Network Working Group Lily Cheng
Internet Draft
Expiration Date: January 2002 (Editor)
Yang Cao (Sycamore)
John Ellson (Lucent)
Anwar Elwalid (Lucent)
Takeshi Hashimoto (Japan Telecom)
Hirokazu Ishimatsu (Japan Telecom)
Admela Jukan (Vienna U. of Tech)
Li Mo (Metra Network)
Ananth Nagarajan (Sprint)
Yoshihito Oyama (Japan Telecom)
Lijun Qian (Lucent)
Iraj Saniee (Lucent)
Ed Snyder (PhotonEx)
Shinya Tanaka (Japan Telecom)
Maarten Vissers (Lucent)
Indra Widjaja (Lucent)
Yangguang Xu (Lucent)
Susumu Yoneda (Japan Telecom)
July 2001
A Framework for Internet Network Engineering
draft-cheng-network-engineering-framework-01.txt
Status of this Memo
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Cheng et. al. [Page 1]
Abstract
This document outlines an early draft of a Network Engineering (NE)
framework. It defines the Network Engineering function and discusses
the differences between Traffic Engineering (TE) and Network
Engineering. It identifies network architecture and major functional
capabilities for Network Engineering. Network Engineering provides a
new set of capabilities that is utilized in conjunction with Traffic
Engineering to optimize the network efficiency, operation, and
utilization.
Table of Contents
1.0 Introduction and Background
1.1 Long-term and Short-term Internet Engineering Processes
1.2 Conventional IP Traffic Engineering and Limitation
1.3 Layered Network
1.4 Conventional IP Network Planning and Limitation
1.5 Terminology
2.0 Network Engineering
2.1 Why
2.2 What
2.3 How
2.4 When
2.5 Where
3.0 Architectural Elements of Network Engineering
3.1 Architectural Overview
3.2 Traffic Information
3.3 Network Topology Information
3.3.1 IP Network Topology Information
3.3.2 Transport Network Topology Information
3.4 Triggering Mechanisms
3.5 Optimization Module
3.6 Link Operations
4.0 Network Engineering and Traffic Engineering - A Closed-loop
relation
5.0 Summary
6.0 Security
7.0 Acknowledgement
8.0 Authors Addresses
9.0 References
Cheng et. al. [Page 2]
1. Introduction and Background
1.1 Long-term and Short-term Internet Engineering Processes
Figure 1 illustrates the long-term and short-term Internet Engineering
model for a network. Traditionally, Network Planning is used to build a
physical network with static topology. Once a network is installed, it
is expected to stay for a long period of time. Traffic Engineering is
then used to optimize network resource utilization for traffic demands
[TE-ash]. It is the optimization of network resources based on a fixed
network topology. It allows traffic to utilize network resources in an
efficient way. Network Planning is a long-term process to optimize
network resources for long-term traffic growth, while Traffic
Engineering is a short-term process to optimize network resources for
short-term traffic fluctuation.
Traffic NE, NE, fiber, fiber
+-------- data Rsc. Pool w. uninstalled NEs & fiber
| | |
| | |
| +----------v----------+ +---------v---------+
^ | Traffic Engineering | | Network Planning |
| | (Short-term) | | (Long-Term) |
| +----------+----------+ +---------+---------+
| | |
| | |
| v v
| ----------------------------------------------
+--<----- Network w. Resources (capacity)
Physical Topology
----------------------------------------------
Figure 1 Long-term and Short-term Internet Engineering Processes
1.2 Conventional IP Traffic Engineering and Limitation
Traffic Engineering, in short, is putting traffic where the capacity is
[ASTN-LN01]. This is contrasted with Network Engineering, which is
establishing capacity where the traffic needs it.
[TE-FRWK] has a detailed definition of Internet Traffic Engineering.
"Internet traffic engineering is defined as that aspect of Internet
Network Engineering dealing with the issues of performance evaluation
and performance optimization of operational IP networks. Traffic
Engineering encompasses the application of technology and scientific
principles to the measurement, characterization, modeling, and control
of Internet traffic [rfc2702]."
Cheng et. al. [Page 3]
In traditional IP traffic engineering, the underlying network topology
is assumed to be relatively static [rfc2702, te-MPLS-diff]. In
particular, the links connecting the IP/MPLS routers in the backbone
are typically provisioned for a long period of time, due to the
difficulties of rapid reconfiguration of physical links.
The main objective of IP/MPLS traffic engineering is efficient mapping
of traffic demands onto the network topology to maximize resource
utilization while meeting QoS constraints such as delay and packet
loss. The traffic demands may be obtained from measurement, projection,
customer prospects, Service Level Agreement (SLA), or combination of
the above. The mapping may be done in a multi-period fashion
corresponding to diurnal or weekly patterns. In a MPLS network, the
mapping is facilitated by establishing explicit label switched paths
(LSP). In a connectionless IP network, the mapping can be attempted by
adjusting IGP weights.
The key assumption of current Internet Traffic Engineering is that the
total network resources for IP routers to use are fixed. This
assumption may be changed by leveraging configurable circuit-switched
networks. Instead of a fixed amount of resources, the allocation of
total network resources for IP routers can now be flexible. The IP
network can get more resources from its provider network, which may be
a transport network that carries IP traffic. It can also return
resources to its provider network. The configurable circuit-switched
network is a flexible transport network, which provides a flexible
network resource pool. However, the resources (bandwidth, links, ports)
of the pool are limited (if there were unlimited, there would be no
point of switching).
IP traffic has the following characteristics:
- IP traffic is variable-speed.
- IP traffic is bursty.
- Destination address is frequently changed (e.g., net surfing).
- A variety of QoS is needed depending on application.
A fixed topology with a fixed amount of bandwidth for Traffic
Engineering does not offer sufficient flexibility to optimally deal
with the characteristics mentioned above, because IP traffic
characteristics change dynamically from moment to moment. The Network
Engineering function described herein offers the potential to overcome
this limitation via dynamic reconfiguration of links according to the
status of the networks, a property that is supported by dynamically
configurable circuit-switched networks.
1.3 Layered Network
Before we discuss the solutions that this paper identifies, we briefly
discuss the notion of a layered network architecture. The concept of
layering enables a separation between a network's logical topology and
its physical routes and resources. In particular, the process for
setting up connections becomes generic to all layers.
Cheng et. al. [Page 4]
Layering refers to a logical decomposition of a network into a number
of distinct layers, which have a well-defined set of associated
characteristics. A layer network may be defined in terms of a <rate,
format>-tuple (or signal type). For example, STS-1 is a different layer
network from STS-3c is a different layer network from STS-12c.
Flexibility can occur at each of these layers, and is usually discussed
in terms of a network's "switching" granularity. For example, an IP
router's switching granularity is an IP packet; a SONET cross-connectÆs
switching granularity might be an STS-1; a photonic cross-connect's
switching granularity is a wavelength (optical channel). Figure 3 shows
some switching hierarchies, where the highest is SDM (Space Division
Multiplexing), the next one WDM (Wavelength Division Multiplexing),
etc.
There are different types of Network Elements (NEs) that can include
components of different network layers depending on the targeted
application (refer to Figure 2).
| |
+-------+
___/ \___
__/ \___
/ \
+-------------------------+
| +--STS-1-+ |
| | \ / | |
| /|/ \/ \ |\ |
| | || /\ |\| | |
| /|/| || _/ \_ | | |\|\ |
|| / \|+--------+ |/ | ||
|| | +-STS-3c-+ | ||
=====| | /|| \ / | |\ | |=======
=====| |-| || \/ --| |-| |=======
|| | | || /\ | | | | ||
|| | \|| _/ \_ | |/ | ||
|| | +--------+ | ||
|| | +-STS-12c+ | ||
| \|\ /|| \ / | |\ /|/ |
| | || \/ |/| | |
| | |\ /\ / | | |
| \|| _/ \_ | |/ |
| +--------+ |
+-------------------------+
+--------+
| |
Figure 2 An example of NE
Cheng et. al. [Page 5]
PDM (packet/cell)
____________________________________________________________
TDM LO (DS-1, VT1.5 etc.) | | |
______________________________V_______ | |
TDM HO (DS-3, STS-1 etc.) | | |
__________________________________V______V____ |
WDM | |
______________________________________V_____________V___
SDM |
__________________________________________V________________
Figure 3 Switching Hierarchies
Another way of describing Network Engineering is that it is the process
of obtaining connections from a provider network (note that in this
discussion we make no assumption that the user and provider are from
different organizations) in support of aggregates of traffic units
(e.g., packets) in the user network. When the resources of the
provider network are switched 1:1 with the traffic units in the user
network, then no Network Engineering function is involved.
At this point, we should introduce and distinguish between the concepts
of layering and aggregation. When layering involves an adaptation of
more than one client signal into a server signal (i.e., multiplexing),
then it is an aggregate of client signals and the layer relationship
can be managed by Network Engineering. When layering is an adaptation
of a single client into a server signal (e.g., DS3 into STS-1) then it
is not a spacial aggregate. If it is also not a temporal aggregate
then the server connections are set-up and torn down one-to-one with
client traffic units, even though thereÆs a layering relationship
between them. When there is no layering relationship, or when the
client/server relationship is 1:1, there is no spacial aggregation, but
there may still be temporal aggregation. Temporal aggregation is when
one provider connection is kept up for the multiple user traffic units.
Thus, Network Engineering is used to control spacial and/or temporal
aggregates of traffic.
Another way to identify an aggregation boundary is to observe bandwidth
time product (BTP) mismatches between traffic units in the user and
provider network. The BTP of the traffic units in the user network is
of finer granularity than the BTP of the traffic units in the provider
network. Multiple IP traffic units are interleaved in time into a
single provider connection, and the holding time of an IP traffic unit
is shorter than the holding time of an optical connection. Tearing down
one or more IP associations may only result in the reduction of
bandwidth utilization in an optical connection. Tearing down an optical
connection can only be done if all carried user IP associations are
terminated or re-routed through another optical connection.
Cheng et. al. [Page 6
Note that the establishment of an IP link usually incurs a certain cost
to the user IP network. It is important that the cost is within a
planned budget. This may involve re-optimization and tearing down some
IP links. The provider network has limited resources, so it is
important that the total value of the links established from the
provider network is maximized.
As another consideration, databases of resources lower than OSI layer 3
are traditionally easy to manage since those resources are mostly
static and changed on a order-by-order basis. However, for configurable
circuit-switched networks, where resources lower than layer 3 are
dynamically changed, it brings a completely new paradigm in how to
manage resource databases. Easy and manageable database systems are
desired.
1.4 Conventional IP Network Planning and Limitations
In conventional IP network, static topology is normally set up at the
network planning time according to the most stringent traffic demand
patterns in a given duration. Because of forecasting mismatch and the
inability of changing the network topology fast enough, Traffic
Engineering limits itself to achieving higher network resource
utilization.
Observe that the static topology of the IP network introduces
limitations. Consider first the case when traffic demands are well
estimated a priori. In this case, provisioning needs to be done
according to the most stringent traffic demand patterns in a given
duration (even under the assumption that the best TE plan, which can
take advantage of multi-period traffic patterns if used). Therefore,
network resources remain under-utilized when traffic demands are light
(e.g., during weekends or evenings) since provisioned links cannot be
released easily.
When the traffic demands cannot be estimated accurately, network
planning may not be done efficiently. For example, if link provisioning
is inadequate, traffic demands can exceed the required network
resources. This may occur because of forecasting mismatch or the
inability of provisioning the network fast enough to meet the growth in
resource requirements. On the other hand, it may be necessary to over-
provision the network due to the difficulties of forecasting the
traffic growth accurately.
Furthermore, if the provisioning cycle (i.e., the time it takes to add
resources to the network) is long, resource provisioning needs to take
into account the projected traffic growth until the beginning of the
next cycle. Consequently the extra network resources may be
significantly under-utilized at the early part of a cycle if the
projected growth is large.
Cheng et. al. [Page 7
With the advent of circuit-switched networks, the client IP networks
can leverage the dynamic nature of the underlying transport topology.
It can achieve higher network resource utilization by dynamically
setting up and tearing down IP links in response to critical traffic
conditions (e.g., overloaded ports, overloaded routers, etc.). This
overcomes the limitation associated with Traffic Engineering, which is
based on a given network topology.
Note that the leverage of a configurable circuit-switched network is
complementary to the use of effective Traffic Engineering schemes for
the IP/MPLS networks. Indeed, it is best to use an effective Traffic
Engineering scheme to optimize the traffic distribution over the
existing network resources before attempting to dynamically change the
underlying transport network resources. We present a first-draft
description of Internet Network Engineering functionality and
capabilities to address the limitation of classic IP Traffic
Engineering and Network Planning.
1.5 Terminology
In this section we present a glossary of terminology that we use in
this paper and follow it up with a description of what we term ôNetwork
Engineeringö as a solution.
Traffic Engineering û Putting traffic where the capacity is [ASTN-LN01].
Network Planning û Network Planning function makes decisions on
installing fiber and Network Equipment (NE) for a network based on
forecast long-term traffic demands.
Network Engineering û Establishing capacity where the traffic needs it.
Link-connection û one channel between subnetworks. That is to say one
unit of capacity between subnetworks. A link connection may or may not
be carrying traffic.
Link û a set of all link connections between a pair of subnetworks that
are equivalent for the purposes of routing. This definition allows a
link to have zero link connections.
An IP link û a unidirectional physical connection between two IP
routers. Note that usually IP links are bi-directional. Any request for
a bi-directional link can then be accomplished by two requests, each
for an uni-directional link. It could be an optical network connection
through the underlying circuit switched network. In this case, an IP
router has logical adjacency with its IP router peer and physical
adjacency with the circuit switch that it is connected to.
A configurable IP link-connection û an IP link, which can be
dynamically setup and released within the circuit-switched layer, thus
may actively change the IP network topology.
Cheng et. al [Page 8
A non-configurable IP link-connection û an IP link, which cannot be
dynamically setup and released within the circuit-switched layer.
User Network û an IP network, which can request for dynamical setup and
release a link within the circuit-switched Network.
Provider Network û a circuit-switched network, which can dynamically
setup and release a link for the user network.
Capacity û The ability of a link or link connection to carry traffic;
this doesnÆt imply the traffic is present or not present.
Traffic û the presence of traffic in the capacity of a link or link
connection.
Overloaded port û A port which has more traffic than the port capacity
Overloaded router û An IP router which has no more port capacity for
additional traffic
Configurability û the ability of the IP layer to add a link, delete a
link, and modify the parameter(s) of a link.
Cheng et. al [Page9]
2. Network Engineering
In this section, we will elaborate
- ôWhyö a network needs a Network Engineering function, which serves
as the motivation of our work,
- ôWhatö Network Engineering is,
- ôHowö a Network Engineering function adds, deletes, modifies
circuit-switched links,
- ôWhenö to activate a Network Engineering function, and
- ôWhereö in the network the NE modifies the user network topology via
modifying circuit-switched link configurations.
2.1 Why
How can Traffic Engineering, which was designed for static topology,
cope with conventional dynamic network topology? We will introduce
here, Network Engineering, to dynamically ôadjustö network topology for
the traditional Traffic Engineering. The network topology considered by
the Network Engineering function consists of a user network and a
provider network. Hence, it is a logical network topology.
Figure 4 illustrates the engineering hierarchy of Internet Engineering
Processes for a network to satisfy traffic demands from both short-term
and long-term perspectives.
Traffic links from Physical Resrc pool
+---- data Provider Network NE, fiber, etc.
| | | |
| | | |
| +-----v----+ +-------v--------+ +-----v-----+
^ | TE | unresol |Network Engnring| unresol | NP |
| |(Shrt-trm)|--------->| (real-time) |---------->|(Long-term |
| +-----+----+ traffic +-------+--------+ traffic +-----+-----+
| | | |
| | | |
| v v v
| -----------------------------------------------------------
+--<----- User Network w. Resources (capacity)
logical Topology
-----------------------------------------------------------
Figure 4 Engineering Hierarchy
Cheng et. al. [Page 10]
We consider a network consisting of a set of IP routers that are inter-
connected either through fixed links or through a set of circuit
switches. That is, there are two logical layers, i.e., IP layer and the
underlying circuit-switched layer. These two logical layers interact in
a user-provider relationship. The circuit-switched layer can be thought
of as merely providing dynamically configurable links for the user
network.
To address the short-term fluctuation of more/less capacity needs for
traffic demands, the Network Engineering function takes/deletes more
links from the provider network, in a near real-time fashion. It is a
function defines how the user network uses the provider network. It
changes the logical user network topology by adding/deleting circuit-
switched links. It supports better and flexible network topology for a
classic Traffic Engineering function, without having to change existing
Traffic Engineering functions.
2.2 What
Network Engineering is a part of a larger Network Planning function,
which makes decisions on installing fiber and Network Equipment (NE)
for a network based on forecast traffic demands. The user network and
the provider network will have independent Network Planning processes.
The computation for Network Planning is typically done offline since it
involves searching on multi-dimensional solution spaces for long-term
traffic growth. Network Engineering (NE) is an automation of the part
of Network Planning of the user network that can be supported from a
provider network. NE provides a more real-time topology changes
according to existing and near-term traffic demands. It assists current
Traffic Engineering function to better optimize the network resource
utilization via topology changes.
Network Engineering that we describe here can be thought of as an
automatic network provisioning procedure. It is to allocate/de-allocate
provider network resources to be used by the user network. In other
words, the intent of Network Engineering is to put the capacity where
it is needed by the traffic. Or conversely, to remove the capacity
where the traffic has diminished.
Internet Network Engineering process is concerned with the management
of the (virtual) links in the IP network based on the traffic demands
that are expected between any two routers in the network (pro-active)
and the actual traffic demands (re-active). The fundamental issue is
design, ranking, and choice of an IP link, which is to be established
by the circuit-switched layer.
It is also worth being able to calculate the number of current open
connections and the maximum number of open connections allowed (due to
limits in capacity). Network Engineering may also add a link or modify
a link (via adding or deleting link connections) on request of a
traffic engineering process (if compliant with policy), which is not
able to complete a connection in the absence of available bandwidth.
Cheng et. al. [Page 11]
2.3 How
To data network, conventional transport networks are "static". They are
provisioned as leased line services. Classic IP TE considers a fixed IP
layer topology.
A distributed transport control plane can provide an on-demand
automatic choice and configuration of underlying circuits to be used in
the IP layer. The new control plane of the transport network transforms
the "dummy pipes" into a foundation for switched connection services, a
service platform that can provide an automatic link provisioning
function rather than simple transmission. This new function enables
numerous network services.
This new paradigm of adding and deleting capacity of the transport
network has profound impacts on conventional data networking. It
changes the data network's basic assumption that the transport network
consists of fixed pipes, i.e., a static network. In the new paradigm,
the transport network can be considered as a configurable backbone.
Packet switches can dynamically adjust the network topology according
to end network traffic to optimize overall network performance.
Much effort has been devoted to the control plane design. That is,
ôhowö to automatically provision a link. Note that Network Engineering
considers user link configuration within a provider domain, hence the
choice of the signaling protocol, which will carry parameters needed
for a Network Engineering function, is not relevant for the time being.
Our work, on the other hand, focuses on ôwhenö and ôwhereö to
automatically provision a link. In this sense, this work complements
the work that is progressing in the CCAMP working group and sub-IP area
in general.
2.4 When
In order to change the logical network topology, Network Engineering
has some basic operations, which include adding a link, deleting a
link, and modifying a link from the circuit-switched layer. We will
elaborate these NE operations in detail later in section 3.6.
Network Engineering also monitors the layered network to determine
- when a new link (or link connection) should be added to the IP
network,
- when an existing link (or link connection) should be modified (i.e.
increased or reduced), or
- when a link (or link connection) should be released.
Network Engineering is a new functional module in addition to
conventional Traffic Engineering. This function is independent of any
network models (e.g., peers, overlay, or augmented)).
Cheng at. al. [Page 12
When should a Network Engineering be invoked to perform the
aforementioned operations? We will define a set of trigger mechanisms
to invoke the Network Engineering function in section 3.4.
2.5 Where
The connection resources available from the provider network are
limited. Network Engineering must choose where the most beneficial
links to add (or to delete/modify). Network Engineering should also
monitor the bandwidth demands from a source/destination relationship in
order to identify the traffic patterns in the network. Where necessary,
a user network's topology can be optimized by e.g. adding direct links
between two heavily overloaded nodes. Decisions are taken based on the
SLA between the user and the provider and the policies set by the
provider network operators.
We will address how Network Engineering optimally choosing ôwhereö to
add/delete/modify links in section 3.5 (Decision-Making Process).
Cheng et. al. [Page 13]
3. Architectural Element of Network Engineering
3.1 Architectural Overview
Figure 5 shows an architecture for Network Engineering. A decision-
making functional module is triggered by some triggering mechanisms
(e.g., proactive input or reactive input), and takes the current
network status (e.g., traffic information and topology information) to
compute the output.
The input of the Network Engineering process is the current measured
state of the user network. Proactive information makes possible traffic
shaping for particular purposes, e.g., busy hour, network overload
threshold, etc. The proactive mechanism might also use the bandwidth
advertising from the circuit network in order to pre-estimate the links
to establish. The bandwidth advertising might be invoked periodically.
Reactive information can trigger the establishment of new links upon
measured performance.
The output of the Network Engineering phase is a target IP link, which
can be configured as a switched circuit. In other words, the result of
the Network Engineering is to add a link, delete a link, or modify
parameters of a link (i.e., via adding/deleting link connections).
+------------------------+
| IP Traffic Information |
+------------|-----------+
+-----------+ |
| Proactive | +------------v-----------+ +--------------+
| Input | Triggers | | | Operations |
+-----------+--------->| IP Network Engineering +-->|(Getting res. |
| Reactive | | (decision-making) | | from Provider|
| Input | +------------^-----------+ | Networks) |
+-----------+ | +--------------+
+------------|------------+
| IP Topology Information |
+-------------------------+
Figure 5 Network Engineering Architecture
3.2 Traffic Information
An IP network has network internal information and network external
information, that can be applied to proactively or reactively
triggering an IP Network Engineering function.
Cheng et. al. [Page 14]
The network internal information deals with the traffic statistics
collected over a certain period of time, based on which particular
traffic flows can be established according to the predictable traffic
patterns. The internal information can also trigger the reconfiguration
of the existing traffic patterns (i.e., Traffic Engineering) for more
efficient service-level guarantees or network throughput. If this
fails, then Network Engineering is attempted. This information is
reactive but can be also used predictively by assuming cyclic traffic
patterns.
The network-external information deals with edge-to-edge traffic
requests. If such a request identifies an amount of resources that is
needed to assess the need for new IP links. This information can be
neither estimated nor measured with complete accuracy. An example of
such information might be a new contract or a new traffic request. In
this case, for example, the predictable traffic patterns as defined by
the long-term traffic measurements have to be revised.
Traffic statistics maybe stationary or non-stationary. For stationary
traffic statistics data, using periodically sampled data to construct a
probability distribution function (PDF) may be useful. This PDF
function is then a good input to the Network Engineering function. For
non-stationary traffic, more data (e.g., bandwidth utilization, etc.)
is needed to perform the Network Engineering function.
Examples of internal information are: packet loss [rfc2680], router
overload, and port overload [newsome01]. Examples of external
information are: SLA violations, or new SLAs. Such information triggers
the network design to automatically configure an IP link. Depending on
the triggering information, configuration can be adding, deleting
circuit links, or modifying existing traffic parameters.
Both external and internal information may result in connection
requests. The network-internal information are obtained based on the
measurements within the user network, and the network-external
information can be estimated based on the service contract information
related to the new traffic.
3.3 Network Topology Information
3.3.1 IP Network Topology Information
In order to perform Network Engineering function, IP routers need to
have the following topology information:
(1) IP routes
These are conventional routes to IP peers. They are standard IP routes
to various destinations learned through conventional IGPs (e.g., ISIS
or OSPF) and EGPs (e.g., BGP).
Cheng et. al. [Page 15]
(2) Forwarding Adjacencies (FA)
Forwarding Adjacencies are IP (i.e., Layer 3) neighbors that are
connected by an underlying circuit-LSP through a provider network.
These connections are dynamic in nature and can be set up and torn down
as needed.
Both IP routes and Forwarding Adjacencies are used for packet
forwarding. Such information is disseminated using IGP or EGP routing
protocols. A provider network treats traffic carrying this kind of
information as user traffic.
(3) Potential FAs (PFA)
PFAs are remote CAGs [BGP/GMPLS]. They represent NEs that belong to the
same client network or to different client networks, which allow NEs in
the local network to connect to it. The NEs represented by a PFA are
not connected yet but can be connected via the provider network. Such a
connection is a direct connection at the IP layer with an underlying
circuit connection that spans multiple ASÆs.
Information about PFAs can be disseminated through BGP extensions in
the provider network, directory service, or yellow page mechanisms.
(4) Accessible IP Routes through the PFAs
This provides information about all the IP routers reachable through a
PFA endpoint. Such information can be used for the IP Network
Engineering function to determine the source and destination of the
circuit connections.
Although this document does not address the issue of how this
information is disseminated, we note here that various options exist
for doing so. These options include dissemination through established
user network connections or a dedicated user network control plane
network.
3.3.2 Server Network Topology Information
For the purpose of IP Network Engineering, it understands the IP
network topology, and does not require circuit network topology
information to compute the output. Since it does not require network
topology information, Network Engineering is independent of any network
models. Existing network models are all able to support a Network
Engineering function.
Cheng et. al. [Page 16]
3.4 Triggering Mechanisms
There is a set of triggering mechanisms, which defines ôwhenö to
activate the Network Engineering function.
1. Direct user request û User should be able to request a Network
Engineering function. For example, an operator may need to do on-
line or off-line capacity planning or business modeling for his
network. Network Engineering provides a most efficient network
topology as a basic standing point for Traffic Engineering to
consider.
2. Response to adding a link û It is among Network Engineering
capability to add a link to the network. The request maybe a result
of future Network Planning of the network or an unexpected traffic
loads. Such a request can also come from Traffic Engineering.
3. Response to deleting a link û It is among Network Engineering
capability to delete a link from the network. The request maybe a
result of future planning to an expected reduced traffic loads. Also
such a request can come from Traffic Engineering.
4. Response to modifying a link û It is among Network Engineering
capability to modify a link to the network. If the request is to
increase the capacity of a link, it maybe a result of future
planning of the network or an unexpected traffic loads. If the
request is to decrease the capacity of a link, it maybe a result of
future planning or reduced traffic loads.
5. Congestion condition û Congestion problem is probably one of the
most studied problems in contemporary Internet networks. When a
congestion condition is not properly handled, it will significantly
degrade network performance. Traffic Engineering should be able to
detect a congestion condition and re-engineers the network. Upon its
limit, then activate Network Engineering function.
6. Router overload û Upon a router overload condition, it is desirable
to find an alternative route for traffic to bypass the overloaded
router.
7. Link overload û Upon a link overload condition, it is desirable to
add more capacity parallel to the congested link. If this is not
feasible, it is desirable to increase capacity over a different
route and redirect some of the existing traffic to the newly added
link to relief the overloaded condition. However, this has to be
done carefully as existing traffic should not get all redirected on
the newly added link, leading to a mere shift in the location of the
link overload condition.
8. Maintenance û In the maintenance phase, it is also desirable to run
Network Engineering function.
9. Failure û Upon a failure situation (e.g., link failure, network
failure, etc.), it is desirable to run Network Engineering function.
Cheng et. al. [Page 17]
10. Routine û If none of the above condition occurs, it is desirable
to run the Network Engineering function on a regular basis.
Routinely running Network Engineering function can insure that the
network is making the most efficient use of it network resources.
The interval of the routine depends on the network sizes and traffic
loads of the network.
3.5 The Decision Making Process
The decision-making process decides ôwhereö to add/delete/modify
circuit-switched links.
The Network Engineering decision making module will be involved in the
path computation depending on the knowledge of the layered network. The
problem of selecting a new link that best satisfies demands for
bandwidth is a multi-dimensional optimization problem, i.e. one that is
mathematically "hard" and probably not possible to compute perfectly,
even in principle. This problem can be decomposed into two parts: link
design, and link choice. The design phase identifies a set of links
that would satisfy some needs; whereas the choice phase chooses a final
set of links based on maximizing the total value.
First of all, link design provides a set of potential links that meets
the following criteria:
1. links that are configurable in the circuit-switched layer (e.g.,
with free ports, and free capacities), and
2. links that has enough capacity to meet traffic demands.
During the design phase, we distinguish different types of links based
on the number of hops the link bridges. The output of link design can
be zero or more candidate links to be ôconfiguredö (e.g., add, delete,
modify) in the circuit-switched layer. If no link is selected, it means
blocking in the circuit layer. This can be unavailable ports or
insufficient capacity.
Secondly in the choice phase, a set of criteria, for choosing a final
link amongst a set of candidate links, is needed. The criteria are
based on the consideration of bandwidth, distance, and duration. Link
choice ranks the set of potential links, selected from the above link
design, according to the following set of parameters:
1. number of hops bridged,
2. bandwidth utilization of the new link,
3. value (or more correctly, rate of return on investment),
4. number of switched-ports spared, or
5. etc.
Cheng et. al. [Page 18]
It then requests the reduced set of maximum value from the potential
links. One implication of the link choice is that a link design may get
refused for reasons of insufficient value.
The value of any link requested can be expressed by
1. multiple attributes (as listed for link choice) or
2. a single metric function of multiple parameters (e.g. bandwidth,
time, distance, etc.). That is, a single valued function of the
parameters.
To avoid the problems of multi-dimensional optimization as described
above, a single metric can be chosen as precedent, based on which a
choice is made if all other requirements are satisfied.
Administrative policies, constraints, directives, and guidance can also
be weighted and contributed to the single metric. Some will be simple
boolean, go-nogo parameters, so if we're converting to cost, nogo
parameters might have to be represented as an infinite cost value to
force rejection of the option.
Other parameters can be given weights and factored in to the single
metric for the multi-dimensional tradeoffs. So far we have been
focussing on shortest-path costing only, but we realize that Network
Engineering must support additional administrative inputs.
Within the circuit layer a choice between candidate switched circuits
can be made for the IP network in order to have the maximum advantages
of a dynamic configuration. All circuits, which may be configured, are
expected to be within the bounds requested by the IP layer, otherwise
the request is rejected.
3.6 Link Operations
As we have mentioned earlier, in order to change the network topology,
Network Engineering has to be able to add, delete, modify circuit-
switched links. We distinguish the following four types of link
operations:
(1) add a link
Adding a link is to add a potential route with zero capacity. This type
of link bridges two or more hops of existing IP links. Note that it
changes the IP network topology without adding new capacity. Routing
tables will need to be updated.
Consider an IP (user) over an circuit (provider) network, where traffic
flows from the source node A to the destination node Z. The following
figure shows adding a new link p-s.
Cheng et. al. [Page 19]
A p q r s Z
O------O......O......O......O-------O
:....................:
(2) add a link connection
Adding a link connection is to increase the capacity of an existing
link. This new link (connection) bridges a single hop of IP link. It
parallels an existing link and increases capacity of this link without
changing the network topology. The following figure shows adding a new
link connection r-s to an existing circuit-switched link r-s.
A p q r s Z
O------O......O......O:::::::O-------O
(3) delete a link connection
This operation is only allowed when the traffic of that link connection
is zero. Deleting a link connection is to decrease the capacity of a
link. It may reduce the capacity of a link to zero.
(4) delete a link
This operation is only allowed when the number of link connections in
the link is zero. That is, when the capacity of the link is zero. To
delete a link means to remove a potential route with zero capacity.
For the purpose of Network Engineering, if we need a new link with some
capacity, we need to add a link (with zero capacity), and then add a
new link connection to increase the capacity of this new link. If we
need to delete a link, we will need to delete all the link connections
in that link before deleting the link.
Cheng et. al. [Page 20]
4 Network Engineering and Traffic Engineering - A Closed-Loop Relation
This section illustrates a closed-loop relationship between Network
Engineering and Traffic Engineering processes (Figure 6). A closed-loop
link provisioning process would automatically configure circuits in the
circuit-switched network [close-loop, oif-197]. The cycle is closed
because changes in bandwidth or topology affect the state of the user
network.
---------------------------------------
+--> the state of the user network
| ---+---------^------------------+------
| | | |
| topology& | topology &
| traffic route Triggers
| updates updates |
| | | |
topology | | |
updates +-v----------+ +------v------+
| | Traffic | traffic | Network |
| | Engineering|--->------| Engineering |-+
^ +------------+ problems +-------------+ |
| |
+----+------+ |
| topology | |
| discovery | |
+----+------+ User Network
--------+---------------------------------------------+---------
| Provider Network
| |
Operation Operations
results requests
| +------------+ |
+---<----------| Operations |-----<-----------+
+------|-----+
^ |
| v
---------------|--------------------
the state of the provider network
------------------------------------
Figure 6 A Closed-loop Procedure for NE and TE
A user network may consist of multiple sub-networks. For the purpose of
discussion the relationship between Network Engineering and Traffic
Engineering, we treat these sub-networks as one user-network. Hence the
ôuser networkö in Figure 5 can be single or multiple sub-network. We do
not wish to further complicate our discussion here.
Cheng et. al. [Page 21
Note that in Figure 5, Traffic Engineering still performs its function
without having to interact with Network Engineering. Traffic
Engineering gets traffic demands and optimally maps them into the
existing network topology. Upon reaching the Traffic Engineering limit
when traffic problems occur (e.g., insufficient capacity, etc.),
Traffic Engineering then turns the problem to Network Engineering for
dynamic topology reconfiguration. Network Engineering can also be run
routinely.
Traffic Engineering mainly decides ôwhenö to use Network Engineering.
Network Engineering computes ôwhereö to change the topology.
5. Summary
In this paper, we have outlined an early draft for an Internet Network
Engineering framework. Traffic problems, which occur due to the
limitations of Traffic Engineering, can trigger Network Engineering
processes to further optimize the network performance. Network
Engineering is to automatically select a link for addition, deletion,
and modification to address Traffic Engineering limitation. Network
Engineering and Traffic Engineering form a closed-loop process to
optimize the network resources.
We also note that the specific choice of technologies is not essential
to a Network Engineering process. It is important to recognize the
problem is recursive. The closed-loop process for Network Engineering
and Traffic Engineering is applicable to any user-provider relationship
networks.
6. Security Issues
This document raises no new security concerns for MPLS signaling.
7. Acknowledgement
The authors would like to express thanks to Siva Sankaranarayanan for
his fruitful comments and technical discussion.
Cheng et. al. [Page22]
8. Authors Addresses
Lily Cheng
John Ellson
Lucent Technologies, Inc.
101 Crawfords Corner Rd
Holmdel, NJ 07733
Email {lilycheng, ellson}@lucent.com
Admela Jukan
Vienna University of Technology
Institute of Communication Networks
Favoritenstrasse 9/388
A-1040 Vienna, Austria
Email admela.jukan@tuwien.ac.at
Maarten Vissers
Lucent Technologies, Inc.
Botterstraat 45, Postbus 18
Huizen, 1270 AA Netherlands
Email mvissers@lucent.com
Yangguang Xu
Lucent Technologies, Inc.
1600 Osgood St.
North Andover, MA08145
Email xuyg@lucent.com
Iraj Saniee
Lijun Qian
Anwar Elwalid
Indra Widjaja
Lucent Technologies, Inc.
600-700 Mountain Ave.
Murry Hill, NJ07974
Email {iis, ljqian, anwar, iwidjaja}@lucent.com
Yang Cao
10 Elizabeth Dr.
Chelmsford, MA 01824
Sycamore Networks
Email yang.cao@sycamorenet.com
Susumu Yoneda (yone@japan-telecom.co.jp)
Hirokazu Ishimatsu (hirokazu@japan-telecom.co.jp)
Takeshi Hashimoto (take_h@nts.japan-telecom.co.jp)
Yoshihito Oyama (oyama@jtlab.net)
Shinya Tanaka (t@nts.japan-telecom.co.jp)
Japan Telecom Co., Ltd.
2-9-1 Hatchobori, Chuo-ku
Tokyo, 104-0032 Japan
Cheng et. al. [Page 23
Li Mo
Metera Networks Inc.
1202 Richardson Drive, Suite 100
Richardson, TX 75080
Email li@metera.com
Ed Snyder
PhotonEx Corporation
200 MetroWest Technology Drive
Maynard, MA01754
Email esnyder@photonex.com
Ananth Nagarajan
Sprint
9300 Metcalf Ave
Overland Park, KS 66212.
ananth.nagarajan@mail.sprint.com
9. References
[newsome01] Newsome, G. "IP Traffic Engineering resulting in Optical
Layer Connections", IETF draft, draft-newsome-mgmtplanerqmts-00.txt,
November 2000.
[TE-ash] Ash J. ôTraffic Engineering & QoS Methods for IP-, ATM-, &
TDM-based Multiservice Networksö, IETF draft, draft-ietf-tewg-qos-
routing-01.txt, March, 2001.
[rfc2702] Awduche D. et. al. "Requirements for Traffic Engineering over
MPLS", RFC2702, September 1999.
[ASTN-LN01] Maarten Vissers, ôASTN Layer Network Architectureö, ITU-T
CD, SG-15, CD-ASTN-LN01, May,2001.
[te-MPLS-diff] Le Faucheur et. al. "Requirements for support of Diff-
serv-aware MPLS Traffic Engineering", IETF draft, draft-ietf-mpls-diff-
te-reqts-00.txt, November 2000.
[te-frame] Awduche, D. et. al. "A framework for Internet Traffic
Engineering" IETF draft, draft-ietf-tewg-framework-02.txt, July 2000.
[rfc2680] Almes, G. et. al. "A One-way Packet Loss Metric for IPPM,"
RFC2680, September 1999.
[closed-loop] Ellson, Cheng, Jukan, et. al. ôClosed-Loop Automatic Link
Provisioningö, IETF draft, draft-ellson-ipo-te-link-provisioning-
00.txt, March, 2001.
[oif-197] Ellson, Cheng, Jukan ôClosed-loop Link Provisioning for
Bandwidth Brokeringö, OIF-197, May, 2001.
Cheng et. al. [Page 24]