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 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.

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:

  1. When using a single mobile broadband modem

  2. 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. 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.