Side_1_360

Some examples of the content of an SLA for an
IP connectivity service are illustrated in Figure 7.

The interface description includes the descrip-
tion of the business interaction points – perfor-
mance reporting point, service access points, and
protocols/formats used for exchanging informa-
tion on these protocols. Traffic pattern is basi-
cally described by the throughput which is
linked to the time-of-day distribution and user’s
behaviour, where different values are allowed
for different time periods. The most mentioned
QoS parameters related to the provision of real-
time services in the IP-based environment are
delay, loss and jitter. Also, availability is proven
to be a very important factor for customers.
Hence, these are usually used in SLAs indepen-
dently of the SLA type. In case of value added
services, additional parameters related to the
quality of customer care, e.g. help desk avail-
ability, mean time to repair, etc. are given as
well.

Applying the 3x3 matrix to the case of a Virtual
Leased Line (VLL), where the access and disen-
gagement functions are not relevant, the QoS
parameters identified for the IP packets transfer
phase can be listed as:

IP packet transfer delay ex- transfer

pressed both as a mean value speed

and variation [Y.1540],

[rfc2330], [rfc2123]

IP packet error ratio [Y.1540], transfer

[rfc2330], [rfc2123] accuracy

IP packet loss ratio [Y.1540] transfer

dependability

IP transfer availability [Y.1540] transfer

dependability

In order to prove delivery of the quality of the

service as agreed in an SLA, the chosen parame-

ters need to be observed whether they are con-

formant to the agreed values or not. Also, the

behaviour of the users has to be observed, so the

provider may react when the user does not obey

the agreement (e.g. generating more traffic than

allowed in the SLA). Therefore, measurement

schemes have to be developed and agreed –

active vs. passive measurement methods, fre-

quency of measurements that are chosen so they

are not too much of an overhead for the servers,

etc. The relevant measurement points need to be

identified, e.g. ingress and egress routers, gate-

Interface description Performance reporting point – web site URL

Business interaction points SAP – IP address/port, phone number for dial up access

Technical interaction points Protocols – IPv4, BGP4, SNMP3

Traffic pattern Throughput 08-19h 384 kbps

Throughput 19-08h 128 kbps

Time of day pattern distribution function included

QoS parameters and Availability 99%

objectives Loss ratio < 5%

Set-up delay < 2 sec

Measurement scheme Measurement points Ingress router, egress router, gateway

Measurement methods Active probing

Tools Ping, traceroute

Granularity 10 minutes

Reaction pattern Discount Availability guarantee breached

1h UA 4h = 1 day service credit

4h UA 8h = 7 days service credit

UA 8h = 30 days service credit

Traffic shaping IF user’s traffic exceeds 2 Mbps

at the ingress THEN discard it

Alarm

Warning

Policy invocation UA = unavailability

user provider

SLA

Service

Legal issues

Charging

• • •
  QoS-related part

QoS-related part

Figure 7 Generic structure of

QoS-related part of an SLA,

some examples