draft-ietf-ipo-impairments-03.txt   draft-ietf-ipo-impairments-04.txt 
Internet Draft John Strand (Editor) Internet Draft John Strand (Editor)
Document: draft-ietf-ipo-impairments-03.txt AT&T Document: draft-ietf-ipo-impairments-04.txt Angela Chiu (Editor)
Informational Track Informational Track AT&T
Expiration Date: March 2003 Angela Chiu (Editor) Expiration Date: May 2003
Celion Networks
September 2002 December 2002
Impairments And Other Constraints On Optical Layer Routing Impairments And Other Constraints On Optical Layer Routing
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are all provisions of Section 10 of RFC2026. Internet-Drafts are
working documents of the Internet Engineering Task Force (IETF), its working documents of the Internet Engineering Task Force (IETF), its
areas, and its working groups. Note that other groups may also areas, and its working groups. Note that other groups may also
distribute working documents as Internet-Drafts. distribute working documents as Internet-Drafts.
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http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
Abstract Abstract
Optical networking poses a number challenges for GMPLS. Optical Optical networking poses a number challenges for GMPLS. Optical
technology is fundamentally an analog rather than digital technology; technology is fundamentally an analog rather than digital technology;
and the optical layer is lowest in the transport hierarchy and hence and the optical layer is lowest in the transport hierarchy and hence
has an intimate relationship with the physical geography of the has an intimate relationship with the physical geography of the
network. This contribution surveys some of the aspects of optical network. This contribution surveys some of the aspects of optical
networks which impact routing and identifies possible GMPLS responses networks which impact routing and identifies possible GMPLS responses
for each: (1) Constraints arising from the design of new software for each: (1) Constraints arising from the design of new software
controllable network elements, (2) Constraints in a single all- controllable network elements, (2) Constraints in a single all-optical
optical domain without wavelength conversion, (3) Complications domain without wavelength conversion, (3) Complications arising in more
arising in more complex networks incorporating both all-optical and complex networks incorporating both all-optical and opaque
opaque architectures, and (4) Impacts of diversity constraints. architectures, and (4) Impacts of diversity constraints.
1. Introduction 1. Introduction
GMPLS [GMPLS] aims to extend MPLS to encompass a number of transport GMPLS [GMPLS] aims to extend MPLS to encompass a number of transport
architectures. Included are optical networks incorporating a number architectures. Included are optical networks incorporating a number
of all-optical and opto-electronic elements such as optical cross- of all-optical and opto-electronic elements such as optical cross-
connects with both optical and electrical fabrics, transponders, and connects with both optical and electrical fabrics, transponders, and
optical add-drop multiplexers. Optical networking poses a number optical add-drop multiplexers. Optical networking poses a number
challenges for GMPLS. Optical technology is fundamentally an analog Impairments And Other Constraints December 2002
Impairments And Other Constraints September 2002
On Optical Layer Routing On Optical Layer Routing
challenges for GMPLS. Optical technology is fundamentally an analog
rather than digital technology; and the optical layer is lowest in rather than digital technology; and the optical layer is lowest in
the transport hierarchy and hence has an intimate relationship with the transport hierarchy and hence has an intimate relationship with
the physical geography of the network. the physical geography of the network.
GMPLS already has incorporated extensions to deal with some of the GMPLS already has incorporated extensions to deal with some of the
unique aspects of the optical layer. This contribution surveys some unique aspects of the optical layer. This contribution surveys some
of the aspects of optical networks which impact routing and of the aspects of optical networks which impact routing and
identifies possible GMPLS responses for each. Routing constraints identifies possible GMPLS responses for each. Routing constraints
and/or complications arising from the design of network elements, and/or complications arising from the design of network elements,
the accumulation of signal impairments, and from the need to the accumulation of signal impairments, and from the need to
skipping to change at page 2, line 40 skipping to change at page 2, line 41
- Section 3 describes constraints arising from the design of new - Section 3 describes constraints arising from the design of new
software controllable network elements. software controllable network elements.
- Section 4 addresses the constraints in a single all-optical - Section 4 addresses the constraints in a single all-optical
domain without wavelength conversion. domain without wavelength conversion.
- Section 5 extends the discussion to more complex networks. - Section 5 extends the discussion to more complex networks.
incorporating both all-optical and opaque architectures. incorporating both all-optical and opaque architectures.
- Section 6 discusses the impacts of diversity constraints. - Section 6 discusses the impacts of diversity constraints.
- Section 7 deals with security requirements. - Section 7 deals with security requirements.
- Section 8 contains acknowledgments. - Section 8 contains acknowledgments.
- Section 9 contains references. - Section 9 contains references.
- Section 10 contains contributing authors’ addresses. - Section 10 contains contributing authorsÆ addresses.
- Section 11 contains editors’ addresses. - Section 11 contains editorsÆ addresses.
2. Sub-IP Area Summary And Justification Of Work 2. Sub-IP Area Summary And Justification Of Work
This draft merges and extends two previous drafts, draft-chiu- This draft merges and extends two previous drafts, draft-chiu-
strand-unique-olcp-02.txt and draft-banerjee-routing-impairments- strand-unique-olcp-02.txt and draft-banerjee-routing-impairments-
00.txt. These two drafts were made IPO working group documents to 00.txt. These two drafts were made IPO working group documents to
form a basis for a design team at the Minneapolis meeting, where it form a basis for a design team at the Minneapolis meeting, where it
was also requested that they be merged to create a requirements was also requested that they be merged to create a requirements
document for the WG. document for the WG.
In the larger sub-IP Area structure, this merged document describes In the larger sub-IP Area structure, this merged document describes
specific characteristics of optical technology and the requirements specific characteristics of optical technology and the requirements
they place on routing and path selection. It is appropriate for the Impairments And Other Constraints December 2002
Impairments And Other Constraints September 2002
On Optical Layer Routing On Optical Layer Routing
they place on routing and path selection. It is appropriate for the
IPO working group because the material is specific to optical IPO working group because the material is specific to optical
networks. It identifies and documents the characteristics of the networks. It identifies and documents the characteristics of the
optical transport network that are important for selecting paths for optical transport network that are important for selecting paths for
optical channels, which is a work area for the IPO WG. It is optical channels, which is a work area for the IPO WG. It is
appropriate work for this WG because the material covered is appropriate work for this WG because the material covered is
directly aimed at establishing a framework and requirements for directly aimed at establishing a framework and requirements for
routing in an optical network. routing in an optical network.
Related documents are: Related documents are:
draft-banerjee-routing-impairments-00.txt draft-banerjee-routing-impairments-00.txt
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draft-hayata-ipo-carrier-needs-00.txt draft-hayata-ipo-carrier-needs-00.txt
draft-many-carrier-framework-uni-01.txt draft-many-carrier-framework-uni-01.txt
draft-papadimitriou-ipo-non-linear-routing-impairm-01.txt draft-papadimitriou-ipo-non-linear-routing-impairm-01.txt
3. Reconfigurable Network Elements 3. Reconfigurable Network Elements
3.1 Technology Background 3.1 Technology Background
Control plane architectural discussions (e.g., [Awduche99]) usually Control plane architectural discussions (e.g., [Awduche99]) usually
assume that the only software reconfigurable network element is an assume that the only software reconfigurable network element is an
optical layer cross-connect (OLXC). There are however other optical layer cross-connect (OLXC). There are however other software
software reconfigurable elements on the horizon, specifically reconfigurable elements on the horizon, specifically tunable lasers and
tunable lasers and receivers and reconfigurable optical add-drop receivers and reconfigurable optical add-drop multiplexers (OADMÆs).
multiplexers (OADM’s). These elements are illustrated in the These elements are illustrated in the following simple example, which
following simple example, which is modeled on announced Optical is modeled on announced Optical Transport System (OTS) products:
Transport System (OTS) products:
+ + + +
---+---+ |\ /| +---+--- ---+---+ |\ /| +---+---
---| A |----|D| X Y |D|----| A |--- ---| A |----|D| X Y |D|----| A |---
---+---+ |W| +--------+ +--------+ |W| +---+--- ---+---+ |W| +--------+ +--------+ |W| +---+---
: |D|-----| OADM |-----| OADM |-----|D| : : |D|-----| OADM |-----| OADM |-----|D| :
---+---+ |M| +--------+ +--------+ |M| +---+--- ---+---+ |M| +--------+ +--------+ |M| +---+---
---| A |----| | | | | | | |----| A |--- ---| A |----| | | | | | | |----| A |---
---+---+ |/ | | | | \| +---+--- ---+---+ |/ | | | | \| +---+---
+ +---+ +---+ +---+ +---+ + + +---+ +---+ +---+ +---+ +
D | A | | A | | A | | A | E D | A | | A | | A | | A | E
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
| | | | | | | | | | | | | | | |
Figure 3-1: An OTS With OADM's - Functional Architecture Figure 3-1: An OTS With OADM's - Functional Architecture
In Fig.3-1, the part that is on the inner side of all boxes labeled In Fig.3-1, the part that is on the inner side of all boxes labeled
"A" defines an all-optical subnetwork. From a routing perspective "A" defines an all-optical subnetwork. From a routing perspective
two aspects are critical: two aspects are critical:
Impairments And Other Constraints September 2002 Impairments And Other Constraints December 2002
On Optical Layer Routing On Optical Layer Routing
- Adaptation: These are the functions done at the edges of the - Adaptation: These are the functions done at the edges of the
subnetwork that transform the incoming optical channel into the subnetwork that transform the incoming optical channel into the
physical wavelength to be transported through the subnetwork. physical wavelength to be transported through the subnetwork.
- Connectivity: This defines which pairs of edge Adaptation - Connectivity: This defines which pairs of edge Adaptation
functions can be interconnected through the subnetwork. functions can be interconnected through the subnetwork.
In Fig. 3-1, D and E are DWDM’s and X and Y are OADM’s. The boxes In Fig. 3-1, D and E are DWDMÆs and X and Y are OADMÆs. The boxes
labeled "A" are adaptation functions. They map one or more input labeled "A" are adaptation functions. They map one or more input
optical channels assumed to be standard short reach signals into a optical channels assumed to be standard short reach signals into a
long reach (LR) wavelength or wavelength group which will pass long reach (LR) wavelength or wavelength group which will pass
transparently to a distant adaptation function. Adaptation transparently to a distant adaptation function. Adaptation
functionality which affects routing includes: functionality which affects routing includes:
- Multiplexing: Either electrical or optical TDM may be used to - Multiplexing: Either electrical or optical TDM may be used to
combine the input channels into a single wavelength. This is combine the input channels into a single wavelength. This is
done to increase effective capacity: A typical DWDM might be done to increase effective capacity: A typical DWDM might be
able to handle 100 2.5 Gb/sec signals (250 Gb/sec total) or 50 able to handle 100 2.5 Gb/sec signals (250 Gb/sec total) or 50
10 Gb/sec (500 Gb/sec total); combining the 2.5 Gb/sec signals 10 Gb/sec (500 Gb/sec total); combining the 2.5 Gb/sec signals
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be tunable over the entire range of wavelengths supported by the be tunable over the entire range of wavelengths supported by the
DWDM. Tunability speeds may also vary. DWDM. Tunability speeds may also vary.
Connectivity between adaptation functions may also be limited: Connectivity between adaptation functions may also be limited:
- As pointed out above, TDM multiplexing and/or adaptation - As pointed out above, TDM multiplexing and/or adaptation
grouping by the adaptation function forces groups of input grouping by the adaptation function forces groups of input
channels to be delivered together to the same distant adaptation channels to be delivered together to the same distant adaptation
function. function.
- Only adaptation functions whose lasers/receivers are tunable to - Only adaptation functions whose lasers/receivers are tunable to
compatible frequencies can be connected. compatible frequencies can be connected.
- The switching capability of the OADMs may also be constrained. - The switching capability of the OADMÆs may also be constrained.
For example: For example:
o There may be some wavelengths that can not be dropped at o There may be some wavelengths that can not be dropped at
all. all.
o There may be a fixed relationship between the frequency o There may be a fixed relationship between the frequency
dropped and the physical port on the OADM to which it is dropped and the physical port on the OADM to which it is
dropped. dropped.
o OADM physical design may put an upper bound on the number o OADM physical design may put an upper bound on the number
of adaptation groupings dropped at any single OADM. of adaptation groupings dropped at any single OADM.
Impairments And Other Constraints September 2002 Impairments And Other Constraints December 2002
On Optical Layer Routing On Optical Layer Routing
For a fixed configuration of the OADMs and adaptation functions For a fixed configuration of the OADMÆs and adaptation functions
connectivity will be fixed: Each input port will essentially be connectivity will be fixed: Each input port will essentially be
hard-wired to some specific distant port. However this connectivity hard-wired to some specific distant port. However this connectivity
can be changed by changing the configurations of the OADMs and can be changed by changing the configurations of the OADMÆs and
adaptation functions. For example, an additional adaptation grouping adaptation functions. For example, an additional adaptation grouping
might be dropped at an OADM or a tunable laser retuned. In each case might be dropped at an OADM or a tunable laser retuned. In each case
the port-to-port connectivity is changed. the port-to-port connectivity is changed.
These capabilities can be expected to be under software control. These capabilities can be expected to be under software control.
Today the control would rest in the vendor-supplied Element Today the control would rest in the vendor-supplied Element
Management system (EMS), which in turn would be controlled by the Management system (EMS), which in turn would be controlled by the
operator’s OS’s. However in principle the EMS could participate in operatorÆs OSÆs. However in principle the EMS could participate in
the GMPLS routing process. the GMPLS routing process.
3.2 Implications For Routing 3.2 Implications For Routing
An OTS of the sort discussed in Sec. 3.1 is essentially a An OTS of the sort discussed in Sec. 3.1 is essentially a
geographically distributed but blocking cross-connect system. The geographically distributed but blocking cross-connect system. The
specific port connectivity is dependent on the vendor design and specific port connectivity is dependent on the vendor design and
also on exactly what line cards have been deployed. also on exactly what line cards have been deployed.
One way for GMPLS to deal with this architecture would be to view One way for GMPLS to deal with this architecture would be to view
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reshaping, also called 3R, which eliminates transparency to bit reshaping, also called 3R, which eliminates transparency to bit
rates and frame format. These transponders are quite expensive and rates and frame format. These transponders are quite expensive and
their lack of transparency also constrains the rapid introduction of their lack of transparency also constrains the rapid introduction of
new services. Thus there are strong motivators to introduce new services. Thus there are strong motivators to introduce
"domains of transparency" - all-optical subnetworks - larger than an "domains of transparency" - all-optical subnetworks - larger than an
OTS. OTS.
The routing of lightpaths through an all-optical network has The routing of lightpaths through an all-optical network has
received extensive attention. (See [Yates99] or [Ramaswami98]). received extensive attention. (See [Yates99] or [Ramaswami98]).
Impairments And Other Constraints September 2002 Impairments And Other Constraints December 2002
On Optical Layer Routing On Optical Layer Routing
When discussing routing in an all-optical network it is usually When discussing routing in an all-optical network it is usually
assumed that all routes have adequate signal quality. This may be assumed that all routes have adequate signal quality. This may be
ensured by limiting all-optical networks to subnetworks of limited ensured by limiting all-optical networks to subnetworks of limited
geographic size which are optically isolated from other parts of the geographic size which are optically isolated from other parts of the
optical layer by transponders. This approach is very practical and optical layer by transponders. This approach is very practical and
has been applied to date, e.g. when determining the maximum length has been applied to date, e.g. when determining the maximum length
of an Optical Transport System (OTS). Furthermore operational of an Optical Transport System (OTS). Furthermore operational
considerations like fault isolation also make limiting the size of considerations like fault isolation also make limiting the size of
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and nonlinearities more troublesome. From a supply perspective, and nonlinearities more troublesome. From a supply perspective,
optical technology is advancing very rapidly, making ever-larger optical technology is advancing very rapidly, making ever-larger
domains possible. In this section we assume that these domains possible. In this section we assume that these
considerations will lead to the deployment of a domain of considerations will lead to the deployment of a domain of
transparency that is too large to ensure that all potential routes transparency that is too large to ensure that all potential routes
have adequate signal quality for all circuits. Our goal is to have adequate signal quality for all circuits. Our goal is to
understand the impacts of the various types of impairments in this understand the impacts of the various types of impairments in this
environment. environment.
Note that as we describe later in the section there are many types Note that as we describe later in the section there are many types
of physical impairments. Which of these need to be dealt with of physical impairments. Which of these needs to be dealt with
explicitly when performing on-line distributed routing will vary explicitly when performing on-line distributed routing will vary
considerably and will depend on many variables, including: considerably and will depend on many variables, including:
- Equipment vendor design choices, - Equipment vendor design choices,
- Fiber characteristics, - Fiber characteristics,
- Service characteristics (e.g., circuit speeds), - Service characteristics (e.g., circuit speeds),
- Network size, - Network size,
- Network operator engineering and deployment strategies. - Network operator engineering and deployment strategies.
For example, a metropolitan network which does not intend to support For example, a metropolitan network which does not intend to support
bit rates above 2.5 Gb/sec may not be constrained by any of these bit rates above 2.5 Gb/sec may not be constrained by any of these
impairments, while a continental or international network which impairments, while a continental or international network which
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Gb/sec connections might have to explicitly consider many of them. Gb/sec connections might have to explicitly consider many of them.
Also, a network operator may reduce or even eliminate their Also, a network operator may reduce or even eliminate their
constraint set by building a relatively small domain of transparency constraint set by building a relatively small domain of transparency
to ensure that all the paths are feasible, or by using some to ensure that all the paths are feasible, or by using some
proprietary tools based on rules from the OTS vendor to pre-qualify proprietary tools based on rules from the OTS vendor to pre-qualify
paths between node pairs and put them in a table that can be paths between node pairs and put them in a table that can be
accessed each time a routing decision has to be made through that accessed each time a routing decision has to be made through that
domain. domain.
4.1 Problem Formulation 4.1 Problem Formulation
Impairments And Other Constraints September 2002 Impairments And Other Constraints December 2002
On Optical Layer Routing On Optical Layer Routing
We consider a single domain of transparency without wavelength We consider a single domain of transparency without wavelength
translation. Additionally due to the proprietary nature of DWDM translation. Additionally due to the proprietary nature of DWDM
transmission technology, we assume that the domain is either single transmission technology, we assume that the domain is either single
vendor or architected using a single coherent design, particularly vendor or architected using a single coherent design, particularly
with regard to the management of impairments. with regard to the management of impairments.
We wish to route a unidirectional circuit from ingress client node X We wish to route a unidirectional circuit from ingress client node X
to egress client node Y. At both X and Y, the circuit goes through to egress client node Y. At both X and Y, the circuit goes through
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[ITU]. More aggressive designs to compensate for PMD may allow [ITU]. More aggressive designs to compensate for PMD may allow
values higher than 10%. (This would be a system parameter dependent values higher than 10%. (This would be a system parameter dependent
on the system design. It would need to be known to the routing on the system design. It would need to be known to the routing
process.) process.)
The PMD parameter (Dpmd) is measured in pico-seconds (ps) per The PMD parameter (Dpmd) is measured in pico-seconds (ps) per
sqrt(km). The square of the PMD in a fiber span, denoted as span- sqrt(km). The square of the PMD in a fiber span, denoted as span-
PMD-square is then given by the product of Dpmd**2 and the span PMD-square is then given by the product of Dpmd**2 and the span
length. (A fiber span in a transparent network refers to a segment length. (A fiber span in a transparent network refers to a segment
between two optical amplifiers.) If Dpmd is constant, this results between two optical amplifiers.) If Dpmd is constant, this results
Impairments And Other Constraints September 2002 Impairments And Other Constraints December 2002
On Optical Layer Routing On Optical Layer Routing
in a upper bound on the maximum length of an M-fiber-span in a upper bound on the maximum length of an M-fiber-span
transparent segment, which is inversely proportional to the square transparent segment, which is inversely proportional to the square
of the product of bit rate and Dpmd (the detailed equation is of the product of bit rate and Dpmd (the detailed equation is
omitted due to the format constraint - see [Strand01] for details). omitted due to the format constraint - see [Strand01] for details).
For older fibers with a typical PMD parameter of 0.5 picoseconds per For older fibers with a typical PMD parameter of 0.5 picoseconds per
square root of km, based on the constraint, the maximum length of square root of km, based on the constraint, the maximum length of
the transparent segment should not exceed 400km and 25km for bit the transparent segment should not exceed 400km and 25km for bit
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transparent segment and number of spans. For example, current transparent segment and number of spans. For example, current
transmission systems are often limited to up to 6 spans each 80km transmission systems are often limited to up to 6 spans each 80km
long. For larger transparent domains, more detailed OSNR long. For larger transparent domains, more detailed OSNR
computations will be needed to determine whether the OSNR level computations will be needed to determine whether the OSNR level
through a domain of transparency is acceptable. This would provide through a domain of transparency is acceptable. This would provide
flexibility in provisioning or restoring a lightpath through a flexibility in provisioning or restoring a lightpath through a
transparent subnetwork. transparent subnetwork.
Assume that the average optical power launched at the transmitter is Assume that the average optical power launched at the transmitter is
P. The lightpath from the transmitter to the receiver goes through M P. The lightpath from the transmitter to the receiver goes through M
Impairments And Other Constraints September 2002 Impairments And Other Constraints December 2002
On Optical Layer Routing On Optical Layer Routing
optical amplifiers, with each introducing some noise power. Unity optical amplifiers, with each introducing some noise power. Unity
gain can be used at all amplifier sites to maintain constant signal gain can be used at all amplifier sites to maintain constant signal
power at the input of each span to minimize noise power and power at the input of each span to minimize noise power and
nonlinearity. A constraint on the maximum number of spans can be nonlinearity. A constraint on the maximum number of spans can be
obtained [Kaminow97] which is proportional to P and inversely obtained [Kaminow97] which is proportional to P and inversely
proportional to SNRmin, optical bandwidth B, amplifier gain G-1 and proportional to SNRmin, optical bandwidth B, amplifier gain G-1 and
spontaneous emission factor n of the optical amplifier, assuming all spontaneous emission factor n of the optical amplifier, assuming all
spans have identical gain and noise figure. (Again, the detailed spans have identical gain and noise figure. (Again, the detailed
equation is omitted due to the format constraint - see [Strand01] equation is omitted due to the format constraint - see [Strand01]
for details.) Lets take a typical example. Assuming P=4dBm, for details.) LetÆs take a typical example. Assuming P=4dBm,
SNRmin=20dB with FEC, B=12.5GHz, n=2.5, G=25dB, based on the SNRmin=20dB with FEC, B=12.5GHz, n=2.5, G=25dB, based on the
constraint, the maximum number of spans is at most 10. However, if constraint, the maximum number of spans is at most 10. However, if
FEC is not used and the requirement on SNRmin becomes 25dB, the FEC is not used and the requirement on SNRmin becomes 25dB, the
maximum number of spans drops down to 3. maximum number of spans drops down to 3.
For ASE the only link-dependent information needed by the routing For ASE the only link-dependent information needed by the routing
algorithm is the noise of the link, denoted as link-noise, which is algorithm is the noise of the link, denoted as link-noise, which is
the sum of the noise of all spans on the link. Hence the constraint the sum of the noise of all spans on the link. Hence the constraint
on ASE becomes that the aggregate noise of the transparent segment on ASE becomes that the aggregate noise of the transparent segment
which is the sum of the link-noise of all links can not exceed which is the sum of the link-noise of all links can not exceed
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some cases a constraint on the total number of networking elements some cases a constraint on the total number of networking elements
(OXC or OADM) along the path. Most impairments generated at OXCs or (OXC or OADM) along the path. Most impairments generated at OXCs or
OADMs, including polarization dependent loss, coherent crosstalk, OADMs, including polarization dependent loss, coherent crosstalk,
and effective passband width, could be dealt with using this and effective passband width, could be dealt with using this
approach. In principle, impairments generated at the nodes can be approach. In principle, impairments generated at the nodes can be
bounded by system engineering rules because the node elements can be bounded by system engineering rules because the node elements can be
designed and specified in a uniform manner. This approach is not designed and specified in a uniform manner. This approach is not
feasible with PMD and noise because neither can be uniformly feasible with PMD and noise because neither can be uniformly
specified. Instead, they depend on node spacing and the specified. Instead, they depend on node spacing and the
characteristics of the installed fiber plant, neither of which are characteristics of the installed fiber plant, neither of which are
likely to be under the system designers control. likely to be under the system designerÆs control.
Examples of the constraints we propose to approximate with a domain- Examples of the constraints we propose to approximate with a domain-
wide margin are given in the remaining paragraphs in this section. wide margin are given in the remaining paragraphs in this section.
It should be kept in mind that as optical transport technology It should be kept in mind that as optical transport technology
evolves it may become necessary to include some of these impairments evolves it may become necessary to include some of these impairments
explicitly in the routing process. Other impairments not mentioned explicitly in the routing process. Other impairments not mentioned
here at all may also become sufficiently important to require here at all may also become sufficiently important to require
incorporation either explicitly or via a domain-wide margin. incorporation either explicitly or via a domain-wide margin.
Other Polarization Dependent Impairments Other polarization- Other Polarization Dependent Impairments Other polarization-
dependent effects besides PMD influence system performance. For dependent effects besides PMD influence system performance. For
example, many components have polarization-dependent loss (PDL) example, many components have polarization-dependent loss (PDL)
[Ramaswami98], which accumulates in a system with many components on [Ramaswami98], which accumulates in a system with many components on
Impairments And Other Constraints September 2002 Impairments And Other Constraints December 2002
On Optical Layer Routing On Optical Layer Routing
the transmission path. The state of polarization fluctuates with the transmission path. The state of polarization fluctuates with
time and its distribution is very important also. It is generally time and its distribution is very important also. It is generally
required to maintain the total PDL on the path to be within some required to maintain the total PDL on the path to be within some
acceptable limit, potentially by using some compensation technology acceptable limit, potentially by using some compensation technology
for relatively long transmission systems, plus a small built-in for relatively long transmission systems, plus a small built-in
margin in OSNR. Since the total PDL increases with the number of margin in OSNR. Since the total PDL increases with the number of
components in the data path, it must be taken into account by the components in the data path, it must be taken into account by the
system vendor when determining the maximum allowable number of system vendor when determining the maximum allowable number of
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Crosstalk Optical crosstalk refers to the effect of other signals on Crosstalk Optical crosstalk refers to the effect of other signals on
the desired signal. It includes both coherent (i.e. intrachannel) the desired signal. It includes both coherent (i.e. intrachannel)
crosstalk and incoherent (i.e. interchannel) crosstalk. Main crosstalk and incoherent (i.e. interchannel) crosstalk. Main
contributors of crosstalk are the OADM and OXC sites that use a DWDM contributors of crosstalk are the OADM and OXC sites that use a DWDM
multiplexer/demultiplexer (MUX/DEMUX) pair. For a relatively sparse multiplexer/demultiplexer (MUX/DEMUX) pair. For a relatively sparse
network where the number of OADM/OXC nodes on a path is low, network where the number of OADM/OXC nodes on a path is low,
crosstalk can be treated with a low margin in OSNR without being a crosstalk can be treated with a low margin in OSNR without being a
binding constraint. But for some relatively dense networks where binding constraint. But for some relatively dense networks where
crosstalk might become a binding constraint, one needs to propagate crosstalk might become a binding constraint, one needs to propagate
the per-link crosstalk information to make sure that the end-to-end the per-link crosstalk information to make sure that the end-to-end
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path crosstalk which is the sum of the crosstalks on all the path crosstalk which is the sum of the crosstalks on all the
corresponding links to be within some limit, e.g. -25dB threshold corresponding links to be within some limit, e.g. -25dB threshold
with 1dB penalty ([Goldstein94]). Another way to treat it without with 1dB penalty ([Goldstein94]). Another way to treat it without
having to propagate per-link crosstalk information is to have the having to propagate per-link crosstalk information is to have the
system evaluate what the maximum number of OADM/OXC nodes that has a system evaluate what the maximum number of OADM/OXC nodes that has a
MUX/DEMUX pair for the worst route in the transparent domain for a MUX/DEMUX pair for the worst route in the transparent domain for a
low built-in margin. The latter one should work well where all the low built-in margin. The latter one should work well where all the
OXC/OADM nodes have similar level of crosstalk. OXC/OADM nodes have similar level of crosstalk.
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maximum number of spans. For the approach described here to be maximum number of spans. For the approach described here to be
useful, it is desirable for this span length limit to be longer than useful, it is desirable for this span length limit to be longer than
that imposed by the constraints which can be treated explicitly. that imposed by the constraints which can be treated explicitly.
When designing a DWDM transport system, there are tradeoffs between When designing a DWDM transport system, there are tradeoffs between
signal power launched at the transmitter, span length, and nonlinear signal power launched at the transmitter, span length, and nonlinear
effects on BER that need to be considered jointly. Here, we assume effects on BER that need to be considered jointly. Here, we assume
that an X dB margin is obtained after the transport system has been that an X dB margin is obtained after the transport system has been
designed with a fixed signal power and maximum span length for a designed with a fixed signal power and maximum span length for a
given bit rate. Note that OTSs can be designed in very different given bit rate. Note that OTSs can be designed in very different
ways, in linear, pseudo-linear, or nonlinear environments. The X-dB ways, in linear, pseudo-linear, or nonlinear environments. The X-dB
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margin approach may be valid for some but not for others. However, margin approach may be valid for some but not for others. However,
it is likely that there is an advantage in designing systems that it is likely that there is an advantage in designing systems that
are less aggressive with respect to nonlinearities, and therefore are less aggressive with respect to nonlinearities, and therefore
somewhat sub-optimal, in exchange for improved scalability, somewhat sub-optimal, in exchange for improved scalability,
simplicity and flexibility in routing and control plane design. simplicity and flexibility in routing and control plane design.
4.5 Other Impairment Considerations 4.5 Other Impairment Considerations
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Constraint Constraint
Today, carriers often use maximum distance to engineer point-to- Today, carriers often use maximum distance to engineer point-to-
point OTS systems given a fixed per-span length based on the OSNR point OTS systems given a fixed per-span length based on the OSNR
constraint for a given bit rate. They may desire to keep the same constraint for a given bit rate. They may desire to keep the same
engineering rule when they move to all-optical networks. Here, we engineering rule when they move to all-optical networks. Here, we
discuss the assumptions that need to be satisfied to keep this discuss the assumptions that need to be satisfied to keep this
approach viable and how to treat the network elements between two approach viable and how to treat the network elements between two
adjacent links. adjacent links.
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In order to use the maximum distance for a given bit rate to meet an In order to use the maximum distance for a given bit rate to meet an
OSNR constraint as the only binding constraint, the operators need OSNR constraint as the only binding constraint, the operators need
to satisfy the following constraints in their all-optical networks: to satisfy the following constraints in their all-optical networks:
- All the other non-OSNR constraints described in the previous - All the other non-OSNR constraints described in the previous
subsections are not binding factors as long as the maximum subsections are not binding factors as long as the maximum
distance constraint is met. distance constraint is met.
- Specifically for PMD, this means that the whole all-optical - Specifically for PMD, this means that the whole all-optical
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for others. for others.
If these assumptions are satisfied, the second issue we need to If these assumptions are satisfied, the second issue we need to
address is how to treat a transparent network element (e.g., MEMS- address is how to treat a transparent network element (e.g., MEMS-
based switch) between two adjacent links in terms of a distance based switch) between two adjacent links in terms of a distance
constraint since it also introduces an insertion loss. If the constraint since it also introduces an insertion loss. If the
network element cannot somehow compensate for this OSNR degradation, network element cannot somehow compensate for this OSNR degradation,
one approach is to convert each network element into an equivalent one approach is to convert each network element into an equivalent
length of fiber based on its loss/ASE contribution. Hence, in length of fiber based on its loss/ASE contribution. Hence, in
general, introducing a set of transparent network elements would general, introducing a set of transparent network elements would
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effectively result in reducing the overall actual transmission effectively result in reducing the overall actual transmission
distance between the OEO edges. distance between the OEO edges.
With this approach, the link-specific state information is link- With this approach, the link-specific state information is link-
distance, the length of a link. It equals to the distance sum of all distance, the length of a link. It equals to the distance sum of all
fiber spans on the link and the equivalent length of fiber for the fiber spans on the link and the equivalent length of fiber for the
network element(s) on the link. The constraint is that the sum of network element(s) on the link. The constraint is that the sum of
all the link-distance over all links of a path should be less than all the link-distance over all links of a path should be less than
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If distributed routing is desired, additional state information will If distributed routing is desired, additional state information will
be required by the routing to deal with the impairments described in be required by the routing to deal with the impairments described in
Sections 4.2 - 4.4: Sections 4.2 - 4.4:
- As mentioned earlier, an operator who wants to avoid having to - As mentioned earlier, an operator who wants to avoid having to
provide impairment-related parameters to the control plane may provide impairment-related parameters to the control plane may
elect not to deal with them at the routing level, instead elect not to deal with them at the routing level, instead
treating them at the system design and planning level if that is treating them at the system design and planning level if that is
a viable approach for their network. In this approach the a viable approach for their network. In this approach the
operator can pre-qualify all or a set of feasible end-to-end operator can pre-qualify all or a set of feasible end-to-end
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optical paths through the domain of transparency for each bit optical paths through the domain of transparency for each bit
rate. This approach may work well with relatively small and rate. This approach may work well with relatively small and
sparse networks, but it may not be scalable for large and dense sparse networks, but it may not be scalable for large and dense
networks where the number of feasible paths can be very large. networks where the number of feasible paths can be very large.
- If the optical paths are not pre-qualified, additional link- - If the optical paths are not pre-qualified, additional link-
specific state information will be required by the routing specific state information will be required by the routing
algorithm for each type of impairment that has the potential of algorithm for each type of impairment that has the potential of
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number of OADM/OXC nodes, and the maximum number of narrow number of OADM/OXC nodes, and the maximum number of narrow
filters, all are bit rate dependent. With the alternative filters, all are bit rate dependent. With the alternative
distance-only approach, the upper bound is the maximum-path- distance-only approach, the upper bound is the maximum-path-
distance. In single-vendor "islands" some of these parameters distance. In single-vendor "islands" some of these parameters
may be available in a local or EMS database and would not need may be available in a local or EMS database and would not need
to be advertised to be advertised
- It is likely that the physical layer parameters do not change - It is likely that the physical layer parameters do not change
value rapidly and could be stored in some database; however value rapidly and could be stored in some database; however
these are physical layer parameters that today are frequently these are physical layer parameters that today are frequently
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not known at the granularity required. If the ingress node of a not known at the granularity required. If the ingress node of a
lightpath does path selection these parameters would need to be lightpath does path selection these parameters would need to be
available at this node. available at this node.
- The specific constraints required in a given situation will - The specific constraints required in a given situation will
depend on the design and engineering of the domain of depend on the design and engineering of the domain of
transparency; for example it will be essential to know whether transparency; for example it will be essential to know whether
chromatic dispersion has been dealt with on a per-link basis, chromatic dispersion has been dealt with on a per-link basis,
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going to be introduced. (We use the term "island" in this discussion going to be introduced. (We use the term "island" in this discussion
rather than a term like "domain" or "area" because these terms are rather than a term like "domain" or "area" because these terms are
associated with specific approaches like BGP or OSPF.) associated with specific approaches like BGP or OSPF.)
We consider the complexities raised by these alternatives now. We consider the complexities raised by these alternatives now.
The first requirement for routing in a multi-island network is that The first requirement for routing in a multi-island network is that
the routing process needs to know the extent of each island. There the routing process needs to know the extent of each island. There
are several reasons for this: are several reasons for this:
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- When entering or leaving an all-optical island, the regeneration - When entering or leaving an all-optical island, the regeneration
process cleans up the optical impairments discussed in Sec. 3. process cleans up the optical impairments discussed in Sec. 3.
- Each all-optical island may have its own bounds on each - Each all-optical island may have its own bounds on each
impairment. impairment.
- The routing process needs to be sensitive to the costs - The routing process needs to be sensitive to the costs
associated with "island-hopping". associated with "island-hopping".
This last point needs elaboration. It is extremely important to This last point needs elaboration. It is extremely important to
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investigating: investigating:
- Advertise the internal topology and constraints of each island - Advertise the internal topology and constraints of each island
globally; let the ingress node compute an end-to-end strict globally; let the ingress node compute an end-to-end strict
explicit route sensitive to all constraints and wavelength explicit route sensitive to all constraints and wavelength
availabilities. In this approach the routing algorithm used by availabilities. In this approach the routing algorithm used by
the ingress node must be able to deal with the details of the ingress node must be able to deal with the details of
routing within each island. routing within each island.
- Have the EMS or control plane of each island determine and - Have the EMS or control plane of each island determine and
advertise the connectivity between its boundary nodes together advertise the connectivity between its boundary nodes together
with additional information such as costs and the bit rates and with additional information such as costs and the bit rates and
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formats supported. As the spare capacity situation changes, formats supported. As the spare capacity situation changes,
updates would be advertised. In this approach impairment updates would be advertised. In this approach impairment
constraints are handled within each island and impairment- constraints are handled within each island and impairment-
related parameters need not be advertised outside of the island. related parameters need not be advertised outside of the island.
The ingress node would then do a loose explicit route and leave The ingress node would then do a loose explicit route and leave
the routing and wavelength selection within each island to the the routing and wavelength selection within each island to the
island. island.
- Have the ingress node send out probes or queries to nearby - Have the ingress node send out probes or queries to nearby
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To determine whether two lightpath routings are diverse it is To determine whether two lightpath routings are diverse it is
necessary to identify single points of failure in the interoffice necessary to identify single points of failure in the interoffice
plant. To do so we will use the following terms: A fiber cable is a plant. To do so we will use the following terms: A fiber cable is a
uniform group of fibers contained in a sheath. An Optical Transport uniform group of fibers contained in a sheath. An Optical Transport
System will occupy fibers in a sequence of fiber cables. Each fiber System will occupy fibers in a sequence of fiber cables. Each fiber
cable will be placed in a sequence of conduits - buried honeycomb cable will be placed in a sequence of conduits - buried honeycomb
structures through which fiber cables may be pulled - or buried in a structures through which fiber cables may be pulled - or buried in a
right of way (ROW). A ROW is land in which the network operator has right of way (ROW). A ROW is land in which the network operator has
the right to install his conduit or fiber cable. It is worth noting the right to install his conduit or fiber cable. It is worth noting
that for economic reasons, ROWs are frequently obtained from that for economic reasons, ROWÆs are frequently obtained from
railroads, pipeline companies, or thruways. It is frequently the railroads, pipeline companies, or thruways. It is frequently the
case that several carriers may lease ROW from the same source; this case that several carriers may lease ROW from the same source; this
makes it common to have a number of carriers fiber cables in close makes it common to have a number of carriersÆ fiber cables in close
proximity to each other. Similarly, in a metropolitan network, proximity to each other. Similarly, in a metropolitan network,
several carriers might be leasing duct space in the same RBOC several carriers might be leasing duct space in the same RBOC
conduit. There are also "carrier's carriers" - optical networks conduit. There are also "carrier's carriers" - optical networks
which provide fibers to multiple carriers, all of whom could be which provide fibers to multiple carriers, all of whom could be
affected by a single failure in the "carrier's carrier" network. affected by a single failure in the "carrier's carrier" network.
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In a typical intercity facility network there might be on the order In a typical intercity facility network there might be on the order
of 100 offices that are candidates for OLXCs. To represent the of 100 offices that are candidates for OLXCÆs. To represent the
inter-office fiber network accurately a network with an order of inter-office fiber network accurately a network with an order of
magnitude more nodes is required. In addition to Optical Amplifier magnitude more nodes is required. In addition to Optical Amplifier
(OA) sites, these additional nodes include: (OA) sites, these additional nodes include:
- Places where fiber cables enter/leave a conduit or right of way; - Places where fiber cables enter/leave a conduit or right of way;
- Locations where fiber cables cross; - Locations where fiber cables cross;
Locations where fiber splices are used to interchange fibers Locations where fiber splices are used to interchange fibers between
between fiber cables. fiber cables.
An example of the first might be: An example of the first might be:
A B A B
A-------------B \ / A-------------B \ /
\ / \ /
X-----Y X-----Y
/ \ / \
C-------------D / \ C-------------D / \
C D C D
(a) Fiber Cable Topology (b) Right-Of-Way/Conduit Topology (a) Fiber Cable Topology (b) Right-Of-Way/Conduit Topology
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route passes near to a small office. To avoid the expense and route passes near to a small office. To avoid the expense and
additional transmission loss only a small number of fibers are additional transmission loss only a small number of fibers are
spliced out of the major route into a smaller route going to the spliced out of the major route into a smaller route going to the
small office. This might well occur in a manhole or hut. An small office. This might well occur in a manhole or hut. An
example is shown in Fig. 6-2(a), where A-X-B is the major route, X example is shown in Fig. 6-2(a), where A-X-B is the major route, X
the manhole, and C the smaller office. The actual fiber topology the manhole, and C the smaller office. The actual fiber topology
would then look like Fig. 6-2(b), where there would typically be would then look like Fig. 6-2(b), where there would typically be
many more A-B fibers than A-C or C-B fibers, and where A-C and C-B many more A-B fibers than A-C or C-B fibers, and where A-C and C-B
might have different numbers of fibers. (One of the latter might might have different numbers of fibers. (One of the latter might
even be missing.) even be missing.)
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C C C C
| / \ | / \
| / \ | / \
| / \ | / \
A------X------B A---------------B A------X------B A---------------B
(a) Fiber Cable Topology (b) Fiber Topology (a) Fiber Cable Topology (b) Fiber Topology
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be diverse. be diverse.
- Two circuits that might be considered diverse for one - Two circuits that might be considered diverse for one
application might not be considered diverse for in another application might not be considered diverse for in another
situation. Diversity is usually thought of as a reaction to situation. Diversity is usually thought of as a reaction to
interoffice route failures. High reliability applications may interoffice route failures. High reliability applications may
require other types of failures to be taken into account. Some require other types of failures to be taken into account. Some
examples: examples:
o Office Outages: Although less frequent than route failures, o Office Outages: Although less frequent than route failures,
fires, power outages, and floods do occur. Many network fires, power outages, and floods do occur. Many network
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managers require that diverse routes have no (intermediate) managers require that diverse routes have no (intermediate)
nodes in common. In other cases an intermediate node might nodes in common. In other cases an intermediate node might
be acceptable as long as there is power diversity within be acceptable as long as there is power diversity within
the office. the office.
o Shared Rings: Many applications are willing to allow o Shared Rings: Many applications are willing to allow
"diverse" circuits to share a SONET ring-protected link; "diverse" circuits to share a SONET ring-protected link;
presumably they would allow the same for optical layer presumably they would allow the same for optical layer
rings. rings.
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to be routed with nuclear damage radii taken into account. to be routed with nuclear damage radii taken into account.
- Conversely, some networks may be willing to take somewhat larger - Conversely, some networks may be willing to take somewhat larger
risks. Taking route failures as an example: Such a network risks. Taking route failures as an example: Such a network
might be willing to consider two fiber cables in heavy duty might be willing to consider two fiber cables in heavy duty
concrete conduit as having a low enough chance of simultaneous concrete conduit as having a low enough chance of simultaneous
failure to be considered "diverse". They might also be willing failure to be considered "diverse". They might also be willing
to view two fiber cables buried on opposite sides of a railroad to view two fiber cables buried on opposite sides of a railroad
track as being diverse because there is minimal danger of a track as being diverse because there is minimal danger of a
single backhoe disrupting them both even though a bad train single backhoe disrupting them both even though a bad train
wreck might jeopardize them both. A network seeking N mutually wreck might jeopardize them both. A network seeking N mutually
diverse paths from an office with less than N diverse ROWs will diverse paths from an office with less than N diverse ROWÆs will
need to live with some level of compromise in the immediate need to live with some level of compromise in the immediate
vicinity of the office. vicinity of the office.
These considerations strongly suggest that the routing algorithm These considerations strongly suggest that the routing algorithm
should be sensitive to the types of threat considered unacceptable should be sensitive to the types of threat considered unacceptable
by the requester. Note that the impairment constraints described in by the requester. Note that the impairment constraints described in
the previous section may eliminate some of the long circuitous the previous section may eliminate some of the long circuitous
routes sometimes needed to provide diversity. This would make it routes sometimes needed to provide diversity. This would make it
harder to find many diverse paths through an all-optical network harder to find many diverse paths through an all-optical network
than an opaque one. than an opaque one.
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discussion suggests that an SRLG should be characterized by 2 discussion suggests that an SRLG should be characterized by 2
parameters: parameters:
- Type of Compromise: Examples would be shared fiber cable, shared - Type of Compromise: Examples would be shared fiber cable, shared
conduit, shared ROW, shared optical ring, shared office without conduit, shared ROW, shared optical ring, shared office without
power sharing, etc.) power sharing, etc.)
- Extent of Compromise: For compromised outside plant, this would - Extent of Compromise: For compromised outside plant, this would
be the length of the sharing. be the length of the sharing.
A CSPF algorithm could then penalize a diversity compromise by an A CSPF algorithm could then penalize a diversity compromise by an
amount dependent on these two parameters. amount dependent on these two parameters.
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Two links could be related by many SRLG's (AT&T's experience Two links could be related by many SRLG's (AT&T's experience
indicates that a link may belong to over 100 SRLG's, each indicates that a link may belong to over 100 SRLG's, each
corresponding to a separate fiber group. Each SRLG might relate a corresponding to a separate fiber group. Each SRLG might relate a
single link to many other links. For the optical layer, similar single link to many other links. For the optical layer, similar
situations can be expected where a link is an ultra-long OTS). situations can be expected where a link is an ultra-long OTS).
The mapping between links and different types of SRLGs is in The mapping between links and different types of SRLGÆs is in
general defined by network operators based on the definition of each general defined by network operators based on the definition of each
SRLG type. Since SRLG information is not yet ready to be SRLG type. Since SRLG information is not yet ready to be
discoverable by a network element and does not change dynamically, discoverable by a network element and does not change dynamically,
it need not be advertised with other resource availability it need not be advertised with other resource availability
information by network elements. It could be configured in some information by network elements. It could be configured in some
central database and be distributed to or retrieved by the nodes, or central database and be distributed to or retrieved by the nodes, or
advertised by network elements at the topology discovery stage. advertised by network elements at the topology discovery stage.
6.2 Implications For Routing 6.2 Implications For Routing
Dealing with diversity is an unavoidable requirement for routing in Dealing with diversity is an unavoidable requirement for routing in
the optical layer. It requires dealing with constraints in the the optical layer. It requires dealing with constraints in the
routing process but most importantly requires additional state routing process but most importantly requires additional state
information the SRLG relationships and also the routings of any information û the SRLG relationships and also the routings of any
existing circuits from the new circuit is to be diverse to be existing circuits from the new circuit is to be diverse û to be
available to the routing process. available to the routing process.
At present SRLG information cannot be self-discovered. Indeed, in a At present SRLG information cannot be self-discovered. Indeed, in a
large network it is very difficult to maintain accurate SRLG large network it is very difficult to maintain accurate SRLG
information. The problem becomes particularly daunting whenever information. The problem becomes particularly daunting whenever
multiple administrative domains are involved, for instance after the multiple administrative domains are involved, for instance after the
acquisition of one network by another, because there normally is a acquisition of one network by another, because there normally is a
likelihood that there are diversity violations between the domains. likelihood that there are diversity violations between the domains.
It is very unlikely that diversity relationships between carriers It is very unlikely that diversity relationships between carriers
will be known any time in the near future. will be known any time in the near future.
Considerable variation in what different customers will mean by Considerable variation in what different customers will mean by
acceptable diversity should be anticipated. Consequently we suggest acceptable diversity should be anticipated. Consequently we suggest
that an SRLG should be defined as follows: (i) It is a relationship that an SRLG should be defined as follows: (i) It is a relationship
between two or more links, and (ii) it is characterized by two between two or more links, and (ii) it is characterized by two
parameters, the type of compromise (shared conduit, shared ROW, parameters, the type of compromise (shared conduit, shared ROW,
shared optical ring, etc.) and the extent of the compromise (e.g., shared optical ring, etc.) and the extent of the compromise (e.g.,
the number of miles over which the compromise persisted). This will the number of miles over which the compromise persisted). This will
allow the SRLGs appropriate to a particular routing request to be allow the SRLGÆs appropriate to a particular routing request to be
easily identified. easily identified.
7. Security Considerations 7. Security Considerations
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On Optical Layer Routing On Optical Layer Routing
We are assuming OEO interfaces to the domain(s) covered by our We are assuming OEO interfaces to the domain(s) covered by our
discussion (see, e.g., Sec. 4.1 above). If this assumption were to discussion (see, e.g., Sec. 4.1 above). If this assumption were to
be relaxed and externally generated optical signals allowed into the be relaxed and externally generated optical signals allowed into the
domain, network security issues would arise. Specifically, domain, network security issues would arise. Specifically,
unauthorized usage in the form of signals at improper wavelengths or unauthorized usage in the form of signals at improper wavelengths or
with power levels or impairments inconsistent with those assumed by with power levels or impairments inconsistent with those assumed by
the domain would be possible. With OEO interfaces, these types of the domain would be possible. With OEO interfaces, these types of
layer one threats should be controllable. layer one threats should be controllable.
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A key layer one security issue is resilience in the face of physical A key layer one security issue is resilience in the face of physical
attack. Diversity, as describe in Sec. 6, is a part of the attack. Diversity, as describe in Sec. 6, is a part of the
solution. However, it is ineffective if there is not sufficient solution. However, it is ineffective if there is not sufficient
spare capacity available to make the network whole after an attack. spare capacity available to make the network whole after an attack.
Several major related issues are: Several major related issues are:
- Defining the threat: If, for example, an electro-magnetic - Defining the threat: If, for example, an electro-magnetic
interference (EMI) burst is an in-scope threat, then (in the interference (EMI) burst is an in-scope threat, then (in the
terminology of Sec. 6) all of the links sufficiently close terminology of Sec. 6) all of the links sufficiently close
together to be disrupted by such a burst must be included in a together to be disrupted by such a burst must be included in a
single SRLG. Similarly for other threats: For each in-scope single SRLG. Similarly for other threats: For each in-scope
threat, SRLGs must be defined so that all links vulnerable to a threat, SRLGÆs must be defined so that all links vulnerable to a
single incident of the threat must be grouped together in a single incident of the threat must be grouped together in a
single SRLG. single SRLG.
- Allocating responsibility for responding to a layer one failure - Allocating responsibility for responding to a layer one failure
between the various layers (especially the optical and IP between the various layers (especially the optical and IP
layers): This must be clearly specified to avoid churning and layers): This must be clearly specified to avoid churning and
unnecessary service interruptions. unnecessary service interruptions.
The whole proposed process depends on the integrity of the The whole proposed process depends on the integrity of the
impairment characterization information (PMD parameters, etc.) and impairment characterization information (PMD parameters, etc.) and
also the SRLG definitions. Security of this information, both when also the SRLG definitions. Security of this information, both when
stored and when distributed, is essential. stored and when distributed, is essential.
This document does not address control plane issues, and so control- This document does not address control plane issues, and so control-
plane security is out of scope. plane security is out of scope. IPO control plane security
considerations are discussed in [Rajagopalam02]. Security
considerations for GMPLS, a likely control plane candidate, are
discussed in [Mannie02].
8. Acknowledgments 8. Acknowledgments
This document has benefited from discussions with Michael Eiselt, This document has benefited from discussions with Michael Eiselt,
Jonathan Lang, Mark Shtaif, Jennifer Yates, Dongmei Wang, Guangzhi Jonathan Lang, Mark Shtaif, Jennifer Yates, Dongmei Wang, Guangzhi
Li, Robert Doverspike, Albert Greenberg, Jim Maloney, John Jacob, Li, Robert Doverspike, Albert Greenberg, Jim Maloney, John Jacob,
Katie Hall, Diego Caviglia, D. Papadimitriou, O. Audouin, J. P. Katie Hall, Diego Caviglia, D. Papadimitriou, O. Audouin, J. P.
Faure, L. Noirie, and with our OIF colleagues. Faure, L. Noirie, and with our OIF colleagues.
9. References 9. References
Impairments And Other Constraints December 2002
On Optical Layer Routing
9.1 Normative References 9.1 Normative References
Impairments And Other Constraints September 2002
On Optical Layer Routing
[Chaudhuri00] Chaudhuri, S., Hjalmtysson, G., and Yates, J., [Chaudhuri00] Chaudhuri, S., Hjalmtysson, G., and Yates, J.,
"Control of Lightpaths in an Optical Network", Work in Progress, "Control of Lightpaths in an Optical Network", Work in Progress,
draft-chaudhuri-ip-olxc-control-00.txt. draft-chaudhuri-ip-olxc-control-00.txt.
[Goldstein94] Goldstein, E. L., Eskildsen, L., and Elrefaie, A. F., [Goldstein94] Goldstein, E. L., Eskildsen, L., and Elrefaie, A. F.,
Performance Implications of Component Crosstalk in Transparent Performance Implications of Component Crosstalk in Transparent
Lightwave Networks", IEEE Photonics Technology Letters, Vol.6, No.5, Lightwave Networks", IEEE Photonics Technology Letters, Vol.6, No.5,
May 1994. May 1994.
[ITU] ITU-T Doc. G.663, Optical Fibers and Amplifiers, Section [ITU] ITU-T Doc. G.663, Optical Fibers and Amplifiers, Section
II.4.1.2. II.4.1.2.
[Kaminow97] Kaminow, I. P. and Koch, T. L., editors, Optical Fiber [Kaminow97] Kaminow, I. P. and Koch, T. L., editors, Optical Fiber
Telecommunications IIIA, Academic Press, 1997. Telecommunications IIIA, Academic Press, 1997.
[Mannie02] Mannie, E. (ed.), "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", Interned Draft, draft-ietf-ccamp-
gmpls-architecture-03.txt, August, 2002.
[Rajagopalam02] Rajagopalam, B., et. al., "IP over Optical Networks:
A Framework", Internet Draft, draft-ietf-ipo-framework-02.txt June,
2002.
[Strand01] J. Strand, A. Chiu, and R. Tkach, "Issues for Routing in [Strand01] J. Strand, A. Chiu, and R. Tkach, "Issues for Routing in
the Optical Layer", IEEE Communications Magazine, Feb. 2001, vol. 39 the Optical Layer", IEEE Communications Magazine, Feb. 2001, vol. 39
No. 2, pp. 81-88; also see "Unique Features and Requirements for The No. 2, pp. 81-88; also see "Unique Features and Requirements for The
Optical Layer Control Plane", Internet Draft, draft-chiu-strand- Optical Layer Control Plane", Internet Draft, draft-chiu-strand-
unique-olcp-01.txt, work in progress, November 2000. unique-olcp-01.txt, work in progress, November 2000.
[Strand01b] J. Strand, R. Doverspike, and G. Li, "Importance of [Strand01b] J. Strand, R. Doverspike, and G. Li, "Importance of
Wavelength Conversion In An Optical Network", Optical Networks Wavelength Conversion In An Optical Network", Optical Networks
Magazine, May/June 2001, pp. 33-44. Magazine, May/June 2001, pp. 33-44.
[Yates99] Yates, J. M., Rumsewicz, M. P. and Lacey, J. P. R., [Yates99] Yates, J. M., Rumsewicz, M. P. and Lacey, J. P. R.,
"Wavelength Converters in Dynamically-Reconfigurable WDM Networks", "Wavelength Converters in Dynamically-Reconfigurable WDM Networks",
IEEE Communications Surveys, 2Q1999 (online at IEEE Communications Surveys, 2Q1999 (online at
www.comsoc.org/pubs/surveys/2q99issue/yates.html). www.comsoc.org/pubs/surveys/2q99issue/yates.html).
9.2 Informative References 9.2 Informative References
Impairments And Other Constraints December 2002
On Optical Layer Routing
[Awduche99] Awduche, D. O., Rekhter, Y., Drake, J., and Coltun, R., [Awduche99] Awduche, D. O., Rekhter, Y., Drake, J., and Coltun, R.,
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Control With Optical Crossconnects", Work in Progress, draft- Control With Optical Crossconnects", Work in Progress, draft-
awduche-mpls-te-optical-01.txt. awduche-mpls-te-optical-01.txt.
[Bra96] Bradner, S., "The Internet Standards Process -- Revision 3," [Bra96] Bradner, S., "The Internet Standards Process -- Revision 3,"
BCP 9, RFC 2026, October 1996. BCP 9, RFC 2026, October 1996.
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Edwards, W., "Performance Monitoring in Photonic Networks in Support Edwards, W., "Performance Monitoring in Photonic Networks in Support
of MPL(ambda)S", Internet draft, work in progress, March 2000. of MPL(ambda)S", Internet draft, work in progress, March 2000.
Impairments And Other Constraints September 2002
On Optical Layer Routing
[Doverspike00] Doverspike, R. and Yates, J., "Challenges For MPLS in [Doverspike00] Doverspike, R. and Yates, J., "Challenges For MPLS in
Optical Network Restoration", IEEE Communication Magazine, February, Optical Network Restoration", IEEE Communication Magazine, February,
2001. 2001.
[Gerstel 2000] O. Gorstel, "Optical Layer Signaling: How Much Is [Gerstel 2000] O. Gorstel, "Optical Layer Signaling: How Much Is
Really Needed?" IEEE Communications Magazine, vol. 38 no. 10, Oct. Really Needed?" IEEE Communications Magazine, vol. 38 no. 10, Oct.
2000, pp. 154-160 2000, pp. 154-160
[KRB01a] Kompella, K., et.al., "IS-IS extensions in support of [KRB01a] Kompella, K., et.al., "IS-IS extensions in support of
Generalized MPLS," Internet Draft, draft-ietf-gmpls- extensions- Generalized MPLS," Internet Draft, draft-ietf-gmpls- extensions-
skipping to change at page 25, line 38 skipping to change at page 26, line 4
Communications Review, August 2001, pp. 20-21. Communications Review, August 2001, pp. 20-21.
[Ramaswami98] Ramaswami, R. and Sivarajan, K. N., Optical Networks: [Ramaswami98] Ramaswami, R. and Sivarajan, K. N., Optical Networks:
A Practical Perspective, Morgan Kaufmann Publishers, 1998. A Practical Perspective, Morgan Kaufmann Publishers, 1998.
[Tkach98] Tkach, R., Goldstein, E., Nagel, J., and Strand, J., [Tkach98] Tkach, R., Goldstein, E., Nagel, J., and Strand, J.,
"Fundamental Limits of Optical Transparency", Optical Fiber "Fundamental Limits of Optical Transparency", Optical Fiber
Communication Conf., Feb. 1998, pp. 161-162. Communication Conf., Feb. 1998, pp. 161-162.
10. Contributing Authors 10. Contributing Authors
Impairments And Other Constraints December 2002
On Optical Layer Routing
This document was a collective work of a number of people. The text This document was a collective work of a number of people. The text
and content of this document was contributed by the editors and the and content of this document was contributed by the editors and the
co-authors listed below. co-authors listed below.
Ayan Banerjee Ayan Banerjee
Calient Networks Calient Networks
5853 Rue Ferrari 5853 Rue Ferrari
San Jose, CA 95138 San Jose, CA 95138
Email: abanerjee@calient.net Email: abanerjee@calient.net
Dan Blumenthal Dan Blumenthal
Calient Networks Calient Networks
Impairments And Other Constraints September 2002
On Optical Layer Routing
5853 Rue Ferrari 5853 Rue Ferrari
San Jose, CA 95138 San Jose, CA 95138
Email: dblumenthal@calient.net Email: dblumenthal@calient.net
John Drake John Drake
Calient Networks Calient Networks
5853 Rue Ferrari 5853 Rue Ferrari
San Jose, CA 95138 San Jose, CA 95138
Email: jdrake@calient.net Email: jdrake@calient.net
skipping to change at page 26, line 44 skipping to change at page 27, line 4
James V. Luciani James V. Luciani
900 Chelmsford St. 900 Chelmsford St.
Lowell, MA 01851 Lowell, MA 01851
Email: james_luciani@mindspring.com Email: james_luciani@mindspring.com
Robert Tkach Robert Tkach
Celion Networks Celion Networks
1 Sheila Dr., Suite 2 1 Sheila Dr., Suite 2
Tinton Falls, NJ 07724 Tinton Falls, NJ 07724
Impairments And Other Constraints December 2002
On Optical Layer Routing
Email: bob.tkach@celion.com Email: bob.tkach@celion.com
Yong Xue Yong Xue
WorldCom, Inc. WorldCom, Inc.
22001 Loudoun County Parkway 22001 Loudoun County Parkway
Ashburn, VA 20147 Ashburn, VA 20147
Email: yxue@cox.com Email: yxue@cox.com
11. Editors Addresses 11. EditorsÆ Addresses
Angela Chiu Angela Chiu
Impairments And Other Constraints September 2002 AT&T Labs
On Optical Layer Routing 200 Laurel Ave., Rm A5-1F13
Middletown, NJ 07748
Celion Networks Phone:(732) 420-9061
1 Sheila Dr., Suite 2 Email: chiu@research.att.com
Tinton Falls, NJ 07724
Phone:(732) 747-9987
Email: alchiu@ieee.org
John Strand John Strand
AT&T Labs AT&T Labs
200 Laurel Ave., Rm A5-1D33 200 Laurel Ave., Rm A5-1D33
Middletown, NJ 07748 Middletown, NJ 07748
Phone:(732) 420-9036 Phone:(732) 420-9036
Email: jls@research.att.com Email: jls@research.att.com
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