Networking

Data-Link Layer

Data-Link (Layer 2)

• Groups Data into frames (layer 3 - packets)
• Responsible for point-to-point communications
• Each point is called a 'node.' Nodes aren't always computers. They can be Fitbits, routers, light switches, and more.

Layer 2 Protocols

• Ethernet (wired/WiFi)
• USB (Universal Serial Bus)
• Bluetooth
• CAN-Bus (Cars and industrial equipment)
• I2C (Communication in-circuit)

Data-Link Sublayers

• Media Access Control (MAC)
• Logical Link Control (LLC - not used much now, allowed TCP/IP to share the line with other protocols)

Network Topology

Point-to-Point

Network Topology

Line

Network Topology

Bus

Network Topology

Ring

Network Topology

Star

Network Topology

Star - Reality

Network Topology

Mesh (one hop)

Network Topology

Fully Connected

Media Access Control

• Carrier Sense Multiple Access with Collision Detection
• CSMA/CD
• Older wired Ethernet works this way.
• Wi-Fi works this way
• Listen, see if anyone is talking. If no one is, talk.
• Detect if another node started talking. If so, stop, wait random time, try again.
• Like normal talking.

Media Access Control

• Early in networking, engineers said "Let people talk when they want to? That's crazy! Must be more formal."
• Token-Ring competed with Ethernet
• A 'token' was passed around a ring topology, and only the node with the token could talk.
• Like a 'speaking stick'
• Good in 'real-time' systems, as Ethernet could have unpredictable delays.

Media Access Control

• Avoiding collisions with Ethernet?
• In wired communications, use a 'star' topology. No shared media, no collisions.

Data-Link Protocols

• A protocol is an exact agreement on how we pass data
• Anyone following the protocol should be able to communicate with anyone else following that same protocol.
• If a lot of people use a protocol, it is called a standard protocol, or just standard.
• Opens competition. For example, any vendor can make devices that hook up to WiFi.

Data-Link Protocols

• Wired Networks - Ethernet standards grouped under IEEE 802.3
• WiFi - Ethernet standards grouped under IEEE 802.11
• Vehicles and Industrial Equipment - CAN-bus standards administered by ISO
• USB connections: Multiple companies came together. 1.0, 2.0, 3.0, etc.
• Bluetooth: Started as IEEE, now multiple companies work together.

Wired Ethernet

• Current Standard is IEEE 802.ab that runs at 1 Gbit per second, backwards compatible.
  • Divide by 8 to get gigabyte per second = 125 MByte/sec
  • Gb = Gigabit / GB = Gigabyte
  • There a required gap between frames, preamble, plus overhead = 118 MByte/second
• Newer standard is 802.3ae Fast Ethernet at 10Gb/second.
• Older standard is 100 Mb/s = 802.3u Fast Ethernet
• Note - Not all wired is Ethernet!

Wi-Fi Standards

• Original standard was 802.11
• Next ones added letters. Like 802.11b.
• Got confusing with all the letters. Starting in 2018, new standard that is consumer-friendly.

Wi-Fi Standards

Wireless

What Kind of WiFi am I Running?

Service Set Identifier (SSID)

• WSID is the name when you try to connect to Wi-Fi
• Sending out the SSID is called a 'broadcast'
• You can turn this off. People can still connect if they know the name. A bit more secure, but less convenient.

Wireless Security

• None. Completely unencrypted. Anyone can see all traffic, and anyone can connect. Open access.
• Wired Equivalent Privacy (WEP) - Original 'secure' protocol. Now has known vulnerabilities. Don't use this.
• Wi-Fi Protected Access (WPA) - Outdated. Don't use.
• Wi-Fi Protected Access version 2 (WPA2) - Current standard. Use this.
• Wi-Fi Protected Access version 3 (WPA3) - Updated 2018 standard. Only use if you know all devices can support it.

Wireless Security - WPA2/3

• You can select one of two modes.
• PSK - Pre-shared key. You give someone a password and they can access the Internet. Great for coffee shops, small business.
  • Quick set-up.
  • Someone leaves you don't want to have access to the network? Reset everyone's key.
  • Can't really tell who's connected.
• Enterprise - Everyone logs in with their own user id and password.
  • Need a professional to set up and integrate with login system.
  • You get logs of who's connected.
  • One person leaves? Just disable that one account.

WPA Encryption Standards

• Temporal Key Integrity Protocol - TKIP
  • Older, don' use.
• Advanced Encryption Standard - AES
  • Use this.

WPA - Summary

• Small place - Use WPA2-PSK (AES)
• Medium or larger - Use WPA2-Enterprise (AES)

The Ethernet Frame

Preamble

• Alternating 1's and 0's
• 7 bytes
• 7 x 8 = 56 of 10101010101010...
• Allows Manchester Encoding to time the gap between each transition.

Frame Delimiter

• One byte
• Ends with two ones in a row

10101010 10101010 10101010 10101010 10101010 10101010 10101010 10101011

Preamble

Delimiter