Side_1_360

dynamics cannot be realised if the mechanisms

for negotiation and management are not in place.

Some work is done in the Internet2 project on

bandwidth brokers and dynamic SLA negotia-

tion [I2-site].

Depending on the interface an SLA is related to,

it can be either vertical – between two actors on

different layers, or horizontal – between two

actors on the same layer. One example is a con-

figuration as shown in Figure 3, where ISP1 has

to rely upon both ISP2 (horizontal relationship

formalised in the horizontal SLA) and upon the

Network Operator 1 (NO1) (vertical relationships

formalised in the vertical SLA) in order to fulfil

the demands of its user served via interface X.

Note that depending on the user tye, the SLA at

the interface X may be either vertical (e.g.

human end-user) or horizontal (e.g. another

provider).

Depending on the logical location of the parties

involved in the SLA, it can be:

• Internal – made between two different depart-
  ments/business units within a company;


• External – made between two different legal
  actors, i.e. two companies.

Also, depending on the performance level (of the

service offered) handled in the SLA, three main

categories of SLAs are recognised (Figure 4):

1.Application-level SLA– covers the service

end-to-end, i.e. including not only the network

infrastructure edge-to-edge but application(s)

and Customer Premises Equipment (CPE),

implying that an actor playing the role of net-

work operator only, cannot provide such an

SLA since it does not have control over either

Figure 3 A simple example of
relationships in multi-provider
Internet environment

Figure 4 Illustrating different
types of SLAs depending on the
scope of the service provided

ISP1 ISP2

NO1

NO2

X

Vertical SLA

Horizontal SLA

Logical relationship

Physical relationship

NO NO NO

SP SP

Network level SLA

Service Provider SLA

Application level SLA