Framework for dynamic optical virtual private networks (VPNs): architecture and analysi

Optical wavelength division multiplexing (WDM) technology, which has a high bandwidth capacity, is becoming apractical reality with recent technological advances [1]. Suchnetworks are expected to play a dominant role in the nextgeneration networks. Currently, communication trafficcontains more and more types of traffic flows, includingmultimedia information, which has different delay and jitterrequirements from some non-real-time traffic. Thus, there isgreat diversity of service requirements among traffic flowson optical networks. All these requirements cannot be metby the currently deployed synchronous network technology(SONET/SDH). This motivates the consideration of opticalvirtual private networks (VPN). In optical VPNs, customerscan contract for a variety of network resources such as linkbandwidth, wavelength, or optical connection ports. Theoptical VPN service gives customers private ownership oftheir optical bandwidth, including the capability to control,manage, monitor and provision optical circuits, without theburden of maintaining a physical network infrastructure.Optical VPNs provide a new revenue stream for serviceproviders.A VPN is an overlay network that is built above a publicnetwork infrastructure, providing the VPN user with aprivate network using tunnelling, encryption and authentication mechanisms [2]. VPNs are gaining increasedacceptance due to their economic benefits and the maturingtechnology. VPNs may be built above different types ofpublic network, such as frame relay, ATMor the Internet.The primary advantages of VPNs over the Internet are theircost-effectiveness and flexibility. However, the disadvantages of VPNs over the Internet are lack of reliability andsufficient quality of service (QoS) mechanisms.Recently, there have been proposals to embed offlineVPNs over WDMoptical networks [3, 4]. The proposal in[3] requires that VPN users have pre-allocated all the lightpaths to different traffic streams. This is hard to handlewhen burst or no pre-planned traffic streams occur andrequires dynamic lightpaths setup, In this paper, we furtherexplore the problem of online VPN design, in particularWDMrouted networks [1]. The WDMrouted networkprovides an 'optical connection' layer which consists ofseveral lightpaths. A lightpath is defined as an all-opticalconnection from the source node to destination node,traversing several intermediate optical wavelength routingnodes.The basic difference between the online VPN and offlineVPN is that lightpaths in an online VPN can bedynamically set up and released when necessary; lightpathsin an offline VPN are pre-defined and cannot be changedduring the transmission process.An architecture for an online VPN over WDMisproposed and a preliminary study conducted. The networkarchitecture considered is as follows. A network providerowns an optical WDMbackbone network and providescapacity to users (e.g. large corporations) requiring VPNservices. A VPN is specified by a set of nodes that need tobe interconnected. The network provider accommodates theVPNs its objective being to maximise the total traffic ofVPNs and to optimise use of the backbone capacity. Theproposed architecture separates the different VPNs in theoptical domain by providing lightpaths with differenttransmission qualities to meet the different VPN topologies.Borrowing items from asynchronous transfer mode (ATM),we consider the following three types of traffic.Constant bit rate (CBR): CBR classified traffic is normallyintended for traffic with very stringent timing requirements.This type of traffic requires a constant cell transmission ratefor the entire duration of the connection.Variable bit rate (VBR): this service is intended for burstytraffic, such as transaction processing applications andLAN interconnection.Unspecified bit rate (UBR) and available bit rate (ABR):UBR traffic is for applications which send data across thenetwork with no guarantee when that data will arrive at itsdestination. ABR is similar in the sense that it makes use ofany available bandwidth and reduces the transmission ratewhen the network is congested.The QoS model proposed allows three types of VPN:static, optical burst switching(OBS) and alternative VPNs.The static type has a set of dedicated or shared pre-allocatedlightpaths to transmit its packets. This type has the highestquality of service and thus is only applicable to traffic withconstant bit rate (CBR). The burst type requires dynamically setup lightpaths when traffic streams with variable bitrate (VBR) have requests. We tend to set up the dynamiclightpath using optical burst switching (OBS). The alternative type provides a service to the traffic streams whichhas no guarantee, e.g. UBR or ABR traffic. Lightpath setuptakes a long time due to the two-way reservation methodadopted.There are several advantages for this architecture. First,by setting up lightpaths for the VPN traffic stream, packetsdo not need any buffer once they enter the optical corenetwork and flows can guarantee minimum delay andreliability. Furthermore, by routing or switching opticalsignals to different routes in the optical domain without anyO/E/O conversion, one can reduce the complexity of theoptical switching and simplify management of networks in awide area network.