Design of a Model-Based SLA Management Service and Its Applications over Distributed SOA Environments - Grid Computing: Infrastructure, Service, and Applications - page 262

4. SLA proposal1 is transmitted from SAP1 to the service provider's
local memory. If the service provider is willing to give an offer
based on SLA proposal1, an SLA proposal2 is created by
the service provider by i lling the other details and attaching its
signature.

5. The SLA proposal2 is propagated from the service provider's local
memory to the SAP2, which locates at the service provider's
side.

6. The SLA proposal2 is transmitted from SAP2 to the client, and
cached in the client's local memory.

7. An SLA will be established if the service client adds its digital
signature on SLA proposal2 to create an SLA.

8. The SLA copy is pushed from the client's local memory to SAP1.

9. The SLA is delivered to the service provider for him/her to keep
locally. Once the service provider receives the SLA, an ACK sig-
nal will be returned to the client to acknowledge receiving
the SLA.

Step 0 is executed by operation getSLATemplates() in the SLA-based ser-
vice. Steps 1, 2, 6, and 7 are done by the respective operations in a client
library for operating the SLA proposal object and pushing the objects to
the client's local SAP. Steps 3, 4, and 5 are completed by invoking propose-
SLA() in the SLA-based service. In Step 8, the client calls an explicit method
(e.g., addMySignature) to add its signature in the SLA.
The mechanisms of managing SLA copies via SLA Manager, as shown
in Figure 10.7 , make sure that both the service provider and its client have
all the versions of the SLA proposals and the i nal SLA, and what's more,
they are synced up with each other during the SLA negotiations.

10.4.2.6 Signing the SLA Proposals

We dei ne an SLA as being active if and only if both the service provider
and its client have signed an SLA proposal. However, the sequence regard-
ing which party signs i rst is l exible. Depending on who signs i rst, the
negotiation sequences may change. For example, in a client-initiated SLA
negotiation, the client may sign the original SLA proposal1 when it creates
SLA proposal1. Hence, an agreement will be reached once the service pro-
vider agrees to SLA proposal1. The established SLA therefore has signa-
tures from both the service provider and the client.
For some circumstances, the client may not sign the original SLA pro-
posal1 but may be waiting for the service provider to i ll in the next level
details before signing the agreement, as shown in Figure 10.7. If the ser-
vice provider is the i rst to sign, an additional interaction is required for