What is the power output of a USB port? - Super User
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As the title says, what's the power output of a USB port?
Is it a standard value, or it may change depending on manufacturer/model, and so on?
If that value is not standard, how can one determine it?
2,73052956
As stated in
The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire to power connected USB devices.
A unit load is defined as 100 mA in USB 2.0, and 150 mA in USB 3.0. A device may draw a maximum of 5 unit loads (500 mA) from a port in USB 2.0; 6 (900 mA) in USB 3.0.
As power is equal to current times voltage, all you have to do is multiply 5V with the current the device is drawing from the port.
Note there also exists a convention for charging devices. These kinds of ports allow for currents up to 1.5 A (also using 5V). However, the USB port is rated to withstand current up to 5 A--so some manufacturers may go out of spec and offer a higher maximum current.
3,60031837
There are USB power adapters on the market explicitly stating "10W adapter". As USB is 5V the 10W result in 2A = 2000 mA. The net effect is that devices connected to this adapter charges its battery 4 times faster than with a "normal" 500 mA USB port.
I used the 'Battery Doctor' free app to determine how much amperage the usb charging port is offering. I use the word offering intentionally, since each device has a maximum amperage amount that it will take in regardless of what is offered.
I found that my 3.0 port on my hp envy laptop, which has a lightning bolt next to it offers 1.5 amps (1500mA), while the 2.0 usb offers only 0.5 amps (500mA).
Although some forums have stated that it is not possible for an app to determine the amount of amps offered to a device, the Battery Doctor app clearly states amps offered accurately and immediately on my ipad (although it may only display up to the maximum allowed by the device - I have not tried this). I have tested the app with a 1.8 amp out wall charger, and a 2.1 amp out power bank, and both are marked as such on the charger. The amperage readings displayed accurately and immediately on the app.
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How To Port Forward a Router
How To Port Forward a Router
If you are new to networking, there are some basics you should understand before you can fully grasp the concept of port forwarding. Don't worry, we'll take it easy!
Before we dive too far into this, we would like to answer some of the questions that you might have on a basic level.
What is Port Forwarding?
Port forwarding is a method of making a computer on your network accessible to computers on the Internet, even though you are behind a router.
It is commonly used for hosting game servers, peer to peer downloading, and voice over IP type applications. There are many other reasons you may need to forward a port, this is not an exhaustive list.
What are Ports?
Ports are virtual pathways on which information on the Internet travel. There are 65,536 ports to choose from. A good analogy is to think of ports like extensions on a phone sytstem.
What are some commonly used ports?
Every program on your computer that uses the internet is programmed to send its packets through specific ports. Sometimes the ports are selected arbitrarily by the programmers of the software, but other times programmers will use a more standard port depending on the functionality of the software. Here are a few examples of industry standard uses for common ports:
HTML pages: port 80
FTP file transferring: port 21
POP3 email: port 110
MSN Messenger: port 6901 and ports
For more information on the ports that specific programs use, please see our . There you will find the ports that you need to port forward for any application including
and uTorrent.
Now that you have a basic understanding of port forwarding, let's dive a bit deeper
Every device on the internet has at least one .
Every IP address is divided up into many . When one computer sends data to another computer, it sends it from a port on an IP address to a port on an IP address.
A port can only be used by one program at a time.
With that out of the way, we should talk about NAT. NAT, or Network Address Translation, is a technology that allows each device on your network to have its own IP address.
While each device in your network has its own IP address, from the outside, every request coming out of all of those devices appears to be coming from the single publicly visible IP address assigned to you by your Internet Service Provider.
Lets say you want to browse the web. We suggest port forwarding. For instance, when you click on this link to our site, , the request doesn't go straight out to the Internet. Instead, the request goes to your router, which makes a note of which internal device is requesting the information, then sends that request out to the Internet. When our web server responds, your router will know exactly which device to relay that response back to.
It works exactly the same in reverse! When a computer on the Internet requests, for example, a web page from your IP address, your router needs to figure out which internal device is a web server so the request can be filled. NAT can handle such requests in certain circumstances. For the rest, you need to know about port forwarding.
Luckily, you have almost all the information you need already. What if your router just doesn't know which internal device has a web server running? All you need to do is tell it: "Router, please send any requests for web pages to my server." That's what you'd say if this were Star Trek, but we're not quite there yet, so for now you need to sign in to your router's configuration utility and tell it which services are running on which internal devices.
For example ... Have an FTP server running on an internal computer with IP address 192.168.1.123? Tell your router to FORWARD all requests that come in on port 21 to 192.168.1.123. Need your internal web server to be accessible to the public? Forward port 80.
Sure, you can get complicated if you want, but for the most part it's just that easy.
Oh, you want to complicate things? Have TWO web servers running? Well, port forwarding can still come to the rescue. See, while each of your internal web servers might be answering on port 80 (192.168.0.2:80, 192.168.0.3:80), you can still make them both accessible on the Internet.
Say your public IP address is 20.1.1.1. You can make up a forwarding rule in your router that says that all requests to http://20.1.1.1:80 should be forwarded to 192.168.0.2:80, and all requests to
http://20.1.1.1:8080 should be forwarded to 192.168.0.3:80! No need to pick and choose. That works when we have the easy ability to change the port that is requested as in the example above. A bigger problem arises when you can't change the requested port, perhaps because you're using an application that won't allow you to specify an alternate port. Remember #3 way up above? It says that a port can only be used by one program at a time, so if we want to have two web servers, we can't have them BOTH answer on 20.1.1.1:80. The router wouldn't know which internal device to forward the request to! This is a reasonably big pitfall for those new to port forwarding.
Hopefully, this has demystified port forwarding a bit. If you're ready, head straight into the . Still confused?
Try running over the information above a few more times. If you would prefer to set up your forwards with just one click instead of setting it all up manually, take a look at .
If you can think of any way we can make this information more clear, please let us know by using our comments page.
Written by
Jason Bauer is an owner and programmer . You can find more of his articles .GET UPDATES BY EMAIL
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Whenever an application wants to make itself accessible over the network, it claims a TCP/IP port, which means that port can’t be used by anything else. So if you need to use an in-use port, how do you tell what application is holding it?
There’s a number of ways to tell what application has the port locked, but we’ll walk through the built-in way using the command line and Task Manager, and then a great freeware application that does it all in one utility.
Use Built-In Tools to See What is Listening on a Port
The first step is to use a command-line tool to see what ports are in use, and use a special flag that tells us which port is assigned to each Windows process identifier number. Then we can use that number to look up exactly which process it is.
Open up a command prompt and type in the following—you may have to open in Administrator mode to see all processes:
netstat -ab | more
This will immediately show you a list, although it’s maybe a little complicated. You’ll see the process name in the list, and you can search for it.
You can also use this other method, which takes an extra step, but makes it easier to locate the actual process:
netstat -aon | more
If you look on the right-hand side, you’ll see where I’ve highlighted the list of PIDs, or Process Identifiers. Find the one that’s bound to the port that you’re trying to troubleshoot—for this example, you’ll see that 0.0.0.0:80, or port 80, is in use by PID 4708.
Now you can simply open up Task Manager—you might have to use the option to Show Processes for All Users, and then you’ll be able to find the PID in the list. Once you’re there, you can use the End Process, Open File Location, or Go to Service(s) options to control the process or stop it.
Use CurrPorts to View What is Listening
If you aren’t really the command-line type, or you’d rather just use a simple utility to do it all in one step, you can use the excellent freeware CurrPorts utility by NirSoft, one of our favorite freeware authors.
Just open up the utility, and you can see everything—processes, ports, remote ports, the full path to the process.
If you double-click on any of the items, you’ll see every single detail.
You can also use CurrPorts to directly kill the process if you want.
Published 11/13/14
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Go check your email!What is a port scan attack?
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I have a Symantec VPN/firewall 200 in place. I have an address for the WAN in place, and my LAN seems to be protected...
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behind the firewall. However, in the firewall log I keep receiving &port scan attack& messages. What is a port scan attack?
Ports are like little doors on your system. Most packets leaving your machine come out of a certain door. They are destined for another door on another system. There are two different protocols that use ports: TCP and UDP. Each of these two protocols has 65,536 different ports. Various Internet services listen on certain well-known doors. For example, Web servers usually listen on TCP port 80. Mail servers usually listen on TCP door port 25.
An attacker launches a port scan to see what ports are open, with a listening service, on your machine. A port scan attack, therefore, occurs when an attacker sends packets to your machine, varying the destination port. The attacker can use this to find out what services you are running and to get a pretty good idea of the operating system you have. Most Internet sites get a dozen or more port scans per day. As long as you harden your firewall and minimize the services allowed through it, these attacks shouldn't worry you.
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