Dec 12, 2009

Markov Model

What is a Markov Model?
Markov models are some of the most powerful tools available to engineers and scientists for analyzing complex systems. This analysis yields results for both the time dependent evolution of the system and the steady state of the system.

For example, in Reliability Engineering, the operation of the system may be represented by a state diagram, which represents the states and rates of a dynamic system. This diagram consists of nodes (representing a possible state of the system, which is determined by the states of the individual components & sub-components) connected by arrows (representing the rate at which the system operation transitions from one state to the other state). Transitions may be determined by a variety of possible events, for example the failure or repair of an individual component. A state-to-state transition is characterized by a probability distribution. Under reasonable assumptions, the system operation may be analyzed using a Markov model.
A Markov model analysis can yield a variety of useful performance measures describing the operation of the system. These performance measures include the following:

  • system reliability
  • availability
  • mean time to failure (MTTF)
  • mean time between failures (MTBF)
  • the probability of being in a given state at a given time
  • the probability of repairing the system within a given time period (maintainability)
  • the average number of visits to a given state within a given time period
and many other measures.

The name Markov model is derived from one of the assumptions which allows this system to be analyzed; namely the Markov property. The Markov property states: given the current state of the system, the future evolution of the system is independent of its history. The Markov property is assured if the transition probabilities are given by exponential distributions with constant failure or repair rates. In this case, we have a stationary, or time homogeneous, Markov process. This model is useful for describing electronic systems with repairable components, which either function or fail. As an example, this Markov model could describe a computer system with components consisting of CPUs, RAM, network card and hard disk controllers and hard disks.
The assumptions on the Markov model may be relaxed, and the model may be adapted, in order to analyze more complicated systems. Markov models are applicable to systems with common cause failures, such as an electrical lightning storm shock to a computer system. Markov models can handle degradation, as may be the case with a mechanical system. For example, the mechanical wear of an aging automobile leads to a non-stationary, or non-homogeneous, Markov process, with the transition rates being time dependent. Markov models can also address imperfect fault coverage, complex repair policies, multi-operational-state components, induced failures, dependent failures, and other sequence dependent events.

Dec 8, 2009

Out-of-Band (OOB) Splice

What is the OOB Splice?

An OOB splice is an independent, separate TCP connection made on the first connection between two peer Steelhead appliances used to transfer version, licensing and other OOB data between peer Steelhead appliances. An OOB connection must exist between two peers for connections between these peers to be optimized. If the OOB splice dies all optimized connections on the peer Steelhead appliances will be terminated.

The OOB connection is a single connection existing between two Steelhead appliances regardless of the direction of flow. So if you open one or more connections in one direction, then initiate a connection from the other direction, there will still be only one connection for the OOB splice. This connection is made on the first connection between two peer Steelhead appliances using their in-path IP addresses and port 7800 by default. The OOB splice is rarely of any concern except in full transparency deployments.

Case Study
In the example below, the Client is trying to establish connection to Server-1:

Issue 1: After establishing inner connection, the Client will try to establish an OOB connection to the Server-1. It will address it by the IP address reported by Steelhead (SFE-1) which is in probe response ( Clearly, the connection to this address will fail since 10.2.x.x addresses are invalid outside of the firewall (FW-2).

Resolution 1: In the above example, there is one combination of address and port (IP:port) we know about, the connection the client is destined for which is Server-1. The client should be able to connect to Server-1. Therefore, the OOB splice creation code in sport can be changed to create a transparent OOB connection from the Client to Server-1 if the corresponding inner connection is transparent.

How to Configure
There are three options to address the problem of the OOB splice connection established mentioned in Issue 1 above. In a default configuration the out-of-band connectio uses the IP addresses of the client-side Steelhead and server-side Steelhead. This is known as correct addressing and is our default behavior. However, this configuration will fail in the network topology described above but works for the majority of networks. The command below is the default setting in a Steelhead appliance’s configuration.

in-path peering oobtransparency mode none

In the network topology discussed in Issue 1, the default configuration does not work. There are
two oobtransparency modes that may work in establishing the peer connections; destination and
full. When destination mode is used, the client uses the first server IP and port pair to go through the Steelhead appliance with which to connect to the server-side Steelhead appliance and the client-side Steelhead IP and port number chosen by the client-side Steelhead appliance. To change to this configuration use the following CLI command:

in-path peering oobtransparency mode destination

In oobtransparency full mode, the IP of the first client is used and a pre-configured on the clientside Steelhead appliance to use port 708. The destination IP and port are the same as in destination mode, i.e., that of the server. This is the recommended configuration when VLAN transparency is required. To change to this configuration use the following CLI command:

in-path peering oobtransparency mode full

To change the default port used the by the client-side Steelhead appliance when oobtransparency mode full is configured, use the following CLI command:

in-path peering oobtransparency port

It is important to note that these oobtransparency options are only used with full transparency. If the first inner-connection to a Steelhead was not transparent, the OOB will always use correct



Mobile Solution Complements Broader Steelhead Appliance Deployment and Speeds Enterprise IT Infrastructure Performance; Provides Acceleration for Windows 7 and 64-bit Systems

SAN FRANCISCO – November 02, 2009 – Riverbed Technology (NASDAQ: RVBD), the IT infrastructure performance company for networks, applications and storage, today announced upcoming enhancements to its Mobile WAN optimization solution to address the productivity challenges global organizations face when managing remote and mobile workforces. Riverbed® Steelhead® Mobile increases employee productivity while on the road, working from home or connected wirelessly in the office by providing application performance improvements. With this release, Riverbed will provide acceleration for Windows 7 and 64-bit systems for mobile end users. In addition, organizations will be able to take advantage of improved flexibility and simplified manage ment functionality to provide mobile workers with accelerated performance no matter where they are working throughout the world.

"As companies focus on consolidating their data through private cloud initiatives, the distance between their employees and critical data is growing--employees are becoming more mobile, working from a variety of locations outside of the office. This means that as centralization of data and IT infrastructure continues, remote access is becoming more of a challenge," said Eric Wolford, senior vice president of marketing and business development at Riverbed. "With Steelhead Mobile 3.0, we are able to deliver to customers a solution that not only accelerates important Windows 7 and 64-bit applications while on the road, but also complements their broader Steelhead appliance deployment."

"Riverbed's leadership in the WAN optimization market can be attributed to product innovation and focus on creating a comprehensive WAN optimization solution. The company has maintained a focus on customer priorities and ever-changing IT requirements," said Cindy Borovick, research vice president at IDC. "Enterprise IT departments are being pressed to improve IT efficiency and employee productivity with a reduced IT budget. As more companies move forward with IT consolidation projects to cut costs, performance for end users is a concern. Mobile WAN optimization can help overcome this challenge by improving the performance of critical enterprise applications for remote and mobile workers."

Steelhead Mobile 3.0 introduces enhancements that allow organizations to provide their mobile workers with better access and performance, eliminating slow performance as a barrier to mobility.

Accelerate Windows 7 and 64-bit Systems for Mobile Users
Riverbed continues to deepen its optimization of Windows and other Microsoft applications, such as SharePoint, Office, Server and CRM, so that enterprises can provide accelerated access to and improved performance of Microsoft applications to remote and mobile workers. With Steelhead Mobile 3.0, Riverbed provides acceleration benefits to Windows 7 and 64-bit systems.

Organizations will have the ability to support Microsoft's catalog of modern operating systems and advanced platforms. Through Riverbed's comprehensive solution, companies will have the flexibility to upgrade operating systems or migrate to platforms while obtaining consistent application performance.

Web Applications – Up to 60X Faster
Enterprises are utilizing HTTP and HTTPS for everything from e-commerce to mission-critical applications. They are the underlying protocols for all Web-based applications used to communicate internally with employees and externally with partners and customers. By optimizing these protocols, users can dramatically reduce the amount of data that they need to send over the WAN, while at the same time streamlining the chatty behavior of transport and application protocols. With Mobile 3.0, as with the Steelhead appliances, these benefits are extended further to the application layer for HTTP and HTTPS users to make Web applications even faster while maintaining the preferred enterprise trust model. The common architecture of the Steelhead appliance and Steelhead Mobile gives organizations a single comprehensive solution to increase the performance of key Web-based applications.

By employing URL learning, page parsing, embedded object pre-fetching and metadata acceleration modes, Steelhead Mobile further reduces the chattiness and delays that plague enterprise Web-based applications. With these additional tools, business-critical applications used today such as SharePoint, intranet portals and Web-based document management systems, as well as Web-enabled ERP and CRM applications like SAP NetWeaver, JD Edwards and Siebel, all receive application acceleration of up to 60x.

Branch Warming – Immediate Acceleration Regardless of Location
Riverbed has extended its technological leadership by improving integration with the Steelhead appliance, allowing workers to take advantage of even more of the benefits of the Riverbed Optimization System (RiOS®) while working remotely.

With Steelhead Mobile 3.0, Riverbed introduces Branch Warming, which allows mobile and branch office users to share optimized data and experience even greater overall acceleration. By sharing the data references between the data stores of the Steelhead Mobile client and the branch office Steelhead appliance, mobile workers not only take advantage of all of the optimization benefits of the Steelhead appliance but are also able to contribute data references from their data store to help improve performance for the entire branch office, enabling "warm" performance regardless of location.

Dancker, Sellew & Douglas has approximately 40 users that have benefited from the acceleration capabilities of Steelhead Mobile for the past two years. "With Mobile 3.0 we are experiencing the same stellar acceleration that our team has grown accustomed to – for example, I have a user working in a remote office in East Syracuse that is experiencing 67% data reduction and 3X performance gains," said Michael Vassallo, Senior Network Administrator. "We've found that the new Branch Warming feature helps our users switch seamlessly from working wirelessly to connecting back to a branch office with a Steelhead appliance. It greatly improves efficiency."

Steelhead Mobile 3.0 is expected to be generally available on December 2, 2009.

Forward Looking Statements
This press release contains forward-looking statements, including statements relating to the expected demand for Riverbed's products and services, statements regarding performance results of Riverbed solutions, including Steelhead Mobile 3.0, and statements relating to Riverbed’s ability to meet the needs of distributed organizations. These forward-looking statements involve risks and uncertainties, as well as assumptions that, if they do not fully materialize or prove incorrect, could cause our results to differ materially from those expressed or implied by such forward-looking statements. The risks and uncertainties that could cause our results to differ materially from those expressed or implied by such forward-looking statements include our ability to react to trends and challenges in our business and the markets in which we operate; our ability to anticipate market needs or develop new or enhanced products to meet those needs; the adoption rate of our products; our ability to establish and maintain successful relationships with our distribution partners; our ability to compete in our industry; fluctuations in demand, sales cycles and prices for our products and services; shortages or price fluctuations in our supply chain; our ability to protect our intellectual property rights; general political, economic and market conditions and events; and other risks and uncertainties described more fully in our documents filed with or furnished to the Securities and Exchange Commission. More information about these and other risks that may impact Riverbed’s business are set forth in our Form 10-Q filed with the SEC on October 30, 2009. All forward-looking statements in this press release are based on information available to us as of the date hereof, and we assume no obligation to update these forward-looking statements. Any future product, feature or related specification that may be referenced in this release are for information purposes only and are not commitments to deliver any technology or enhancement. Riverbed reserves the right to modify future product plans at any time.

About Riverbed
Riverbed Technology is the IT infrastructure performance company. The Riverbed family of wide area network (WAN) optimization solutions liberates businesses from common IT constraints by increasing application performance, enabling consolidation, and providing enterprise-wide network and application visibility – all while eliminating the need to increase bandwidth, storage or servers. Thousands of companies with distributed operations use Riverbed to make their IT infrastructure faster, less expensive and more responsive. Additional information about Riverbed (NASDAQ: RVBD) is available

Riverbed Technology, Riverbed, Steelhead, RiOS, Interceptor, Think Fast, the Riverbed logo, Mazu, Profiler and Cascade are trademarks or registered trademarks of Riverbed Technology All other trademarks used or mentioned herein belong to their respective owners.

Kristalle Ward
Riverbed Technology

Renee Lyall
Riverbed Technology

Dec 7, 2009

Riverbed Cascade Gateways vs Cascade Profiler vs Cascade Sensor

Cascade Gateways collects network flow data already existing in an organization’s network provides intelligent de-duplication retaining information on where each flow was recorded, and sends this condensed data to the Cascade Profiler.

Cascade Profiler complements this information with layer 7 application and response time data retrieved from a Cascade Sensor deployed in the datacenter. These records are then further enhanced with user identification information provided by active directories, switch port information, QoS, and SNMP data. The result is a complete view of a business application flow from the back end server to the users desktop.

Cascade also provides an extensive set of integrations, with management systems typically deployed in an IT environment to further streamline workflows and provide value across multiple operations teams.