Connecting the Edge Broadband Technologies and the Power of the VPN
Introduction:
The Last Mile Connection
The way users connect to the internet has fundamentally shifted from slow dial-up to diverse, high-speed broadband services. These technologies—ranging from wired copper and coaxial systems to advanced wireless standards—not only provide access but also introduce unique challenges regarding security, scalability, and bandwidth sharing.
Part I: Wired Broadband Access Technologies
These technologies leverage existing physical infrastructure to deliver high-speed IP services.
1. 📞 Digital Subscriber Line (DSL)
DSL utilises existing twisted-pair copper telephone lines to transmit high-bandwidth data, providing a permanent connection to subscribers.
Mechanism: The DSL modem converts the Ethernet signal from the user device into a DSL signal. At the provider's central office, the DSL Access Multiplexer (DSLAM) multiplexes (groups) multiple DSL subscriber lines onto a single high-capacity link, typically using Time-Division Multiplexing (TDM).
Use Case: A popular choice for enterprise IT departments serving remote workers, though users must first connect via an ISP before establishing an IP connection to the company network.
2. 📺 Cable Internet Access
Cable internet uses the same Hybrid Fibre-Coaxial (HFC) infrastructure as cable television to deliver broadband services.
Mechanism: The essential component at the provider's headend is the Cable Modem Termination System (CMTS), which sends and receives digital signals from the user's cable modem. cable modem.
Limitation: All local subscribers share the same bandwidth on a particular segment. As more users join the service, the available bandwidth may drop below the expected speed, especially during peak usage times.
| Technology | Infrastructure Used | Provider Equipment | Key Limitation |
| DSL | Existing Copper Telephone Lines | DSLAM (Multiplexer) | Speed is distance-dependent (attenuation). |
| Cable | Hybrid Fiber-Coaxial (HFC) | CMTS (Termination System) | Shared bandwidth leads to congestion issues during peak usage. |
Part II: Wireless Broadband Access Technologies
Wireless technologies utilise the available radio spectrum, offering flexibility and reach, particularly in areas lacking fixed infrastructure.
1. Local and Metropolitan Wireless Solutions
Municipal Wi-Fi: City-wide wireless networks implemented to provide high-speed internet access (free or low-cost) or for exclusive city use (police and fire departments).
Subscribers typically use a wireless modem with a powerful directional radio antenna. WiMAX (Worldwide Interoperability for Microwave Access): Governed by the IEEE 802.16 standard, WiMAX offers high-speed wireless access over wide coverage areas, similar to mobile phone networks.
Subscribers need a WiMAX receiver within range of a dedicated WiMAX tower (up to 50 km).
2. Global Wireless Solutions (Cellular and Satellite)
| Technology | Standard/Abbreviation | Key Characteristics | Primary Use Case |
| Cellular Data | 3G/4G, LTE (Long-Term Evolution) | Uses radio waves via mobile network towers; offers true WAN access. | Connecting mobile users (smartphones/tablets) and remote locations where a fixed WAN is unavailable. |
| Satellite Internet | VSAT (Very Small Aperture Terminal) | Bidirectional communication via dish; high latency but wide availability. | Rural areas lacking cable or DSL access. Download speed is significantly faster than upload speed (e.g., upload $\approx 1/10 \text{th}$ of download speed). |
Part III: Security and The Virtual Private Network (VPN)
When remote workers use broadband services (DSL, cable, or wireless) to access a corporate-wide area network (WAN) over the public internet, security risks are inherent. VPN technology is the standard solution to mitigate these risks.
A. The VPN Connect
A VPN establishes an encrypted connection between private networks over a public network (the internet).
B. Benefits of VPN Technology
| Benefit | Description |
| Cost Savings | Eliminates the need for expensive dedicated WAN links and modem banks by leveraging the public internet infrastructure. |
| Security | Provides the highest level of security for data transmission through advanced encryption and authentication protocols. |
| Scalability | Easy to add new remote users or sites, leveraging the ISP's existing internet infrastructure without adding substantial proprietary hardware. |
| Broadband Compatibility | Supported by all major broadband providers (DSL and cable), making it ideal for remote and mobile workers. |
|
VPN
Type |
Description |
Endpoint
Hardware |
Primary
Use Case |
|
Site-to-Site
VPN |
Connects entire
networks (e.g., a branch office network to the company
headquarters network). |
A VPN
gateway (router, firewall, or dedicated VPN device) at each site. |
Connecting
two fixed geographic locations. |
|
Remote
Access VPN |
Allows
individual hosts (mobile users, remote workers) to securely access the
corporate network over the internet. |
VPN
client software or a web client installed on the remote host
(PC/laptop/tablet). |
Securing access for individuals travelling or working from home. |
ISDN (Integrated Services Digital Network)
⚙ ISDN is a circuit-switching technology that allows the local loop of a public telephone network to carry digital signals, thus providing a higher-capacity switched connection. ISDN changes the internal connections of the PSTN so that they carry a time-division multiplexed (TDM) digital signal instead of an analogue signal. TDM allows two or more signals, or streams, to be transferred as sub-channels within a communication channel. The signals appear to be transferred simultaneously, but physically, they are transferred one after the other on the channel. There are two types of ISDN interfaces:
⚙ BRI (Basic Rate Interface):
BRI ISDN technology is intended for consumers and small businesses. It is a basic version of ISDN and offers two 64 kbit/s B channels and one 16 kbit/s D channel. The BRI D channel is designed for control. It is often underutilised because it only has two B channels to control. PRI (Primary Rate Interface): ISDN is also available for larger installations. In North America, PRI offers 23 64 kbit/s B channels and one 64 kbit/s D channel for a total throughput of up to 1.544 Mbit/s. This also includes a portion for synchronisation. In Europe, Australia, and other parts of the world, PRI ISDN offers 30 B channels and one D channel for a total throughput of up to 2.048 Mbit/s, including synchronisation information.
The BRI's call setup time is less than one second, and the 64 kbps B channel offers greater capacity than the analogue modem. For even more capacity, a second B channel can be activated to provide a total of 128 kbps. While not suitable for video, this allows for multiple simultaneous voice calls in addition to data traffic.
Another common application of ISDN is to provide additional capacity when needed on a leased line connection. The leased line is sized to carry average traffic loads, and ISDN is added during peak periods. The ISDN line is also used as a backup line in case the leased line fails. ISDN rates are calculated per B channel and are similar to those of analogue voice connections. With an ISDN PRI, multiple B channels can be connected between two terminals. This enables video conferencing and high-speed data connections without latency or jitter. However, multiple connections over long distances can be expensive.
⚙ Frame Relay
Frame Relay is a simple Layer 2 non-broadcast multiple access (NBMA) WAN technology used to connect enterprise LANs. It is possible to use only a single router interface to connect multiple sites via persistent virtual circuits. These persistent virtual circuits are used to carry both voice and data traffic between a source and a destination. They provide speeds up to 4 Mbps, with some providers offering even higher speeds. The edge router only needs one interface, even when multiple virtual circuits are in use. The small leased line to the Frame Relay network edge enables cost-effective connections between multiple dispersed LANs.
Frame Relay creates permanent virtual circuits identified by a Data Link Connection Identifier (DLCI). These permanent virtual circuits and DLCIs enable bidirectional communication from one DTE device to another. For example, in the illustration, R1 uses DLCI 102 to reach R2, while R2 uses DLCI 201 to reach R1.
ATM (Asynchronous Transfer Mode) Technology
ATM (Asynchronous Transfer Mode) technology can transfer voice, video, and data over private and public networks. It relies on a cell-based architecture, rather than a frame-based architecture. ATM cells always have a fixed length of 53 bytes. The 53-byte ATM cell contains a 5-byte ATM header, followed by 48 bytes of ATM payload data. Small, fixed-length cells are well-suited for carrying voice and video traffic because this traffic is not tolerant of delays. Video and voice traffic do not have to wait for the completion of larger data packet transmissions. The 53-byte ATM cell is less efficient than the larger Frame Relay frames and packets. Furthermore, the ATM cell has at least 5 bytes of overhead for each 48-byte payload.
When the cell
carries segmented network layer packets, the overhead is greater because the ATM switch
must be able to regroup the packets at the destination.
A typical ATM line requires almost 20% more bandwidth than Frame Relay to carry the
same volume of network layer data. ATM technology was designed for scalability and
to support speeds of T1/E1 or OC-12 (622 Mbps) and beyond. ATM offers both
permanent and switched virtual circuits, although permanent virtual circuits are
more common with WANs. As with other shared technologies, ATM allows multiple
virtual circuits on a single leased line connection to the network edge.
MPLS (MultiProtocol Label Switching)
MPLS switching is a high-performance, multiprotocol WAN technology. It redirects data from one router to the next based on shortest path labels rather than on IP network addresses. MPLS has several distinct characteristics. It is multiprotocol, meaning it can carry any useful data, such as IPv4, IPv6, Ethernet, ATM, DSL, and Frame Relay traffic. It uses labels that tell the router what to do with the packet. These labels identify the paths between remote routers, rather than between endpoints, and while MPLS forwards IPv4 and IPv6 packets, everything else is switched. MPLS is a service provider technology. Leased lines transmit bits between sites, and Frame Relay and Ethernet WANs transmit frames between sites. However,
MPLS can transmit all types of packets between sites. MPLS can encapsulate packets. It supports various network protocols. It supports many WAN technologies, including carrier/eCarrier, Ethernet, ATM, Frame Relay, and DSL links.
The example topology in the illustration demonstrates the use of MPLS. Note that different sites can connect to the MPLS cloud using different access technologies. In the illustration, CE refers to the customer edge, PE is the provider's edge router that adds and removes tags, and P is an internal provider router that switches the tagged MPLS packets.
Note: MPLS is primarily a service provider WAN technology.
VSAT (Very Small Aperture Terminal)
All the private WAN technologies presented so far use copper or fibre optic cables.
What if an organisation needs a connection in a remote location where no service provider offers WAN services?
VSAT (Very Small Aperture Terminal) technology is a solution that uses satellite communications to create a private WAN. A VSAT is a small satellite dish similar to those used for internet or home television. VSATs create a private WAN while providing connectivity for remote locations.
The router connects to a satellite dish pointed at the service provider's satellite, which is in geostationary orbit.
The signals must cover a distance of approximately 35.786 kilometres (22.236 miles) to reach the satellite and return. In the example shown in the figure below, the antenna.
The VSAT on the roof of the building communicates with a satellite located thousands of kilometres away in space.