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Archive for September, 2008

What is UDP?

September 28th, 2008 No comments

User Datagram Protocol or UDP is part of the Internet Protocol suite, using which, programs running on different computers on a network can send short messages known as Datagrams to one another. UDP can be used in networks where TCP is traditionally used, but unlike TCP, it does not guarantee reliability or the right sequencing of data. Datagrams may go missing without notice, or arrive in a different order from the one in which they were sent.

Though these factors might seem to suggest that UDP is not a useful protocol, it still finds good use in particular areas where speed, more than reliability, is of utmost importance. Since UDP does not have the overhead of checking whether the data has reached the destination every time it is sent, it makes the protocol that much faster and more efficient. UDP is often used for time-sensitive applications where missing data is preferred to late-arriving data.

UDP is a stateless protocol which is useful for servers engaged in answering short queries from a large number of clients. While TCP is mainly used for communication between a server and a single client, UDP is used for packet broadcast or multicasting whereby the data is sent to all the clients in the network.

Since UDP lacks any kind of mechanism to control or avoid network congestion, other forms of network-based control mechanisms need to be implemented to ensure smooth flow of traffic in a UDP network. One of the solutions being designed to tackle this problem is DCCP or Datagram Congestion Control Protocol which is aimed at monitoring and controlling traffic congestion in a UDP network.

A typical IP network consists of five layers:

1. The Physical Layer consisting of the actual channel for data flow like coaxial, twisted pair or fiber optic cables
2. The Data Link Layer implementing Wi-Fi, ISDN, GPRS etc
3. The Network / Internet Layer
4. Transport Layer implementing TCP, UDP etc
5. Application Layer running DNS, FTP, HTTP, POP3, SMTP, Telnet etc

As shown above, UDP belongs to the fourth layer. Although the entire amount of UDP traffic in a network is a small fraction of the whole, a number of key application in the fifth layer like DNS and SNMP or simple network management protocol use UDP.

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What is TCP?

September 28th, 2008 No comments

TCP (Transmission Control Protocol) is the main transport protocol utilized in IP networks.

The TCP protocol exists on the Transport Layer of the OSI Model.

The TCP protocol is a connection-oriented protocol which provides end-to-end reliability.

By connection-oriented, we mean that before two network nodes can communicate using TCP, they must first complete a handshaking protocol to create a connection.

When we say that TCP provides end-to-end reliability, we mean that TCP includes mechanisms for error detection and error correction between the source and the destination.

These properties of TCP are in contrast to UDP, which is connectionless and unreliable.

Higher layer protocols which utilize TCP include HTTP, SMTP, NNTP, FTP, telnet, SSH, and LDAP.

Diagram of the TCP Header

                        TCP Header Format
-----------------

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Destination Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Acknowledgment Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data | |U|A|P|R|S|F| |
| Offset| Reserved |R|C|S|S|Y|I| Window |
| | |G|K|H|T|N|N| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum | Urgent Pointer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Additional Reading on TCP

The TCP protocol is defined in RFC 793: Transmission Control Protocol.



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What is the OSI model?

September 28th, 2008 No comments

The OSI model is a reference model which most IT professionals use to describe networks and network applications.

The OSI model was originally intended to describe a complete set of production network protocols, but the cost and complexity of the government processes involved in defining the OSI network made the project unviable. In the time that the OSI designers spent arguing over who would be responsible for what, TCP/IP conquered the world.

The Seven Layers of the OSI Model

The seven layers of the OSI model are:

Layer Name
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical

The easiest way to remember the layers of the OSI model is to use the handy mnemonic “All People Seem To Need Data Processing”:

Layer Name Mnemonic
7 Application All
6 Presentation People
5 Session Seem
4 Transport To
3 Network Need
2 Data Link Data
1 Physical Processing

The functions of the seven layers of the OSI model are:

Layer Seven of the OSI Model

The Application Layer of the OSI model is responsible for providing end-user services, such as file transfers, electronic messaging, e-mail, virtual terminal access, and network management. This is the layer with which the user interacts.

Layer Six of the OSI Model

The Presentation Layer of the OSI model is responsible for defining the syntax which two network hosts use to communicate. Encryption and compression should be Presentation Layer functions.

Layer Five of the OSI Model

The Session Layer of the OSI model is responsible for establishing process-to-process commnunications between networked hosts.

Layer Four of the OSI Model

The Transport Layer of the OSI model is responsible for delivering messages between networked hosts. The Transport Layer should be responsible for fragmentation and reassembly.

Layer Three of the OSI Model

The Network Layer of the OSI model is responsible for establishing paths for data transfer through the network. Routers operate at the Network Layer.

Layer Two of the OSI Model

The Data Link Layer of the OSI model is responsible for communications between adjacent network nodes. Hubs and switches operate at the Data Link Layer.

Layer One of the OSI Model

The Physical Layer of the OSI model is responsible for bit-level transmission between network nodes. The Physical Layer defines items such as: connector types, cable types, voltages, and pin-outs.

The OSI Model vs. The Real World

The most major difficulty with the OSI model is that is does not map well to the real world!

The OSI was created after many of todays protocols were already in production use. These existing protocols, such as TCP/IP, were designed and built around the needs of real users with real problems to solve. The OSI model was created by academicians for academic purposes.

The OSI model is a very poor standard, but it’s the only well-recognized standard we have which describes networked applications.

The easiest way to deal with the OSI model is to map the real-world protocols to the model, as well as they can be mapped.

Layer Name Common Protocols
7 Application SSH, telnet, FTP
6 Presentation HTTP, SMTP, SNMP
5 Session RPC, Named Pipes, NETBIOS
4 Transport TCP, UDP
3 Network IP
2 Data Link Ethernet
1 Physical Cat-5

The difficulty with this approach is that there is no general agreement as to which layer of the OSI model to map any specific protocol. You could argue forever about what OSI model layer SSH maps to.

A much more accurate model of real-world networking is the TCP/IP model:

TCP/IP Model
Application Layer
Transport Layer
Internet Layer
Network Interface Layer

The most significant downside with the TCP/IP model is that if you reference it, fewer people will know what you are talking about!

For a better description of why the OSI model should go the way of the dodo, disco, and DivX, read Kill the Beast: Why the Seven-Layer Model Must Die.

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13 Keys to a Healthy Diet

September 27th, 2008 No comments

Developing healthy eating habits isn’t as confusing or as restrictive as many people imagine. The first principle of a healthy diet is simply to eat a wide variety of foods. This is important because different foods make different nutritional contributions.

Secondly, fruits, vegetables, grains, and legumes—foods high in complex carbohydrates, fiber, vitamins, and minerals, low in fat, and free of cholesterol—should make up the bulk of the calories you consume. The rest should come from low-fat dairy products, lean meat and poultry, and fish.

You should also try to maintain a balance between calorie intake and calorie expenditure—that is, don’t eat more food than your body can utilize. Otherwise, you will gain weight. The more active you are, therefore, the more you can eat and still maintain this balance.

Following these three basic steps doesn’t mean that you have to give up your favorite foods. As long as your overall diet is balanced and rich in nutrients and fiber, there is nothing wrong with an occasional cheeseburger. Just be sure to limit how frequently you eat such foods, and try to eat small portions of them.

You can also view healthy eating as an opportunity to expand your range of choices by trying foods—especially vegetables, whole grains, or fruits—that you don’t normally eat. A healthy diet doesn’t have to mean eating foods that are bland or unappealing.

The following basic guidelines are what you need to know to construct a healthy diet.

1 Eat plenty of high-fiber foods—that is, fruits, vegetables, beans, and whole grains. These are the “good” carbohydrates—nutritious, filling, and relatively low in calories. They should supply the 20 to 30 grams of dietary fiber you need each day, which slows the absorption of carbohydrates, so there’s less effect on insulin and blood sugar, and provides other health benefits as well. Such foods also provide important vitamins, minerals, and phytochemicals (plant chemicals essential to good health).

2 Make sure to include green, orange, and yellow fruits and vegetables—such as broccoli, carrots, cantaloupe, and citrus fruits. The antioxidants and other nutrients in these foods may help protect against developing certain types of cancer and other diseases. Eat five or more servings a day.

3 Limit your intake of sugary foods, refined-grain products such as white bread, and salty snack foods. Sugar, our No.1 additive, is added to a vast array of foods. Just one daily 12-ounce can of soda (160 calories) can add up to 16 pounds over the course of a year. Many sugary foods are also high in fat, so they’re calorie-dense.

4 Cut down on animal fat. It’s rich in saturated fat, which boosts blood cholesterol levels and has other adverse health effects. Choose lean meats, skinless poultry, and nonfat or low-fat or nonfat dairy products.

5 Cut way down on trans fats, supplied by hydrogenated vegetable oils used in most processed foods in the supermarket and in many fast foods.

6 Eat more fish and nuts, which contain healthy unsaturated fats. Substitute olive or canola oil for butter or stick margarine.

7 Keep portions moderate, especially of high-calorie foods. In recent years serving sizes have ballooned, particularly in restaurants. Choose a starter instead of an entrée, split a dish with a friend, and don’t order supersized anything.

8 Keep your cholesterol intake below 300 milligrams per day. Cholesterol is found only in animal products, such as meats, poultry, dairy products, and egg yolks.

9 Eat a variety of foods. Don’t try to fill your nutrient requirements by eating the same foods day in, day out. It is possible that not every essential nutrient has been identified, and so eating a wide assortment of foods helps to ensure that you will get all the necessary nutrients. In addition, this will limit your exposure to any pesticides or toxic substances that may be present in one particular food.

10 Maintain an adequate calcium intake. Calcium is essential for strong bones and teeth. Get your calcium from low-fat sources, such as skim milk and low-fat yogurt. If you can’t get the optimal amount from foods, take supplements.

11 Try to get your vitamins and minerals from foods, not from supplements. Supplements cannot substitute for a healthy diet, which supplies nutrients and other compounds besides vitamins and minerals. Foods also provide the “synergy” that many nutrients require to be efficiently used in the body.

12 Maintain a desirable weight. Balance energy (calorie) intake with energy output. Exercise and other physical activity are essential.

13 If you drink alcohol, do so in moderation. That is one drink a day for women, two a day for men. A drink is defined as 12 ounces of beer, 4 ounces of wine, or 1.5 ounces of 80-proof spirits. Excess alcohol consumption leads to a variety of health problems. And alcoholic beverages can add many calories to your diet without supplying nutrients.

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MDP presidential Candidate Nasheed and Gaumee Ithihaad Leader DR Waheed as his running mate

September 22nd, 2008 No comments


The Winning Combination that undecided voters are looking for, and a combination the rest of the candidates to FEAR


Today e-mails and message came to our mobiles at an unexpected time by very enthusiastic voters. Of those most are the people who belong to the swing voter’s category the undecided. Their enthusiasm and reaction from our contacts around Maldives indicated that we have found the winning combination for Maldives voters.

It seems that people still undecided, about who to vote for, Nasheed has given them a reason, formed a lure, a chemistry that they cannot refuse by making Dr Waheed his running mate.

Anni with his brand new clean slogan, with a total remake over of MDP so far has been seen as a lone candidate, but many with his special make over of the party and himself has started believing that MDP had struck a code with ethics and yet somewhat are still not hundred percent convinced. However with DR Waheed who left MDP according to many due to MDP’s then revolutionary methods of pressure, has come back to MDP. This subtle man, with his peace loving strong morals coming back to MDP and accepting Nasheed is the last conviction that voter need that MDP is for real and they indeed has reformed.

More than that with Waheed supporting Nasheed every step of the way the party will stick with its new found love for peace and harmony. In addition with Dr Waheed’s experience in internal and external relations, his back ground in the education sector of Maldives and the world, foreign affairs experience, MDP can put Maldives on an economic and political course that can make the country a success story. His legacies and CV as a local and international dealings, with the extreme support Anni has both domestically and from other democracies of the world the combination of these two characters will turn the face of this campaign

It is extremely likely that the election campaign will have a completely new twist within the next few days itself and that Nasheed, DR Waheed and MDP will rise against all odds of the past। Particularly it is likely that the choice for all the undecided voters which still is a majority, will choose MDP. Therefore combined with support from die hard fans of MDP which still exist in every corner of Maldives, with the support, the popularity, solidarity and leadership of Dr Waheed brings on, combined with his party supporters they have the power to over take, not only, DR Hassan Saeed, Gasim Ibrahim, but also DRP candidate HE Maumoon Abdul Gayoom. Waheed /Nasheed combination is a huge challenge that unless some extensive, new strategy is adopted and extensive campaign of a combative nature not started by DRP and the rest in the race, with absolute conviction we can forecast that our next President will be Mr, Mohamed Nasheed, DR Waheed the vice President and MDP the ruling party.

by allaboutmaldives

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pregnancy

September 16th, 2008 No comments

nammi and mishi, originally uploaded by Jinaa.com.

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Scientists Test World’s Fastest Wireless Network

September 15th, 2008 No comments

Scientists in Pisa, Italy claim to have set a new world record for the fastest wireless data transmission. They report that during an uninterrupted 12-hour experiment, they were able to achieve throughput speeds above 1.2 Terabits per second; which they say beats the previous wireless data transmission speed record of 160 Gigabits per second by Korean scientists. The researchers claim that speeds of this magnitude can typically only be achieved using fiber optics.

The technology that the Pisa scientists utilized to achieve such high bandwidth, actually shares a significant similarity with fiber optics: Both technologies use optical communications. Unlike Wi-Fi or microwave communications, which use radio-based transmissions, the Pisa scientists used a Technology called free-space optical communications, which transmits data using light. The Harvard Broadband Communication Laboratory provides this explanation of Free-Space Optical Communications:

“Free space optical communications is a line-of-sight (LOS) technology that transmits a modulated beam of visible or infrared light through the atmosphere for broadband communications। In a manner similar to fiber optical communications, free space optics uses a light emitting diode (LED) or laser (light amplification by stimulated emission of radiation) point source for data transmission. However, in free space optics, an energy beam is collimated and transmitted through space rather than being guided through an optical cable. These beams of light, operating in the TeraHertz portion of the spectrum, are focused on a receiving lens connected to a high sensitivity receiver through an optical fiber.”

The Pisa researchers.
(Credit: Corriere Della Sera.it)

Free space optical communications has often been considered as means for “inter-satellite communications” of spacecraft, as “it is possible to transmit tens of megabits per second or more over many thousands of kilometers, using moderate laser average powers of the order of a few watts” in the vacuum of space. On Earth, however, there are a number of challenges that currently limit the range of free space optical communications to only a few kilometers.

The Harvard Broadband Communication Laboratory states, “although relatively unaffected by rain and snow, free space optical communication systems can be severely affected by fog and atmospheric turbulence.” Fog is a problem because the size of water droplets in fog “can modify light characteristics or completely hinder the passage of light through a combination of absorption, scattering, and reflection.” One atmospheric problem is “scintillation,” which is essentially air pockets with different densities that act as lenses that impact the “temporal and spatial variation in light intensity.” Another atmospheric issue is “beam wander,” which is “when turbulent wind current (eddies) larger than the diameter of the transmitted optical beam cause a slow, but significant, displacement of the transmitted beam.”

One of the biggest challenges that free space optical communications faces–whether in space or on Earth–is that communications are limited to line-of-site. Unlike some radio communications, free space optical communications requires that no obstacles interfere with the beam, and it cannot bend around objects.

The Pisa team is made up of scientists from the Sant’Anna School of Advanced Studies of Pisa, Waseda University in Tokyo, and the National Institute of Information and Communications Technology in Tokyo. The team is led by Ernesto Ciaramella, who is an Associate Professor in Telecommunication at Sant’Anna. Ciaramella proposes that one way to get around a number of these limitations would be to develop a communications technology that uses a combination of “photonics and radio.” While Ciaramella did not elaborate on how such a scenario would be implemented, it is possible to envision a system where free space optical communications is used for back-end communications, and radio-based communications (such as Wi-Fi or WiMAX) are used for the last hundred feet or “last mile.”

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Mosquitoe

September 9th, 2008 No comments

Mosquitoe, originally uploaded by Jinaa.com.

Mosquitoes are insects which make up the family Culicidae. They have a pair of scaled wings, a pair of halteres, a slender body, and long legs. The females of most mosquito species suck blood (hematophagy) from other animals, which has made them the most deadly disease vectors known to man, killing millions of people over thousands of years and continuing to kill millions per year by the spread of diseases.

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Red Hat, Fedora Servers Face Hack Attack

September 8th, 2008 1 comment


A rare Linux security breach occurred when Red Hat Enterprise Linux and Fedora project servers were compromised by an illegal intrusion. Red Hat advised Red Hat Enterprise Linux and Fedora customers on how to determine if they had been affected. Red Hat security specialists say the Fedora package signing key was not breached.

Last week, Red Hat security specialists had a problem on their hands when they detected an illegal intrusion on the company’s computer systems. The attack affected both the Red Hat Enterprise Linux servers and the servers of the Fedora Project, a Linux-based operating system supported by Red Hat.

Servers were instantly taken offline. Red Hat issued an advisory to its customers, telling them how to check to see if they had been compromised and offering an updated version of the affected packages, including Red Hat Enterprise Linux 4 and Red Hat Enterprise Linux 5.

“Security specialists and administrators have been working since [they discovered the attack] to analyze the intrusion and the extent of the compromise, as well as reinstall Fedora systems,” said Paul W. Fields, Fedora’s project leader. “We are using the requisite outages as an opportunity to do other upgrades for the sake of functionality as well as security.”

Affected Systems

A system used for signing Fedora packages was compromised, according to Fields. He also said he believes the intruder did not steal the pass phrase used to secure the Fedora package signing key, but had not yet confirmed that.

“While there is no definitive evidence that the Fedora key has been compromised, because Fedora packages are distributed via multiple third-party mirrors and repositories, we have decided to convert to a new Fedora signing key,” Fields said.

Red Hat has built a custom hardware solution to prevent having to disclose private keys to developers. “Assuming that [this was done correctly], there was no risk of their key being compromised,” said Justin Cappos, a post-doc student at the University of Washington who has studied and written papers on the subject. “Someone was able to get a token, but was not actually able to get the key.”

Packages obtained by Red Hat Enterprise Linux subscribers via the Red Hat Network were not at risk, according to the company.

Fields also pleaded with users to come forward and contact Red Hat’s legal team if they have any information about the intrusion.

Vulnerabilities Exposed

A group of techies at the University of Arizona wanted to prove how easy it is for a malicious person to obtain a mirror (a Web site that is an exact copy of another Web site, often used for downloads). So the group of post-doc, undergraduate students and their associate professor ran an experiment where they created a fake company name, leased a server from a provider, and created a fake administrator.

“We were able to get our mirror listed on every distribution we tried,” wrote the group in a paper about their experiment.

The experiment included Fedora along with Debian, Ubuntu and openSUSE. Mirrors set up by the group were contacted by thousands of clients, including military and government computers.

Cappos, who worked on the project while a student at the University of Arizona, said the problems that exist in this area are not unique to Fedora or Red Hat. They are prevalent across a wide variety of distributions.

“Distributions have done a great job at looking at code created by developers. What receives a lot less attention is how they package the code and get it to the users,” Cappos said.

Another problem, according to Cappos, is how developers get the code into main depositories. “This is an area that I don’t think distributions have paid just as close attention to. There is a lot of work that they need to do in this area.”

How To Handle the Tampering

Red Hat has provided a shell script that lists the affected OpenSSH packages (Linux 4, i386 and x86_64 architectures only; and Linux 5 x86_64 architecture only) and can verify that none of them are installed on a system. Users are being asked to go to the Red Hat Web site, where they will find scripts to run to test their systems.

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‘Sexercise’ will keep you healthy and young

September 6th, 2008 No comments


According to British health experts if you want to get fit forget the gym, jogging round the park and doing sit ups, a workout between the sheets is a more effective and enjoyable way of keeping healthy.

The British National Health Service is recommending that for those too busy to fit regular exercise into their schedule, sex will not only lower the risk of heart attacks but will help people live longer.

According to the NHS during “sexercise” endorphins released at orgasm stimulate immune system cells, which also helps target illnesses like cancer, as well as wrinkles.

While sexual health experts agree there is evidence that sex has benefits for mental wellbeing, they say claims of a reduced risk of heart disease and cancer could not be scientifically proven.

The NHS however claims the theory is backed by science and clinical evidence.

The advice, entitled “Get more than zeds in bed”, is one of several sexual health-related articles to be found on the NHS Direct website and claims sex with a little energy and imagination provides a workout worthy of an athlete.

The article also says orgasms even prevent wrinkles and frown lines from deepening.

The NHS says that sex uses every muscle group, gets the heart and lungs working hard, and burns about 300 calories an hour.

The advice suggests “regular romps this winter” could lead to a better body and a younger look, make hair shine and skin smooth.

The article also claims goes that orgasms release “painkillers” into the bloodstream, which help keep mild illnesses such as colds and aches and pains away.

Healthy bones and muscles, and a feeling of wellbeing are they say a guaranteed result of the production of extra oestrogen and testosterone hormones which sex engenders.

Sexperts, sorry I mean experts on sex say that one of the greatest benefits you can get from sexercise is a release of endorphins in the brain that act as a natural drug induced high, or a heightened sense of well being. During the act of having sex your body is releasing endorphins making you feel stimulated all over and when you have an orgasm you get a sudden hormonal rush which floods your entire system. After the orgasm you feel not only satisfied but relaxed and at ease. Sexercise might just be one of the most productive of all forms of exercise, very few other forms of exercise provide such a tremendous overall feeling of satisfaction.

It is believed sexercise has a number of health related benefits like lowering the risk of heart attack although I personally thought it might have increased that risk for some elderly guys if they had maybe just a little too much fun too often, but apparently not. The more sexercise the better if you want to live longer the sexperts say. I don’t think many people would argue with their doctor if they advised them to engage in more sexercise and less walking. Having an orgasm is supposed to increase the body’s immune system and minimize the risk of cancer. I’m not quite sure how these sexperts get all their information but I’m not one to complain.

It has also been suggested that engaging in regular sexercise can help keep the skin looking smooth and wrinkle free and the hair looking silky and vibrant. It all sounds good and I doubt many people if any would complain when it was time for a sexercise session unlike they may complain before a workout in the gym or running around the block a few times on a hot day.

Performing sexercise is healthy for both men and women. Sexercise encourages testosterone production in men and oestrogen production in women which helps keep the muscles and bones healthy and strong. So although you may have once only considered having sex for fun or making babies, now you might want to consider incorporating sexercise into your daily or weekly workout schedule. Hmmm sounds like some food for thought. specially with for me 🙂 Guess why ???

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