ways, etc. Different metrics may be agreed as
well, e.g. IETF’s IP Performance Metrics
(IPPM) [rfc2330]. The results of monitoring and
measurements can be input to the other parts of
the system, e.g. charging and billing system by
sending alarms for initiation of different charg-
ing schemes after the various situations occur,
etc.
Reaction patterns cover technical actions like
alarms, warnings, messages sent to the user that
did not obey the agreed traffic pattern, or it can
result in abandoning the service usage. It may
also involve some traffic engineering actions,
like traffic shaping, call admission control initia-
tion after receiving a trigger from the monitoring
system, policy initiation, etc. On the other hand,
economic reactions are much more obvious to
the user, and are expressed as e.g. discounts
when the quality has not been delivered by the
provider as it was agreed in the SLA. Different
compensation schemes are often used in today’s
SLAs as will be shown in the next chapter.
5 SLAs for IP-based Services
in Practice
It is easier to capture the importance of an SLA
when a case study is examined. The examples
below will illustrate how the structure described
before can be used in practice. The elements of
the QoS-related part of an SLA can be identified
in a more or less similar form in all examples
illustrated in this chapter. Note that the actual
content may differ, e.g. selection of parameters,
values, statistics, but the structure is not diverg-
ing. This section aims at highlighting the fact
that the structure could be generic and standard-
ised, while the content may differ for a particular
service, interface observed, provider involved, etc.
Examples described here include SLAs for some
of the services offered by UUNet and Epoch
Internet™.
5.1 UUNet’s SLAs
Businesses realised the advantages of the IP
technology, but they want their services to be
guaranteed to them. For example, they want fast,
reliable and robust Internet access. UUNet
[uunet], a Worldcom company, was one of the
first ISPs understanding the need to offer guar-
antees in the form of an SLA to its customers.
UUNet offers a wide range of services. A range
of services provided may vary depending on the
country in focus.
- Internet access, including dial-up and remote
access (suitable for single users, SME, or
companies with many remote workers, i.e.
with a need for home-office solution), dedi-
cated access over DSL, ATM, FR for compa-
nies in the USA which have higher needs than
remote access, and LL dedicated access;- Hosting/co-location services;
- IP VPN and Internet security solutions;
- Internet multicasting;
- Wholesale services for ISPs and carriers (used
by AOL, CompuServe, etc.).
The services offered by UUNet are rated as
rather popular, as shown for example in the fact
that 78 % of Times ‘Top 100’ companies and
63 % of Times ‘Top 1000’ companies use
UUNet [top100]. UUNet offers SLAs for the
Internet access service that are universal in
structure but figures may deviate for each of
the countries UUNet is operating in.A brief summary of the SLA for Internet access
service would include the fact they are network
connectivity SLAs of the cloud type. This type is
used since it supports similar applications across
different access points, and is the easiest to spec-
ify, track and manage. UUNet monitors the net-
work continuously to ensure that all the metrics
defined in SLAs are satisfied. UUNet does not
specify strict delay bounds, but instead provides
an average delay. The SLAs [uunet1] include
guarantees on:Network qualityincluding:- delay~ averaged monthly ≤65/85/120 ms,
for US/European/Trans-Atlantic networks,
respectively, measured as RTD by using
ICMP6)echo messages; - packet delivery rate= monthly averaged
≥99 % for US, EU, Trans-Atlantic links, ser-
vice quality (network availability of 100 % of
the time, apart from scheduled maintenance in
time windows agreed with the customer).
Service qualityincluding 100 % availability for
the network, e.g. for the VPN service UUNet
uses pingto monitor the customer’s router every
two minutes to determine network availability.
If the router does not respond after three pings,
UUNet will deem the service unavailable and let
the customer know immediately. Failure to do so
will result in the customer’s account being cred-
ited for that day. The estimated number of lost
ping packets yields information about the avail-6)ICMP measurements will replace the current NTP measurements (run each 15 minutes) as the
technology used to gather the data on delay.