Similar to many projects that have evolved from research initiated by the European Space Agency, the Canadian Space Agency and NASA, the characteristic reliability and scalability of the solutions they develop later on solve an unanticipated problem using the same techniques think about Velcro!
This article explains how Space Communication Protocol Specification (pronounced skips) based bandwidth optimizers are being installed in Mobile Satellite Services (MSS) networks to increase the bandwidth to remote mobile users worldwide. This was not an original goal, but the strategic thinking involved in SCPS research laid the foundation for the rapid adoption of the same solution.
Mobile Satellite Services History
In 1994, at the request of the U.N.s International Maritime Organization, a not-for-profit company called the International Maritime Satellite Organization (Inmarsat) was created to establish a satellite communications network for the maritime community, primarily to improve the safety of life at sea. The Inmarsat satellite network quickly expanded into the aero and commercial community, providing global satellite communications to private planes and other mobile users, such as media reporters and researchers.
Inmarsat was converted to a private company in 1999 and the bulk of the operation became Inmarsat PLC, while a smaller part of the organization branched off to became a regulatory body called the International Mobile Satellite Organization (IMSO).
MSS Service Offerings
While the scope of the original network has changed dramatically over the intervening years, the name Inmarsat has come to represent general mobile satellite services with access to both voice and data from virtually anywhere on the globe. However, more and more operators continue to deliver similar services.
The original data offering included an Integrated Services Data Network (ISDN) type connection, operating as a single, or bonded, 64Kbps link, which today remain widely used around the world by the media, military, researchers, NGOs and commercial users. These ISDN services are time based, with users paying by the minute for the amount of time the terminal is connected to the network.
With the recent completion of a constellation of very large satellites called the I-4, which include advancements in technology such as spot beams, Mobile Satellite Services users now have access to an always-on high speed GPRS type service called Broadband Global Area Network (BGAN). This is an IP based connection operating at 492 Kbps with coverage almost anywhere on the globe. Other new services with guaranteed bandwidth are also available in limited coverage areas, but at this point the user demand for remote wireless bandwidth from everywhere seems insatiable.
Broadband services such as BGAN are volume-based, so users pay for the amount of data sent in Mega Bytes (MB), rather than by the amount of time they are connected.
Any mobile MSS user can set up a small portable terminal with an integrated antenna quite easily. For other applications, tracking antennas can be used on ships, aircraft, and other vehicles. The BGAN network is a critical adjunct to military satellite communications based on its global footprint, lightweight terminals, and ease-of-use. This makes inter-operation with encryption devices a critical aspect of any value-added solutions a Distribution Partner may choose to offer. Inmarsat also provides global maritime distress and safety service (GMDSS) to ships and aircraft as a public service for no charge.
Understanding The SCPS Specification
The Space Communication Protocol Specification (SCPS) originated with aerospace research that began with a desire to increase the communications bandwidth between on-board spacecraft payloads and Earth stations. Once in operation, it was quickly recognized that these same techniques also worked very well when optimizing the complete end-to-end wireless link from ground-station to ground-station. Researchers were also pleasantly surprised that standards-based TCP proxy techniques had only positive effects across all of their TCP based applications, which led to wide acceptance across the space community and eventually the DoD.
This pioneering research in bandwidth optimization resulted in the SCPS specification and has been widely used in space communications for more than 10 years. The SCPS combines recommendations for the use of several standard Internet Engineering Task Force (IETF) protocols as well as methods for the dynamic and transparent negotiation of other unique vendor options, such as advanced TCP acknowledgement schemes, error recovery methods and data compression capabilities.
The Interoperable Performance Enhancing Proxy
The (I-PEP) specification from SatLabs builds on the SCPS specification by defining the default minimum options that must be supported to ensure basic operation between any two I-PEP compliant devices, which would use the SCPS specification to communicate. The specification also accommodates more sophisticated option negotiation when any two SCPS devices bracket a link with similar capabilities, leading to the use of advanced algorithms by the vendor community; otherwise the default options are used across the wireless segment and vendor interoperability is assured.
While the IETF has introduced some standards for TCP improvement over the years, the SCPS specification and specialized wireless optimization algorithms developed by vendors for space communication continue to deliver the most efficient wireless optimization capabilities today.
SCPS based acceleration is converging with Mobile Satellite Services in two key areas. On hub-side systems, Logical Network Classes are being used to apply rate controls and traffic prioritization to each individual remote terminal. On the remote side, small portable SCPS devices are being introduced to compliment the portable MSS terminal.
How Wireless Optimization Works
A SCPS based wireless optimizer will split (or proxy) TCP connections between any two remote networks. As SCPS functionality is designed for installation in the network infrastructure, ideally bracketing the wireless space segment, no pre-configuration is required as would be necessary for an application accelerator installation.
Any two networks that have a SPCS device installed in-line will optimize data over the wireless link when connecting clients and servers. If no optimization device is installed on a network, traffic passes without further modification, and the SCPS vectors added to the TCP options are simply ignored.
When data is secure, the optimizer is installed in-line prior to any encryption, ensuring that the data is fully optimized then encrypted. This chaining can be external, when using Type 1 military encryption devices, but it is also common to find IPSec functionality internally combined with wireless optimization on many devices.
Once in operation, a SCPS optimizer will dynamically open a new TCP connection over the wireless link for each originating session on the LAN. SCPS vectors are added to the TCP options in the SYN packet and attempt to negotiate the best set of algorithms the device is capable of supporting. Based on the CPU and Memory of the device on each end, different types of error recovery and data compression may be used, but this negotiation and the functions themselves remain completely transparent to end users.
Complex rate control algorithms, QoS, and data compression can be applied to each session by the optimizer on each end of the wireless link. Once packets arrive at the receiving end, they are forwarded along using standard TCP. By design, this standards-based TCP performance enhancing proxy technique is completely transparent to the network routing elements, the end users, and to TCP applications. The optimizer is installed in-line with user data that is to be optimized, but from a networking perspective, can operate as a transparent Layer 2 bridge or a full Layer 3 IP router.
As SCPS optimization functions operate at the TCP layer, existing optimizer solutions can be rapidly adopted into any wireless environment. Existing rate control algorithms designed for dynamic links are very effective over MSS networks and hub side logic ensures that deployments are economical and scalable.
MSS Distribution Partners
When an organization or an individual purchases Mobile Satellite Services, they work with a Distribution Partner that delivers service and support for various offerings in a specific vertical market such as maritime, aviation, military, or commercial. These satellite Distribution Partners compete for end-user business based on the value-added features they offer.
User terminals delivered by a Distribution Partner are provisioned so that any session can land at any Earth station with proper authentication credentials pre-configured into each terminal. Each Distribution Partner maintains a connection to the global MPLS backbone that is used to inter-connect the Satellite Access Stations (SAS) and the centralized data centers. Distribution Partners often share co-location facilities with the satellite provider, which also provides a meet-me-point for traditional wire-line ISP and voice network interconnections.
Once each terminal is authenticated over the satellite network at the SAS, the Radio Access Network (RAN) matches each terminal to a Distribution Partner and the service offering. The user session can arrive from a SAS located anywhere in the world. Once the terminal is identified, the data is routed over the correct MPLS Label Switched Path with the proper quality of service settings directly to the Distribution Partners point of presence.
This MPLS and co-location architecture is important as we consider the convergence of Space Communication Protocol Specification (SPCS) based optimizers, originally designed for VSAT and SCPC links, with Mobile Satellite Services, as the hub-side SCPS optimizer will be installed in the data center with other equipment belonging to each DP.
Historically and contractually, the satellite communications provider delivers basic connectivity, but value- added features such as wireless optimization have generally been left to each Distribution Partner. This situation has enabled a competitive and progressive environment in Mobile Satellite Services by encouraging the Distribution Partners to continue to enhance their service offerings.
MSS Network Deployments
Today, QoS features on hub-side SCPS devices have evolved to support optimization for users of different types of wireless networks, such as VSAT and SCPC in a single appliance. Using these same Logical Network Class capabilities, an MSS Distribution Partner can quickly enable their network for select users to achieve higher throughput when they use a remote, SCPS capable device. Each remote network is independently delivered the benefit of protocol acceleration, data compression and pre-fetching based on a logical class assignment. An MSS Distribution Partner typically will combine offerings such as Swift64, BGAN, and streaming services in a single hub appliance.
Once a Distribution Partner installs a hub optimizer in the satellite co-location facility, or at their own point of presence, possibly over a tunnel, any remote users with a XipStick, or any users behind a small or medium XA-Appliance, or even users that are running an embedded version of XipOS in another device such as an aviation router, will have their combined TCP data transparently accelerated and optimized, generally achieving 3x to 10x un-optimized bandwidth.
From a provisioning perspective, the provider can use routing policies to determine whether to forward the remote user traffic to the hub optimizer or selectively bypass unauthorized users. This flexibility leads to the business option for each Distribution Partner of charging a fee for a premium service or simply increasing capacity for all users.
XipStick Portable Optimizer
Just as important in solving the economic and technical challenges of deploying wireless optimization from the hub side, is the need to deliver an economical, self-contained and portable remote device.
The recently announced XipStick portable optimizer measures only 3 ½ x 2 ¾ x ¾ -inches and is powered from a USB port on the remote PC or from an external power supply. The user installs the XipStick between the remote PC or LAN hub and the wireless terminal, just like a VSAT or SCPC satellite user would install a larger appliance. Once connected to the network, the hub optimizer at the Distribution Partners co-location facility brackets the link and SCPS negotiation takes place. Wireless optimization features available on the XipStick include protocol acceleration, streaming data compression and Internet pre-fetching based on the SCPS specification, with an optional IPSec client.
The benefits of protocol acceleration apply to all TCP based connections and will reduce initial server connection times by at least a third. Depending on the content being optimized, users may see bandwidth gains from 3x to 10x based on the type of data being transferred. Some are highly compressible, while others cannot be further compressed. Typical web surfing users will also receive the benefits of TCP fast start and web pre-fetching and see an average one third the page load time of an un-optimized session, often higher.
As many MSS users are aware, in the early years of MSS network deployments, software based optimizers were offered to address some of the issues now being discussed high latency, high bit error rates, asymmetric connections and mobility. If we consider that the bandwidth of these early services was typically a maximum of 128Kbps, it would be reasonable to assume a single user or PC utilizing this link.
However, as link speeds increase, we find that these connections now typically support more than just a single user, often serving an entire remote LAN with multiple users or devices. When data from more than one device is being optimized, it is important that the optimization function observe all of the data being sent, maintaining priority for voice and other select data and not over-driving the link capacity and causing packet loss, as would occur if multiple PC based soft client optimizers were being used. Each would attempt to ratchet up the capacity of the link, but would in turn cause packet loss and retransmissions to other users.
As packet rates increase, it is also necessary to add CPU and Memory to drive the optimization function so as not to burden the host operating system, which has lead to the release of the XipStick portable wireless optimizer. While designed for MSS networks, the system architecture and XipStick can be used in any wireless data network including terrestrial wireless networks like WiMAX.
Advanced hub side logic allows unique rate controls, error recovery and data compression for each remote site and combined with small, portable optimizers in the field increase the typical MSS data rate for all TCP applications by a factor of 3x to 10x.
The increased capacity of an optimized connection for commercial and government networks on a global scale is enabling applications that could not operate on the limited bandwidth available otherwise.