The ns Manual (formerly ns Notes and Documentation)1 - NM Lab at ...
The ns Manual (formerly ns Notes and Documentation)1 - NM Lab at ... The ns Manual (formerly ns Notes and Documentation)1 - NM Lab at ...
Chapter 41PackMime-HTTP: Web Traffic GenerationThe PackMime Internet traffic model was developed by researchers in the Internet Traffic Research group at Bell Labs, basedon recent Internet traffic traces. PackMime includes a model of HTTP traffic, called PackMime-HTTP. The traffic intensitygenerated by PackMime-HTTP is controlled by the rate parameter, which is the average number of new HTTP connectionsstarted each second. The PackMime-HTTP implementation in ns-2, developed at UNC-Chapel Hill, is capable of generatingHTTP/1.0 and HTTP/1.1 (persistent, non-pipelined) connections.The goal of PackMime-HTTP is not to simulate the interaction between a single web client and web server, but to simulatethe TCP-level traffic generated on a link shared by many web clients and servers.A typical PackMime-HTTP instance consists of two ns nodes: a server node and a client node. It is important to note thatthese nodes do not correspond to a single web server or web client. A single PackMime-HTTP client node generates HTTPconnections coming from a “cloud” of web clients. Likewise, a single PackMime-HTTP server node accepts and serves HTTPconnections destined for a “cloud” of web servers. A single web client is represented by a single PackMime-HTTP clientapplication, and a single web server is represented by a single PackMime-HTTP server application. There are many clientapplications assigned to a single client ns node, and many server applications assigned to a single server ns node.In order to simulate different RTTs, bottleneck links, and/or loss rates for each connection, PackMime-HTTP is often usedin conjunction with DelayBox (see Chapter 22). DelayBox is a module developed at UNC-Chapel Hill for delaying and/ordropping packets in a flow according to a given distribution. See Section 41.3 for more information on using PackMime-HTTPand DelayBox together.The PackMime HTTP traffic model is described in detail in the following paper: J. Cao, W.S. Cleveland, Y. Gao, K. Jeffay,F.D. Smith, and M.C. Weigle , “Stochastic Models for Generating Synthetic HTTP Source Traffic”, Proceedings of IEEEINFOCOM, Hong Kong, March 2004.41.1 Implementation DetailsPackMimeHTTP is an ns object that drives the generation of HTTP traffic. Each PackMimeHTTP object controls the operationof two types of Applications, a PackMimeHTTP server Application and a PackMimeHTTP client Application. Each ofthese Applications is connected to a TCP Agent (Full-TCP). Note: PackMime-HTTP only supports Full-TCP agents.Each web server or web client cloud is represented by a single ns node that can produce and consume multiple HTTPconnections at a time (Figure 41.1). For each HTTP connection, PackMimeHTTP creates (or allocates from the inactivepool, as described below) server and client Applications and their associated TCP Agents. After setting up and starting each363
(nsnode) clientcloudPackM ime(nsnode) servercloudandAgentsFigure 41.1: PackMimeHTTP Architecture. Each PackMimeHTTP object controls a server and a client cloud. Each cloudcan represent multiple client or server Applications. Each Application represents either a single web server or a single webclient.serverApplicationsandAgents clientApplicationsconnection, PackMimeHTTP sets a timer to expire when the next new connection should begin. The time between newconnections is governed by the connection rate parameter supplied by the user. New connections are started according to theconnection arrival times without regard to the completion of previous requests, but a new request between the same client andserver pair (as with HTTP 1.1) begins only after the previous request-response pair has been completed.PackMimeHTTP handles the re-use of Applications and Agents that have completed their data transfer. There are 5 pools usedto maintain Applications and Agents – one pool for inactive TCP Agents and one pool each for active and inactive client andserver Applications. The pools for active Applications ensure that all active Applications are destroyed when the simulationis finished. Active TCP Agents do not need to be placed in a pool because each active Application contains a pointer to itsassociated TCP Agent. New objects are only created when there are no Agents or Applications available in the inactive pools.41.1.1 PackMimeHTTP Client ApplicationEach PackMimeHTTP client controls the HTTP request sizes that are transferred. Each PackMimeHTTP client takes thefollowing steps:• if the connection is persistent and consists of more than one request, then the client samples all request sizes, responsesizes, and inter-request times for the connection• if the connection only consists of one request, then the client samples the request size and the response size• send the first HTTP request to the server• listen for the HTTP response• when the entire HTTP response has been received, the client sets a timer to expire when the next request should bemade, if applicable• when the timer expires, the next HTTP request is sent, and the above process is repeated until all requests have beencompleted364
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Chapter 41PackMime-HTTP: Web Traffic Gener<strong>at</strong>ion<strong>The</strong> PackMime Internet traffic model was developed by researchers in the Internet Traffic Research group <strong>at</strong> Bell <strong>Lab</strong>s, basedon recent Internet traffic traces. PackMime includes a model of HTTP traffic, called PackMime-HTTP. <strong>The</strong> traffic inte<strong>ns</strong>itygener<strong>at</strong>ed by PackMime-HTTP is controlled by the r<strong>at</strong>e parameter, which is the average number of new HTTP connectio<strong>ns</strong>started each second. <strong>The</strong> PackMime-HTTP implement<strong>at</strong>ion in <strong>ns</strong>-2, developed <strong>at</strong> UNC-Chapel Hill, is capable of gener<strong>at</strong>ingHTTP/1.0 <strong>and</strong> HTTP/1.1 (persistent, non-pipelined) connectio<strong>ns</strong>.<strong>The</strong> goal of PackMime-HTTP is not to simul<strong>at</strong>e the interaction between a single web client <strong>and</strong> web server, but to simul<strong>at</strong>ethe TCP-level traffic gener<strong>at</strong>ed on a link shared by many web clients <strong>and</strong> servers.A typical PackMime-HTTP i<strong>ns</strong>tance co<strong>ns</strong>ists of two <strong>ns</strong> nodes: a server node <strong>and</strong> a client node. It is important to note th<strong>at</strong>these nodes do not correspond to a single web server or web client. A single PackMime-HTTP client node gener<strong>at</strong>es HTTPconnectio<strong>ns</strong> coming from a “cloud” of web clients. Likewise, a single PackMime-HTTP server node accepts <strong>and</strong> serves HTTPconnectio<strong>ns</strong> destined for a “cloud” of web servers. A single web client is represented by a single PackMime-HTTP clientapplic<strong>at</strong>ion, <strong>and</strong> a single web server is represented by a single PackMime-HTTP server applic<strong>at</strong>ion. <strong>The</strong>re are many clientapplic<strong>at</strong>io<strong>ns</strong> assigned to a single client <strong>ns</strong> node, <strong>and</strong> many server applic<strong>at</strong>io<strong>ns</strong> assigned to a single server <strong>ns</strong> node.In order to simul<strong>at</strong>e different RTTs, bottleneck links, <strong>and</strong>/or loss r<strong>at</strong>es for each connection, PackMime-HTTP is often usedin conjunction with DelayBox (see Chapter 22). DelayBox is a module developed <strong>at</strong> UNC-Chapel Hill for delaying <strong>and</strong>/ordropping packets in a flow according to a given distribution. See Section 41.3 for more inform<strong>at</strong>ion on using PackMime-HTTP<strong>and</strong> DelayBox together.<strong>The</strong> PackMime HTTP traffic model is described in detail in the following paper: J. Cao, W.S. Clevel<strong>and</strong>, Y. Gao, K. Jeffay,F.D. Smith, <strong>and</strong> M.C. Weigle , “Stochastic Models for Gener<strong>at</strong>ing Synthetic HTTP Source Traffic”, Proceedings of IEEEINFOCOM, Hong Kong, March 2004.41.1 Implement<strong>at</strong>ion DetailsPackMimeHTTP is an <strong>ns</strong> object th<strong>at</strong> drives the gener<strong>at</strong>ion of HTTP traffic. Each PackMimeHTTP object controls the oper<strong>at</strong>ionof two types of Applic<strong>at</strong>io<strong>ns</strong>, a PackMimeHTTP server Applic<strong>at</strong>ion <strong>and</strong> a PackMimeHTTP client Applic<strong>at</strong>ion. Each ofthese Applic<strong>at</strong>io<strong>ns</strong> is connected to a TCP Agent (Full-TCP). Note: PackMime-HTTP only supports Full-TCP agents.Each web server or web client cloud is represented by a single <strong>ns</strong> node th<strong>at</strong> can produce <strong>and</strong> co<strong>ns</strong>ume multiple HTTPconnectio<strong>ns</strong> <strong>at</strong> a time (Figure 41.1). For each HTTP connection, PackMimeHTTP cre<strong>at</strong>es (or alloc<strong>at</strong>es from the inactivepool, as described below) server <strong>and</strong> client Applic<strong>at</strong>io<strong>ns</strong> <strong>and</strong> their associ<strong>at</strong>ed TCP Agents. After setting up <strong>and</strong> starting each363
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