Eventually, it gained widespread popularity because of the development needs of connecting many local area networks together through some kind of WAN (wide area network). 

- “Catenet” was the original term that was used for the inter network. 

- Inter network includes many types of other networks such as the PAN or personal area network. 

- Gateways were the network elements that were originally used for connecting various networks in predecessor of the internet called the ARPANET. 

- Today, these connecting devices are more commonly known as the internet routers. 

- There is a type of interconnection between the various networks at the link layer of the networking model. 

- This layer is particularly known as the hardware centric layer and it lies below the TCP/ IP logical interfaces level. 

Two devices are mainly used in establishing this interconnection:

Ø  Network switches and

Ø  Network bridges

- Even now this cannot be called as inter networking rather, the system is just a single and large sub-network. 

- Further, for traversing these devices no inter networking protocol is required. 

- However, it is possible to convert a single network in to an inter network. 

- This can be done by making various segments out of the network and also making logical divisions of the segment traffic using the routers. 

- The internet protocol suite has been particularly designed for providing a packet service. 

- This packet service offered by the IPS is quite unreliable. 

- The elements that maintain a network state and are intermediate in the network are avoided by the architecture. 

- The focus of the architecture is more on the end points of the active communication session.

- For a reliable transfer of the data, a proper transport layer protocol must be used by the applications. 

- One such protocol is the TCP (transmission control protocol) and it is capable of providing a reliable stream for communication. 

- Sometimes a simpler protocol such as the UDP (user datagram protocol) might be used by the applications. 

- The applications using this protocol carry out only those tasks for which reliable data delivery is not required or for which realtime is required. 

Examples of such tasks include voice chat or watching a video online etc. Inter networking uses two architectural models namely:

1. OSI or the open system interconnection model: This model comes with 7 layer architecture that covers the hardware and the software interface.
2. TCP/ IP model: The architecture of this model is somewhat loosely defined when compared with the OSI model. 

What is a choke packet?

- The networks often experience problems with congestion and flow of the traffic. 

- While implementing flow control a special type of packet is used throughout the network. 

- This packet is known as the choke packet. 

- The congestion in the network is detected by the router when it measures the percentage of the buffers that are actually being used. 

- It also measures the utilization of the lines and average length of the queues. 

- When the congestion is detected, the router transmits choke packets throughout the network. 

- These choke packets are meant for the data sources that are spread across the network and which have an association with the problem of congestion. 

- These data sources in turn respond by cutting down on the amount of the data that they are transmitting. 

- A choke packet has been found to be very useful in the maintenance tasks of the network. 

- It also helps in maintaining the quality to some extent. 

- In both of these tasks, it is used for informing the specific transmitters or the nodes that the traffic they are sending is resulting in congestion in the network. 

- Thus, the transmitters or the nodes are forced to decrease the rate at which they are generating traffic. 

- The main purpose of the choke packets is controlling the congestion and maintaining flow control throughout the network. 

- The router directly addresses the source node, thus causing it to cut down its data transmission rate. 

- This is acknowledged by the source node by making reductions by some percentage in the transmission rates. 

- An example of the choke packet commonly used by the most of the routers is the source quench packet by ICMP (internet control message protocol).  

- The technique of using the choke packets for congestion control and recovery of the network involves the use of the routers. 

- The whole network is continuously monitored over by the routers for any abnormal activity.

- Factors such as the space in the buffers, queue lengths and the line utilization are checked by the routers. 

- In case the congestion occurs in the network, the choke packets are sent by the routers to the corresponding parts of the network instructing them to reduce the throughput. 

- The node that is the source of the congestion has to reduce its throughput rate by a certain percentage that depends on the size of the buffer, bandwidth that is available and the extent of the congestion. 

- Sending the choke packets is the way of routers telling the nodes to slow down so that the traffic can be fairly distributed over the nodes. 

- The advantage of using this technique is that it is dynamic in nature. 

- The source node might send as much data as required while the network might inform that it is sending large amounts of traffic.

- The disadvantage is that it is difficult to know by what factor the node should reduce its throughput.

- The amount of the congestion being caused by this node and the capacity of the region in which congestion has occurred is responsible for deciding this. 

- In practical, this information is not instantly available. 

- Another disadvantage is that after the node has received the choke packet, it should be capable of rejecting the other choke packets for some time. 

- This is so because many additional choke packets might be generated during the transmission of the other packets. 

The question is for how long the node is supposed to ignore these packets? 

- This depends up on some dynamic factors such as the delay time. 

- Not all congestion problems are same, they vary over the network depending up on its topology and number of nodes it has. 

Explain multicast routing?

- Multicast routing is also known as the IP multicast. 

- For sending the IP (internet protocol) data-grams to a group of receivers who are interested in receiving the data-grams, multicast routing is used.

- The data-grams are sent to all the receivers in just one transmission. 

- Multicast routing has got a special use in the applications that require media streaming on private networks as well as internet. 

- Multicast routing is IP specific version. 

- A more general version is the multicast networking.

- Here, the multicast address blocks are especially reserved in IPv6 and IPv4. 

- Broadcast addressing has been replaced by multicast addressing in IPv6. 

- Broadcast addressing was used in IPv4. 

- RFC 1112 describes the multicast routing and in 1986 it was standardized. 

This technique is used for the following types of real – time communication over the IP infrastructure of the network:

Ø  Many – to – many

Ø  One – to – many

- It scales up to receiving population that is large enough and it does not require either knowledge regarding the receivers and the identity of the receivers. 

- Network infrastructure is used efficiently by the multicast efficiently and requires source sending packet to a large number of receivers only once. 

- The responsibility of the replication of the packet is of the nodes which are nothing but the routers and the network switches.

- The packet has to be replicated till it reaches the multiple receivers. 

- Also, it is important that the message is sent only once over the link.   

- UDP or the user data gram protocol is the mostly used protocol of low level. 

- Even though if this protocol does not guarantees reliability i.e., the packets might get delivered or get lost. 

- There are other multicast protocols available that are reliable such as the PGM or the pragmatic general multicast. 

It has been developed for adding the following two things a top the IP multicast:

Ø  Retransmission and

Ø  Loss detection

The following 3 things are key elements of an IP multicast:

1. Receiver driven tree creation
2. Multicast distribution tree
3. IP multicast group address

- The receivers and the sources use the last for sending as well as receiving the multicast messages. 

- The group address serves as the destination address of the data packets for the sources whereas it is used for informing the network whether or not the receivers want those packets.

- Receivers need a protocol for joining a group. 

- One most commonly used protocol for this purpose is the IGMP i.e., the internet group management protocol. 

- The multicast distribution trees are set up using this protocol. 

- Once a group has been joined by the receiver, the PIM (protocol independent multicast) protocol is used for constructing a multicast distribution tree for this group. 

- The multicast distribution trees set up with the help of this protocol are used for sending the multicast packets to the members of the multicast group. 

PIM can be implemented in any of the following variations:

1. SM or sparse mode
2. DM or dense mode
3. SSM or source specified mode
4. SDM or sparse – dense mode or bidirectional mode (bidir)

- Since 2006, the sparse mode is the most commonly used mode. 

- The last two variations are more scalable and simpler variations of PIM and are also popular. 

- An active source is not required for carrying out an IP multicast operation and knowing about the group’s receivers. 

- The receiver drives the construction of the IP multicast tree. 

- The network nodes which lie closer to receiver are responsible for initiating this construction.

- This multicast then scales to a receiver population that is large enough. 

- It is important for a multicast router to know which all multicast trees can be reached in the network. 

- Rather, it only requires knowledge of its downstream receivers. 

- This is how the multicast – addressed services can be scaled up. 

What is meant by flow based routing?

- The routing algorithm that considers the flow in the network is known as flow based routing. 

- It takes into consideration the amount of traffic flowing in the network before making a decision regarding the outgoing link over which the packet has to be sent. 

- The ability to characterize the traffic flow’s nature with respect to time is the key to the successful implementation of the flow based routing. 

- For any given line, if we know what is its average flow or capacity we can very well compute the mean packet delay of the line using the queuing theory. - This is the basic idea behind the implementation of this algorithm. 

- This idea reduces the size of the problem i.e., only the minimum average delay has to be calculated for the sub net and nothing else. 

- Thus, the flow based routing considers the load and topology of the network while other routing algorithms do not. 

- In few networks, the mean data flow existing between two nodes might be predictable as well as relatively stable. 

- There occur such conditions under which the average traffic between the two points is known. 

- In such conditions the mathematical analyzation of the flow is possible. 

- This calculation can be used in the optimization of the routing protocol. 

- The flow weighted average can be straightforward calculated which in turn can be used for the calculation of the mean packet delay of the entire sub-net. 

The flow based routing algorithm requires the following things in advance:

Ø  Topology of the subnet

Ø  Traffic matrix

Ø  Capacity matrix

Ø  A routing algorithm

- Information flow based routing algorithms are commonly used in the wireless sensor networks. 

- These days, the measure of information is being used a criterion for the analyzation of the performance of the flow based routing algorithms. 

- One research has put forward an argument stating that since the sensor network is driven by the objective of the estimation of a 2D random field, the information flow must be maximized over the entire field and the sensor’s lifetime. 

In response to this algorithm two types of flow based routing algorithm have been designed namely:

1. Maximum information routing (MIR) and
2. Conditional maximum information routing (CMIR)

- Both of these algorithms have proved to be quite significant when compared to the exiting algorithm – maximum residual energy path or MREP.

About MREP Algorithm

 

- This proves to be quite effective in conservation of the energy. 

- The battery energy which is limited is taken as the most important resource. - For the maximization of the lifetime, the energy consumption has to be balanced throughout the nodes. 

- This should be done in proportion to the resource reserves. 

- This is better than routing for the minimization of the absolute consumed power.

About MIR Algorithm

 

- The ideology behind the MIR algorithm is that there is inequality between the nodes. 

- For example, two very close nodes might not provide twice as much information provided by a lonely node. 

- Therefore, the nodes that provide more information are only given preference. 

- An additional penalty according to the node’s contribution is added to the node for achieving the above mentioned preference. 

- Dijkstra’s algorithm is used for the computation of the shortest path. 

- This helps in sending the data to the sensor as per both the information of the origin and the power consumed.

About CMIR Algorithm

- This one is a hybrid algorithm and makes use of MIR to some extent and then uses MREP algorithm for the rest of the cycle. 

- This hybrid version is better than the above two standalone algorithms since it runs better.