Network Orchestration: Orchestration is an important characteristic for cloud computing. Orchestration implies creation of networked entities that facilitate successful implementation of cloud computing. The key here is in facilitating this communication, for which we require a common control plane. The control plane orchestrates network function among disparate entities, thereby provisioning a cloud computing service. To do so, it is necessary to create an interaction between the end-user requirements (application) and the network entities, all done by the control plane. Orchestration requires cross-layer and cross-domain intelligence. Once again, achieving such functionality is best suited for the data layer with VLAN (virtual LAN) tags and MPLS (multiprotocol label switching) labels defined in a proprietary manner.

Automation of Consolidation and Virtualization Functions: Scalability implies automation in virtualization of resources and orchestrating services ondemand. Automation is achieved through a user defined control plane that is subject to network-wide acceptance. Hence, at one level the control plane must have user interfaces with rich graphical content and programmable knocks for user definition of services, and at another level it must be standardized and accepted by the most basic of network elements to be able to control these boxes. If we do not automate the collection of storage, servers, and network elements to support cloud computing, then we cannot achieve scalability, without which the benefits of cloud computing are clearly missing. In contrast, if we do automate, then the solution can become relatively generic, implying that it can be sub-optimal (in performance) or cannot meet the specific needs of a customer.

Integration of Sub-Modules: The last aspect of cloud computing that the network must take into account is completeness. Often when tasks are divided across a network, they are managed by different entities and it is the job of the network to provide fault tolerant paths between these entities or sub-modules, integrating these to produce a seamless cloud computing environment. Pro - tection and restoration functions in a cloud are best dealt with at the lower layers with layer-2 fast-reroute or layer-1 line-protection.

In particular, WDM (wavelength-division multiplexing) at the optical layer, SONET/SDH or Ethernet at the data layer, and IP at the network layer are the dominant choices in the metro network. What this implies is that an IP mesh network consisting of core routers at select locations forms a meshed IP network. This is supported by SONET/SDH rings or Carrier Ethernet which is further provisioned on WDM rings. The protocol stack is subjected to different classes of network elements: end-users, network elements (for transport, switching etc.), storage elements, and processors (server blades).

Network Change While efficient planning can do a great deal to reduce CAPEX (capital expenditures), the mechanism can fail for on-demand service provisioning. The key is to get the fundamentals of networking correct when it comes to supporting cloud computing applications. The triple mantras of virtualization- consolidation-orchestration are to be followed at every step of the network design. Classically the cloud is a virtual topology, an overlay over a physical mesh of layer 1-4 boxes. As the above figure shows, it is a tic-tac-toe game among storage, processors, end-users on one side, and the network elements — optical, switches, routers — at the other side. As each of these two entities are put-forward, the resultant must be an element of the virtualization-consolidation- orchestration mantra. This will ensure low-CAPEX and low-OPEX (operating expenses).