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differently by different networks along a path,

leading to a vast number of options. Harmon-

ising the service levels may result in easier

interconnection and service provision in mul-

tiprovider environments, although service lev-

els could also be seen as a competitive factor.

Service discovery as mentioned above be-

comes even more requested for such configu-

rations. Between the different networks this

could also ask for enhancing the set of routing

protocol attributes, including some describing

the service levels supported.

• Measuring service level and delivery. In sell-
  ing a service level to a customer, it is central
  to have means in place in order to document
  that the service has been delivered as agreed.
  Another purpose of such measurements could
  be as a basis for admission control and routing.


• Accounting for service levels. In case various
  service levels are to be offered, corresponding
  range of tariffing levels should be used as
  well. A technical argument is that use of more
  network resources should be reflected in a
  higher tariff. Naturally, other arguments may
  go against such a conclusion. This technical
  argument points towards application of usage-
  based charging.

According to [RFC2990] the following aspects

are included in an architecture for service level/

QoS level:

a) Control the network response such that it is

consistent and predictable;

b) Control the network response such that the

service level is provided as agreed:

c) Allow establishment of agreed service level in

advance;

d) Control contention for network resources such

that the appropriate service levels are achieved;

e) Control contention for network resources such

that a fair allocation is achieved (although fair

has not been defined);

f) Allow for efficient utilisation of network

resources while providing a range of service

levels.

All these issues have to be addressed in order to

ensure that the service levels can be provided.

Actually, all these have to be in place in a coher-

ent way to offer end-to-end service levels in

agreed ways.

In addition to the issues listed above, more unan-

swered questions are found for interdomain con-

figurations, like how to efficiently handle the set

of SLAs in a multi-service and multi-provider

configuration.

6.3 Overview of Further Challenges

In addition to the issues discussed above, more

aspects can be looked at. The following descrip-

tion of the open issues is centred around the

groups depicted in Figure 9:

• The network nodes sphere representing vari-
  ous nodes involved for IP transport, e.g.
  routers and hosts/terminals. Various segments
  of an operator’s network, including access and
  core, are part of this. User terminals and rele-
  vant parts of applications can also be included.
  Typical issues are related to ensuring and
  monitoring performance of traffic flows, con-
  figuring resources, and so forth.

Figure 9 A grouping of
challenges related to ensuring
QoS for IP-based services

Regulator, vendors

User - Provider Service

Level Agreement

Multiple providers

may be involved

User

business

Provider

business

Actual delivery

Service, service control, service management etc.

IP transport, network nodes, network management etc.