Telecommunications for Internet Access

Modems

The term "modem" is a blend of the first syllables of "modulate" and "demodulate." These devices, in use for decades, convert digital signals into analog waveforms for transmission, then demodulate them back into their original digital form. Many technologies, including cable modems and industrial control environments, still rely on asynchronous communications due to their reliability, well-established standards, and broad vendor support.

Digital Subscriber Line

Digital subscriber line (DSL) technology initially allowed traditional telecommunications companies to provision greater bandwidth for their customers than would be available across the same circuit-based wiring plant used by modems. Subsequent improvements in technology increased these capabilities to compete directly with other broadband services. There are several methods of implementing DSL:

• Asymmetric digital subscriber line (ADSL). The downstream transmission rates are much greater than upstream ones, typically up to 8 Mbps downstream and 384 Kbps upstream.
• Rate-adaptive DSL (RADSL). The upstream transmission rate is tuned automatically based on the quality of the line and adjustments made to the modem.

There are two significant issues with all variations of DSL:

• There is a limit to the length of the phone line between the central office (CO) and the customer. The precise limit depends on several factors, including the quality of the cable and transmission rates. In other words, the customer cannot be too far from the CO.
• DSL allows users to be connected to the internet for much longer intervals. Certainly, this is convenient for the user, but extended time exposed to the internet greatly increases the risk of being attacked. To mitigate this serious risk, it is imperative that the host has a firewall, vendor security patches are installed, and dangerous and unused protocols are disabled.

• Symmetric digital subscriber line (SDSL). SDSL uses the same rates for upstream and downstream transmissions.
• Very high bit rate DSL (VDSL). VDSL supports much higher transmission rates than other DSL technologies, such as 52 Mbps downstream and 2 Mbps upstream.

Cable Modem

Originally used to provide broadcast TV, the

Cable modem users must take the growth of data bandwidth demands from same precautions as DSL users:

users of cable TV caused cable operators to ensure that PCs on the home implement technology that allowed them network have a personal firewall, to provide data services using part of the install vendor security patches, available radio frequency (RF) bandwidth in their coaxial cabling plants. The basic and disable dangerous and unused technology translates a digital signal protocols.

through a cable modem and demodulates the signal at the cable provider's "head end,"

At a high level, this is the cable modem while sharing the available bandwidth with process: the various customers similarly connected.

• When a cable modem is powered on, it

Over time, the Data Over Cable Service is assigned upstream and downstream Interface Specifications (DOCSIS) standard channels. for this technology evolved, improving the upload and download speeds and, with

• Next, it establishes timing parameters

the adoption of the DOCSIS 3.0 standard, by determining how far it is from the providing enhanced encryption services head end (core of the cable network).

to protect the transmissions. DOCSIS evolved from version 1, with up to 40 Mbps

• The cable modem makes a Dynamic Host

downstream and 10 Mbps upstream, to 3.1

Configuration Protocol (DHCP) request with Full Duplex, supporting multi-gigabit to obtain an IP address.

symmetrical speeds exceeding 10 Gbps To help protect the cable provider from both downstream and upstream. piracy and protect its users from having Like DSL, cable modems make it practical their data intercepted by other cable for home users to remain connected to users, the modem and head end exchange the internet for an extended time, which cryptography keys. From that point exposes cable modem users to the same forward, all traffic between the two ends is risks as DSL users.

encrypted.

Economic theory suggests that markets

system. Field trials in several nations, do not experience true competition until however, have shown that scaling BPL beyond small test deployments is difficult there are at least three competitors for a product or service. In some environments, to achieve, as it has been actively opposed broadband over power line (BPL) provides by the traditional bandwidth providers and an alternative to the telco/cable duopoly other users of RF spectrum concerned with and remains an attractive option when interference. supported by the electrical power grid. While BPL may not be a cost-effective way

Delivering broadband over the existing to meet growing consumer and business low-and medium-voltage electric power needs for higher bandwidth internet distribution network, BPL speeds are services in many markets, it may be an ideal comparable to DSL and cable modem | solution for niche applications. In 2019, the speeds. IEEE adopted a revised BPL standard, which Because it is effective in homes where the used frequency division multiplexing to support Internet of Things (loT) applications.

communications devices can be connected through the home power wiring, BPL was

This may provide a viable alternative to other envisioned to deliver broadband throughout dedicated data technologies that run on a rural, residential, and light business areas separate media from the power distribution via the existing electrical power distribution grid.

Ingress and egress controls are the first line of defense for an organization. From a networking perspective, every internet address, port number, and protocol must be controlled, managed, and monitored for security issues. The edge network should provide layered controls to repel malicious, unwanted traffic as early as possible. To be efficient and cost-effective, the design should make use of a deny-all approach, other than the expected IP addresses and port numbers, at the earliest opportunity in the data flow. This reduces traffic arriving at more sophisticated solutions that require more processing power, such as stateful firewalls and reverse proxies. Many of these control points will reside in a DMZ.

Organizations are increasingly using voluntary peering agreements to exchange traffic, which are also subject to controls. Some cloud providers use the term "peering" to describe one method of exchanging traffic between two virtual private clouds (VPCs).