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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Draft 3 Document: draft-ietf-ipo-impairments-01.txt Angela Chiu 4 Expiration Date: May 2002 Robert Tkach 5 Celion Networks 7 James Luciani 8 Crescent Networks 10 Ayan Banerjee 11 John Drake 12 Dan Blumenthal 13 Calient Networks 15 Andre Fredette 16 Nan Froberg 17 PhotonEx 19 John Strand (Editor) 20 AT&T 22 Impairments And Other Constraints On Optical Layer Routing 24 Status of this Memo 26 This document is an Internet-Draft and is in full conformance with 27 all provisions of Section 10 of RFC2026. Internet-Drafts are 28 Working documents of the Internet Engineering Task Force (IETF), its 29 areas, and its working groups. Note that other groups may also 30 distribute working documents as Internet-Drafts. 32 Internet-Drafts are draft documents valid for a maximum of six 33 months and may be updated, replaced, or made obsolete by other 34 documents at any time. It is inappropriate to use Internet-Drafts as 35 reference material or to cite them other than as "work in progress." 37 The list of current Internet-Drafts can be accessed at 38 http://www.ietf.org/ietf/1id-abstracts.txt. 39 The list of Internet-Draft Shadow Directories can be accessed at 40 http://www.ietf.org/shadow.html. 42 Abstract 43 Optical networking poses a number challenges for GMPLS. Optical 44 technology is fundamentally an analog rather than digital technology; 45 and the optical layer is lowest in the transport hierarchy and hence 46 has an intimate relationship with the physical geography of the 47 network. This contribution surveys some of the aspects of optical 49 Impairments And Other Constraints November 2001 50 On Optical Layer Routing 52 networks which impact routing and identifies possible GMPLS responses 53 for each: (1) Constraints arising from the design of new software 54 controllable network elements, (2) Constraints in a single all- 55 optical domain without wavelength conversion (3) Complications 56 arising in more complex networks incorporating both all-optical and 57 opaque architectures, and (5) Impacts of diversity constraints. 59 1. Introduction 61 GMPLS [GMPLS] aims to extend MPLS to encompass a number of transport 62 architectures. Included are optical networks incorporating a number 63 of all-optical and opto-electronic elements such as optical cross- 64 connects with both optical and electrical fabrics, transponders, and 65 optical add-drop multiplexers. Optical networking poses a number 66 challenges for GMPLS. Optical technology is fundamentally an analog 67 rather than digital technology; and the optical layer is lowest in 68 the transport hierarchy and hence has an intimate relationship with 69 the physical geography of the network. 71 GMPLS already has incorporated extensions to deal with some of the 72 unique aspects of the optical layer. This contribution surveys some 73 of the aspects of optical networks which impact routing and 74 identifies possible GMPLS responses for each. Routing constraints 75 and/or complications arising from the design of network elements, 76 the accumulation of signal impairments, and from the need to 77 guarantee the physical diversity of some circuits are discussed. 79 Since the purpose of this draft is to further the specification of 80 GMPLS, alternative approaches to controlling an optical network are 81 not discussed. For discussions of some broader issues, see 82 [Gerstel2000] and [Strand2001]. 84 The organization of the contribution is as follows: 86 - Section 2 is a section requested by the sub-IP Area 87 management for all new drafts. It explains how this document 88 fits into the Area and into the IPO WG, and why it is 89 appropriate for these groups. 90 - Section 3 describes constraints arising from the design of 91 new software controllable network elements. 92 - Section 4 addresses the constraints in a single all-optical 93 domain without wavelength conversion. 94 - Section 5 extends the discussion to more complex networks 95 incorporating both all-optical and opaque architectures. 96 - Section 6 discusses the impacts of diversity constraints. 97 - Section 7 deals with security requirements. 99 Impairments And Other Constraints November 2001 100 On Optical Layer Routing 102 - Section 8 contains acknowledgments. 104 2. Sub-IP Area Summary And Justification Of Work 105 This draft merges and extends two previous drafts, draft-chiu- 106 strand-unique-olcp-02.txt and draft-banerjee-routing-impairments- 107 00.txt. These two drafts were made IPO working group documents to 108 form a basis for a design team at the Minneapolis meeting, where it 109 was also requested that they be merged to create a requirements 110 document for the WG. 112 In the larger sub-IP Area structure, this merged document describes 113 specific characteristics of optical technology and the requirements 114 they place on routing and path selection. It is appropriate for the 115 IPO working group because the material is specific to optical 116 networks. It identifies and documents the characteristics of the 117 optical transport network that are important for selecting paths for 118 optical channels, which is a work area for the IPO WG. It is 119 appropriate work for this WG because the material covered is 120 directly aimed at establishing a framework and requirements for 121 routing in an optical network. 123 Related documents are: 124 draft-banerjee-routing-impairments-00.txt 125 draft-parent-obgp-01.txt 126 draft-bernstein-optical-bgp-00.txt 127 draft-hayata-ipo-carrier-needs-00.txt 128 draft-many-carrier-framework-uni-01.txt 130 3. Reconfigurable Network Elements 132 3.1 Technology Background 134 Control plane architectural discussions (e.g., [Awduche99]) usually 135 assume that the only software reconfigurable network element is an 136 optical layer cross-connect (OLXC). There are however other 137 software reconfigurable elements on the horizon, specifically 138 tunable lasers and receivers and reconfigurable optical add-drop 139 multiplexers (OADM�s). These elements are illustrated in the 140 following simple example, which is modeled on announced Optical 141 Transport System (OTS) products: 143 Impairments And Other Constraints November 2001 144 On Optical Layer Routing 146 + + 147 ---+---+ |\ /| +---+--- 148 ---| A |----|D| X Y |D|----| A |--- 149 ---+---+ |W| +--------+ +--------+ |W| +---+--- 150 : |D|-----| OADM |-----| OADM |-----|D| : 151 ---+---+ |M| +--------+ +--------+ |M| +---+--- 152 ---| A |----| | | | | | | |----| A |--- 153 ---+---+ |/ | | | | \| +---+--- 154 + +---+ +---+ +---+ +---+ + 155 D | A | | A | | A | | A | E 156 +---+ +---+ +---+ +---+ 157 | | | | | | | | 159 Figure 3-1: An OTS With OADM's - Functional Architecture 161 In Fig.3-1, the part that is on the inner side of all boxes labeled 162 "A" defines an all-optical subnetwork. From a routing perspective 163 two aspects are critical: 164 - Adaptation: These are the functions done at the edges of the 165 subnetwork that transform the incoming optical channel into the 166 physical wavelength to be transported through the subnetwork. 167 - Connectivity: This defines which pairs of edge Adaptation 168 functions can be interconnected through the subnetwork. 170 In Fig. 3-1, D and E are DWDM�s and X and Y are OADM�s. The boxes 171 labeled "A" are adaptation functions. They map one or more input 172 optical channels assumed to be standard short reach signals into a 173 long reach (LR) wavelength or wavelength group which will pass 174 transparently to a distant adaptation function. Adaptation 175 functionality which affects routing includes: 176 - Multiplexing: Either electrical or optical TDM may be used to 177 combine the input channels into a single wavelength. This is 178 done to increase effective capacity: A typical DWDM might be 179 able to handle 100 2.5 Gb/sec signals (250 Gb/sec total) or 50 180 10 Gb/sec (500 Gb/sec total); combining the 2.5 Gb/sec signals 181 together thus effectively doubles capacity. After multiplexing 182 the combined signal must be routed as a group to the distant 183 adaptation function. 184 - Adaptation Grouping: In this technique, groups of k (e.g., 4) 185 wavelengths are managed as a group within the system and must be 186 added/dropped as a group. We will call such a group an 187 "adaptation grouping". Other terms frequently used are "wave 188 group" and �waveband�. Groupings on the same system may differ 189 in basics such as wavelength spacing, which constrain the type 190 of channels which they can accommodate. 191 - Laser Tunability: The lasers producing the LR wavelengths may 192 have a fixed frequency, may be tunable over a limited range, or 194 Impairments And Other Constraints November 2001 195 On Optical Layer Routing 197 be tunable over the entire range of wavelengths supported by the 198 DWDM. Tunability speeds may also vary. 200 Connectivity between adaptation functions may also be limited: 201 - As pointed out above, TDM multiplexing and/or adaptation 202 grouping by the adaptation function forces groups of input 203 channels to be delivered together to the same distant adaptation 204 function. 205 - Only adaptation functions whose lasers/receivers are tunable to 206 compatible frequencies can be connected. 207 - The switching capability of the OADM�s may also be constrained. 208 For example: 209 o There may be some wavelengths that can not be dropped at 210 all. 211 o There may be a fixed relationship between the frequency 212 dropped and the physical port on the OADM to which it is 213 dropped. 214 o OADM physical design may put an upper bound on the number 215 of adaptation groupings dropped at any single OADM. 217 For a fixed configuration of the OADM�s and adaptation functions 218 connectivity will be fixed: Each input port will essentially be 219 hard-wired to some specific distant port. However this connectivity 220 can be changed by changing the configurations of the OADM�s and 221 adaptation functions. For example, an additional adaptation grouping 222 might be dropped at an OADM or a tunable laser retuned. In each case 223 the port-to-port connectivity is changed. 225 These capabilities can be expected to be under software control. 226 Today the control would rest in the vendor-supplied Element 227 Management system (EMS), which in turn would be controlled by the 228 operator�s OS�s. However in principle the EMS could participate in 229 the GMPLS routing process. 231 3.2 Implications For Routing 233 An OTS of the sort discussed in Sec. 3.1 is essentially a 234 geographically distributed but blocking cross-connect system. The 235 specific port connectivity is dependent on the vendor design and 236 also on exactly what line cards have been deployed. 238 One way for GMPLS to deal with this architecture would be to view 239 the port connectivity as externally determined. In this case the 240 links known to GMPLS would be groups of identically routed 241 wavebands. If these were reconfigured by the external EMS the 242 resulting connectivity changes would need to be detected and 243 advertised within GMPLS. If the topology shown in Fig. 32-1 became 244 a tree or a mesh instead of the linear topology shown, the 245 connectivity changes could result in SRLG changes. 247 Impairments And Other Constraints November 2001 248 On Optical Layer Routing 250 Alternatively, GMPLS could attempt to directly control this port 251 connectivity. The state information needed to do this is likely to 252 be voluminous and vendor specific. 254 4. Wavelength Routed All-Optical Networks 256 The optical networks presently being deployed may be called "opaque" 257 ([Tkach98]): each link is optically isolated by transponders doing 258 O/E/O conversions. They provide regeneration with retiming and 259 reshaping, also called 3R, which eliminates transparency to bit 260 rates and frame format. These transponders are quite expensive and 261 their lack of transparency also constrains the rapid introduction of 262 new services. Thus there are strong motivators to introduce 263 "domains of transparency" - all-optical subnetworks - larger than an 264 OTS. 266 The routing of lightpaths through an all-optical network has 267 received extensive attention. (See [Yates99] or [Ramaswami98]). 268 When discussing routing in an all-optical network it is usually 269 assumed that all routes have adequate signal quality. This may be 270 ensured by limiting all-optical networks to subnetworks of limited 271 geographic size which are optically isolated from other parts of the 272 optical layer by transponders. This approach is very practical and 273 has been applied to date, e.g. when determining the maximum length 274 of an Optical Transport System (OTS). Furthermore operational 275 considerations like fault isolation also make limiting the size of 276 domains of transparency attractive. 278 There are however reasons to consider contained domains of 279 transparency in which not all routes have adequate signal quality. 280 From a demand perspective, maximum bit rates have rapidly increased 281 from DS3 to OC-192 and soon OC-768 (40 Gb/sec). As bit rates 282 increase it is necessary to increase power. This makes impairments 283 and nonlinearities more troublesome. From a supply perspective, 284 optical technology is advancing very rapidly, making ever-larger 285 domains possible. In this section we assume that these 286 considerations will lead to the deployment of a domain of 287 transparency that is too large to ensure that all potential routes 288 have adequate signal quality for all circuits. Our goal is to 289 understand the impacts of the various types of impairments in this 290 environment. 292 4.1 Problem Formulation 294 We consider a single domain of transparency without wavelength 295 translation. Additionally due to proprietary natures of DWDM 296 transmission technology, we assume that the domain is either single 297 vendor or architected using a single coherent design philosophy, 298 particularly with regard to the management of impairments. 300 Impairments And Other Constraints November 2001 301 On Optical Layer Routing 303 We wish to route a unidirectional circuit from ingress client node X 304 to egress client node Y. At both X and Y, the circuit goes through 305 an O/E/O conversion which optically isolates the portion within our 306 domain. We assume that we know the bit rate of the circuit. Also, 307 we assume that the adaptation function at X may apply some Forward 308 Error Correction (FEC) method to the circuit. We also assume we know 309 the launch power of the laser at X. 311 Impairments can be classified into two categories, linear and 312 nonlinear. (See [Tkach98] for more on impairment constraints). 313 Linear effects are independent of signal power and affect 314 wavelengths individually. Amplifier spontaneous emission (ASE), 315 polarization mode dispersion (PMD), and chromatic dispersion are 316 examples. Nonlinearities are significantly more complex: they 317 generate not only impairments on each channel, but also crosstalk 318 between channels. 320 In the remainder of this section we first outline how two key linear 321 impairments (PMD and ASE) might be handled by a set of analytical 322 formulae as additional constraints on routing. We next discuss how 323 the remaining constraints might be approached. Finally we take a 324 broader perspective and discuss the implications of such constraints 325 on control plane architecture and also on broader constrained domain 326 of transparency architecture issues. 328 4.2 Polarization Mode Dispersion 330 For a transparent fiber segment, the general rule for the PMD 331 requirement is that the time-average differential group delay (DGD) 332 between two orthogonal state of polarizations should be less than 333 fraction a of the bit duration, T=1/B, where B is the bit rate. The 334 value of the parameter a depends on three major factors: 1) margin 335 allocated to PMD, e.g. 1dB; 2) targeted outage probability, e.g. 336 4x10-5, and 3) sensitivity of the receiver to DGD. A typical value 337 for a is 10% [ITU]. More aggressive designs to compensate for PMD 338 may allow values higher than 10%. (This would be a system parameter 339 dependent on the system design. It would need to be known to the 340 routing process.) 342 The PMD parameter (Dpmd) is measured in pico-seconds (ps) per 343 sqrt(km). The square of the PMD in a fiber span, denoted as span- 344 PMD-square is then given by the product of Dpmd**2 and the span 345 length. (A fiber span in a transparent network refers to a segment 346 between two optical amplifiers.) If Dpmd is constant, this results 347 in a upper bound on the maximum length of an M-fiber-span 348 transparent segment, which is inversely proportional to the square 349 of the product of bit rate and Dpmd.(tThe detailed equation is 350 omitted due to the format constraint - see [Strand01] for details). 352 Impairments And Other Constraints November 2001 353 On Optical Layer Routing 355 For older fibers with a typical PMD parameter of 0.5 picoseconds per 356 square root of km, based on the constraint, the maximum length of 357 the transparent segment should not exceed 400km and 25km for bit 358 rates of 10Gb/s and 40Gb/s, respectively. Due to recent advances in 359 fiber technology, the PMD-limited distance has increased 360 dramatically. For newer fibers with a PMD parameter of 0.1 361 picosecond per square root of km, the maximum length of the 362 transparent segment (without PMD compensation) is limited to 10000km 363 and 625km for bit rates of 10Gb/s and 40Gb/, respectively. Still 364 lower values of PMD are attainable in commercially available fiber 365 today, and the PMD limit can be further extended if a larger value 366 of the parameter a (ratio of DGD to the bit period) can be 367 tolerated. In general, the PMD requirement is not an issue for most 368 types of fibers at 10Gb/s or lower bit rate. But it will become an 369 issue at bit rates of 40Gb/s and higher. 371 If the PMD parameter varies between spans, a slightly more 372 complicated equations results (see [Strand01]), but in any event the 373 only link dependent information needed by the routing algorithm is 374 the square of the link PMD, denoted as link-PMD-square. It is the 375 sum of the span-PMD-square of all spans on the link. 377 4.3 Amplifier Spontaneous Emission 379 ASE degrades the optical signal to noise ratio (OSNR). An acceptable 380 optical SNR level (SNRmin) which depends on the bit rate, 381 transmitter-receiver technology (e.g., FEC), and margins allocated 382 for the impairments, needs to be maintained at the receiver. In 383 order to satisfy this requirement, vendors often provide some 384 general engineering rule in terms of maximum length of the 385 transparent segment and number of spans. For example, current 386 transmission systems are often limited to up to 6 spans each 80km 387 long. For larger transparent domains, more detailed OSNR 388 computations will be needed to determine whether the OSNR level 389 through a domain of transparency is acceptable. This would provide 390 flexibility in provisioning or restoring a lightpath through a 391 transparent subnetwork. 393 Assume that the average optical power launched at the transmitter is 394 P. The lightpath from the transmitter to the receiver goes through M 395 optical amplifiers, with each introducing some noise power. Unity 396 gain can be used at all amplifier sites to maintain constant signal 397 power at the input of each span to minimize noise power and 398 nonlinearity. A constraint on the maximum number of spans can be 399 obtained [Kaminow97] which is proportional to P and inversely 400 proportional to SNRmin, optical bandwidth B, amplifier gain G-1 and 401 spontaneous emission factor n of the optical amplifier, assuming all 402 spans have identical gain and noise figure. (Again, the detailed 403 equation is omitted due to the format constraint - see [Strand01] 404 for details.) Let�s take a typical example. Assuming P=4dBm, 406 Impairments And Other Constraints November 2001 407 On Optical Layer Routing 409 SNRmin=20dB with FEC, B=12.5GHz, n=2.5, G=25dB, based on the 410 constraint, the maximum number of spans is at most 10. However, if 411 FEC is not used and the requirement on SNRmin becomes 25dB, the 412 maximum number of spans drops down to 3. 414 For ASE the only link-dependent information needed by the routing 415 algorithm is the noise of the link, denoted as link-noise, which is 416 the sum of the noise of all spans on the link. Hence the constraint 417 on ASE becomes that the aggregate noise of the transparent segment 418 which is the sum of the link-noise of all links can not exceed 419 P/SNRmin. 421 4.4 Approximating The Effects Of Some Other Impairment Constraints 423 There are a number of other impairment constraints that we propose 424 to approximate with a domain-wide margin on the OSNR, plus some 425 constraint on the total number of networking elements (OXC or OADM) 426 in some cases. Most impairments generated at OXCs or OADMs, 427 including polarization dependent loss, coherent crosstalk, and 428 effective passband width, are dealt with using this approach. In 429 principle, impairments generated at the nodes can be bounded by 430 system engineering rules because the node elements can be designed 431 and specified in a uniform manner. This approach is not feasible 432 with PMD and noise because neither can be uniformly specified. 433 Instead, they depend on node spacing and the characteristics of the 434 installed fiber plant, neither of which are likely to be under the 435 system designer�s control. 437 Examples of the constraints we propose to approximate with a domain- 438 wide margin are given in the remaining paragraphs in this section. 439 It should be kept in mind that as optical transport technology 440 evolves it may become necessary to include some of these impairments 441 explicitly in the routing process. Other impairments not mentioned 442 here at all may also become sufficiently important to require 443 incorporation either explicitly or via a domain-wide margin. 445 Other Polarization Dependent Impairments Other polarization- 446 dependent effects besides PMD influence system performance. For 447 example, many components have polarization-dependent loss (PDL) 448 [Ramaswami98] which accumulates in a system with many components on 449 the transmission path. The state of polarization fluctuates with 450 time and its distribution is very important also. It is generally 451 required to maintain the total PDL on the path to be within some 452 acceptable limit, potentially by using some compensation technology 453 for relatively long transmission systems, plus a small built-in 454 margin in OSNR. Since the total PDL increases with the number of 455 components in the data path, it must be taken into account by the 456 system vendor when determining the maximum allowable number of 457 spans. 459 Impairments And Other Constraints November 2001 460 On Optical Layer Routing 462 Chromatic Dispersion In general this impairment can be adequately 463 (but not optimally) compensated for on a per-link basis, and/or at 464 system initial setup time. A low margin in OSNR can be put in to 465 account for any mismatch in dispersion compensation. Today most used 466 compensation devices are based on DCF (Dispersion Compensation 467 Fiber). DCF provides per fiber compensation by means of a spool of 468 fiber with a CD coefficient opposite to the fiber. Due to the 469 imperfect matching between the CD slope of the fiber and the DCF some 470 lambdas can be over compensated while others can be under 471 compensated. Moreover DCF modules can be found with fixed length of 472 compensating fiber; this means that sometimes it is impossible to 473 find a DCF module that exactly compensates the CD introduced by the 474 fiber. These effects introduce what is known as residual CD. Residual 475 CD varies with the frequency of the wavelength. Knowing the 476 characteristics of both of the fiber and the DCF modules along the 477 path, this can be calculated with a sufficient degree of precision. 478 However this is a very challenging task. In fact the per-wavelength 479 residual dispersion needs to be combined with other information in 480 the system (e.g. types fibers to figure out the amount of 481 nonlinearities) to obtain the net effect of CD either by simulation 482 or by some analytical approximation. It appears that the 483 routing/control plane should not be burdened by such a large set of 484 information while it can be handled at the system design level. 485 Therefore it will be assumed until proven otherwise that residual 486 dispersion should not be reported. For high bit rates, dynamic 487 dispersion compensation may be required at the receiver to clean up 488 any residual dispersion. 490 Crosstalk Optical crosstalk refers to the effect of other signals on 491 the desired signal. It includes both coherent (i.e. intrachannel) 492 crosstalk and incoherent (i.e. interchannel) crosstalk. Main 493 contributors of crosstalk are the OADM and OXC sites that use a DWDM 494 multiplexer/demultiplexer (MUX/DEMUX) pair. For a relatively sparse 495 network where the number of OADM/OXC nodes on a path is low, 496 crosstalk can be treated with a low margin in OSNR without being a 497 binding constraint. But for some relatively dense networks where 498 crosstalk might become a binding constraint, one needs to propagate 499 the per-link crosstalk information to make sure that the end-to-end 500 path crosstalk which is the sum of the crosstalks on all the 501 corresponding links to be within some limit, e.g. �25dB threshold 502 with 1dB penalty ([Goldstein94]). Another way to treat it without 503 having to propagate per-link crosstalk information is to have the 504 system evaluate what the maximum number of OADM/OXC nodes that has a 505 MUX/DEMUX pair for the worst route in the transparent domain for a 506 low built-in margin. The latter one should work well where all the 507 OXC/OADM nodes have similar level of crosstalk. 509 Impairments And Other Constraints November 2001 510 On Optical Layer Routing 512 Effective Passband As more and more DWDM components are cascaded, 513 the effective passband narrows. The number of filters along the 514 link, their passband width and their shape will determine the end- 515 to-end effective passband. In general, this is a system design 516 issue, i.e., the system is designed with certain maximum bit rate 517 using the proper modulation format and filter spacing. Then For 518 linear systems, the filter effect can be turned into a constraint on 519 the maximum number of OADM/OXCnarrow filters with the condition that 520 filters in the systems are at least as wide as the one in the 521 receiver. Because traffic at lower bit rates can tolerate a 522 narrower passband, the maximum allowable number of OADMs/OXCsnarrow 523 filters will increase as the bit rate decreases. 525 Nonlinear Impairments It seems unlikely that these can be dealt with 526 explicitly in a routing algorithm because they lead to constraints 527 that can couple routes together and lead to complex dependencies, 528 e.g. on the order in which specific fiber types are traversed. Note 529 that different fiber types (standard single mode fiber, dispersion 530 shifted fiber, dispersion compensated fiber, etc.) have very 531 different effects from nonlinear impairments. A full treatment of 532 the nonlinear constraints would likely require very detailed 533 knowledge of the physical infrastructure, including measured 534 dispersion values for each span, fiber core area and composition, as 535 well as knowledge of subsystem details such as dispersion 536 compensation technology. This information would need to be combined 537 with knowledge of the current loading of optical signals on the 538 links of interest to determine the level of nonlinear impairment. 539 Alternatively, one could assume that nonlinear impairments are 540 bounded and result in X dB margin in the required OSNR level for a 541 given bit rate, where X for performance reasons would be limited to 542 1 or 2 dB, consequently setting a limit on the maximum number of 543 spans. For the approach described here to be useful, it is desirable 544 for this span length limit to be longer than that imposed by the 545 constraints which can be treated explicitly. When designing a DWDM 546 transport system, there are tradeoffs between signal power launched 547 at the transmitter, span length, and nonlinear effects on BER that 548 need to be considered jointly. Here, we assume that an X dB margin 549 is obtained after the transport system has been designed with a 550 fixed signal power and maximum span length for a given bit rate. 551 Further work is required to determine the validity of this approach. 552 However, it is likely that there is an advantage in designing 553 systems which are less aggressive with respect to nonlinearities, 554 and therefore somewhat sub-optimal, in exchange for improved 555 scalability, simplicity and flexibility in routing and control plane 556 design. 558 4.5 Other Impairment Considerations 560 Impairments And Other Constraints November 2001 561 On Optical Layer Routing 563 There are many other types of impairments which that can degrade 564 performance. In this section we briefly mention one other type of 565 impairment, which we propose be dealt with by either by the system 566 designer or by the transmission engineers at the time the system is 567 installed. If dealt with successfully in this manner they should not 568 need to be considered in the dynamic routing process. 570 Gain Nonuniformity and Gain Transients For simple noise estimates to 571 be of use, the amplifiers must be gain-flattened and must have 572 automatic gain control (AGC). Furthermore, each link should have 573 dynamic gain equalization (DGE) to optimize power levels each time 574 wavelengths are added or dropped. Variable optical attenuators on 575 the output ports of an OXC or OADM can be used for this purpose, and 576 in-line devices are starting to become commercially available. 577 Optical channel monitors are also required to provide feedback to 578 the DGEs. AGC must be done rapidly if signal degradation after a 579 protection switch or link failure is to be avoided. 581 Note that the impairments considered here are treated more or less 582 independently. By considering them jointly and varying the tradeoffs 583 between the effects from different components may allow more routes 584 to be feasible. If that is desirable or the system is designed such 585 that certain impairments (e.g. nonlinearities) need to be considered 586 by a centralized process, then distributed routing is not the one to 587 use. 589 4.6 Other Considerations 591 Routing in an all-optical network without wavelength conversion 592 raises several additional issues: 594 - Since the route selected must have the chosen wavelength 595 available on all links, this information needs to be considered 596 in the routing process. This is discussed in [Chaudhuri00], where 597 it is concluded that advertising detailed wavelength 598 availabilities on each link is not likely to scale. Instead they 599 propose an alternative method which probes along a chosen path to 600 determine which wavelengths (if any) are available. This would 601 require a significant addition to the routing logic normally used 602 in OSPF. Others have proposed simultaneously probing along 603 multiple paths. 605 - Choosing a path first and then a wavelength along the path is 606 known to give adequate results in simple topologies such as rings 607 and trees ([Yates99]). This does not appear to be true in large 608 mesh networks under realistic provisioning scenarios, however 610 Impairments And Other Constraints November 2001 611 On Optical Layer Routing 613 ([Strand01b]). Instead significantly better results are achieved 614 if wavelength and route are chosen simultaneously. This approach 615 would however also have a significant affect on OSPF. 617 4.7 Implications For Routing and Control Plane Design 619 If distributed routing is desired, Aadditional state information 620 will be required by the routing to explicitly deal with the 621 impairments described in Sections 4.2 - 4.4: 623 - Additional link-specific state information will be required by the 624 routing algorithm for each type of impairment that has the 625 potential of being limiting for some routes. The link-dependent 626 information identified above for PMD is link-PMD-square which is 627 the square of the total PMD on a link. For ASE the link-dependent 628 information identified is link-noise which is the total noise on a 629 link. Other link-dependent information includes link-span-length 630 which is the total number of spans on a link, link-crosstalk or 631 OADM-OXC-number which is the total crosstalk or the number of 632 OADM/OXC nodes on a link, respectively, and OADM-OXCfilter-number 633 which is the number of OADM/OXCnarrow filters on a link. 635 . In addition to the link-specific information, bounds on each of 636 the impairments need to be quantified. Since these bounds are 637 determined by the system designer's impairment allocations, these 638 will be system dependent. For PMD, the constraint is that the sum 639 of the link-PMD-square of all links on the transparent segment is 640 less than the square of (a/B) where B is the bit rate. Hence, the 641 required information is the parameter "a". For ASE, the constraint 642 is that the sum of the link-noise of all links is no larger than 643 P/SNRmin. Thus, the information needed include the launch power P 644 and OSNR requirement SNRmin. The minimum acceptable OSNR, in 645 turn, depends on the strength of the FEC being used and the 646 margins reserved for other types of impairments. Other bounds 647 include the maximum span length of the transmission system, the 648 maximum path crosstalk andor the maximum number of OADM/OXC 649 nodes,and the maximum number of narrow filters, both of whichall 650 are bit rate dependent. In single-vendor �islands� some of these 651 parameters may be available in a local or EMS database and would 652 not need to be advertised 654 . It is likely that the physical layer parameters do not change 655 value rapidly and could be stored in some database; however these 656 are physical layer parameters that today are frequently not known 657 at the granularity required. If the ingress node of a lightpath 658 does path selection these parameters would need to be available at 659 this node. 661 Impairments And Other Constraints November 2001 662 On Optical Layer Routing 664 . The specific constraints required in a given situation will depend 665 on the design and engineering of the domain of transparency; for 666 example it will be essential to know whether chromatic dispersion 667 has been dealt with on per-link basis, and whether the domain is 668 operating in a linear or nonlinear regime. 670 . As optical transport technology evolves, the set of constraints 671 that will need to be considered either explicitly or via a domain- 672 wide margin may change. The routing and control plane design 673 should therefore be as open as possible, allowing parameters to be 674 included as necessary. 676 . In the absence of wavelength conversion, the necessity of finding 677 a single wavelength that is available on all links introduces the 678 need to either advertise detailed information on wavelength 679 availability, which probably doesn't scale, or have some mechanism 680 for probing potential routes with or without crankback to 681 determine wavelength availability. Choosing the route first, and 682 then the wavelength, may not yield acceptable utilization levels 683 in mesh-type networks. 685 5. More Complex Networks 687 Mixing optical equipment in a single domain of transparency that has 688 not been explicitly designed to interwork is beyond the scope of 689 this document. This includes most multi-vendor all-optical networks. 691 An all-optical network composed of multiple domains of transparency 692 optically isolated from each other by OEO devices (transponders) is 693 more plausible. A network composed of both "opaque" (optically 694 isolated) OLXC's and one or more all-optical "islands" isolated by 695 transponders is of particular interest because this is most likely 696 how all-optical technologies (such as that described in Sec. 2) are 697 going to be introduced. (We use the term "island" in this discussion 698 rather than a term like "domain" or "area" because these terms are 699 associated with specific approaches like BGP or OSPF.) 701 We consider the complexities raised by these alternatives now. 703 The first requirement for routing in a multi-island network is that 704 the routing process needs to know the extent of each island. There 705 are several reasons for this: 706 . When entering or leaving an all-optical island, the regeneration 707 process cleans up the optical impairments discussed in Sec. 3. 708 . Each all-optical island may have its own bounds on each 709 impairment. 710 . The routing process needs to be sensitive to the costs associated 711 with "island-hopping". 713 Impairments And Other Constraints November 2001 714 On Optical Layer Routing 716 This last point needs elaboration. It is extremely important to 717 realize that, at least in the short to intermediate term, the 718 resources committed by a single routing decision can be very 719 significant: The equipment tied up by a single coast-to-coast OC-192 720 can easily have a first cost of $10**6, and the holding times on a 721 circuit once established is likely to be measured in months. 722 Carriers will expect the routing algorithms used to be sensitive to 723 these costs. Simplistic measures of cost such as the number of 724 "hops" are not likely to be acceptable. 726 Taking the case of an all-optical island consisting of an "ultra 727 long-haul" system like that in Fig. 32-1 embedded in an OEO network 728 of electrical fabric OLXC's as an example: It is likely that the ULH 729 system will be relatively expensive for short hops but relatively 730 economical for longer distances. It is therefore likely to be 731 deployed as a sort of "express backbone". In this scenario a carrier 732 is likely to expect the routing algorithm to balance OEO costs 733 against the additional costs associated with ULH technology and 734 route circuitously to make maximum use of the backbone where 735 appropriate. Note that the metrics used to do this must be 736 consistent throughout the routing domain if this expectation is to 737 be met. 739 The first-order implications for GMPLS seem to be: 740 . Information about island boundaries needs to be advertised. 741 . The routing algorithm needs to be sensitive to island transitions 742 and to the connectivity limitations and impairment constraints 743 particular to each island. 744 . The cost function used in routing must allow the balancing of 745 transponder costs, OXC and OADM costs, and line haul costs across 746 the entire routing domain. 748 Several distributed approaches to multi-island routing seem worth 749 investigating: 750 . Advertise the internal topology and constraints of each island 751 globally; let the ingress node compute an end-to-end strict 752 explicit route sensitive to all constraints and wavelength 753 availabilities. In this approach the routing algorithm used by the 754 ingress node must be able to deal with the details of routing 755 within each island. 756 . Have the EMS or control plane of each island determine and 757 advertise the connectivity between its boundary nodes together 758 with additional information such as costs and the bit rates and 759 formats supported. As the spare capacity situation changes, 760 updates would be advertised. In this approach impairment 761 constraints are handled within each island and impairment-related 762 parameters need not be advertised outside of the island. The 763 ingress node would then do a loose explicit route and leave the 764 routing and wavelength selection within each island to the island. 766 Impairments And Other Constraints November 2001 767 On Optical Layer Routing 769 . Have the ingress node send out probes or queries to nearby gateway 770 nodes or to an NMS to get routing guidance. 772 6. Diversity 774 6.1 Background On Diversity 776 "Diversity" is a relationship between lightpaths. Two lightpaths are 777 said to be diverse if they have no single point of failure. In 778 traditional telephony the dominant transport failure mode is a 779 failure in the interoffice plant, such as a fiber cut inflicted by a 780 backhoe. 782 Why is diversity a unique problem that needs to be considered for 783 optical networks? So far, data network operators have relied on 784 their private line providers to ensure diversity and so have not had 785 to deal directly with the problem. GMPLS makes the complexities 786 handled by the private line provisioning process, including 787 diversity, part of the common control plane and so visible to all. 789 To determine whether two lightpath routings are diverse it is 790 necessary to identify single points of failure in the interoffice 791 plant. To do so we will use the following terms: A fiber cable is a 792 uniform group of fibers contained in a sheath. An Optical Transport 793 System will occupy fibers in a sequence of fiber cables. Each fiber 794 cable will be placed in a sequence of conduits - buried honeycomb 795 structures through which fiber cables may be pulled - or buried in a 796 right of way (ROW). A ROW is land in which the network operator has 797 the right to install his conduit or fiber cable. It is worth noting 798 that for economic reasons, ROW�s are frequently obtained from 799 railroads, pipeline companies, or thruways. It is frequently the 800 case that several carriers may lease ROW from the same source; this 801 makes it common to have a number of carriers� fiber cables in close 802 proximity to each other. Similarly, in a metropolitan network, 803 several carriers might be leasing duct space in the same RBOC 804 conduit. There are also "carrier's carriers" - optical networks 805 which provide fibers to multiple carriers, all of whom could be 806 affected by a single failure in the "carrier's carrier" network. 808 In a typical intercity facility network there might be on the order 809 of 100 offices that are candidates for OLXC�s. To represent the 810 inter-office fiber network accurately a network with an order of 811 magnitude more nodes is required. In addition to Optical Amplifier 812 (OA) sites, these additional nodes include: 814 Impairments And Other Constraints November 2001 815 On Optical Layer Routing 817 - Places where fiber cables enter/leave a conduit or right of way; 818 - Locations where fiber cables cross; 819 - Locations where fiber splices are used to interchange fibers 820 between fiber cables. 822 An example of the first might be: 824 A B 825 A-------------B \ / 826 \ / 827 X-----Y 828 / \ 829 C-------------D / \ 830 C D 832 (a) Fiber Cable Topology (b) Right-Of-Way/Conduit Topology 834 Figure 6-1: Fiber Cable vs. ROW Topologies 836 Here the A-B fiber cable would be physically routed A-X-Y-B and the 837 C-D cable would be physically routed C-X-Y-D. This topology might 838 arise because of some physical bottleneck: X-Y might be the Lincoln 839 Tunnel, for example, or the Bay Bridge. 841 Fiber route crossing (the second case) is really a special case of 842 this, where X and Y coincide. In this case the crossing point may 843 not even be a manhole; the fiber routes might just be buried at 844 different depths. 846 Fiber splicing (the third case) often occurs when a major fiber 847 route passes near to a small office. To avoid the expense and 848 additional transmission loss only a small number of fibers are 849 spliced out of the major route into a smaller route going to the 850 small office. This might well occur in a manhole or hut. An 851 example is shown in Fig. 6-2(a), where A-X-B is the major route, X 852 the manhole, and C the smaller office. The actual fiber topology 853 would then look like Fig. 6-2(b), where there would typically be 854 many more A-B fibers than A-C or C-B fibers, and where A-C and C-B 855 might have different numbers of fibers. (One of the latter might 856 even be missing.) 858 Impairments And Other Constraints November 2001 859 On Optical Layer Routing 861 C C 862 | / \ 863 | / \ 864 | / \ 865 A------X------B A---------------B 867 (a) Fiber Cable Topology (b) Fiber Topology 869 Figure 6-2. Fiber Cable vs Fiber Topologies 871 The imminent deployment of ultra-long (>1000 km) Optical Transport 872 Systems introduces a further complexity: Two OTS's could interact a 873 number of times. To make up a hypothetical example: A New York - 874 Atlanta OTS and a Philadelphia - Orlando OTS might ride on the same 875 right of way for x miles in Maryland and then again for y miles in 876 Georgia. They might also cross at Raleigh or some other intermediate 877 node without sharing right of way. 879 Diversity is often equated to routing two lightpaths between a 880 single pair of points, or different pairs of points so that no 881 single route failure will disrupt them both. This is too simplistic, 882 for a number of reasons: 884 - A sophisticated client of an optical network will want to derive 885 diversity needs from his/her end customers' availability 886 requirements. These often lead to more complex diversity 887 requirements than simply providing diversity between two 888 lightpaths. For example, a common requirement is that no single 889 failure should isolate a node or nodes. If a node A has single 890 lightpaths to nodes B and C, this requires A-B and A-C to be 891 diverse. In real applications, a large data network with N 892 lightpaths between its routers might describe their needs in an 893 NxN matrix, where (i,j) defines whether lightpaths i and j must 894 be diverse. 896 - Two circuits that might be considered diverse for one 897 application might not be considered diverse for in another 898 situation. Diversity is usually thought of as a reaction to 899 interoffice route failures. High reliability applications may 900 require other types of failures to be taken into account. Some 901 examples: 902 o Office Outages: Although less frequent than route failures, 903 fires, power outages, and floods do occur. Many network 904 managers require that diverse routes have no (intermediate) 906 Impairments And Other Constraints November 2001 907 On Optical Layer Routing 909 nodes in common. In other cases an intermediate node might 910 be acceptable as long as there is power diversity within 911 the office. 912 o Shared Rings: Many applications are willing to allow 913 "diverse" circuits to share a SONET ring-protected link; 914 presumably they would allow the same for optical layer 915 rings. 916 o Disasters: Earthquakes and floods can cause failures over 917 an extended area. Defense Department circuits might need 918 to be routed with nuclear damage radii taken into account. 919 - Conversely, some networks may be willing to take somewhat larger 920 risks. Taking route failures as an example: Such a network 921 might be willing to consider two fiber cables in heavy duty 922 concrete conduit as having a low enough chance of simultaneous 923 failure to be considered "diverse". They might also be willing 924 to view two fiber cables buried on opposite sides of a railroad 925 track as being diverse because there is minimal danger of a 926 single backhoe disrupting them both even though a bad train 927 wreck might jeopardize them both. A network seeking N mutually 928 diverse paths from an office with less than N diverse ROW�s will 929 need to live with some level of compromise in the immediate 930 vicinity of the office. 932 These considerations strongly suggest that the routing algorithm 933 should be sensitive to the types of threat considered unacceptable 934 by the requester. Note that the impairment constraints described in 935 the previous section may eliminate some of the long circuitous 936 routes sometimes needed to provide diversity. This would make it 937 harder to find many diverse paths through an all-optical network 938 than an opaque one. 940 [Chaudhuri00] introduced the term "Shared Risk Link Group" (SRLG) to 941 describe the relationship between two non-diverse links. The above 942 discussion suggests that an SRLG should be characterized by 2 943 parameters: 944 - Type of Compromise: Examples would be shared fiber cable, shared 945 conduit, shared ROW, shared optical ring, shared office without 946 power sharing, etc.) 947 - Extent of Compromise: For compromised outside plant, this would 948 be the length of the sharing. 949 A CSPF algorithm could then penalize a diversity compromise by an 950 amount dependent on these two parameters. 952 Impairments And Other Constraints November 2001 953 On Optical Layer Routing 955 Two links could be related by many SRLG's (AT&T's experience 956 indicates that a link may belong to over 100 SRLG's, each 957 corresponding to a separate fiber group. Each SRLG might relate a 958 single link to many other links. For the optical layer, similar 959 situations can be expected where a link is an ultra-long OTS). 961 The mapping between links and different types of SRLG�s is in 962 general defined by network operators based on the definition of each 963 SRLG type. Since SRLG information is not yet ready to be 964 discoverable by a network element and does not change dynamically, 965 it need not be advertised with other resource availability 966 information by network elements. It could be configured in some 967 central database and be distributed to or retrieved by the nodes, or 968 advertised by network elements at the topology discovery stage. 970 6.2 Implications For Routing 971 Dealing with diversity is an unavoidable requirement for routing in 972 the optical layer. It requires dealing with constraints in the 973 routing process but most importantly requires additional state 974 information � the SRLG relationships and also the routings of any 975 existing circuits from the new circuit is to be diverse � to be 976 available to the routing process. 978 At present SRLG information cannot be self-discovered. Indeed, in a 979 large network it is very difficult to maintain accurate SRLG 980 information. The problem becomes particularly daunting whenever 981 multiple administrative domains are involved, for instance after the 982 acquisition of one network by another, because there normally is a 983 likelihood that there are diversity violations between the domains. 984 It is very unlikely that diversity relationships between carriers 985 will be known any time in the near future. 987 Considerable variation in what different customers will mean by 988 acceptable diversity should be anticipated. Consequently we suggest 989 that an SRLG should be defined as follows: (i) It is a relationship 990 between two or more links, and (ii) it is characterized by two 991 parameters, the type of compromise (shared conduit, shared ROW, 992 shared optical ring, etc.) and the extent of the compromise (e.g., 993 the number of miles over which the compromise persisted). This will 994 allow the SRLG�s appropriate to a particular routing request to be 995 easily identified. 997 7. Security Considerations 999 The solution developed to address the requirements defined in this 1000 document must address security aspects. 1002 Impairments And Other Constraints November 2001 1003 On Optical Layer Routing 1005 8. Acknowledgments 1007 This document has benefited from discussions with Michael Eiselt, 1008 Jonathan Lang, Mark Shtaif, Jennifer Yates, Dongmei Wang, Guangzhi 1009 Li, Robert Doverspike, Albert Greenberg, Jim Maloney, John Jacob, 1010 Katie Hall, Diego Caviglia, D. Papadimitriou, O. Audouin, J. P. 1011 Faure, L. Noirie, and with our OIF colleagues. 1013 References: 1015 [ABB01] Ashwood-Smith, P., et. al., "Generalized MPLS Signaling 1016 Functional Description,_ Internet draft, draft-ietf- generalized- 1017 mpls-signaling-00.txt, work in progress, March 2001. 1019 [Ashwood00] Ashwood-Smith, P. et al., "MPLS Optical/Switching 1020 Signaling Functional Description", Work in Progress, draft-ashwood- 1021 generalized-mpls-signaling-00.txt. 1023 [Awduche99] Awduche, D. O., Rekhter, Y., Drake, J., and Coltun, R., 1024 "Multi-Protocol Lambda Switching: Combining MPLS Traffic Engineering 1025 Control With Optical Crossconnects", Work in Progress, draft- 1026 awduche-mpls-te-optical-01.txt. 1028 [Bra96] Bradner, S., "The Internet Standards Process -- Revision 3," 1029 BCP 9, RFC 2026, October 1996. 1031 [CBD00] Ceuppens, L., Blumenthal, D., Drake, J., Chrostowski, J., 1032 Edwards, W., "Performance Monitoring in Photonic Networks in 1033 Support of MPL(ambda)S", Internet draft, work in progress, March 1034 2000. 1036 [Chaudhuri00] Chaudhuri, S., Hjalmtysson, G., and Yates, J., 1037 "Control of Lightpaths in an Optical Network", Work in Progress, 1038 draft-chaudhuri-ip-olxc-control-00.txt. 1040 [Doverspike00] Doverspike, R. and Yates, J., "Challenges For MPLS in 1041 Optical Network Restoration", IEEE Communication Magazine, February, 1042 2001. 1044 [Gerstel 2000] O. Gorstel, "Optical Layer Signaling: How Much Is 1045 Really Needed?", IEEE Communications Magazine, vol. 38 no. 10, Oct. 1046 2000, pp. 154-160 1048 Impairments And Other Constraints November 2001 1049 On Optical Layer Routing 1051 [Goldstein94] Goldstein, E. L., Eskildsen, L., and Elrefaie, A. F., 1052 Performance Implications of Component Crosstalk in Transparent 1053 Lightwave Networks", IEEE Photonics Technology Letters, Vol.6, No.5, 1054 May 1994. 1056 [ITU] ITU-T Doc. G.663, Optical Fibers and Amplifiers, Section 1057 II.4.1.2. 1059 [Kaminow97] Kaminow, I. P. and Koch, T. L., editors, Optical Fiber 1060 Telecommunications IIIA, Academic Press, 1997. 1062 KRB01a] Kompella, K., et.al., "IS-IS extensions in support of 1063 Generalized MPLS," Internet Draft, draft-ietf-gmpls- extensions- 1064 01.txt, work in progress, 2001. 1066 [KRB01b] Kompella, K., et. al., "OSPF extensions in support of 1067 Generalized MPLS," Internet draft, draft-ospf-generalized- mpls- 1068 00.txt, work in progress, March 2001. 1070 [Moy98] Moy, John T., OSPF: Anatomy of an Internet Routing Protocol, 1071 Addison-Wesley, 1998. 1073 [Ramaswami98] Ramaswami, R. and Sivarajan, K. N., Optical Networks: 1074 A Practical Perspective, Morgan Kaufmann Publishers, 1998. 1076 [Strand01] J. Strand, A. Chiu, and R. Tkach, �Issues for Routing in 1077 the Optical Layer�, IEEE Communications Magazine, Feb. 2001, vol. 39 1078 No. 2, pp. 81-88; also see "Unique Features and Requirements for The 1079 Optical Layer Control Plane", Internet Draft, draft-chiu-strand- 1080 unique-olcp-01.txt, work in progress, November 2000. 1082 [Strand01b] J. Strand, R. Doverspike, and G. Li, �Importance of 1083 Wavelength Conversion In An Optical Network�, Optical Networks 1084 Magazine, accepted for publication. Available from the author. 1086 [Tkach98] Tkach, R., Goldstein, E., Nagel, J., and Strand, J., 1087 "Fundamental Limits of Optical Transparency", Optical Fiber 1088 Communication Conf., Feb. 1998, pp. 161-162. 1090 [Yates99] Yates, J. M., Rumsewicz, M. P. and Lacey, J. P. R., 1091 "Wavelength Converters in Dynamically-Reconfigurable WDM Networks", 1092 IEEE Communications Surveys, 2Q1999 (online at 1093 www.comsoc.org/pubs/surveys/2q99issue/yates.html). 1095 Impairments And Other Constraints November 2001 1096 On Optical Layer Routing 1098 Authors' Addresses: 1100 Ayan Banerjee 1101 Calient Networks 1102 5853 Rue Ferrari 1103 San Jose, CA 95138 1104 Email: abanerjee@calient.net 1106 Dan Blumenthal 1107 Calient Networks 1108 5853 Rue Ferrari 1109 San Jose, CA 95138 1110 Email: dblumenthal@calient.net 1112 Angela Chiu 1113 Celion Networks 1114 1 Shiela Dr., Suite 2 1115 Tinton Falls, NJ 07724 1116 Phone:(732) 747-9987 1117 Email: angela.chiu@celion.com 1119 John Drake 1120 Calient Networks 1121 5853 Rue Ferrari 1122 San Jose, CA 95138 1123 Email: jdrake@calient.net 1125 Andre Fredette 1126 PhotonEx Corporation 1127 200 Metrowest Technology Dr. 1128 Maynard, MA 01754 1129 Email: fredette@photonex.com 1131 Nan Froberg 1132 PhotonEx Corporation 1133 200 Metrowest Technology Dr. 1134 Maynard, MA 01754 1135 Email: nfroberg@photonex.com 1137 James V. Luciani 1138 900 Chelmsford St. 1139 Lowell, MA 01851 1140 +1 978 275 3182 1141 james_luciani@mindspring.com 1143 John Strand 1144 AT&T Labs 1145 200 Laurel Ave., Rm A5-1D06 1146 Middletown, NJ 07748 1148 Impairments And Other Constraints November 2001 1149 On Optical Layer Routing 1151 Phone:(732) 420-9036 1152 Email: jls@research.att.com 1154 Robert Tkach 1155 Celion Networks 1156 1 Shiela Dr., Suite 2 1157 Tinton Falls, NJ 07724 1158 Phone:(732) 747-9909 1159 Email: bob.tkach@celion.com