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A broadband remote access server (BRAS, B-RAS or BBRAS) routes traffic to and from broadband remote access devices such as
A broadband remote access server (BRAS, B-RAS or BBRAS) routes traffic to and from broadband remote access devices such as digital subscriber line access multiplexer
A digital subscriber line access multiplexer (DSLAM, often pronounced ''DEE-slam'') is a network device, often located in telephone exchanges, that connects multiple customer digital subscriber line (DSL) interfaces to a high-speed digital co ...
s (DSLAM) on an Internet service provider
An Internet service provider (ISP) is an organization that provides services for accessing, using, or participating in the Internet. ISPs can be organized in various forms, such as commercial, community-owned, non-profit, or otherwise private ...
's (ISP) network. BRAS can also be referred to as a broadband network gateway or border network gateway (BNG).{{cite web, title=TR-101 Migration to Ethernet-Based DSL Aggregation, url=https://www.broadband-forum.org/technical/download/TR-101_Issue-2.pdf, website=Broadband Forum, accessdate=12 April 2018
The BRAS sits at the edge of an ISP's core network
A backbone or core network is a part of a computer network which interconnects networks, providing a path for the exchange of information between different LANs or subnetworks. A backbone can tie together diverse networks in the same building ...
, and aggregates user sessions from the access network
An access network is a type of telecommunications network which connects subscribers to their immediate service provider. It is contrasted with the core network, which connects local providers to one another. The access network may be further ...
. It is at the BRAS that an ISP can inject policy management and IP quality of service
Quality of service (QoS) is the description or measurement of the overall performance of a service, such as a telephony or computer network, or a cloud computing service, particularly the performance seen by the users of the network. To quantitat ...
(QoS).
The specific tasks include:
* Aggregates the circuits from one or more link access devices such as DSLAM
A digital subscriber line access multiplexer (DSLAM, often pronounced ''DEE-slam'') is a network device, often located in telephone exchanges, that connects multiple customer digital subscriber line (DSL) interfaces to a high-speed digital co ...
s
* Provides layer 2 connectivity through either transparent bridging or PPP sessions over Ethernet
Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...
or ATM sessions
* Enforces QoS policies
* Provides layer 3 connectivity and routes IP traffic through an Internet service provider
An Internet service provider (ISP) is an organization that provides services for accessing, using, or participating in the Internet. ISPs can be organized in various forms, such as commercial, community-owned, non-profit, or otherwise private ...
’s backbone network to the Internet
A DSLAM
A digital subscriber line access multiplexer (DSLAM, often pronounced ''DEE-slam'') is a network device, often located in telephone exchanges, that connects multiple customer digital subscriber line (DSL) interfaces to a high-speed digital co ...
collects data traffic from multiple subscribers into a centralized point so that it can be transported to a switch or router over a Frame Relay, ATM, or Ethernet connection.
The router provides the logical network termination. Common link access methods include PPP over Ethernet (PPPoE
The Point-to-Point Protocol over Ethernet (PPPoE) is a network protocol for encapsulating Point-to-Point Protocol (PPP) frames inside Ethernet frames. It appeared in 1999, in the context of the boom of DSL as the solution for tunneling packet ...
), PPP over ATM (PPPoA
In computer networking, the Point-to-Point Protocol over ATM (PPPoA) is a layer 2 data-link protocol typically used to connect domestic broadband modems to ISPs via phone lines. It is used mainly with DOCSIS and DSL carriers, by encapsulating PP ...
) encapsulated sessions, bridged Ethernet over ATM or Frame Relay
Frame Relay is a standardized wide area network (WAN) technology that specifies the physical and data link layers of digital telecommunications channels using a packet switching methodology. Originally designed for transport across Integrated Se ...
(RFC 1483/RFC 1490), or just plain Ethernet. In the case of ATM or Frame Relay based access, individual subscribers are identified by Virtual Circuit IDs. Subscribers connected over Ethernet-based remote access devices are usually identified by VLAN
A virtual local area network (VLAN) is any broadcast domain that is partitioned and isolated in a computer network at the data link layer (OSI layer 2).IEEE 802.1Q-2011, ''1.4 VLAN aims and benefits'' In this context, virtual, refers to a physi ...
IDs or MPLS
Multiprotocol Label Switching (MPLS) is a routing technique in telecommunications networks that directs data from one node to the next based on labels rather than network addresses. Whereas network addresses identify endpoints the labels identif ...
tags. By acting as the network termination point, the BRAS is responsible for assigning network parameters such as IP addresses to the clients. The BRAS is also the first IP hop from the client to the Internet.
The BRAS is also the interface to authentication, authorization and accounting systems (see RADIUS
In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...
).
See also
*Digital subscriber line access multiplexer
A digital subscriber line access multiplexer (DSLAM, often pronounced ''DEE-slam'') is a network device, often located in telephone exchanges, that connects multiple customer digital subscriber line (DSL) interfaces to a high-speed digital co ...
(DSLAM)
* Internet Protocol Control Protocol In computer networking, Internet Protocol Control Protocol (IPCP) is a Network Control Protocol (NCP) for establishing and configuring Internet Protocol over a Point-to-Point Protocol link. IPCP is responsible for configuring the IP addresses as w ...
(IPCP)
* Multi-service access node
A multi-service access node (MSAN), also known as a multi-service access gateway (MSAG), is a device typically installed in a telephone exchange (although sometimes in a roadside serving area interface cabinet) which connects customers' telephone l ...
(MSAN)
References