Network Simulations in Omnet++ - repost
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The Job is to be done using OMNET++
A small start-up company plans to set up a wireless network for the employees to easily give them access to the internet and Voice over IP(VoIP) service without having to make an expensive Ethernet wiring to every desk. Your task as a consultant is to simulate the proposed network and identify potential weakness.
Figure to be provided:
The figure shows a draft of the network. All employee computers are roughly uniformly distributed in a 400m square quadratic area around the WLAN access point. The stations usually do not move and can be considered stationary. The WLAN is based on IEEE [url removed, login to view] with 11 Mbits/s and the access point is connected via Fast Ethernet (IEEE 802.3, 100 Mbits/s) to a router with an integrated DSL modem.
The company has three different options for internet access, a Symmetric DSL (SDSL) connection with either 2, 4 or 6 Mbits/s with a delay of 15ms.
Three kinds of applications have to be considered: Users browsing the Web, users using VoIP and long lasting data transmissions like FTP.
The VoIP codec uses a constant data rate of 50 packets per second. A voice packet consists of 32 bytes of payload plus protocol headers. The VoIP application uses the Real-time Transport Protocol(RTP) over User Datagram Protocol (UDP) over Internet Protocol version (IOv4).
For a good quality of service (Qos) of a VoIP connection, the maximum acceptable end-to-end delay is 120ms, i.e the time when the voice data is required in the application of the receiver is at maximum 120ms after the packet is generated at the sender. If a packet arrives too late it will be dropped and considered as lost. The maximum acceptable packet loss rate for VoIP is 5%.
Web traffic is expected to be one HTTP request/response followed by some exponetially distributed reading tice time before the next request/response is issued. The size of the HTTP responses is also expected to be exponentially distributed. The mean values for the distributions are indicated in the parameter sheet.
It is expected that on the average there are four FTP file transfers, either all four incoming(wireless stations downloading data) or two incoming and two outgoing transfers.
Besides the FTP transfers, on average two users browse the Web and one user is using a VoIP connection. Each user uses only one application at a time. The TCP/IP implementation of the operating systems is based on TCP New Reno and the receiver side advertises a receive window of 100 times the Maximum Segment Size(MSS).
Your customer has several questions about the proposed network which he/she would like you to answer:
- What are the average delays and loss rates for the VoIP connection ?
- Is a 2, 4 or Mbits/s Internet connection the best choice ?
- Where are the main bottlenecks of each variant ? Where does packet loss occur and why ?
- What happens if you increase the number of VoIP connections?
- Which changes would you suggst to improve the performance?
The examination and discussion should be on four incoming FTP data transmissions.
--For Ethernet, the Maximum Transmission Unit (MTU) is 1500 bytes and this limits the size for the Protocol Data Units (PDU) of the upper layers. However, the PDUs should be as large as possible to reduce protocol overhead.
--VoIP traffic is bidirectional.
--Give indications for the confidence of your simulation results.
Report will be written at the end
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