OpenVLC is an open-source, software-defined, flexible, low-cost Visible Light Communication platform. The software solution is implemented as a Linux driver that can communicate directly with the cape and the Linux networking stack.Visible Light Communication, sometimes also referred to as “LiFi" uses standard off-the-shelf visible light LEDs to transmit data using the visible light spectrum.
Enabling secure management and distribution of live, linear and on demand video, Video Cloud migrates traditional broadcast transmission, cloud based media management, security and online streaming capabilities into a scalable, cloud-based alternative to traditional premise-based video delivery architectures.
Enabling secure management and distribution of live, linear and on demand video, Video Cloud migrates traditional broadcast transmission, cloud based media management, security and online streaming capabilities into a scalable, cloud-based alternative to traditional premise-based video delivery architectures.
This is a technical training presentation on the renewed satcom Newtec DVB-S2 Calculator v2.17 and covers:
- DVB-S
- DVB-S2
- S2 Extensions
For all current Azimuth, Elevation and MDM series (both demods and modems) and includes Sat3Play terminals.
Officially launched beginning of June 2013, this DVB-S2 calculator replaces its widely spread predecessor (which had over 7,000 downloads).
To download the calculator: http://www.newtec.eu/services-training/dvb-s2-calculator
In this webinar presentation, presented on May 8, 2012, Steven Soenens from Newtec talked about :
Delivering uptime and quality of service:
- built in MPEG Transport Steam Analyzer
- Carrier ID insertion in the Network Information Table (NIT)
Bandwidth efficiency optimization technologies:
- Automated Equalink® predistortion, providing up to 10% bandwidth gain
- Clean Channel TechnologyTM, improving efficiency by up to 15%
Future-proof solutions:
- easy upgrade from ASI to GbE, from IF-band to L-band
- DVB-S2 extensions and RF Carrier ID - capabilities are anticipated to become available
Learn more about Newtec Dialog release 1.2 along with two reference cases
Newtec were hosting an info session at IBC2015 to introduce an updated version of its multiservice platform Newtec Dialog which guarantees optimal modulation and bandwidth allocation, whether it is being used for broadcast, enterprise, mobility or HTS networks.
This session was enriched by our partners from Intelsat and Network Innovations, talking about their service offerings based on Newtec Dialog.
Speakers:
- Main Newtec Speaker: Kevin McCarthy, VP of Market Development
- Reference with Guest Speaker from Intelsat (IntelsatOne Prism): Peter Ostapiuk, Head of Media Product Services
- Reference with Guest Speakers from Network Innovations (MAVERICK): John Stoltz, Vice President, Media & Enterprise
For more information visit our website www.newtec.eu
Visible light communication (vlc) systemsCKSunith1
The attached narrated power point presentation attempts to explain the working principle, block diagram, layer model, standards, advantages, disadvantages and modulation schemes as applicable to Visible Light Communication Systems (VLC). The material will be useful for KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
The attached narrated power point presentation classifies Optical Wireless Communication Systems into indoor and outdoor system types and throws light on the visible spectrum used for optical communications. Block diagram and working principle of Visible Light Communication Systems (VLC) , Architecture and Layer Model of VLC as well as the different modulation schemes used for VLC are also discussed. The material will be useful for KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
This is a technical training presentation on the renewed satcom Newtec DVB-S2 Calculator v2.17 and covers:
- DVB-S
- DVB-S2
- S2 Extensions
For all current Azimuth, Elevation and MDM series (both demods and modems) and includes Sat3Play terminals.
Officially launched beginning of June 2013, this DVB-S2 calculator replaces its widely spread predecessor (which had over 7,000 downloads).
To download the calculator: http://www.newtec.eu/services-training/dvb-s2-calculator
In this webinar presentation, presented on May 8, 2012, Steven Soenens from Newtec talked about :
Delivering uptime and quality of service:
- built in MPEG Transport Steam Analyzer
- Carrier ID insertion in the Network Information Table (NIT)
Bandwidth efficiency optimization technologies:
- Automated Equalink® predistortion, providing up to 10% bandwidth gain
- Clean Channel TechnologyTM, improving efficiency by up to 15%
Future-proof solutions:
- easy upgrade from ASI to GbE, from IF-band to L-band
- DVB-S2 extensions and RF Carrier ID - capabilities are anticipated to become available
Learn more about Newtec Dialog release 1.2 along with two reference cases
Newtec were hosting an info session at IBC2015 to introduce an updated version of its multiservice platform Newtec Dialog which guarantees optimal modulation and bandwidth allocation, whether it is being used for broadcast, enterprise, mobility or HTS networks.
This session was enriched by our partners from Intelsat and Network Innovations, talking about their service offerings based on Newtec Dialog.
Speakers:
- Main Newtec Speaker: Kevin McCarthy, VP of Market Development
- Reference with Guest Speaker from Intelsat (IntelsatOne Prism): Peter Ostapiuk, Head of Media Product Services
- Reference with Guest Speakers from Network Innovations (MAVERICK): John Stoltz, Vice President, Media & Enterprise
For more information visit our website www.newtec.eu
Visible light communication (vlc) systemsCKSunith1
The attached narrated power point presentation attempts to explain the working principle, block diagram, layer model, standards, advantages, disadvantages and modulation schemes as applicable to Visible Light Communication Systems (VLC). The material will be useful for KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
The attached narrated power point presentation classifies Optical Wireless Communication Systems into indoor and outdoor system types and throws light on the visible spectrum used for optical communications. Block diagram and working principle of Visible Light Communication Systems (VLC) , Architecture and Layer Model of VLC as well as the different modulation schemes used for VLC are also discussed. The material will be useful for KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
Marco Canini
TU Berlin / Telekom Innovation Labs
Research Track Part 1
ONS2015: http://bit.ly/ons2015sd
ONS Inspire! Webinars: http://bit.ly/oiw-sd
Watch the talk (video) on ONS Content Archives: http://bit.ly/ons-archives-sd
Ultra sonic sensor network communicating using NRF 24L01 radioAshok Raj
• Designed mixed signal circuit for ultrasonic sensor network using Arduino shield as programmed processor and NRF24L01 as the radio, PAMAS protocol was used for better efficiency.
• Software used: Arduino
Information Technology
Rrjeta Kompjuterike. Computer Networks.
Vetëm për qëllime edukative. For Educational Purposes Only.
NOTE: Some text does not display correctly (behind image) because SlideShare deformed it during upload.
Disa nga tekstet nuk duket mire apo duken mas fotove ketu ka faj SlideShare.
9.) audio video ethernet (avb cobra net dante)Jeff Green
Replacing a crossbar switch with ‘virtual’ IP packet switching - The ability to expand video-over-IP systems ‘one piece at a time’ and the decentralized nature of the matrix makes the technology very compelling for any size or scope of AV project.. AV-over-IP is the transport of AV signals over a standard Ethernet network, including…
HD Video (e.g. HDMI, DVI)
Audio
Control Signals (e.g. IR)
Peripheral Signals (e.g. USB)
Does Dante require special switches? No. We strongly recommend that Gigabit switches be used due to the clear advantages in performance and scalability.
Does Dante require a dedicated network infrastructure? No, a dedicated network infrastructure is not required. Dante-enabled devices can happily coexist with other equipment making use of the network, such as general purpose PCs sending and receiving email and other data.
Does Dante require any special network infrastructure? No, special network infrastructure is not required. Since Dante is based upon universally accepted networking standards, Dante-enabled devices can be connected using inexpensive off-the-shelf Ethernet switches and cabling.
What features are important when purchasing a switch? Dante makes use of standard Voice over IP (VoIP) Quality of Service (QoS) switch features, to prioritize clock sync and audio traffic over other network traffic. VoIP QoS features are available in a variety of inexpensive and enterprise Ethernet switches. Any switches with the following features should be appropriate for use with Dante:
Gigabit ports for inter-switch connections
Quality of Service (QoS) with 4 queues
Diffserv (DSCP) QoS, with strict priority
Totally new to AV over IT? This may help. If you have worked with any of the popular protocols, your time is better spent in other sessions. AV over IT methods vary in application of OSI model. Audio Networking - One RJ45 and CAT5 cable for dozens of signal paths. Switches can provide hardware time stamping which allows synchronization, offsets, and corrections. All covered in IEEE 1588.
Ethernet Timing & Priority Standards - All audio over Ethernet protocols require Priority, Sequence, & Sync
Differentiated Services / Quality of Service (DiffServ, QoS)
Priority by data type (Clock Sync and Audio Packets over Email)
Traffic prioritized based upon tags in IP Header (Layer 3)
Priority number assigned by manage switch to each packet
Real-time Transport Protocol (RTP)
Keeps data sequenced in the right order
Time stamp on UDP header
Works with RTCP (Real Time Control Protocol) for QoS and Sync
Variation: RTSP (Real Time Streaming Protocol) works on TCP and not UDP
Does not reserve resources or provide for quality of service
Precision Timing Protocol (PTP)
IEEE 1588
Sub-microsecond accuracy to synchronize subnets
Layer 2 - Switches provide hardware-based time stamping
Kirill Tsym discusses Vector Packet Processing:
* Linux Kernel data path (in short), initial design, today's situation, optimization initiatives
* Brief overview of DPDK, Netmap, etc.
* Userspace Networking projects comparison: OpenFastPath, OpenSwitch, VPP.
* Introduction to VPP: architecture, capabilities and optimization techniques.
* Basic Data Flow and introduction to vectors.
* VPP Single and Multi-thread modes.
* Router and switch for namespaces example.
* VPP L4 protocol processing - Transport Layer Development Kit.
* VPP Plugins.
Kiril is a software developer at Check Point Software Technologies, part of Next Generation Gateway and Architecture team, developing proof of concept around DPDK and FD.IO VPP. He has years of experience in software, Linux kernel and networking development and has worked for Polycom, Broadcom and Qualcomm before joining Check Point.
GridMate - End to end testing is a critical piece to ensure quality and avoid...ThomasParaiso2
End to end testing is a critical piece to ensure quality and avoid regressions. In this session, we share our journey building an E2E testing pipeline for GridMate components (LWC and Aura) using Cypress, JSForce, FakerJS…
Why You Should Replace Windows 11 with Nitrux Linux 3.5.0 for enhanced perfor...SOFTTECHHUB
The choice of an operating system plays a pivotal role in shaping our computing experience. For decades, Microsoft's Windows has dominated the market, offering a familiar and widely adopted platform for personal and professional use. However, as technological advancements continue to push the boundaries of innovation, alternative operating systems have emerged, challenging the status quo and offering users a fresh perspective on computing.
One such alternative that has garnered significant attention and acclaim is Nitrux Linux 3.5.0, a sleek, powerful, and user-friendly Linux distribution that promises to redefine the way we interact with our devices. With its focus on performance, security, and customization, Nitrux Linux presents a compelling case for those seeking to break free from the constraints of proprietary software and embrace the freedom and flexibility of open-source computing.
Dr. Sean Tan, Head of Data Science, Changi Airport Group
Discover how Changi Airport Group (CAG) leverages graph technologies and generative AI to revolutionize their search capabilities. This session delves into the unique search needs of CAG’s diverse passengers and customers, showcasing how graph data structures enhance the accuracy and relevance of AI-generated search results, mitigating the risk of “hallucinations” and improving the overall customer journey.
Epistemic Interaction - tuning interfaces to provide information for AI supportAlan Dix
Paper presented at SYNERGY workshop at AVI 2024, Genoa, Italy. 3rd June 2024
https://alandix.com/academic/papers/synergy2024-epistemic/
As machine learning integrates deeper into human-computer interactions, the concept of epistemic interaction emerges, aiming to refine these interactions to enhance system adaptability. This approach encourages minor, intentional adjustments in user behaviour to enrich the data available for system learning. This paper introduces epistemic interaction within the context of human-system communication, illustrating how deliberate interaction design can improve system understanding and adaptation. Through concrete examples, we demonstrate the potential of epistemic interaction to significantly advance human-computer interaction by leveraging intuitive human communication strategies to inform system design and functionality, offering a novel pathway for enriching user-system engagements.
In his public lecture, Christian Timmerer provides insights into the fascinating history of video streaming, starting from its humble beginnings before YouTube to the groundbreaking technologies that now dominate platforms like Netflix and ORF ON. Timmerer also presents provocative contributions of his own that have significantly influenced the industry. He concludes by looking at future challenges and invites the audience to join in a discussion.
PHP Frameworks: I want to break free (IPC Berlin 2024)Ralf Eggert
In this presentation, we examine the challenges and limitations of relying too heavily on PHP frameworks in web development. We discuss the history of PHP and its frameworks to understand how this dependence has evolved. The focus will be on providing concrete tips and strategies to reduce reliance on these frameworks, based on real-world examples and practical considerations. The goal is to equip developers with the skills and knowledge to create more flexible and future-proof web applications. We'll explore the importance of maintaining autonomy in a rapidly changing tech landscape and how to make informed decisions in PHP development.
This talk is aimed at encouraging a more independent approach to using PHP frameworks, moving towards a more flexible and future-proof approach to PHP development.
GDG Cloud Southlake #33: Boule & Rebala: Effective AppSec in SDLC using Deplo...James Anderson
Effective Application Security in Software Delivery lifecycle using Deployment Firewall and DBOM
The modern software delivery process (or the CI/CD process) includes many tools, distributed teams, open-source code, and cloud platforms. Constant focus on speed to release software to market, along with the traditional slow and manual security checks has caused gaps in continuous security as an important piece in the software supply chain. Today organizations feel more susceptible to external and internal cyber threats due to the vast attack surface in their applications supply chain and the lack of end-to-end governance and risk management.
The software team must secure its software delivery process to avoid vulnerability and security breaches. This needs to be achieved with existing tool chains and without extensive rework of the delivery processes. This talk will present strategies and techniques for providing visibility into the true risk of the existing vulnerabilities, preventing the introduction of security issues in the software, resolving vulnerabilities in production environments quickly, and capturing the deployment bill of materials (DBOM).
Speakers:
Bob Boule
Robert Boule is a technology enthusiast with PASSION for technology and making things work along with a knack for helping others understand how things work. He comes with around 20 years of solution engineering experience in application security, software continuous delivery, and SaaS platforms. He is known for his dynamic presentations in CI/CD and application security integrated in software delivery lifecycle.
Gopinath Rebala
Gopinath Rebala is the CTO of OpsMx, where he has overall responsibility for the machine learning and data processing architectures for Secure Software Delivery. Gopi also has a strong connection with our customers, leading design and architecture for strategic implementations. Gopi is a frequent speaker and well-known leader in continuous delivery and integrating security into software delivery.
Observability Concepts EVERY Developer Should Know -- DeveloperWeek Europe.pdfPaige Cruz
Monitoring and observability aren’t traditionally found in software curriculums and many of us cobble this knowledge together from whatever vendor or ecosystem we were first introduced to and whatever is a part of your current company’s observability stack.
While the dev and ops silo continues to crumble….many organizations still relegate monitoring & observability as the purview of ops, infra and SRE teams. This is a mistake - achieving a highly observable system requires collaboration up and down the stack.
I, a former op, would like to extend an invitation to all application developers to join the observability party will share these foundational concepts to build on:
Unlocking Productivity: Leveraging the Potential of Copilot in Microsoft 365, a presentation by Christoforos Vlachos, Senior Solutions Manager – Modern Workplace, Uni Systems
Elevating Tactical DDD Patterns Through Object CalisthenicsDorra BARTAGUIZ
After immersing yourself in the blue book and its red counterpart, attending DDD-focused conferences, and applying tactical patterns, you're left with a crucial question: How do I ensure my design is effective? Tactical patterns within Domain-Driven Design (DDD) serve as guiding principles for creating clear and manageable domain models. However, achieving success with these patterns requires additional guidance. Interestingly, we've observed that a set of constraints initially designed for training purposes remarkably aligns with effective pattern implementation, offering a more ‘mechanical’ approach. Let's explore together how Object Calisthenics can elevate the design of your tactical DDD patterns, offering concrete help for those venturing into DDD for the first time!
LF Energy Webinar: Electrical Grid Modelling and Simulation Through PowSyBl -...DanBrown980551
Do you want to learn how to model and simulate an electrical network from scratch in under an hour?
Then welcome to this PowSyBl workshop, hosted by Rte, the French Transmission System Operator (TSO)!
During the webinar, you will discover the PowSyBl ecosystem as well as handle and study an electrical network through an interactive Python notebook.
PowSyBl is an open source project hosted by LF Energy, which offers a comprehensive set of features for electrical grid modelling and simulation. Among other advanced features, PowSyBl provides:
- A fully editable and extendable library for grid component modelling;
- Visualization tools to display your network;
- Grid simulation tools, such as power flows, security analyses (with or without remedial actions) and sensitivity analyses;
The framework is mostly written in Java, with a Python binding so that Python developers can access PowSyBl functionalities as well.
What you will learn during the webinar:
- For beginners: discover PowSyBl's functionalities through a quick general presentation and the notebook, without needing any expert coding skills;
- For advanced developers: master the skills to efficiently apply PowSyBl functionalities to your real-world scenarios.
GraphSummit Singapore | The Art of the Possible with Graph - Q2 2024Neo4j
Neha Bajwa, Vice President of Product Marketing, Neo4j
Join us as we explore breakthrough innovations enabled by interconnected data and AI. Discover firsthand how organizations use relationships in data to uncover contextual insights and solve our most pressing challenges – from optimizing supply chains, detecting fraud, and improving customer experiences to accelerating drug discoveries.
Threats to mobile devices are more prevalent and increasing in scope and complexity. Users of mobile devices desire to take full advantage of the features
available on those devices, but many of the features provide convenience and capability but sacrifice security. This best practices guide outlines steps the users can take to better protect personal devices and information.
2. OpenVLC
• Linux based Open-source, software-defined, flexible, low-cost Visible
Light Communication platform
• Developed by IMDEA Networks Institute, and the project is co-led by
Prof. Domenico Giustiniano and by Dr. Qing Wang
3. OpenVLC…
• OpenVLC Mission
– The lack of an open-source reference platform for VLC networks is hindering the
progress of the research community
– A general-purpose platform would add momentum to VLC research and would open
up new avenues of VLC research and spark the interest of researchers and
engineers.
– IMDEA Networks Institute take an initial step toward the design of OpenVLC, an
open-source software-defined VLC platform for fast prototyping of new system
protocols to build a LiFi network
– Cost-effective yet powerful credit-card-sized embedded board.
4. VLC
• Visible Light Communication (VLC), sometimes also referred to as
“LiFi" uses standard off-the-shelf visible light LEDs to transmit data
using the visible light spectrum
• VLC is receiving strong attention from the designers of the 5G
networks and beyond
• VLC can enable new pervasive wireless systems in the context of
Internet of Things.
5. OpenVLC Components
• The software solution is implemented as a Linux driver that can communicate
directly with the cape and the Linux networking stack
• In OpenVLC, the VLC interface is set up as a new communication interface
that can take advantage of the vast range of Linux tools.
• OpenVLC Components are,
– BEAGLEBONE Black (BBB) Board (needs Rev C; to use the high-power LED in the cape,
you need to connect an external 5V power supply to the BBB): cost $ 45- $ 60; AM3359
1GHz CPU, 4 timers, 65 GPIOs
– OpenVLC1.1 cape: the VLC front-end
– OpenVLC1.1 driver: software defined PHY and MAC layer, implemented as a Linux driver
8. OpenVLC Design Flexibility
• OpenVLC cape (front-end transceiver) includes
three optical components:
– a low-power LED
– a high-power LED,
– and a photodiode (PD)
• The low-power LED can be reused for both the
transmitting and receiving of light signals
• Design has been proved to be resilient to ambient
light interference without additional electronic
processing
• Another advantage of exploiting the low-power LED
for reception rather than adding a PD is the lower
cost of LEDs Compared to photodiodes.
9. OpenVLC Software Defined Solution
• The software-defined transmitter (TX) selector
can choose the TX between the low-power
LED and the high-power LED
• The software-defined receiver (RX) selector
can select the RX between the PD and the
low-power LED
• The low-power LED can be reused for both
the transmitting and receiving of light signals
• Primitives are implemented to build various
PHY and MAC layer protocols in the Linux
operating system.
10. OpenVLC Software Defined Solution…
• VLC can be a valuable component to RF
Communication
• Developed based on IEEE 802.15.7 standard
• IEEE 802.15.7 standard specifies three PHY layers,
which support data rate varying from 11:67 kb/s to
96 Mb/s short range communication
• Photodiodes used as a receiver or a reverse-biased
LED (rather than a photodiode) is used as a receiver
to implement a bidirectional LED-to-LED
communication
• Studied and designed with the fundamental issues
of the design of a low-complexity embedded
solution, such as efficient collision detection MAC
protocol and light flicker elimination.
VLC Communication Network
11. OpenVLC Software Defined Solution…
• Bidirectional Communication
– OpenVLC's front-end transceiver reuses the same
LED for both transmitting and receiving light signals
– An advantage of exploiting the LED for reception
rather than adding a photodiode is the lower cost of
LEDs compared to photodiodes
– Permits to reduce the design complexity and increase
the resilience to ambient (e.g., sun light) noise without
additional signal processing.
– OpenVLC Platform includes a TransConductance
Amplifier (TCA) for transmission, a TransImpedance
Amplifier (TIA) and an Analog-to-Digital Converter
(ADC) for reception, a tristate-output buffer, and
ancillary circuitry for transmission and reception.
Diagram of the OpenVLC platform
12. OpenVLC Software Defined Solution…
• A software-defined Transmitter (TX)/Receiver
(RX) switch is used to change the LED operation
mode between TX and RX through the GPIO pins:
– In TX Mode
▫ The buffer is enabled and encoded signals are first
amplified by the TCA and then fed to the forward-biased
LED
– In RX Mode
▫ In RX mode, the buffer is disabled to avoid current
leakages to the TCA circuitry, and the light signal is
received by the reverse-biased LED
▫ The small photocurrent is then amplified by the TIA
▫ Finally, an ADC converts the output analog signals to
digital signals, which are then sent to the decoder through
the Serial Peripheral Interface (SPI)
Diagram of the OpenVLC platform
13. OpenVLC Software Defined Solution…
• Software-Defined PHY Layer
– The software stack of OpenVLC is illustrated in
OpenVLC Network Stack
– Primitives are implemented to build various PHY and
MAC layer protocols in the Linux operating system.
– TX, RX and TX/RX switching
▫ In TX mode, the BBB outputs the signal to be
transmitted to the anode of LED for a symbol period of
T
▫ In RX mode, the small photo-current is amplified by
the TIA and then sampled by the ADC and converted
into a digital signal. The BBB samples the output of
the ADC at fixed intervals of T.
OpenVLC Network Stack
14. OpenVLC Software Defined Solution…
• Software-Defined PHY Layer
– The TX and RX mode through a software-
defined controller running on the BBB
▫ Implemented primitives write_to_led(symbol)
and read_from_adc() to transmit and receive
one symbol, respectively
– The LED switches between TX and RX mode
through a software-defined controller running
on the BBB
▫ Implemented prim-itives switch_to_tx() and
switch_to_rx() allow to switch the LED between
TX and RX mode.
OpenVLC Network Stack
15. OpenVLC Software Defined Solution…
• Modulation and Detection
– Adopt intensity modulation for data transmission
– Binary information is mapped to the presence
(symbol HIGH) or absence (symbol LOW) of the
visible light carrier
– At the transmitter, we use the On-OFF
Keying (OOK) modulation and the Manchester Run
Length Limited (RLL) code
– Therefore, bit 1 is mapped to symbol sequence
LOW-HIGH, and bit 0 is mapped to HIGH-LOW
– At the receiver, demodulation is performed with
direct detection. Based on received signal's
voltage, the receiver detects received signal as the
sequence of symbols HIGH and LOW that are then
converted to binary data.
16. OpenVLC Software Defined Solution…
• Preamble
– The PHY layer transmits each frame with a fixed-length preamble, consisting of an alternate
sequence of HIGH and LOW starting with a HIGH symbol
– The numbers of HIGH and LOW symbols in the preamble are the same
– To convert symbols into binary data, an adaptive symbol detection threshold is adopted
– The threshold has to be adaptive because the received light intensity is greatly affected by
the free path loss attenuation of light transmitted from the TX to the RX
– This detection threshold is obtained on a per-frame basis by averaging out the digital
samples of the preamble sequence
– The end of the preamble is marked by a Special Frame Delimiter (SFD).
17. OpenVLC Software Defined Solution…
• Software-Defined MAC Layer
– The MAC layer generates two types of frames
▫ DATA frames and Acknowledgement (ACK) frames
– The frame contains the payload length (Length) of this frame.
If the frame has no payload (i.e., Length=0), it is inferred to
be an ACK. Otherwise, it is recognized as a DATA frame.
– The Length field takes 1 byte and each frame carries a
payload varying from 0 to 255 bytes
– The destination address (Dst) and source address (Src)
follow the Length field and each occupies 2 bytes
– The 2-byte field Protocol identifies the upper layer protocol
encapsulated in the frame payload
– Fields from the Length to the Protocol form the MAC header
– A two-byte Cyclic Redundancy Check (CRC) over the MAC
header and frame payload is appended to the end of each
frame.
18. OpenVLC Software Defined Solution…
• Software-Defined MAC Layer – Carrier Sensing
– Wireless MAC protocols usually employ carrier sensing to
reduce collisions
– In OpenVLC platform, provides two type of carrier sensing
▫ Basic sensing and fast sensing
– Both are implemented in the PHY layer and can be invoked
by the MAC layer
– In basic sensing
▫ The platform reads a certain number of continuous symbols
▫ The channel is assessed to be busy if one or more symbols are
detected as HIGH symbols
▫ Otherwise it is assessed to be clear
– In fast sensing
▫ operates on per symbol basis
▫ The channel is assessed to be clear if the symbol is detected as LOW,
or else it is assessed to be busy
▫ Provides primitives basic_sensing() and fast_sensing() to perform basic
and fast sensing, respectively
19. OpenVLC Software Defined Solution…
• Software-Defined MAC Layer – MAC Access Protocol
– Employed the contention-based Carrier Sensing Multiple
Access/Collision Detection (CSMA/CD) MAC protocol to ensure fair
channel access among all VLC nodes and reduce the impact of
collisions
– When a frame is available for transmission, the MAC first calls the
basic sensing of the PHY layer and then the frame is transmitted
immediately if the PHY layer reports the channel is clear
– When the channel is assessed to be busy, the MAC starts a backoff
counter
– The counter is initialized with an integer value randomly drawn from a
uniform distribution within the range (0, CW-1].
– The contention window CW is initialized as CWmin, where CWmin is the
smallest
– The PHY layer keeps sensing the channel and each time the channel is
assessed to be clear, the counter is decremented
– The frame is transmitted when the counter reaches zero.
20. OpenVLC Software Defined Solution…
• Software-Defined MAC Layer – MAC Access Protocol
– Upon frame transmission, the transmitter can engage in fast sensing. This
occurs when the transmitter sends a LOW symbol of the Manchester code, as
it powers down the LED and is therefore able to switch the LED to RX mode to
receive a symbol
– The received symbol is sufficient for fast sensing and afterwards, the LED is
switched back to TX mode to carry on the transmission
– The transmitter alternates between TX and RX mode during data transmission
– If the transmitter detects a collision, i.e., the channel is assessed to be busy
through fast sensing for no less than Bfs times, the ongoing transmission is
immediately interrupted
– The illustration of the backoff mechanism, basic sensing, and fast sensing in
CSMA/CD
– After successfully receiving a frame, the receiver sends an ACK to the
transmitter
– If the transmitter has not received an ACK within the timeout, it retransmits the
frame and doubles the CW (until it reaches a pre-defined CWmax threshold
that denotes the maximal size of the contention window)
– The frame is dropped when a pre-defined number of retransmissions fail.
21. OpenVLC Software Defined Solution…
• Software-Defined MAC Layer – Interfacing with the Internet Layer
– Implement the MAC protocol as well as part of the PHY layer as a new driver of the Linux
operating system
– The MAC protocol will become transparent to various applications if it can connect with
the Internet layer
– Implement two primitive functions vlc_mac_tx(skb) and vlc_mac_rx(vlc_pkt).
– The vlc_mac_tx(skb) is called by the Internet layer to move packets to the MAC layer,
where are enqueued and wait for transmission scheduling
– The vlc_mac_rx(vlc_pkt) receives packets from the PHY layer, checks their protocols,
and decides whether or not to send them to the Internet layer
– By invoking these two functions, any MAC protocols can easily interact with the Internet
layer.