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Domain Name System (DNS) messages contain requests and responses. Requests have the question while responses have the answer. There are 3 types of DNS messages, such as queries, responses and updates.
There are 3 scenarios to show the problems that an intruder could cause when inserting DNS messages into and removing DNS messages from the network.
Redirection of clients to unauthorized domain controllers.
In this scenario, a client asks for the address of a domain controller by sending a DNS query. A wrong address of an illegal domain controller will be returned to client by a compromised DNS server. Besides that, it may happen for the DNS traffic. Spoofing and seizure of the DNS traffic in response may direct the clients to unauthorized domain controllers as well. As a conclusion, the client request may pass the secure information to that rogue domain controller. It will cause to the additional damage too.
Domain controllers and clients cannot find other domain controllers.
In this scenario, a computer will send a DNS query to a server. The clients and servers will do not know each other when the computer receives an invalid IP addresses. They cannot entry the directory if the clients cannot find the domain controllers. And if the domain controllers cannot get the other domain controllers, therefore it will stop function the directory.
In this scenario, when a client sends out a DNS query, the attacker will return back with a thousand of DNS responses. This scenario, we call it as clients flooding. Lack of authentication of the responses is the main cause of this scenario. As if it is creating from the expected name server, the attack is made to appear. However, the client does not have the ability to authenticate the original response although it has a strong authentication. Other than DNS spoofing, the attacker can use it to host name spoof an application.
The problem of providing QoS guarantees cannot be solved simply by throwing bandwidth as there will never have enough bandwidth to use to solve it.
Besides bandwidth, other solutions are:
Routing - QoS Routing (QoSR)
QoSR allows choosing network routes with adequate resources to make request from QoS parameters. The purposes of QoSR are to accomplish the global effectiveness in resource utilization and to fulfil the QoS requirements for each of the admitted connection. QoSR algorithm is used to provide QoS guarantees. In routing algorithm, packet is sent on the shortest path to destination. The characteristic of QoSR algorithm is to use dynamically obtained information about load at each of the links, to decide which path that a flow should be routed to.
Figure 1 above show that, all the flow starts from 1 and ends at 5. The flow will start to choose the path 1-2-3-4-5. When the path of 1-2-3-4-5 is loaded, then traffic will be switched to another path, path 1-2-6-7-4-5. Therefore, it will raise the load on path 1-2-6-7-4-5. After that, when the path 1-2-3-4-5's load decrease, the traffic will be switched to path 1-2-6-7-4-5 again. Therefore, the high instability in the performance will be observed by following these two paths of the best effort traffic.
QoSR algorithm has 2 ways: 1. For flows, it uses the general static shortest path routing that demand for QoS guarantee. 2. For best-effort traffic, it uses dynamically to get load information in order to compute the shortest path routes. This technique is same with distributing load information.
Resource reservation - Resource Reservation Protocol (RSVP)
RSVP is a protocol which provides QoS guarantee for a network. It is used to ask for specific qualities of service by a host from the network for particular applications flows. It is also used to send QoS requests by routers to all nodes that along the paths of the flows, establish and keep state to offer the requested service. Generally, along the data path, RSVP requests will result in resources that are reserved in every node.
RSVP uses to send the stream, takes the request through the network and visits every node in the network. RSVP will make a stream resource reservation for every node. At each node, RSVP will communicate with 2 local decision modules, one is admission control (the node has enough resources or not to give the requested QoS) and the other one is policy control (the user has administrative authorization or not to make the reservation) in order to make a resource reservation.
If one of them fails of checking, an error notification will be returned to the application process from the RSVP program. On the other hand, if two of the modules success of checking, the RVSP daemon sets parameters in a packet classifier and packet scheduler to get the desired QoS.
Medium access - Medium Access Control (MAC)
MAC is used to provide QoS guarantees to support the real time traffic. Multiple Access Collision Avoidance (MACA) protocol is a new MAC schema which is used to cover for the CSMA/CA for improving the throughput and for supporting real time traffic in QoS guarantees.
In MACA, a request-to-send (RTS) mini packet is sent by a source to transmission use. When it is successful, the destination will return a clear-to-send (CTS) mini packet. At the same time, the source will send its data packet as well. With CSMA, MACA may increase the network's throughput in the environments which do not have hidden nodes. To decrease the problems of hidden nodes, CTS in MACA that is sent by the destination, has prevented the nodes in its neighborhood.
Skype is a software application that uses Voice over Internet Protocol (VoIP) technology to make connection from computer to traditional phones or mobiles. This is one of the top features in Skype, calling landlines and mobiles to someone with an easy way and cheapest price. We call it as Skype Out.
The rating of PC to phone calls by Skype as follow:
Skype Out is a fee-based service. We use Skype in computer to call someone who is using a traditional phone. With Skype Out, we need to pre-purchase minutes which similar with calling card in order to make phone calls. And the people we are calling will don't know that we are using a Skype to make that call.
Figure above show that a process of calling out from a Skype network to a traditional phone.
There are few steps to follow when using Skype Out to make calls on Skype network and terminate on traditional mobile or phone network.
Click the Call phones tab. - In the main window of Skype, you will see a 'Call phones' tab at the below of the main window. Click on that. It will come out a page in right hand side which shows a key pad with numbers, a Buy Skype Credit button.
Click on the flag menu and change the country. - You will see a flag icon. Click on that flag icon, you can change the country on it. Select the country you want to call if you are calling abroad.
Click the phone numbers on key pad or type the numbers. - You can click the phone numbers that you want to call to or just simply enter the numbers beside the flag icon.
Click the Call button. - After checking the number you had entered, click on the green 'Call' button in order to start a call.
Click Save button. - Click the 'Save' button under the dial pad if you want to call that numbers always. You can just find it in your 'Contacts' which at the top of the main window at the next time.
Skype Out Cost
There are 2 ways to pay for making phone calls.
Pay As You Go
You can use it when you need. You just need to add the money to your account and start for calling. You can also call to abroad with low rates.
During Pay As You Go plan, a connection fee will be incurred as you pay the phone calls using Skype Credit or Skype Pro. This fee is counted based on your account currency and not the country where you are calling. It applies to all calls to landline and mobiles phones.
In the European Union, when buying Skype Credit, you will be charged a 15 percent Value Added Tax (VAT) for your billing address. The rates of Skype Credit are per minutes.
Pay monthly or annually
It can save up to 60% of the money compare with Pay As You Go package. You can make a phone call any time and any day you want without any contract. It is not incur a connection fee.
In monthly subscription, there has Unlimited Europe and Unlimited World plans to choose for calling to a lot of different country.
For Unlimited Europe plan, it just cost â‚¬5,99/month in order to make unlimited calls to landline phones in more than 20 European countries, such as Austria, Italy, Russia, Switzerland, United Kingdom and Portugal.
For Unlimited World plan, it needs â‚¬9,99/month to make unlimited calls to landline and mobile phones (some countries) in 40 countries worldwide. For example: Argentina, Chine (landlines & mobiles), Japan, Malaysia (landlines), Canada (landlines & mobiles), and Taiwan.
One of the cons for Skype of PC-to-phone services is, we cannot use Skype to make an emergency call, such as 911 in United State. For example: you cannot be successful to dial 911 using Skype in United State.