What are uses of WiMax technology?

- The WiMax technology has been used since a long time to provide assistance to the communication process.

- This area has seen major deployment of wimax technology especially in Indonesia during the calamity of tsunami in the year of 2004. 

- The WiMax technology brought in the possibilities of providing broadband access that helped a big deal in regeneration of the communication. 

- The organizations such as FEMA and FCC (federal communications commission) felt the need of wimax in their communication process. 

- The WiMax applications with high efficiency are available today.

- It is known to offer a broad base for the customers and the services had been improved by adding mobility feature to them.

- The service providers use the WiMax technology for providing various services such as mobile and Internet access, voice, video and data. 

There are other advantages of using wimax technology.  

- You get to save a lot of prospective cost and at the same time you get efficiency in services.

- It is even capable of allowing the video making, VOIP calling and data transfers at high speeds.

- The mobile community has been upgraded so much with the coming of the WiMax technology.

- However, there are three main applications offered by WiMax namely backhaul, consumer connectivity and business.

- The real augmentation has been drawn to communications through WiMax technology because of which they can benefit both from the data transmission and video apart from voice. 

- This has facilitated quick response from the applications as per the situation.  

- A temporary communication services can be deployed by a client using WiMax technology.

- It can even speed up the network according to the circumstances and events.  

- This has got us access to visitors, employees and media on a temporary basis.  

- If we are located in the range of the tower, it is quite easy for us to gain access to the equipment of the premises of for the events.

The factors that make the wimax technology so powerful are the following:

> high bandwidth

> high quality services

> security

> deployment

> full duplex consisting of DSL

> reasonable cost

For some applications, the wimax technology is used exclusively as in the following:

1. A means of connecting for the small and medium sized businesses.  - This technology has enabled these businesses to progress day by day.

- The connectivity offered by WiMax technology is good enough to attract clients.  

- It then provides them a number of services such as that of hotspots and so on.  

- Therefore, this application has gotten into spot light.

2. Backhaul

- The most important application of the WiMax technology is the range.

- This is so because using WiMax tower can be used as a means to connect with the other WiMax towers through line-of-sight communication which involves using microwave links. 

- This connectivity between two towers is called as backhaul.  

- It is capable of covering up to 3000 miles. 

- The WiMax network is even sufficient for covering remote and rural areas.

3. The nomadic broadband is another application of wimax technology which can be considered as an extended plan of wifi.

- The access points provided by WiMax technology might be less in number but they offer very high security.  

- Many companies use the WiMax base station for the development of the business.

What are advantages and limitations of Wi-Fi?

The Wi-Fi has its own set of advantages and limitations. 

Advantages of WiFi

- WiFi makes the deployment of local Area Networks or LANs quite cheap.  

- There are some areas where the cables cannot be installed such as in historical buildings and outdoor areas. 

- But these spaces do not have any problem in hosting a wireless LAN.  

- Wireless Network adapters are being built into almost all the laptops by the manufacturers.

- A basic level of service is provided at which different brands concerning and client network interfaces access points that are competing with each other can inter-operate. 

- The products that have been certified by Wi-Fi alliance show back word compatibility. 

- A standard device for WiFi will work at any place in the whole world unlike our phones. 

- The WPA2 or the WiFi protected access encryption is secure provided a condition that the pass phrase used is quite strong.  

- The new protocols use for WMM i.e., Quality of service increase the suitability of the Wi-Fi regarding its use in latency - sensitive applications. 

- WMM is a power saving mechanism that is used for extending the life of the battery. 

Limitations of WiFi

- Inconsistency of the operation and spectrum assignments poses a problem worldwide.  

- The range all the WiFi networks is limited. 

- A wireless access point typically uses a stock antenna having a range of 100 m outdoors and 25m indoors.

- The frequency band is a major factor for producing variations in the range.  

- The range of Wi-Fi with a 2.4 ghz frequency block is better when compared with the 5.0 ghz frequency block Wi-Fi. 

- Some wireless routers come with detachable antennas. 

- These antennas can be removed for improving the range. 

- In their place upgraded antennas can be fitted. 

- The benefit of these antennas is that they have high directional gain at the remote devices. 

- The local regulations limit the maximum amount of power that can be transmitted by a Wi-Fi. 

- The power consumption of Wi-Fi is quite higher than the other standards.  

- This is so because of the reach requirements of the wireless LAN applications.

- There are technologies available that provide a propagation range that is much shorter. 

- One such technology is Bluetooth and has very low power consumption.  

- Other technologies such as zigbee have low power consumption, a long range but provides low data rate. 

- The most commonly used wireless encryption standard is WEP or wired equivalent privacy. 

- Even this standard has been proven to be breakable even if correct configuration is used. 

- This problem was addressed by WPA or Wi-Fi protected access standard to some extent. 

- By default the wireless access points use the encryption free mode. 

- The wireless security is disabled because of which the LAN can be openly accessed. 

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 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. 

Flooding - a kind of static algorithm

An algorithm designed for the distribution of the material to each and every part of the graph is referred to as the flooding algorithm. 

- The algorithm has got its name from the concept that involves inundation caused by a flood. 

- The main application of these algorithms is in graphics and computer networking. 

- These algorithms also come very handy in solving a number of mathematical problems. 

- Examples of such problems that are graph theory problems, maze problems and so on. 

- Flooding algorithm though it sounds complicated is quite a simple one. 

- Here, every incoming packet is sent via every outgoing link. 

- Only the link through which the packet arrived is saved. 

This algorithm has many applications in the following:

1. Systems that require bridging, systems like use net.
2. Peer to peer file sharing.
3. Used as a part of the routing protocols such as the DVMRP, OSPF etc.
4. Used in protocols used for the adhoc wireless networks.

Nowadays the flooding algorithm is available with its many variants. The following are two main steps that each variant follows while working:

1. Each node in the network might act as both receiver and the transmitter.
2. The incoming message is forwarded by the receiving node to each of its neighboring nodes except the one which is the source code.

- This causes the message to be delivered to each and every part of the network that is reachable. 

- Algorithms are required as a precaution for avoiding the wastage of the infinite loops and the duplicate deliveries and for allowing the messages for expiring. 

- All these issues are addressed partially by a variant of the flooding algorithm called the selective flooding.

- The usual flooding algorithm sends the packets to all the routers that lie in the same direction. 

- But the selective flooding algorithm does not send the packet to each router rather it selects only few of them which lie in the right direction approximately. 

Advantages and Disadvantages of Flooding Algorithm

Advantages:

1. If it is possible for delivering the packet, it will be delivered but a number of times.
2. In flooding algorithm every path in the network is naturally utilized and so the shortest path is also used.
3. The implementation of the flooding algorithm is quite simple.

Disadvantages:

1. The cost of the flooding algorithm can be very high because a lot of bandwidth is wasted. Even if there is one destination of the message, it will be sent to all the hosts on the network unnecessarily. If in case there occurs a denial of service attack or a ping flood, the reliability of the whole network will be affected badly.
2. In the computer network, the message might get duplicated. This in turn can increase the load on the bandwidth of the network. This will call for increasing the complexity of the processing for rejecting the duplicates of the messages.
3. The packets that are duplicate might keep on circulating forever, if the following precautions are not taken:

Ø  Using a time to live count or a hop count to be included with every packet. The value of the count has to include the number of the nodes through which the packets have to be passed while on the way to destination.

Ø  Each and every node should be used for keeping track of every packet that passes through it and a packet should be forwarded only once.

Ø  The network topology must be enforced without any loops. 

What are data gram sub-nets?

- A data gram is defined as the basic transfer unit used in the networks that operate with the help of packet switching network. 

- In such networks, the time of the arrival and delivery is not guaranteed. 

- Also, the network services do not guarantee that whether it will be an ordered delivery or not. 

- The first project to use the data grams was the CYCLADES which was again a packet switching network. 

- The hosts in this network were responsible for making a reliable delivery rather than relying on the network for doing so. 

- This they did using the data grams that were themselves so unreliable and by associating the mechanisms of the end to end protocols. 

- According to Louis Pouzin, there are two sources from which came the inspiration for the data grams namely the Donal Davie’s studies and simplicity of the things. 

- The concept of the data gram sub-net was eventually adopted for the formulation of the protocols such as apple talk, Xerox network systems and of course the internet protocol.

- Data grams are used at the first 4 layers of the OSI model. 

- Each layer has its own name for the data grams as we mention below:

1. Layer 1: chip (CDMA)
2. Layer 2: frames (IEEE 802.3 and IEEE 802.11), cell (ATM)
3. Layer 3: data packet
4. Layer 4: data segment

- A data gram is a data packet that is self-reliant. 

- This means it does not rely on any of the exchanges made earlier since the fixed connection between the two points of communication has no connection such as in a majority of the telephonic conversations. 

- Virtual circuits and data gram sub-nets are two equally opposite things. 

Data gram is defined as an independent and self-contained data entity by the RFC 1594 that carries sufficient information required for routing from one source to another without relying on the transporting network and the earlier exchanges between the two same hosts.

- The services offered by the data gram sub nets can be compared to the mail delivery services. 

- This is so because the user needs to mention only the destination address.

- However, this service does not give any guarantee of whether the data gram will be delivered or not and also does not provide any confirmation upon successful delivery of the packet. 

- These are of course two major disadvantages of the data gram sub nets. 

- In data gram sub nets, the data grams or the data packets are routed along a route that is created at the same time. 

- In data gram sub nets the routes are not predetermined. 

- This again has its disadvantages. 

- Also, the order in which the data grams have to be sent or received is not considered. 

- In some cases, a number of data grams having same destination might travel along various different routes.

- There are two components of every data gram namely the header and the data payload.

- The former consists of all the information that is enough for the routing purpose from source to the destination without being dependent on the exchanges that were made before between the network and the equipment. 

- The source as well the destination address might be included in the header as a kind of a field. 

- The data that is to be transmitted is stored in the latter part of the data gram. 

- In some cases the data payloads might be nested in to the tagged header. 

- This process is commonly known as the encapsulation. 

- There are various types of data grams for which various standards are defined by the internet protocol or IP. 

Give advantages of frame relay over a leased phone line?

Frame relay and leased phone lines are two of the physical connection media for setting up the connections. 

Advantages of Frame Relay over Leased Phone Line

- Frame relay is a kind of the standardized WAN (wide area network) technology for specifying the logical link as well as physical link layers of the digital telecommunication channels. 

- It is done by the means of a packet switching methodology.

- The frame relay technology has been designed for transportation across the ISDN (integrated services digital network) infrastructure. 

- Today, it is used in the context of a number of network interfaces. 

- Frame relays are commonly implemented for VoFR (voice over frame relay).  - It is used as an encapsulation technique for the data. 

- The frame relays are used between the WANs and the LANS.

- A private line or a leased line is provided to the user that connects to the frame relay node. 

- The frequently changing path is transparent to the WAN protocols used extensively by the end users. 

- Data is transmitted via these networks and the frame relay network handles all this.

- One advantage of the frame relays over the leased lines is that they are less expensive and this is what that makes the frame relays so popular in the telecommunications industry.

- Another advantage of the frame relays over the leased lines that make them popular is that they have user equipment that can be configured with extreme simplicity in the frame relay network. 

- The usage of the Ethernet over the fiber optics communication is high. 

- This has led to using the frame relay protocol and encapsulation by the dedicated broadband services like DSL and cable modem, VPN, MPLS etc. 

- However, there are a number of rural regions in India where there is still an absence of the cable modem and DSL services.

- In such areas, the only option for the non-dial-up connection is the frame relay line of 64 Kbit/ s.

- Thus, it might be used by some retail chain to connect with the WAN of their corporate. 

- The aim of the designers of the frame relay is to offer a telecommunication service for transmitting the cost efficient data between the various end points in the WAN and the local area networks in an intermittent traffic. 

- The data is put in to units of variable sizes called the frames by the frame relay process. 

- The required error correction process is left up to the end points. 

- This error correction includes re-transmission of the data. 

- This increases the speed of the overall transmission of data. 

- A PVC or the permanent virtual circuit is provided by the network so that when a customer looks at a dedicated connection and not having to pay for leased line that is full time engaged. 

- The route by which each frame travels to the destined end point is figured out by the service provider and thus he decides the charges based up on the usage. 

- A level of the service quality can be selected by the enterprise. 

- The frames can be prioritized while the importance of the other frames is reduced. 

- The frame relay can run on systems such as the following:

Ø  Fractional T – 1

Ø  Full T – carrier

Ø  E – 1

Ø  Full E carrier

- A frame relay provides mid-range services between ATM (asynchronous transfer mode) and the ISDN operating at a speed of 128 Kbps. 

- Not only it provides the services, it also complements them. 

- The base of the frame relay technology is provided by the X.25 packet switching that has been designed for data transmission over the analog voice lines.

What are advantages and disadvantages of having international standards for network protocols?

Without rules governing the exchange of data and establishment of connections between networks, there would have a big chaos in the industry. These rules are called line protocols and are very crucial for the inter-networking and communication across the networks. 

The mode and the speed of communication are controlled by what are called the communications software packages. These network protocols are defined by the international standards. However, having international standards for the protocols has got both advantages and disadvantages. 

- A number of standard network protocols for carrying out several functions such as routing, packetizing, and addressing and so on. 

- All these protocols lay out a standard definition of how the routing and addressing has to be done. 

- They also define the specifications for the structure of the packets to be transferred between different hosts. 

- Some commonly used routing protocols are:

Ø  X.25

Ø  IPX/ SPX

Ø  TCP/ IP

Ø  OSI

- The OSI stands for open systems interconnection. 

- Early networking systems had a big problem which was that there was a lack of consistency between the protocols employed by several types of different computers. 

- As a consequence of this problem, the international standards came in to the picture. 

- Thus, international standards were established for the various data transmission protocols. 

- For example, OSI is a set of standard protocols developed by ISO (international standards organization).

- In this model, the functionalities of the network protocols have been divided in to seven layers of the communication rules or protocols. 

- The purpose of this model is to identify the functions being offered by the system. 

- The following three layers appear in the host systems and other units such as processor and control unit etc.:

1. Physical layer
2. Data link layer
3. Network layer

- The leftover layers are found in the host systems only. 

Advantages of having International Standards

Ø  If all the systems are following the same standard, it becomes easy for everyone to connection to everyone else. In other words, the international standards provide easy interconnectivity.

Ø  If any standard is widely used, it gains economies of scale. For example, VLSI chips etc.

Ø  With all the systems using the same standard, the installation and the maintenance of the connections become quite easy.

Ø  Software designed by the developers from all over the world, won’t have any problem in interfacing with the host system and the other software. They will work well with a wide range of operating systems and hardware since both are using the same standard.

Disadvantages of having International Standards

Ø  Poor standards may be formed as a result of the frequent standardization.

Ø Once the standard is adopted internationally, it’ll be difficult to make changes to it. It will be difficult to introduce new and better techniques in to it.

Ø  If a problem occurs, it has to be seen as an international problem.

Ø The manufacturers and companies will be bound to follow the same international standards and so they won’t be able to develop something better of their own.

Ø  Large multinational companies won’t be able to pool everyone in to using their proprietary protocols and therefore no huge profits.

TCP/ IP protocol was developed to make communication easy between the dissimilar systems. A number of hardware and software vendors support this protocol ranging from mainframes to microcomputers. A number of corporations, universities and govt. agencies are making use of this protocol.