What is WiMax technology?

Worldwide inter-operability for microwave access or wimax is standard developed for wireless communications that has been designed so as to deliver data rates of 30-40 mbps. The update in the technology in the year 2011 upgraded the technology to provide around 1 gbps for the stations that were fixed. 

- The Wimax forum is responsible for naming the technology as Wimax. 

- This forum was formed in the year of 2001 for the promotion of the inter-operability and conformity of this standard. 

- The Wimax has been defined by the forum as the technology based up on standards that enable the last mile wireless broadband delivery as alternative for the DSL and the cable thing. 

- The IEEE 802/ 16’s interoperability implementations are referred to as the WiMax. 

- The wimax forum has ratified this family of standards. 

- By virtue of the certification provided by this forum, the vendors are able to sell mobile and fixed products that are wimax certified. 

- This is done for ensuring that a level of inter-operability is maintained at par with the other products that have been also certified for the same profile. 

- The ‘fixed wimax’ is the name given to the original IEEE 802.16 standards.

- ‘Wifi on steroids’ is the term used to refer to WiMax sometimes. 

It has got a number of applications such as in:

Ø  Broadband connections

Ø  Cellular back-haul

Ø  Hot spots and so on.

- This technology shares some similarity with the Wifi technology however, this one is more capable of transmitting data at greater distances.

It is because of its range and bandwidth that the WiMax is suitable for the following applications:

Ø  Provides services such as the IPTV services and VoIP (telecommunications services).

Ø  Provides mobile broadband connectivity that is portable across the cities and countries and that can be accessed via different kinds of devices.

Ø  Provides an alternative for DSL and cable in the form of wireless last mile broadband access.

Ø  Acts as a source of internet connectivity.

Ø  Metering and smart grids.

- This technology can be used at home for providing internet access across the countries. 

- This has also caused a rise in the market competition. 

- The WiMax is even economically feasible. 

- Mobile wimax has been used as a replacement for the technologies like CDMA, GSM that are cellular phone technologies.  

- The technology has also been used as an overlay for increasing the capacity.  

- The fixed wimax is now used for 2g, 3g and 4g networks as a wireless back-haul technology in almost all the nations whether they are developed or developing.  

- In some states of North America, this technology is provided through a numbered of copper wire line connections. 

- On the other hand, the technology is back hauled via satellites in case of the remote cellular operations.  

- While in other cases even microwave Links are used. 

- The bandwidth requirements of the WiMAX demand more substantial back-haul when compared to other legacy cellular applications. 

- In some of the cases, the sites have been aggregated by the operators by use of Wireless Technology.  

- The traffic is then introduced to the fiber networks as per the convenience.  

- The technologies that provide triple play services are directed compatible with the WiMAX.  

- These services might include multi-casting and quality of service. 

- WiMax has been widely used for providing assistance in the communications. 

- The Intel Corporation has donated the hardware for WiMax technology for assisting the FCC (federal communications commission) and FEMA etc.

- The subscribers’ stations or SS are the devices which are used for connecting to a WiMAX Network. 

- These devices might be portable such as the following:

      > Handsets and smart phones

      > PC peripheral such as USB dongles, PC Cards and so on. 

      > Embedded devices in notebooks.

What is link encryption method?

- Link encryption method is one of the classic methods used in the digital communications for the application of the crypto.

- Link encryption method has been designed for hiding the secrets and preventing the forgery of data. 

- It is quite a simple concept that has been discussed here and it fits for all the types of existing applications and software used in the communication.  

- Even though this method does not works well enough for most of the applications, it is the simplest of all. 

- Link encryption method is a security measure that should be used only if your security objectives match with those of the link encryption method. 

- It is commonly used in the applications where a boundary has to be maintained between the internal users and the external users. 

- With the link encryption it gets easy for the internal users to share data whereas it is just the opposite for the external users. 

- It provides transparent protection except for the separation that is maintained between the two classes of the users. 

Below we mention some security objectives that can be met with the link encryption:

Ø  Maintaining confidentiality: Our systems of course store very sensitive data. While exchanging the data with other systems, it is required that the risk of leakage involved should be as minimum as possible.

Ø  Communication with the outsiders: Obviously, we do not want to share our data with the unwanted outsiders and unauthorized sites and so we want these to be blocked. Such exchanges should be prevented from happening even by carelessness or accident.

Ø  Hiding data traffic: As much as possible we want our data and its details to be shielded from the outsiders. This data might contain information about the destination host and other info necessary for communication control. However, here it is assumed that the information will not be leaked by the insiders.

Ø  Familiarity and safety: We rank these two factors above the cost.

Ø  Protection of the data transfers: We need protection for our data against any sort of tampering or forgery by the outsiders during the transition. An assurance is important.  This objective is unconditionally met by this link encryption method.

- From security standpoint, a design is yielded by the link encryption that is highly reliable. 

- If in your organization some security parameter has been established that is strong enough, link encryption is the best technique for its maintenance. 

- A strict control is kept over the flow of physical documents through this security parameter. 

- The link encryption provides a complementary protection for the flow of the electronic documents. 

- We can have an environment with every data link that traverses the boundary having encryptors. 

- The documents will be kept within the parameter limits. 

- The data leaving the parameter will be protector by means of the encryptors. 

- Link encryption method is being used since years in banking organizations and military communications for providing secure links. 

- The link encryption uses the in-line encryptors as its building blocks.

- This hardware devices takes plain text and converts it into cipher text.

The encryptors have their own vulnerabilities as mentioned below:

Ø  Rewrite attacks: It is also known as the plain-text attack, it is used for forging the messages. Few crypto algorithms are vulnerable to these attacks.

Ø  Replay attacks: Most of us think that the encrypted data is self-validating and so by matching the encryptor with its keys a sensibly de-crypting message can be generated. Since the encrypted data is accessible to the outsiders, they can also access the message that decrypts sensibly.

Ø  Covert signaling attacks: This attack is based on the idea that there is always a way to leak info if there exists an internal process that tries to do so. 

How can firewalls secure a network?

Firewalls in computer systems are either software based or hardware based. But they have the same purpose of keeping a control over the incoming as well as the outgoing traffic. 

In this article we discuss about how the network is secured by the firewalls. 

- This control is maintained through the analyzation of the data packets. 

- After analyzation, the firewall’s work is to determine whether to allow these packets to pass or not. 

- This decision is taken based up on some set of rules.

- With this set of rules, a barrier is established by the firewall between the external network that is not considered as secure and trusted and the internal network which is secure and trusted. 

- Most of the personal computer’s operating systems come with a built-in software based firewall for providing protection against the threats from external networks. 

- Some firewall components might also be installed in the intermediate routers in the network. 

- Also some firewalls have been designed to perform routing as well.

There are different types of firewalls which function differently.This classification of the firewalls is based up on the place where the communication is taking place i.e., whether at the network layer or the application layer.

Packet filters or network layer: 

- Firewalls used at the network layer are often termed as the packet filters. 

- This firewall operates at low level of the protocol stack of the TCP/ IP and so does not allow the packets to pass through it unless they satisfy all the rules. 

- These rules might be defined by the administrator of the firewall. 

- These firewalls can also be classified in to two categories namely the stateless firewalls and the state-ful firewall. 

- The former kind use less memory and operates faster in the simple filters, thus taking less time for filtering. 

- These firewalls are used for filtering the stateless network protocols i.e., the protocols which do not follow the session concept. 

- These firewalls are not capable of making complex decisions based up on the state of the communication. 

- The latter kind maintains the context of the active sessions. 

- This state info is used by these firewalls for speeding up the packet processing. 

- A connection is described using any of the properties such as the UDP or TCP ports, IP addresses and so on. 

- If a match is found between an existing connection and the packet, it is allowed to pass. 

- Today firewalls have capabilities of filtering the packets based up on attributes like IP addresses of source and destination hosts, protocols, originator’s netblock, TTL values and so on.

Application layer Firewalls: 

- Firewalls of this type work on the TCP/ IP stack’s application level. 

- All the packets traveling in and out of the application are intercepted by this firewall. 

- This leads to blocking of the other packets also. 

- Firstly, all the packets are inspected for any malicious content for preventing the outspread of the Trojans and worms. 

- Some additional inspection criteria might be used for adding some extra latency to the packet forwarding. 

- This firewall determines whether a given connection should be accepted by a process. 

- This function is established by the firewalls by hooking themselves in to the socket calls for filtering the connections. 

- These application layer firewalls are then termed as the socket filters.

- There way of working is somewhat similar to the packet filters except that the rules are applied to every process rather than connections. 

- Also, the rules are defined using the prompts for those processes that have not been provided with a connection. 

- These firewalls are implemented in combination with the packet filters.

What are the parameters of QoS - Quality of Service?

With the arrival of the new technologies, applications and services in the field of networking, the competition is rising rapidly. Each of these technologies, services and applications are developed with an aim of delivering QoS (quality of service) that is either better with the legacy equipment or better than that. The network operators and the service providers follow from trusted brands. Maintenance of these brands is of critical importance to the business of these providers and operators. The biggest challenge here is to put the technology to work in such a way that all the expectations of the customers for the availability, reliability and quality are met and at the same time the flexibility for quick adaptation of the new techniques is offered to the network operators. 

What is Quality of Service?

- The quality of service is defined by its certain parameters which play a key role in the acceptance of the new technologies. 

- The organization working on several specifications of QoS is ETSI.

- The organization has been actively participating in the organization of the inter-operability events regarding the speech quality.

- The importance of the QoS parameters has been increasing ever since the increasing inter-connectivity of the networks and interaction between many service providers and network operators for delivering communication services.

- It is the quality of service that grants you the ability for the making parameters specifications based up on multiple queues in order to shoot up the performance as well as the throughput of wireless traffic as in VoIP (voice over internet), streaming media including audio and video of different types. 

- This is also done for usual IP over the access points.

- Configuration of the quality of service on these access points involves setting many parameters on the queues that are already there for various types of wireless traffic. 

- The minimum as well as the maximum wait times are also specified for the transmission. 

- This is done through the contention windows. 

- The flow of the traffic between the access point and the client station is affected by the EDCA (AP enhanced distributed channel access) parameters. 

- The traffic flow from client to the access point is controlled by the station enhanced distribution channel access parameters. 

Below we mention some parameters:

Ø  QoS preset: The options listed by the QoS are WFA defaults, optimized for voice, custom and WFA defaults.

Ø  Queue: For different types of data transmissions between AP – to – client station, different queues are defined:

- Voice (data 0): Queue with minimum delay and high priority. Data which is time sensitive such as the streaming media and the VoIP are automatically put in this queue.

- Video (data 1): Queue with minimum delay and high priority. Video data which is time sensitive is put in to this queue automatically.

- Best effort (data 2): Queue with medium delay and throughput and medium priority. This queue holds all the traditional IP data. 

- Background (data 3): Queue with high throughput and lowest priority. Data which is bulky, requires high throughput and is not time sensitive such as the FTP data is queued up here.

Ø AIFS (inter-frame space): This puts a limit on the waiting time of the data frames. The measurement of this time is taken in terms of the slots. The valid values lie in the range of 1 to 255.

Ø Minimum contention window (cwMin): This QoS parameter is supplied as input to the algorithm for determining the random back off wait time for re-transmission.

Ø cwMax

Ø maximum burst

Ø wi – fi multimedia

Ø TXOP limit

Ø Bandwidth

Ø Variation in delay

Ø Synchronization

Ø Cell error ratio

Ø Cell loss ratio

What is meant by Quality of Service provided by network layer?

- The QoS or the quality of service is such a parameter that refers to a number of aspects of computer networks, telephony etc. 

- This parameter allows transportation of traffic as per some specific requirements. 

- Technology has advanced so much now computer networks can also be doubled up as the telephone networks for doing audio conversations. 

- The technology even supports the applications which have strict service demands. 

- The ITU defines the quality of service in telephony. 

It covers all the requirements concerning all the connection’s aspects such as the following:

Ø  Service response time

Ø  Loss

Ø  Signal – to – noise ratio

Ø  Cross – talk

Ø  Echo

Ø  Interrupts

Ø  Frequency response

Ø  Loudness levels etc.  

- The GoS (grade of service) requirement is one subset of the QoS and consists of those aspects of the connection that relate to its coverage as well as capacity. 

- For example, outage probability, maximum blocking probability and so on. 

- In the case of the packet switched telecommunication networks and computer networking, the resource reservation mechanisms come under the concept of traffic engineering. 

- QoS can be defined as the ability by virtue of which the different applications, data flows and users can be provided with different priorities. 

- It is important to have QoS guarantees if the capacity of the network is quite insufficient. 

- For example, voice over IP, IP-TV and so on. 

- All these services are sensitive to delays, have fixed bit rates and have limited capacities.

- The protocol or network supporting the QoS might agree up on some traffic contract with the network node’s reserve capacity and the software. 

- However, the quality of service is not supported by the best effort services. 

-Providing high quality communication over such networks provides a alternative to the QoS control mechanisms that are complex. 

- This happens when the capacity is over-provisioned so much that it becomes sufficient for the peak traffic load that has been expected. 

- Now since the network congestion problems have been eliminated, the QoS mechanisms are also not required. 

- It might be sometimes be taken as the level of the service’s quality i.e., the GoS. 

- For example, low bit error probability, low latency, and high bit rate and so on. 

- QoS can also be defined as a metric that reflects up on the experienced quality of the service.

- It is the cumulative effect that can be accepted. 

Certain types of the network traffic require a defined QoS such as the following:

Ø  Streaming media such as IPTV (internet protocol television), audio over Ethernet, audio over IP etc.

Ø  Voice over IP

Ø  Video conferencing

Ø  Telepresence

Ø  iSCSI, FCoE tec. Storage applications

Ø  safety critical applications

Ø  circuit emulation service

Ø  network operations support systems

Ø  industrial control systems

Ø  online games

- All the above mentioned services are examples of the inelastic services and a certain level of latency and bandwidth is required for them to operate properly. - On the other hand, the opposite kind of services such as the elastic services can work with any level of bandwidth and latency. 

- An example of these type of services is the bulk file transfer application based up on TCP.

- A number of factors affect the quality of service in the packet switched networks. 

- These factors can be broadly classified in to two categories namely technical and the human factors. 

The following factors are counted as the human factors:

Ø  reliability

Ø  scalability

Ø  effectiveness

Ø  maintainability

Ø  grade of service and so on.

- ATM (asynchronous transfer mode) or GSM like voice transmissions in the circuit switched networks have QoS in their core protocol. 

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. 

What is meant by load shedding?

The network is monitored by the network monitoring systems. These systems need to be robust and must be capable of inevitably coping with the situations in which the overload occurs. The network gets overloaded because of the nodes generating large volumes of data at high rates. Overload might also occur because of the burstiness of the traffic in its normal course of operation. For reducing the load of the network, load shedding techniques are applied. 

- Load shedding techniques have to be followed if the network is under a lot of stress. 

- This has to be done while monitoring the network for avoiding the packet loss that otherwise might be uncontrollable. 

- Load shedding involves sampling the incoming traffic. 

- CoMo or continuous monitoring has been developed to serve this purpose. 

- It uses such a load shedding scheme which can infer the query’s cost using the relation between the set of features of the traffic and the actual resource usage without having any knowledge of the plug-ins. 

- Here, traffic feature can be defined as a counter describing the incoming traffic’s particular property. 

The property might be any of the following:

Ø  Number of packets

Ø  Number of bytes

Ø  Flows

Ø  Unique IP destination address and so on.

- The CoMo consists of a prediction and the load shedding sub-system for intercepting the packets prior to sending them to the plug-in from the filter.

- A traffic query is implemented by this plug-in. 

- The system completes the process in 4 phases. 

- In the first phase, it forms a batch of packets for each 100ms of the traffic. - It then processes each of these batches for extracting a predefined traffic features’ set that is quite large. 

- From these, the most relevant sets are selected by the feature selection sub-system based up on the present stats of the CPU usage of the query. 

- The selected subset is then supplied as input for the “multiple linear regression subsystem”. 

- This is done for the prediction of the CPU cycles that the query requires for processing the whole batch. 

- If the prediction is greater than the capacity of the system, the batch is pre-processed by the load shedding subsystem for discarding the packet’s portion. 

- The batch is discarded through packet or flow sampling. 

Load shedding is now being seen as an effective method for curbing the overload situations even in the real time systems. 

- It involves shedding excess of the load in such a way that the stability of the system is not disturbed and also the system buffers do not experience any overflows. 

- The idea for applying the technique of load shedding in the field of networking has been adopted from the concept of the electric power management.

- Here, the electric current is intentionally disconnected on particular lines when the demands for the power supply are higher than what is being supplied.

- CoMo is an open source system and can be quickly implemented and can be used for further deploying other network monitoring applications. 

- The system has been written using C language and uses a feature rich API. 

- The system works by predicting the CPU usage of the system and thus anticipates about the resource requirements bursts that might occur in future. 

- The load shedding scheme used by the CoMo has the capability of automatically identifying the features using which the resource usage can be best modeled for each monitoring application.

- This identification is made according to the previous resource usage measurements. 

- These measurements are then used for determining the system’s overall load and by what percentage the load must be shed.