1. Support

1. Programs

1. Register

1. Tech Info Library

1. Software

1. Documentation

1. Policies & Procedures

1. Best Practices

1. Product Lifecycle
2. Evaluate
3. Procure
4. Deploy
5. Operate
6. Extend
7. ITIL
8. Service Support
9. Service Delivery

1. Contact Support

ITIL: Service Delivery

Availability Management

Maintaining availability and reliability of IT services is the goal of the Availability Management discipline. To meet ITIL objectives for this discipline, IT must take actions to ensure availability levels meet established service level targets and proactively seek availability improvements where needed.

Monitoring Link Availability

Packeteer’s access-link monitoring feature, also known as high availability, allows PacketShaper to respond to the occurrence of WAN link failures. When the basic mode of high availability is enabled, the PacketShaper polls the configured router(s) every 30 seconds to assess the WAN interface status (link up or link down) of the WAN link interfaces. If a link goes down, PacketWise automatically adjusts the total available capacity by subtracting out the capacity of the down link. As part of this process, it will adjust the access link size and resize Inbound and/or Outbound partitions to reflect the available bandwidth.

When advanced mode is enabled, PacketWise can help prevent the overloading of an interface. The PacketShaper will use SNMP polling to assess the actual throughput of each configured WAN link interface; the configured routers are polled every 30 seconds. When an interface approaches its configured capacity, PacketWise will begin pacing the traffic sent to the router to prevent overloading any interface. This pacing will also greatly reduce the number of retransmissions. PacketWise begins adjusting the partition sizes early in order to ensure gradual, smooth adjustments, as well as to give you time to modify policies if desired. PacketWise will poll the router frequently, and once there is evidence that the links are out of danger of being overloaded, it will gradually increase the size of the partition(s).

Monitoring Application Availability

PacketShaper's and ReportCenter's historical reporting can provide highly granular availability reports for each individual application running over the network. A good place to start is with the TCP Network Health report. This report includes the following graphs for a particular traffic class:

• TCP Health (Connections, Aborts, Server Ignores, Server Refuses)
• Class Utilization with Peaks
• Transaction Delay
• Packet Round-Trip Time

By analyzing and comparing the graphs in this report, you can deduce the application's availability for a particular time period.

In addition, you can view statistics for the app-availability% measurement variable. This variable calculates the percentage of time a service is available.

Monitoring Network Brownouts

PacketShaper's monitoring tools can measure not only up/down availability of WAN links and application services running over them, but also application response times and network congestion, which can indicate decaying conditions or brownouts. The network is still technically "up" but performance is so slow that the applications can't actually be used. By viewing graphs of your link and key applications, you can see when performance starts to degrade — a sign of an impending failure or brownout. Or you can configure adaptive response agents to monitor your link and applications and automatically notify you when performance is unacceptable.

In addition, Packeteer's TCP Rate Control proactively eliminates the build-up of congestion in router queues at the edge of the network. TCP Rate Control is an advanced congestion-avoidance mechanism whose goal is to prevent traffic from being sent at rates higher than the WAN connection, thereby greatly reducing queuing in router buffers and improving overall efficiency. Because congestion is one of the major sources of network brownouts, TCP Rate Control can help improve the availability of applications and the network.

Loss and Latency Mitigation

One way to increase application availability is to eliminate factors that cause sessions to drop: substantial packet loss, latency, and jitter. Determining why packets are being dropped and taking steps to reduce the number of packet drops, will likely improve the availability of an application, with the added benefit of increasing user satisfaction. The Shaping Module's control features, including TCP Rate Control, help avoid dropped packets, but if you suspect retransmissions are a problem on your network, PacketShaper provides you with the tools to investigate. See Assess Wasted Network Capacity for details.

In high-latency environments such as satellite links, high bit error rates (BER) and packet loss are inevitable, although there is a solution: Packeteer’s Acceleration Module. Acceleration technology minimizes the effects of high latency due to distance delay and can alleviate the effects of packet loss and retransmissions. TCP sessions are wrapped in a protective tunnel that shields them from packet loss. Refer to the discussion on acceleration in the Xpress Overview or you can read the Acceleration white paper. Note that the Acceleration Module requires PacketWise v8.0 or higher.

Synthetic Transactions

The PacketShaper not only measures the response time of every real transaction that occurs on the network, it also has the ability to generate synthetic transactions for checking performance and availability at times when there isn't any real user traffic. When this feature is configured, the PacketShaper will initiate synthetic pings, web, or other TCP transactions at periodic intervals to verify the availability of critical servers, as well as collect performance data. See Use Standardized, Artificial Traffic for Analysis.

View the other disciplines in the ITIL Service Delivery area:

Service Level Management  

Capacity Management

Continuity Management

Cost Management

Security Management