Satellite communications offer mobility and communications for military operations in remote locations where terrestrial-based connectivity is not available, or is too expensive. Unfortunately, satellite connectivity brings many challenges that can impair network performance in delivering mission-critical information and applications. High-latency transport and application protocol inefficiencies, adverse weather, and interference are just a few of the causes that slow the delivery of applications and limit the amount of traffic that can run over a satellite link. Compounding these problems is interoperability among disparate military networks that can jeopardize mission-critical communications.

This diagram shows satellite communications using SPCS-enabled WOC at the head-end and a WOC at one remote site. Software is deployed at a second remote site.

To address some of these issues, NASA and the Department of Defense (DoD) jointly created the Space Communications Protocol Standards (SCPS) protocol suite that has been deployed throughout the U.S. military. SCPS-TP is designed to overcome transport protocol interoperability problems and enable satellite WAN links to have a greater amount of traffic flow.

The U.S. DoD operates in areas of the world where bandwidth is extremely scarce and expensive. The military is very mobile, and communications can be time sensitive. Providing a comprehensive solution for reliable and fast military communications has become an ever-increasing challenge — balancing security, speed of delivery and bandwidth consumption.

Two Requirements

There are two requirements for improving reliability, performance and interoperability.

First Requirement

As mentioned above, the SCPS protocol suite was jointly developed by NASA and the DoD. However, an SCPS implementation that has become the “defacto standard” transport protocol is SkipWare from Global Protocols, a protocol engineering firm specializing in the development and integration of bandwidth efficient, error-tolerant protocol solutions based on SCPS. SkipWare is the industry’s first commercial SCPS implementation. SCPS addresses these issues with a set of protocols that offer:

  • Best possible use of limited bandwidth
  • High link utilization
  • Power conservation
  • Traffic prioritization
  • Tolerance of intermittent connectivity
  • High forward/return link asymmetry
  • Adaptation to the environmental stress of wireless networks
Satellite traffic is negatively affected by TCP and application turns, and network distance

The SCPS protocols are based on current Internet protocols, and are fully interoperable with IETF standards. The technology addresses issues related to throughput, reliability, and efficiency when transporting Internet traffic over stressed links. SCPS mitigates throughput degradation associated with latency and asymmetry, and employs a series of error-resistant technologies that provide rapid recovery from packet loss. The SCPS protocol includes:

File handling – SCPS File Protocol, or SCPS-FP, is optimized for the uploading of spacecraft commands and software, and downloading collections of telemetry data.

Retransmission control – SCPS Transport Protocol, (SCPS-TP) is optimized to provide reliable end-to-end delivery of spacecraft command and telemetry messages between computers that are communicating over a network containing one or more potentially unreliable space data transmission paths.

Data protection – SCPS Security Protocol, (SCPS-SP) provides end-to-end security and integrity for message exchange.

Networking – SCPS Network Protocol, (SCPS-NP) supports connectionless and connection-oriented routing of messages through networks containing space or other wireless data links.

Second Requirement

WAN optimization solutions from companies such as Stampede Technologies provide performance and bandwidth availability improvements for Internet-based satellite communications. Satellite WANs require acceleration and optimization technologies that squeeze greater amounts of traffic into a satellite link, and accelerate traffic to deliver applications more quickly to users.

Many WAN optimization controllers (WOCs) are not SCPS-compliant, and lack the interoperability required by military personnel, while standalone SCPS implementations have limited acceleration capabilities. However, there are solutions on the market specifically designed to accelerate, optimize, and provide interoperability for military satellite communications. These solutions offer robust optimization and acceleration, with integrated SPCS.

WAN optimization solutions with integrated SPCS provide optimization and acceleration technologies that address network bandwidth constraints, high-latency, transport and application protocol inefficiencies, non-essential traffic, and application contentions. These solutions can save as much as 75% of bandwidth capacity, while dramatically increasing information delivery.

The benefits:

  • Improve application delivery times
  • Improve WAN response times
  • Optimize connectivity with any SCPS-TP-based military network
  • Reduce the amount of data that is sent over the satellite link
  • Reduce the number of transport & application round trips required to complete transactions
  • Offload tasks from clients and servers
  • Secure data - end-to-end

Adverse Affects

The primary factors that adversely affect satellite Internet traffic are:

High Latency – Latency reduces the amount of data transmitted through a network link, regardless of how much bandwidth is available. Latency has significant adverse affects on TCP and web-based applications that require extensive handshaking. For satellite communications, a major challenge to the performance of Internet applications is the latency between two earth stations connected by a satellite. On terrestrial-based WANs, latency can range from 0.1ms to 200ms; on a satellite link, latency can be 1,000ms. Because of latency, even though you pay every month for a certain amount of bandwidth, in reality, you may not be getting the full value of the connection.

Transport Protocol Inefficiencies – TCP has a maximum window size of 64 kilobytes. For each round trip, TCP only allows 64KB to be sent. For example, a 64MB file over a satellite WAN requires many round trips in order to complete the transmission.

Chatty Application Protocols – Web applications have their own protocols with similar challenges to TCP, and can be even more inefficient. For example, Web pages are comprised of many separate objects. Each object is requested by the user and retrieved sequentially. Web applications can generate hundreds of round trips by themselves, and can also have window sizes 15% - 20% smaller than TCP, requiring even more round trips.

WAN Optimization

WAN optimization and acceleration technologies solve traffic delays and inefficiencies in a number of ways.

Bandwidth Optimization – Satellite WAN links can be costly, especially in remote locations and foreign countries where options are limited. Bandwidth optimization squeezes more bandwidth into network links. Optimizing bandwidth doesn’t necessarily help with throughput, particularly on high-latency links and chatty applications.

TCP Acceleration – To address the inefficiencies of TCP, WAN optimization manages network connections in several ways to reduce the impact on the network, application servers, and user devices. WAN optimization solutions maintain a consistent pool of connections (multiplexing) between themselves and the Web servers. Web servers are offloaded from managing connections, and isolated from session disconnects. Using client optimization technology, a persistent connection between the client and the optimization appliance is maintained, even when browsers close and reopen sessions. These sessions are multiplexed across multiple connections, improving throughput and response time.

HTTP(S) Acceleration – HTTP(S) acceleration enables browser traffic to be intermixed across multiple “pipelines”. A key advantage of using client-side optimization is that communication resources can be shared across multiple applications, and HTTP requests and responses from applications are intermixed simultaneously across multiple concurrent sessions. HTTP acceleration serves as a platform for the consolidation and aggregation of all Web traffic. Individual objects or pieces of objects can be split into any size and multiplexed with other object data and then reconstructed.

Caching - Caching positions frequently requested content closer to users requesting the data. Caching maintains copies of routinely accessed data to eliminate unnecessary requests to Web servers.

Cache differencing maintains identical copies of the browser’s cache on the local WAN optimization device. Cache differencing understands what data has changed, and transfers only the changed data.

Pre-Caching helps eliminate network bottlenecks, and improves end-user response times. Administrators can define content that is automatically distributed (Pre-Cached) to specific users at off-peak hours. During a predefined time, the end-user devices will pre-cache the content, enabling instant access.

Compression – Compression eliminates non-essential information. Compressing data reduces network traffic and accelerates the delivery of time-sensitive information. GZIP Compression is a technique used to compress data sent to browsers; this reduces the text portions of pages. However, GZIP is not used for attachment compression, or inbound compression from the browser. GZIP cannot be used to compress HTTP headers, cookies or image data. To accomplish this, bi-directional compression is used to reduce the data size through intelligent compression techniques. When a WAN optimization solution is deployed in a two-sided environment (at the head-end and remote sites), bi-directional compression provides compression for HTTP headers, cookies, text and data objects, JPEG files with image reduction, file attachments and file uploads and downloads.

Quality of Service (QoS) – QoS uses queuing to provide preferential treatment for classes of traffic. Traffic Shaping ensures on-time delivery of time-critical information, allowing different TCP ports to be assigned to individual applications. Specific port assignments, priorities and policies can be assigned at the database-level, guaranteeing QoS for mission-critical applications.

Summary

Military satellite communications are vital not only for mission-critical operations, but also important for deployed military personnel to communicate with family and colleagues back home. Today’s satellites use Internet technology that is inherently hampered by TCP and application protocol inefficiencies, latency and adverse environmental conditions that can impair network performance, reliability, and bandwidth utilization. Additionally, open-source standards are critical for ensuring complete transport protocol interoperability among disparate military networks.

WAN optimization and acceleration solutions that integrate SCPS can substantially reduce the amount of nonessential traffic over a satellite WAN, while increasing throughput. These solutions are able to provide military personnel with fast, reliable and secure access to mission-critical information.

This article was written by Gordon Dorworth, President and CEO, Stampede Technologies (Dayton, OH). For more information, contact Mr. Dorworth at This email address is being protected from spambots. You need JavaScript enabled to view it., or visit http://info.hotims.com/28055-403.


Embedded Technology Magazine

This article first appeared in the July, 2010 issue of Embedded Technology Magazine.

Read more articles from this issue here.

Read more articles from the archives here.