The definition of remote working is changing. Whether an employee is telecommuting or working at a branch office, they require the same connectivity to headquarters, to each other, and to business applications such as inventory and sales data. Many SMEs use the Internet to provide connectivity across the WAN and it behooves them to keep Internet uptime at a maximum; however, many SMEs feel that the cost of availability is too expensive. There is, however, a cost-effective, reliable solution -installing WAN Link controllers for accessible and reliable remote access. While small to medium-sized businesses may be familiar with the use of WAN optimization controllers in multi-homed networks to bundle two or more WAN links and/or service providers to connect their LAN to the Internet, these devices may also be used to interconnect between sites to ensure reliability and optimum performance for critical applications with uninterrupted connectivity.

Site-to-site channel bonding enables two or more locations equipped with specialized WAN optimization controllers to provide WAN link aggregation load balancing and failover capabilities. These WAN link controllers communicate over multiple networks using the combined throughput of multiple and diverse WAN links at multiple sites. This technology allows local and remote sites to send and receive large data files as if they were directly connected by a physical high-capacity link - at a fraction of the cost of supporting such a link. Examples include health care centers that need to send MRI files to remote sites for analysis and diagnosis; and advertising agencies with local sites that send large graphics-intensive files such as advertising layouts to remote sites.

The WAN optimization controllers used for site-to-site channel bonding are located between the LAN network and WAN connections at each site. They include Ethernet ports that allow businesses to connect (or multihome) to two or more ISPs (up to 15 depending on the controller). Internet sessions generated on the LAN are then automatically load-balanced based on available resources and directed to WAN links with the available bandwidth required by the outgoing traffic. In this way, the combined throughput of all the WAN links is available for sending and receiving Internet traffic between sites. Should one WAN link fail, the controller automatically senses the failure and reroutes traffic to properly functioning WAN link(s). When the failed link is restored, it is immediately placed back into service.

The benefits of these WAN optimization controllers are twofold. First, WAN link redundancy with automatic failover eliminates the potentially costly problem of Internet outages. Second, aggregating bandwidth from any type of ISP and WAN link, even the least costly, allows businesses to cost-effectively and incrementally increase bandwidth as business needs require. This saves many businesses the expense of migrating to dedicated point-to-point connections or costly high-capacity lines, and therefore, paying for unused bandwidth. Rather than needing to add an expensive T-1, businesses are better able to manage bandwidth consumption, mitigating the requirement for additional capacity and monthly OPEX.

Site-to-Site Channel Bonding
For site-to-site channel bonding, WAN optimization controllers with intelligent link load balancing are installed at both a local and remote site and manage traffic over the Internet between the two sites using the combined (or bonded) bandwidth of multiple ISP or WAN connections. Each site connected by such a bonded link is assigned a unique identifier that allows it to be differentiated from other sites. Each site is also configured with addressing information for both the local and remote end of the bonded link. This allows the WAN optimization controller at the local site to identify traffic that should be sent across the bonded link and direct it to the specified IP addresses on the WAN link(s) of the remote site. When the WAN optimization controller identifies such outgoing traffic, it is disassembled at the packet level into separate streams of data, then encapsulated for transmission through the bonded channels and sent over all available WAN links. Since each encapsulated packet contains addressing information for a specific remote location, data is easily reassembled at that location.

A typical example of how site-to-site channel bonding works starts with a business that sends data from a local headquarters site to a remote branch site. Each site uses a WAN optimization controller to load balance IP traffic over two 768 kbps WAN links. By using two relatively low-cost links, the business avoids the necessity of upgrading to a more expensive T3 connection, which would provide more capacity than the business needs, and avoids a single-point-of-failure.

Adding a WAN link controller enables a company to add bandwidth while saving costs. For example, a school district had three bonded T1 lines providing 4.5Mbps of bandwidth between locations. After deploying a WAN link controller from Ecessa, the district eliminated one of the bonded T1 lines, saving $875.00 per month. Instead it added two 5Mbps DSL lines that cost $180.00 per month, and increased total bandwidth to 12Mbps.

The school district was able to nearly triple its bandwidth capacity (an additional 7.5Mbps), while saving $695.00 per month.

When the WAN optimization controller at the local site detects traffic to be sent to the remote site, it breaks the traffic down into two separate streams and sends the streams simultaneously over its two WAN ports to the two WAN ports of the WAN optimization controller at the remote (bonded) site. The WAN optimization controller at the bonded site, then reassembles the two separate streams into the original data and delivers it to the LAN. With two streams of traffic simultaneously sent and received over two separate 768 kbps lines, throughput for the traffic is effectively doubled. In other words, the traffic is delivered to the remote LAN in roughly half the time needed if both sites had a single 768 WAN connection. If the WAN optimization controller at both sites were connected to additional low-cost ISP links, the time needed to deliver the traffic to the remote site would be reduced even further.

Meanwhile, the WAN optimization controller continues to provide uninterrupted communication in the event of a WAN link failure. In the event of such a failure, traffic traveling to its corresponding IP network across the bonded channel will simply use another channel that is configured on a functional WAN link. When the failed WAN is restored, it is immediately placed back into service.

In this example of site-to-site channel bonding, each site has two Internet connections that are combined into a bonded channel. Sites are assigned a unique identifier that allows for differentiation between multiple sites. Each site is configured with addressing information for both the local and remote ends of the bonded channel. This allows the WAN access appliance to easily identify traffic that should be sent across this link.

The type of traffic sent between sites using channel bonding usually consists of large data files ranging from hundreds of megabytes to several gigabytes in size. Transferring such files would normally require expensive or dedicated lines, and file transfers would abort if a line failed. Site-to-site channel bonding thus becomes a cost-effective option for businesses that need to send large files from local to remote sites, but may not be able to afford the cost and considerable complexity involved in maintaining high-bandwidth links.

Remote Backup
Site-to-site channel bonding is also an effective method for backing up data from a local site to a remote site without the expense of high-capacity links. Data to be backed up is simply sent from a primary site to a backup site using the techniques described earlier. The speed of the file transfers depends on the number of WAN links bonded by the WAN optimization controller at each site. Among other uses, this makes it easier and more reliable to transfer data to backup sites that are used in disaster recovery scenarios.

Summary
Site-to-site channel bonding provides businesses with two major benefits. By allowing traffic to be sent between bonded sites over multiple WAN links, business can use the combined throughput of lower-cost links to transmit large files, such as video or raw image files. This can make site-to-site channel bonding a much less costly alternative to installing expensive high-bandwidth links. An even greater benefit for many businesses is redundancy. Site-to-site channel bonding allows for uninterrupted communication in the event of a WAN link failure at any site. If a WAN link fails, traffic traveling to its corresponding IP network across the bonded channel will simply use a channel that is configured on a functional WAN link. When the failed WAN link is restored, any channels configured on that WAN link automatically begin load balancing traffic. This feature is especially useful for businesses that have remote offices constantly communicating with servers at a central location.