Page 645 - Cloud computing: From paradigm to operation

XaaS 3

service offerings) or distributed (e.g., achieved through consecutive SLA establishments) approaches. SLA
specifications in cross-service scenarios should either include the common terms (limiting however end-to-
end quality provision to these terms) or be implemented through links between SLAs (e.g., one SLA for each
service with enriched specification to include links to the SLAs of other services), as a protocol to enable
interaction between different layers and entities.
SLAs identify, in a clear and precise way, the responsibilities and obligations of all involved entities, as well as
their boundaries and limits.

NaaS can be used to support other cloud service CSP's network related activities (e.g., provide network
connectivity, deliver network services and provide network management services), where a logically isolated
CSC cloud in the CSP's data centre allows a CSC to provision a private, isolated partition of the cloud where
the CSC can use cloud capabilities in a virtual network, often using CSC-defined IP address ranges. A CSC cloud
can have multiple subnets in a data centre. Network connectivity between the remote CSC and CSC cloud,
for example, may include the following:
• IPsec VPN connection over public Internet (CSP edge VPN gateway – CSC premises VPN gateway);
• Dedicated network connection over private lines (CSP edge VPN gateway – customer premises
equipment (CPE));
• IPsec VPN connection over private lines (CSP edge VPN gateway – CSC premises VPN gateway);
• VPN connection with a software appliance over public Internet (software VPN appliance – CSP edge
Internet gateway - CSC premises VPN gateway, where Internet gateway only routes VPN connection
over public Internet);
• Multi-protocol label switching (MPLS) VPN connections.
Cloud services needs interconnecting multiple CSC clouds into a contiguous virtual network as well as to meet
this requirement NaaS may provide followings:
• Software VPN appliance based connections between CSC clouds for intra-cloud and inter-cloud
(software VPN appliance at CSC cloud-1 – Internet gateway – Internet gateway – software VPN
appliance at CSC cloud-2, where Internet gateway only routes VPN connection, over public
Internet for inter-cloud case);
• Software VPN appliance to physical VPN connection between CSC clouds (VPN gateway at CSC cloud-
1 – Internet gateway – software VPN appliance at CSC cloud-2, where Internet gateway only routes
VPN connection);
• CSC managed CSC cloud-to-CSC cloud routing over physical IPsec VPN connections using CSC
equipment and public Internet or private lines (VPN gateway at CSC cloud-1 – CSC equipment – VPN
gateway at CSC cloud-2).

Bibliography

[b-IETF RFC 4364] IETF RFC 4364 (2006), BGP/MPLS IP Virtual Private Networks (VPNs).

[b-EC SLA] European Commission Directorate General Communications Networks, Content
and Technology Unit E2 – Software and Services, Cloud, (Brussels, June 2013),
Cloud Computing Service Level Agreements – Exploitation of Research Results.

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