Respan Dataset Explorer

I need the numbers

As mentioned before, there is no one-size-fits-all answer for the percentage of out-of-order packets in Wi-Fi networks due to the myriad variables involved. However, to give some rough numbers, in a well-maintained and non-congested Wi-Fi environment, the percentage of out-of-order packets can be expected to be quite low:

- **Optimal Conditions**: Under ideal circumstances with strong signal strength and minimal interference, the out-of-order packet percentage could be below 1%.
  
- **Typical Use**: In typical usage scenarios with some interference from other devices and physical obstructions, the out-of-order packet percentage might range from 1% to 3%.

- **High Interference or Poor Conditions**: In environments with significant interference, weak signals, or heavy network traffic, the out-of-order packet percentage could climb higher, potentially ranging between 5% and 10%.

Please note that these figures are estimates and can vary widely based on the factors affecting the wireless environment. Additionally, modern Wi-Fi standards and technologies include mechanisms to reduce the impact of out-of-order packets, such as block acknowledgment and frame aggregation in 802.11n (Wi-Fi 4) and later standards, which help enhance overall network reliability.

For accurate measurements, you'd have to analyze the specific Wi-Fi network in question using network diagnostics tools that can capture and analyze traffic patterns, such as Wireshark or specialized wireless performance monitoring software. These tools can give you the exact percentage of out-of-order packets over a given time and under specific network loads and conditions.

Is out of order packet amount correlates with packet loss?

Out-of-order packet delivery can correlate with packet loss in TCP networks, but the two are not equivalent and one does not necessarily directly cause the other. Here's how they can be related:

1. **Symptoms of Similar Problems**: Both out-of-order packet delivery and packet loss can be symptoms of issues such as network congestion, link quality problems, or changes in the network path. For example, if packets are being routed along multiple paths with varying latencies, you might experience both out-of-order packets (due to different travel times) and packet loss (if one path is more prone to errors or congestion).

2. **Retransmissions**: A TCP sender will retransmit a packet if it doesn't receive an acknowledgment within a certain window of time—assuming the packet is lost. These retransmissions can sometimes be received out of order, particularly if the original packet was not actually lost but rather delayed and arrives after its retransmitted copy.

3. **Packet Loss Recovery**: When TCP recovers from packet loss, the reordering of packets can occur. As packets are retransmitted, the order in which they are received by the receiver may not match the order in which they were sent, especially if subsequent packets bypass the delayed ones.

4. **Flow Control and Congestion Avoidance**: Both mechanisms in TCP can be involved when dealing with packet loss and may indirectly affect packet ordering. For instance, TCP's congestion control algorithms may slow down the sending rate after detecting packet loss, which can also temporarily lead to out-of-order packets until the network stabilizes.

However, it is also entirely possible to observe out-of-order packets without any actual packet loss:

- **Packet Reordering**: Packets can be reordered because of network elements like multi-layer switches performing uneven load balancing or due to different path lengths when packets are routed through a network.

In a well-constructed network with minimal interference and congestion, out-of-order packets are typically rare, as are packet losses. In networks with higher latencies, such as satellite communications, or in congested wireless environments, you might see an increase in both out-of-order packet delivery and packet loss.

In summary, while there can be a correlation between out-of-order packets and packet loss because both can result from similar network issues, the presence of one does not always indicate the presence of the other. Network engineers often distinguish between these two phenomena when diagnosing and addressing network performance issues.

I need a percentage of the correlation in different cases, can you give me these numbers?

Determining a specific percentage that represents the correlation between out-of-order packet delivery and packet loss across various cases is challenging without empirical data from real-world networks. The correlation will be affected by the unique conditions and configurations of each network, making it difficult to generalize across different cases with a single set of statistics.

However, I can describe different scenarios and discuss how they might influence the relationship between out-of-order packet delivery and packet loss:

1. **High-Quality Wired Networks**: In reliable and well-configured wired networks (such as a corporate LAN), you might experience very low packet loss (close to 0%) and out-of-order packets might also be a rare occurrence. The correlation here could be non-existent or negligible.

2. **Wi-Fi and Other Wireless Networks**: Wireless networks are more prone to interference, which can contribute to both packet loss and out-of-order packets. You might see a low to moderate correlation, depending on the level of signal interference, as mild interference might cause packets to arrive out of order without being lost.

3. **Mobile Networks**: Mobile networks (3G, 4G/LTE, 5G) are highly variable due to factors like user mobility, signal quality, and network congestion. In these networks, out-of-order packet delivery might correlate more strongly with packet loss, particularly in congested or low-signal areas.

4. **Satellite Communications**: Due to the long round-trip times, retransmission delay in case of packet loss might increase the likelihood of out-of-order packets. However, sophisticated error-correction mechanisms are usually in place, and the correlation between packet loss and out-of-order packets may depend heavily on the specific system's design and the external conditions affecting the signal.

5. **High-Performance Networks with Advanced Traffic Management**: Networks that use traffic shaping, load balancing, or advanced routing techniques such as MPLS might experience very low packet loss alongside a very low incidence of out-of-order packets, leading to a low correlation between the two.

In summary, the correlation between out-of-order packet delivery and packet loss can vary broadly, and assigning a specific percentage to these correlations would be speculative without concrete data. In practice, precise correlation percentages are determined by network engineers and researchers who conduct thorough analyses on networks using various tools and methodologies to collect data specific to the environment under study. If a reliable percentage is required, it may be necessary to perform targeted network assessments and analyses or to review detailed performance reports provided by networking equipment vendors or research studies conducted in similar settings.

Can I use kevent function on iPhone?

Yes, you can use the `kevent` function on iPhone within the constraints of Apple's APIs available for iOS. The `kevent` function is part of the BSD kernel's kqueue event notification mechanism, which is available on iOS as it's based on Darwin, the UNIX-like system that underpins both macOS and iOS.

The kqueue/kevent system allows for asynchronous event notifications on various types of objects, including file descriptors, processes, and signals, which can be used to build efficient, non-blocking I/O operations in an application.

However, it's essential to understand that while you have access to `kevent` and related APIs for development, there are some restrictions on iOS in terms of what you can do with these APIs compared to macOS or other UNIX-like systems. For example, sandboxing on iOS imposes limitations on file system access and inter-process communication, which may restrict how you leverage the `kevent` function.

To use `kevent` on iOS, you would generally be working with network sockets or monitoring local resources that your app has access to adhere to Apple's App Store guidelines and the sandboxing environment of iOS.

Lastly, if you're developing for iOS, using higher-level abstractions like Grand Central Dispatch (GCD) or the Network framework might be more appropriate for most use cases. Apple often recommends using these abstractions as they are easier to work with and provide a more "Cocoa-like" feel while taking advantage of the underlying system capabilities, including kqueue and kevent, in an optimized way. GCD, in particular, provides an easy way to work with asynchronous events and may internally use kqueue for efficiency.

In summary, you can use the `kevent` function on iPhone, but you should be aware of the iOS environment's limitations and prefer to use higher-level iOS frameworks when possible.

What's latest version of Darwin? in what year its last update?

As of my last update in early 2023, information about the latest version of Darwin, which is the core operating system that is a subset of macOS and is also shared by iOS, iPadOS, tvOS, and watchOS, might not be current. However, Apple typically updates Darwin with each major release of its operating systems.

The version of Darwin typically corresponds to the version of macOS. For instance, macOS Big Sur (11.x) was running on Darwin 20, and macOS Monterey (12.x) was based on Darwin 21. The most recent publicly available version of macOS is macOS Ventura, released in October 2022, and it would be based on a newer version of Darwin, likely Darwin 22.

Apple doesn't always prominently advertise the version number of Darwin itself, and the updates to Darwin come as part of the updates to macOS. To find the specific version of Darwin running on a Mac:

1. Open the Terminal application.
2. Type the command: `uname -r` and press Enter.

This will output the release number of the Darwin kernel that's running on the system. The output is typically a set of numbers separated by dots (e.g., 21.4.0).

To check the latest version of iOS, you can go to Settings > General > Software Update on an iOS device. Since iOS is based on the same core as macOS, it receives updates in parallel with macOS, and its Darwin core is updated accordingly. For transparency, Apple also releases source code for components of Darwin on its open source website, but the updates here might lag behind the actual releases within macOS or iOS: https://opensource.apple.com/

Please note that this information might be outdated depending on when you are checking. For the most current version and update year of Darwin, you would need to look at the latest release information for macOS or iOS at the time of your inquiry.

Can I download and installed Darwin?

Darwin is the open source Unix-like base for macOS, iOS, and other Apple operating systems, but it is not available as a standalone, installable operating system that you can download and install like you might with Linux distributions or FreeBSD.

However, Apple does release portions of the Darwin source code to the public, which can be found at the Apple Open Source website (https://opensource.apple.com/). This includes the source for components like the XNU kernel, Bonjour networking, and other foundational elements of the operating system.

For those interested in a Unix-like experience similar to macOS, there are a few paths to explore:

1. **PureDarwin**: PureDarwin is a community project that aims to make a bootable and usable version of the open source components from Darwin. As it strives to be binary compatible with macOS, it uses the same open source components provided by Apple. While the project exists, it may not be up to date with the latest versions, and its usability as an everyday operating system might be limited. You can check their project page for more information and downloads (http://www.puredarwin.org/).

2. **macOS**: If you're interested in the full experience with the graphical user interface, you need to use an actual version of macOS, which is available only on Apple's Mac hardware or in a virtual environment within the terms of Apple's software licensing agreement.

3. **Linux or BSD**: For those who want a free open source UNIX-like system with wider support, Linux or FreeBSD could be an alternative. While not the same as Darwin, they share many Unix principles, utilities, and a similar command-line experience.

In summary, while you cannot directly download and install Darwin as a complete, ready-to-use operating system, you can work with the available open source parts, contribute to or experiment with projects like PureDarwin, or choose a related Unix-like operating system for a similar experience.

Does PureDarwin have sufficient set of drivers?

As of my last knowledge update in early 2023, PureDarwin faced significant challenges in terms of driver support. The PureDarwin project aims to create an operating system from the open source components released by Apple as part of Darwin. However, Apple does not open-source many of the drivers, especially those for specific hardware like graphics cards, network devices, and other peripherals that are used in Mac computers. The lack of these proprietary drivers is a significant hurdle for PureDarwin and any similar projects attempting to create a fully functional system based on Darwin sources.

Consequently, PureDarwin may not have a complete set of drivers necessary to support a wide range of hardware. Generic drivers and those that have been open-sourced can be used to provide basic functionality, but advanced features enabled by proprietary drivers on macOS are typically lacking.

Driver support for things like advanced graphics acceleration, certain Wi-Fi chipsets, power management, and specialty hardware is usually limited. This can result in PureDarwin being more suitable for experimental purposes or for running on a limited range of hardware with basic capabilities, rather than as a daily driver operating system.

For up-to-date information, it would be necessary to check the PureDarwin project's official documentation or repositories to see what progress might have been made regarding driver support. If you're considering using PureDarwin on specific hardware, you should look into the project's community forums or contact contributors to understand the current state of hardware compatibility.

What lf net.ipv4.tcp_notsent_lowat is 1 and is 0??

The `net.ipv4.tcp_notsent_lowat` is a Linux kernel parameter that specifies the threshold at which the TCP stack makes a writable callback to the socket layer for transmission queue ("not sent queue") data that has not yet been sent on the network. This writable callback is used by non-blocking sockets when they have been previously unable to send data (e.g., the send buffer was full).

Here's the difference between setting `net.ipv4.tcp_notsent_lowat` to 1 and to 0:

1. **When `net.ipv4.tcp_notsent_lowat` is set to 1**:
   - This means that the kernel will wait until there is at least 1 byte of unsent data in the TCP send queue before it triggers a writable callback. This setting allows for very low latency notifications to the application that it can send more data without necessarily waiting for the whole send buffer to be emptied or the application request for the send buffer's state. The goal is to optimize the application's network throughput by notifying it as soon as it can send additional data, even though it can result in more frequent wake-ups and potentially smaller writes.
   
2. **When `net.ipv4.tcp_notsent_lowat` is set to 0**:
   - The zero value is treated as a special case. When set to 0, it essentially disables the low watermark feature, and the TCP stack will fall back to its standard behavior of notifying the application only when there's a significant amount of space available in the send buffer (by default, when the number of available bytes is greater than or equal to the socket's `SO_SNDLOWAT` option, which often defaults to 2048). This reduces the frequency of wakeup events for applications waiting to send data, but it may introduce more latency before an application is notified that it can send more data.

Changing the value of `net.ipv4.tcp_notsent_lowat` can affect the trade-offs between performance (throughput and latency) and application wakeup (CPU utilization). It is generally an advanced setting that should be modified only when you have specific requirements or when tuning the system for particular application behaviors or network characteristics.

For applications sensitive to wake-up latency that have their sockets in non-blocking mode or using asynchronous I/O, setting `net.ipv4.tcp_notsent_lowat` to a low non-zero value can be beneficial. However, for most general use cases, the default value (which is typically treated as disabled) should suffice without needing to alter this parameter.

Are you sure?

Apologies for the confusion. It looks like I made an error in my explanation. Let's clarify the functionality of the `net.ipv4.tcp_notsent_lowat` kernel parameter.

The `net.ipv4.tcp_notsent_lowat` parameter, introduced in the Linux kernel, sets a threshold for the number of bytes pending transmission (data written to the socket by the application but not yet acknowledged by the receiver) at which the networking stack should wake up applications polling for write events on the socket.

The behavior is as follows:

- **When `net.ipv4.tcp_notsent_lowat` is set to 0**: This effectively disables the feature, and the system will not trigger the writable event based on unacked but not sent data. Instead, it will use the available space in the queue as the trigger. The application will be woken up when there's more room in the send queue.

- **When `net.ipv4.tcp_notsent_lowat` is set to a value greater than 0**: The feature is enabled, and the application will be woken up for sending more data when the amount of outstanding but not yet sent data drops below the configured threshold. For example, setting it to 1 means that if there is at least one byte of capacity in the send queue, the application will be woken up to write more data to the socket.

The practical effect of setting `net.ipv4.tcp_notsent_lowat` to a low positive value is that it can reduce the latency for the application to send data at the cost of potentially more frequent wake-ups, increased CPU usage, and smaller send operations. It can be beneficial for applications that require low-latency network communications.

Bear in mind that tuning these parameters should be done carefully, as the specific effect may vary depending on the particular workload and network conditions. It is recommended to perform thorough testing to ensure that any changes to network parameters result in the desired performance improvements without unintended side effects.

If net.ipv4.tcp_notsent_lowat=1 then if there is 1 unsent byte that the buffer is available for writing?

No, that's incorrect. I apologize for the previous confusion. Let me clarify what `net.ipv4.tcp_notsent_lowat` represents once more.

The `net.ipv4.tcp_notsent_lowat` parameter is not about the amount of space available in the send buffer, but rather the amount of data that is written to the send buffer by the application but has not yet been sent or is not yet in flight (i.e., data that has not been transmitted or for which the transmission has not yet been confirmed).

When `net.ipv4.tcp_notsent_lowat` is set to a value, such as 1, this indicates the amount of unsent data that must be reached before the write poll (epoll or select call) is woken up. So if you set it to 1:

- If there are already unsent bytes equal to or greater than `tcp_notsent_lowat`, the application's write poll won't be woken up.
- If there are fewer unsent bytes than the value of `tcp_notsent_lowat` (i.e., 0 unsent bytes when `tcp_notsent_lowat` is set to 1), the application's write poll will be woken up so that it can write more data to the socket.

This means that, with `net.ipv4.tcp_notsent_lowat` set to 1, the kernel will wake up polling on the socket whenever the amount of data that has been queued but not yet sent by TCP falls below this threshold, indicating that the application can send more data without waiting for a large amount of free space to become available.

Setting `net.ipv4.tcp_notsent_lowat` to 1 helps reduce latency for transmitting data at the cost of potentially increased system calls, which could impact CPU usage. However, it should be adjusted according to the needs of the application and after careful consideration since the setting might not be ideal for every scenario.