Patent Publication Number: US-2007115898-A1

Title: Use of wireline networks to access 3G wireless services

Description:
BACKGROUND  
      Wireless communication devices such as mobile phones have become ubiquitous in many places. Many mobile phones are capable of operation within third generation (“3G”) communication networks. 3G communication networks can handle voice (telephone calls), data, and multimedia (combinations of video, audio or data) at high data rates, using both circuit-switched and packet-switched networks as appropriate.  
      A circuit-switched network dedicates a physical path to a single connection between two end-points in the network for the duration of the connection. A packet-switched network (for example, an Internet Protocol (“IP”)-based network) is “connectionless,” routing relatively small units of data called data packets through a network based on a destination address contained within each packet. The same path is shared by data packets having different destination addresses.  
      The Universal Mobile Telecommunications System (“UMTS”) is a group of communication protocols designated for use by certain 3G communication networks (“UMTS Networks”). An organization called the Third Generation Partnership Project (“3GPP”) defines communication standards for use within UMTS Networks. The 3GPP has defined a system called the 3GPP IP Multimedia Subsystem (“IMS”), which is referred to as the “IMS System.” The IMS System is a part of the UMTS Network that is responsible for providing packet-switched services, such as Voice over Internet Protocol (“VoIP”) services, to user equipment, such as mobile phones. A wide and ever-increasing variety of user equipment and packet-switched services are available. Examples of other packet-switched services include, but are not limited to, email, web surfing, and tunneling of cellular/telephony calls.  
      The challenges of security and reliability posed by wireless VoIP are being addressed by the IMS System. One important feature of the IMS System is that a mobile phone can securely gain access to a packet-based service regardless of how the mobile phone accesses the IMS System. The IMS System is therefore referred to as being “access network agnostic”.  
      One type of mobile phone, a phone that is capable of making or receiving calls in one or more cellular modes and also in a wireless local access network (“WLAN”) mode, would take advantage of the access network agnosticism of the IMS System, allowing users of such a dual-mode phone to use their mobile phones in more environments than ever before.  
      In one or more cellular modes, the dual-mode phone would access the IMS System using licensed radio frequency spectrum and a cellular air interface protocol, such as a wideband code division multiple access (“W-CDMA”) air interface protocol. In the WLAN mode, the dual-mode phone would use different, generally unlicensed, radio frequency spectrum and non-cellular air interface protocols to access the IMS System. One example of a non-cellular air interface protocol is the Wireless Fidelity (“WiFi”) series of protocols promulgated by the Institute of Electrical and Electronics Engineers (“IEEE”).  
      The environments in which dual-mode phones could be used would be further expanded if wireline service providers such as cable television operators take advantage of the access network agnosticism of the IMS System. For example, certain changes to cable access networks would allow WLAN-enabled mobile phones to access the IMS System through wireless cable modem connections. A user could then initiate a VoIP call (and access other packet-switched services provided by a UMTS Network) using his mobile phone wherever he happened to be, in the car, in a cafe with a WiFi hotspot, in an office having wireless Internet access points, or at home with wireless access to a cable modem.  
      Changes to cable access networks that would allow WLAN-enabled mobile phones to access the IMS System, however, may be expensive or complicated for cable service providers to implement. There is no single piece of equipment for use in a cable access network that currently has the functionality to allow mobile phones to access the IMS System. If new or different devices are added to the cable access network to provide such functionality, the development and deployment costs of the new devices may be high. Also, additional or different interfaces between the new devices and the cable access network would likely be needed. Existing equipment in the cable access network might not be able to examine the signaling within or between the new devices, which would make it more difficult to provide appropriate levels of security and quality of service in the existing cable access network.  
      Cost-effective solutions for enabling users of wireless devices, such as mobile phones, to access 3G packet-switched services using cable access networks are needed. There is a need for a single piece of equipment, located within the cable access network, to serve as a point of interconnection between the cable access network and a 3G communication network, and to provide for appropriate levels of security and quality of service within the cable access network. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a simplified functional block diagram of a Third Generation Partnership IP Multimedia Subsystem system, which is referred to as an “IMS System”.  
       FIG. 2  is a message sequence chart illustrating a general process by which a mobile phone uses WLAN access network(s) shown in  FIG. 1  to directly access the IMS System shown in  FIG. 1 .  
       FIG. 3  is a simplified functional block diagram of an exemplary multimedia architecture, within which the access node shown in  FIG. 4  may be used.  
       FIG. 4  is a functional block diagram of an access node usable in the access network of the multimedia architecture shown in  FIG. 3 .  
       FIG. 5  is a message sequence chart illustrating a process by which a mobile phone uses the access node shown in  FIG. 4  to access the IMS System shown in  FIG. 1 . 
    
    
     DETAILED DESCRIPTION  
      Methods, devices, and computer programs for using a cable network to access a packet-switched service delivered by a 3G communication network, such as a UMTS communication network (a 3GPP IMS, for example), are discussed herein. A wireless communication device such as a mobile phone requests access to the packet-switched service, which for discussion purposes is a Voice over Internet Protocol (“VoIP”) service. The request is received by an access node, such as a cable modem termination system (“CMTS”) device, which is located in a hybrid fiber-optic/coaxial cable (“HFC”) network.  
      In general, the access node serves as a point of interconnection between the mobile phone and the 3G communication network. More specifically, the access node implements the packet data gateway (“PDG”) function and/or the wireless access gateway (“WAG”) function specified by a document entitled “3GPP TS 23.234 (V6.2.0), 3GPP system to Wireless Local Area Network (WLAN) interworking,” referred to as the “WLAN Interworking Specification”, published in 2004 by the Services and System Aspects Technical Specification Group of the 3GPP. In accordance with certain aspects of the WLAN Interworking Specification, the access node serves as an endpoint of a packet data tunnel, which establishes a security association between the mobile phone and the access node. The packet data tunnel may be established using an IP security (“IPSec”) protocol. The packet data tunnel is also used to establish a level of quality of service (“QoS”) for packet data communicated between the 3G communication network and the mobile phone. In this manner, security and QoS is maintained in the cable access network.  
      Consumers, service providers, and manufacturers would benefit from the use of the access node described herein. Consumers would experience access to services such as VoIP in more places than ever before, in a unified manner. Cable television operators could increase the applicability of their service offerings to broader market segments, without having to deploy additional equipment to implement the PDG function(s) in their HFC networks. Manufacturers may gain larger market share with fewer product development efforts.  
      The foregoing description has been provided to introduce a selection of concepts in a simplified form. The concepts are further described below. Elements or steps other than those described above are possible, and no element or step is necessarily required. The foregoing description is not intended to identify key features or essential features of the claimed subject matter, nor is it intended for use as an aid in determining the scope of the claimed subject matter.  
      Turning to the drawings, where like numerals designate like components,  FIG. 1  is a simplified functional block diagram of a Third Generation Partnership Project IP Multimedia Subsystem (“3GPP IMS”) system  10  (referred to as “IMS System  10 ”). User equipment  16  accesses IMS System  10  through either Home Network  12  or Visited Network  14  using wireless local area network (“WLAN”) access network(s)  18 . IMS System  10  includes a visited packet data gateway (“V-PDG”)  24  in Visited Network  14  and a home PDG (“H-PDG”)  26  in Home Network  12 . V-PDG  24  and H-PDG  26  are network nodes that serve as points of interconnection between WLAN access network(s)  18  and IMS System  10 .  
      System  10  also includes authentication, authorization, and accounting (“AAA”) server  22  (described further below), databases  23 , and application servers  20 . Application servers  20  are computing systems having well known internal arrangements that are responsible for implementing the logic (for example, call flows, database access, and user interface interaction) for delivery of specific packet-switched services  21  to user equipment  16 . Within IMS System  10 , communication between functions occurs over Internet Protocol (“IP”) network  25 .  
      For discussion purposes, user equipment  16  will be referred to as a mobile phone, and packet-switched services  21  will be referred to as Voice over Internet Protocol (“VoIP”) services. The mobile phone may be a dual-mode mobile phone, which is capable of making or receiving voice, data, and multimedia calls in both a traditional cellular mode, and in a WLAN mode. In the cellular mode, the dual-mode phone uses a radio access network (“RAN”) to communicate with the UMTS Network. A RAN supports communication over licensed radio frequency spectrum using a cellular air interface protocol, such as a wideband code-division multiple access (“W-CDMA”) air interface protocol. In the WLAN mode, the dual-mode phone uses a WLAN, such as a Wireless Fidelity (“WiFi”) network, to access the UMTS Network. A WLAN supports communication over (often unlicensed) radio frequency spectrum using non-cellular air interface protocols. WiFi refers to the 802.11 series of non-cellular air interface protocols promulgated by the Institute of Electrical and Electronics Engineers (“IEEE”).  
      Home Network  12  is a Universal Mobile Telecommunications System (“UMTS”) network with which mobile phone  16  is registered for use. A home network in general, and Home Network  12  in particular, is operated by a service provider with which a user of a mobile phone has contracted to receive communication services, such as VoIP services.  
      Visited Network  14  is a different network than Home Network  12 . Visited Network  14  is often another UMTS Network in a different geographical area than Home Network  12 , and may be operated by a different service provider. Roaming agreements between an operator of Home Network  12  and operators of various visited networks, such as Visited Network  14 , allow mobile phone users to access packet-switched services offered by their home networks when roaming in geographical areas served by visited networks.  
      WLAN access networks  18  provide mobile phone  16  with direct or indirect access to IMS System  10 . A document entitled “3GPP TS 23.234 (V6.2.0), 3GPP system to Wireless Local Area Network (WLAN) interworking” (referred to herein as the “WLAN Interworking Specification”) is incorporated by reference into this document. The WLAN Interworking Specification was published in 2004 by the Services and System Aspects Technical Specification Group of the 3GPP, and its stated intent is to extend 3GPP services and functionality to the WLAN access environment.  
      One important feature provided by the WLAN Interworking Specification is that it is “access network agnostic.” Access network agnostic means that a user endpoint (a user endpoint is any equipment in possession of a user), such as mobile phone  16 , can securely access IMS System  10  regardless of the access network or access point used.  
      With continuing reference to  FIG. 1 ,  FIG. 2  is a message sequence  200  chart illustrating one example of the operation of system  10  in accordance with the WLAN Interworking Specification.  FIG. 2  illustrates the case where WLAN access network(s)  18  provide direct access to IMS System  10 . Mobile phone  16  uses WLAN access network  18  in Visited Network  14  to directly access IMS System  10  to place a VoIP call, cellular call, or use another IP multimedia service supported by the subscriber&#39;s Home Network  12 . For example, a mobile phone user who has traveled away from home places a call in the vicinity of a WLAN access network or access point, such as a local WiFi hotspot in a coffee shop or an airport. VoIP services  21  are supplied by application servers  20  in the user&#39;s Home Network  12 .  
      First, mobile phone  16  attempts to register with Home Network  12 . The mobile phone performs a Domain Name System (“DNS”) query  203  to obtain, within DNS response  205 , the IP address(es) of certain functions within Home Network  12 , such as the IP addresses of H-PDG  26  or AAA server  22 . WLAN access network  18  receives DNS query  203  and produces DNS response  205 .  
      WLAN access network  18  includes a WLAN access point, such as a WLAN access node (“WLAN AN”)  202 , and one or more intermediate elements, such as a WLAN access gateway (“WAG”)  204 . WAG  204  is an element specified by the WLAN Interworking Specification that is responsible for routing data to/from the WLAN access network  18 . Among other things, WAG  204  allows billing information to be generated for users accessing IMS System  10  through visited networks, such as Visited Network  14 . WAG  204  also implements the correct routing of data packets before and after the establishment of access network tunnel (“AN tunnel”)  206  (discussed further below) and end-to-end tunnel  210  (also discussed further below), and serves as a filter for data packets. A filter functions as a firewall, it determines which data packets to allow through the firewall.  
      Next, V-PDG  24  and/or H-PDG  26  use AAA server  22  to perform authentication, authorization, and accounting (“AAA”) activities that allow admission of mobile phone  16  into IMS System  10 . Visited Network  14  (and V-PDG  24 ) may not have enough information to authenticate mobile phone  16 , so AAA  22  within Home Network  12 , which stores the authentication credentials of mobile phone  16 , may be contacted. Data packets relating to AAA activities are forwarded by WAG  204  to V-PDG  24 , and the information is used by service providers for billing purposes.  
      AAA activities have been defined and standardized by the Internet Engineering Task Force (“IETF”). Authentication is the process of identifying a user. Authorization is the process of enforcing policies, determining what types or qualities of activities, resources, or services the user is permitted to use. Authentication may also encompass the authorization process. In the process of authentication, for example, certain service profiles (information regarding approved services and service options, such as voicemail greetings, call forwarding information, and the like) may be established. Accounting measures the billable resources a user accesses during use of a system. Examples of billable resources include the amount of time a user has spent using a particular system, or the amount of data a user has sent or received using the system.  
      Each mobile phone registered for use in IMS System  10  has a unique set of authentication credentials used for gaining access to IMS System  10 . As indicated by arrows  208 , V-PDG  24  relays data packets generated by mobile phone  16  to AAA  22 , to confirm that validity of the authentication credentials of mobile phone  16 . AAA server  22  compares mobile phone  16 &#39;s authentication credentials against authentication credentials stored in database  23  (shown in  FIG. 1 ), which may be a home subscriber service database or another type of data storage device. If the authentication credentials match, mobile phone  16  is granted access to IMS System  10 . If the authentication credentials do not match, authentication fails and access to IMS System  10  may be denied. AAA  22  also records all access activity, which is used by service providers for billing purposes.  
      Once mobile phone  16  is authenticated and authorized to use VoIP service  21 , AAA  22  assigns mobile phone  16  an IP address, which functions as the mobile phone&#39;s identity for the duration of the handset&#39;s registration through this Visited Network.  
      Using the mobile phone&#39;s assigned IP address, AN tunnel  206  is established between mobile phone  16  and V-PDG  24 . A tunnel is a bidirectional, secure, logical connection between two entities. Tunnels are used when it is desirable to authenticate or encrypt data. Tunnels specify a security association between the connected entities, and the security association defines the parameters for the authentication and encryption algorithms. A security association is specified using a Security Parameter Index (“SPI”) and the IP address of an entity. The SPI and the IP address together uniquely identify a particular security association. The SPI is a number, which may be pseudo-randomly derived or manually specified.  
      Within AN tunnel  206 , communications between network devices such as mobile phone  16  and devices that implement functions within IMS System  10 , such as WAG  204 , V-PDG  24 , or H-PDG  26 , pass through, at each network interface, seven vertical layers of the well-known abstract model that defines internetworking (the “Internetworking Model”): layer  1 , the Physical Layer; layer  2 , the Data Link Layer; layer  3 , the Network Layer; layer  4 , the Transport Layer; layer  5 , the Session Layer; layer  6 , the Presentation Layer; and layer  7 , the Application Layer.  
      At the Application Layer, mobile phone  16  uses a predetermined application-layer protocol, such as the Session Initiation Protocol (“SIP”), for communicating with V-PDG  24 . SIP is an IETF standard protocol for the initiation, management, and termination of multimedia sessions between users of IP-based networks.  
      At the transport layer, security of individual data packets traveling via AN tunnel  206  is provided by IP Security (“IPsec”) protocols. IPsec protocols were also developed and promulgated by the IETF.  
      AN tunnel  206  is used for the establishment of additional access rules/policies, such as establishment of appropriate levels of quality of service (“QoS”) within access network  18 . V-PDG  26  ensures an appropriate level of QoS for the call within AN tunnel  206 .  
      A level of QoS is a defined level of performance in a data communications system. In a VoIP context, an appropriate level of QoS ensures that VoIP calls are delivered without annoying blips. UMTS networks, including IMS Systems, offer four different levels of QoS for four types of traffic: conversational class (voice, video telephony, video gaming); streaming class (multimedia, video on demand, webcast); interactive class (web browsing, network gaming, database access); and background class (email, short messaging service, and downloading).  
      Finally, an end-to-end tunnel  210  is established between mobile phone  16  and H-PDG  26 . Note that AAA activities are also performed at this stage of the mobile phone&#39;s access to IMS System  10 , as shown by arrows  211 . Using end-to-end tunnel  210 , data packets from mobile phone  16  are forwarded to particular application servers  20  that provide VoIP service  21 . H-PDG  26  registers the endpoints of end-to-end tunnel  210  and routes SIP messages to the appropriate application server  20 . Thus, the user of mobile phone  16  is able to carry on a VoIP call using IMS System  10 , and appropriate levels of security and QoS are maintained within WLAN access network  18 .  
      The user of mobile phone  16  may also want to use his phone to place VoIP calls in areas without good RAN access to IMS System  10 , or without WLAN access networks  18  that directly access IMS System  10 . For example, the user may want, but be unable, to use the VoIP service he has on his mobile phone at home, but he does not have good cellular coverage at home, and his Internet access, even if it is wirelessly accessible, is provided by his cable company. It would be desirable if a WLAN-equipped cable modem, for example, could serve as a wireless access point for a dual-mode cellular/WLAN mobile phone, and if the mobile phone could use the cable access network to indirectly access IMS System  10  to make a VoIP call, in a manner transparent to the user of the mobile phone.  
      Because IMS System  10  is access network agnostic, wireline service providers such as cable television operators, which operate packet-switched networks such as hybrid fiber optic/coaxial cable (“HFC”) networks, are in fact positioned to enable their networks to serve as access networks to IMS System  10 .  
       FIG. 3  is a simplified functional block diagram of a generic multimedia architecture  300  for delivering multimedia services over a two-way HFC cable network. Multimedia services  301  are provisioned within IP network  302  and delivered to a clients  304  and  305  using wireline access network  306 . Clients  304  and  305  are generally software applications disposed in user devices such as computers and mobile phones, respectively. Client  305  is configured for wireless communication with WLAN access point  309 .  
      Wireline access network  306  generally uses the Data Over Cable Service Interface Specification (“DOCSIS®”) set of protocols and standards (for example, DOCSIS 1.1 or DOCSIS 2.0) to transfer data packets between an infrastructure device  308  (such as a cable modem) and a device  310  that serves as a point of connection between wireline access network  306  and IP network  302 , such as a cable modem termination system (“CMTS”). It will be appreciated that other protocols and standards may be used in different types of wireline access networks.  
      In multimedia architecture  300 , certain activities (analogous to authentication, authorization, and accounting activities performed by AAA server  22  (shown in  FIG. 1 ) allow admission of client  304  to multimedia architecture  300 . Such activities are performed by application manager  312  and policy server  314 , and records of such activities are maintained by a record keeping server  316 . In addition, application manager  312  and policy server  314  are used to establish appropriate QoS levels for the delivery of multimedia services  301  to client  304 . Application manager  312  requests a level of QoS on behalf of a client application  304 , and policy server  314  is used to authorize and commit to the QoS request(s).  
      Multimedia architecture  300  could provide support for WLAN-enabled mobile phones wishing to use access network  306  to indirectly access IMS System  10 , so that users could make VoIP calls and obtain other services. If the multimedia architecture implements the protocols set forth in the WLAN Interworking Specification for accessing IMS System  10  using a visited network (which is generally desirable to avoid requiring mobile phone manufacturers to incorporate an additional set of standards into mobile phones), then a further increase in the environments in which users could use their mobile phones and other wireless devices would be realized.  
      The WLAN Interworking Specification provides that the IMS System&#39;s AAA server  22  (shown in  FIG. 1 ) supplies an IP address to user endpoints such as mobile phones that desire to receive services from the IMS System. The WLAN Interworking Specification also requires that a mobile phone must locate a PDG in the mobile phone&#39;s home network to receive services from the IMS System.  
      As shown and discussed in connection with  FIGS. 1 and 2 , a mobile phone roaming outside of the geographic area covered by its home network engages in a two-step process to access services  21  provided by IMS System  10 , with certain AAA activities being performed at each step. First, a PDG in the visited network is contacted (for example, V-PDG  24  in Visited Network  14 ), and the PDG in the visited network performs certain AAA activities required to admit the user into IMS System  10  and to receive an IP address. Second, a PDG in the home network is contacted (for example, H-PDG  26  in Home Network  12 ), and the PDG in the home network also performs certain AAA activities before coordinating the supply of services (with application servers  20 ) to the IP address assigned to the user.  
      Referring again to  FIG. 3 , if multimedia architecture  300  does not include a PDG-like function in access network  306 , then a mobile phone accessing an IMS System indirectly using multimedia architecture  300  would not receive the benefit of tunnels in wireline access network  306 , which provide both security and a mechanism to enforce QoS levels in the access network. If, on the other hand, multimedia architecture  300  does specify a PDG-like function in access network  306 , and if the function is implemented by device manufacturers using additional equipment, it may be an overly expensive or complicated solution for cable television operators to implement. It is generally desirable to minimize the amount of new equipment that service providers must install to achieve new functionality. In this manner, costs are controlled not only for service providers, but also for their customers.  
       FIG. 4  is a functional block diagram of an access node  400  usable in access network  306  (shown in  FIG. 3 ) to provide access to packet-switched services supplied by IMS System  10  to a WLAN-enabled client, such as client  305  in mobile phone  16 ) that communicates wirelessly with cable modem  308  equipped with WLAN access point  309 . One example of a commercially available CMTS in which the functions of access node  400  may be implemented is Motorola&#39;s BSR64000 CMTS.  
      Computing unit  430  includes certain functional components that may be used to implement, may be accessed by, or may be included in, access node  400 . A processor  402  is responsive to computer-readable media  404  and to computer programs  406 .  
      Processor  402 , which may be a real or a virtual processor, controls functions of access node  400  by executing computer-executable instructions.  
      Computer-readable media  404  represents any number and combination of computer readable media, in any form, now known or later developed, capable of recording or storing computer-readable data. In particular, computer-readable media  404  may be, or may include, a semiconductor memory (such as a read only memory (“ROM”), any type of programmable ROM (“PROM”), a random access memory (“RAM”), or a flash memory, for example); a magnetic storage device (such as a floppy disk drive, a hard disk drive, a magnetic drum, a magnetic tape, or a magneto-optical disk); an optical storage device (such as any type of compact disk or digital versatile disk); a bubble memory; a cache memory; a core memory; a holographic memory; a memory stick; a paper tape; a punch card; or any combination thereof. Computer-readable media may also include data embodied in any form of wireline or wireless transmission, such as packetized and/or non-packetized data carried by a modulated carrier signal.  
      Computer programs  406  represent any signal processing methods or stored instructions that electronically control predetermined operations on data. In general, computer programs  406  are computer-executable instructions implemented as software components according to well-known practices for component-based software development, and encoded in computer-readable media (such as computer-readable media  404 ). Computer programs  406 , however, may be implemented in software, hardware, firmware, or any combination thereof.  
      Cable network interface  450  represents one or more interconnections, within the Internetworking Model, between wireline access network  306  (for example, an HFC cable network) and access node  400 .  
      IP network interface  460  represents one or more interconnections, within the Internetworking Model, between access node  400  and both IP network  302  associated with multimedia architecture  300  (shown in  FIG. 3 ) and IP network  25  (shown in  FIG. 1 ) associated with IMS System  10  (also shown in  FIG. 1 ).  
      Interface function block  408  represents aspects of the functional arrangement of various computer programs  406  that pertain to the receipt and processing of data packets by access node  400 . Data packets received at a given network interface, such as cable network interface  450  or IP network interface  460 , may traverse one or more of the seven vertical layers of the Internetworking Model. As such, interface function block  408  may represent data interfaces, operations support interfaces, and the like (implemented, for example, by routers, switches, modems, or other network connection support devices or software).  
      PDG function block  410  represents aspects of the functional arrangement of various computer programs  406  that implement PDG functions for a visited network, as set forth in the WLAN Interworking Specification. Such PDG functions include, but are not limited to, the ability of access node  400  to terminate IPsec tunnels, the ability of access node  400  to admit a WLAN-enabled client  305  to IMS System  10  using multimedia architecture  300  by interacting with application manager  312  and/or policy server  314 , and the ability of access node  400  to establish QoS levels in access network  306  that are compatible with QoS levels established in IMS System  10 .  
      WAG function block  411  represents aspects of the functional arrangement of various computer programs  406  that implement WAG functions (discussed in connection with  FIG. 2 ) set forth in the WLAN Interworking Specification.  
      Cryptography/acceleration hardware block  480  represents well-known hardware, firmware, or software needed terminate IPsec tunnels, which are often encrypted and therefore computation-intensive to manage. One example of an implementation of cryptography/acceleration hardware block  480  is a collection of commercially available semiconductors that support different types of encryption/decryption standards specified by the IETF for use with IPsec tunnels.  
      With continuing reference to  FIGS. 1-4 ,  FIG. 5  is a message sequence chart illustrating a process by which a WLAN-enabled device, such as mobile phone  16 , uses access node  400  to gain access to IMS System  10  using a wireline access network to place a VoIP call. For exemplary purposes, access node  400  is implemented by a CMTS in a cable access network.  
      For discussion purposes, assume that the user of mobile phone  16  discussed in connection with  FIG. 2  has returned home, and wishes to place a VoIP call using his mobile phone. There is no reliable cellular coverage in his house, but he does have wireless Internet access through his cable modem. The mobile phone user places the VoIP call inside his house, and mobile phone  16  uses WLAN access point  309  that is associated with cable modem  308  to contact wireline access network  306 , which provides indirect access to IMS System  10 .  
      First, mobile phone  16  attempts to register with its Home Network. Associating mobile phone  16  with WLAN access point  309  uses well-known procedures, such as those defined for IEEE 802.11 access points. A DNS query  203  is performed to obtain, within DNS response  205 , the IP address(es) of certain functions within Home Network  12 , such as the IP addresses of H-PDG  26  or AAA server  22 . Wireline access network  306  receives DNS query  203  and produces DNS response  205 . As shown, wireline access network  306  includes cable modem  308 , which is equipped with WLAN access point  309 , and access node  400 .  
      Next, PDG function  410  within access node  400  uses application manager  312  and policy server  314  to perform and/or coordinate AAA activities, represented by arrows  508 . Data packets relating to AAA activities are forwarded, via application manager  312  and policy server  314 , by access node  400  to AAA server  22 . If AAA server  22  determines that mobile phone  16  has valid authentication credentials, mobile phone  16  is granted access to IMS System  10 . Once mobile phone  16  is authenticated and authorized to use VoIP service  21 , AAA  22  assigns mobile phone  16  an IP address, which functions as the mobile phone&#39;s identity for the duration of the handset&#39;s registration through this Visited Network.  
      Using the mobile phone&#39;s assigned IP address, AN tunnel  506  is established between mobile phone  16  and access node  400 . Thus, a security association is established between mobile phone  16  and access node  400 . At the Application Layer, mobile phone  16  uses SIP for communicating with access node  400 , and at the transport layer, security of individual data packets traveling within AN tunnel  506  is provided by IPsec protocols.  
      Appropriate levels of QoS are established by application manager  312  and/or policy server  314  using AN tunnel  506 , as represented by arrows  509 . Access node  400  ensures the appropriate levels of QoS for the call within AN tunnel  506 .  
      Finally, end-to-end tunnel  510  is established between mobile phone  16  and H-PDG  26 . Note that AAA activities are also performed at this stage, as shown by arrows  511 . Using end-to-end tunnel  510 , data packets are forwarded between mobile phone  16  and appropriate application server(s)  20  that provides VoIP service  21 .  
      Thus, the user of mobile phone  16  is able to carry on a VoIP call using VoIP service  21  in IMS System  10 , with access node  400  being disposed in wireline access network  306  and serving as a point of interconnection between mobile phone  16  and IMS System  10 . Appropriate levels of security and QoS are maintained by access node  400  wireline access network  306 .  
      Consumers, service providers and manufacturers would benefit from the use of access node  400  within a wireline access network. Consumers would experience access to services such as VoIP in more places than ever before, in a unified manner. Service providers (both cellular service providers and cable television operators) could increase the applicability of their service offerings to broader market segments, and also spread out the costs of delivering those services over more users. Use of access node  400  would also provide service providers with a straightforward upgrade path to virtually any solution that would allow mobile phones to roam into IMS Systems indirectly via multimedia architecture  300 . Using access node  400 , service providers would not necessarily be required to deploy completely new PDG systems in their HFC networks. Equipment and software makers may gain larger market shares with fewer product development efforts, because packet-switched services developed for use within IMS Systems could be used by user equipment operating in both wireline and wireless networks.  
      Moreover, use of access node  400  provides the ability to support delivery of appropriate QoS for wireless access through the cable access network. Integration of the PDG function within access node  400  allows access network devices to examine signaling, and to establish QoS in a secure manner, without creating additional or different interfaces between the PDG function and the access network. This is much more difficult when the PDG is a separate device, because access network devices may not be able to examine the signaling.  
      Exemplary configurations of user endpoints  16 , IMS System  10 , multimedia architecture  300 , access node  400 , and elements thereof have been described. It will be appreciated that such configurations may include fewer, more, or different components or functions than those described.  
      For example, user endpoints include any equipment in possession of an end user, including but not limited to a personal or office-based computer system, any type of communication device or adapter, a media system, and the like, either standing alone, or included in other devices. Packet-switched services are any services, now known or later developed, that are delivered using packet-switched technology, including telephony and non-telephony services (for example, messaging, fax services, email services, Internet access services, navigation services, gaming, video conferencing, video streaming, and multimedia provisioning). AAA  22 , application manager  312 , and policy server  314  may be implemented by one or more devices, co-located or remotely located, in a variety of ways.  
      It will be further appreciated that aspects of computer programs are not limited to any specific embodiments of computer software or signal processing methods. Functions described herein are processes that convey or transform data in a predictable way, and may generally be implemented in hardware, software, firmware, or any combination thereof.  
      Moreover, while certain elements described herein may function as “agents” or “clients”, such elements need not be implemented using traditional client-server architectures in which computer application programs are configured to cause clients, such as consumer devices, to request services from server-based service providers in a network, but may be implemented in any suitable manner.  
      When one element is indicated as being responsive to another element, the elements may be directly or indirectly coupled. Connections depicted herein may be logical or physical in practice to achieve a coupling or communicative interface between elements. Connections may be implemented as inter-process communications among software processes.  
      It will be still further appreciated that other and further forms of the embodiments may be devised without departing from the spirit and scope of the appended claims, and it is therefore intended that the scope of this invention will be governed by the following claims.