Patent Publication Number: US-2004042446-A1

Title: Maintaining routing information in a passive optical network

Description:
[0001] This application claims priority from U.S. Provisional Application Serial No. 60/386,129, filed May 31, 2002, the entire content of which is incorporated herein by reference. 
    
    
     
       TECHNICAL FIELD  
       [0002] The invention relates to computer networking and, more particularly, to the maintenance of routing information within a passive optical network (PON).  
       BACKGROUND  
       [0003] A passive optical network (PON) can deliver voice, video and other data among multiple network nodes using a common optical fiber link. Passive optical splitters and combiners enable a number of network nodes to share the optical fiber link. Each network node terminates the optical fiber link for a residential or business subscriber, and is sometimes referred to as a subscriber premises node. A PON typically includes a PON interface having multiple, independent PON interface modules that serve multiple optical fiber links. In the case of data services, the PON interface receives data packets from an Internet Service Provider (ISP) for transmission to network nodes.  
       SUMMARY  
       [0004] In general, the invention is directed to techniques for creating and maintaining routing information within a passive optical network (PON). More specifically, a PON interface monitors communications between clients and one or more servers and generates routing information that associates the clients with respective PON interface modules of the PON interface based on the monitored communications. The routing information may, for example, associate network addresses leased to the clients by the servers with associated PON interface modules. The PON interface routes the traffic within the PON in accordance with the generated routing information.  
       [0005] For example, the PON interface may receive a Dynamic Host Configuration Protocol (DHCP) request to obtain a network address from a client represented by a network node within the PON. The PON interface maps a particular interface module on which the client resides to unique client information, e.g., a media access control (MAC) address or other identifier, included in the DHCP request. The PON interface forwards the request to a DHCP server, which returns a DHCP response indicating an administered Internet Protocol (IP) address and lease time for the requesting client. Upon receipt of the DHCP response, the PON interface updates the mapping to create routing information for routing packets to the administered IP addresses.  
       [0006] In one embodiment, the invention provides a method comprising monitoring communications between one or more servers and clients of a passive optical network, generating routing information to associate each of the clients with respective interface modules of a passive optical network interface based on the monitored traffic, the passive optical network interface communicatively coupling the servers and the clients, and routing traffic within the passive optical network in accordance with the generated routing information.  
       [0007] In another embodiment, the invention provides an interface for coupling one or more servers to clients within a passive optical network, the interface comprising a plurality of interface modules to transmit information to the clients via a plurality of optical fiber links, each of the interface modules corresponding to a particular one of the optical fiber links, and routing information that associates each of the clients with respective ones of the interface modules in order to route traffic to the clients, wherein the interface monitors communications between the clients and the servers in order to generate the routing information.  
       [0008] In a further embodiment, the invention provides a passive optical network comprising a plurality of network nodes to provide passive optical network services to one or more clients, at least one server to assign network addresses to the clients of the network nodes, an interface that includes a plurality of interface modules to transmit information to subsets of the network nodes, wherein the interface includes routing information that associates each of the interface modules with the clients of the respective subsets of network nodes.  
       [0009] The invention may provide one or more advantages. In particular, the invention operates in accordance with Layer  3 , i.e., the network layer, routing information to provide the PON with more efficient routing. Layer  2  information, i.e., data link layer information, does not need to be carried across PON  10 . Also, this technique enables the use of Layer  3  security methods, and lower cost switching methods associated with Layer  3  switching and routing. In addition, the technique provides ease of administration because Layer  2  methods of routing, such as Virtual Local Area Network (VLAN) tagging, are not required. The techniques further allow for non-repudiation of traffic origination, and isolation of IP traffic anomalies to a specific interface. In general, for a PON access network using DHCP Boot-Relay for IP address assignment to clients, this technique provides a way for the access network to establish DHCP IP address routing information to specific PON interface modules.  
       [0010] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
     [0011]FIG. 1 is a block diagram illustrating a passive optical network (PON).  
     [0012]FIG. 2 is a block diagram illustrating a PON in which groups of network nodes couple to a PON interface that includes multiple PON interface modules, each with a corresponding Dynamic Host Configuration Protocol (DHCP) relay agents.  
     [0013]FIG. 3 is a block diagram illustrating a PON in which groups of network nodes couple to a PON interface that includes multiple PON interface modules, each of which corresponds to a common DHCP relay agent.  
     [0014]FIG. 4 is a flowchart illustrating interaction of various PON components to create and maintain routing information in accordance with the invention.  
     [0015]FIG. 5 is a flowchart illustrating an exemplary mode of operation of a PON interface handling an inbound packet. 
    
    
     DETAILED DESCRIPTION  
     [0016]FIG. 1 is a block diagram illustrating a passive optical network (PON)  10 . PON  10  can be arranged to deliver voice, data and video content (generally “information”) to a number of network nodes via optical fiber links  11 . For example, a PON interface  12  may receive voice information from the public switched telephone network (PSTN)  14  via a switch facility  16 . In addition, PON interface  12  may be coupled to one or more Internet service providers (ISPs)  18  via a router  20 .  
     [0017] As further shown in FIG. 1, PON interface  12  may receive video content  22  from video content suppliers via a streaming video headend  24 . In each case, PON interface  12  receives the information, and distributes it along optical fiber links  11 A and  11 B (collectively optical fiber links  11 ) to groups  26 A and  26 B (collectively groups  26 ) of network nodes  28 A,  28 B,  28 C and  28 D (collectively nodes  28 ). Each of groups  26  is coupled to a particular one of optical fiber links  11 .  
     [0018] Furthermore, each of optical fiber links  11  may be connected to a particular interface module of PON interface  12 . In this manner, respective interface modules of PON interface  12  and groups  26  of network nodes  28  terminate opposite ends of optical fiber links  11  in order for communication between PON interface  12  and network nodes  28 . PON interface  12  may be coupled to any number of fiber links  11 . Accordingly, FIG. 1 shows only two fiber links  11 A,  11 B for purposes of illustration.  
     [0019] Network nodes  28  include hardware for receiving information from PON  10  via optical fiber links  11 , and delivering the information to one or more devices associated with respective network nodes  28 . For example, each of network nodes  28  may serve as a PON access point for one or more computers, network appliances, televisions, set-top boxes, wireless devices, or other similar devices. PON interface  12  may be located near or far from a group  26  of network nodes  28 . In some existing networks, however, PON interface  12  may reside in a central office situated within approximately ten miles from each of network nodes  28 .  
     [0020] A network node  28  may be located at any of a variety of locations, including residential or business sites. In addition, a single network node  28  may operate on a shared basis to deliver information to two or more closely located residences or businesses via copper or additional optical fiber connections, either directly or via a network hub, router or switch. A group  26  of network nodes  28  may refer to nodes served by PON interface  12  via a common optical fiber link  11 . Each group  26  in FIG. 1 contains two network nodes  28  for purposes of illustration. However, a group  26  may include a single network node  28 , or numerous network nodes  28 .  
     [0021] Network nodes  28  also may include hardware for transmitting information over PON  10 . For example, a network node  28  may transmit voice information over PSTN  14  via PON interface  12  and switch facility  16  in the course of a telephone conversation. In addition, a network node  28  may transmit data to a variety of network nodes on the Internet via ISP  18 , router  20  and PON interface  12 . Multiple network nodes  28  typically transmit over a common optical fiber link  11  using time division multiplexing techniques.  
     [0022] As described above, each of network nodes  28  may serve as a PON access point for one or more devices. Each of the devices to which network nodes  28  serve as a PON access point have a network address, such as an Internet Protocol (IP) address, that is used to route packets within a local area network (LAN) of the PON. In this manner, numerous IP addresses may correspond to a single network node  28 . The IP addresses may be IPv4 addresses, IPv6 addresses, or a combination thereof.  
     [0023] Network nodes  28  in different groups  26  served by different optical fiber links  11  may be assigned IP addresses within a common subnet scope, thereby conserving IP addresses and promoting increased IP address usage. PON interface  12  maintains routing information and stores the routing information in an archive. The routing information may be used to route traffic to appropriate interface modules of PON interface  12 . More specifically, the routing information associates IP addresses assigned to the devices served by network nodes  28  with corresponding interface modules of PON interface  12 .  
     [0024] In general, as will be described, PON interface  12  uses the Dynamic Host Configuration Protocol (DHCP) protocol to assign IP addresses and create Layer- 3  routing information, i.e., routing information mapping IP addresses to interface modules, for PON  10 . In accordance with the invention, PON interface  12  monitors communications between a DHCP server and a DHCP client, i.e., a device served by a network node  28 , and generates routing information that maps each interface module of PON interface  12  with an associated set of IP addresses based on the monitored communications.  
     [0025] The techniques used to generate the routing information allow PON  10  to associate DHCP assigned IP addresses across its network as well as establish corresponding routing of IP packets across its network. The techniques work within the DHCP protocol of the client and server, and can be labor saving because there is a reduced need for manual administration of IP address routing. In addition, the techniques allow routing to be established between individual nodes  28  and interface modules of PON interface  12  by monitoring the dialog of the commonly known DHCP protocol.  
     [0026] Because the techniques of the invention operate at Layer  3 , i.e., the network layer, the routing information provides PON  10  with more efficient routing. In particular, Layer  2  information, i.e., data link layer information, does not need to be carried across PON  10 . Also, this technique enables the use of Layer  3  security methods, and lower cost switching methods associated with Layer  3  switching and routing. In addition, the technique provides ease of administration because Layer  2  methods of routing, such as Virtual Local Area Network (VLAN) tagging, are not required. The techniques further allow for non-repudiation of traffic origination, and isolation of IP traffic anomalies to a specific interface. In general, for a PON access network using DHCP Boot-Relay for IP address assignment to clients, this technique provides a way for the access network to establish DHCP IP address routing information to specific PON interface modules.  
     [0027] Exemplary components for implementing PON  10  are commercially available from Optical Solutions, Inc., of Minneapolis, Minn., and designated by the tradename Fiberpath 400™, including the Fiberdrive™ headend bay interface and the Fiberpoint™ subscriber premise nodes.  
     [0028]FIG. 2 is a block diagram illustrating a PON  10  with groups  26  of network nodes  28  coupled to multiple PON interface modules  34 A- 34 M (collectively interface modules  34 ) within PON interface  12 . PON interface  12  may include multiple PON interface modules  34 , e.g., arranged in a common chassis. Each PON interface module  34  may form an independent Ethernet interface that serves a group  26  of network nodes  28  coupled to a common optical fiber link  11 . Hence, PON interface module  34  and network nodes  28  terminate opposite ends of optical fiber link  11 .  
     [0029] Each of PON interface modules  34  may further incorporate a respective DHCP relay agent  38 A- 38 N (collectively DHCP relay agents  38 ) that passes DHCP messages between a DHCP client represented on one of network nodes  28  and one of DHCP servers  36 A- 36 N (collectively DHCP servers  36 ), which may be maintained by respective ISPs  18 . For example, DHCP relay agents  38  may generate DHCP proxy requests, and transmit the requests to DHCP servers  36  for the group  26  of network nodes  28  served by the respective PON interface module  34 .  
     [0030] In some embodiments, an optical fiber link  11  may include a pair of optical fibers, forming an outgoing link and an incoming link. As shown in FIG. 2, PON interface modules  34  receive information from one or more ISPs  18 A- 18 N (collectively ISPs  18 ) via network routers  20 A- 20 N (collectively routers  20 ), and transmit the information to network nodes  28  via optical fiber link  11 . As a result, different ISPs  18  can serve network nodes  28  via a common optical fiber link  11 , providing the DHCP clients with a choice among two or more of ISPs  18 . Similarly, PON interface modules  34  receive information from network nodes  28 , and transmit the information to one or more of ISPs  18  via respective ones of routers  20 .  
     [0031] PON  10 , illustrated in FIG. 2, may use DHCP relay techniques to provide IP addresses to clients represented on network nodes  28 . In accordance with the invention, PON interface  12  associates a DHCP obtained IP address for a client with a respective PON interface module  34  on which the client resides and generates routing information to reflect the associations. For example, DHCP relay agent  38  monitors DHCP communications between DHCP servers  36  and the DHCP clients of network nodes  28  and updates the routing information that associates each PON interface module  34  with an associated set of IP addresses based on the monitored DHCP communications.  
     [0032] Routing IP packets between PON interface  12  and network nodes  28  may be based on the association gleaned from monitoring DHCP relay dialog between DHCP servers  36  and the DHCP clients of network nodes  28 . By monitoring the DHCP IP address assignment given to a client by the DHCP server that administers IP addresses to the client, a unique routing path through a PON may be constructed. This association between the assigned IP address and respective PON interface module  34  exists for the duration of the DHCP defined lease or until the client releases the IP address per the protocol.  
     [0033] More specifically, when a DHCP client wants to obtain an IP address, it broadcasts a DHCP request on a corresponding LAN segment that is attached to the Ethernet device of the respective network node  28 . The DHCP client device may want to obtain an IP address upon reboot or upon expiration of a previously leased IP address. Network node  28  may forward the DHCP request to PON interface  12  via the PON. The DHCP request protocol includes information that makes the request unique to the DHCP client. For example, the DHCP request may include a media access control (MAC) address of the client device.  
     [0034] PON interface  12  uses the information to create a mapping between the unique information from the DHCP request, e.g., the MAC address of the client device, and PON interface module  34  on which the DHCP client resides. For example, if a client device that resides on node  28 A of group  26 A sends the DHCP request, PON interface  12  creates a mapping that associates the MAC address of the DHCP client device of node  28 A with PON interface module  34 A. PON interface  12  forwards the DHCP request to the provisioned DHCP server  36  via the respective DHCP relay agent  36  of PON interface module  34 . The DHCP request may be provisioned with DHCP relay parameters such as a particular DHCP server  36  and a gateway address to which the DHCP request should be forwarded.  
     [0035] PON  12  receives a DHCP response from the respective DHCP server  36  and determines the particular PON interface module  34  to which to forward the DHCP response. The DHCP response may contain information, such as the MAC address of the destination DHCP client device, which PON interface  12  inspects to determine the appropriate PON interface module  34  for forwarding of the packet. Particularly, PON  12  determines the appropriate PON interface module  34  for forwarding the packet using the mapping that associates the MAC address of the client device with a respective PON interface module  34 .  
     [0036] The IP address administered in the DHCP response, i.e., leased to the requesting DHCP client, may be used to update the mapping to create routing information  39  on PON interface  12  for forwarding packets. Specifically, PON interface  12  may update the mapping to associate the IP address leased to the DHCP client with a respective PON interface module  34 . In this manner, routing information  39  is updated so that the PON interface modules  34  on PON interface  12  represent the administered IP address when associated routing entities are forwarding data to the specified IP address. In other words, PON interface  12  routes communications through PON  10  in accordance with routing information  39 .  
     [0037] PON interface  12  forwards the DHCP response to network node  28  that represents the DHCP client making the request. Network node  28  forwards the DHCP response to the original requesting DHCP client. Network node  28  may also use the administered IP address, and other information contained in the DHCP response, such as an IP subnet scope, to determine whether forwarding of packets inside the IP address space scope of the DHCP client should be done by network node  28  or whether the DHCP client device is trying to communicate with devices that are locally attached. For example, network node  28  may only forward addresses that are within the IP subnet scope indicated within the response.  
     [0038] The DHCP response also contains lease-time information that may be monitored. The lease time determines the amount of time the requesting DHCP client may use the allocated IP address. PON interface  12  monitors all DHCP protocol traffic between respective DHCP servers  36  and DHCP clients. Monitoring traffic between DHCP servers  36  and the client allows PON  12  to identify leasing events, such as the DHCP client releasing the administered IP address, attempting to renew the lease time, or DHCP server  36  declining the renewal of the IP address.  
     [0039] If the address is released, for instance, PON interface  12  may update routing information  39  to delete the representation of the path to the former DHCP client for which the IP address was administered. In other words, PON interface  12  may delete the mapping of the administered IP address to respective PON interface module  34  from routing information  39 . In the event that the DHCP client does not renew the address within the lease time period, the administered IP address will be removed from routing information  39  maintained by PON interface  12  upon expiration of the lease time period.  
     [0040]FIG. 3 is a block diagram illustrating another exemplary PON  40 . PON  40  conforms substantially to PON  10  illustrated in FIG. 2, but PON  40  includes a PON interface  41  in which PON interface modules  34  each correspond to a common DHCP relay agent  42 . In this manner, a single DHCP relay agent  42  passes DHCP messages between a DHCP clients represented on network nodes  28  and DHCP servers  36  for all of PON interface modules  34  of PON interface  41 . Further, DHCP relay agent  42  updates routing information  39  upon identifying DHCP communications that include network address lease information.  
     [0041]FIG. 4 is a flowchart illustrating interaction of various PON components to create and maintain routing information, such as routing information  39  (FIG. 2), in accordance with the invention. Network node  28  receives a DHCP request for an IP address from a DHCP client represented by the particular network node  28 , and transmits the DHCP request to PON interface  12  via PON  16  ( 43 ,  44 ). For example, upon reboot or lease expiration, the DHCP client may broadcast a DHCP request on a corresponding LAN segment attached to network node  28 .  
     [0042] PON interface  12  and, more specifically, a respective one of PON interface modules  34  receives the DHCP request from network node  28  ( 46 ). The DHCP request may include information, such as a MAC address, that is unique to the requesting DHCP client. PON interface  12  creates a unique mapping based on the client information contained in the DHCP request and PON interface module  34  on which the client resides, i.e., PON interface module  34  that received the DHCP request ( 48 ). For example, PON interface  12  may create a mapping that associates MAC addresses corresponding to DHCP clients of network nodes  28  with respective PON interface modules  34  associated with network nodes  28 .  
     [0043] PON interface module  34  relays the request to a DHCP relay agent  38  ( 50 ). DHCP relay agent  38  may be a centralized DHCP relay agent that communicates traffic between network nodes  28  and DHCP servers  36  for all of PON interface modules  34 . Alternatively, each PON interface module  34  may incorporate a DHCP relay agent  38 . The DHCP request may further contain relay parameters that specify a particular one of DHCP servers  36  to receive the request, or a particular gateway address. DHCP relay agent  38  transmits a DHCP proxy request to the appropriate DHCP server  36  on behalf of the requesting DHCP client ( 52 ).  
     [0044] Upon receipt of the DHCP proxy request, DHCP server  36  retrieves an IP address from a pool of available IP addresses within the selected subnet scope reserved by the corresponding ISP  18  ( 54 ,  56 ). DHCP server  36  then transmits a DHCP response, which contains an IP address lease, to PON interface  12  ( 58 ). The response specifies an IP address and a duration for which the IP address will remain in force for the requester. The response may further include an IP address subnet scope, MAC address of the requesting DHCP client, or other information related to the lease.  
     [0045] Upon receipt of a DHCP response from DHCP server  36 , PON interface  12  determines which of PON interface modules  34  receives the forwarded DHCP response ( 60 ). For example, PON interface  12  may extract a MAC address of the requesting DHCP client from the DHCP response and inspect the mapping of MAC addresses to PON interface modules  34  to determine the appropriate PON interface module  34  to route the packet to. Furthermore, PON interface  12  may update the mapping in order to generate routing information that associates the IP address administered in the response with the respective PON interface module  34  for routing packets ( 62 ). For example, PON interface may generate routing information to map a particular IP address to an appropriate PON interface module  34 . In this manner, PON  12  creates routing information that may be used to route incoming packets to an appropriate PON interface module within PON interface  12  and thus for forwarding data to specified destination IP addresses.  
     [0046] PON interface  12  forwards the DHCP response to network node  28  representing the DHCP client via the appropriate one of PON interface modules  34  in accordance with the routing information ( 64 ). Network node  28  receives the response from the respective PON interface module  34 , and forwards the response to the requesting DHCP client ( 66 ,  68 ). Network node  28  uses information contained in the DHCP response to determine the appropriate DHCP client to forward the packet to.  
     [0047] For example, the DHCP response may include a MAC address of the DHCP client, which network node  28  uses to forward the packet destined for the DHCP client. Network node  28  may further use information, such as the administered IP address and IP subnet scope, contained in the response for routing packets sourced from the DHCP client. For example, a DHCP client may send a packet to a printer device that is locally attached. Network node  28  realizes that the communication from the DHCP client is to a locally attached device, and does not forward the packet to PON  10 .  
     [0048] PON interface  12  continues to monitor traffic between the DHCP client on network node  28  and DHCP server  36  in order to maintain accurate routing information ( 70 ). Because each administered IP address has a lease time, PON interface  12  may monitor DHCP traffic to ensure the accuracy of the routing information. For example, in the event that the DHCP client releases the IP address, PON interface  12  may update routing information to reflect the change. Furthermore, PON interface  12  may track the lease time for an administered IP addresses. In this case, PON interface  12  may update routing information upon expiration of the lease period. When tracking lease times it may be important to monitor DHCP traffic to update lease times in the event the client renews the lease of the administered IP address.  
     [0049]FIG. 5 is a flowchart illustrating an exemplary mode of operation of PON interface  12  handling an inbound packet. PON interface  12  receives an inbound packet ( 72 ). The inbound packet may be from a DHCP client represented on one of network nodes  28  or from an ISP  18 . PON interface  12  determines whether the packet contains DHCP communications ( 74 ). When the packet does not contain DHCP communications, PON interface  12  inspects routing information to determine which of PON interface modules  34  should receive packet ( 76 ). PON interface  12  forwards the packet to the appropriate PON interface module  34  in accordance with the routing information ( 78 ). PON interface module  34  forwards the packet to network nodes  28 , and the particular network node  28  that represents the destination address of the packet retrieves the packet from PON  10  and forwards the packet to the DHCP client associated with the destination address.  
     [0050] When the packet contains DHCP communications, such as DHCP requests and responses, PON interface  12  checks the contents of the packet for information regarding the lease of IP addresses, a process referred to as snooping ( 80 ,  82 ). When the packet contains any sort of IP lease information, PON interface  12  updates the routing information to reflect changes in the IP lease information ( 84 ). For example, if a new IP address lease is administered, routing information may be updated to map the administered IP address to a specific PON interface module  34  that represents a DHCP client that leases the IP address contained in the DHCP request. When the packet does not contain information regarding the lease of IP addresses, PON interface  12  inspects the routing information to determine a path for forwarding the packet and forwards the packet is forwarded in accordance with the routing information ( 78 ).  
     [0051] Various embodiments of the invention have been described. Although the exemplary embodiments are described in terms of assigned IP addresses, devices served by network nodes may be assigned other types of network addresses used to route packets to and from the devices. Additionally, although the techniques of the invention are described in terms of DHCP, the techniques may be applied to optical networks that use other communication protocols for assigning network addresses to clients, such as Bootstrap Protocol (BOOTP). These and other embodiments are within the scope of the following claims.