draft-ietf-ipo-impairments-04.txt   draft-ietf-ipo-impairments-05.txt 
Internet Draft John Strand (Editor) Internet Draft John Strand (Editor)
Document: draft-ietf-ipo-impairments-04.txt Angela Chiu (Editor) Document: draft-ietf-ipo-impairments-05.txt Angela Chiu (Editor)
Informational Track AT&T Informational Track AT&T
Expiration Date: May 2003 Expiration Date: November 2003
December 2002 May 2003
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.
skipping to change at page 2, line 4 skipping to change at page 2, line 4
complex networks incorporating both all-optical and opaque complex networks incorporating both all-optical and 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
Impairments And Other Constraints December 2002 Impairments And Other Constraints May 2003
On Optical Layer Routing On Optical Layer Routing
challenges for GMPLS. Optical technology is fundamentally an analog 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
skipping to change at page 2, line 35 skipping to change at page 2, line 35
The organization of the contribution is as follows: The organization of the contribution is as follows:
- Section 2 is a section requested by the sub-IP Area management - Section 2 is a section requested by the sub-IP Area management
for all new drafts. It explains how this document fits into the for all new drafts. It explains how this document fits into the
Area and into the IPO WG, and why it is appropriate for these Area and into the IPO WG, and why it is appropriate for these
groups. groups.
- 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 authorsÆ addresses. - Section 10 contains contributing authors' addresses.
- Section 11 contains editorsÆ addresses. - Section 11 contains editors' 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
Impairments And Other Constraints December 2002 Impairments And Other Constraints May 2003
On Optical Layer Routing On Optical Layer Routing
they place on routing and path selection. It is appropriate for the 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.
skipping to change at page 3, line 32 skipping to change at page 3, line 32
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 software optical layer cross-connect (OLXC). There are however other software
reconfigurable elements on the horizon, specifically tunable lasers and reconfigurable elements on the horizon, specifically tunable lasers and
receivers and reconfigurable optical add-drop multiplexers (OADMÆs). receivers and reconfigurable optical add-drop multiplexers (OADM's).
These elements are illustrated in the following simple example, which These elements are illustrated in the following simple example, which
is modeled on announced Optical Transport System (OTS) products: is modeled on announced Optical 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 |---
---+---+ |/ | | | | \| +---+--- ---+---+ |/ | | | | \| +---+---
skipping to change at page 4, line 5 skipping to change at page 4, line 5
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 December 2002 Impairments And Other Constraints May 2003
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 DWDMÆs and X and Y are OADMÆs. The boxes In Fig. 3-1, D and E are DWDM's and X and Y are OADM's. 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
skipping to change at page 4, line 47 skipping to change at page 4, line 47
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 OADMÆs may also be constrained. - The switching capability of the OADM's 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 December 2002 Impairments And Other Constraints May 2003
On Optical Layer Routing On Optical Layer Routing
For a fixed configuration of the OADMÆs and adaptation functions For a fixed configuration of the OADM's 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 OADMÆs and can be changed by changing the configurations of the OADM's 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
operatorÆs OSÆs. However in principle the EMS could participate in operator's OS's. 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
skipping to change at page 6, line 5 skipping to change at page 6, line 5
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 December 2002 Impairments And Other Constraints May 2003
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
skipping to change at page 7, line 4 skipping to change at page 7, line 4
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 December 2002 Impairments And Other Constraints May 2003
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
skipping to change at page 8, line 4 skipping to change at page 8, line 4
[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 December 2002 Impairments And Other Constraints May 2003
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
skipping to change at page 9, line 4 skipping to change at page 9, line 4
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 December 2002 Impairments And Other Constraints May 2003
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.) LetÆs take a typical example. Assuming P=4dBm, for details.) Let's 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
skipping to change at page 9, line 43 skipping to change at page 9, line 43
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 designerÆs control. likely to be under the system designer's 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 December 2002 Impairments And Other Constraints May 2003
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
skipping to change at page 11, line 4 skipping to change at page 11, line 4
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
Impairments And Other Constraints December 2002 Impairments And Other Constraints May 2003
On Optical Layer Routing On Optical Layer Routing
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.
skipping to change at page 12, line 4 skipping to change at page 12, line 4
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
Impairments And Other Constraints December 2002 Impairments And Other Constraints May 2003
On Optical Layer Routing On Optical Layer Routing
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
skipping to change at page 13, line 5 skipping to change at page 13, line 5
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.
Impairments And Other Constraints December 2002 Impairments And Other Constraints May 2003
On Optical Layer Routing On Optical Layer Routing
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
skipping to change at page 14, line 4 skipping to change at page 14, line 4
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
Impairments And Other Constraints December 2002 Impairments And Other Constraints May 2003
On Optical Layer Routing On Optical Layer Routing
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
the maximum-path-distance, the upper bound of all paths. the maximum-path-distance, the upper bound of all paths.
4.7 Other Considerations 4.7 Other Considerations
Routing in an all-optical network without wavelength conversion Routing in an all-optical network without wavelength conversion
raises several additional issues: raises several additional issues:
- Since the route selected must have the chosen wavelength - Since the route selected must have the chosen wavelength
available on all links, this information needs to be considered available on all links, this information needs to be considered
in the routing process. This is discussed in [Chaudhuri00], in the routing process. One approach is to propagate
where it is concluded that advertising detailed wavelength information throughout the network about the state of every
availabilities on each link is not likely to scale. Instead wavelength on every link in the network. However, the state
they propose an alternative method which probes along a chosen required and the overhead involved in processing and
path to determine which wavelengths (if any) are available. maintaining this information is proportional to the total
This would require a significant addition to the routing logic number of links (thus, number of nodes squared), maximum number
normally used in OSPF. Others have proposed simultaneously of wavelengths which keeps doubling every couple of years), and
probing along multiple paths. the frequency of wavelength availability changes, which can be
very high. Instead [Hjßlmt²sson00] proposes an alternative
method which probes along a chosen path to determine which
wavelengths (if any) are available. This would require a
significant addition to the routing logic normally used in
OSPF. Others have proposed simultaneously probing along
multiple paths.
- Choosing a path first and then a wavelength along the path is - Choosing a path first and then a wavelength along the path is
known to give adequate results in simple topologies such as known to give adequate results in simple topologies such as
rings and trees ([Yates99]). This does not appear to be true in rings and trees ([Yates99]). This does not appear to be true in
large mesh networks under realistic provisioning scenarios, large mesh networks under realistic provisioning scenarios,
however. Instead significantly better results are achieved if however. Instead significantly better results are achieved if
wavelength and route are chosen simultaneously ([Strand01b]). wavelength and route are chosen simultaneously ([Strand01b]).
This approach would however also have a significant effect on This approach would however also have a significant effect on
OSPF. OSPF.
4.8 Implications For Routing and Control Plane Design 4.8 Implications For Routing and Control Plane Design
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:
Impairments And Other Constraints May 2003
On Optical Layer Routing
- 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
Impairments And Other Constraints December 2002
On Optical Layer Routing
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
being limiting for some routes. Note that for one operator, PMD being limiting for some routes. Note that for one operator, PMD
might be the only limiting constraint while for another, ASE might be the only limiting constraint while for another, ASE
skipping to change at page 15, line 51 skipping to change at page 16, line 4
links is no larger than P/SNRmin. Thus, the information needed links is no larger than P/SNRmin. Thus, the information needed
include the launch power P and OSNR requirement SNRmin. The include the launch power P and OSNR requirement SNRmin. The
minimum acceptable OSNR, in turn, depends on the strength of the minimum acceptable OSNR, in turn, depends on the strength of the
FEC being used and the margins reserved for other types of FEC being used and the margins reserved for other types of
impairments. Other bounds include the maximum span length of the impairments. Other bounds include the maximum span length of the
transmission system, the maximum path crosstalk or the maximum transmission system, the maximum path crosstalk or the maximum
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
Impairments And Other Constraints May 2003
On Optical Layer Routing
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
Impairments And Other Constraints December 2002
On Optical Layer Routing
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,
and whether the domain is operating in a linear or nonlinear and whether the domain is operating in a linear or nonlinear
regime. regime.
skipping to change at page 16, line 48 skipping to change at page 17, line 4
An optical network composed of multiple domains of transparency An optical network composed of multiple domains of transparency
optically isolated from each other by O/E/O devices (transponders) optically isolated from each other by O/E/O devices (transponders)
is more plausible. A network composed of both "opaque" (optically is more plausible. A network composed of both "opaque" (optically
isolated) OLXC's and one or more all-optical "islands" isolated by isolated) OLXC's and one or more all-optical "islands" isolated by
transponders is of particular interest because this is most likely transponders is of particular interest because this is most likely
how all-optical technologies (such as that described in Sec. 2) are how all-optical technologies (such as that described in Sec. 2) are
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.)
Impairments And Other Constraints May 2003
On Optical Layer Routing
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:
Impairments And Other Constraints December 2002
On Optical Layer Routing
- 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
realize that, at least in the short to intermediate term, the realize that, at least in the short to intermediate term, the
resources committed by a single routing decision can be very resources committed by a single routing decision can be very
skipping to change at page 17, line 53 skipping to change at page 18, line 4
- The cost function used in routing must allow the balancing of - The cost function used in routing must allow the balancing of
transponder costs, OXC and OADM costs, and line haul costs transponder costs, OXC and OADM costs, and line haul costs
across the entire routing domain. across the entire routing domain.
Several distributed approaches to multi-island routing seem worth Several distributed approaches to multi-island routing seem worth
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
Impairments And Other Constraints May 2003
On Optical Layer Routing
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
Impairments And Other Constraints December 2002
On Optical Layer Routing
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
gateway nodes or to an NMS to get routing guidance. gateway nodes or to an NMS to get routing guidance.
skipping to change at page 18, line 43 skipping to change at page 18, line 48
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, ROWÆs are frequently obtained from that for economic reasons, ROW's 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 carriersÆ fiber cables in close makes it common to have a number of carriers' fiber cables in close
proximity to each other. Similarly, in a metropolitan network, proximity to each other. Similarly, in a metropolitan network,
Impairments And Other Constraints May 2003
On Optical Layer Routing
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.
Impairments And Other Constraints December 2002
On Optical Layer Routing
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 OLXCÆs. To represent the of 100 offices that are candidates for OLXC's. 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 between Locations where fiber splices are used to interchange fibers 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 \ /
skipping to change at page 19, line 47 skipping to change at page 20, line 4
not even be a manhole; the fiber routes might just be buried at not even be a manhole; the fiber routes might just be buried at
different depths. different depths.
Fiber splicing (the third case) often occurs when a major fiber Fiber splicing (the third case) often occurs when a major fiber
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
Impairments And Other Constraints May 2003
On Optical Layer Routing
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.)
Impairments And Other Constraints December 2002
On Optical Layer Routing
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
Figure 6-2. Fiber Cable vs Fiber Topologies Figure 6-2. Fiber Cable vs Fiber Topologies
skipping to change at page 20, line 46 skipping to change at page 21, line 4
lightpaths to nodes B and C, this requires A-B and A-C to be lightpaths to nodes B and C, this requires A-B and A-C to be
diverse. In real applications, a large data network with N diverse. In real applications, a large data network with N
lightpaths between its routers might describe their needs in an lightpaths between its routers might describe their needs in an
NxN matrix, where (i,j) defines whether lightpaths i and j must NxN matrix, where (i,j) defines whether lightpaths i and j must
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
Impairments And Other Constraints May 2003
On Optical Layer Routing
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
Impairments And Other Constraints December 2002
On Optical Layer Routing
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.
o Disasters: Earthquakes and floods can cause failures over o Disasters: Earthquakes and floods can cause failures over
an extended area. Defense Department circuits might need an extended area. Defense Department circuits might need
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 ROWÆs will diverse paths from an office with less than N diverse ROW's 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.
[Chaudhuri00] introduced the term "Shared Risk Link Group" (SRLG) to [Hjßlmt²sson00] introduced the term "Shared Risk Link Group" (SRLG)
describe the relationship between two non-diverse links. The above to describe the relationship between two non-diverse links. The
discussion suggests that an SRLG should be characterized by 2 above examples and discussion given at the start of this section
parameters: suggests that an SRLG should be characterized by 2 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.)
Impairments And Other Constraints May 2003
On Optical Layer Routing
- 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.
Impairments And Other Constraints December 2002
On Optical Layer Routing
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 SRLGÆs is in The mapping between links and different types of SRLG's 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
skipping to change at page 22, line 48 skipping to change at page 22, line 52
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 SRLGÆs appropriate to a particular routing request to be allow the SRLG's appropriate to a particular routing request to be
easily identified. easily identified.
7. Security Considerations Impairments And Other Constraints May 2003
Impairments And Other Constraints December 2002
On Optical Layer Routing On Optical Layer Routing
7. Security Considerations
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.
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, SRLGÆs must be defined so that all links vulnerable to a threat, SRLG's 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
skipping to change at page 23, line 53 skipping to change at page 24, line 5
discussed in [Mannie02]. 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 Impairments And Other Constraints May 2003
Impairments And Other Constraints December 2002
On Optical Layer Routing On Optical Layer Routing
9.1 Normative References 9. References
[Chaudhuri00] Chaudhuri, S., Hjalmtysson, G., and Yates, J., 9.1 Normative References
"Control of Lightpaths in an Optical Network", Work in Progress,
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.
[Hjßlmt²sson00] Gsli Hjßlmt²sson, Jennifer Yates, Sid Chaudhuri and
Albert
Greenberg, "Smart Routers - Simple Optics: An Architecture for the
Optical Internet, IEEE/OSA Journal of Lightwave Technology, December
2000,, Vo 18, Issue 12 , Dec. 2000 , pp. 1880 -1891.
[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 [Mannie02] Mannie, E. (ed.), "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", Interned Draft, draft-ietf-ccamp- Switching (GMPLS) Architecture", Interned Draft, draft-ietf-ccamp-
gmpls-architecture-03.txt, August, 2002. gmpls-architecture-03.txt, August, 2002.
[Rajagopalam02] Rajagopalam, B., et. al., "IP over Optical Networks: [Rajagopalam02] Rajagopalam, B., et. al., "IP over Optical Networks:
A Framework", Internet Draft, draft-ietf-ipo-framework-02.txt June, A Framework", Internet Draft, draft-ietf-ipo-framework-02.txt June,
2002. 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.
Optical Layer Control Plane", Internet Draft, draft-chiu-strand-
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 Impairments And Other Constraints May 2003
Impairments And Other Constraints December 2002
On Optical Layer Routing On Optical Layer Routing
9.2 Informative References
[Awduche99] Awduche, D. O., Rekhter, Y., Drake, J., and Coltun, R., [Awduche99] Awduche, D. O., Rekhter, Y., Drake, J., and Coltun, R.,
"Multi-Protocol Lambda Switching: Combining MPLS Traffic Engineering "Multi-Protocol Lambda Switching: Combining MPLS Traffic Engineering
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.
[CBD00] Ceuppens, L., Blumenthal, D., Drake, J., Chrostowski, J., [CBD00] Ceuppens, L., Blumenthal, D., Drake, J., Chrostowski, J.,
Edwards, W., "Performance Monitoring in Photonic Networks in Support Edwards, W., "Performance Monitoring in Photonic Networks in Support
skipping to change at page 25, line 48 skipping to change at page 26, line 5
[Passmore01] Passmore, D., "Managing Fatter Pipes," Business [Passmore01] Passmore, D., "Managing Fatter Pipes," Business
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 Impairments And Other Constraints May 2003
Impairments And Other Constraints December 2002
On Optical Layer Routing On Optical Layer Routing
10. Contributing Authors
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
skipping to change at page 26, line 53 skipping to change at page 27, line 4
2400 North Glenville Drive 2400 North Glenville Drive
Richardson, TX 75082 Richardson, TX 75082
Email: taha.landolsi@wcom.com Email: taha.landolsi@wcom.com
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
Impairments And Other Constraints May 2003
On Optical Layer Routing
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. EditorsÆ Addresses 11. Editors' Addresses
Angela Chiu Angela Chiu
AT&T Labs AT&T Labs
200 Laurel Ave., Rm A5-1F13 200 Laurel Ave., Rm A5-1F13
Middletown, NJ 07748 Middletown, NJ 07748
Phone:(732) 420-9061 Phone:(732) 420-9061
Email: chiu@research.att.com Email: chiu@research.att.com
John Strand John Strand
AT&T Labs AT&T Labs
 End of changes. 

This html diff was produced by rfcdiff 1.25, available from http://www.levkowetz.com/ietf/tools/rfcdiff/