rtd round trip delay

September 1, 2020

What is Network Round-Trip Delay?

Network Round Trip Delay Impact Application Performance?

Round trip delay (RTD), a.k.a. Round trip time (RTT), or ping time, is the duration of time it takes for a signal to reach its destination across a network and then for an acknowledgment signal to return to the originator. This measurement includes all delays caused by routing, transmission medium, and network traffic. The return signal does not have to follow the same path that the initial signal took.

How do you measure Network Round-Trip Delay?

Using standard ping tools found on most computers, network round trip delay can be tested easily from the command line. The ping time or ping rate is typically measured in milliseconds (ms). The standard ping is measured for either Round Trip Time (RTT) or Time to First Byte (TTFB). RTT is the total time it takes for a data packet to go from the client and return from the server, and it is the standard reporting measurement. TTFB is the time it takes for the server to get the first byte of client data, and should be half the time as RTT on the same path.

Application Performance and Network Round Trip Delay

Impact of RTT on Application Performance

Round trip delay is closely related to network latency. RTD is the measure on which network latency and network jitter are calculated, and because of this, it shares the same impacts that latency and jitter have on quality of service (QoS). As RTD increases so does network latency, and as the variance between RTDs in a transmission increases so does the jitter.

What are the factors that impact Round-Trip Delay (RTD)?

• Transmission Medium—Network traffic speed is limited by the physical connections that it travels through. Because a signal can only travel as fast as the medium of transport allows, understanding the slowest and fastest mediums along a signals route becomes crucial in controlling RTD. For example, fiber optic cable is roughly 100x faster than coax cable, and over greater distances mostly fiber optic is used. However, leading into most homes, some variation of metal cable is used for the internet. This means, at these points of medium change, we can expect there to be transmission delays as signal slows down to when passing from fiber optic to travel across the copper medium. Further, inside the home or office, the signal may then be sent to computers via wifi, changing medium once again.
• Local Area Network Traffic—Local network traffic causes congestion which can bottleneck the network. This directly impacts both transmitting and receiving signals from connected devices. For example, the use of streaming services by multiple devices on the same network will cause congestion, but for other users trying to send and receive transmissions they may experience increases in RTD.
• Server Response Time—On the opposite side of a transmission from the requesting user is the server response. How quickly a server can respond to a request will impact the RTD. In fact, this is a classic attack by cybercriminals, known as a denial-of-service attack (DoS) when a server is flooded by requests in order to overload it and either stall access or deny it completely. Based on this example, the main principle for servers is the number of requests it must attend to, the greater the amount, the more likely it will impact RTD .
• Internet Routing And Congestion—Perhaps the aspect affecting round trip delay that is least controlled by IT departments is the routing of a signal across the internet. A signal travels from sender to receiver and back through a route that will pass through any number of nodes along the internet. Each node has its own network traffic that the signal must pass through, which factors into the RTD calculation. Generally the greater number of nodes that the signal travels through the more congestion it must contend with and ultimately the longer the signal will take.
• Physical Distance Of Transmission—Closely related to the transmission medium, the physical distance a signal must travel to reach its destination is limited by the laws of physics and the speed of light. In most long distance transmissions, fiber optics use light to send massive amounts of data efficiently, but even that is not instantaneous.

Related Terms

Network Latency

Network latency is the duration of time it takes a data packet to travel from its source to its destination across a network. In terms of user experience, network latency translates to how fast a user’s action produces a response from a network, say how quick a web page accesses and loads over the internet, or the responsiveness of an online game to the gamer’s commands.

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RTD (Round Trip Delay)

Round Trip Delay (RTD) refers to the total time taken for a signal or data packet to travel from a source to a destination and then back again. It is a measure of the latency or delay experienced in a round trip communication between two points in a network.

RTD is typically measured in milliseconds (ms) or microseconds (μs) and is influenced by several factors, including:

• Propagation Delay: This is the time it takes for a signal to travel from the source to the destination. It depends on the distance between the two points and the speed of propagation in the medium through which the signal is transmitted. For example, in a fiber optic network, the propagation delay is relatively low due to the high speed of light in the optical fiber.
• Transmission Delay: This is the time taken to transmit the data over the network. It depends on the data rate (bandwidth) of the network connection. Higher bandwidth connections can transmit data faster, reducing the transmission delay.
• Processing Delay: This is the time taken by network devices, such as routers or switches, to process the data packets. It includes the time for packet forwarding, routing table lookups, and any other operations performed by the network devices.
• Queuing Delay: In a congested network, data packets may experience queuing delay when they are waiting in a buffer or queue to be transmitted. The queuing delay depends on the network congestion level and the priority given to different types of traffic.

To measure RTD, a device typically sends a test packet or a signal to the destination and measures the time it takes for the packet to return. This can be done using various tools or protocols, such as Internet Control Message Protocol (ICMP) ping or round-trip time (RTT) measurements in network monitoring tools.

RTD is an important metric for assessing network performance and quality of service. It is particularly critical in real-time applications, such as voice and video communication or online gaming, where low latency is crucial for a smooth user experience. High RTD can result in delays, packet loss, or degraded performance, affecting the overall quality of communication or application responsiveness.

Network administrators and engineers monitor RTD to identify and troubleshoot performance issues, optimize network configurations, or select the most suitable network paths or service providers for their requirements.

Improved Preamble Detection and Round-Trip Delay Estimation for Random Access in High-Mobility Airborne Communication Systems

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Implementing High-Speed Double-Data Rate (DDR) SDRAM Controllers on FPGA

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• Eduardo Picatoste-Olloqui 19 ,
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• Atilà Herms-Berenguer 20  

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This paper deals with the FPGA-implementation of a high-speed interface for DDR SDRAMs. We aim to achieve a performance, in terms of bandwidth, comparable to ASIC implementations. The novelty of this paper is to present the design techniques that lead to high performance memory controllers. First of all, we compile the specific hardware features available in FPGA families. In the second place, we depict a memory interface data path architecture adapted for implementation on Xilinx and Altera FPGAs. Finally, we explain the design rules to meet timing requirements (round trip delay) for successful operation. The discussion is complemented with timing measurements for a Virtex-II based memory interface and with timing calculations performed for Stratix.

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Ryan, K.: DDR SDRAM Functionality and Controller Read Data Capture. Micron Design Line 8(3) (1999)

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JEDEC: JEDEC Standard Double Data Rate (DDR) SDRAM Specification, JESD79. Available on-line (2002)

Altera Corp.: DDR SDRAM Controller MegaCore Function User Guide. Available on-line (2004)

Northwest Logic: DDR SDRAM Controller. Datasheet. Available on-line (2004)

Tran, J.: Synthesizable DDR SDRAM Controller. Xilinx Application Note XAPP200. Available on-line (2003)

Altera Corp.: Using the Stratix and Stratix GX DDR Round Trip Delay (RTD) Calculator. Available from Altera under request (2003)

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Hewlett-Packard, R&D Technology Lab., Digital ASICs, 08174, Sant Cugat del Valles (Barcelona), Spain

Eduardo Picatoste-Olloqui, Francisco Cardells-Tormo & Jordi Sempere-Agullo

Department of Electronics, University of Barcelona (UB), Marti i Franques 1, 08028, Barcelona, Spain

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Picatoste-Olloqui, E., Cardells-Tormo, F., Sempere-Agullo, J., Herms-Berenguer, A. (2004). Implementing High-Speed Double-Data Rate (DDR) SDRAM Controllers on FPGA. In: Becker, J., Platzner, M., Vernalde, S. (eds) Field Programmable Logic and Application. FPL 2004. Lecture Notes in Computer Science, vol 3203. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-30117-2_30

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Using RTD to analyze your Wi-Fi Networks and fix slow Wi-Fi

Feb 5, 2020

Henrique salvador, product bytes.

Recently, I started receiving alerts from Domotz that several devices were coming offline and online every few minutes. After some quick investigating, I realized that all the alerts were associated with devices that were connected to my Wi-Fi network and are located in my living room.

Ah ok… makes sense. I’ve always thought those are devices were a little too far away from my Access Point!

Domotz Round Trip Delay to the rescue

I opened the Domotz app, navigated to a smart plug that’s in my living room and noticed the RTD (Round Trip Delay) charts.

All devices had a higher latency starting on Sunday, even showing packet loss , which was not normal for some of the devices.

How I fixed my offline devices using RTD to analyze the Wi-Fi Network

The next day I changed my Wi-Fi channel and noticed a significant improvement.

On Monday night I checked the network to make sure that I had chosen the Wi-Fi channels correctly. I scanned my network using the Wi-Fi Analyzer and found that a neighbour of mine had overlapped the channels I was using before! Without Domotz I would never have figured that out. This is a huge benefit of Domotz real-time alerts and having the Domotz platform continually monitor the network .

Even after changing channels I decided to take things one step further, hoping I could improve the network even more. That week I added a new, additional AP in the room. Looking back at my Round Trip Delay chart, everything seems to be working much better now:

Even the tests with iPerf 3 have improved significantly with the new AP, see here before and after:

Sure, I may be a bit biased as a Domotz employee, this is the amazing value of having Domotz monitor my network and using the Round Trip Delay feature. Without Domotz I would not have seen this issue, and struggled to find a fix!

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