What is DHCP and Network Recovery?
By: Paul Vail
4 Min Read
25 Jul, 2021
In a previous article on Battery Modulation we discussed how LAVA’s technology prolongs the lifespan of mobile devices, and the differences between CABM and RBM. However, RBM technology has an additional capability that should be explored more in depth – Network Recovery. This article will provide an explanation of DHCP, how it is used for wired networking with Samsung mobile devices, and how LAVA’s Network Recovery feature, paired with the LAVA Tablet Manager application, protects against DHCP dropout.
Many eSynC adapters are capable of providing Samsung mobile devices with 10/100 Fast Ethernet connections. This adapter capability, in part, relies on standard Ethernet support built into Samsung tablets and smartphones. Wired network capabilities are often preferred over Wi-Fi solutions as Ethernet is proven to be more reliable and bring a greater level of security. Devices supporting wired Ethernet operation provide two distinct options: static IP address setup and dynamic IP address setup. In static IP configurations, the user or network admin must manually assign and reserve an IP address for the device being connected. This ensures that the device in question will always be supplied with the same IP address, this option may be preferential or a requirement depending on the circumstances. In dynamic IP, these settings are assigned by a DHCP server every time the device connects.
Dynamic Host Configuration Protocol (DHCP) is a standard network management protocol that is used to automatically assign IP addresses, and other network parameters, to devices configured for dynamic IP. When using DHCP, the network settings are allocated by a DHCP common server, eliminating the need to set up each individual device. The use of dynamic IP addresses and DHCP is the default setting for all Samsung mobile devices.
The network addressing parameters setup by DHCP includes:
- IP Address
- Network Mask
- DNS Address
- Default Router (aka Gateway) – usually where DHCP server is located
In addition, the information provided by the DHCP server includes a lease time – the allocated time that a device reserves a specific IP address. This ensures that the pool of available IP addresses is not used up by devices which have been off-line for an extended period of time. A typical lease time is 24 hours long, however it can range from minutes to months at a time. Ultimately, the exact quantity of time is determined by the system administrator when the DHCP Server is set up. When the lease time is near expiration the device will contact the DHCP server to try and renew the lease. Once the lease time has expired, a mobile device is obligated to cease use of the DHCP provided parameters.
Usually when a DHCP Server request fails, a mobile device repeats the request several times over a 30 to 60 second window. In the event this initial request fails, Samsung’s TCP/IP implementation makes no further attempts – with no valid addressing information, no network connectivity is possible. This event is also referred to as DHCP dropout. That being said, other TCP/IP enabled devices periodically retry in an attempt to get the device back onto the network. Failure to contact a DHCP Server can occur on a large or busy network for many reasons. For example, someone may accidentally disconnect the network cable while moving shelving around in a retail or warehouse environment. There is ultimately no programmatic way for a standard Android application to restart the DHCP lookup; the designers of Android did not foresee this issue so no function call exists. There are techniques that can be used on a rooted tablet, however rooting a tablet negates the manufacturer warranty, eliminating this as a practical solution. The only way to restart the DHCP lookup and bring the device back on-line is to do one of the following:
- Restart the mobile device (power off and then back on)
- Unplug the network cable and plug it back in.
- Unplug the Ethernet adapter and plug it back in.
- Enter the setup menu, turn Ethernet off and then back on
- Use a LAVA network adapter with Network Recovery (and Battery Modulation support)
The Network Recovery feature is a two part solution featuring a LAVA RBM capable adapter (from the eSTS or eSynC families) and the LAVA Tablet Manager application (LTM). The LTM application monitors the state of the mobile device and issues commands to the LAVA adapter when corrective action is needed. When the network connection has been unavailable for more than a few minutes, a command is issued to the LAVA adapter requesting the network adapter be reset. Restarting the Ethernet portion of the adapter is equivalent to unplugging and reconnecting the Ethernet cable or adapter. Upon detecting an Ethernet adapter being connected, Android issues a DHCP request. When a reset is attempted, the Android Toast message “LTM – RESET ETHERNET” is reported.
The initial restart takes place if no network connection is seen for approximately 1 minute. If the connection is not restored, repeated attempts are made until a connection is restored. There are 2 options for the handling of subsequent attempts. Option 1 gradually increases the duration between connection attempts with time-out intervals of 2, 3, 5, and 8 minutes. After the first 3 reset attempts, subsequent attempts are made every 8 minutes. Option 2 repeats subsequent attempts every 2 minutes.
Changing the LTM application Network Recovery settings is handled by the configuration menu built into LTM. To access Network Recovery Mode open the LTM app > Go To Configuration > Ethernet Settings > Network Recovery Mode (See Image Below)
The configuration file can also be manually changed and copied from device to device. Note that the Network Recovery feature is enabled by default. LAVA’s Network Recovery technology automates the network restart, which is critical for embedding a device in an enclosure or kiosk.
Much like a vehicle airbag, Network Recovery is a safety feature that goes unused until it is necessary. While DHCP dropout is unlikely to happen frequently, there is always a possibility that it will occur. Having an automated failsafe to restore a mobile device’s network connection eliminates the time and resources required to manually reset the connection, while providing both an added level of protection and peace of mind.