The original design philosophy for the underlying technology that enables the Internet was founded on providing multiple alternative routings from one computer to another. By re-establishing the original “Internet” approach to communications channels, the communications can continue through most communications outages. Internet routing employs automatic fallback to alternative channels which assures continuous communications under most circumstances. Establishing redundant physical connections further improves reliability, but it is also possible to bond channels together to achieve faster communications. This was one approach used by some vendors of V.32 telephony modems to achieve better communications throughput. Today, there is a wide variety of physical channels available to designers of embedded systems.

A basic tenant of systems design is to avoid all single point failures if practical. Within embedded systems that include communications to other systems, the highest probability of failure lies with the communications channel. For any system that relies on communication with another system, the failure of a sole communications link generally leads to systems failure. The answer to this point failure is to add another communications link.

Companies like Australia’s NewSat actively deploy backup and emergency communications to supplement their mainline offerings.  Despite the ever-shrinking size of electronics, physical limitations impose minimum footprint sizes for systems that use satellite links.


Systems that include redundant communications links can use all available channels to increase bandwidth. Or, the links may be used in fallback configurations to increase systems reliability and availability. The process of using multiple links to increase bandwidth is variously called:

  • Link aggregation
  • trunking
  • link bundling
  • Ethernet/network/NIC bonding
  • NIC teaming


For LAN connections, more than one physical port is configured to be bonded. But not all bonding schemes increase the channel bandwidth.  For example, the Linux bonding driver provides a method for aggregating multiple network interfaces into a single logical interface. How the bonded interfaces behave depends on the bonding mode selected in the driver. For Linux, the bonding driver modes provide either hot standby or load balancing.

  • Round-robin
  • Transmit packets in sequential order from the first available NIC through the last - provides both load balancing and fault       tolerance.
    • Active-backup
      • Only one NIC in the bond is active. A different NIC becomes active if the active NIC fails - provides fault tolerance only.
    • XOR
    • Selects the same NIC for each destination MAC address - provides load balancing and fault tolerance.
      • Broadcast
        • transmits on all NICs - provides fault tolerance.
      • IEEE 802.3ad Dynamic link aggregation
      • Adaptive transmit load balancing
        • channel bonding that does not require any special switch support - if the receiving NIC fails, another NIC takes over the       MAC address of the failed receiving NIC.
      • Adaptive load balancing
        • The Linux bonding driver overwrites the source hardware address with the hardware address of one of the NICs in the bond       - different peers use different hardware addresses.



      Bonding may take place at any one of the three lowest level OSI layers.  Wireless and power line devices are generally bonded at layer 1 while Ethernet links are typically bonded at the data link layer (layer 2). It is also possible to bond at the network protocol (layer 3) such as Internet Protocol (IP). Bonding was originally the domain of infrastructure companies using large scale hardware. But the advances in CPUs have moved the potential of bonding from near the central office towards the outer edges of the communications network.


      Edge Access is a pioneering company in the VoIP business focusing on emergency communications. Edge Access’ equipment was deployed to New Orleans, Louisiana during hurricane Katrina. The equipment facilitated the first voice call from the devastated area. The electronics required to perform this embedded task was a bit bigger than a full size PC tower, but the use of a satellite link makes the footprint of the complete package footprint to be defined by the size of the satellite dish.  Edge also manufactures VoIP systems based on other communication links that are smaller in size.


      Norco (1) has another smaller, lower power approach to assuring reliable communications. The BIS 6623 can provide 3G/4G connections with voice, video, and data. Presented as a way of maintaining mission critical communications in an ever-expanding application of data types in emergency communications, the 6625 is a fan-less design base in the Intel® Atom™ 6xx processor.


      BIS-6625 Block Diagram.jpg




      Norco’s BIS-6623 is an example of using commercially available communications channels in a redundant manner to provide critical communications for systems used by emergency services and others. The system employs standard protocol stacks to manage multiple channels simultaneously under Microsoft® Corporation’s (2) Windows® embedded Operating Systems. Fallback protocols are implemented in software to select (or even bond) between available channels.

      The hardware platform Is available in several standard versions and comes standard with a 1 GHz processor clock rate and 1 G of DDR2 memory. Alternative standard versions are available including one based on the 600 MHz Tunnel Creek, and OS-less bare hardware option.


      Norco identifies third party wireless hardware suppliers Huawei and Sierra Wireless products to enable wireless communications. The 3G-capable Sierra Wireless AirCard® 503 2-in-1 Data Card provides PC Card and PC Card Express form factors in one package. Redundancy for the BIS-6623 is achieved by loading two or more 3G cards (or USB modems) into the 6625. If you are using the Windows operating system, device bonding is determined by how you set up the Windows drivers. Keep in mind that although the Norco product is aimed at wireless situations, these compact products also have other connections including USB and Ethernet.


      Bare hardware options for the BIS-6625 can run any OS that supports Tunnel Creek. So, Wind River Systems (3) Linux product for telecommunications carrier grade applications brings high software reliability to the compact Norco form factor.


      The Intel Atom processor family enables many small form-factor designs. Intel Embedded Alliance Premiere members Advantech (4), Emerson (5), Kontron (6), and RadiSys (7) all offer a variety of configurations. You can learn more about these and other Alliance members’ Atom-based products at Intel’s convenient membership web site.


      Communications channel bonding is increasingly becoming a viable option for embedded systems, but consider the totality of the environment that your system operates within. Single points of failure may exist in switches and routers outside your embedded system.

      Can your next embedded system benefit from redundant communications?




      1. Norco is an Associate member of the Intel Embedded Alliance
      2. Microsoft Corporation is an Associate member of the Intel Embedded Alliance
      3. Wind River Systems is an Associate member of the Intel Embedded Alliance
      4. Advantech is a Premiere member of the Intel Embedded Alliance
      5. Emerson is a Premiere member of the Intel Embedded Alliance
      6. Kontron is a Premiere member of the Intel Embedded Alliance
      7. RadiSys is a Premiere member of the Intel Embedded Alliance




      Henry Davis
      Roving Reporter (Intel Contractor)
      Intel® Embedded Alliance