2.2 Access Network Technologies

Access network technologies connect homes and businesses to the internet. From DSL using phone lines to cable leveraging TV infrastructure, these "last mile" connections vary in speed and reliability. Fiber optics offer the fastest speeds but require new infrastructure.

These technologies bridge end-user devices to the core internet, enabling web browsing, email, and streaming. While DSL and cable are more widely available, fiber optics provide superior bandwidth and distance capabilities, though at higher costs.

Access Network Technologies

Access network technologies comparison

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• Digital Subscriber Line (DSL) utilizes existing telephone lines for data transmission provides bandwidth up to 100 Mbps (ADSL, VDSL)
  • Asymmetric: download speed higher than upload speed
  • Performance limited by distance from the central office (5 km)
• Cable Internet leverages coaxial cable television infrastructure offers bandwidth up to 1 Gbps (DOCSIS 3.1)
  • Bandwidth shared among users in the same neighborhood leads to potential network congestion during peak hours
• Fiber Optics transmits data using light pulses through thin glass or plastic fibers achieves bandwidth up to 10 Gbps or higher (GPON, EPON)
  • Symmetric: equal download and upload speeds
  • Enables longer transmission distances without significant signal degradation (100 km)
  • Higher installation costs compared to DSL and cable due to new infrastructure requirements

Role of access networks

• Access networks bridge the gap between end-user devices (computers, smartphones) and the core internet infrastructure (backbone networks)
• Provide the "last mile" connectivity from the internet service provider (ISP) to the customer premises (homes, offices)
• Enable end-users to access internet services, such as web browsing (HTTP), email (SMTP), and streaming (Netflix, YouTube)
• Serve as the entry point for end-user traffic into the internet ecosystem facilitating communication with other networks and servers

Advantages vs limitations of technologies

• Bandwidth limitations impact user experience and service quality
  • DSL and cable have lower maximum bandwidth compared to fiber optics (100 Mbps vs 10 Gbps)
  • Shared bandwidth in cable networks can lead to slower speeds during peak usage times (evenings, weekends)
• Distance limitations affect the availability and performance of access networks
  • DSL performance degrades with increasing distance from the central office limiting its reach (5 km)
  • Fiber optics can transmit signals over longer distances without significant loss enabling wider coverage (100 km)
• Infrastructure availability determines the ease and cost of deployment
  • DSL and cable leverage existing telephone and television infrastructure, respectively reducing deployment costs
  • Fiber optics require new infrastructure deployment, which can be costly and time-consuming (trenching, laying cables)
• Cost considerations impact the adoption and accessibility of access network technologies
  • DSL and cable are generally more affordable than fiber optics for end-users due to lower infrastructure costs
  • Fiber optics offer higher bandwidth and reliability but come at a higher price point for both providers and consumers

Components of access networks

• ###customer_premises_equipment_(CPE)_0### enables end-users to connect to the access network
  • Modems convert digital signals from the end-user device to analog signals for transmission over the access network
    1. DSL modems use discrete multitone (DMT) modulation to transmit data over telephone lines
    2. Cable modems employ quadrature amplitude modulation (QAM) to send data over coaxial cables
  • Residential gateways combine the functions of a modem and a router to facilitate home networking (Wi-Fi, Ethernet)
• Access Multiplexers aggregate traffic from multiple subscribers and connect them to the ISP's backbone network
  • ###digital_subscriber_line_access_multiplexer_(dslam)_0### aggregates multiple DSL subscriber lines and connects them to the ISP's network (ATM, Ethernet)
  • Cable Modem Termination System (CMTS) aggregates traffic from multiple cable modems and connects them to the ISP's network (DOCSIS)
  • Optical Line Terminal (OLT) serves as the endpoint of the fiber optic network at the ISP's central office, connecting to multiple Optical Network Units (ONUs) at customer premises (GPON, EPON)