interval for collecting and returning the infor-
mation. A similar trade-off is also seen for the
distributed scheme, although then the deci-
sions are made by each router. A drawback of
a centralised scheme is commonly that a sin-
gle point of failure is introduced, implying
that the central function is available and has
sufficiently processing capacity for the
scheme to work efficiently.- Localvs. global information. Local informa-
tion refers to a portion of the region/domain
considered by the TE system. An example is
delay for a particular LSP. Global information
refers to the whole region/domain considered. - Prescriptivevs. descriptive. When a prescrip-
tive approach is used, a set of actions would
be suggested by the TE system. Such an
approach can be either corrective (an action to
solve an existing or predicted anomaly) or
perfective (an action suggested without identi-
fying any particular anomaly). A descriptive
approach characterises the network state and
assesses the impact from exercising various
policies without suggesting any specific
action. - Open loopvs. closed loop. In an open loop
approach, the control actions do not use feed-
back information from the network. Such
feedback information is used when a closed
loop approach is followed. - Tacticalvs. strategic. A tactical approach con-
siders a specific problem, without taking into
account the overall solutions, tending to be ad
hoc in nature. A strategic approach considers
the TE problem from a more organised and
systematic perspective, including immediate
and longer-term consequences.- Intradomainvs. interdomain. Interdomain
traffic engineering is primarily concerned with
performance of traffic and networks when the
traffic flows cross a domain, e.g. between two
operators. Both technical and administrative/
business concerns make such a TE activity
more complicated. One example is based on
the fact that Border Gateway Protocol version
4 (BGP-4), being the (default) standard rout-
ing protocol, does not carry full information
like an interior gateway protocol (e.g. no
topology and link state information). In a busi-
ness sense it would not be likely that two par-
ties, being potential competitors, would reveal
all that data of their network. Another aspect
is the presence of relevant SLAs that govern
the interconnection, including description of
traffic patterns, QoS, measurements and reac-
tions. An SLA may explicitly or implicitly
specify a Traffic Conditioning Agreement
(TCA, which defines classifier rules as well
as metering, marking, discarding and shaping
rules.
- Intradomainvs. interdomain. Interdomain
A specific TE system can then be categorised by
applying the criteria listed above.6 Further Issues
6.1 Basic Questions and Factors
Several forces are influencing on the evolution
of IP-based networks, see Figure 8.A number of basic questions can be raised re-
lated to the future of Internet/IP-based network:- Will the current Internet routing mechanisms
operate as steadily more hosts and networks
are added? - How is it possible to automate mechanisms
for storing and locating information about
individual users? - How is it possible to automate mechanisms
for storing and locating information about ser-
vices offered by hosts? - How to incorporate vendor-independent and
automated mechanisms that allow monitoring
and control of traffic and network resources? - How can relevant protocols be adapted, or
supplemented, to accommodate new applica-
tions that have specific requirements (e.g. high
throughput, short delays)? - How can emerging business configurations
be supported, allowing for multiple services,
access forms and a range of providers/opera-
tors.
Figure 8 Factors influencing
the evolution of IP-based net-
works, adapted from
[Come88]
IP-based network,
<Internet>New
applications
Accomodation
of new groupsIncreased load
and expansionNew hardware and
communication technologies