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ITIL: Service Delivery

Continuity Management

Continuity Management ensures the availability and rapid restoration of IT services in the event of a serious incident or disaster. In includes both reactive and proactive measures. Examples of incidents that could disrupt business continuity include natural disasters (such as earthquakes and hurricanes), acts of terror (nuclear strikes), and a building fire or flood. Or perhaps it could be something more mundane, such as an extended power outage.

Many tools are available for managing the continuity of lower-level network services such as links and routers, but one element of business continuity that is often overlooked is managing the traffic that runs over the redundant infrastructure.

Controlling Congestion Surges on Recovery

When network service is restored after even a brief outage, there are huge traffic surges as servers and sessions try to reconnect. Mail that had built up in send queues gets sent, file transfers that were in process get restarted, and database or file synchronizations may be triggered. The result of all this bulk traffic is continued brownouts, even though connectivity has been restored. PacketShaper's congestion management policies provide the tools to prevent this problem.

PacketShaper's Shaping Module employs several technologies to control the rate at which traffic flows to and from a WAN or Internet link. Packeteer’s rate control technologies — TCP Rate Control and UDP Rate Control — collaborate to force a smooth, even flow rate that maximizes throughput and prevents congestion.

TCP Rate Control     Packeteer’s TCP Rate Control operates behind the scenes for all traffic with rate policies, optimizing limited-capacity links. TCP Rate Control overcomes TCP’s shortcomings, preventing congestion on both inbound and outbound traffic. TCP Rate Control paces traffic, telling the end stations to slow down or speed up. It’s no use sending packets any faster if they will be accepted only at a particular rate once they arrive. Rather than discarding packets from a congested queue, TCP Rate Control paces packets to prevent congestion.

UDP Rate Control     The PacketShaper can pace the flow of UDP data, regulating the flow of UDP packets before they traverse a congested access link. A variety of the Shaping Module’s control mechanisms assist in managing UDP traffic. A priority policy is best for UDP traffic that is transaction-oriented. A rate policy is best for persistent UDP traffic because its guaranteed bits-per-second option can ensure a minimum rate for each UDP flow. For example, you could give 24 Kbps to each VoIP stream.

Swamped Failover Links

One challenge often associated with failover/emergency backup WAN links is that they may not have the same amount of bandwidth as the circuit they are replacing. Whether cost prohibitive or simply physically impossible due to lack of service in the location, replacing a large circuit with a smaller one can cause tremendous congestion problems even if the physical failover went smoothly and access wasn't technically lost. This congestion may cause sessions to slow or even drop, causing the same net effect as if the link had gone down. To avoid this, PacketShaper can detect a link-size change and automatically adjust the access link size to reflect the available bandwidth.

Packeteer’s access-link monitoring feature, also known as high availability, allows PacketShaper to respond to the occurrence of WAN link failures. When access-link monitoring is enabled, PacketWise can adjust partitions appropriately to prevent overloading any given WAN link and to account for lost available capacity due to router or link failure.

Redundant Topologies

To avoid network disruption due to equipment failure, most enterprises configure redundant topologies with duplicate routers, switches, and so forth. PacketShaper units integrate in high availability and redundant environments including HSRP (Hot Standby Routing Protocol) and VRRP (Virtual Router Redundancy Protocol). For the PacketShapers to function in redundant topologies, you connect each unit into each redundant network path and directly connect the two units. This configuration provides PacketShaper redundancy in case one of the units fails. In addition, if equipment on one of the redundant paths fails, a PacketShaper will be in place to perform its bandwidth management responsibilities. This capability is called direct standby.

The direct standby feature can operate in a redundant topology that is set up to do load balancing (in other words, traffic flows through both paths) or one that is set up as a backup in case of component failure (traffic flows through one path).

View the other disciplines in the ITIL Service Delivery area:

Service Level Management  

Capacity Management

Availability Management

Cost Management

Security Management