Month: September 2016

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Faster WiFi: 802.11ac and 802.11ad

I must be out of touch with WiFi networking. The last thing I remember is when 802.11n came out and supported up to 72 Mbps network speeds. Last year, I think we finally jettisoned our last computing device that was 802.11g. Oh wait, I forgot about my home security system. It still uses an 802.11g 2 GHz network — the same frequency that commonly gets interference from microwave ovens, old bluetooth devices, cordless phones, baby monitors, and more.

While I’ve been “out of touch”, 802.11ac has become available. It operates at 5 Ghz and in most home networks, will run no faster than 800 Mbps. The iPhone 6 and LG Nexus 6 support 802.11ac. The 5 GHz frequency range gets less interference than the 2 GHz range.

In the next few years, WiGig (aka 802.11ad) will become available. It operates in the 60 GHz range, and supports streaming 4K video, and can offer throughput of up to 7 Gbit/s.

I look forward to faster WiFi. In the meantime, when I have the need for speed, I use a wired ethernet connection.

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UPnP, SSDP, mDNS, LLMNR, etc. on the home network

Sometime in the distant past, I was aware of Universal Plug and Play (UPnP), but I didn’t know much about it. It’s a technology that allows devices in the home to talk to each other without prior configuration — it allows auto-discovery and configuration of printers and media servers, among other things.

The auto-discovery happens via SSDP (Simple Service Discovery Protocol). A device joins a network and announces “I’m here!”, and then other device can choose to respond. Even if the device gets a different IP address, it can still be uniquely identified by its unique identifier (UUID).

Here’s more information about UPnP and related protocols that run on the home network:

https://en.wikipedia.org/wiki/Zero-configuration_networking

UPnP:

UPnP protocol (no authentication):

  • Discovery (SSDP)
  • Description – HTTPU and HTTPMU
  • Control
  • Event notification
  • Presentation

UPnP has well defined device profiles for:

  • Audio & Video — DLNA, and

  • Routers:

    • Internet Gateway Device Protocol

    • Retrieve external IP addr

    • Enumerate port mappings
    • Add/Remove port mappings & port forwarding: firewall-hole-punching

  • Devices Profile for Web Services (DPWS)

Other protocols that help on the home network:

  • LLMNR: Link-local Multicast Name Resolution — implemented by Microsoft in Windows.
  • mDNS (multicast DNS) runs on port 5353. Uses .local hostnames.
  • DNS-SD: DNS service discovery. Can use DNS or mDNS.

Apple’s Bonjour uses mDNS and DNS-SD. Linux’s Avahi uses IPv4LL, mDNS, and DNS-SD. Linux’s systemd has “systemd-resolve”, a command-linetool to resolve hostnames on a network via DNS, mDNS, and LMMNR.

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Runtime debugging tools for Linux

Here’s a useful presentation on Linux debugging tools — tools that don’t require source code, additional prints or logging.

http://jvns.ca/blog/2016/09/17/strange-loop-talk/

  • strace has a new flag that I didn’t know about: -y, which prints the paths that are associated with file descriptors.

  • opensnoop lets you see the details of open() calls across the entire system, or for an individual process, or for paths containing certain characters, or it can print the file paths that couldn’t be opened.

  • pgrep shows the stack trace of a running process, which can be useful to get an idea of what a program spends most of its time doing.

  • dstat shows system resource stats. It is a replacement for vmstat, iostat and ifstat.

  • htop — a more beautiful ‘top’, and easier to use. I still mostly use ‘top’ because it is installed by default. Other great tools I use include ‘powertop’ and ‘iotop’.

  • ngrep — an alternative to tcpdump, but allows the use of regexes to match plain-text data in packets.

  • tcpdump — useful when troubleshooting network connections between servers.

  • wireshark — a more UI-friendly tool than tcpdump, with dissectors for most protocols