Subscriber Management Concepts

Module Overview

This module provides an overview over subscriber management and broadband access technologies and corresponding concepts. There are no exercises in this module.

Overview

Broadband internet access refers to high-speed internet connectivity for residential and business customers (known as subscribers) that provides fast and reliable data transmission. It allows users to access the internet for various purposes such as browsing, streaming media, online gaming, and more.

From an service provider’s point of view, the access network extends the backbone network to hundreds or thousands of sites called central offices (COs) in order to physically connect customers using various access technologies.

Building Blocks

subscriber overview
Figure 1. Broadband Network Building Blocks

Residential Gateway

A customer premises equipment (CPE) or residential gateway (RG) is a device that serves as the interface between a user’s local area network (LAN) and the internet service provider (ISP). The main task of the residential gateway is to set up and maintain a subscriber session and to forward IP packets between the provider network and the home network. It most often includes a modem to directly connect to the service providers access network.

A home gateway typically provides additional services including network address translation (NAT), firewall service, wireless access point, and VoIP gateway.

Access Network

There are several technologies used to implement the access access network, each with its own advantages and limitations. Here is an overview of some of the most popular access technologies.

Digital Subscriber Line (DSL) technology uses existing copper telephone lines to provide internet connectivity. It utilizes different frequencies for voice and data transmission, allowing simultaneous use of the telephone line for calls while accessing the internet. DSL connections are typically asymmetrical, i.e., the download speed is higher than the upload speed. A crucial factor for the usable download and upload speed is the physical distance to the ISP’s central office location.

There are different variations of DSL, e.g., Asymmetric DSL (ADSL) with up to 24Mbps download rate and Very High Bitrate DSL (VDSL) with up to 100Mbps download rate. The different types of DSL technologies are sometimes summarized as xDSL. With xDSL, a DSL modem at the customer site (usually integrated into the residential gateway) is connected to a Multi-Service Access Node (MSAN) using either ATM or Ethernet as a Layer-2 protocol. The MSAN aggregates hundreds of subscribers. Prior to the deployment of MSANs, DSL Access Multiplexers (DSLAMs) were used for this purpose.

Cable internet utilizes the same coaxial cable infrastructure that carries cable television signals. Cable internet access requires a cable modem at the customer site (usually integrated into the residential gateway) which connects to a Cable Modem Termination System (CMTS) at the cable operator facility and Data Over Cable Service Interface Specification (DOCSIS) is used as a communication protocol. Users can access the internet with download rates up to 1Gbps. Similar to DSL, the transfer rates are usually asymmetric. Multiple users in the same neighborhood share the available bandwidth, which can result in decreased speeds during peak usage hours.

Fiber optic technology offers the highest speeds among broadband technologies. It uses thin, transparent optical fibers made of glass or plastic to transmit data as pulses of light. Fiber-optic cables can transmit large amounts of data over long distances with minimal signal loss. Fiber connections can deliver symmetrical speeds, providing the same upload and download speeds. However, deploying fiber optic infrastructure requires significant investment and is more commonly found in urban areas. Fiber connections can be deployed in different ways:

  • Fiber-to-the-Home (FTTH) refers to the deployment of fiber optic cables directly to individual customer premise. With FTTH, the fiber optic connection is extended all the way to the user’s home, providing a dedicated fiber connection for each subscriber. This technology offers the highest speeds and capacity as it utilizes fiber optic cables for both the upload and download of data. FTTH provides symmetrical speeds, ensuring that the upload speed is the same as the download speed. FTTH requires an Optical Network Terminal (ONT) which connects to an Optical Line termination (OLT) device at the ISP’s end via a passive optical network (PON).

  • Fiber-to-the-Building (FTTB) involves bringing fiber optic cables to a building, such as an apartment complex, office building, or business park. The fiber termination point is usually located within the building’s telecommunications or equipment room. From there, the connection is distributed to individual units using existing copper cabling. In FTTB deployments, a Distribution Point Units (DPU) is interconnected to the ISP’s PON network.

  • Fiber-to-the-Curb (FTTC) involves extending the fiber optic connection to a distribution point or cabinet located near the user’s premises, typically at the curbside or in a nearby equipment enclosure. From the distribution point, the connection is then delivered to the user’s location using existing copper cables.

Broadband Network Gateway (BNG)

The BNG is a key component in the network infrastructure of an ISP. It serves as the access point for subscriber connections and manages the aggregation, authentication, and routing of traffic between the subscriber’s network and the internet. A BNG can also support Virtual Private Network (VPN) services, which provide secure remote access to business networks. In general, a BNG is access-agnostic supporting various access technologies, including xDSL, fiber access, etc.

BNGs are responsible for establishing and terminating subscriber sessions, and applying quality of service (QoS) policies. When a subscriber connects to the ISP’s network, the BNG authenticates the user, assigns an IP address, and manages the flow of data between the subscriber’s device and the internet. Optionally it can also provide accounting information about subscriber sessions. Subscriber sessions are built upon an underlying protocols, e.g.,

  • Point-to-Point Protocol over Ethernet (PPPoE)

  • Internet Protocol over Ethernet (IPoE)

RBFS provides a modular, scalable subscriber management implementation called the next-generation access infrastructure (ng-access) which supports protocols such as PPPoE, L2TPv2, DHCPv4/v6, and RADIUS. The RBFS subscriber management infrastructure is designed for carrier-grade services in regard to scalability and robustness. One of the challenges for carrier networks is interworking with numerous client devices and various vendors which require a well-implemented, industry-proven access protocol stack, including support for all relevant RFCs.

subscriber daemons
Figure 2. Next Generation Access Infrastructure

There are four main daemons in the RtBrick distributed access architecture:

  • subscriber is the central application, keeping the current subscriber state as well as being responsible for Authentication, Authorization, and Accounting (AAA), either local, via RADIUS, or other methods

  • pppoed is the daemon to handle PPPoE and PPP sessions establishment, maintenance, and teardown

  • l2tpd is the daemon used for L2TPv2 tunnel and session handling

  • ipoed is the daemon used for IPoE subscriber handling including DHCP and DHCPv6 protocol handling