=================================
Mobile broadband legs & modems
=================================

SD-WAN can use USB and PCIe mobile broadband modems as legs.
Mobile broadband legs are very different than wireline and fixed
wireless legs connected over Ethernet, so please consider the following
requirements and recommendations when using mobile legs.

Managing mobile provider settings
----------------------------------

Mobile broadband legs must be configured with the carrier's Access Point
Name (APN) and in rare cases, a username and password. In order to
centralize and simplify this configuration, APNs are specified in mobile
broadband provider profile records in the Administration section of the
management server. Before adding a mobile broadband leg, you must create
at least one mobile provider profile.

Refer to `Mobile providers <../policies/mobile-providers.html>`__ for
details on managing profiles.

System requirements
--------------------

Mobile broadband legs have special system requirements, as follows:

-  Operating system version: Debian 7 ("Wheezy"). Debian 6 ("Squeeze")
   does not support mobile broadband legs.
-  Linux kernel: the kernel version must be 3.14 or later. The default
   Debian Wheezy kernel, 3.2, may not contain drivers for some modems.
   Bonders imaged since late 2014 have the 3.16 kernel installed by
   default. A bonder's kernel version is shown on its node details page,
   and the kernel version can be upgraded remotely by following the
   instructions in `Upgrading Linux
   kernel <../nodes/upgrading-and-replacing-a-node/upgrading-linux-kernel.html>`__.

Supported devices
------------------

SD-WAN supports numerous USB and PCIe mobile broadband modems.
Modems are controlled through an open-source application called
ModemManager, so SD-WAN should support the same modems
supported by ModemManager. ModemManager's hardware compatibility list is
available here:
http://www.freedesktop.org/wiki/Software/ModemManager/SupportedDevices/

Known working modems
---------------------

The following modems are known to have been used in at least one
SD-WAN installation:

USB
^^^^

-  Huawei K4505
-  Huawei E1691
-  ZTE MF821
-  ZTE MF668
-  Sierra Wireless AC330U
-  Novatel Wireless Ovation MC547

-  Novatel Wireless Ovation MC679

PCIe
^^^^^

-  Sierra Wireless MC7700
-  Sierra Wireless MC7354
-  Sierra Wireless MC7304
-  Telit HE910-D

Best practices
---------------

Using multiple mobile broadband legs
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

SD-WAN needs no configuration, other than the mobile provider
profile, in the following environments:

#. When using a single mobile broadband modem
#. When using multiple modems from a single wireless provider

However, when using two or more modems from different providers,
SD-WAN needs some additional configuration to ensure that each modem
connects to the appropriate provider and APN. To ensure that a specific
modem connects to a specific provider, you need to supply each modem's
IMEI, a number that uniquely identifies the modem. This allows
SD-WAN to know which modem is meant to connect to each different
mobile provider. The device IMEI is usually printed on the packaging and
on the device itself, frequently behind the battery or SIM card cover.

Minimizing SD-WAN monitoring data usage
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

In order to monitor latency and quickly detect when a leg has failed,
SD-WAN sends frequent check packets between the bonder and
aggregator on each leg. In common default configurations, these packets
are sent at intervals up to every 100 ms for normal legs, and every
second for failover legs. This monitoring traffic can add up to about 6
GB/month of data for normal legs, and 600 MB/month for failover legs.

To reduce the amount of data used for these checks, you can adjust the
check frequency by changing values on the bond edit page. For details,
see the `leg ping and fail time
documentation <managing-bonds.html>`__. For example, to reduce
check data usage to 60 MB/month for failover legs, you could change the
failover leg ping time option to 10,000 ms, or 10 seconds. We recommend
that you also change the fail time option to three times the ping time
option, in order to avoid detecting the leg as down too quickly if only
a few check packets are lost.

Monitoring data usage
^^^^^^^^^^^^^^^^^^^^^^

Most mobile broadband data plans have very low data usage caps compared
to wireline connections—for example, a few GBs/month compared to
hundreds of GBs/month. Overage charges are also much more expensive than
for wireline plans. To minimize the risk of significantly exceeding the
data usage cap of a mobile data plan, we recommend that you frequently
check data usage from your carrier's normal reporting applications until
you know a bond's average daily or weekly usage. If a plan is getting
close to its limit, consider changing the mobile broadband leg from a
normal leg to a failover leg, or setting its link mode to idle so that
it will not be used for bonded traffic but can still be used for
managing the device if all the other legs fail.
