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SECURITY AND PRIVACY
Isolation between coexisting VNs can only provide a certain level of security and privacy through the use of secured tunnels, encryptions, and so on; but it does not obviate the prevalent threats, intru- sions, and attacks to the physical layer and VNs. In addition to that, security and privacy issues spe- cific to network virtualization must also be identi- fied and explored. For example, programmability of the network elements can increase vulnerability if secure programming models and interfaces are unavailable. All these issues require close exami- nation to create a realistic NVE.
INTEROPERABILITY ISSUES
End-to-end VNs can span across multiple admin- istrative domains, each using possibly heteroge- neous networking technologies and management frameworks. Enabling virtualization in each of these technologies requires specific solutions for provisioning, operation, and maintenance. Inter- actions between such contrasting underlying infrastructures, while providing a generic and transparent management interface for SPs to easily compose and manage VNs, remains a daunting task. In addition, identification of the necessity, scope, and required interfaces for end- to-endcommunication across multiple VNs deserves close scrutiny.
NETWORK VIRTUALIZATION ECONOMICS
Unlike traditional networks where bandwidth is the chief commodity, virtual nodes are equally important as virtual links in an NVE. SPs are the buyers in this economy, whereas InPs are the sellers. There can also be brokers who act as mediators between the buyers and sellers. End users also participate as buyers of services from different SPs.
Traditionally, there are two general types of marketplaces: centralized and decentralized. Centralized marketplaces are efficient, but vul- nerable and not scalable. On the other hand, fully decentralized marketplaces are extensible andfault-tolerant, but prone to malicious behav- ior and inefficiency. To find a trade-off between these two options, existing work on peer-to-peer (P2P) marketplaces can be extended to the domain of network virtualization.
CONCLUSION
Amid current trends of virtualizing practically every aspect of computing (e.g., operating sys- tems, servers, and data centers), network virtual- ization stands at a unique point in the virtualization design space. On one hand, it is necessary to have a virtualized network to inter- connect all other virtualized appliances to give each of the virtual entities a complete semblance of their native counterparts.
On the other hand, after enjoying years of rapid growth, the progress of the Internet and networking in general has come to a standstill. Most researchers now agree that a redesign is a
bare necessity, not luxury. Network virtualization can take a leading role in this scenario to pro- mote innovation through disruptive technologies. This realization has given birth to several pro- jects all over the world that are directly or indi- rectly related to network virtualization (Table 2).
The materialization of an NVE needs to sat- isfy the requirements set by its characteristics and design goals, but fulfilling these require- ments is not so easy. More insights into the chal- lenges outlined in this article are needed for an open, flexible, and heterogeneous networking environment to become a reality.
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