Abstract:
An Ethernet Metropolitan Area Network provides connectivity to one or more customer premises to packet-bases services, such as ATM, Frame Relay, or IP while advantageously providing a mechanism for assuring security and regulation of customer traffic. Upon receipt of each customer-generated information frame, an ingress Multi-Service Platform (MSP) “tags” the frame with a customer descriptor that specifically identifies the recipient customer. In practice, the MSP tags each frame by overwriting the Virtual Local Area Network (VLAN) identifier with the routing descriptor. Using the customer descriptor in each frame, a recipient Provider Edge Router (PER) or ATM switch can map the information as appropriate to direct the information to the specific customer. In addition, the customer descriptor may also include Quality of Service (QoS) allowing the recipient Provider Edge Router (PER) or ATM switch to vary the QoS level accordingly.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/833,739, filed on Jul. 9, 2010, (which is currently allowed) entitled “TECHNIQUE FOR ETHERNET ACCESS TO PACKET-BASED SERVICES”, which is a continuation of Ser. No. 11/493,157, filed on Jul. 25, 2006, (now U.S. Pat. No. 7,769,006) entitled “TECHNIQUE FOR ETHERNET ACCESS TO PACKET-BASED SERVICES”, which is a continuation of U.S. patent application Ser. No. 10/001,545, filed on Oct. 31, 2001, (now U.S. Pat. No. 7,092,389) entitled “TECHNIQUE FOR ETHERNET ACCESS TO PACKET-BASED SERVICES”, which is a continuation-in-part of U.S. patent application Ser. No. 09/772,360, filed Jan. 30, 2001, (now U.S. Pat. No. 7,120,150) entitled “TECHNIQUE FOR ETHERNET ACCESS TO PACKET-BASED SERVICES”, wherein all of the above cited applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates to a technique enabling access to packet-based services, such as IP, Frame Relay, and ATM, through an Ethernet Protocol network. 
     BACKGROUND ART 
     Presently, communication service providers, such as AT&amp;T, offer high-speed data communications service to customers through a variety of access mechanisms. For example, a customer may gain network access through a private line connection, i.e., a direct link to the communications service provider&#39;s network. Private line access provides a dedicated port not shared by anyone else with facility bandwidth available exclusively to the particular customer. Unfortunately, private line access is expensive, and is practical only for customers that have very high traffic capacity requirements. 
     As an alternative to private line access, communications service providers such as AT&amp;T also offer virtual circuit access allowing several customers to logically share a single circuit, thus reducing costs. Such shared circuits, typically referred to as Permanent Virtual Circuits, allow communication service providers to guarantee customer traffic flows that are distinguishable from each other, are secure, and allow customers to enjoy different service features. An example of such a technique for offering such shared service is disclosed in U.S. Pat. No. 6,081,524, assigned to AT&amp;T. 
     Presently, there is a trend towards using Ethernet networks in place of Frame Relay and ATM networks especially for transporting traffic among two or more premises belonging to the same customer. Ethernet-based Metropolitan Area Networks (MANs) currently exist in many areas and offer significant cost advantages on a per port basis, as compared to Frame Relay and ATM service. Transmission speeds as high as 100, 1000 or even 10,000 MB/second are possible with such Ethernet MANs. Moreover, optical Ethernet MANs typically offer a rich set of features, flexible topology and simple-end-to end provisioning. 
     Present-day Ethernet-based MANs lack the ability to logically separate traffic received from different customers, giving rise to issues of data security. Moreover, such present day Ethernet-based MANs lack the ability to manage bandwidth among customers, thus preventing the network from regulating customer traffic to assure equitable access. Thus, there is a need for a technique for routing data in an Ethernet protocol network that overcomes the aforementioned disadvantages. 
     BRIEF SUMMARY OF THE INVENTION 
     Briefly, in accordance with a preferred embodiment, a method is provided for routing data in an Ethernet protocol network having a plurality of platforms, each serving one or more customers. A first platform receives at least one frame from a sending site (e.g., a first customer&#39;s premises) that is destined for a receiving site (e.g., another premises belonging to the same or a different customer.) After receiving the frame, the first platform overwrites a portion of the frame with a customer descriptor that specifically identifies the sending customer. In practice, the first platform may overwrite a Virtual Local Area Network (VLAN) field that is typically employed by the sending customer for the purposes of routing data among various VLANs at the sending premises. Rather than overwrite the VLAN field in the frame, the first platform could overwrite another field, such as the source address field, or could even employ a “shim” header containing the customer descriptor. All further use of the term customer descriptor implies that any of the above or similar techniques could be used. 
     After overwriting the frame with the customer descriptor, the sending platform routes the frame onto the MAN for routing among the other platforms, thereby sharing trunk bandwidth and other resources, but logically distinct from other customers&#39; traffic with different customer descriptors. A destination address in the frame directs the frame to its corresponding endpoint. Upon receipt of the frame, the receiving platform uses the customer descriptor to segregate the frame for delivery to the proper destination, especially in the event where different customers served by the same platform use overlapping addressing plans. Thus, the customer descriptor in each frame advantageously enables the receiving platform to distinguish between different customers served by that platform. 
     For traffic with a destination beyond the MAN, this method provides a convenient and efficient way to map the customer descriptor to similar identifiers in a Wide Area Network (WAN), such as a Permanent Virtual Circuit (PVC), a Virtual Private Network (VPN), or an MPLS Label Switched Circuit. 
     Overwriting each frame with the customer descriptor thus affords the ability to logically segregate traffic on the Ethernet MAN to provide Virtual Private Network (VPN) services of the type offered only on more expensive Frame Relay and ATM networks. Moreover, the customer descriptor used to tag each frame can advantageously include Quality of Service (QoS) information, allowing the sender to specify different QoS levels for different traffic types, based on the Service Level Agreement (SLA) between the customer and the communications service provider. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an Ethernet Protocol Metropolitan Area Network (MAN) in which each frame is tagged with a customer descriptor in its VLAN field in accordance with the present principles; 
         FIG. 2  illustrates a sample frame for transmission over the network of  FIG. 1 ; 
         FIG. 3  illustrates a portion of the MAN showing the various stages in the tagging process; 
         FIG. 4  illustrates a portion of a MAN showing the use of the priority bits within the VLAN field to establish different quality of service levels; 
         FIG. 5  illustrates a portion of a MAN showing the manner in which frames are mapped to different Permanent Virtual Circuits by an ATM switch; 
         FIG. 6  illustrates a portion of a MAN showing the manner in which frames are mapped into different Multi-Protocol Label Switching (MPLS) tunnels; 
         FIG. 7  illustrates a portion of a MAN showing the manner in which frames are mapped into different service networks; 
         FIG. 8  illustrates a portion of a prior art Ethernet protocol network in which the VLAN on an incoming frame received at an ingress port of a switch extends directly to frame output by the switch at an egress port; and 
         FIG. 9  illustrates a portion of an alternate preferred embodiment of the invention in which a VLAN tag on a frame received at an ingress port of a switch is mapped to a second tag that is unique to an egress port of the switch which outputs the frame. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts an Ethernet Protocol Metropolitan Area Network (MAN)  10  comprised of a plurality of Multi-Service Platforms (MSPs)  12   1 - 12   n  where n is an integer, each MSP taking the form of an Ethernet switch or the like. In the illustrated embodiment n=4, although the network  10  could include a smaller or larger number of MSPs. A fiber ring or SONET ring infrastructure  14  connects the platforms  12   1 - 12   4  in daisy-chain fashion allowing each MSP to statistically multiplex information onto, and to statistically de-multiplex information off the ring infrastructure  14 . 
     Each of MSPs  12   1 - 12   3  serves at least one, and in some instances, a plurality of premises  16  belonging to one or more customers. In the illustrated embodiment of  FIG. 1 , the MSP  12   1  serves a single customer premises  16   1  belonging to customer  1  whereas, the MSP  12   2  serves premises  16   2 , and  16   3  belonging to customers  2  and  3 , respectively. The MSP  12   3  serves a single premises  16   4  that belongs to customer  3 . The MSPs  12   1 - 12   3  are linked to their corresponding premises via 10, 100 or 1000 MB links  19 . The MSP  12   4  bears the legend “CO MSP” because it serves as a central office to route traffic from the MAN  10  to a Provider Edge Router (PER)  18  for delivery to other networks, such as Frame Relay, ATM, MPLS networks or the Internet as discussed hereinafter. By the same token, the PER  18  can route traffic from such other networks onto the MAN  10  via the CO MSP  124 . 
     The traffic routed onto and off of the MAN  10  by each MSP takes the form of one or more frames  20  depicted in  FIG. 2 . Heretofore, traffic routed onto the MAN  10  from a particular customer&#39;s premises was combined with other customers&#39; traffic with no logical separation, thus raising security concerns. Moreover, since all customers&#39; traffic share the same bandwidth, difficulties existed in prior art Ethernet MANs in regulating the traffic from each customer&#39;s premises, and in affording different customers different Quality of Service (QoS) levels in accordance with individual Service Level Agreements. 
     These difficulties are overcome in accordance with the present principles by “tagging” each frame  20  routed onto the MAN  10  at a particular MSP, say MSP  12   3 , with a customer descriptor  22 ′ (best seen in  FIG. 2 ) that identifies the customer sending that frame. As discussed in greater detail below, each MSP receiving a frame  20  on the fiber ring infrastructure  14  uses the customer descriptor  22 ′ in that frame to maintain distinct routing and addressing tables that are assigned to each customer served by that MSP. This permits each customer to use its own addressing plan without fear of overlap with other customers, as the customers are all maintained as logically separate. 
       FIG. 2  depicts the structure of an exemplary Ethernet protocol frame  20  specified by Ethernet Standard 802.1Q. Among the blocks of bytes within each frame  20  is a Virtual Local Area Network (VLAN) Identifier  22  comprised of sixteen bits. In practice, the VLAN identifier  22 , in conjunction with a VLAN flag  23  within the frame, facilitates routing of the frame within a customer&#39;s premises to a particular VLAN. However, the VLAN identifier  22  has no influence on routing of the frame  20  after receipt at a MSP. 
     In accordance with the present principles, the prior disadvantages associated with conventional Ethernet networks, namely the lack of security and inability to regulate QoS levels, are overcome by overwriting the VLAN identifier  22  in each frame  20  with the customer descriptor maintained by the service provider. Overwriting the VLAN identifier  22  of  FIG. 2  of each frame  20  with the customer descriptor  22 ′ serves to “tag” that frame with the identity of its sending customer, thus affording each MSP in the MAN  10  the ability to route those frames only among the premises belonging to that same sending customer. Such tagging affords the operator of the MAN  10  the ability to provide security in connection with frames transmitted across the network, since frames with. customer ID A would not be delivered to any premises of customer with ID B. As an example, two or more customers served by a single MSP may use overlapping IP addressing schemes. In the absence of any, other identifier, the MSP receiving frames with overlapping IP addresses lacks the ability to assure accurate delivery. 
     In the illustrated embodiment depicted in  FIG. 2 , each MSP of  FIG. 1  tags each outgoing frame  20  by overwriting the VLAN identifier  22  with the customer descriptor  22 ′. However, tagging could occur in other ways, rather than overwriting the VLAN identifier  22 . For example, the source address block  25  within the frame  20  could be overwritten with the customer descriptor  22 ′. Alternatively, the data field  21  could include a shim header comprising the customer descriptor  22 ′. 
     The tagging of each frame  20  with the customer descriptor  22 ′ affords several distinct advantages in connection with routing of the frames through the MAN  10 . First, as discussed above, the tagging affords each recipient MSP the ability to distinguish traffic destined for customers with overlapping address schemes, and thus allows for segregating traffic on the MAN  10 . Further, tagging each frame  20  with the customer descriptor  22 ′ enables mapping of the frames from a MAN  100  depicted in  FIG. 3  to corresponding one of a plurality of customer Virtual Private Networks  26   1 - 26   3  within an MPLS network  28 . As seen in  FIG. 3 , an MSP  1202  within the MAN  100  receives traffic from premises  160   1 ,  160   2 , and  160   3  belonging to customer  1 , customer  2  and customer  3 , respectively, which enjoy separate physical links to the MSP. Upon receipt of each frame from a particular customer, the MSP  120   2  overwrites that frame with the customer descriptor  22 ′ corresponding to the sending customer. 
     After tagging each frame, the MSP  120   2  statistically multiplexes the frames onto the fiber ring infrastructure  14  for transmission to a CO MSP  120   4  for receipt at a destination PER  180  that serves the MPLS network  28  within which are customer Virtual Private Networks  26   1 - 26   3 . Using the customer descriptor  22 ′ in each frame, the PER  180  maps the frame to the corresponding VPN identifier associated with a particular one of customer Virtual Private Networks  26   1 - 263  to properly route each frame to its intended destination. 
     The tagging scheme of the present invention also affords the ability to route frames with different QoS levels within a MAN  1000  depicted in  FIG. 4 . As seen in  FIG. 4 , an MSP  12002  within the MAN  1000  receives traffic from premises  1600   2 , and  1600   3  belonging to customer  2  and customer  3 , respectively, which enjoy separate physical links to the MSP, allowing each to send frames into the MAN. In the illustrated embodiment of  FIG. 4 , the frames originating from the premise  1600   2  may contain either voice or data and have a corresponding QoS level associated with each type of frame. Upon receiving such frames, the MSP  1200   2  overwrites the frame with the customer descriptor  22 ′ corresponding to the particular customer sending the frame. The customer descriptor  22 ′ will not only contain the identity of the sending customer, but the corresponding QoS level associated with that frame. 
     After tagging each frame, the MSP  1200   2  statistically multiplexes the frames onto the fiber ring infrastructure  14  for transmission to a CO MSP  1200   4  for receipt at a destination PER  1800  that serves an MPLS network  280  within which are customer Virtual Private Networks  2602  and  260   3 . Using the customer descriptor  22 ′ in each frame, the PER  1800  of  FIG. 4  maps the frame to the corresponding customer VPN to properly route each frame to its intended customer VPN. Further, the PER  1800  of  FIG. 4  also maps the QoS level specified in the customer descriptor in the frame to assure that the appropriate quality of service level is applied to the particular frame. 
     In the above-described embodiments, the frames of customer traffic have been assumed to comprise IP packets that terminate on a router (i.e., Provider Edge Routers  18 ,  180  and  1800 ) and that the VPNs employ MPLS-BGP protocols. However, some customers may require multi-protocol support, or may otherwise require conventional PVCs so that the traffic streams must be mapped into Frame Relay or ATM PVCs as depicted in  FIG. 5 , which illustrates a portion of a MAN  10000  having a CO MSP  12000   4  serving an ATM switch  30  that receives traffic from the MAN. As seen in  FIG. 5 , each of premises  16000   1 ,  16000   2  and  16000   3  belonging to customer  1 , customer  2  and customer  3 , respectively, may send frames for receipt at MSP  120002  in the MAN  10000 . The MSP  12000   2  tags each frame with the corresponding customer descriptor prior to statistically multiplexing the data for transmission on the fiber ring infrastructure  14  to the CO MSP  12000   4  for receipt at the ATM switch  30 . The ATM switch  30  then maps each frame to the appropriate PVC in accordance with the customer descriptor  22 ′ in the frame in a manner similar to the mapping described with respect to  FIG. 3 . Thus, the ATM switch  30  could map the frame to one of Frame Relay recipients&#39;  32   1 ,  32   2 , or  32   3 , ATM recipients  32   4  or  32   5  or IMA (Inverse Multiplexing over ATM) recipient  326 . 
       FIG. 6  depicts a portion of a MAN network  100000  that routes frames onto separate MPLS tunnels  40   1 - 40   3  (each emulating a private line  32  in an MPLS network  28000 ) in accordance with the customer descriptor  22 ′ written into each frame by a MSP  120000   2  in the MAN. Each of customer premises  160000   1 ,  160000   2  and  160000   3  depicted in  FIG. 6  sends information frames for receipt at MSP  120000   2 . The MSP  120000   2  tags each frame with the customer descriptor prior to statistically multiplexing the data for transmission on the fiber ring infrastructure  14  for delivery to a CO MSP  120000   4  that serves a PER  18000 . The PER  18000  translates (maps) the customer descriptors written onto the frames by the MSP  120000   2  into the MPLS tunnels  40   1 - 40   3  to enable the PER to route the traffic to the intended customer. 
       FIG. 7  depicts a portion of a MAN network  1000000  for routing traffic (i.e., frames) onto separate networks in accordance with the customer descriptor written into each the frame by a MSP  120000   2  in the MAN. Each of customer premises  1600000   2  and  1600000   3  depicted in  FIG. 7  sends frames for receipt by the MSP  1200000   2 . The MSP  1200000   2  tags each frame with the customer descriptor  22 ′ prior to statistically multiplexing the data for transmission on the fiber ring infrastructure  14  for delivery to a CO MSP  1200000   4  that serves a PER  180000 . In accordance with the customer descriptor, the PER  1800000  of  FIG. 7  routes traffic to a particular one of several different networks, e.g., an Intranet VPN  42   1 , a voice network  42   2  and the Internet  42   3 , in accordance with the customer descriptor  22 ′ written onto the frame by the MSP  1200000   2 . 
     Referring to  FIG. 8 , a prior art Ethernet switch  20000000  receives Ethernet frames at one of a plurality of input (ingress) ports, exemplified by ports  22000000 ,  24000000 , and  26000000 , from one a corresponding one of networks  28000000 ,  30000000  and  32000000 , respectively. The frames are destined for an endpoint (not shown) served by a Wide Area Network (WAN)  36000000  linked to an egress port  40000000  of the switch  20000000  by an Ethernet trunk  38000000 . Each Ethernet frame received at one of the ingress switch ports  22000000 ,  24000000 , and  26000000  carries a tag, which in accordance with the IEEE 802.1Q Standard, identifies the Virtual Local Area Network (VLAN) that originated the frame. Thus, for example, a frame originated at network  32000000  associated with a VLAN having an Identification Designation (ID) of 5 will carry a tag with the corresponding VLAN ID. The VLAN address is twelve bits, offering the ability designate as many as 4096 separate VLANs. 
     A VLAN domain extends across any set of connected Ethernet switches, and therefore the address space of 4096 individual VLANs is shared across such an extended network of switches. In the past, the VLAN tag associated with an incoming Ethernet frame received at one of the ingress switch ports will extend directly to the egress switch port. Hence, the VLAN tag of an Ethernet frame received at the ingress port  26000000  extends directly to the egress port  40000000  on which the switch outputs the frame. The direct extension of the VLAN tag between the Ethernet switch ingress and egress ports increases the difficulty in the sharing and administration of the limited VLAN address space, as it now has to be coordinated across any connected group of Ethernet networks, even if they only are connected by termination on a common WAN access switch, as shown in  FIG. 8 . It also limits the size of a single switch in terms of VLAN capacity, being confined to 4096 VLANs on any given switch. 
     Referring to  FIG. 9 , in accordance with the present invention, the significance of the VLAN tag is localized to each physical port on the Ethernet switch  2000000 , instead of being global to a network. At an ingress switch port, say port  22000000 , the VLAN tag is still used to discriminate between different customer&#39;s traffic or services, but the switch  2000000  is free to re-write the tag to another value that is unique to the physical egress port  40000000 . In other words, the switch  20000000  may terminate traffic from many independent networks, each using the full 4096 VLAN address space, and internally map the traffic using a unique tuple of (Physical port, VLAN ID) to the switch output ports (only one of which is shown). This dramatically increases the scale achievable with a single switch, which is, by virtue of the mapping of tags from an ingress to egress port is now limited only by 4096 VLAN IDs on each physical port, rather than a total 4096 VLANs as is the case of the prior network of  FIG. 8 . 
     The above-described embodiments merely illustrate the principles of the invention. Those skilled in the art may make various modifications and changes that will embody the principles of the invention and fall within the spirit and scope thereof.