The document provides an overview of implementing 802.11 wireless networks in the ns-2 network simulator. It discusses:
1) Key components of ns-2 including the event scheduler, network components, and support for wireless extensions.
2) Implementation of the 802.11 physical layer including propagation models and sending/receiving packets.
3) Implementation of the 802.11 MAC layer including states, timers, CSMA/CA, and a capture model.
4) An example of adding Rayleigh fading to analyze its impact on TCP and UDP performance over distance.
The document discusses the implementation of various networking protocols and VLAN using the Network Simulator 2 (NS2). It summarizes TCP, UDP, ad-hoc routing protocols like AODV, DSR, DSDV and how they are simulated in NS2. It also discusses how to configure VLANs in NS2 by creating network bridges and attaching Ethernet interfaces to VLAN IDs. The document provides examples of simulating protocols and configuring VLANs to segment traffic between virtual LANs in NS2.
This document discusses functions and techniques of the data link layer, including line discipline, flow control, and error control. It describes flow control as procedures that tell a sender how much data it can transmit before waiting for an acknowledgement. It also explains stop-and-wait and sliding window protocols for flow control and includes diagrams of normal operation and scenarios involving damaged frames, lost frames, and lost acknowledgements.
- The document discusses the simulation and performance analysis of the AODV routing protocol for mobile ad-hoc networks using the NS-2.34 network simulator.
- It describes the basic principles and operation of AODV, the experimental setup used including varying parameters like node speed and number of connections, and the performance metrics measured like packet delivery fraction and routing overhead.
- The results of simulations run by varying these parameters are presented and analyzed to understand AODV performance under different conditions.
NS-2 is an open-source discrete event network simulator for networking research. It supports simulation of TCP, routing protocols and other network protocols. NS-2 includes both an OTcl interpreter for setting up simulations and C++ code for implementing network components and protocols. Simulations are run by executing OTcl scripts that create nodes, links, and traffic and schedule events over time.
The document describes the implementation of three differentiated service queuing disciplines - strict priority queuing, weighted fair queuing, and weighted round robin queuing - in the Network Simulator 3 (ns-3). It provides background on the theoretical models for each queuing discipline. The implementations classify packets into queues based on user-defined criteria and schedules packets out of the queues according to the specific algorithm for each queuing discipline (priority, virtual finish time, round-robin weight). Validation experiments confirmed the implementations simulate the queuing disciplines correctly according to analytical expectations. Usage instructions are provided to configure the modules in ns-3 simulations.
The document discusses data link control and framing in computer networks. It describes two main functions of the data link layer: defining frames and performing error detection on frames. It also discusses different types of framing such as fixed-size framing and variable-size framing using character-oriented and bit-oriented protocols. Specific protocols discussed include Stop-and-Wait ARQ which uses positive acknowledgments and retransmissions, and Go-Back-N ARQ which allows for pipelining of multiple frames before requiring an acknowledgment.
Design and implementation of low latency weighted round robin (ll wrr) schedu...ijwmn
Today’s wireless broadband networks are required to provide QoS guarantee as well as fairness to
different kinds of traffic. Recent wireless standards (such as LTE and WiMAX) have special provisions at
MAC layer for differentiating and scheduling data traffic for achieving QoS. The main focus of this paper is
concerned with high speed packet queuing/scheduling at central node such as base station (BS) or router to
handle network traffic. This paper proposes novel packet queuing scheme termed as Low Latency
Weighted Round Robin (LL-WRR) which is simple and effective amendment to weighted round robin (WRR)
for achieving low latency and improved fairness. Proposed LL-WRR queue scheduling scheme is
implemented in NS-2 considering IEEE 802.16 network [1] with real time video and Constant Bit Rate
(CBR) audio traffic connections. Simulation results show improvement obtained in latency and fairness
using LL-WRR. The proposed scheme introduces extra complexity of computing coefficient but its overall
impact is very small.
This document discusses multiple access protocols for wireless networks. It describes random access methods like ALOHA and slotted ALOHA, controlled access methods using reservation, polling, and token passing, and channelization methods including FDMA, TDMA, and CDMA. Examples are provided to illustrate the calculation of throughput for various access loads in ALOHA and slotted ALOHA networks.
The document discusses the implementation of various networking protocols and VLAN using the Network Simulator 2 (NS2). It summarizes TCP, UDP, ad-hoc routing protocols like AODV, DSR, DSDV and how they are simulated in NS2. It also discusses how to configure VLANs in NS2 by creating network bridges and attaching Ethernet interfaces to VLAN IDs. The document provides examples of simulating protocols and configuring VLANs to segment traffic between virtual LANs in NS2.
This document discusses functions and techniques of the data link layer, including line discipline, flow control, and error control. It describes flow control as procedures that tell a sender how much data it can transmit before waiting for an acknowledgement. It also explains stop-and-wait and sliding window protocols for flow control and includes diagrams of normal operation and scenarios involving damaged frames, lost frames, and lost acknowledgements.
- The document discusses the simulation and performance analysis of the AODV routing protocol for mobile ad-hoc networks using the NS-2.34 network simulator.
- It describes the basic principles and operation of AODV, the experimental setup used including varying parameters like node speed and number of connections, and the performance metrics measured like packet delivery fraction and routing overhead.
- The results of simulations run by varying these parameters are presented and analyzed to understand AODV performance under different conditions.
NS-2 is an open-source discrete event network simulator for networking research. It supports simulation of TCP, routing protocols and other network protocols. NS-2 includes both an OTcl interpreter for setting up simulations and C++ code for implementing network components and protocols. Simulations are run by executing OTcl scripts that create nodes, links, and traffic and schedule events over time.
The document describes the implementation of three differentiated service queuing disciplines - strict priority queuing, weighted fair queuing, and weighted round robin queuing - in the Network Simulator 3 (ns-3). It provides background on the theoretical models for each queuing discipline. The implementations classify packets into queues based on user-defined criteria and schedules packets out of the queues according to the specific algorithm for each queuing discipline (priority, virtual finish time, round-robin weight). Validation experiments confirmed the implementations simulate the queuing disciplines correctly according to analytical expectations. Usage instructions are provided to configure the modules in ns-3 simulations.
The document discusses data link control and framing in computer networks. It describes two main functions of the data link layer: defining frames and performing error detection on frames. It also discusses different types of framing such as fixed-size framing and variable-size framing using character-oriented and bit-oriented protocols. Specific protocols discussed include Stop-and-Wait ARQ which uses positive acknowledgments and retransmissions, and Go-Back-N ARQ which allows for pipelining of multiple frames before requiring an acknowledgment.
Design and implementation of low latency weighted round robin (ll wrr) schedu...ijwmn
Today’s wireless broadband networks are required to provide QoS guarantee as well as fairness to
different kinds of traffic. Recent wireless standards (such as LTE and WiMAX) have special provisions at
MAC layer for differentiating and scheduling data traffic for achieving QoS. The main focus of this paper is
concerned with high speed packet queuing/scheduling at central node such as base station (BS) or router to
handle network traffic. This paper proposes novel packet queuing scheme termed as Low Latency
Weighted Round Robin (LL-WRR) which is simple and effective amendment to weighted round robin (WRR)
for achieving low latency and improved fairness. Proposed LL-WRR queue scheduling scheme is
implemented in NS-2 considering IEEE 802.16 network [1] with real time video and Constant Bit Rate
(CBR) audio traffic connections. Simulation results show improvement obtained in latency and fairness
using LL-WRR. The proposed scheme introduces extra complexity of computing coefficient but its overall
impact is very small.
This document discusses multiple access protocols for wireless networks. It describes random access methods like ALOHA and slotted ALOHA, controlled access methods using reservation, polling, and token passing, and channelization methods including FDMA, TDMA, and CDMA. Examples are provided to illustrate the calculation of throughput for various access loads in ALOHA and slotted ALOHA networks.
This document discusses multiple access protocols at the data link layer. It covers random access protocols like ALOHA and CSMA, as well as controlled access protocols including polling, reservation, and token passing. Random access allows any station to transmit at any time by using carrier sensing, collision detection, and random backoff times to avoid collisions. Controlled access requires stations to get permission before transmitting via polling, reservations, or a circulating token.
The document summarizes key concepts about the transport layer from Chapter 3, including:
- The transport layer provides logical communication between application processes running on different hosts. It uses multiplexing and demultiplexing to direct data between applications.
- The main Internet transport protocols are UDP (connectionless) and TCP (connection-oriented and reliable). TCP provides congestion control while UDP does not.
- Reliable data transfer requires mechanisms like sequence numbers, acknowledgments, timeouts, and retransmissions to handle packet loss and out-of-order delivery over unreliable networks. Stop-and-wait and pipelined protocols like Go-Back-N and Selective Repeat are introduced.
- TCP provides
This document provides an overview of multiple access protocols for shared wireless media. It discusses random access protocols like ALOHA, slotted ALOHA, CSMA, CSMA/CD, and CSMA/CA. ALOHA protocols allow stations to transmit whenever they have data, which can cause collisions. Slotted ALOHA and CSMA protocols reduce collisions by coordinating transmissions. The document also covers controlled access protocols like reservation, polling, and token passing that establish transmission rights to avoid collisions. It includes frame formats, throughput calculations, and flow diagrams to illustrate how each protocol manages access to the shared channel.
The document describes the implementation of the Ad-hoc On-Demand Distance Vector (AODV) routing protocol in the Network Simulator 2 (NS-2). It discusses the file dependencies of AODV, the general flow of AODV operation through an example, the trace format used in NS-2, and some of the main implementation files and functions in AODV including timers, routing table management, and packet handling functions.
The document discusses the Medium Access Control (MAC) sublayer of the data link layer and various protocols for determining which device can access a shared communication channel. It focuses on static and dynamic channel allocation problems in local area networks (LANs) and wireless networks. Static allocation wastes bandwidth by assigning each user a fixed portion of the channel even when they are not transmitting. Dynamic protocols like ALOHA and carrier sense multiple access (CSMA) aim to improve channel utilization by allowing users to transmit only when the channel is idle.
Scheduling and Resource allocation in 802.11ax (WIFI 6)RESHAN FARAZ
--> IIITD Course Project.
--> Implementation of Scheduling and Resource allocation in 802.11ax using NS-3.
-->Modified Largest Weighted Delay First.
--> Comparison of Round Robin Scheduling with Modified Largest Weighted Delay First.
-->Source Code:-https://github.com/reshan9b11/MLWDF_WN_PROJECT
This document summarizes key aspects of TCP traffic control as covered in Chapter 12. It discusses TCP flow and congestion control, including how the transmission rate is determined by incoming ACKs. It then covers traffic control fields in the TCP header, credit allocation mechanisms, and the impact of window size on throughput. The document also summarizes TCP congestion control techniques like slow start, congestion avoidance, fast retransmit, fast recovery, and limited transmit. It notes the differentiating impact of "mice vs. elephant" flows on network congestion.
COMPARISON OF HIGH SPEED CONGESTION CONTROL PROTOCOLSIJNSA Journal
Congestion control limits the quantity of information input at a rate less important than that of the transmission one to ensure good performance as well as protect against overload and blocking of the network. Researchers have done a great deal of work on improving congestion control protocols, especially on high speed networks. In this paper, we will be studying the congestion control alongside low and high speed congestion control protocols. We will be also simulating, evaluating, and comparing eight of high speed congestion control protocols : Bic TCP, Cubic TCP, Hamilton TCP, HighSpeed TCP, Illinois TCP, Scalable TCP, Compound TCP and YeAH TCP, with multiple flows.
This document discusses unit 2 of a course on high speed networks. It covers queuing analysis and models, including single server queues, effects of congestion and congestion control, traffic management, and congestion control in packet switching networks and frame relay. It provides an overview of key concepts like performance measures, solution methodologies, queuing system concepts, stability and steady-state, and causes of delay and bottlenecks. It also discusses analytical and simulation approaches to modeling queues and provides examples.
SOLUTION MANUAL OF COMPUTER ORGANIZATION BY CARL HAMACHER, ZVONKO VRANESIC & ...vtunotesbysree
1) The document provides solutions to problems from Chapter 1 and Chapter 2 of a computer organization textbook.
2) In Chapter 1, it discusses basic computer structure, performance improvement through overlapping operations, and performance comparisons between RISC and CISC processors. In Chapter 2, it covers machine instructions, binary representations of numbers, assembly language programming, and addressing modes.
3) Some of the problems solved include calculating non-overlapped and overlapped execution times, comparing RISC and CISC processors under different clock rates, implementing addition and subtraction in binary, writing assembly code to calculate a dot product, and designing programs that use indexed addressing modes.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
Comparison of TCP congestion control mechanisms Tahoe, Newreno and VegasIOSR Journals
The widely used reliable transport protocol TCP, is an end to end protocol designed for the wireline
networks characterized by negligible random packet losses. This paper represents exploratory study of TCP
congestion control principles and mechanisms. Modern implementations of TCP contain four intertwined
algorithms: slow start, congestion avoidance, fast retransmit, and fast recovery. In addition to the standard
algorithms used in common implementations of TCP, this paper also describes some of the more common
proposals developed by researchers over the years. We also study, through extensive simulations, the
performance characteristics of four representative TCP schemes, namely TCP Tahoe, New Reno and Vegas
under the network conditions of bottleneck link capacities for wired network
Advanced Comuter Architecture Ch6 Problem SolutionsJoe Christensen
This document contains problems and solutions related to pipelining and superscalar techniques in computer architecture. It discusses speedup factors, efficiency, throughput, and latency for a pipelined processor. It also analyzes the DEC Alpha architecture in terms of scalability and addresses a multiprocessor implementation. Several problems are solved related to reservation tables, collision vectors, state transition diagrams, and determining minimum average latency for pipeline scheduling.
This document discusses multiple access protocols for wireless networks. It begins by describing random access protocols like ALOHA and slotted ALOHA. It then covers controlled access protocols using reservation, polling, and token passing. Finally, it discusses channelization protocols using frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). Throughout are examples calculating throughput for different access loads and determining minimum frame sizes.
This document evaluates and compares the performance of seven high-speed TCP congestion control protocols: Bic TCP, Cubic TCP, Hamilton TCP, HighSpeed TCP, Illinois TCP, Scalable TCP and YeAH TCP. It first provides background on the need for high-speed congestion control as internet speeds have increased. It then summarizes the algorithms and mechanisms of each protocol. The document aims to simulate and compare the performance of these protocols with multiple flows, in order to determine the best approach for high-speed networks.
Improvement of Congestion window and Link utilization of High Speed Protocols...IOSR Journals
This document summarizes a research paper that proposes using a k-nearest neighbors (k-NN) algorithm to help high-speed transport layer protocols like CUBIC better distinguish between packet drops due to network congestion versus other factors like noise. The k-NN algorithm would analyze patterns in packet drop history to classify new drops, helping protocols avoid unnecessary window size reductions when drops are not actually due to congestion. The document provides background on high-speed protocols, issues like underutilization from treating all drops as congestion, and how incorporating k-NN classification could improve protocols' performance in noisy network conditions.
Simulation of a Wireless Sub Network using QualNETDaksh Raj Chopra
This report has two scenarios - First one having 2 connections, UDP and TCP. Another scenario has 4 TCP connections having a comparison with and without fading.
Data link control protocols provide flow control and error control to ensure reliable data transmission. Flow control prevents buffer overflow by regulating transmission rate. Error control detects and corrects errors through techniques like error detection, acknowledgments, and retransmissions of damaged frames. Common protocols include stop-and-wait, go-back-N, and selective reject under HDLC which is a widely used standard.
This document discusses trends in embedded systems and multiprocessor system-on-chips (MPSoCs). It summarizes issues with traditional bus and crossbar networks for SoCs like latency, priority, bandwidth limitation, and cost. It then describes a routing congestion-aware and power-aware mapping algorithm for MPSoCs that arranges task graphs by latency constraint severity and maps cores to tiles to minimize congestion while meeting latency constraints.
SIMULATIVE ANALYSIS OF CHANNEL AND QoS AWARE SCHEDULER TO ENHANCE THE CAPACIT...IAEME Publication
Here a new MAC scheduling mechanism for the downlink of LTE systems named Channel and Qos Aware Scheduler is analyzed. This scheduler is based on a Channel and QoS aware algorithm which performs joint time and frequency scheduling. The relevance of the scheduler comes in to play in a situation in which the number of data hungry users are at the rising edge and they demand for traffics that have very tight QoS requirement in terms of bit rate and delay.eg:- VoIP, Video conferencing & Online Gaming. The performance of the scheduler is evaluated by means of network simulations in LTE single cell scenario with mixed traffic and compared the results with state of the art LTE downlink schedule rs. The results shows that in a realistic scenario in which quality of channel varies over time as well a s frequency, CQA scheduler significantly outperforms other schedulers in terms of provided Q oS.
Scheduler performance in manycore architecturechiportal
This document discusses scheduler performance in many-core architectures. It presents several benchmark applications run on a Plural many-core system simulator. The benchmarks demonstrate issues like unbalanced workload distribution and latency hiding. Several solutions are proposed, including queue sharing, scheduling awareness of long tasks, and using finer granularity tasks. Analysis of the simulation results helps evaluate these solutions.
This document discusses multiple access protocols at the data link layer. It covers random access protocols like ALOHA and CSMA, as well as controlled access protocols including polling, reservation, and token passing. Random access allows any station to transmit at any time by using carrier sensing, collision detection, and random backoff times to avoid collisions. Controlled access requires stations to get permission before transmitting via polling, reservations, or a circulating token.
The document summarizes key concepts about the transport layer from Chapter 3, including:
- The transport layer provides logical communication between application processes running on different hosts. It uses multiplexing and demultiplexing to direct data between applications.
- The main Internet transport protocols are UDP (connectionless) and TCP (connection-oriented and reliable). TCP provides congestion control while UDP does not.
- Reliable data transfer requires mechanisms like sequence numbers, acknowledgments, timeouts, and retransmissions to handle packet loss and out-of-order delivery over unreliable networks. Stop-and-wait and pipelined protocols like Go-Back-N and Selective Repeat are introduced.
- TCP provides
This document provides an overview of multiple access protocols for shared wireless media. It discusses random access protocols like ALOHA, slotted ALOHA, CSMA, CSMA/CD, and CSMA/CA. ALOHA protocols allow stations to transmit whenever they have data, which can cause collisions. Slotted ALOHA and CSMA protocols reduce collisions by coordinating transmissions. The document also covers controlled access protocols like reservation, polling, and token passing that establish transmission rights to avoid collisions. It includes frame formats, throughput calculations, and flow diagrams to illustrate how each protocol manages access to the shared channel.
The document describes the implementation of the Ad-hoc On-Demand Distance Vector (AODV) routing protocol in the Network Simulator 2 (NS-2). It discusses the file dependencies of AODV, the general flow of AODV operation through an example, the trace format used in NS-2, and some of the main implementation files and functions in AODV including timers, routing table management, and packet handling functions.
The document discusses the Medium Access Control (MAC) sublayer of the data link layer and various protocols for determining which device can access a shared communication channel. It focuses on static and dynamic channel allocation problems in local area networks (LANs) and wireless networks. Static allocation wastes bandwidth by assigning each user a fixed portion of the channel even when they are not transmitting. Dynamic protocols like ALOHA and carrier sense multiple access (CSMA) aim to improve channel utilization by allowing users to transmit only when the channel is idle.
Scheduling and Resource allocation in 802.11ax (WIFI 6)RESHAN FARAZ
--> IIITD Course Project.
--> Implementation of Scheduling and Resource allocation in 802.11ax using NS-3.
-->Modified Largest Weighted Delay First.
--> Comparison of Round Robin Scheduling with Modified Largest Weighted Delay First.
-->Source Code:-https://github.com/reshan9b11/MLWDF_WN_PROJECT
This document summarizes key aspects of TCP traffic control as covered in Chapter 12. It discusses TCP flow and congestion control, including how the transmission rate is determined by incoming ACKs. It then covers traffic control fields in the TCP header, credit allocation mechanisms, and the impact of window size on throughput. The document also summarizes TCP congestion control techniques like slow start, congestion avoidance, fast retransmit, fast recovery, and limited transmit. It notes the differentiating impact of "mice vs. elephant" flows on network congestion.
COMPARISON OF HIGH SPEED CONGESTION CONTROL PROTOCOLSIJNSA Journal
Congestion control limits the quantity of information input at a rate less important than that of the transmission one to ensure good performance as well as protect against overload and blocking of the network. Researchers have done a great deal of work on improving congestion control protocols, especially on high speed networks. In this paper, we will be studying the congestion control alongside low and high speed congestion control protocols. We will be also simulating, evaluating, and comparing eight of high speed congestion control protocols : Bic TCP, Cubic TCP, Hamilton TCP, HighSpeed TCP, Illinois TCP, Scalable TCP, Compound TCP and YeAH TCP, with multiple flows.
This document discusses unit 2 of a course on high speed networks. It covers queuing analysis and models, including single server queues, effects of congestion and congestion control, traffic management, and congestion control in packet switching networks and frame relay. It provides an overview of key concepts like performance measures, solution methodologies, queuing system concepts, stability and steady-state, and causes of delay and bottlenecks. It also discusses analytical and simulation approaches to modeling queues and provides examples.
SOLUTION MANUAL OF COMPUTER ORGANIZATION BY CARL HAMACHER, ZVONKO VRANESIC & ...vtunotesbysree
1) The document provides solutions to problems from Chapter 1 and Chapter 2 of a computer organization textbook.
2) In Chapter 1, it discusses basic computer structure, performance improvement through overlapping operations, and performance comparisons between RISC and CISC processors. In Chapter 2, it covers machine instructions, binary representations of numbers, assembly language programming, and addressing modes.
3) Some of the problems solved include calculating non-overlapped and overlapped execution times, comparing RISC and CISC processors under different clock rates, implementing addition and subtraction in binary, writing assembly code to calculate a dot product, and designing programs that use indexed addressing modes.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
Comparison of TCP congestion control mechanisms Tahoe, Newreno and VegasIOSR Journals
The widely used reliable transport protocol TCP, is an end to end protocol designed for the wireline
networks characterized by negligible random packet losses. This paper represents exploratory study of TCP
congestion control principles and mechanisms. Modern implementations of TCP contain four intertwined
algorithms: slow start, congestion avoidance, fast retransmit, and fast recovery. In addition to the standard
algorithms used in common implementations of TCP, this paper also describes some of the more common
proposals developed by researchers over the years. We also study, through extensive simulations, the
performance characteristics of four representative TCP schemes, namely TCP Tahoe, New Reno and Vegas
under the network conditions of bottleneck link capacities for wired network
Advanced Comuter Architecture Ch6 Problem SolutionsJoe Christensen
This document contains problems and solutions related to pipelining and superscalar techniques in computer architecture. It discusses speedup factors, efficiency, throughput, and latency for a pipelined processor. It also analyzes the DEC Alpha architecture in terms of scalability and addresses a multiprocessor implementation. Several problems are solved related to reservation tables, collision vectors, state transition diagrams, and determining minimum average latency for pipeline scheduling.
This document discusses multiple access protocols for wireless networks. It begins by describing random access protocols like ALOHA and slotted ALOHA. It then covers controlled access protocols using reservation, polling, and token passing. Finally, it discusses channelization protocols using frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). Throughout are examples calculating throughput for different access loads and determining minimum frame sizes.
This document evaluates and compares the performance of seven high-speed TCP congestion control protocols: Bic TCP, Cubic TCP, Hamilton TCP, HighSpeed TCP, Illinois TCP, Scalable TCP and YeAH TCP. It first provides background on the need for high-speed congestion control as internet speeds have increased. It then summarizes the algorithms and mechanisms of each protocol. The document aims to simulate and compare the performance of these protocols with multiple flows, in order to determine the best approach for high-speed networks.
Improvement of Congestion window and Link utilization of High Speed Protocols...IOSR Journals
This document summarizes a research paper that proposes using a k-nearest neighbors (k-NN) algorithm to help high-speed transport layer protocols like CUBIC better distinguish between packet drops due to network congestion versus other factors like noise. The k-NN algorithm would analyze patterns in packet drop history to classify new drops, helping protocols avoid unnecessary window size reductions when drops are not actually due to congestion. The document provides background on high-speed protocols, issues like underutilization from treating all drops as congestion, and how incorporating k-NN classification could improve protocols' performance in noisy network conditions.
Simulation of a Wireless Sub Network using QualNETDaksh Raj Chopra
This report has two scenarios - First one having 2 connections, UDP and TCP. Another scenario has 4 TCP connections having a comparison with and without fading.
Data link control protocols provide flow control and error control to ensure reliable data transmission. Flow control prevents buffer overflow by regulating transmission rate. Error control detects and corrects errors through techniques like error detection, acknowledgments, and retransmissions of damaged frames. Common protocols include stop-and-wait, go-back-N, and selective reject under HDLC which is a widely used standard.
This document discusses trends in embedded systems and multiprocessor system-on-chips (MPSoCs). It summarizes issues with traditional bus and crossbar networks for SoCs like latency, priority, bandwidth limitation, and cost. It then describes a routing congestion-aware and power-aware mapping algorithm for MPSoCs that arranges task graphs by latency constraint severity and maps cores to tiles to minimize congestion while meeting latency constraints.
SIMULATIVE ANALYSIS OF CHANNEL AND QoS AWARE SCHEDULER TO ENHANCE THE CAPACIT...IAEME Publication
Here a new MAC scheduling mechanism for the downlink of LTE systems named Channel and Qos Aware Scheduler is analyzed. This scheduler is based on a Channel and QoS aware algorithm which performs joint time and frequency scheduling. The relevance of the scheduler comes in to play in a situation in which the number of data hungry users are at the rising edge and they demand for traffics that have very tight QoS requirement in terms of bit rate and delay.eg:- VoIP, Video conferencing & Online Gaming. The performance of the scheduler is evaluated by means of network simulations in LTE single cell scenario with mixed traffic and compared the results with state of the art LTE downlink schedule rs. The results shows that in a realistic scenario in which quality of channel varies over time as well a s frequency, CQA scheduler significantly outperforms other schedulers in terms of provided Q oS.
Scheduler performance in manycore architecturechiportal
This document discusses scheduler performance in many-core architectures. It presents several benchmark applications run on a Plural many-core system simulator. The benchmarks demonstrate issues like unbalanced workload distribution and latency hiding. Several solutions are proposed, including queue sharing, scheduling awareness of long tasks, and using finer granularity tasks. Analysis of the simulation results helps evaluate these solutions.
Abstract— Scheduler is the backbone of intelligence in a LTE network. Scheduler will often have clashing needs that can make its design very complex and non-trivial.
The overall system throughput needs to be maintained at the best possible value without sacrificing the cell edge user experience.
In this paper, authors compared different scheduler designs for voice and packet services. They explained the role of configuration parameters through simulations. These parameters control the tradeoff between the sector throughput and the fairness in system through. They explained a possible scheduler implementation.
eNodeB software architecture for dual core SoC
Scheduler interface
Core 0: Soft real time function
Core 1: Hard real time function
PHY control
Receive data from PHY
Presentation by Mr. Vibin Chander, CEO, Shabari Software Solutions, CBE during the Faculty development Programm on NS2 organized by Department of Computer Science, Rathinam College of Arts and Computer Science (Autonomous), Eachanari, Coimbatore - 641021.
- HSUPA (Enhanced Uplink) improves the uplink capabilities of WCDMA networks by providing higher data rates, reduced latency, and improved system capacity. It complements HSDPA for downlink improvements.
- The NodeB scheduler controls UE uplink transmissions to manage interference levels. It uses scheduling requests and grants to determine each UE's allowed transmission power and data rate.
- In soft handover, the serving cell schedules transmissions while UE monitors grants from all cells to support HARQ and reliable transmission.
A Novel Parameterized QoS based Uplink and Downlink Scheduler for Bandwidth/D...IDES Editor
Recent developments in Broadband Wireless
Access (BWA), caused users to use multimedia, real–time
and high bandwidth intensive applications that lead to a
new era of research and development in wireless
networks. IEEE 802.16 standard has come forward as
BWA solution to fulfill the requirements of users. Even
though IEEE 802.16 standard defines scheduling service
flows and quality of service parameters, but scheduling of
these flows to maintain QoS and fairness among flows is
left open for researchers. In this paper we developed a
scheduling architecture for IEEE 802.16 in both uplink
and downlink directions. Our scheduling architecture
includes QoS parameters like maximum sustained rate,
maximum latency, tolerated jitter, minimum reserved
bandwidth, request transmission policy, traffic priority,
burst size, SDU size and queue information for various
scheduling service flows. We use First in First out (FIFO),
Earliest Deadline First (EDF) and Self Clocked Fair
Queuing (SCFQ) to schedule different flows to achieve
QoS and efficient bandwidth utilization.
Many energy-efficient Receiver Initiated Asynchronous Duty-Cycle MAC protocol for wireless sensor
networks (WSNs) have been proposed. Most nodes suffer from significant performance Degradation for burst traffic,
due to randomly waking up to communicate with each other. The proposed protocol is new receiver initiated
asynchronous duty-cycle MAC protocol for burst traffic . By adaptively adjusting beacon time of the receiver and it
schedules the sender listening time based on scheduled period, by this high energy efficiency and low end-to-end packet
delivery latency for burst traffic is achieved. We have evaluated the performance of MAC through detailed ns- 2
simulation. The simulation results show that this protocol reduce end-to-end packet delivery latency and energy
consumption under various data rates in different topologies compared with RI-MAC.
Keywords— Wireless sensor networks, duty-cycle, receiver-initiated, low latency, energy-efficient
RTH-RSS Mac: Path loss exponent estimation with received signal strength loca...IOSR Journals
The document summarizes a study on integrating received signal strength path-loss exponent (RSS PLE) estimation localization into the Real Time Hybrid MAC (RTHMAC) protocol. RTHMAC combines TDMA and FDMA to provide soft real-time communication for wireless sensor networks. The study develops a new RTH-RSS MAC protocol that replaces the initialization and discovery phases of RTHMAC with an RSS PLE localization technique called IDRSS-PLE. This aims to minimize delay, maximize network lifetime by decreasing energy consumption of nodes. Simulations show that using RSS PLE localization, RTH-RSS MAC is able to achieve less energy consumption and shorter localization response times compared to the classical RTHMAC protocol.
The document summarizes MAC protocols for wireless mesh networks. It begins with an introduction to wireless mesh network architectures and important definitions. It then discusses single channel MAC protocols like S-MAC, T-MAC, and a new TDMA-based protocol. It also covers multi-channel MAC protocols classifications and examples like CC-MMAC and SSCH MAC. The document provides detailed explanations of the mechanisms and concepts behind various single and multi-channel MAC protocols.
This document provides an overview of TCP performance modeling and network simulation using the ns-2 simulator. It begins with background on TCP congestion control algorithms like slow start, congestion avoidance, fast retransmit, and fast recovery. Two analytical models for TCP throughput - a simple model and a more complex model - are described. The document then provides instructions on installing and using the ns-2 network simulator and Otcl scripting language. It explains how to create network topologies in ns-2 including nodes, links, agents and applications. Tracing, monitoring and running simulations are also covered. The document concludes with an example simulation study comparing TCP throughput models to ns-2 results.
Fault tolerant wireless sensor mac protocol for efficient collision avoidancegraphhoc
In sensor networks communication by broadcast methods involves many hazards, especially collision. Several MAC layer protocols have been proposed to resolve the problem of collision namely ARBP, where the best achieved success rate is 90%. We hereby propose a MAC protocol which achieves a greater success rate (Success rate is defined as the percentage of delivered packets at the source reaching the destination successfully) by reducing the number of collisions, but by trading off the average propagation delay of transmission. Our proposed protocols are also shown to be more energy efficient in terms of energy dissipation per message delivery, compared to the currently existing protocol.
IRJET- QOS Based Bandwidth Satisfaction for Multicast Network Coding in M...IRJET Journal
The document proposes a new multicast routing protocol for mobile ad hoc networks (MANETs) that provides bandwidth guarantees while reducing total bandwidth consumption. It constructs multiple multicast trees to fully utilize residual bandwidth across paths. Randomized network coding is used so redundant packets are avoided and destinations receive innovative coded packets from different routes. The protocol estimates available bandwidth on routes using a variable bit rate to improve accuracy. Simulation results show the protocol reduces delay and retransmission rates compared to existing protocols, improving bandwidth usage in MANETs.
The document discusses different protocols for reliable data transfer over noisy channels:
- Stop-and-Wait ARQ uses a sender and receiver finite state machine with only two possible sequence numbers (0,1) to ensure reliable transfer. It has low bandwidth utilization.
- Go-Back-N ARQ allows multiple packets "in flight" using a sender window and cumulative acknowledgments, improving utilization but requiring retransmission of all packets in the window if any are lost.
- Selective Repeat ARQ further improves efficiency by having the receiver acknowledge each packet individually and allowing the sender to retransmit only lost packets, avoiding resending already received packets. It buffers packets to allow out-of-order delivery to the upper layer.
This document proposes a methodology for incorporating uplink delay constraints into LTE cell planning for smart grid applications. It presents the following:
1) A semi-analytical approach is proposed to evaluate uplink transmission delays considering buffering delays before scheduling, packet transmission/retransmission delays over the air interface, and constraints from smart grid standards.
2) Analytical models are used to estimate buffering delays before scheduling based on queue length and service rate. Packet transmission delays are estimated considering packet segmentation, link adaptation, resource block allocation and retransmissions.
3) A cell planning algorithm is described that incorporates these delay metrics to validate compliance with smart grid delay constraints and determine the maximum cell range based on
This document proposes a methodology for incorporating uplink delay constraints into LTE cell planning for smart grid applications. It presents the following:
1) A semi-analytical approach is proposed to evaluate uplink transmission delays considering buffering delays before scheduling, packet transmission/retransmission delays over the air interface, and constraints from smart grid standards.
2) Analytical models are used to estimate buffering delays before scheduling based on queue length and service rate. Packet transmission delays are estimated considering packet segmentation, link adaptation, resource block allocation and retransmissions.
3) A cell planning algorithm is analyzed that incorporates these delay metrics to validate compliance with smart grid delay constraints defined in standards. Path loss, interference
This document provides an overview of key concepts in TCP (Transmission Control Protocol) including:
- TCP segment structure with fields like sequence numbers, acknowledgement numbers, and windows.
- Mechanisms for reliable data transfer like cumulative acknowledgements, timeouts, and retransmissions.
- Flow control using advertised receive windows to limit unacknowledged data.
- Connection management using three-way handshakes to initialize connections and four-way handshakes to close connections in an orderly manner.
The document summarizes key aspects of the transport layer. It discusses how the transport layer provides logical communication between application processes running on different hosts by abstracting physical network details. It then describes the services provided by the transport layer including connection-oriented and connectionless services. It also discusses topics like quality of service, transport service primitives, addressing, connection establishment and release, flow control, multiplexing, and crash recovery for the transport layer.
This document discusses various transport layer protocols for mobile networks. It begins by describing TCP and its mechanisms for congestion avoidance, flow control, slow start, and retransmission. It then covers several TCP variants including Tahoe, Reno, and Vegas. It also discusses indirect TCP, Snoop TCP, and Mobile TCP which aim to optimize TCP for wireless networks by handling retransmissions locally or splitting the connection. The document provides details on the algorithms and functioning of these different protocols.
The document summarizes key concepts related to reliable data transfer over computer networks. It discusses principles of reliable data transfer including error detection, receiver feedback, and retransmission. It introduces stop-and-wait and sliding window protocols, specifically RDT 1.0, 2.0, 2.1, 2.2 and 3.0 which handle increasingly challenging scenarios like bit errors, lost packets, and pipelining. The final section summarizes the Go-Back-N sliding window protocol that allows limited in-flight packets to improve throughput compared to stop-and-wait protocols.
The document summarizes the principles and evolution of reliable data transfer protocols. It begins with an overview of reliable data transfer and its importance. It then describes the initial RDT 1.0 protocol which assumes a perfectly reliable channel. It introduces RDT 2.0 which adds error detection, receiver feedback through ACKs/NAKs, and retransmissions to handle bit errors over unreliable channels. Subsequent versions add sequence numbers to prevent duplicate packets, evolve to using just ACKs, and introduce timers and retransmissions to handle packet losses. Finally, it overviews pipelined protocols like Go-Back-N which improve efficiency by allowing multiple outstanding packets.
This document provides information on setting up wireless simulations in NS-2 including:
1) Details on configuring wireless node parameters, channels, propagation models, interfaces, and routing protocols.
2) Examples of generating node mobility using the setdest script and generating traffic using cbrgen.
3) The format of DSR trace files and how to calculate routing overhead and packet delivery ratio from these files using AWK.
This document summarizes key aspects of the transport layer:
- The transport layer provides logical communication between application processes running on different hosts and handles reliable data transfer.
- It provides both connection-oriented and connectionless services to the application layer. Quality of service parameters like throughput and delay can be negotiated.
- Transport layer protocols like TCP and UDP are described. TCP provides reliable byte-stream delivery using connections while UDP provides best-effort unreliable datagram delivery.
Osc mac duty cycle with multi helpers ct mode wi-lem technology in wireless s...ijwmn
Recently, Wireless Sensor Networks (WSNs) grow to be one of the dominant technology trends; new needs
are continuously emerging and demanding more complex constraints in a duty cycle, such as extend the life
time communication . The MAC layer plays a crucial role in these networks; it controls the communication
module and manages the medium sharing. In this work we use OSC-MAC tackles combining with the
performance of cooperative transmission (CT) in multi-hop WSN and the Wi-Lem technology
This document summarizes key concepts about congestion control in TCP including:
- TCP uses additive increase multiplicative decrease (AIMD) to dynamically adjust the congestion window size and maintain efficiency and fairness.
- TCP has slow start and congestion avoidance states that govern how the congestion window is adjusted in response to acknowledgements.
- TCP responds to packet loss through fast retransmit, fast recovery, and halving the congestion window size to reduce congestion according to protocols like Tahoe, Reno, and New Reno.
Minimizing Hidden Node Problem in Vehicular Ad-hoc Network (VANET)
Tr ns802 11
1. A Tutorial of 802.11 Implementation in ns-2
Yue Wang
MobiTec Lab, CUHK
1. Introduction to ns-2
1.1 ns-2
Ns-2 [1] is a packet-level simulator and essentially a centric discrete event scheduler to schedule
the events such as packet and timer expiration. Centric event scheduler cannot accurately emulate
“events handled at the same time” in real world, that is, events are handled one by one. However,
this is not a serious problem in most network simulations, because the events here are often
transitory. Beyond the event scheduler, ns-2 implements a variety of network components and
protocols. Notably, the wireless extension, derived from CMU Monarch Project [2], has 2
assumptions simplifying the physical world:
(1) Nodes do not move significantly over the length of time they transmit or receive a packet.
This assumption holds only for mobile nodes of high-rate and low-speed. Consider a node with the
sending rate of 10Kbps and moving speed of 10m/s, during its receiving a packet of 1500B, the
node moves 12m. Thus, the surrounding can change significantly and cause reception failure.
(2) Node velocity is insignificant compared to the speed of light. In particular, none of the
provided propagation models include Doppler effects, although they could.
1.2 GloMoSim
GloMoSim [3] is another open-source network simulator based on a parallel discrete event
scheduler. Hopefully, it can emulate the real world more accurately. However, it is hard to debug
parallel programs. Although GloMoSim currently only supports pure wireless networks, it
provides more physical-layer models than ns-2, as shown in Table 1 [4].
2. Table 1. Physical layer and propagation models available in GloMoSim, ns-2 and OPNET
1.3 Ns-2 Basics
Ns-2 directory structure
As shown in Figure 1, the C++ classes of ns-2 network components or protocols are implemented
in the subdirectory “ns-2”, and the TCL library (corresponding to configurations of these C++
instances) in the subdirectory of “tcl”.
Figure 1. Ns-2 directory structure
Network Components
Network components are Node, Link, Queue, etc. Some of them are simple components, that is,
they are created from the corresponding C++ classes; The other are compound components, that is,
they are composed multiple simple C++ classes, e.g. Link are composed of Delay (emulating
propagation delay) and Queue. In general, in ns-2, all network components are created, plugged
and configured from TCL.
Example: Plug MAC into NetIF (Network Interface)
Class MAC {
void send (Packet* p);
3. void recv(Packet*, Handler* h);
NsObject* target_ //an instance of NetIF
}
Event Scheduling
Events are something associated with time. class Event is defined by {time, uid, next, handler},
where time is the scheduling time of the event, uid is the unique id of the event, next is the next
scheduling event in the event queue that is a linklist, and handler points to the function to handle
the event when the event is scheduled. Events are put into the event queue sorted by their time,
and scheduled one by one by the event scheduler. Note that class Packet is subclass of class Event
as packets are received and transmitted at some time. And all network components are subclass of
class Handler as they need to handle events such as packets.
The scheduling procedure (void Scheduler::schedule(Handler* h, Event* e, double delay)) is
shown in Figure 2. The event at the head of the event queue is delivered to its hander of some
network object. Then, this network object may call other network object, and finally some new
events are inserted into the event queue.
Figure 2. Discrete Event Scheduler
Example: A and B are two mobile nodes. And A sends packet p to B (suppose they are within the
tx range).
A::send (Packet* p) {target_->recv(p)} //target_ is B; call B::recv
B::recv(Packet*, Handler* h = 0) {
…
Scheduler::instance().schedule(target_, p, tx_time) //target_ is B; schedule the packet at the
// time of (current_time + tx_time)
…
}
Example: Timer is another kind of Event that is handled by TimerHandler
class TimerHandler: public Handler
4. resched(double delay) //the time expires at the time of (current_time + delay)
handle(Event *e){
expire (Event *e) //the virtual handling function overloading by users
}
Note: In ns, NO REAL time, timer, recv, send and packet flows in the sense of UNIX network
programming.
2. 802.11 Implementation
2.1 Physical Layer
Figure 3 Schematic of a mobile node under the CMU Monarch wireless extensions to ns.
Figure 3 shows the network components in the mobile node and the data path of sending and
receiving packets. In this section, we describe the basic function of the physical layer and MAC is
5. detailed in the next section.
Channel (channel.cc)
The function of class Channel is to deliver packets from a wireless node to its neighbors within the
sensing range.
I. Stamp txinfo in the packets before sending:
p->txinfo_.stamp((MobileNode*)node(), ant_->copy(), Pt_, lambda_)
Note: Here node() are the pointer of the sending node, ant_->copy() is the antenna’s parameters
such as the height of the antenna, Pt_ is the transmitting power, and lamba_ is the wavelength of
light. These information is used for the receiving node to calculate the receiving power.
II. Send packets to the nodes within the sensing range distCST_ to be sensed or received by
these nodes.
distCST_ = wifp->getDist(wifp->getCSThresh(), wifp->getPt(), 1.0, 1.0,
highestZ , highestZ, wifp->getL(), wifp->getLambda());
Note: distCST is calculated by the parameters such as CS Threshold, transmission power, antenna
gains, antenna heights, system loss factor, and wavelength of light.
NetIF (wireless-phy.cc)
The function of class WirelessPhy is to send packets to Channel and receive packet from Channel.
I. Packet Sending
channel_->recv(p, this);
II. Packet Reception, sendUp()
//calculate Rx power by path loss models
Pr = propagation_->Pr(&p->txinfo_, &s, this)
if (Pr < CSThresh_) {
pkt_recvd = 0; // cannot hear it
…
}
if (Pr >= CSThresh_ && Pr < RXThresh_){
pkt_recvd = 1;
hdr->error = 1; // error reception, for Carrier Sense
…
}
if (Pr >= RXThresh_) {
pkt_recvd = 1;
hdr->error = 0; // maybe correct reception
…
}
6. Note: First, ns-2 calculates the receiving power Pr by the tx_info_ of p and the receiver this. When
Pr is less than CSThresh_ (Carrier Sense Threshold), the receiver cannot sense it; else, the receiver
can sense it and even receive it without error in the case that Pr > RXThresh_ (Reception
Threshold, and RXThresh_ > CSThresh_). Besides, successful reception also depends on the
packet’s SIR is larger than CPThresh_ (Capture Threshold), which is checked in MAC layer.
2.2 MAC
MAC (mac-802_11.cc)
The function of class Mac802_11 has 2 functions. On sending, it uses CSMA/CA medium access
mechanism; On receiving, it adopts SIRT (SIR Threshold) based reception (Capture).
State Transition Diagram
Figure 4. 802.11 MAC state transition diagram
State transition diagram can help us write or read network programs. Thus, before analyzing
802.11 source codes in ns-2, we first show the reference 802.11 MAC state transition diagram [5]
in Figure 4 that is somewhat different with ns-2. First, we need to find out the basic states.
7. Elementary States
enum MacState {
MAC_IDLE = 0x0000,
MAC_POLLING = 0x0001, // ns 802.11 does not implement Polling
MAC_RECV = 0x0010,
MAC_SEND = 0x0100,
MAC_RTS = 0x0200,
MAC_CTS = 0x0400,
MAC_ACK = 0x0800,
MAC_COLL = 0x1000
};
MacState rx_state_ //can be MAC_IDLE, MAC_RECV, MAC_COLL
MacState tx_state_//can be MAC_IDLE, MAC_SEND, MAC_RTS, MAT_CTS, MAC_ACK
double nav_ //expiration of Network Allocation Vector
//channel is idle
int is_idle() {
if (tx_state_ == MAC_IDLE && rx_state_ == MAC_IDLE
&& nav_ <= NOW)
return 1;
else
return 0;
}
Note: The above is_idle() check whether the channel is idle at the moment when it is called.
MAC Timers
Timers are very important in 802.11 in triggering channel access. The following shows the basic
timers and their functions.
BackoffTimer mhBackoff_
void start(int cw, int idle);// if is_idle(), start to count down; else freeze the timer
void pause(); //freeze the timer when the
void resume(double difs);//resume to count down after DIFS
void handle(Event *); //send RTS or DATA after it times out
int busy(); //Is counting down
DeferTimer mhDefer_
void start(double defer);//start to count down
8. void handle (Event *);//eg. send CTS or ACK after SIFS expires
int busy(); //Is counting down
IFTimer mhIF_; // interface timer, set interface state active when transmitting
NavTimer mhNav_; // NAV timer
RxTimer mhRecv_; //completion of incoming packets, call recvHandler()
TxTimer mhSend_; //sending timeout (e.g. no ACK received), call sendHandler()
Recv/Send functions
void setTxState (MacState newState) //For tx_state_
void setRxState (MacState newState)//For rx_state_
void checkBackoffTimer() {
if(is_idle() && mhBackoff_.paused())
mhBackoff_.resume(phymib_.getDIFS());
if(! is_idle() && mhBackoff_.busy() && ! mhBackoff_.paused())
mhBackoff_.pause();
}
Note: the above sample codes show how receiving and sending will change MAC state and further
control the backoff timer.
/* Note: nav_ expires also mean channel is idle, then call mhBackoff_resume() */
void set_nav(u_int16_t us) {
double now = Scheduler::instance().clock();
double t = us * 1e-6;
if((now + t) > nav_) {
nav_ = now + t;
if(mhNav_.busy())
mhNav_.stop();//reset nav_
mhNav_.start(t);
}
}
Note: NAV timer is set by RTS or CTS to indicate the residual time of data transmission. However,
it is extended in ns-2 to also reflect the residual time before channel becomes idle, and thus can
replace the function of carrier sense. The usage is, update the NAV timer with the transmission
time of either received packets or sensed packets, set_nav (txtime(p)). When NAV timer expires,
navHandler() is called to resume backoff timer.
CSMA/CA
recv function is generally the entry of most network protocols (handling packets from both uplayer
and downlayer). For outgoing packets, it will call send function that is the entry of CSMA/CA.
9. void recv(Packet *p, Handler *h) {
struct hdr_cmn *hdr = HDR_CMN(p);
//handle outgoing packets
if(hdr->direction() == hdr_cmn::DOWN) {
send(p, h); //CSMA/CA
return;
}
…
//else, handle incoming packets
}
void send(Packet *p, Handler *h) {
…
if(mhBackoff_.busy() == 0) {
if(is_idle()) {
if (mhDefer_.busy() == 0) {
/*
* If we are already deferring, there is no
* need to reset the Defer timer.
*/
rTime = (Random::random() % cw_)
* (phymib_.getSlotTime());
mhDefer_.start(phymib_.getDIFS() + rTime);
}
} else {
/*
* If the medium is NOT IDLE, then we start
* the backoff timer.
*/
mhBackoff_.start(cw_, is_idle());
}
}
}
Capture Model
Ns-2 uses a simplified capture model: When multiple packets collide at the receiver, only the first
packet can be successfully received if its Rx Power should be larger than any of the other packets
by at least CPThresh (10dB in ns-2).
void recv(Packet *p, Handler *h){
…
10. //Handle incoming packets
/*
* When there is no packet reception, log receiving p at pktRx_
*/
if(rx_state_ == MAC_IDLE) {
setRxState(MAC_RECV);
pktRx_ = p;
mhRecv_.start(txtime(p));// schedule the reception of this packet in txtime
//setRxState(MAC_IDLE) again after reception.
}
/*
* When there is already a packet reception (in pktRx_), calculate the inference
*/
else {
//Simplified SIR calculation (Comparison of two signals)
if(pktRx_->txinfo_.RxPr / p->txinfo_.RxPr >= p->txinfo_.CPThresh) {
capture(p);//pktRx_ can be correctly received;
//recalculate when the channel will be idle
} else {
collision(p);//stop receving pktRx_ (i.e. mhRecv.stop() )
//recalculate when the channel will be idle
}
}
}
2.3 An example of user extension: Add Fading
r2
r −
The probability density function of Rayleigh fading is pdf ( r ) = e 2σ 2
, where r stands for
σ 2
P
1 −P
Voltage. As Power = c . r2, the probability density function for Power is pdf ( P ) = e , where
P
P stands for Power. And P is the mean of P, that is, Pr by path loss. So, we add the fading
calculation after pass loss calculate Pr ().
#include <random.h>
…
int WirelessPhy::sendUp(Packet *p) {
double Pr;
…
11. if (propagation_) {
s.stamp((MobileNode*)node(), ant_, 0, lambda_);
Pr = propagation_->Pr(&p->txinfo_, &s, this);
/* Add Rayleigh fading (neglect time-correlation)*/
double mean = Pr;
Pr = Random::exponential(mean);
if (Pr < CSThresh_)
…
}
We do two experiments in 11Mbps 802.11 networks to see the impacts of Rayleigh fading. The
default tx power Pt is 0.28, and thus tx range and sensing range are calculated as 250m and 550m.
The first experiment (Figure 5) is to test TCP performance. We vary the distance d from 50m to
250m. Figure 6 shows TCP throughputs as the function of the distance. When d becomes larger,
fading can cause more packet loss and thus reduce TCP throughputs significantly.
Figure 5. TCP under Rayleigh fading (Node 0 sends TCP packets to BS )
Figure 6. TCP Throughputs a function of the distance from BS (a) Without Fading (b) Rayleigh Fading
The second experiment (Figure 7) is to test UDP performance (assume saturate condition). We set
Pt of Node 0 be 10 times of the default Pt (SIR is 10), where Node 0 must capture when its
packets collide with Node 1 at BS suppose there is no fading. As shown in Figure 8, fading
aggravates the unfairness of two senders as their loss rate is dominated by Pt instead of capture,
when d becomes larger.
12. d d
Node 0 BS Node 1
(Pt = 3.0) (Pt = 0.28)
Figure 7. Capture under Rayleigh fading (Node 0 and 1 send CBR packets to BS)
(a)
(b)
Figure 8. UDP Throughputs and Captures/Collisions at a function of the distance from BS (a) Without
Fading (b) Rayleigh Fading
Finally, our simple implementation of fading does not consider the time correlation. For this
feature, please refer to CMU’s fading patch [6].
2.4 Bugs in ns-2
Assumptions
Simulators always need assumptions to make their calculations viable (recall Section 1.1).
However, when some assumptions are crucial in your simulations, you must be careful. For
example, there is no scanning for WLAN (Discovery/Select/Authentication/Association) in ns-2,
mobile nodes are associated with their BS automatically if they have the same pre-defined domain.
If you want to study the overhead of scanning, you should make your extension.
Standard Misinterpretation
13. Ns-2 may misinterpret some network protocols, even standard for it is an open project. For
example, we find ns-2 802.11 implementation seems abuse EIFS (set_nav(usec(phymib_.getEIFS()
+ txtime(p))) // whenever p is error, defer EIFS) [7]. Actually, in Figure 7, the node with Pt 0.28
will has more throughput before we let getEIFS() return 0 to eliminate the effect of EIFS.
3. Reference
[1] The network simulator - ns-2, http://www.isi.edu/nsnam/ns/
[2] The CMU Monarch Project’s Wireless and Mobility Extensions to ns,
http://www.monarch.cs.cmu.edu/
[3] GloMoSim, http://pcl.cs.ucla.edu/projects/glomosim/
[4] Effects of Wireless Physical Layer Modeling in Mobile Ad Hoc Networks, MOBICOM 2001
[5] Ad Hoc Wireless Network, PRENTICE HALL 2004
[6] Additions to the NS network simulator to handle Ricean and Rayleigh fading,
http://www.ece.cmu.edu/wireless/
[7] EIFS, Section 9.2.3.4, ANSI/IEEE Std 802.11, 1999 Edition