A Guide to Broadband Remote Access Servers (BRAS, B-RAS, or BBRAS)

Key Points

• BBRAS are multiservice access node (MSAN) independent.
• BBRAS is a common, access-agnostic operational model.
• BBRAS provides a single point for change control.

What Is BBRAS, BRAS, or B-RAS?: Explained

BBRAS, BRAS, and B-RAS are all different acronyms for broadband remote access servers. A BRAS routes traffic going in and out of broadband remote access devices such as digital subscriber line access multiplexers, DSLAM for short. The different acronyms are a result of the early Internet era when naming conventions had yet to be standardized. In fact, BRAS, B-RAS, and BBRAS are sometimes also called broadband network gateways or border network gateways (BNGs).

ISPs use different connection types and infrastructure to create their independent networks, but they all need to access the same World Wide Web. A BRAS acts as a specialized server designed around an ISP’s network and connection type that allows for the convergence of Internet traffic from multiple sources including cable, DSL, Ethernet, or wireless broadband signals. With the different sources put on a single pathway, signal traffic can more easily be sent to and from the ISP’s DSLAM.

In short, BRAS are used to simplify network traffic pathways. As a center point for traffic, they are much more useful for quick network organization. They can aggregate circuits from one or more link access devices like DSLAMs. They can be used as a control point for ISPs to inject policy management and control IP quality of service (QoS).

As home networks have grown to include wireless area networks (WAN), local area networks (LAN) over ethernet, and direct computer to computer connections, the need for organizing signals and traffic to the correct device is even more vital. Home routers are used as an access gateway in the house. The signal is then transmitted by a common link access method such as a PPPoE connection to the ISP’s DSLAM. Then, an entire area’s userbase is sorted through the ISP’s BRAS before being sent through to the access gateway to the true internet.

Specific tasks BRAS performs include:

• Providing layer 2 connectivity through transparent bridging or PPPoE connections or ATM sessions
• Providing layer 3 connectivity and routing IP traffic through an ISP’s backbone network (core network) to the Internet
• Enforcing QoS policies
• Converging multiple signal sources into a single flow of traffic
• Assigning network parameters such as IP addresses to client devices
• Interfacing with authentication, authorization, and accounting systems

How to Use BBRAS, BRAS, or B-RAS

Broadband remote access servers are routing machines used just outside the core of an ISP’s internet access server. They are automatically in use when Internet users access a webpage or web-based services.

If you are interested in how BRAS functions now and have in the past, I would recommend looking through the DSL Forum TR-025, TR-059, and TR-101. While they do not describe the technical aspects of building a server, they do outline the architecture to set up a server to be used as BRAS and even include software tools to help achieve the build.

How to Learn BBRAS, BRAS, or B-RAS

If you’re interested in learning more about broadband remote access servers, the DSL Forum TR-025, TR-059, and TR-101 outline the architecture and structure of how BBRAS are made and used. You can also use the resources provided by the Broadband Forum at the official Broadband Forum website.

The Broadband Forum is an excellent source for networking resources, initiatives, and news.

The Difference Between BBRAS and RAS

During the days of dial-up internet service, subscriber connections were verified with authentication dial-in user service that communicated with remote access servers which allowed the connection of computers outside the LAN. RAS connections typically required PPP software that was installed on the subscriber’s PC to allow the user to log in with a user id provided by their ISP for authentication dial-in user service. RAS also required the use of multi-server access nodes (MSAN) to manage the service connection type the subscriber was attempting to use. As internet connection types evolved and expanded beyond phone lines, a new type of authentication was required.

Broadband remote access servers were the replacement for dial-up’s antiquated RAS system. It is MSAN-free and supports a variety of connection types such as PPPoE WAN offered by ATT ISP services. It was designed to allow larger bandwidth connections and more connections at the same time. RAS could easily be overwhelmed by congestion which, in turn, could deny users permission to the internet access gateway. With BRAS, ISPs can manage many more subscribers in an area with unique home setups whether they use PPPoE connections such as PPPoE WAN or others.

Broadband Remote Access Server: Release History

During the early days of the Internet, Internet access required that service subscribers dial-up from their PC to a bank of Remote Access Servers (RAS), which were connected to the Internet. Eventually, Point-to-Point Protocol (PPP) was adopted to allow the ISP operator to easily manage subscriber connections. This was done through special software that required installation on the subscriber’s PC. A prime example would be AOL services that used to come with a disc that carried the PPP protocol stack. The connection would be established and then verified by logging into the service through the operator-provided PPP user id.

As technology quickly evolved, authentication dial-in user service was replaced with “broadband” access such as DSL or cable connections to provide an “always-on” service. Due to the constant connection of these newer broadband services, dial-up RAS servers were replaced with B-RAS to handle the increased constant traffic.

Early BBRAS machines were limited to specific bandwidth support under the assumption that only a small percentage of subscribers would be actively using bandwidth at a given moment. Even if half or more of the service subscribers were logged onto the network concurrently, very few would request access to new pages or hit “enter” at the exact same time. BBRAS traffic is also TCP-based and not performed in real-time. This means that if a packet is lost due to bandwidth congestion, TCP will find and retransmit the packets.

The basic architecture for broadband was originally defined by DSL Forum TR-025 in November 1999. It was designed around the idea that assumed only one service was provided to subscribers. As the Internet and Internet services evolved, so did the architecture. In September 2003, DSL Forum TR-059 introduced Quality of Service which allowed broadband networks to send Voice over IP along with data.

The use of the Internet didn’t stop growing. Fiber optics, cable, and satellite connections were formed to allow access to the web from anywhere and in-home networking devices allowed for PPPoE WAN connections and more. To accept these different signals and bring them together to be useful, BBRAS were reworked to migrate to Ethernet-based broadband aggregation as outlined in the DSL Forum TR-101.

Broadband Remote Access Server: End of Development

Broadband remote access servers are still in heavy use among ISPs as they sort out traffic from multiple ISP subscribers to the core network of the service. Developments to BRAS architecture and protocol are now handled by a conglomerate of broadband developers who communicate and research together through the Broadband Forum.

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