Monday, March 26, 2012

Use an iPad or iPhone as a Mobile TFTP Server

As network engineers, through the course of our work we often find ourselves out in the field working at either a remote location or on an un-familiar network diagnosing and troubleshooting issues, performing maintenance, or deploying new equipment. Quite often, this also involves upgrading code on network equipment, backing up configurations, or when called in to save the day (called a MacGyver - thanks Tom for that flashback) sometimes we even have to restore configurations or download a bug-free version of code to fix an issue.

If we are MacGyver, then our Swiss-Army knife is the trusty old TFTP protocol. Sure, it can be slow. Yes, it can have trouble traversing firewalls due to dynamically negotiated transfer ports. But it is about as widespread in networking equipment as file transfer protocols can get. SCP or SFTP would be better, but frankly have not been widely implemented.

We also love using our mobile devices just as much as non-geeks! Tom also did a nice write-up on a terminal console cable solution for iPads that is now widely popular among engineers. Today, I would like to highlight another useful application for network management from an iPad.

Now with Dropbox integration and large file size transfers (>32 MB)!
 Key features:
* Full TFTP Server
* Supports file size transfers >32MB
* Dropbox integration - upload and download files from Dropbox
* One-touch Dropbox file upload
* Block size > 512 bytes
* WiFi IP address refresh
* Full logging
* Standard "swipe" to delete files

From the description, a few features really stand out. First, it supports file sizes larger than 32 MB. This is an absolute requirement for working on modern networks. Any wireless engineer who has managed code images on a controller-based WLAN system can attest that equipment images are growing larger by the month due to the rapid expansion of feature sets and supported thin-AP platforms (which typically have AP code embedded in the controller image). Second, and this is the hook for me, full Dropbox support! Yep, cloud syncing of image files, configuration backups, licenses, SSL/TLS certificates, etc. for easy retrieval and upload to networking equipment. If there was one complaint that I have about tablets in general, it’s the lack of a file system. Well, Dropbox and other cloud services go a long way to make that a non-issue. But it requires every application to integrate with the service independently. Luckily for us, TFTP Server does. Third, it supports running in the background. This frees up the user to switch between apps and multi-task. This allows complete network management using only your mobile device; you can console into the equipment and host a TFTP server all at the same time without requiring two separate devices.

Okay, enough description about the app. Let’s start using it.

Once you’ve downloaded it from the app store and launch it, you will see the main screen:

It consists of a slider button to turn the TFTP server on or off, and handily displays your current wireless IP address (Wi-Fi only, no hosting over 3G/4G).
Then, there are 3 tabs that control the operation of the app:
1.       Log – displays the server log to monitor server status and TFTP file transfer progress.
2.       My Files – displays a list of the files available on the mobile device, which have been synched from the Dropbox account.
3.       Dropbox – controls Dropbox integration and selection of files to sync with the mobile device.

The first step in configuring the application is to ensure you also have the Dropbox app downloaded and signed into your account. Designate a folder as the TFTP root directory for hosting files.

Second, open the TFTP Server app and go to the Dropbox tab. Click the Settings button to configure the TFTP root directory and link it to your Dropbox account. From here you can also Upload all Files that have been uploaded to the mobile device TFTP server and store them back on Dropbox.

Click Done and go back to the Dropbox tab. A new Show Files button is now displayed. Clicking on it will now pull up the TFTP root directory on Dropbox and allow you to select files to sync with the local system. Select any files that you need to host from the mobile TFTP server, then click Done. The files will be pulled down to the iPad / iPhone.

Once the files have been pulled down, you will see them in the My Files tab.

Okay, now it’s time for an actual file transfer. From the main screen, ensure that you are connected to a Wi-Fi network and have a valid IP address. Then turn on the TFTP server.

In a separate app (or device), console or SSH into the network device and initiate the TFTP file transfer. Here, I used SecureCRT for simplicity of writing this post.

The file transfer starts, and is visible in the Log tab on the TFTP Server app.

The transfer from the mobile device is noticeably slower than hosting it using laptop or an actual server. But the trade-off which sacrifices a bit of speed for complete mobility is likely worth it for most situations, especially when out in the field and a TFTP server is not available, or is located across a high-latency WAN circuit.

You can see the file transfer completes successfully in the terminal:

Overall, the TFTP Server app works well, is bug-free from what I have seen, and allows me to use only my mobile device in many instances, making my shoulder bag a little bit lighter. My shoulder thanks you!

Revolution or Evolution? – Andrew’s Take
As a network engineer, being thrown into “enemy” territory and unfamiliar networks can sometimes leave us scrambling to perform the simplest of tasks. At the same time engineers, like everyone else, are looking for ways to “do more with less”. In our varied travels, this means many of us are looking for ways to be more productive while carrying less equipment around. Being highly mobile improves our productivity and takes some of the strain out of travel.

Using an iPad or iPhone for complete network management is getting closer to reality with applications like TFTP Server now available. It’s not all that glamorous, but hey, when is an engineer’s work really ever glamorous. The little things in our day-to-day work can make all the difference in getting the job done while keeping our stress levels to a minimum.

Having this app handy is one of those little things that makes our job easier. Hurrah to that!


Disclaimer – I was provided a free copy of the TFTP Server app by the developer, but all reviews and conclusions are wholly my own and were not paid for consideration.

Wednesday, March 21, 2012

Thursday, March 8, 2012

Apple iPad 3 Wi-Fi Specifications

Update 15-March-2012 - As I mentioned, I'd have more information once iFixit performed their teardown of the new unit. Well they're doing it right now... Wi-Fi, Bluetooth, FM chipset - confirmed it's a Broadcom BCM4330. Sadly, it doesn't look like 40MHz support will be possible :(

So, Apple announced "the new iPad" yesterday (aka - the iPad 3). I've done some digging on it at the FCC for Wi-Fi specifications and here is what I've found out.

First, the new iPad models fall under the following FCC IDs:
  • Wi-Fi Only FCC ID is BCGA1416
  • Verizon LTE FCC ID is BCGA1403
  • AT&T LTE FCC ID is BCGA1430

I'm only interested in the Wi-Fi specs, so I've looked up the Wi-Fi only model (A1416) at the FCC OET Equipment Authorization database. It's worth noting that much of the Bluetooth and Wi-Fi testing and certification was performed on the Verizon LTE model (A1403) and covers the other two models as well.

Wi-Fi and Bluetooth Capabilities
From the FCC test reports we can gather the following certification details:

  • 1x1:1 MIMO (1 spatial stream)
  • 20 MHz wide channels only
  • 65 Mbps max raw data rate (likely)
  • Bluetooth 4.0 including Low Energy mode and High Speed alternate MAC/PHY (leveraging the Wi-Fi chipset to offload large data transfer)

The combo Wi-Fi and Bluetooth chipset used by the iPad 3 is definitely NOT the same Broadcom chip used in the iPad 2 and iPhone 4 (which used the Broadcom BCM43291HKUBC). We won't know for sure what chipset is being used because the FCC internal photos are currently marked "Confidential" until 05-Aug-2012. However, once iPad 3 devices start shipping on 16-Mar there should be an iFixit teardown to give us insight.

My guess is that there are significant hardware improvements under the hood, which Apple may not be leveraging at time of initial release but may drop an update later on down the road. We know for sure from the FCC test reports that it support Bluetooth 4.0, which should be a major improvement over 2.1 + EDR found in the iPad 2. If Apple is using another Broadcom combo chip, which is highly likely, it could be the BCM4334 which is designed for smartphones and tablets. Broadcom product literature even includes very "Apple-esque" verbiage around highly mobile devices and push-email. This would be an intriguing choice since that chip offers single-stream 802.11n, dual-band operation, and 40MHz wide channels. Broadcom also lists concurrent dual-band capability for Wi-Fi client access on one band while simultaneously using Wi-Fi Direct or Wireless Display on the other band using what they call "advanced switching techniques."

If Apple does drop a software update at a later date for the iPad 3, we could see Wi-Fi specs bumped to:
  • 1x1:1 MIMO (1 spatial stream)
  • 40 MHz wide channels
  • Short Guard Interval (SGI) support
  • 150 Mbps max raw data rate
However, this may or may not happen. Support for 40 MHz channels would be a nice upgrade to enhance the product as it ages and keep it relevant. But it could have significant battery life implications which may make Apple hesitant to adopt. Also, SGI support is possible but unlikely since the chipsets used in the iPad 1 and iPad 2 were similarly capable but was not implemented by Apple (as Keith Parsons did an excellent job of analyzing on his blog).

iPad 3 Supported
Frequency Bands
Frequency Bands Supported
Note - All frequency ranges reference center channel frequencies from low to high channel.

ISM (2402 - 2480 MHz) - Bluetooth Frequency Hopping (FHSS)
ISM (2402 - 2480 MHz) - Bluetooth 4.0 Low Energy (BT LE)

ISM (2412 - 2462 MHz)
ISM (5745 - 5825 MHz)

UNII-1 (5180 - 5240 MHz)
UNII-2 (5260 - 5320 MHz)
UNII-2 Extended (5500 - 5700 MHz)
UNII-3 (5745 - 5805 MHz)

The good news here is that the iPad will support operation using 20 of 23 available UNII channels. This should help enterprise network administrators plan for infrastructure deployments that can utilize the UNII-2 Extended frequency band. The 3 channels that are disabled (ch 120-128) in the 5600 - 5650 MHz range are disallowed for operation in the U.S. by the FCC DFS regulations due to Terminal Doppler Weather Radar (TDWR) systems.

Administrators have been reluctant to enable use of these channels in their networks because few clients have supported it. Enabling it on the APs would therefore result in "black holes" where clients would not be able to connect to the network. However, as more clients support this band administrators should look to verify client compatibility across the range of devices they support and, if possible, enable use of this band for greater Wi-Fi network capacity to meet the growing need for high-density deployments.

Additionally, channel 165 (ISM 5825 MHz) is available for use in the new iPad 3. However, few if any network administrators typically enable support for this channel in their deployments.

Antenna Gain
Here you can see the internal antenna gain in the iPad 3:

iPad 3 Integrated Wi-Fi Antennas

Power Output
Power output varies based on the exact frequency of transmission or channel of operation due to FCC regulations that limit spurious side-band emissions. Therefore, power output is usually lower on frequencies at the lower and upper edges of the bands. For simplicity, I will provide the range of power output values reported by the FCC across each band. For detailed information, see the FCC test reports.

FHSS - 10.80 to 11.90 dBm
Bluetooth 4.0 Low Energy - 8.70 - 8.90 dBm

The Wi-Fi values get even more complicated because of the variations in spectral masks used by different 802.11 physical layer technologies. I've summarized the FCC test results into the following table for easier reference.

iPad 3 Wi-Fi Output Power (Average)

FCC Regulations Update
It appears that in May 2011, the FCC adopted new requirements for client device operation in the UNII-2 and UNII-2 Extended bands with regards to radar detection capabilities (or lack thereof). It reads:

Devices to be approved as UNII clients need to show compliance with the general requirements of Section 15.202, in addition to the technical requirements of Part 15E.  According to the requirements of Section 15.202, a client device must rely on a master device to initiate a network if the client device does not have radar detection capability.  Such a client device cannot initiate, or be configured to initiate, any transmissions including transmissions from probes, beacons or support ad-hoc modes of operation.  The operation of a device as a Group Owner for Wi-Fi Direct in the bands is therefore limited only where it is approved as a master according to the requirements of Section 15.202 (see KDB # 594280).

So, a client device can avoid implementing radar detection as long as the manufacturer certifies that it will not operate in ad-hoc or peer-to-peer mode. The device must only perform passive scanning to find a "master device" (e.g. an access point) that is capable of radar detection and is already operating on the frequency. In addition, this also applies to Wi-Fi Direct operation by the device.

Apple and other device manufacturers are now required to submit a DFS Attestation, similar to the following: 

Apple iPad 3 (A1416) DFS Attestation Letter

Although at first glance the iPad 3 appears to be similarly capable as the iPad 2, the underlying hardware could be much more powerful. Whether or not Apple decides to release a software update to unleash greater Wi-Fi transfer speeds at a later date is unknown, but could form the basis for a strategy to keep the iPad 3 unit relevant as a low-end option once the next version of the iPad is released, likely supporting 802.11ac for even greater speeds.

Additionally, the support for DFS channels in both the UNII-2 and UNII-2 Extended bands is a great sign for Wi-Fi networks to enable greater capacity.

Andrew vonNagy