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STUDENT DIGITAL NEWSLETTER ALAGAPPA INSTITUTIONS |
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Adam Helms, MD
Give forwarding tables for P skin care quotes eurax 20 gm cheap, Q and R assuming they connect to each other and to each of their own customers acne jeans cheap eurax 20gm with mastercard. Now suppose A switches from provider P to provider Q skin care equipment wholesale cheap 20gm eurax visa, and takes its address block with it acne disease cheap eurax 20gm with visa. Do not assume P is willing to forward traffic from R destined for its ex-customer A acne between eyebrows generic 20 gm eurax visa. This time acne xyl buy eurax 20gm fast delivery, P and R do not connect directly; they route traffic to one another via Q. In addition, customer B is multihomed and has a secondary connection to provider R; customer D is also multihomed and has a secondary connection to provider P. R and P use these secondary connections to send to B and D respectively; however, these secondary connections are used only within R and P respectively. Assuming all Megacorp traffic must enter and exit in Chicago, what is the route of traffic to and from the San Diego office to a client also in San Diego? Suppose Megacorp gives up and gets a separate geographical prefix for each office, eg 12. However, Megacorp now wants to be sure that interoffice traffic stays on its internal network. In 13 Routing-Update Algorithms, we considered interior routing-update protocols: those in which all the routers involved are under common management. That management can then dictate the routing-update protocol to be used, and also the rules for assigning per-link costs. For both Distance-Vector and Link State methods, the per-link cost played an essential role: by trying to minimize the cost, we were assured that no routing loops would be present in a stable network (13. But now consider the problem of exterior routing; that is, of choosing among routes that have been offered by independent neighboring organizations. The routing-update protocol has to be universal, so any pair of neighboring organizations will be able to communicate. And link costs are difficult to use, because there are multiple incompatible ways of measuring link cost. If A wanted to use one of the interior routing-update protocols to choose its path to D, it would face several purely technical problems. Second, what if B measures its path costs using the hopcount metric, while C assigns costs based on bandwidth, or congestion, or pecuniary considerations? But apples-and-oranges comparison of different metrics would completely undermine the intended use of those metrics to influence the selection of which links should carry the most traffic. Sharing link-cost information without a common administrative policy to set those costs does not, in practical terms, make sense. But A also faces a larger issue: to reach D it must rely on having its traffic carried by an outsider either B or C. Outsiders are likely not inclined to offer this service without some form of compensation, either monetary or through reciprocal exchange. If A reaches an understanding with B on this matter of traffic carriage, then A does not want its traffic routed via C even if that latter route is of lower technical cost. The Internet Draft draft-lapukhov-bgp-ecmpconsiderations-01 addresses this further. As an example of this, consider the network below, in which we consider Autonomous Systems also to be destinations. A large almost-leaf site might also carry a small amount of transit traffic for one particular related (but autonomous! To choose the one route that we will use, it may combine a mixture of optimization rules and policy rules. Import filtering can also be done in the best-path-selection stage, by having the best-path-selection process ignore routes from selected neighbors. The next stage is best-path selection, to pick the preferred routes from among all those just imported. Very commonly, larger sites will have preferences based on contractual arrangements with particular neighbors. That example, however, demonstrates instability; domains are encouraged to set their rules in accordance with some standard principles, below, to avoid this. While this superficially resembles a shortest-path algorithm, the real work should have been done in administratively assigning local preference values. The final significant step of the route-selection phase is to apply the Multi-Exit-Discriminator value, 15. If this situation is detected, it would probably be addressed in the local-preferences phase. These routes are then communicated to the actual routers, which are often different devices. The graph is flat from 2001 to 2002, reflecting the aftereffects of the so-called dot-com bubble. Overall the increase with time is roughly quadratic, but in the last decade has been closer to linear. The graph does not entirely represent growth of the Internet; it also represents fragmentation. In recent years, only smaller address blocks have been available, and so many sites and providers have cobbled together their Internet presence from multiple such blocks, where they might have preferred a single block. This should either be R1 or should lead to R1, which will then route the traffic properly (not necessarily on to B1). Routes can have multiple tags corresponding to membership in multiple communities. A customer would have to find out from the provider what communities the provider defines, and what their numeric codes are. For autonomous systems with multiple interconnection points, the Multi-Exit Discriminator above also may play a large role. Two common options A and B might agree to regarding link1 are no-transit and backup. One way to automate this is for A and B to view their default-route path (eg to 0. A might then be able to keep tweaking this cost until the inbound loads are comparable, but there is no guarantee (or even likelihood) this will be stable. B avoids this problem by not advertising to C that it can reach A and D, and similarly with C. If B advertises to A that it can reach D, then A may accept that route, and send all its D-bound traffic via B, with C not involved at all. If B and C both advertise to A that they can reach D, then A has a choice, which it will make via its best-path-selection rules. But in such a case A will want to be sure that it does not end up paying full price to both B and C to carry its traffic while using only one of them. It is quite possible that B advertises to A that it can reach D, but does not advertise to D that it can reach A. As we have seen, B advertises to A that it can reach D only if A has paid for this privilege; perhaps D prefers to do business with C rather than with B. In that case, A-to-D traffic would travel via B, while D-to-A traffic would travel via C. If autonomous systems C and P have a customer-to-provider relationship, with C as the customer and P as the provider, then C is paying P to carry some or all of its traffic to the "outside world". P may not carry all such traffic, because C may also be a customer of another provider P1. C may also have its own sub-customers, such as C1: P P C In offering itself as a provider, P will export all the routes it has, from all sources, to C, in effect telling C "this is what I can reach". If C has no other providers it might accept these routes in the form of a single default-route entry pointing to P; if C has another provider P1 then it might accept some routes from P and some from P1. If C has customers of its own, such as C1, then it will also export those routes to P. To summarize, a provider does export its non-customer routes to its customer, but a customer generally does not export its non-customer routes to its providers. A nominal customer might, for example, agree to provide transit service for some set of destinations, in exchange for a lower-priced rate for the handling of its other traffic. Nonetheless, the rule is largely accurate, and provides a helpful starting point to understanding customer-provider relationships. Now let us consider a peer-to-peer relationship, which is a connection between two transit providers that have agreed to exchange all their customer traffic with each other; thus carrying transit traffic for one another. Often the idea is for the interconnection to be seen as equally valuable by both parties (eg because the parties exchange comparable volumes of traffic); in such a case the relationship would likely be "settlement-free", that is, involving no monetary exchange. If, however, the volume flow is significantly asymmetric then compensation can certainly be negotiated, making the relationship more like customer-to-provider. Peers do not, however, generally export their non-customer routes, in either direction. If it were to do so, then P1 would carry non-customer transit traffic from P2 to P3. The so-called tier-1 providers are those that are not customers of anyone; these represent the top-level "backbone" providers. Finally, some autonomous system relationships that do not fit the customer-to-provider or peer-to-peer patterns can be characterized as sibling-to-sibling. Siblings may also be nominal competitors who intend to use their mutual link as a cooperative backup, as in 15. Siblings typically export everything to one another both customer and non-customer routes and thus do potentially use their connection for transit traffic in both directions (although they may rank routes through one another at low preference, so as to use the shared link only when nothing else is available). We can summarize the three kinds of relationships in terms of how they export non-customer routes: · in peer-to-peer relationships, non-customer routes are not exported in either direction. This may be fortunate, as sibling relationships, with universal and bidirectional route export, tend to introduce the greatest complexity. One problematic sibling case is the following, in which P1 and P2 are providers for C1 and C2, respectively, and C1 and C2 are siblings: P1 P2 C1 siblings C2 Suppose P1 exports to C1 a route to destination D. If C2 treats this as a customer route, it will export it to P2, in which case C1 and C2 are now providing transit service to traffic from P2 bound for D. Sibling relationships can be tamed considerably, however, if we adopt a requirement that collections of linked siblings act as a unit, keeping track of the original non-sibling source (that is, customer, provider or peer) of each route. Let us say that autonomous systems S and S1 are in the same sibling family if there 15. We can then define the following property: Selective Export Property: A sibling family satisfies this property if, whenever one member of the family learns of a route from a provider (respectively peer or customer) then all other members of the family treat the route as a provider (respectively peer or customer) route when deciding whether to export. In other words, in the situation diagrammed above, in which C1 has learned of a route to D from its provider P1, C2 will also treat this route as a non-customer route and will not export it to P2. We can also specialize the relationships to a particular set of destinations, or even to an individual destination; for example, autonomous systems C and P might be said to have a customer-to-provider relationship for destination D if C learned its route to D from a non-customer, does not export this route to P, and P does export to C its own route to D. There is a supposition here that the regional provider has multiple connections, and has contracted with that particular transit backbone only for certain routes. Links to the left of the peer-to-peer link (that is, closer to A) are either customerСprovider links or siblingСsibling links; that is, they are non-downwards. To the right of the peer-to-peer link, there are only providerСcustomer or siblingСsibling links; that is, these are non-upwards. Intuitively, autonomous systems on the right (non-upwards) part of the path export the route to D as a customer route. Autonomous systems on the left (non-downwards) part of the path export the route from provider to customer. The no-valley theorem can be seen as an illustration of the power of the restrictions built into the customerto-provider and peer-to-peer export rules. Choose the largest i for which this arrangement appears, and let k be the position of the first subsequent upward link, so that · Ai to Ai+1 is provider-to-customer · Aj to Aj+1 is sibling-to-sibling for i<j<k-1 · Ak-1 to Ak is customer-to-provider. Then the route to D was acquired by Ak-1 from its provider Ak, and so is a provider route. It therefore cannot export this non-customer route to different provider Ai, a contradiction. If the hypotheses of the no-valley theorem hold only for routes involving a particular destination or set of destinations, then the theorem is still true for those routes. More complex rules exist that allow for cases when the local preference values can be equal; one such rule states that strict inequality is only required when r2 is a provider route. Other straightforward rules handle the case of sibling relationships, eg by requiring that siblings have local preference rules consistent with the use of their shared connection only for backup. Because they do export this route to one another, they are siblings in the sense of the previous section. While Q could thus block access to D, it would not be able to make use of those addresses. From the definition of the customer-provider relationship, Q will only advertise to P its "customer routes": its own routes, and the customer routes of its own customers. Now suppose R is a customer of Q that advertises address block B to Q, and Q in turn advertises B to P: P РQ R-B. This time, however, for complete validation P will also need evidence that R is a customer of Q. This second verification path validation is beyond the scope of origin validation. However, if this is not established, Q might potentially be attempting to block access to B, at least partially, by claiming a route to 15. There is one additional, though less malicious, common error: accidentally and mistakenly offering transit service. P may now route all its traffic to D via Q, which the latter may be ill-prepared to handle.
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The ordinary and customary meaning skin care qualifications order eurax 20gm with amex, to a person skilled in the art acne laser 20gm eurax with amex, of the term "hardened acne quiz generic 20 gm eurax free shipping," refers acne facial purchase 20gm eurax free shipping, at the earliest acne quick treatment discount 20 gm eurax with mastercard, to the point in time that the cement reaches final set acne yellow sunglasses buy cheap eurax 20gm line. It is at this juncture that the cement is first classified as "hardened" by persons skilled in the art. Indeed, only after cement has reached final set can it reasonably be strength-tested - it would be impossible to attempt to fracture a cube-shaped piece of cement if the cement mix still has a slump. Once the cement reaches final set, it may become still harder and stronger, but the point in time of final set is when it becomes "hardened. The question raised by the parties is whether the claimed increase in compressive strength must appear at every time of measurement thereafter, or only at some point(s) thereafter. Put differently, does the patent cover only the admixture shown in scenario four, below, where the compressive strength of the concrete with the admixture is superior at all times after hardening, or does it also cover the admixtures shown in scenarios five and six, where compressive strength is superior only early or late in the life of the hardened concrete? The plain language does not suggest that the cement will be stronger for a while, but then only equally strong as a cement without the admixture; nor does the plain language suggest that the cement will only become stronger some time long after it has hardened. Rather, a layman would understand the ordinary and customary meaning of the claim language to assert that, if you compare two cement mixes after they have hardened - one with and one without the admixture - the one with the admixture would be stronger. Furthermore, a layman would understand that the strength of the two cement mixes must be measured at similar points in time - the patent is not claiming that a 5-day-old cement mix with the additive will be stronger than a 25-day-old plain cement mix. Rather, if you compare two hardened cement mixes of equal age, the one containing the admixture will have higher compressive strength. The "background of the invention" section of the patent notes that the "invention relates to admixture compositions for incorporation into hydraulic cement mixes. As noted earlier, the specification lists 72 examples of cement mixes to which were added various admixture formulations. These Tables generally show that the 1-day, 3-day, 7-day, and 28-day compressive strength measurements for cement mixes to which were added the patented three-component admixtures are stronger than the same mixes without the admixture. Thus, for example, Table X, mix 29 shows that the admixture increased 1-day compressive strength by 45% and 3-day compressive strength by 12%. Some of the Tables present compressive strength data for only the 1-day time period. While the scope of the claims should not be limited to the preferred embodiment or specific examples, the claims should be read in view of their specification. The Burge patent is directed at a cement admixture with the "significant object" of providing "early strength. The specification then makes special mention of the fact that the "rapid development of early strength, that is to say, 9 to 15 hours after preparation, can be clearly recognized. In other words, the Burge patent uses the term "early strength" to mean the first two days after final set; after this time, the compressive strength is no longer referred to as "early," so that early strength does not mean, say, the first 28 days after final set. In contrast, the Rosskopf patent (which, itself, cites Burge) is directed at increasing "the compressive strength" of cement mixes, not just the "early" compressive strength. Further, the Rosskopf patent specification makes special mention of "the early (one day) compressive strength" data. Finally, the expert testimony at the Markman hearing made clear that: (1) the compressive strength of concrete normally increases with time over the first 28 days, and then levels off; and (2) measurements of compressive strength are commonly measured at the end of 16 hours, and then at the end of 1, 3, 7, 28, 60, and 365 days. This is expected to give a clinical advantage for (-)-omeprazole, since the number of patients healed from the acid-related disease is expected to be higher, and healing is also expected to be achieved within a shorter time frame. Thus, the Court finds that one skilled in the art would understand the term "faster" in the disputed phrase to be referring to a comparison of (-)-omeprazole to omeprazole. Accelerated Release the next term at issue is the preamble term "accelerated release. As an initial matter, it argues that construction of the preamble claim term accelerated release is unnecessary because it should not be read to limit the claims as it relates to only the purpose of the patent rather than a structural limitation. Alternatively, it asserts that accelerated release means that the rate of release of the blowing agent occurs more quickly than what the rate of release would be without channels perforating the foam. As previously explained, a preamble is a claim limitation if it is necessary to provide meaning to the claimed invention. Conversely, it is not a limitation if the claimed invention is complete and the preamble only states a purpose or intended use of the invention. Here, the preamble states as follows: "A method for providing accelerated release of a blowing agent from an extruded plastic foam. Further, in light of the specification and prosecution histories, it is plain that the claims require accelerated release. Interpretation begins with the words in a claim, which should generally be ascribed their ordinary and customary meaning. The ordinary meaning of the word accelerated is to increase over what would otherwise be the case. In addition to examining ordinary meaning, "it is always necessary to review the specification to determine whether the inventor has used any terms in a manner inconsistent with their ordinary meaning. The specification acts as a dictionary when it expressly defines terms used in the claims or when it defines terms by implication. In the case at bar, the specification defines the term to mean that "the blowing agent permeates from the foam into channels to accelerate the release of blowing agent from what the rate would be without channels. Nor is there any rate or quantity of release of blowing agent from the foam after perforation is set forth, other than a rate a release greater than a foam with no channels. Accordingly, the court finds that it would be improper to limit the claim language to sulfur-based systems. Because the meaning of this term is likely outside the understanding of the prospective jurors, the parties should include a definition of this term in the jury materials. The court finds that the definition proposed by Adco is suitable: "a package that includes a compound to cross-link the polymer chains of the rubbery polymer, and for reducing the time needed to complete such cross-linking. As evidence of this point, Baxter points to the inability of the Patent Office examiner, inventor, prosecuting patent attorney, and experts to define this claim term. Baxter principally relies on two cases from the Federal Circuit Court of Appeals, and one case from the Eastern District of Texas, as the legal foundation for its argument. Affirming the district court, the Federal Circuit stated that "the scope of claim language cannot depend solely on the unrestrained, subjective opinion of a particular individual purportedly practicing the invention. Some objective standard must be provided in order to allow the public to determine the scope of the claimed invention. The court determined that any possible construction of "fragile gel" would include subjective terms that render the claims indefinite. The court opined that neither the specification nor any other evidence provided an objective standard for determining the scope of the amorphous terms. As such, Talecris argues that it is not necessary for Claim 1 to recite numeric limits of acceptability based on a particular test for a particular product as it would unfairly and unnecessarily limit Claim 1. Talecris distinguishes Datamize and Halliburton from this case by pointing out that those cases involved the purely subjective terms "aesthetically pleasing" and "fragile gel," respectively. In both instances, the claim terms were judged as lacking an "objective anchor" that identified the bounds of the claims for one skilled in the art. Here, the court is persuaded that "acceptable level suitable for intravenous administration" is not purely subjective, and therefore not analogous to Datamize and Halliburton. To the contrary, the record reflects that the phrase has meaning to those of ordinary skill in the art, albeit the determination of that meaning may depend on a number of variables, and the ultimate determination of acceptability may be temporally distant from the time in which the inventive steps of the claim are performed. What the Federal Circuit observed in SmithKline, the court finds especially applicable here: "[b]readth is not indefiniteness. Applying the legal principles discussed above, the court finds no issue of indefiniteness with these claim terms. The plain and ordinary meaning of these claim terms - 202 - Jump to: A B C D E F G H I J K L M N O P Q R ST UVW XY Z are sufficiently definite such that one skilled in the art would understand the bounds of the claim when read in light of the specification. Plaintiff argues a person of ordinary skill in the art would understand the term "acetylation" to have the same meaning, with simply a different tense, as the term "acetylated," which is used in the specification. Defendants argue that "4-amino-1-hydroxybutane-1, 1-biphosphonic acid" in claim 1 should be construed to encompass only the free acid form. Defendants maintain that the specification distinguishes between salts and acids, therefore strengthening their position that claim 1 refers only to a single acid compound. For example, Defendants point out that Table 6 distinguishes between formulations containing "4-amino-1-hydroxybutan-1, 1-biphosphonic acid" and those containing "4amino-1-hydroxybutan-1, 1-biphosphonic acid, sodium salt. Additionally, Defendants direct the Court to the examples in the patent specification. For example, Defendants point out that examples 1 through 4 describe the manufacture of acids, whereas, the manufacture of salts is described separately in examples 5 through 8. According to Defendants, the patentee disclaimed the coverage of salts through claim amendments made during the prosecution history. Finally, in support of their contention that acid and sodium are not used interchangeably, Defendants point to affidavits of Merck scientists, Dr. Rodan, which describe differences between the effects of alendronic acid and alendronate sodium. Additionally, in support of its position, Merck directs the Court to Table 6 of the specification. Table 6 lists typical pharmaceutical formulations containing amino-butan-diphosphonic acid. The first entry under the heading "Opercolated Capsules" lists 4-amino-1-hydroxybutan-1, 1-biphosphonic acid, sodium salt as the first referenced acid. Thus, Merck contends, the specification clearly and implicitly defines "4-amino-1-hydroxybutane- - 203 - Jump to: A B C D E F G H I J K L M N O P Q R ST UVW XY Z 1, 1-biphosphonic acid" as encompassing its sodium salt forms. In addition, Merck again points to Table 6 of the specification, where two other formulations are disclosed which are effervescent granules and formulations suitable for injection. Merck contends that although these formulations are listed as containing 4-amino-1-hydroxybutan-1, 1-biphosphonic acid, both formulations are a sodium salt solution. Tables 7 and 8 depict results obtained by administering different bisphosphonates to rats. However, the text does not specify whether the free acid or sodium salt forms were administered. Merck argues that this demonstrates that those of skill in the art recognize that the administration of free acid versus sodium salt is immaterial to the compounds efficacy in inhibiting bone reabsorption. In Novo Nordisk, the Federal Circuit, bypassing an ordinary meaning analysis, determined that a term was implicitly disclosed in the specification as encompassing both forms of human growth hormone. Merck contends that Novo Nordisk is highly analogous to the case at bar and urges the Court to adopt its reasoning in reference to its interpretation of claim 1. Finally, Merck maintains that the amendments made during the prosecution of the patent are irrelevant in this case because the first claims that were submitted were composition claims, whereas, the approved claim was a method of use claim and therefore the amendments did not result in a narrowing of coverage. Rather, "the claim language itself is of paramount importance," and therefore the specification and prosecution history need only be consulted to give the necessary context to the claim language. Additionally, a court may consider extrinsic evidence, including expert and inventor testimony, dictionaries and learned treatises in order to assist it in construing the true meaning of the language used in the Patent. Thus, the specification and other evidence may assist in determining the meaning of a claim, but it may not be used to impose limitations on a claim not found in the words of the claim itself. The phrase "4-amino-1-hydroxybutane-1, 1biphosphonic acid" is not explicitly defined in the patent. If claim 1 were still a composition claim the chemistry section would be highly instructive. Therefore, pharmacological effects described in the biological section are more pertinent to the claim. Recker testified, there are no distinctions between the free acid and sodium salt forms in reference to the measurement of toxicity and biological effects. And so I-even though he said salt here, in my view and in the view of an ordinary clinical scientist, he would be referring to a sodium salt as well, particularly when you look at the context of this whole section of the-Patent. In Table 6, under the section titled Opercolated Capsules, 4-amino-hydroxybutane-1, 1-biphosphonic acid, sodium is listed. Hanzlik testified that Tables 7 and 8, which depict results obtained by administering different bisphosphonates to rats, would be useless to a scientist because they do not list which form was used i. In addition, the Court finds this issue to be analogous to the issue before the Federal Circuit in Novo Nordisk v. The Federal Circuit held that the term was implicitly defined in the specification and encompassed both forms. Similarly, in the case at bar the specification, especially in Tables 7 and 8, implicitly defines "4-amino-1-hydroxybutane-1, 1-biphosphonic acid" to encompass both the sodium salt and free acid forms. Under the doctrine of prosecution history estoppel, the burden is on the patentee to prove that he did not surrender an equivalent during the prosecution of the patent. However, the analysis is different when the court is construing the claim language. The Federal Circuit has recognized the distinction in the analysis of prosecution history in claim construction and under the doctrine of equivalents and has stated: Claim interpretation in view of the prosecution is a preliminary step in determining literal infringement, while prosecution history estoppel applies as a limitation on the range of equivalents if, after the claims have been properly interpreted, no literal infringement has been found. The limit on the range of equivalents that may be accorded a claim due to prosecution history estoppel is simply irrelevant to the interpretation of those claims. In order to prove that a patentee has disclaimed a meaning to a term during the prosecution history, for purposes of claim construction, the challenger "must prove that the patentee made clear representations during the prosecution history which limit the scope of his claim. In this case, the Defendants can point to no specific evidence in the prosecution history that the patentee "made clear representations during the prosecution history which limit the scope of his claim. The Court finds that the fact that the patentee amended a composition claim to a method claim does not amount to a clear representation that the patentee limited the scope of his claim to the free acid form of 4-amino-1-hydroxybutane-1, 1-biphosphonic acid. Therefore for the aforementioned reasons, the Court construes the term 4-amino-1-hydroxybutane-1, 1-biphosphonic acid, to include both free acid and sodium salt forms. The court found that the claimed method whereby 4amino-1-hydroxybutane-1,1-biphosphonic acid is used to treat urolithiasis and bone reabsorption disorders (such as osteoporosis) is infringed by administration of the acid salt. The therapeutic agent of the claim is 4-amino-1-hydroxybutane1,1-biphosphonic acid, whose application is exemplified in the specification in formulations that include the salt and admixtures of the biphosphonic acid with a salt-forming material.
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Using two OpenFlow tables in Pox requires the loading of the so-called Nicira extensions (hence the "nx" in the module name here) acne gender equality discount eurax 20gm amex. The no-match actions for each table are set during the handling of the ConnectionUp events acne holes in face eurax 20gm online. The priority is here set to 1; the Pox default priority which will be used (implicitly) for later acne attack generic 20 gm eurax overnight delivery, more-specific flow-table entries is 32768 acne 6 days after ovulation buy 20 gm eurax otc. The first step is to arrange for table 0 to forward to the controller and to table 1 acne jensen boots sale generic eurax 20 gm otc. First comes the table 0 match on the packet source; if there is a match acne pustules eurax 20 gm for sale, then the source address has been seen by the controller, and so the packet is no longer forwarded to the controller (it is forwarded to table 1 only). Similarly, when h2 replies, s1 will have h2 added to its table 0, and then to its table 1. This example and the next are not part of the standard distributions of either Mininet or Pox. Unlike the other examples discussed here, these examples consist of Mininet code to set up a specific network topology and a corresponding Pox controller module that is written to work properly only with that topology. Most real networks evolve with time, making such a tight link between topology and controller impractical (though this may sometimes work well in datacenters). The purpose here, however, is to illustrate specific OpenFlow possibilities in a (relatively) simple setting. The number of trunk lines is K=2 by default, but can be changed by setting the variable K. We will prevent looping of broadcast traffic by never flooding along the s2s4 link. Only h1Сh2 flows will have their routing vary; flows h2Сh1 will always take the s1s3 path. It does not matter if the original connection is opened from h1 to h2 or from h2 to h1. After that, subsequent connections alternate in roundrobin fashion between s1s3 and s2s4. These objects will eventually contain information about what neighbor switch or host is reached by each switch port, but at this point none of that information is yet available. The next step is the handling of LinkEvent messages, which are initiated by the discovery module. At this point the controller knows the switches and port numbers at each end of the link. The controller then reports this to our multitrunkpox module via a LinkEvent event. Nothing is yet known about directly connected neighbor hosts though, as hosts have not yet sent any packets. Once hosts h1 and h2 exchange a pair of packets, the associated PacketIn events tell multitrunkpox what switch ports are connected to hosts. If we execute h1 ping h2, for example, then afterwards the information contained in the SwitchNode graph is complete. The switch s5 will see this packet and forward it to the controller, where the PacketIn handler will process it. If no path exists, we create one, first picking a trunk: trunkswitch = picktrunk(flow) path = findpath(flow, trunkswitch) the first path will be the Python list [h1, s5, s1, s3, s6, h2], where the switches are represented by SwitchNode objects. The supposedly final step is to call result = create path entries(flow, path) to create the forwarding rules for each switch. With the path as above, the SwitchNode objects know what port s5 should use to reach s1, etc. Very soon, s6 will know how to reach h2, and so create path entries will succeed. If we run everything, create two xterms on h1, and then create two ssh connections to h2, we can see the forwarding entries using ovs-ofctl. Let us run ovs-ofctl dump-flows s5 Restricting attention only to those flow entries with foo=tcp, we get (with a little sorting) cookie=0x0. The switch s5 reaches host h1 via port 3, which can be seen in the last two entries above, which correspond to the reverse h2Сh1 flows. It does, however, make it easier to view connections with ovs-ofctl before they disappear. A production implementation would need a finite timeout, and then would have to ensure that connections that were idle for longer than the timeout interval were properly re-established when they resumed sending. The multitrunk strategy presented here can be compared to Equal-Cost Multi-Path routing, 13. A flow-table trafficmatching entry can forward traffic to a so-called group instead of out via a port. The action of a select group is then to select one of a set of output actions (often on a round-robin basis) and apply that action to the packet. In principle, we could implement this at s5 to have successive packets sent to either s1 or s2 in round-robin fashion. In practice, Pox support for select groups appears to be insufficiently developed at the time of this writing (2017) to make this practical. The topology is somewhat the reverse of the previous example: there are now three hosts (N=3) at each end, and only one trunk line (K=1) (there are also no left- and right-hand entry/exit switches). This would normally lead to chaos, but the servers are not allowed to talk to one another, and the controller ensures that the servers are not even aware of one another. The node r is a router, not a switch, and so its four interfaces are assigned to separate subnets. The router r then connects to the only switch, s; the connection from s to the controller c is shown. If we run the programs and create xterm windows for h1, h2 and h3 and, from each, connect to 10. If we create three connections and then run ovs-ofctl dump-flows s and look at tcp entries with destination address 10. OpenFlow packet-forwarding rules are set up on demand, when traffic between two hosts is first seen. This module is compatible with topologies with loops, provided the spanning tree module is also loaded. We can see the spanning tree module in action if we create a Mininet network of four switches in a loop, as in exercise 9. We can also verify, with ovs-ofctl dump-flows, that the s1s2 link is not used at all, not even for s1s2 traffic. The l2 multi module, on the other hand, creates a full map of all network links (separate from the map created by the spanning tree module), and then calculates the best route between each pair of hosts. To calculate the routes, l2 multi uses the Floyd-Warshall algorithm (outlined below), which is a form of the distance-vector algorithm optimized for when a full network map is available. If we run the example above using the Mininet rectangle topology, we again find that the spanning tree has disabled flooding on the s1s2 link. However, if we have h1 ping h2, we see that h1Сh2 traffic does take the s1s2 link. If there is, we concatenate the i-to-k and k-to-j paths to create a new i-to-j path, which we will call P. Suppose we try to eliminate the source addresses from the l2 pairs implementation. Suppose we make the following change to the above strategy: · if a packet from ha to hb arrives at switch S, and S reports the packet to the controller, and the controller knows how to reach both ha and hb from S, then the controller installs forwarding rules into S for destinations ha and hb. Suppose we try to implement an Ethernet switch as follows: · the default switch action for an unmatched packet is to flood it and send it to the controller. In the future, S will not report packets with these destinations to the controller. Traffic is sent in the network below: 794 30 Mininet An Introduction to Computer Networks, Release 2. Show that, if the traffic is as follows: h1 pings h2, h3 pings h1, then all three switches learn where h3 is. Show that, if the traffic is as follows: h1 pings h2, h1 pings h3, then none of the switches learn where h3 is. Broadcast packets are always sent to the controller, as there is no destination match. Create a Mininet network with four hosts and four switches as below: h1 s1 s2 h2 h4 s4 s3 h3 the switches should use an external controller. However, some of the outcomes described may be of interest even to those not planning on designing their own simulations. An alternative to simulation, network emulation, involves running actual system networking software in a multi-node environment created through containerization or virtualization; we present this in 30 Mininet. An important advantage of simulation over emulation, however, is that as emulations get large and complex they also get bogged down, and it can be hard to distinguish results from artifacts. Because ns-3 is not backwards-compatible with ns-2 and the programming interface has changed considerably, we take the position that ns-3 is an entirely different package, though one likely someday to supercede ns-2 entirely. While there is a short introduction to ns-3 in this book (32 the ns-3 Network Simulator), its use is arguably quite a bit more complicated for beginners, and the particular simulation examples presented below are well-suited to ns-2. While ns-3 supports more complex and realistic modeling, and is the tool of choice for serious research, this added complexity comes at a price in terms of configuration and programming. The standard ns-2 tracefile format is also quite easy to work with using informal scripting. The simplest way to install ns-2 is probably with the "allinone" distribution, which does still require compiling but comes with a very simple install script. Perhaps the simplest approach for Windows users is to install a Linux virtual machine, and then install ns-2 under that. It is also possible to compile ns-2 under the Cygwin system; an older version of ns-2 may still be available as a Cygwin binary. To create an ns-2 simulation, we need to do the following (in addition to a modest amount of standard housekeeping). As the simulated applications generate packets for transmission, the ns-2 system calculates when these packets arrive and depart from each node, and generates simulated acknowledgment packets as appropriate. That is, if a node begins sending a simulated packet from node N1 to N2 at time T=1. N2 will then respond at that same instant, if a response is indicated, eg by enqueuing the packet or by forwarding it if the queue is empty. Advanced use of ns-2 (and ns-3) often involves the introduction of randomization; for example, we will in 31. While it is possible to seed the random-number generator so that different runs of the same experiment yield different outcomes, we will not do this here, so the randomnumber generator will always produce the same sequence. A consequence is that the same ns-2 script should yield exactly the same result each time it is run. For simple use, learning the general Tcl syntax is not necessary; one can proceed quite successfully by modifying standard examples. Comments can not be appended to a line that contains a statement (although it is possible first to start a new logical line with;). This differs from the throughput the total bytes sent in two ways: the latter includes both packet headers and retransmitted packets. The ack0 value above includes no retransmissions; we will occasionally refer to it as "goodput" in this sense. Here is the topology we will build, with the delays and bandwidths: A 10 Mbps 10 ms delay R 800 kbps = 100 pkt/s 50 ms delay B the smaller bandwidth on the RB link makes it the bottleneck. We therefore set packetSize to 960 so the actual transmitted size is 1000 bytes; this makes the bottleneck bandwidth exactly 100 packets/sec. We want the router R to have a queue capacity of 6 packets, plus the one currently being transmitted; we set queue-limit = 7 for this. The ns-2 default maximum window size is 20; we increase that to 100 with $tcp0 set window 100; otherwise we will see an artificial cap on the cwnd growth (in the next section we will increase this to 65000). Perhaps the simplest thing to do at this point is to view the animation with nam, using the command nam basic1. In the animation we can see slow start at the beginning, as first one, then two, then four and then eight packets are sent. During the linear-increase phase the bottleneck link is at first incompletely utilized; once the bottleneck link is saturated the router queue begins to build. After that, all losses have been handled with fast recovery (we can tell this because cwnd does not drop below half its previous peak). Upon close examination, these line segments are slightly concave, as discussed in 22. Individual flights of packets can just be made out at the lower-left end of each tooth, especially the first. The bulk of the trace-file lines are event records; three sample records are below. If the first field was "+", "-" or "d", this is the number of the node doing the enqueuing, dequeuing or dropping. This value can be set via the fid variable in the Tcl source file; an example appears in the two-sender version below. The three trace lines above represent the arrival of packet 28 at R, the enqueuing of packet 28, and then the dropping of the packet. Mixed in with the event records are variable-trace records, indicating a particular variable has been changed. It was initially 1 at the start of the simulation, and was incremented upon arrival of each of ack0, ack1, ack2 and ack3. The first line shows the ack counter reaching 3 (that is, the arrival of ack3); the second line shows the resultant change in cwnd.
Lonicera aureoreticulata (Honeysuckle). Eurax.
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