Teaching from Home: Network Support Perspectives

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ABSTRACT

CoViD-19 has fundamentally changed teaching and learning from K-12 schools to colleges and universities around the world, where many instructors have to deliver their lectures, tutorials and even labs from their home, through the Internet. A lot of challenges are encountered due to the sudden and massive move to online teaching, for education institutions, educators and support staff, and students and their parents. In this paper, we examine the challenges of ``teaching from home'' with the viewpoint of information technology (IT) education in general and computer network support in particular, and offer some suggestions through our experience in Spring and Summer 2020 with input from IT support professionals, to create the very needed discussion among educators on this timely topic, which can be useful for Fall 2020 and beyond. Online teaching may become a considerable mode of course delivery in the post-pandemic era, even without another similar event.

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multi-link wired and multi-hop wireless networks

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3 NETWORK TECHNOLOGIES INVOLVED

3.1 Host Computers

Most online conferencing, lecturing and meeting (CLM, e.g., Blackboard, WebEx, Zoom, etc) tools can run as a standalone application (normally requires download and installation on Windows, MacOS and Linux desktop or laptop computers), or an app (light-weight application on portable devices such as iOS and Android tablet computers or smart phones), or even in a Web browser (without additional download and installation and thus operating systems, OS, independent). Besides user preferences, here we are concerned about their impact on the network support for online teaching.

3.1.1 Desktop, Laptop or Tablet?

The choice of desktop, laptop or tablet computers for online teaching is mainly device availability and user preferences. Different educational institutions may have different policies to bring institutional equipment home for work or teaching, and some educators have to use their personal devices. Most desktop computers come with Ethernet network interface controller (NIC), for wired network connectivity most common in workplace. At home, Ethernet wall socket may not be available, so alternate wires (see Section 3.2.2) or wireless (Section 3.2.3) interfaces and adapters are needed. For laptop computers, most of them come with WiFi interfaces for mobility, but WiFi coverage may vary at home and have high interference from neighbors (see Section 3.2.3). Some old laptops may have Ethernet NIC embedded, and for newer ones, external Ethernet or additional WiFi adapters via PCMCIA or USB ports are also feasible. Tablet computers are very convenient for annotation during online lecturing, and most of them only have embedded WiFi and some may have cellular Internet capabilities (e.g., through 4G or the upcoming 5G mobile communication systems). For tablets and smartphones, external Ethernet interface may be possible through dedicated adapters with micro-USB, Lightning or USB-C connectors. The form factor further affects the sensitivity of internal antennas, as well as human body (hand and grip gestures) shadowing effect on WiFi signals.

recommendation: a laptop (with battery and mains connected, in case of any power outage) with external monitor and wired ethernet adapters, for audio, video broadcasting and screen sharing, and optionally a touch-screen tablet or phone to tune in and receive the broadcast for quality monitoring and finger/stylus annotation

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3.1.2 Windows, Mac OS or Linux?

Windows, MacOS and Linux, and their tablet and smartphone counterparts such as iOS and Android, all have the capability of being connected to the Internet through the standard TCP/IP protocol stack. Again, the choice for teaching is mainly personal preferences but dependent on the device availability. From the viewpoint of network support, all these mainstream operating systems come with some network diagnosis tools, such as ping for end-host reachability and traceroute (or tracert on Windows) to discover the routing path. More advanced tools (e.g., tcpdump to capture packets and observe protocol interactions) with better user interface (wireshark) are also available with additional packages or installation, e.g., Windows or MacOS Network or Wireless Diagnostics. Popular network performance testing websites, e.g., speedtest.net, further allow users to check their achievable download and upload throughput and ping time to one of available test servers (often auto-selected by testing websites according to the user location and server availability and load) through any web browser, thus OS independent and convenient. These tools are useful for teachers at home too.

e.g.,

Code: Select all

ping 8.8.8.8
traceroute 8.8.8.8

to google dns server for network liveness and connectivity and http://speedtest.net for network performance

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3.1.3 Other Necessary Peripherals

Besides host computers running online CLM tools, instructors may choose to use wireless camera (for multi-view), headset (microphone with in or on-ear buds) and in-hand presenters to enrich their presentation. Many of these devices use either Bluetooth, WiFi or proprietary radio technologies, but often in the same license-free channels as WiFi, which may cause some extra noise and interference. Also many of these devices are powered by batteries, and use power-saving techniques extensively to reduce the need of frequent recharging, at the cost of additional delay for audio and video, increasing the mouth-to-ear delay and variation (e.g., voice cutoff or skipping at the beginning of a talk spurt). Whenever possible, wired connectivity (e.g., by USB) of such peripherals to host computer is preferred, especially when the host computer relies on WiFi for Internet access.

e.g., https://www.reviewgeek.com/38434/why-do ... %20earbuds.

In the end, Bluetooth headphones and earbuds experience at least 32ms of audio latency. But that’s only in ideal circumstances. You’re more likely to run into a 100-300ms delay, especially while using true wireless earbuds.

not an issue for enjoying/watching incoming audio/video

Thankfully, that 100-500ms delay time isn’t a death-blow for watching video, so long as your headphones and phone (or computer) support the Bluetooth 5.0 audio standard.

but can be a killer for audio/video/lecture broadcasting, especially with live interaction too

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3.2 Home Networks

As the “last-meter” technology, home network is responsible to interconnect home computers and connect them to the Internet.

3.2.1 Ethernet Structured Wiring

Ethernet is the most preferred way of constructing local-area computer networks (LAN), and universally adopted in workplace such as office and commercial buildings. It also becomes common in newly-built houses and apartment buildings. Wherever Ethernet is available, it is highly recommended to host computers for reliability and consistency. Even if the host computer does not have an Ethernet interface, various Ethernet adapters are available for different desktop, laptop and tablet computers and smart phones. However, for most existing houses, Ethernet wiring is not available, and it is very expensive and cumbersome to retrofit for Ethernet structured wiring. Thus, the following options can be considered and are in fact more widely used at home.

how many people have (real) ethernet (with structured wiring) at home?

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3.2.2 No-New-Wires Home Backbone

Most existing houses have telephone and television cables wired and sockets installed in some if not all rooms on different floors. Regardless, almost all rooms have power line and outlets for electricity. IP television (IPTV) at the beginning of this century has witnessed the booming of the so-called no-new-wires (NNW) technologies, to transport Ethernet frames over telephone, television and electricity wires, through an extra adapter connected to computers by wired or wireless Ethernet or USB. Older adapters and technologies only allow networking over a given type of wires, e.g., HPNA for telephone wires, MoCA for coaxial cables and HomePlug for power lines, and the connectivity is limited, so is the capacity, as each kind of these wires shares their capacity, sometimes even with neighbors. The newer adapters following the G.hn standards can run over different wires, and some even multiple (different kinds of) wires, greatly improving availability and capacity. However, when compared with the switched Ethernet, MoCA is still the second choice due to the high noise,interference and collision in the house as shown in Figure 2.

https://en.wikipedia.org/wiki/HomePNA https://en.wikipedia.org/wiki/HomePlug https://en.wikipedia.org/wiki/Multimedi ... x_Alliance also just fyi---not associated with these websites or endorsing any products at all https://www.google.com/search?q=hpna+adapters https://10-0-0-0-1.org/reviews/moca-adapters/

Best MoCA Adapters of 2020 – Complete Round-up

https://www.techradar.com/news/the-best ... e-adaptors

Best powerline adapter 2020: The best HomePlug kits

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3.2.3 Wireless Home Network

WiFi probably is the most common home network technology preferred by many users, especially due to the support for portability and mobility. However, running on 2.4GHz license-free industrial, scientific and medical (ISM) and 5GHz unlicensed wireless channels also means WiFi has to compete with other WiFi and household devices such as cordless phones, microwave ovens and baby monitors. Particularly the high-power microwave ovens running in 2.4GHz frequency bands can easily kill any ongoing WiFi or Bluetooth sessions, as shown in Figure 2 around ping#30 for WiFi 2.4GHz, despite various techniques to avoid so. For office buildings, WiFi access points (AP) and channel allocation have been carefully surveyed and arranged, so the interference between nearby APs is minimized. However, in a home environment, WiFi AP is collocated with Internet service provider (ISP)’s modem, depending on the location of point of entry to a house. A single WiFi AP often cannot have an adequate coverage for the entire house, especially when the AP is located at a corner of a house where the modem is located. Even worse, users can easily find many WiFi APs around their house by a simple channel scan, as shown in Figure 4, some even stronger than their own (e.g., Cable and DSL-2.4GHz and 5GHz). Certain coordination with neighbors is possible but not always feasible. Compared with Ethernet, WiFi has much higher delay and more variation as shown in Figure 2. We will focus on how to address this problem in Section 4.1, which is one of the two main technical contributions of this paper.

Figure 2: Ping from host to WiFi AP vs Ethernet or MoCA.

ping-wifi-moca-hppa-eth.gif (17.55 KiB) Viewed 9242 times

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3.3 Internet Access

The “last-mile” ISPs are responsible to provide Internet connectivity to end users. Based on the communication infrastructure that ISPs use, common consumer-market Internet access technologies are summarized below and further compared for online teaching.

3.3.1 Fiber, Cellular or Satellite?

Fiber optics are the most common communication medium used by the Internet backbone and commercial Internet access networks commonly found in business organizations, education institutions and government agencies,mainly due to its high capacity and cost, often associated with the need to lay down the fiber optical cable. Fiber to the node, curb, building and home (FTTN/C/B/H, or FTTx) starts to appear on the consumer market, especially in some countries with emerging economy and highly-concentrated population. However, it is still not readily available in many places around the world at consumer level, other than some pilot projects such as Google Fiber. Cellular coverage is almost ubiquitous in urban and suburban areas, but the high cost of data plans in many countries still limits it to an emergency replacement or backup only for home Internet access. Similar concerns are for satellite-based Internet access.

anyone has got their starlink tested? https://www.starlink.com/ please share some results here as well

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3.3.2 Telephone Service Providers

DSL through telephone service providers is one of two most common home Internet access technologies. Initially designed to carry voice traffic with limited bandwidth and data rate, unshielded twisted pairs (UTP) are the most common wires from telephone companies to customer premises in local loop. Dial-up modem was the first widely adopted Internet access technology, followed by DSL where larger bandwidth is freed over shorter distance through the same UTP wires with limited capacity and susceptible to electromagnetic noise and interference. However, due to the wide availability of dedicated telephone wires to most houses, DSL is still very popular, although some telephone companies are now motivated to bring fiber optics to consumers in selected markets. DSL is less likely affected by neighbors.

to be exact by being affected by neighbors https://www.speedguide.net/faq/is-dsl-d ... dwidth-136

Is DSL dedicated, while Cable modems shared bandwidth ?

A common misconception is that residential DSL is dedicated bandwidth, while Cable modems provide shared medium.

This is only partly true - for the segment between you and the ISP's central office, and that is rarely the bottleneck of the connection. From the Central Office out to the Internet, both Cable and DSL share your ISP's backbones, whatever they are. Residential broadband is oversubscribed, whether cable or DSL - usually with 20+ times as many subscribers as the maximum backbone capacity. Since your ISP's backbones and peering arrangements are often the bottleneck of the connection, and it is shared medium, both residential DSL and Cable may experience slowdowns at peak times.

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3.3.3 Television Service Providers

Coaxial cables due to its shield construction and thus much wider bandwidth and better electromagnetic properties, were initially used for cable TV broadcasting.With the booming of the Internet, television service providers also upgraded their infrastructure with bidirectional power amplifiers and hybrid fiber-cable (HFC) networks to provide Internet services. Due to the large link bandwidth, cable modem (CM) often can provide higher data rates than their DSL competitors. On the other hand, neighbors do share the same drop cable, and thus the band-width and achievable throughput can vary significantly.

As shown in Figure 3, DSL has smaller delay and less variation than Cable modem, as the latter is indeed affected by neighbors. Compared with Figure 2, the “last-mile” delay around 10ms is actually smaller and more stable than the “last-meter” in-home WiFi.

Figure 3: Ping from home to first ISP router: Cable vs DSL.

ping-cable-dsl.gif (9.72 KiB) Viewed 9237 times

https://www.highspeedinternet.com/resou ... y%20faster.

DSL vs. Cable: Which Is Right for You?

https://measuringbroadbandamerica.com/

Measuring Broadband America

https://crtc.gc.ca/eng/internet/proj.htm

Broadband Measurement Project (Canada)

https://www.fastmetrics.com/internet-co ... ountry.php

Internet Speeds by Country (Mbps)

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4 IMPROVEMENT FOR ONLINE TEACHING

Based on the summary and comparison of existing technologies above, in this section we focus on how to improve WiFi home networks and leverage both DSL and CM ISPs for reliability.

4.1 WiFi Interference Avoidance

Many home Internet access issues are actually the problem caused by WiFi networks at home. Service providers often advise their customers to troubleshoot their Internet access problems with a wired Ethernet cable to their so-called modem, AP or router. A ping and traceroute can easily identified the additional delay caused by home WiFi networks, due to the poor coverage and severe interference. The following approaches can address these issues with the technologies already existing in most homes.

4.1.1A Better (Al)located WiFi AP

As analyzed above, WiFi home networks have two major issues: coverage and interference. Most DSL or cable modems come with an IEEE 802.11a/b/g/n/ac WiFi AP running in 2.4GHz and 5GHz, with 20, 40 or 80MHz-wide channels. Normally speaking, the higher the operation frequency, more and wider channels available, and shorter the transmission range at the same transmission power due to more signal attenuation (path loss), as shown in Figure 4 with received power in dBm as a quality (Q) indicator, so higher Q for 2.4GHz channels (1 to 14) than 5GHz ones (36 to 165). Thus, the choice of operation frequency and communication channel depends on the location of WiFi AP and host computer for online teaching, as well as the nearby appliances (particularly microwave ovens) and neighbor APs. Many newer APs allow them to “automatically” select a channel based on observation, and some and third-parties (e.g., WiFi Analyzer) offer tools to survey and visualize wireless channels to help consumers choose a less congested channel with stronger signals, e.g., the purposely spaced out 5GHz channels in Figure 4. Nevertheless, a single WiFi AP, as the default setting for many users (channel 1, 11, 40 and 140), still suffers the whole-house coverage and interference problems.

Figure 4: Home WiFi signals in 2.4GHz and 5GHz channels.

channel-scan.jpg (159.21 KiB) Viewed 9233 times

https://play.google.com/store/apps/deta ... i.analyzer

Wifi Analyzer – Apps on Google Play

and many similar apps/tools too

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4.1.2 Wired Interconnected WiFi APs

For some houses, a single WiFi AP is not sufficient to cover the entire house well, especially when the DSL or cable modem is at one corner of the house. To improve the coverage, multiple WiFi APs at different locations can be deployed and interconnected by Ethernet cables if available through the LAN ports of these APs, which is very similar to the setting in workplace. If Ethernet is not available, NNW in Section 3.2.2 can be used, as shown in Figure 1. With multiple WiFi APs, certain coordination is needed to designate one as the Internet gateway to the outside world with DSL or cable modem, and other APs running in access point mode only, with coordinated addressing and routing if multiple subnets exist. On the other hand, these WiFi APs can run in different channels to minimize the interference among themselves. Instructors can choose the best operation frequency and channel for their host computer. This is often the best home network configuration. Unfortunately, Ethernet is not always available and NNW can introduce delay variation and security concerns.

wifi roaming at workplace? e.g., https://support.apple.com/en-ca/HT203068

About wireless roaming for enterprise
Learn about how devices running iOS and iPadOS roam in an enterprise Wi-Fi environment.

This article is intended for system administrators for a school, business, or other organization.

you can have it at home too

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4.1.3 Wireless Interconnected WiFi APs

On the other hand, when neither Ethernet nor NNW links are available, WiFi APs can be interconnected without wires through wireless distribution system (WDS) [7], which is equivalent to a wired home network backbone. Such approach is often used in cellular systems to interconnect BSs in their wireless backhaul network. Not all DSL or cable modems with integrated AP support WDS in their stock firmware, but many off-the-shelf consumer WiFi APs, especially those powered by OpenWRT and DD-WRT, can be easily configured to support WDS and have more advanced and flexible configuration. Due to the wireless interconnection, further attention on channel selection is needed to avoid the interference between the home backbone and access networks. By associating to nearby APs, WDS offers a smooth roaming experience, similar to a wired backbone.

https://en.wikipedia.org/wiki/Wireless_ ... ion_system

A wireless distribution system (WDS) is a system enabling the wireless bridging of access points in an IEEE 802 network. It allows an extended network to be created using wireless IEEE 802.11 (Wi-Fi) access points without the traditional requirement for wires to link them. The notable advantage of WDS over other solutions is that it preserves the MAC addresses of client frames across links between access points, thus mixtures of ethernet and WDS connections can be treated as a single network.

https://openwrt.org/docs/guide-user/net ... figuration

Wi-Fi extender / repeater / bridge configuration

https://wiki.dd-wrt.com/wiki/index.php/ ... er_network

WDS Linked Router Network

also "mesh" as well

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4.2 WAN Reliability Augmentation

Both consumer-grade DSL and cable Internet access services suffer reliability issues, far below what fiber optics can offer in commercial workplace. For instructors to lose connection to the Internet, even briefly or intermittently, is unacceptable for a potentially large group of students during lectures. In the following, we examine and compare DSL and CM-based Internet access, and the possibility to leverage both ISPs when feasible to improve reliability.

4.2.1 DSL vs Cable Modem

As discussed in Section 3.3.2 and 3.3.3, DSL and cable both have their pros and cons. DSL is not affected by neighbors but has limited bandwidth and is more susceptible to noise and interference. CM has more bandwidth but has to share the capacity with neighbors, especially for the uplink. E.g., an advertised 25/5Mbps (for down and uplink, respectively) DSL plan only achieves a 3Mbps uplink, but the ping time from the DSL modem to the first DSL ISP router is lower and more stable due to the dedicated uplink. An advertised 50/5Mbps CM plan can achieve a 59Mbps downlink during off-peak hours, but its ping time to the first CM ISP router is a bit higher and highly variable due to the shared capacity, as shown in Figure 3. According to most CLM platforms, a 500kbps uplink is sufficient for a standard-definition video stream, which is well accommodated by most DSL and CMlinks, but delay and loss affect the live video streaming much more.

However, from the DSL and CM ISP networks to CLM data centers, depending on how and where CLM providers deploy their services, the varying bandwidth and delay can cause additional QoS fluctuation, as illustrated in Table 1 with traceroute to a public enhanced DNS server. In terms of reliability, both DSL and CM can vary by providers and regions, the cable plant and supporting infrastructures. Consumer-grade ISPs and plans also have routine maintenance and unexpected outage without guaranteed backup and recovery allowed by their service agreement. Thus, relying on one DSL or CM service provider is often not sufficient for high reliability. Paying higher cost for a business service plan is an option, but in the following we explore other more flexible alternatives.

Table 1: Traceroute from home to 1.1.1.1: Cable vs DSL ISP

traceroute-1.jpg (33.37 KiB) Viewed 9227 times

your mileage may vary with your service providers on what they advertise vs deliver