Abstract:
A DSLAM aggregation topology VLAN bundling mechanism includes an edge device port that receives a packet from a Digital Subscriber Line Access Multiplexer (DSLAM) device, the packet including an inner Virtual Local Area Network (VLAN) tag that identifies a Digital Subscriber Line (DSL) subscriber. A processor of the edge device adds an outer VLAN tag to the packet, the outer VLAN tag identifying the DSLAM and a destination server coupled to an Ethernet access network. It is emphasized that this abstract is provided to comply with the rules requiring an abstract that will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. 37 CFR 1.72(b).

Description:
RELATED APPLICATIONS 
     The present application is related to co-pending application Ser. Nos. 11/117,016 filed Apr. 28, 2005, entitled, “Metro Ethernet Network With Scaled Broadcast And Service Instance Domains”; 11/117,250 filed Apr. 28, 2005, entitled, “A Comprehensive Model For VPLS”; and 11/117,249 filed Apr. 28, 2005, entitled, “Scalable System And Method For DSL Subscriber Traffic Over An Ethernet Network”, which applications are assigned to the assignee of the present application. 
     FIELD OF THE INVENTION 
     The present invention relates generally to data communications systems; more specifically, to subscriber access and communications over a high-speed network. 
     BACKGROUND OF THE INVENTION 
     Digital Subscriber Line (DSL) technology is widely-used today for increasing the bandwidth of digital data transmissions over the existing telephone network infrastructure. In a typical system configuration, a plurality of DSL subscribers are connected to a service provider (SP) network through a Digital Subscriber Line Access Multiplexer (DSLAM), which concentrates and multiplexes signals at the telephone service provider location to the broader wide area network. Basically, a DSLAM takes connections from many customers or subscribers and aggregates them onto a single, high-capacity connection. The DSLAM may also provide additional functions such as routing or Internet Protocol (IP) address assignment for the subscribers. 
     Asynchronous Transfer Mode (ATM) protocol networks have traditionally been utilized for communications between DSLAM devices and web feature servers such as Broadband Remote Access Servers (BRAS) and Layer 3 Virtual Private Network (L3VPN) servers. A BRAS is a device that terminates remote users at the corporate network or Internet users at the Internet service provider (ISP) network, and commonly provides firewall, authentication, and routing services for remote users. The ATM protocol is an international standard in which multiple service types (such as voice, video, or data) are conveyed in fixed-length “cells” over point-to-point network connections. ATM networks need a virtual circuit (VC) to be set up across the network before data transfer may occur. That is, communication between a subscriber and a feature server requires allocation of a separate VC. Data packet cells travel through the ATM switches from the user network interface (UNI) to the network node interface (NNI) through a process called Virtual Path Identifier/Virtual Channel Identifier (VP/VCI) translation. The VPI/VCI identifiers are used by the ATM switches to switch/direct the subscriber traffic to a given feature server, and in the reverse direction to forward server traffic to a given DSLAM/subscriber, without ambiguity. Furthermore, the VPI/VCI mechanism is used by the feature server to identify the subscriber. By way of background, U.S. Pat. No. 6,801,533 teaches a system and method for proxy signaling in a DSLAM and generally describes a DSL network that includes communication transfer of signals from a DSLAM to a remote access server over a high-speed ATM network. Transmission of packet data over an ATM network is also taught in U.S. Pat. No. 6,785,232. 
     Ethernet is a technology that originated based on the idea of peers on a network sending messages in what was essentially a common wire or channel. Each peer has a globally unique key, known as the Media Access Control (MAC) address to ensure that all systems in an Ethernet have distinct addresses. Most modern Ethernet installations use Ethernet switches (also referred to as “bridges”) to implement an Ethernet “cloud” or “island” that provides connectivity to the attached devices. The switch functions as an intelligent data traffic forwarder in which frames are sent to ports where the destination device is attached. Examples of network switches for use in Ethernet network environments are found in U.S. Pat. Nos. 6,850,542, 6,813,268 and 6,850,521. 
     As the use of Ethernet has become more widespread, researchers and service providers have developed a variety of methods and systems for data transmission using Ethernet technology. For example, U.S. Pat. No. 6,829,252teaches a DSLAM device that incorporates a means of transporting Ethernet frame data over a very high-speed DSL (VDSL) transport facility. According to this approach, Ethernet frames are encapsulated within High-Level Data Link Control (HDLC) protocol formatted VDSL frames, which are then transmitted over a plurality of point-to-point links to customer sites. Ethernet-based DSL methods and systems are also described in U.S. Pat. No. 6,785,265. 
     The proliferation of Ethernet has also led service providers to seek ways of using Ethernet access network technology instead of ATM network technology to connect and aggregate DSLAM traffic to BRAS and other feature servers. However, achieving the three basic requirements of: (1) directing subscriber traffic to a given feature server depending on the requested service; (2) identifying the subscriber at the feature server; and (3) directing feature server traffic to a given subscriber in the reverse direction—all without any ambiguity—has proven difficult. 
     According to one proposal, Dynamic Host Configuration Protocol (DHCP) relay agents or Point-to-Point over Ethernet (PPPOE) intermediate agents are incorporated into the network edge device, e.g., the DSLAM or Ethernet access switch. (PPPOE is a specification for connecting Ethernet users to the Internet through a common broadband medium such as a DSL.) In this approach, the Ethernet edge device provides the DHCP server or Remote Authentication Dial-In User Service/Authentication, Authorization and Accounting (RADIUS/AAA) server with the same information it would normally receive from a BRAS DHCP relay agent or from a BRAS RADIUS client function in an ATM network. Although this proposal solves the problem of identifying the subscriber at the feature server, it fails to satisfy the other two requirements listed above. 
     In another proposal, the edge device translates the source MAC address of the subscriber packets into a new MAC address encoded with a DSLAM ID and line ID. This translation is performed such that the resultant MAC address is unique within the service provider network. When the packet is received by the feature server, the subscriber ID is extracted from the source MAC address. This proposal, however, suffers from several drawbacks that include limited DSLAM ID and port ID space, problems with reverse mapping of the provider MAC address to a subscriber MAC address, and security issues. Additionally, this approach is inadequate for multipoint applications where a separate broadcast domain (e.g., separate VLAN) is needed per service instance. 
     Thus, what is a needed is an alternative system and method for data communications between DSLAM devices and feature servers over an Ethernet network that overcomes the shortcomings of past approaches. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be understood more fully from the detailed description that follows and from the accompanying drawings, which however, should not be taken to limit the invention to the specific embodiments shown, but are for explanation and understanding only. 
         FIG. 1  is a diagram showing a network topology according to one embodiment of the present invention. 
         FIG. 2  illustrates a VLAN bundling model in accordance with one embodiment of the present invention. 
         FIG. 3  illustrates a VLAN bundling model in accordance with another embodiment of the present invention. 
         FIG. 4  is a generalized circuit schematic block diagram of a network node. 
     
    
    
     DETAILED DESCRIPTION 
     A DSL network VLAN bundling mechanism that provides DSL subscriber identification over an Ethernet network, and which further provides feature server selection and forwarding of subscriber traffic to a given feature server, and in the reverse direction forwarding traffic back to a given subscriber without ambiguity, is described. In the following description specific details are set forth, such as device types, protocols, configurations, etc., in order to provide a thorough understanding of the present invention. However, persons having ordinary skill in the networking arts will appreciate that these specific details may not be needed to practice the present invention. 
     A computer network is a geographically distributed collection of interconnected subnetworks for transporting data between nodes, such as intermediate nodes and end nodes. A local area network (LAN) is an example of such a subnetwork; a plurality of LANs may be further interconnected by an intermediate network node, such as a router, bridge, or switch, to extend the effective “size” of the computer network and increase the number of communicating nodes. Examples of the end nodes may include servers and personal computers. The nodes typically communicate by exchanging discrete frames or packets of data according to predefined protocols. In this context, a protocol consists of a set of rules defining how the nodes interact with each other. 
     As shown in  FIG. 4 , each node  50  typically comprises a number of basic subsystems including a processor subsystem  51 , a main memory  52  and an input/output (I/O) subsystem  55 . Data is transferred between main memory (“system memory”)  52  and processor subsystem  51  over a memory bus  53 , and between the processor and I/O subsystems over a system bus  56 . Examples of the system bus may include the conventional lightning data transport (or hyper transport) bus and the conventional peripheral component [computer] interconnect (PCI) bus. Node  50  may also comprise other hardware units/modules  54  coupled to system bus  56  for performing additional functions. Processor subsystem  51  may comprise one or more processors and a controller device that incorporates a set of functions including a system memory controller, support for one or more system buses and direct memory access (DMA) engines. In general, the single-chip device is designed for general-purpose use and is not heavily optimized for networking applications. 
     In a typical networking application, packets are received from a framer, such as an Ethernet media access control (MAC) controller, of the I/O subsystem attached to the system bus. A DMA engine in the MAC controller is provided a list of addresses (e.g., in the form of a descriptor ring in a system memory) for buffers it may access in the system memory. As each packet is received at the MAC controller, the DMA engine obtains ownership of (“masters”) the system bus to access a next descriptor ring to obtain a next buffer address in the system memory at which it may, e.g., store (“write”) data contained in the packet. The DMA engine may need to issue many write operations over the system bus to transfer all of the packet data. 
     The present invention leverages the frame format and some of the functionality defined in the proposed IEEE 802.1 ad specification that supports the so-called “Q-in-Q” encapsulation (also known as VLAN bundling or tag stacking) mechanism. According to this draft standard, each data packet includes an upper (i.e., outer) 12-bit VLAN tag and a lower (i.e., inner) 12-bit VLAN tag. In accordance with one embodiment of the present invention, the inner VLAN tag is used to identify the customer or subscriber, and the outer VLAN tag is utilized to specify the DSLAM and feature server pair. 
       FIG. 1  is a diagram showing a DSLAM access/aggregation network topology  10 , which includes and Ethernet access network  12  with user-facing provider edge (u-PE) devices  22  &amp;  23  connected to a network-facing provider edge (n-PE) device  28  through one or more bridges or switches  25  &amp;  26 , also frequently referred to as provider edge aggregation (Agg-PE) devices. (In the context of the present application, the terms “bridge” and “switch” are considered synonymous.) The left-hand side of  FIG. 1  shows a plurality of DSLAMs (e.g., devices  18  &amp;  19 ) coupled to u-PE device  23 . Each DSLAM aggregates a plurality of customers or subscribers. For example, customer edge (CE) devices  14  &amp;  15  (respectively representing residential DSL subscriber  14  and business DSL subscriber  15 ) are shown connected to the input ports of DSLAM  18 . Similarly, customer edge (CE) devices  16  &amp;  17  are shown connected to DSLAM  19 . On the right-hand side of  FIG. 1  n-PE device  28  is shown connected to a plurality of service nodes, which include BRAS server  30  and L3VPN server  31 . 
       FIG. 2  illustrates the concept of VLAN bundling in accordance with one embodiment of the present invention. The top portion of  FIG. 2  shows a path from CE device  15  to feature server  31 , which path passes through DSLAM  18 , u-PE device  23 , Ethernet access network  12 , and n-PE device  28 . Data packet format diagrams are shown under each corresponding network connection. 
     In the example of  FIG. 2 , VLAN bundling functionality is performed by the edge switch (i.e., u-PE device  23 ), with a processor of DSLAM  18  mapping the subscriber VLAN (line-id) and the requested service type into an IEEE 802.1q VLAN tag. As is well known, the IEEE 802.1q specification defines a standard for inserting Virtual Local Area Network (VLAN) information into Ethernet frames. For example, according to the existing standard, a 12-bit tag that uniquely identifies the subscriber VLAN is inserted into an Ethernet frame at DSLAM  18 . Thereafter, the customer frame sent by CE device  15  arrives at u-PE device  23  with a data packet format consistent with the IEEE 802.1q specification, which format includes a customer MAC header, a subscriber VLAN tag, a Layer 2 protocol data unit (L2PDU) payload, and a service provider Frame Check Sum (FCS). 
     In the exemplary embodiment of  FIG. 2 , u-PE device  23  is a standard IEEE 802.1ad switch that adds an outer VLAN tag which specifies the DSLAM/feature server connection. In other words, the outer VLAN tag identifies the pair of DSLAM and feature server devices (e.g., devices  18  &amp;  31 ) so that data packets always arrive at the correct network destination. The inner VLAN tag identifies the subscriber, which, in the present example, is utilized to identify the subscriber connected through CE device  15 , as distinguished from the residential subscriber connected to CE device  14 . 
     Practitioners in the networking arts will appreciate that since a unique VLAN (outer tag) is used to uniquely identify a DSLAM and feature server pair, the data traffic in the forward direction (i.e., from left-to-right in  FIG. 2 ) gets forwarded only to the specified feature server. The same is true in the reverse direction. When the frame arrives at feature server  31 , the subscriber line-id may be determined by examination of the inner VLAN tag. Furthermore, since a unique outer VLAN tag is used per DSLAM/server pair, a separate broadcast domain is used per DSLAM/server pair across access network  12 , thereby avoiding potential conflicts that might otherwise occur when subscribers&#39; MAC addresses on different DSLAMs overlap. Moreover, since a unique inner VLAN tag is utilized within each DSLAM, any potential conflict from overlapping subscribers&#39; MAC addresses within a given DSLAM is similarly avoided. 
     Those of skill in the networking arts will understand that the IEEE 802.1p specification enables Layer 2 switches to prioritize traffic and perform dynamic multicast filtering. The prioritization specification works at the media access control (MAC) framing layer (i.e., Open Systems Interconnection model Layer 2). In accordance with another embodiment of the present invention, the limitation of 4,094DSLAM/feature server pairs imposed by the 12-bit VLAN tag field may be extended through the use of the 802.1p bits. In this embodiment, the DSLAM adds the inner tag to represent the subscriber line-id only, with the service type being reflected in the 802.1p bits. The edge switch (e.g., u-PE device  23 ) uses this combination of both 802.1q (VLAN id) and 802.1p bits to determine the outer VLAN tag, thereby increasing to 32K the total number of DSL subscribers/requested service connections that can be supported (i.e., 4K subscriber lines with each line supporting up to 8 different services.) In this case, the outer VLAN tag still represented the associated DSLAM and requested service as before. 
       FIG. 3  illustrates a VLAN bundling model in accordance with another embodiment of the present invention in which VLAN bundling is performed at the DSLAM edge device, e.g., DSLAM  18 . Note that this embodiment is essentially the same as that shown in  FIG. 2 , except that the functionality for adding the outer VLAN tag previously performed by u-PE device  23  is now performed by DSLAM  18 . That is, DSLAM  18  is configured to perform IEEE 802.1ad bundling, wherein DSLAM  18  adds first and second VLAN tags to the customer frame. The first VLAN tag identifies the Digital Subscriber Line (DSL) subscriber, and the second VLAN tag identifies the DSLAM/feature server pair. 
     Note that in the embodiment of  FIG. 3 , if ATM encapsulation of frames is used between CE device  15  and DSLAM  18 , then an ATM VC (VPI/VCI) is mapped to the inner VLAN tag of the IEEE 802.1ad frame, and the outer VLAN tag represents the DSLAM and the selected service on that DSLAM. For instance, if the ATM VC is associated with a particular data service, then the outer VLAN tag represents both the associated DSLAM as well as the data service type. 
     It should also be understood that elements of the present invention may also be provided as a computer program product which may include a machine-readable medium having stored thereon instructions which may be used to program a computer (e.g., a processor or other electronic device) to perform a sequence of operations. Alternatively, the operations may be performed by a combination of hardware and software. The machine-readable medium may include, but is not limited to, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, magnet or optical cards, propagation media or other type of media/machine-readable medium suitable for storing electronic instructions. For example, elements of the present invention may be downloaded as a computer program product, wherein the program may be transferred to a node or switch by way of data signals embodied in a carrier wave or other propagation medium via a communication link (e.g., a modem or network connection). 
     Additionally, although the present invention has been described in conjunction with specific embodiments, numerous modifications and alterations are well within the scope of the present invention. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.