Connecting to the Internet

Internet Connection Technologies

The Evolution: Dial-up to Fiber

Technology	Medium	Speed	Still Used?
Dial-up	Phone line (PSTN)	Up to 56 Kbps	Rare - only in very rural areas
DSL	Phone line (copper)	1-100 Mbps	Yes, declining
Cable	Coaxial cable	10-1000 Mbps	Yes, very common
Fiber (FTTP)	Fiber optic	100 Mbps - 10 Gbps	Yes, growing rapidly
T1 / T3	Dedicated copper	1.5 / 45 Mbps	Legacy business lines
Satellite	Radio waves	10-100 Mbps	Rural / remote areas
Cellular (4G/5G)	Radio waves	10 Mbps - 1+ Gbps	Yes, everywhere

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Dial-up and Modems

The first home internet connections used the Public Switched Telephone Network (PSTN) - the same lines used for phone calls. A modem (modulator/demodulator) converted digital data into audible tones for transmission over voice lines.

• Baud rate = bits per second over the phone line
• Maxed out at 56 Kbps (1990s standard)
• Tied up the phone line during use - no simultaneous calls
• Usenet (1979, Duke University) was one of the first services to use dial-up networking

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DSL - Digital Subscriber Line

DSL also uses phone lines but operates at higher frequencies that don’t interfere with voice calls - so you can talk and browse simultaneously.

Type	Upload / Download	Max Speed	Use Case
ADSL (Asymmetric)	Upload slower than download	~24 Mbps down / 3.5 Mbps up	Home users (browsing, streaming)
SDSL (Symmetric)	Equal upload and download	~1.5 Mbps each way	Businesses (hosting, VoIP)
VDSL (Very High Bitrate)	Asymmetric, much faster	~52 Mbps down / 16 Mbps up	Closer to DSLAM required

• DSLAM (Digital Subscriber Line Access Multiplexer) = the ISP-side equipment that aggregates DSL connections
• Speed degrades with distance from the DSLAM

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Cable Broadband

Cable internet piggybacks on the coaxial cable infrastructure originally built for cable TV. It uses frequency bands that don’t interfere with TV signals.

• Shared bandwidth model - you share cable bandwidth with neighbors until the signal reaches the ISP’s CMTS (Cable Modem Termination System)
• Speeds can slow during peak usage hours
• DOCSIS (Data Over Cable Service Interface Specification) is the standard that defines cable internet speeds - DOCSIS 3.1 supports up to 10 Gbps downstream

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Fiber Connections

Fiber uses light pulses through glass strands. It’s the fastest, most reliable consumer technology available.

Type	Fiber reaches…	Last mile	Speed
FTTN (Fiber to the Neighborhood)	Street cabinet	Copper to homes	25-100 Mbps
FTTB (Fiber to the Building)	Building basement	Copper inside building	100-500 Mbps
FTTH / FTTP (Fiber to the Home/Premises)	Your home	All fiber	1-10 Gbps

• ONT (Optical Network Terminator) is the demarcation point - converts fiber protocols to Ethernet for your LAN
• Fiber doesn’t degrade over distance like copper and is immune to electromagnetic interference

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T-Carrier Technologies (Legacy)

Line	Capacity	Speed	How
T1	24 channels x 64 Kbps	1.544 Mbps	Twisted pair copper, dedicated
T3 (DS3)	28 multiplexed T1s	44.736 Mbps	Dedicated, expensive

Originally designed by AT&T to carry multiple phone calls over a single cable. Later repurposed for data. Mostly replaced by fiber and cable, but still found in some legacy business installations.

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WAN Technologies

A WAN (Wide Area Network) connects geographically separated LANs. When a business has offices in different cities, a WAN links them together.

WAN Architecture

   Office A (LAN)              Office B (LAN)
       │                           │
  [WAN Router]                [WAN Router]
       │                           │
  ─── Local Loop ───┐    ┌─── Local Loop ───
                    │    │
              ┌─────┴────┴─────┐
              │   ISP Core     │
              │   Network      │
              └────────────────┘

• Demarcation point = where your network ends and the ISP’s begins
• Local loop = the connection between your demarcation point and the ISP’s core network
• WAN router (also called edge/border router) = sits at the boundary, has both a WAN interface (modem) and a LAN interface (Ethernet)

WAN Protocols

Protocol	Layer	How it works	Status
PPP (Point-to-Point)	Data Link	Byte-oriented protocol for direct device-to-device links. Supports authentication (PAP/CHAP), compression, error detection.	Still used (DSL)
PPPoE (PPP over Ethernet)	Data Link	PPP frames encapsulated in Ethernet frames. Common for DSL connections.	Common
Frame Relay	Data Link / Physical	Packet switching over PVCs (permanent) or SVCs (temporary). Low overhead.	Legacy
ATM	Data Link	Fixed-size 53-byte cells. Good for real-time traffic.	Legacy
MPLS	Between L2/L3	Label-based switching - short labels instead of full IP lookups. Fast path forwarding.	Widely used by ISPs

WAN Optimization Techniques

Technique	What it does
Compression	Reduce data size before transmission
Deduplication	Store one copy of repeated files, use pointers
Traffic shaping	Prioritize important traffic (bandwidth throttling, rate limiting, QoS classification)
Local caching	Store frequently accessed files locally
Protocol optimization	Tune protocols for high-bandwidth, low-latency needs

SD-WAN vs Traditional WAN

Software-Defined WAN (SD-WAN) is a software overlay that simplifies WAN management:

Aspect	Traditional WAN	SD-WAN
Cost	Expensive dedicated lines	Uses cheaper internet links
Management	Hardware-centric, manual config	Software-defined, centralized
Flexibility	Rigid topology	Dynamic path selection
Cloud access	Backhauled through data center	Direct cloud on-ramp

Note

Point-to-point VPNs (site-to-site VPNs) are increasingly replacing traditional WAN technologies. They create encrypted tunnels between sites over the public internet - cheaper and simpler than dedicated lines, especially as businesses move services to the cloud.

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Wireless Networking

The 802.11 (Wi-Fi) Family

Wi-Fi operates on radio waves in specific frequency bands. The IEEE 802.11 standards define how devices communicate wirelessly.

Standard	Wi-Fi Name	Year	Frequency	Max Speed	Key Feature
802.11b	Wi-Fi 1	1999	2.4 GHz	11 Mbps	First widely adopted
802.11a	Wi-Fi 2	1999	5 GHz	54 Mbps	Higher speed, shorter range
802.11g	Wi-Fi 3	2003	2.4 GHz	54 Mbps	Backward compatible with b
802.11n	Wi-Fi 4	2009	2.4 / 5 GHz	600 Mbps	MIMO, channel bonding
802.11ac	Wi-Fi 5	2014	5 GHz	6.9 Gbps	MU-MIMO, 160 MHz channels
802.11ax	Wi-Fi 6	2019	2.4 / 5 GHz	9.6 Gbps	OFDMA, TWT, WPA3 required
802.11ax	Wi-Fi 6E	2020	2.4 / 5 / 6 GHz	9.6 Gbps	New 6 GHz band, more channels

2.4 GHz vs 5 GHz vs 6 GHz

Band	Range (indoor)	Channels	Penetration	Issues
2.4 GHz	~45m (150 ft)	11-14 (only 3 non-overlapping: 1, 6, 11)	Best - passes through walls	Crowded, interference from Bluetooth/microwaves
5 GHz	~12m (50 ft)	25+ non-overlapping	Moderate	Less interference, shorter range
6 GHz	~12m (50 ft)	59 channels (14 x 80MHz, 7 x 160MHz)	Lower	Wi-Fi 6E only, very clean spectrum

Wi-Fi 6 Key Technologies

Technology	What it does
OFDMA	Splits channels to serve multiple devices simultaneously (vs one at a time)
MU-MIMO	Multiple antennas serve multiple clients in parallel (8x8 streams)
TWT (Target Wake Time)	Devices sleep when not transmitting - saves battery for IoT
1024-QAM	More data per transmission symbol (25% throughput increase)
BSS Coloring	Reduces interference from neighboring networks

802.11 Frame Structure

An 802.11 wireless frame has more address fields than Ethernet because wireless communication involves access points as intermediaries:

Field	Size	Purpose
Frame Control	2 bytes	Frame type, version, flags
Duration	2 bytes	How long the channel will be reserved
Address 1 (Destination)	6 bytes	Destination MAC
Address 2 (Source)	6 bytes	Source MAC
Address 3 (Receiver)	6 bytes	Access point MAC (for infrastructure mode)
Address 4 (Transmitter)	6 bytes	Used in mesh/WDS mode
Sequence Control	2 bytes	Fragment and sequence numbers
Data Payload	0-2304 bytes	Actual data
FCS	4 bytes	CRC checksum

Note

4 MAC addresses vs Ethernet’s 2: Wireless frames need to track the original source, final destination, AND the access point (receiver/transmitter) that’s relaying the frame between the wireless and wired networks.

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Wireless Network Configurations

Type	Description	Use Case
Infrastructure	Devices connect through access points (most common)	Offices, homes
Ad-hoc	Devices connect directly peer-to-peer, no AP needed	Quick file sharing, disaster relief
Mesh	Devices relay for each other, self-healing if a node fails	Large coverage areas, smart home

Wireless Channels

Channels are specific frequency slices within a band. Overlapping channels cause interference.

2.4 GHz Band - 14 channels, only 3 non-overlapping:

 Ch 1       Ch 6       Ch 11
  ├──────┤   ├──────┤   ├──────┤
  2412 MHz   2437 MHz   2462 MHz

Use channels 1, 6, and 11 for multi-AP deployments
to avoid co-channel interference

# Scan available wireless networks and their channels
sudo iwlist wlan0 scan | grep -E "ESSID|Channel|Signal"

# Check your Wi-Fi interface details
iw dev wlan0 info

# See which channel you're on
iwconfig wlan0

# On macOS
/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -s

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Wireless Security

Wireless signals broadcast through the air - anyone in range can potentially intercept them. Encryption is essential.

Protocol	Year	Encryption	Key Size	Status
WEP	1997	RC4	40/104 bit	Broken - crackable in minutes. Never use.
WPA	2003	TKIP (RC4-based)	128 bit	Deprecated - vulnerabilities found
WPA2	2004	AES-CCMP	128/256 bit	Standard - still widely used
WPA3	2018	AES-GCMP-256	192/256 bit	Latest - recommended for new deployments

WPA3 Improvements

WPA3-Personal:

• SAE (Simultaneous Authentication of Equals) replaces the PSK 4-way handshake - resistant to dictionary attacks and KRACKs
• Forward secrecy - even if your password is later compromised, previously captured traffic can’t be decrypted
• More resistant to offline brute-force attacks

WPA3-Enterprise:

• GCMP-256 encryption (stronger than WPA2’s 128-bit AES-CCMP)
• OWE (Opportunistic Wireless Encryption) - encrypts open network traffic (coffee shop Wi-Fi)
• DPP (Device Provisioning Protocol) - QR code / NFC-based setup replaces WPS
• 384-bit HMAC-SHA for message integrity
• ECDHE/ECDSA for faster, more secure key exchange

Additional Wireless Security

• MAC filtering - whitelist specific MAC addresses on the access point. Adds a layer but is easily spoofed.
• SSID hiding - stops broadcasting the network name. Security through obscurity - doesn’t stop determined attackers.
• 802.1X / RADIUS - enterprise authentication where each user has unique credentials (not a shared password)

# Check your wireless security protocol
iw dev wlan0 info
# type: managed
# channel: 36 (5180 MHz)

# See connected network security details
nmcli device wifi show-password

# Scan for nearby networks and their security
nmcli device wifi list
# SSID          SECURITY    CHAN  SIGNAL
# MyNetwork     WPA2        6     85
# CoffeeShop    --          1     72    <-- OPEN! Avoid or use VPN

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Cellular Networking

Cellular networks divide geographic areas into cells, each served by a cell tower that broadcasts and receives radio signals.

Generation	Speed	Key Feature
2G (GSM)	Up to 50 Kbps	First digital voice + SMS
3G	Up to 2 Mbps	Mobile internet, video calls
4G LTE	Up to 100 Mbps	Streaming, modern mobile apps
5G	Up to 10+ Gbps	Ultra-low latency, IoT, AR/VR

• Adjacent cells use non-overlapping frequency bands to avoid interference (same concept as Wi-Fi channels 1, 6, 11)
• Cell towers are like wireless access points but with much larger range (kilometers vs meters)
• Beyond phones: tablets, laptops, cars, IoT sensors, and industrial equipment use cellular connections

Tip

For IT troubleshooting: If a user has poor cellular connectivity indoors, the building may block radio signals. Solutions include Wi-Fi calling, femtocells (mini cell towers), or cellular signal boosters.

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