求Opnet中前景流量和背景流量概念解释

[csc_csc_csc]

如题

[yynetsdk]

没用过。

[地瓜1996]

Explicit Traffic

“Explicit traffic” is packet-by-packet traffic, in which the simulation models each packet-related event (packet created, packet queued, packet transmitted, etc.) that occurs during the simulation. Explicit traffic modeling provides the most accurate results because it models all protocol effects. However, this also results in longer simulations and higher memory usage (because the simulation allocates memory for each individual packet).

There are three general methods for explicitly modeling traffic:

 Packet generation – You can configure certain node objects to generate streams of generic packets. This is a basic method of adding traffic to a network topology.

 application demands – You can create application demands to represent the traffic flowing between two nodes. The traffic generated by application demands can be purely discrete (explicit), purely analytic (background), or a combination of these two (hybrid).

 Application traffic models – You can include a set of models for generating traffic based on standard applications such as FTP, HTTP, voice, and e-mail. You can also use the generic “custom application” model to represent a broad range of applications (such as multi-tier ERP transactions) that do not correspond to the traffic patterns of standard network applications.

Background Traffic

“Background traffic” is analytically modeled traffic that affects the performance of explicit traffic by introducing additional delays. Unlike explicit traffic, background traffic can affect not only discrete event simulations, but also flow analyses. Discrete event simulations that include background traffic use the hybrid simulation model. This model includes the effects of background traffic to calculate queue build-ups on intermediate devices and delays based on the queue length, at any time during in the simulation. Because each packet that produces traffic on the network is not explicitly modeled, using background traffic can speed up simulations considerably.

Background traffic takes three forms:

 Traffic Flows – A traffic flow describes an end-to-end flow of traffic from a source to one or more destination nodes. You can create traffic flows manually, using traffic flow objects (covered later in this chapter). You can also import traffic flows from text files and spreadsheets. If you have a license for the XDI (eXpress Data Import) module, you can also import traffic from programs like Netflow Collector and NetScout nGenius.

 Baseline Loads – This type of traffic (also called “static background utilization”) represents traffic as a background load on a link, node, connection, or LSP. Unlike a traffic flow, which can span multiple links and nodes, a traffic load is “static” and applies to one object. You can convert existing link loads to traffic flows, which allows flow analyses to account for these loads. You can import baselines from external ASCII files; if you have a license for the XDI (eXpress Data Vendor Import) module, you can also import data from programs like CA eHealth–Network, MRTG and InfoVista.

 Application demands – You can use application demands to represent background traffic flowing between two nodes. Besides background traffic, you can also configure application demands to be purely discrete (explicit) traffic, or a combination of these two (hybrid).