Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L12/00—Data switching networks
  • H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
  • H04L12/2854—Wide area networks, e.g. public data networks
  • H04L12/2856—Access arrangements, e.g. Internet access
  • H04L12/2858—Access network architectures
  • H04L12/2859—Point-to-point connection between the data network and the subscribers
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L12/00—Data switching networks
  • H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
  • H04L12/46—Interconnection of networks
  • H04L12/4633—Interconnection of networks using encapsulation techniques, e.g. tunneling

Definitions

• the invention relates to a network arrangement having first, second and third networks, one or more hosts connected to the first network, an access server for linking the first and second networks and one or more access routers for linking the second and
• the Internet has, in recent years, assumed greater and greater importance as business- and residential users have demanded access to information of all types, including not only text but also images and, as a further sophistication, sound and video.
• IP Internet Protocols
• IP is capable of transferring all these disparate forms of communication over the same network infrastructure and allows video and other forms of communications to share the same bandwidth.
• QoS Quality of Service
• the three main role-players in the delivery of an D? service are the customer, the Network Access Provider and the Service Provider.
• the ISPs maintain Access Routers (not shown) which link up with the Internet 16.
• the customer cannot connect directly with the Internet, but must go through the Access Network first, and this then provides him with a transport channel to the ISP of his choice. Once he is linked to the ISP via such a channel, he can then request the service that he requires from the ISP.
• the network model includes a selection protocol between the customer and the Access Network to set up the transport channel; an access network protocol representing the transport channel between the customer and the service provider, and a service access protocol between the customer and the service provider.
• the service access protocol is supported by the access network protocol.
• An example of an actual architecture typifying this model is shown in Figure 2 and is based on the present-day PSTN (Public Switched Telephone Network) system.
• the customer equipment Customer Premises Equipment, CPE 20
• CPE 20 Customer Premises Equipment
• a series of Service Providers 26 are accessible via the PSTN system via a pool of modems 28 at the ISP-end.
• the selection protocol of Figure 1 is represented by the PSTN dialling facility
• the access network protocol is represented by the telephone switched circuit linking the modems 22 and 28
• the service access protocol is represented by the PPP (point to point) protocol.
• the telephone circuit provides a guaranteed 64 Kbps data channel, which is possibly slightly reduced by modem technology.
• the PPP session has a one-to-one relationship with the telephone circuit, it inherits its QoS.
• the QoS class provided by the PSTN is forced and cannot be specified in the selection protocol.
• the PSTN system is essentially a narrowband system and inherently, therefore, ill-suited to the kind of service convergence mentioned at the beginning.
• All the ATM features are available from the customer premises to the ISP via the access network, so that the customer is provided with QoS guarantees for different classes of service all the way from his end (source-end) to the destination-end.
• the desired QoS parameters are sent by the user along with the address of the desired end- point over the UNI (user-network interface) to the switch 32.
• a network arrangement comprising a first (40, 46; 82, 83), a second (50, 88) and a third (87) network; one or more hosts (42) connected to the first network; an access server (48, 84) for linking the first and second networks and one or more access routers (52, 86) for linking the second and third networks, in which
• - information packets are multiplexed over one or more tunnels (54, 90) in the second network;
• - PPP is employed as an access-network protocol and as a service-access protocol between the one or more hosts and the one or more access routers, and
• the first network may include an Ethernet network configured to operate under
• the access server is preferably provided with the following functions:
• One or more tags employed during a discovery phase of the PPPoE protocol may be provided with information relevant to the requesting of desired QoS parameters.
• the tags may be Service_Name tags.
• the first network may include an access network (83), the access server may be a
• the access network may communicate with the access server using ATM and the access server and the third network (87) may communicate over tunnels (90).
• Figure 1 is diagram of a network-architecture model
• Figure 2 shows the model of Figure 1 incorporating a PSTN architecture
• Figure 3 shows the model of Figure 1 incorporating an ATM architecture
• Figure 4 is a diagram of a network model for PPP over Ethernet
• Figure 5 is a block diagram showing the functions of a network arrangement in accordance with a first embodiment of the invention.
• FIG. 6 shows a PPPoE-based network architecture in accordance with the first embodiment
• Figure 7 shows an Ethernet LAN in one scenario in connection with the possibility of the need for QoS functioning at the Ethernet layer in relation to the first embodiment
• Figure 8 shows an ATM-based network architecture in accordance with a second embodiment of the invention.
• PPPoE APPP over Ethernets
• Ethernet LAN 40 comprising the commonly used
• bus-type structure connected to a series of CPE devices, or Aclients ⁇ 42, is connected
• NT Network Terminal
• PPPoE server 48 which performs the function of an Access Server, as described above.
• the server 48 which can be termed a PPP switch, communicates across a network 50 to the Access Routers 52 of a number of ISPs.
• the network 50 conveys the message packets through
• Atunnels ⁇ 54 using as a protocol the L2TP (Layer 2 Tunnelling Protocol).
• Tunnelling is a process whereby packets are Aencapsulated ⁇ in the PPP switch 48 before entering the network 50 and unpacked at the other end by the Access Routers 52, the original addressing and data information remaining unchanged. Thus the mode of transport of the original packet-information is transparent to the user.
• PPPoE Physical Ethernet interface
• PPPoE client a driver that is simply added to a PC, for example
• a very simple modem is all that is required at the user end to bridge the Ethernet frames received from the user to the Access Server 48 over the ATM-based access network.
• the Access Server 48 interprets the PPPoE protocol and conveys the PPP session to the ISP chosen by the user.
• PPP has the role of both access network protocol and service access protocol, as opposed to merely the service access protocol as in the PSTN and ATM-SVC arrangements described earlier. Also the PPPoE protocol is sufficiently rich and flexible to perform all the functions of a selection protocol.
• the PPP switch is the flexibility point of the Access Network. It switches the
• PPP sessions towards their respective chosen ISPs treating the PPP protocol as an access network protocol and not as a service access protocol. (The latter should transparently cross all the access network components, including the access-network protocol switches).
• L2TP as the tunnelling protocol not only allows the tunnelling process to take place, but also provides a multiplexing function which allows multiple PPP sessions to use the same tunnel.
• the invention provides for the PPP protocol to have its own QoS capabilities in order to cater for the variable demands on resources made by the users of the system. This was not needed within the previously described PSTN and ATM scenarios, since there the PPP simply inherited the inherent QoS capability of the underlying access network protocols.
• the present invention equips the PPP network elements, i.e. in the case of the Figure 4 scheme the switch 48, with the following functions:
• Classification - packet frames are tied together with the particular session
• the PPP sessions are associated with specific QoS parameters via a signalling protocol 60 (to be described later) or by a management system via a management channel 62.
• An admission control function 64 checks the availability of the requested resources to see if those parameters can be guaranteed.
• the PPP frames are associated with their respective sessions in the classifier 66 which, in the PPPoE architecture being used here, can discriminate between the sessions using a session identifier field.
• the scheduler 68 serves the different PPP sessions according to their QoS parameter and may be very complex, depending on the granularity of the QoS parameters and the fairness of the service. ("Granularity" here is used to mean the number of possible packet flows, each having a different QoS characteristic).
• scheduling function Possible implementations of the scheduling function are, e.g.: priority FIFO (First In, First Out), WFQ (Weighted Fair Queuing) and (WF) 2 Q (Worst-Case Fair- Weighted Fair Queuing).
• priority FIFO First In, First Out
• WFQ Weighted Fair Queuing
• WF 2 Q Worst-Case Fair- Weighted Fair Queuing
• PPPoE has two separate phases: a Adiscovery phase ⁇ and a Asession phases.
• a host must perform discovery to identify the Ethernet MAC (Media Access Control) address of the access server and set up a PPPoE SESSION_ID.
• Discovery is inherently a client-server relationship, in contrast to PPP which defines a peer-peer relationship.
• the discovery process is so named because in this process a host (the Aclient ⁇ ) discovers an access server (the Aserver ⁇ ).
• the host there may be a number of access servers with which the host can communicate.
• the host is able to discover all access servers and then select one.
• both the host and the selected access server have the information needed to set up their point-to-point connection over Ethernet. No resources are allocated during the discovery phase until a PPP session is established. Once a PPP session is established, both the host and the access server must allocate the resources for a PPP virtual interface.
• the invention uses the afore-mentioned tags present in the discovery phase of the protocol to signal the QoS parameters of the PPP session.
• the tags are in the form of TLVs (Type-Length-Value segments) with the length expressed by a 16-bit integer, so that a tag may be 64 kbits long.
• TLVs Type-Length-Value segments
• AService_Name ⁇ AService_Name ⁇ and the present embodiment of the invention impresses onto this Service_Name tag details of the QoS class required.
• PPP frames are policed and served in the same way that D? packets are managed in QoS-enabled routers.
• PPP sessions are multiplexed over tunnels towards ISPs in the same way that D? packets are multiplexed over datalink (OSI Layer 2) connections.
• the PPPoE protocol serves as a signalling protocol just as the RSVP (Resource Reservation Protocol) serves as a signalling protocol at the network layer (OSI Layer 3).
• RSVP Resource Reservation Protocol
• RSVP messages is standardised, in order to allow the driver in the PC to interpret the protocol and map the parameters onto the priority bits of the Ethernet frames. It is also possible to have a proprietary encoding, i.e. one defined by the access- network operator, if that operator supplied the PPPoE driver to the user. In that case the proprietary encoding must be translated into standardised QoS parameters inside the CPE (customer equipment) in order to be properly mapped onto Ethernet priority bits.
• RSVP to allow the host-user to reserve resources along the route from source to destination.
• the RSVP-enabled routers appearing along the route schedule and prioritize packets to fulfill the QoS requirements.
• Layer 2 level (“datalink layer") between the host and the ISP there is PPP with the QoS-enhancement which has just been
• L2TP protocol at the ISP end For the admission control process to work correctly, the PPP switch must be aware of the QoS characteristics of these underlying protocols. If either of them is not QoS-capable or provides insufficient QoS, the request made by the user cannot be admitted. In the case of L2TP, it is assumed that this protocol is implemented over a QoS-capable network and that the various tunnels involved have a static and known QoS. If this is so, it is sufficient to insert into the PPP switch
• Possible QoS-capable arrangements for L2TP are a dedicated point-to-point link or an IP-based or ATM-based network.
• Ethernet part As regards the Ethernet part, however, the situation is more complex. Where an Ethernet LAN caters mainly for, say, residential or SOHO (Small Office, Home Office) users, it can be assumed that it will have sufficient bandwidth to avoid the need for special queuing, or similar, measures. On the other hand, where a LAN experiences heavy traffic, such measures would have to be taken. In this respect it is helpful that the IEEE 802. lp standard defines a set of priority levels that would facilitate the introduction of QoS into the LAN. However, a complete QoS system would also require the inclusion of admission and policy-enforcement functions.
• FIG. 7 shows an Ethernet LAN 100 connecting several hosts 102 to a PPP switch 104. If it is acknowledged that the critical part of the LAN 100 is the Customer Premises Network, i.e. those portions 106, 108 designated as "private" in Figure 7, then there would be no need to deploy public admission and enforcement mechanisms to guarantee QoS parameters at the Ethernet layer. It can usually be assumed that the Ethernet portion 110 that is shared among several customers 102 is located entirely inside the PPP switch site and supports available bandwidth larger than the sum of the capacity needed by all the customers. On this basis, only the private portions 106, 108 of the Ethernet must be checked against unfair bandwidth allocation, but this is reasonably the responsibility of the owner of the resource.
• SBM Bandwidth Manager
• the present invention envisages the development of a new framework with characteristics similar to the SBM scheme above in order to preserve the QoS parameters contracted by means of PPPoE.
• the situation here could be simplified compared with native SBM, as there is a centralised control point (the PPPoE server). If the PPPoE server were provided with the knowledge of the entire Ethernet access network, it would be able to exercise the Admission Control function during a PPPoE discovery phase. In accordance with the required service, an appropriate IEEE 802. lp priority would be assigned to the service.
• an ATM permanent virtual circuit is established over an access network 83 between the Network Terminal (NT) 80, which is associated with an Ethernet network 82, and an L2TP Access Concentrator (LAC) 84.
• the LAC 84 communicates with an L2TP Network Server (LNS) 86, which may be associated with an ISP or a Corporate router, via a backbone 88.
• LNS L2TP Network Server
• the LAC maps PPP sessions within individual PVCs from the access network 83 to PPP sessions in an L2TP tunnel 90 within a single PVC to the selected ISP. If the network provider wishes to exploit its IP network, the tunnel will be established over IP.
• the LAC provides the operator of the access network 83 with a network concentration point of the individual customer
• PPP consists of three main components: a method for encapsulating user datagrams, or frames, this method involving so-called High-Level Data-Link Control (HDLC); a Link-Control Protocol (LCP) to establish, configure and test the data-link connection, and a Network-Control Protocol (NCP) which establishes and configures different network protocols.
• HDLC High-Level Data-Link Control
• LCP Link-Control Protocol
• NCP Network-Control Protocol
• connection exists between the LAC and the CLE.
• the PPP session is extended from the CLE to the LNS associated with the chosen ISP. Based on the domain name provided in the identification phase of the PPP setup, the LAC will determine the
• the LAC encapsulates the PPP data into L2TP and forwards
• the LNS performs authentication that is appropriate, given the security requirements of the ISP.
• PPP acts both as the access network protocol and as the service access protocol.
• the PPP protocol can be initiated either by the PC or by the NT and several different protocol stacks can be employed to achieve this, including the use of a local L2TP tunnel between host and NT, the use of BMAP (Broadband Modem Access Protocol) and the use of PPP proxy.
• BMAP Broadband Modem Access Protocol
• the local L2TP solution allows the PC to run PPP over L2TP over IP over Ethernet to reach the outgoing NT; BMAP provides a way of mapping ATM over the Ethernet link, and in PPP proxy it is the NT, not the PC, which initiates PPP.
• the LAA scheme there is no authentication and no scheduling in the access server (which in this case is the LAC). While it is possible for the user to request different QoS services (e.g. gold or silver), each service is confined to its own tunnel. Thus all sessions in the same tunnel are treated the same way. The user can request e.g. a gold service by inputting: "MyName@goldisp.net", following the above example.
• QoS services e.g. gold or silver

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Data Exchanges In Wide-Area Networks (AREA)
• Burglar Alarm Systems (AREA)
• Non-Silver Salt Photosensitive Materials And Non-Silver Salt Photography (AREA)

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Cited By (6)

Citations (3)

• 2000
  • 2000-04-12 IT IT2000TO000341A patent/IT1320031B1/it active
• 2001
  • 2001-04-11 WO PCT/IB2001/000698 patent/WO2001078310A2/en active Application Filing
  • 2001-04-11 AU AU93348/01A patent/AU9334801A/en not_active Abandoned

Patent Citations (3)

Non-Patent Citations (6)

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