The Media Gateway (MGW) table holds information about each media gateway managed by the Call Agent. The media gateway can be uniquely addressed by domain name, an IP address, or the TSAP address.
Megaco/H.248 protocol: history
The Media Gateway table has two associated commands: RGW and TGW. The RGW command provisions a gateway as only a Residential GateWay, with the type token automatically set to RGW. The TGW command provisions a gateway as a Trunking GateWay only, with the type token automatically set to TGW. Both of these commands provision the Media Gateway table, but a service provider can use these commands to provide user security to certain individuals based on their roles.
H.323
------
H.225 also for RAS( Registration ,admission,Status)
H.225/Q.931 can be defined as signaling (eg.call setup)
H.245 can be defined as control signaling (eg .Terminal cabability setup )
H.320 can be defined as multimedia service over ISDN
H.321 or H.310 can be defined as multimedia service over B-ISDN
H.322 can be defined as multimedia service over QoS Garenteed networks
H.323 can be defined as multimedia service over packet networks
H.323 can be defined as multimedia service over SCN
Saturday, March 22, 2008
Sunday, March 9, 2008
Badminton Central Guide to choosing Badminton Equipment
I have wanted to write a guide on what equipment badminton should focus on. By nature, badminton requires the player to have a few pieces of equipment to engage in the sports, items such as a racket and a shuttlecock are a must for a badminton player. However, often I see many player places the wrong focus on how they spend their money on equipment. A smart badminton player will spend money effectively to maximize their badminton playing experience.
However, before I start, I would like to point out that no badminton equipment can replace proper badminton skills. If you think you can spend US$200 on a racket and you can instantly play better, you are 105% wrong. A good set of equipment can only bring out the potential of a player with good skills. No equipment can fix your bad skills. Instead, I recommend you spend your money on some good coaching lessons. It will make much more difference in your badminton game than a shiny new racket.
I chose to list the equipment in decreasing order of important, in other words, I reckon that the badminton shoes is the most important equipment that a badminton player has, while their clothing is the least important.
Shoes:
======
Contrary to popular belief, a good set of badminton shoes are the most important piece of equipment a badminton player can have. Badminton players move around the badminton court at an amazing pace, dashes and changes directions on every stroke of the rally, twisting and turning and lunging. All these movements are supported and made possible by the biggest unsung hero, the badminton shoes.
Badminton shoes are designed for badminton movements; a thin but well supported sole with good lateral support keep the player's feet close to the ground, this allows for fast and ankle bending directional changes with lower chance of injury; light weight for faster feet movement; surface hugging gummy soles to grip the indoor surface without slipping.
The amount of torture we subject our lower body to can clearly be seen in people's badminton shoes. A good pair of badminton shoes used by a decent player sometimes last only 3-6 months. At the end of its short life, you will find soles that are worn to the inner support, insoles that are worn through, strong upper leather that gave up and split due to the immense force exerted at it.
Pick your badminton shoes with care, make sure you choose the pair that fits the shape of your feet and thus the most comfortable.
And whatever you do, do not wear running shoes or any other thick soled shoes. They keep your feet too high up in the ground and all it will take is one deep lunge to have your ankle sprained. From then on, you will be in excruciating pain for days and the injury will affect your badminton game for years to come.
Good badminton shoes brands include
Asics,
Hi-Tec,
Mizuno, and
Yonex. Other smaller brands are starting to catching up as well.
String:
=======
The number two unsung hero of the badminton equipment is the badminton string. Afterall, it is the string that is in contact with the shuttle on every stroke. How the string interacts with the shuttle is crucial to the feel of each stroke. Depending on your skill level and the style of your game, you should pick a string and tension that is suitable for your game. String manufacturers usually have ratings of different string characteristics at the back of the string package. Pick the items that are most important for your game.
String tension affects the playability of the string as much as the string itself. The general rule of thumb is that the harder you can hit, the tighter your tension can be. A higher tension rewards a hard hitting while robs power from a light hitter. On the opposite end, a lower tensioned string helps light hitter with a better timed trampoline effect.
There is always the temptation to go higher in tension, but this is a case of bigger is not always better. Higher tension does not give you more power as mentioned above, beginners should always start with lower tension of around 20lbs, adjust it to 22-23lbs when you progress to intermediate and only go up to 25+lbs if you are gain more power in your technique. Using the inappropriate high tension will make the racket unresponsive, decreased power, and will easily cause injury.
Good brands for badminton strings are: Ashaway, Gosen, Mizuno, Yonex.
Recommended tensions:
beginners: 19-20lbs .(i.e. 2.2 lbs == 1 kg)
intermediate players: 21-24lbs.
advance players: 25+ lbs.
Grip:
=====
The number three unsung hero of badminton equipment is the badminton grip. Similar to the string being the interface to the shuttle, the grip is the interface to the badminton players finger and hand. The game of badminton comprises of many very delicate movements and fine control from the players€™s finger and wrist. A proper grip ensure that there is proper actuation and feedback to and from the racket.
Three major factors affects the characteristics of the grip: type, size and tackiness.
Badminton grips falls into two different type, towel and synthetic. The choice of which are personal preference. Towel grip are softer, provides good sweat absorption, but at the same time, is more prone to germ accumulation and needs to be changed often. Synthetic grips are less messy and less prone to accumulation of germs, however, they are not as good as towel grips when it comes to sweat absorption.
The proper grip size to use depends greatly on the player. Obviously a player with larger hands will prefer a larger grip and vice versa. It is often tempting to use a large grip, a large grip gives the false feeling that the racket is lighter and more maneuverable. However, one must again understand that badminton is comprised of subtle, agile and delicate movements in the fingers and wrist, a smaller (but not too small) grip will allow for higher agility and maneuverability of the racket.
Racquet:
=======
Often times badminton players give the racket the most emphasis. If you go into http://www.badmintoncentral.com and you will find that most of the discussion centers on the racket. While the racket is certainly an important equipment, the importance of which is often overrated, and that is the reason why I put the Racket almost next to last in our recommendation list.
The badminton racket is the middleman when transferring force from the player to the shuttle, sitting right between the grip and the string. A badminton racket can be categorized by a few characteristics: shape, stiffness, weight, balance.
Virtually all badminton rackets are made of carbon fiber or graphite. Some manufacturers choose to put in extra ingredients into the racket material like titanium or recently nanocarbon. I want to emphasis that they are only addictives, the 99% of the racket is still graphite and the extra benefits of the additives are very marginal.
Badminton rackets comes in two major head shapes:
1) Isometric/square and
2) Oval.
Oval is the traditional racket shape, it is a slightly bottom heavy oval, almost the shape of an egg. Oval rackets in general have a small but more concentrated sweet spot. Oval fans like the concentration of power around the sweetspot of the racket.
The shape is the Isometric or square which became more popular after the early 1990’s. The Isometric head has a wider and more squared top half of the racket head. The advantage of the isometric is an enlarged sweetspot which give off-centered hit a better response.
The effective stiffness of a badminton racket is similar to the effective of string tension. So I will refer you back to that section. A stiffer racket has the similar effect as a higher tensioned string, while a flexible racket is similar to the lower tension string.
Rackets comes in different weights. Normally the racket alone weighs between 80-95g. Different manufacturers have different rating system, the most popular of which is Yonex’s U system,
Weight Size | Weight (g) | Main Use |
---|---|---|
1U | 95-99.9 | Training Racquets |
2U | 90-94.9 | Attacking Singles |
3U | 85-89.9 | Singles/Attacking Doubles |
4U | 80-84.9 | Doubles/Defensive Singles |
5U | 75-79.9 | Defensive Doubles |
a racket's weight determines how fast one can swing a racket, the lighter a racket, the faster one can swing it with the same force. In general, a lighter racket is more maneuverable than a heavy one. However, before everybody goes out and buy the lightest racket, I also want to point out that lighter isn’t always better. A light racket is less stable than a heavier racket, more force is necessary to keep its path, furthermore, a heavier racket has a larger momentum and thus more effective in transferring its speed and power to the shuttle.
The final racket characteristic is the balance of the racket. Head balanced racket is becoming more popular recently. Head balanced rackets have more mass near the head of the racket. A head balanced racket is more stable and have higher angular momentum when swung. On the contrary, a even balanced racket is more maneuverable.
As you can see, none of the different properties of the above characteristics are strictly better than other. Some players prefers slightly heavier rackets, some prefer slightly lighter, some like even balanced, some like head balanced. What I want to point out is that ultimately, it is a person’s skill level and style that determines what racket is suitable, go try them out if you can to see what fits.
Clothing
======
Badminton clothing is quite simple to choose. Aside from one personal fashion preference, badminton clothing is better kept light and unrestrictive. Shirts needs to be slightly loose and comfortable to allow for arm and body movements. Badminton is a game of sweat, very often we see a badminton player walks out of the court like he just came out of a shower. As it is always uncomfortable to have sweat stuck to one’s skin, sweat absorption and dissipation is thus important. There are many fancy sweat-wicking clothing out there, but from my personal experience, a good cotton t-shirt works well in most situation. If one gets really wet during a game, they are cheap enough so you can have a few spares ones to change into.
Shorts are the preference for most badminton players. Again, choose something that is light and not restrictive to movement, jumps and lunges are done often in badminton.
Again, clothing is mostly personal fashion preference, as long as the clothing allows for the extreme movements in badminton, it is usually quite ok.
I have mentioned it once and I will do it again here, while equipment is essential in badminton, the most important factor in badminton is still one’s badminton skills. Equipment will only have marginal effect on one’s game.
Source: Badminton Central
Guide for Shuttle rules:
http://www.annandale.k12.mn.us/AHS/faculty/pamfliegel/webpage/Badminton%20Study%20Guide1.htm
Compare Yonex Strings
Now let's discuss the string. There are many different brand of string. But Yonex is more widely used. The following is mainly translated from a post by someone who have strung more than 20,000 racquets for professional teams in China. Unfortunately, the original post has been copied too many times. I cannot find his name or contact. Anyway, I strongly appreciate his detailed and professional comment on almost all Yonex strings.I focus on those available on US market. For those I used, I may add some of my own comment. I may also skip some details I think less important.
=====================================================================
First of all. I don't recommend Ti65 and Ti68 string. Except for a more crispy sound, there is nothing good about it. More importantly, the Ti skin on the surface of the string change the consistency of elasticiy of the string. That makes it fragile. The Ti skin also covers up the texture of the string. That reduced the control. Due to the sound, it makes you feel more powerful when you smash. But that is mostly hallucination only.(Normally this is used by professional players. They will restring after the game. If you can afford to do that. Ti string may still be a good choice for you.)
BG65 is most widely used. Mainly because it is the one used by National team for training purpose. But the BG65 used by national team is not the one in seperate bag we found on the market. It is the big reel version. (I guess the 200m Reel)The bag version is softer and smoother. Overall, it is very durable. It provides a good balance between quality and economy
I prefer BG66. It is a very thin string. Only 0.66mm.Extrodinary recillience. Good for beginer or players with relative less power. Cons: It is too thin. So it is easy to break. Also the control is not quite good.
In my opinion, BG70 is not a successful product. Yonex want to make it omnipotent: good recillience, good control and durable. Finally, nothing is very good.
BG80 is a .68mm string. Very good recillience. It is excellent for offensive plan. You can combine it with offensive racquets like NanoSpeed 9000, AT700, Ti10, MP100, etc. Strongly recommended for offensive player. One unqiue feature of BG80 is that you can get the feeling of a string setup at higher tension. (I use BG80 with my Ti10 at 24lb. It is a pretty powerful combination.)
BG85 is relative soft. It has a higher thread count. Its control is excellent, with the recillience second to only BG66. It is good for defensive player.
BGN95. This is not reviewed by the original post. But I used it with my NS9000 at 24lb. Recillience is not as good as BG80. But it is still pretty good overall. Good control and durability. It break only once when my racquet collide with partner's.
Model | Recillience | Feel | Shock Absorption | Control | Durability |
BG-65 | B | Medium | A | A | A |
BG-65Ti | A | Stiff | B | A | A |
BG-66 | A+ | Stiff | A+ | B | B |
BG-68Ti | A+ | Verfy Stiff | A+ | A+ | B |
BG-70Pro | A | Medium | B | A | A |
BG-80 | A+ | Stiff | A | A | A |
BG-85 | A+ | Very Stiff | A | A | C |
BG-95 | A | Stiff | A+ | A+ | A |
Shuttle cork:
Following are the Key Benefits of YONEX Mavis Series of Nylon Shuttlecock:
•Economical and durable Shuttlecock performance.
•Best Shuttle Flight and Characteristics (Close to Feather Shuttle).
•Better Flight pattern (Better then other Nylon shuttles and close to feather shuttlecocks).
•YONEX Mavis shuttlecock recovers in .02 secs (This fast shuttle recovery is better then other brand (.008 sec faster) , while its only .005 sec slower then feather shuttlecock)
Thursday, March 6, 2008
Pthread Creation and Termination
Example: Pthread Creation and Termination
gcc example.c -pthread
#include pthread.h
#include stdio.h
#define NUM_THREADS 5
void *PrintHello(void *threadid)
{
int tid;
tid = (int)threadid;
printf("Hello World! It's me, thread #%d!\n", tid);
pthread_exit(NULL);
}
int main (int argc, char *argv[])
{
pthread_t threads[NUM_THREADS];
int rc, t;
for(t=0; t<= NUM_THREADS; t++){
printf("In main: creating thread %d\n", t);
rc = pthread_create(&threads[t], NULL, PrintHello, (void *)t);
if (rc){
printf("ERROR; return code from pthread_create() is %d\n", rc);
exit(-1);
}
}
pthread_exit(NULL);
}
gcc example.c -pthread
#include pthread.h
#include stdio.h
#define NUM_THREADS 5
void *PrintHello(void *threadid)
{
int tid;
tid = (int)threadid;
printf("Hello World! It's me, thread #%d!\n", tid);
pthread_exit(NULL);
}
int main (int argc, char *argv[])
{
pthread_t threads[NUM_THREADS];
int rc, t;
for(t=0; t<= NUM_THREADS; t++){
printf("In main: creating thread %d\n", t);
rc = pthread_create(&threads[t], NULL, PrintHello, (void *)t);
if (rc){
printf("ERROR; return code from pthread_create() is %d\n", rc);
exit(-1);
}
}
pthread_exit(NULL);
}
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