text:
|Publication number
|Publication type
|Application number
|Publication date
|Mar 19, 2002
|Filing date
|Sep 4, 1997
|Priority date
|May 28, 1997
|Fee status
|Also published as
|Publication number
|Anjur Sundaresan Krishnakumar, Joao Luis Sobrinho
|Original Assignee
|Lucent Technologies Inc.
|Export Citation
|BiBTeX, EndNote, RefMan
|Patent Citations (9), Non-Patent Citations (2), Referenced by (17), Classifications (21), Legal Events (5)
|External Links: USPTO, USPTO Assignment, Espacenet
This application claims the benefit of U.S. Provisional Application Ser. No. 60/050,924, filed May 28, 1997.
Contention-based networks, including local area networks such as Ethernet� networks, were originally designed with bursty data transmission in mind. More recently, such networks have been looked toward to support real-time applications such as voice and video. However, using contention-based networks to carry real-time traffic may be problematic because of such networks' inability to guarantee a maximum, or bounded, delay service and thus their inability to guarantee a desired level of service quality for real-time applications.
In order to address this issue, techniques have been proposed which give a certain degree of priority to real-time traffic. One approach is a pre-emptive approach wherein a station desiring to transmit a real-time packet simply comes on to the network's communications medium, e.g., coaxial cable, and transmits a fixed-length preamble. This causes a collision with any then existing traffic. Pursuant to conventional protocol schemes, the station that was transmitting the existing traffic ceases transmitting upon detecting that the collision occurred. At that point the real-time station which caused to collision simply continues with the transmission of its real-time packet. While serving to provide immediate access for the real-time station, this approach has the disadvantage that any packet that was being transmitted at the time of the collision will have to be retransmitted, thereby reducing the overall efficiency of the network. Moreover, the probability of such a collision increases with increasing network load, thereby increasing the number of collisions and further reducing efficiency at higher network loads.
A more efficient approach is that described for example, in I. Chlamtac, "An Ethernet Compatible Protocol for Real-Time Voice/Data Integration," Computer Networks and ISDN Systems, 10 (1985), Elsevier Science Publishers B.V. (North-Holland), pp. 81-96, in which the various currently active real-time stations establish an order of transmission among themselves and use, for example, the notion of a succession, or chain, wherein the real-time stations transmit one after the other in a way which does not allow the medium to be perceived by the non-real-time stations as being idle. It is only after all the real-time stations have had an opportunity to transmit packets they then have ready that the medium again becomes idle, and thus available to any station then having data to send. See also, for example, Szabo, "An Ethernet compatible protocol to support real time traffic and multimedia applications," Computer Networks and ISDN Systems, Vol. 29, page 335-42, 1997.
Disadvantageously, as more and more real-time stations are added to the chain, the average delay suffered by non-real-time traffic increases due to the reduced time available for such traffic; an increase in the duration of the continuous period over which the non-real-time stations are precluded from getting access to the medium; and an increase in the probability of collisions involving non-real-time stations once the stations of the chain have all finished transmitting. Indeed, given a desired maximum such delay, and especially at high network loads, an upper limit exists on the number of real-time stations that can be allowed to be simultaneously active.
Networks embodying the principles of the invention support the existence of multiple chains. This approach, we have found, allows the network to, in turn, support a higher level of traffic than when only a single chain is allowed, at least at high network loads, given any particular constraint on the acceptable delays for non-real-time traffic.
Preferred embodiments of the invention include a mechanism for enforcing the time separation between the various chains and also include a mechanism for enforcing a predetermined maximum number of stations that each chain can have, in order to allow non-real-time stations to obtain timely access to the medium. Moreover, preferred embodiments account for the fact that the time separation between any two of the chains, even if initially set at an amount which does provide for timely access for non-real-time stations, is subject to change over time due to such factors as stations becoming active and inactive and, in the case of non-pre-emptive systems, due further to the fact that the initiation of the access to the medium by a particular chain may be delayed by the presence of a non-real-time data transmission. In particular, preferred embodiments include mechanisms providing what we call "list maintenance," this involving such actions as joining, or consolidating, chains when their time separation is less than a specified value (as long as the resulting chain does not exceed the above-mentioned length limit), and otherwise increasing to an acceptable value the separation of chains which are close together and not candidates for being joined. List maintenance also includes such actions as a) maintaining the various chains as near as possible to the aforementioned maximum size and b) recovering robustly from non-anticilated,interruptions,as taught in our co-pending U.S. patent application Ser. No. 08/923,302 filed of even date herewith.
FIG. 1 shows a contention-based network in which the invention is illustratively embodied;
FIG. 2 shows the format of packet frames used by real-time stations of the network of FIG. 1;
FIGS. 3 and 4 show, when arranged with FIG. 3 to the left of FIG. 4, an illustrative set of signals applied to the communications medium of the network of FIG. 1;
FIG. 5 illustrates an aspect of so-called list maintenance for chains of stations supported within the network of FIG. 1; and
FIG. 6 shows the signals appearing on the communications medium over a number of so-called access periods.
FIG. 1 shows a contention-based network 10—illustratively an Ethernet� local area network—in which the present invention is implemented. Network 10 includes a coaxial cable transmission medium 11 to which are connected six communications stations. Although the relevant principles of Ethernet operation generally, and of the invention specifically, are illustrated herein in the context of a network supporting those six stations, a typical Ethernet or other network in which the invention may be utilized may include many more stations, up to the maximum allowed by the network specification itself. The stations connected to medium 11 comprise non-real-time stations NRT1 and NRT2 which generate non-real-time signals such as file transfer or other data-type signals. These stations follow the rules of the Ethernet protocol strictly. The stations connected to medium 11 also include real-time stations RT1, RT2 RT3 and RT4. These stations likewise can generate non-real-time signals, and when they do they likewise strictly follow the Ethernet protocol rules. However, stations RT1, RT2, RT3 and RT4 are also capable of generating real-time signals, such as voice and video signals, and when they do they follow a modified version of the Ethernet protocol rules, as described below, as a way of ensuring that they get priority access to medium 11 relative to non-real-time stations NRT1 and NRT2.
FIG. 2 shows the format of the packet frame that is used by the real-time stations when transmitting real-time signals, this format being somewhat different from the standard Ethernet protocol format. The frame of FIG. 2 begins with an optional energy burst 20, followed by Medium Access Control, or MAC header 25; sending station identification, or SID, 26; next station identification, or NID, 27; some real-time protocol-dependent parameters 28; and real-time data 29. The latter comprises the real-time information actually sought to be communicated over the network. This is followed by another optional energy burst, 31. If while transmitting its frame, a real-time station detects a collision, it does not proceed with the transmission of the frame as just described. Rather, it begins the transmission of a blackburst signal 22, comprising a preamble 21 and a number of black slots 24. (The nature of blackburst 22 may be any desired signal as along as it does not contain the Ethernet-defined header preamble.) Assuming that the station achieves access to the communication medium at that time (as described in detail hereinbelow) it then retransmits the packet frame as described above, beginning with the MAC protocol header. (It otherwise ceases transmission for the time being.) The functionalities achieved by the presence of the various fields of this frame are discussed at appropriate points in the sequel.
Attention is now directed to FIGS. 3 and 4 which when arranged with FIG. 3 to the left of FIG. 4 show an illustrative set of signals applied to medium 11 by the various stations. FIGS. 3 and 4 also show the overall composite signal appearing on medium 11.
It is assumed that non-real-time stations NRT1 and NRT2 become ready to transmit packets at times t1 and t2, respectively. However, as can be seen from the composite signal on medium 11, some other station is currently transmitting and hence non-real-time stations NRT1 and NRT2 simply wait. The existing transmission terminates at time t3 and it is presumed that non-real-time station NRT1, because of its physical location on the transmission medium, is the first to observe that the medium has become idle. Following conventional Ethernet protocol, non-real-time station NRT1 waits a prescribed interframe time interval tifs seconds. Having waited tifs after detecting the end of the prior transmission, non-real-time station NRT1 begins transmitting a conventional Ethernet packet at time t4. It is assumed that non-real-time station NRT2 detects the end of the prior transmission sometime after non-real-time station NRT1 does and, after waiting tifs seconds, non-real-time station NRT2 begins transmission at time t5. (Unless stated to the contrary, it will hereinafter be assumed that a station waits for tifs seconds after perceiving the medium to be idle before it begins transmitting—even if that fact is not stated explicitly.) However, both stations subsequently observe at times t7 and t6, respectively, that their transmissions are colliding. Upon observing the collision, each station transmits a conventional Ethernet jam signal of fixed duration, the jam signal being of such a nature that any one or more stations can be transmitting it and yet each will recognize the jam signal as being such. Thus all stations are alerted to the fact that a collision has occurred.
The jam signals transmitted by non-real-time states NRT1 and NRT2, which are of the same duration, terminate at times t9 and t8, respectively, at which point each of them enters a so-called backoff mode in which each station waits for a randomly chosen time interval pursuant to conventional Ethernet protocol, the randomness making it likely that these two stations will not collide again upon their respective subsequent attempts to access the medium. NRT1 exits the backoff mode at time t10 and, finding the medium idle, transmits its packet. It completes its packet transmission at time t12.
In the meantime, station NRT2 exits the backoff mode at time t11 and becomes ready to transmit. Observing that the medium is busy, it waits until the medium becomes idle and ultimately, at time t13, gains access to the medium and completes its packet transmission at time t17.
While non-real-time station NRT2 was transmitting, real-time station RT1, non-real-time station NRT1 and real-time station RT2 all became ready to transmit, at times t14, t15 and t16, respectively. It may be noted that even though it is desired to give some measure of priority to real-time transmissions, local area network 10 does not implement a pre-emptive approach. Thus ongoing transmissions are not interrupted. Rather both real-time and non-real-time stations always wait until the medium becomes idle. Time t17 is indicated as being the point in time that all three stations perceive the medium to have become idle. (In order to simplify the discussion, the actual differences, due to propagation delay, in the times at which stations perceive the medium to be idle will hereinafter be ignored.) All three of those stations begin transmission at time t18 which is t ifs seconds after time t17. Upon observing, sometime after time t18, that a collision occurred, non-real-time station NRT1 transmits a jam signal and enters the backoff mode at time t19. However, real-time stations RT1 and RT2, having also detected the collision, proceed to transmit blackburst signal 22; The contents of the blackburst signal can be any desired signal as long as it does not match to any predefined signal defined by the Ethernet protocol. The duration of the blackburst signal that a real-time station is prepared to generate is a function of the level of access priority that it is desired for that station to then have vis-a-vis other real-time stations. Specifically, in preferred embodiments, the duration of the blackburst signal is directly proportional to the length of time each station has been waiting since it became ready to transmit—in the case of real-time stations RT1 and RT2 that being since times t14 and t16. respectively. Each station transmitting the blackburst signal monitors the medium, and upon perceiving that it is the only station transmitting, stops its blackburst transmission and continues with MAC protocol header 25 and the rest of the FIG. 2 frame. Thus a station may actually transmit fewer black slots than it was prepared to transmit at the time that it initiated its blackburst transmission.
The blackburst signal, more particularly, illustratively consists of a) a preamble, having a duration as described below, and b) an integral number of so-called "black" slots each of duration ≧2τ, which is the round-trip propagation delay on medium 11. The number of black slots that a station should be arranged to be prepared to send is d/tinter, rounded up to the next higher integer value, where d is the time that the station has been waiting and tinter is at least a time given by the length of the packet as shown in FIG. 2 (measuring from the start of the MAC protocol header 25 to the end of the real-time data field 29).
Since real time station RT1 was waiting longer, its blackburst interval is longer than that of RT2. Hence a point in time will be reached at which only RT1 is transmitting a blackburst signal. In particular, real-time station RT1's blackburst transmission ended at time t21, while real-time station RT2's blackburst transmission continued beyond that point. Upon observing, at time t22 that it alone was transmitting a blackburst signal, real-time station RT1 stops its blackburst transmission and continues with the rest of its frame.
Meanwhile real-time station RT2, upon perceiving that real-time station RT1's blackburst transmission was longer than its own ceases transmission and enters a waiting mode.
The overall effect of having the real-time stations transmit a fixed length preamble 21 as part of the blackburst signal is to ensure that all non-real-time stations would have ceased transmission had gone into a backoff mode. To this end, the duration of preamble 21 is equal to the sum of a) the aforementioned round-trip propagation delay on the medium, 2τ and b) the duration of the conventional Ethernet jam signal. Priority will thus have been secured for real-time transmissions without suffering the disruptive effects of a pre-emptive approach. Moreover, as among the real-time stations, the use of the blackburst mechanism ensures that when (as in this embodiment) the duration of the blackburst signal is proportional to the length of time each station has been waiting since it became ready to transmit, the real-time station that was the first to become ready to transmit will be the first to obtain access to the medium. Further description of the use of blackburst signals is found in our co-pending U.S. patent application Ser. No. 08/792327 filed Mar. 8, 1996 and entitled: "A Wireless Lan Distributed Access Procedure Providing Priority For Voice Transmissions."
After real-time station RT1 has completed its transmission, real-time station RT2 gains access to the medium without further delay or collisions inasmuch as no other station is ready to transmit. At time t23 real-time station RT2 starts the transmission of its frame, which continues to completion at time t25. Meantime, at time t24 non-real-time station NRT1 exits the backoff mode and becomes ready to transmit. By then real-time station RT2 is transmitting its frame and non-real-time station NRT1 waits until real-time station RT2 is finished and then begins its transmission at time t26, completing at time t27.
The nature of real-time traffic is that packets transmitted from a sending station to a receiving station, once initiated, will continue over an extended period of time at regular intervals, this being referred to as a "connection." Therefore each one of real-time stations RT1 and RT2 will be transmitting a significant number of packets from this point forward. The mechanisms described to this point will continue to provide them with priority over non-real-time traffic and also provide round-robin access as among the real-time stations. However, if nothing more were to be done, a significant amount of network resources may become consumed in blackburst contention as among the real-time stations—at least at high traffic loads. Advantageously, the packets transmitted by the real-time stations can be chained with one another in such a way that much of that contention is eliminated. In addition, the chaining can be done in such a way that until all packets in the chain have been transmitted, no non-real-time station can obtain access, thereby precluding any collisions with the same and thereby cutting down on the overhead needed for ensuring that priority for the real-time stations to get priority.
The chaining begins when real-time station RT1 observes that after its own transmission ended, real-time station RT2—identified as a real-time station through information in the RT protocol-dependent parameters 28—transmitted its first packet. During its subsequent transmission, which begins at time t29, real-time station RT1 "invites" real-time station RT2 to chain with RT1 for subsequent transmissions. Real time station RT1 does so in its next transmitted frame by setting NID field 27—which was a null character "*"—to the SID 26 found in the frame that real-time station RT2 had transmitted, which is illustratively "2". Real-time station RT2, upon observing this invitation takes access at time t31, immediately after RT1 completes its packet transmission, without waiting tifs seconds, and thereby precludes any non-real-time station from intervening. Real-time station RT1 transmits energy burst 31 at the end of its packet and a similar signal, energy burst 20, is transmitted by real-time station RT2 at the beginning of its packet. The duration of these signals—illustratively the aforementioned 2τ—is chosen such that there can be no idle period on the medium between the two packets, so that non-real-time stations are precluded from attempting to access the medium, the energy bursts serving as a sort of "handoff" signal between the two stations. It will thus be appreciated that energy burst 20 (31) is absent when a station is at the head (tail) of a chain (as described below) or is not part of any chain.
It is assumed that at some point in the past real-time station RT3 became ready to start a connection. However, a real-time station, before it attempts access, will observe the channel for a long enough period to determine whether the possibility exists for it to add itself to an existing chain. In the present example, real-time station RT3, after observing the transmission of real-time station RT2 between times t23 and t25—and after observing the termination of the transmission of non-real-time NRT1 at time t27—sends a conventional Ethernet packet to real-time station RT2, beginning at time t28, requesting that it be invited to be chained to real-time station RT2 beginning with the latter's subsequent transmission. Real-time station RT2 complies by setting its NID field 27 to the ID that had been specified by real-time station RT3 in its request—illustratively "3". Real-time station RT3, upon observing this invitation takes access at time t32, immediately after real-time station RT2 completes its packet transmission, in the same manner that real-time station RT2 had responded to its invitation from real-time station RT1 earlier.
Because each station of a chain "invites" the next one by specifying the latter's ID, the chain is referred to as a "linked-list" or "linked-list chain."
Non-real-time station NRT1 became ready to transmit a packet at time t30 but cannot gain access until time t34, which is tifs seconds after the network becomes idle upon termination of real-time station RT3's transmission at time t33. It is thus seen that each of the presently active real-time stations, by virtue of the linked-list chaining mechanism, obtained priority over non-real-time station NRT1 even though the latter had become ready to transmit all the way back when real-time station RT1 was transmitting.
FIG. 5 illustrates an aspect of so-called "list maintenance." As previously noted, the nature of real-time traffic is that the real-time stations will repetitively access the medium over an extended period of time in a succession of cycles, or access periods, at regular intervals. In order to ensure robust operation, each of the real-time stations, in each access period, sets a timer, when the station accesses the medium, the timer being set to expire in a subsequent—illustratively the next—access period. The time at which the timer expires defines an expected time at which the real-time station in question should access the medium.
It may be observed at this point that different real-time stations have their timers set to expire at instants of time that differ by at least tinter, i.e., the length of the real-time packets. Therefore, if two or more real-time stations are delayed, their delays will differ by at least tinter. As a consequence, the duration of the blackburst signal that each station is prepared to send is guaranteed to differ by at least one black slot, thereby resulting in a unique blackburst contention "winner."
In particular, it is assumed in FIG. 5 that four real-time stations RT1 through RT4 are all active, i.e., have an ongoing connection with another station. Having transmitted packets at times t40, t41, t42 and t43, they set their respective timers to expire at times t50, t52, t54 and t55. The timer interval taccess is illustratively equal to a conventional packetization interval for voice transmissions, which is 25 ms. It is assumed that real-time stations RT1 through RT4 have previously arranged themselves into a linked-list chain in the manner described above and that their transmissions have proceeded normally for some period of time. Moreover, once one of those stations, such as real-time station RT2, becomes ready to drop its connection, it provides an indication of this fact in the last packet of that connection. Upon observing this, station RT1 will begin to invite station RT3, rather than station RT2, thereby re-constituting the chain with one less station.
However, it is possible for a station to discontinue its transmissions without giving any notice, e.g., due to a malfunction of some kind. Thus assume that real-time station RT2 failed to respond to the invitation of real-time station RT1 and thus does not transmit at time t52, as expected. Accordingly remedial action needs to be taken. Station RT2 is in the middle of the linked-list chain, and the station which follows it, real-time station RT3, will not transmit until it "sees" a transmission from station RT2. Thus if nothing more were done, neither station RT3 nor station RT4—referred to herein as the "detached stations"—are able to transmit since they are waiting to observe that their predecessor in the chain has transmitted. Since real-time station RT3 did not receive an invitation at the appropriate time, its timer expires at time t54. This serves as indication to real-time station RT3 that something untoward has occurred.
The above-described blackburst mechanism provides for a recovery procedure which has as its ultimate result the re-chaining of the detached stations in their original order without, in the process, engendering unconstrained contention among those detached stations. In this example, in particular, non-real-time station NRT1 became ready to transmit at time t51 and took access to the network at time t53 when it became idle shortly after the end of real-time station RT1's transmission. Real-time station RT3 thus has to wait until non-real-time station RT1's transmission ends at time t56. Meanwhile, the timer of real-time station RT4 also has expired, at time t55. Thus when the network becomes idle at time t57 both real-time stations RT3 and RT4 attempt to access the network. The same sequence of events as occurred vis-a-vis real-time stations RT1 and RT2 beginning at time t18 comes into play, with the duration of the blackburst signal being directly proportional to the length of the time interval between the expected access time—i.e., the time that the timer expired—and the initiation of the blackburst signal. (As noted earlier, a station, having initiated the transmission of a blackburst signal of particular duration, may terminate the blackburst signal before that full duration has occurred, this being done upon a determination that that station's blackburst signal has become the only blackburst signal being transmitted on the medium.)
Specifically looking again at the FIG. 2 frame, the initial portion thereof includes a first, signal, preamble 21, which is of a sufficient duration to ensure that any of the non-real-time stations then transmitting enter the backoff mode, and further includes a second signal, black slots 24, having a duration which is a function of the expected access time (timer expiry) for the station in question. Since the timer of real-time station RT3 expired first, its blackburst signal will be the longer of the two and hence real-time station RT3 will be the first to gain uncontended access. Real-time station RT3 thereupon invites real-time station RT4, as before, causing real-time stations RT3 and RT4 to reconstitute their prior chaining relationship. The network thus robustly recovers from the non-anticipated interruption of the chain caused by the failure of station RT2.
Other scenarios can also result in the timers of more than one station to expire—even in the absence of any failure per se. For example, it may happen that all of the real-time stations of the linked-list chain comprising stations RT1 through RT4 are operating normally, but a long transmission by a non-real-time station delays head station RT1's access to the medium. Indeed, the delay may be of such duration that the timers of any one or all of the remaining stations of the chain also expire. Here, too, however, the above-described mechanisms ensure that once the medium becomes idle, the head station of the chain will be the one to gain access and that the other stations of the chain will thereafter gain access in their proper order.
In general, it may be observed that as a result of the above-described mechanisms, the head station of a linked-list chain serves as a "proxy" for all the other stations of that chain in terms of securing access to the medium for all of those stations. That is, once the head station has obtained access, no further contention for access to the medium occurs.
The above-cited Chlamtac paper does not explicitly address the issue of untoward chain interruption. However, given its underlying approach of having all the real-time stations join in a single chain, such prior art arrangements would undoubtedly include a mechanism for rejoining detached stations to the original linked list chain. This is shown via-a-vis real-time stations RT3 and RT4 in FIG. 5. In particular, real-time station RT1 has observed that a) the real-time station identified in its own NID field 27—namely real-time station RT2—did not come on to the medium but, rather, b) real-time station RT3 was the next real-time station to do so. Accordingly, real-time station RT1 changes the ID in its NID field 27 to identify real-time station RT3. The latter thereupon responds to this invitation in that cycle, and subsequent cycles, and the linked-list chain is thereby reconstituted as a three-station chain.
In accordance with the principles of the present invention, and contrary to the Chlamtac arrangement, the network shown and described herein does not always join multiple linked-list chains that may exist at any particular point in time into a single linked-list chain. Rather, the present network allows for the possibility of two or more chains existing independently for an indefinite period of time. Following that approach in the example just considered, two chains will have been formed—one comprising the single real-time station RT1 and the other comprising the two real-time stations RT3 and RT4. Subsequent events may cause other stations to chain themselves onto the two existing chains, as previously described. Alternatively the two chains may join themselves back into a single chain, as described hereinbelow but, again, do not always do so.
In particular, FIG. 6 shows the signals appearing on the medium over a number of access periods P1 through P6, all of duration taccess, which occur in the order named but may be separated by other intervening access periods not shown. Each of the transmitted entities is an independent chain marked with a letter and a number, the letter identifying the chain and the number indicating its current length, i.e., the number of stations comprising the chain. Thus, for example, the notation A-3 means that chain A currently comprises three real-time stations. In a first access period, P1, the chains on the network are chains A-3, B-2 and C-2. Each of these chains is separated by some amount of time, the term "separation" being used in the present context to mean the time interval between the end of one chain and the beginning of the subsequent chain. Moreover, it is assumed that those separations remain unchanged in period P2. The separation between chains A-3 and B-2 at this time is denoted ti1.
In the present illustrative embodiment, as long as the separation between two chains is greater than a first minimum value tmin, those chains will be maintained as independent, unjoined, chains. In accordance with a feature of the invention, the time separation between the various chains is preferably kept at least the minimum value tmin in order, for example, to allow non-real-time stations to obtain timely access to the network by providing a window during which they may access the medium without interference from real-time stations. The separation between chains will change over time as stations are added to and dropped from the various chains. Moreover, even in the absence of such events, the separations may change due, for example, to the transmissions of non-real-time stations which may cause the onset of a chain's transmission to become delayed. Thus as shown in the FIG., the separation between chains A-3 and B-2 has become smaller in time period P3, at a value ti2. It is assumed at this point that ti2 has become less than tmin. This fact is observed by the tail station of chain A-3, which also observes that the total length of chains A-3 and B-2 is five. This exceeds a prescribed maximum length for a chain—assumed in this example to be 4—the enforcing of such a maximum length being desirable, in accordance with a feature of the invention, in order to allow non-real-time stations to obtain timely access to the network. The two chains thus cannot be joined together. Rather, in the subsequent time period P4 the tail station of chain A-3 sets an "enforce separation" indication—which is one of the RT protocol-dependent parameters 28. The head station of chain B-2, upon observing this indication, ensures that its next access to the medium is at least tmin seconds after the end of chain A-3. The separation between the chains in time period P4 has now become ti3≧tmin.
After some number of periods have elapsed, the situation is assumed to be as shown in time period P5. By this point, the time initiations of chain B-2 have drifted in such a way that the separation ti4 between chains B-2 and C-2 has become less than tmin. Now, however, the total length of the two chains does not exceed 4 and thus they can be joined. Indeed, in accordance with a feature of the invention, it is desirable that they be joined so as minimize the amount of time that may be taken up by blackburst contentions in the event that the respective onsets of the two chains are delayed such as in the scenario described hereinbelow. In particular, the tail station of chain B-2, upon observing this condition, invites, in period P6, the head station of chain C-2 to join it, using the inviting mechanism described above. The latter thereupon joins the former as previously described, giving rise to a single chain B-4.
A tail station, before issuing a request to join the head station of the following linked-list chain, should assure itself that that head station is not the head of its own chain. This is illustratively accomplished by having the tail station check to see that it has observed since the last cycle at least one of the above-mentioned null characters, *, this being a special character used as NID 27 by the tail station of each chain, the existence of the null character indicating the presence of at least one other linked-list chain.
Unless positive steps are taken to prevent it, it is possible for two tail stations to each attempt, within the same cycle, to join its own linked-list chain to that which follows, thereby potentially creating a chain which exceeds the maximum permissible length. In order to prevent this, the count of the number of stations in the list to which a request-issuing tail station belongs should be made just before the request is issued. The tail station keeps a running count of stations in the list that appear on the medium. That station updates the length of its own chain when it gets invited to transmit while it is monitoring an ongoing list (i.e., it is monitoring its own list). If any previous linked-list chain had invited the current linked-list chain to join it, and the joining had occurred, the result would be reflected in the length count. Thus a decision to issue a join request is made based on the current state of the various chains and thus cannot result in a chain whose length exceeds the permissible maximum.
The mechanism described herein using blackburst signals to allow the stations in a linked-list chain to reconstitute themselves in their original order is operative even if more than one chain is involved. Consider an extreme case wherein the medium was busy with non-real-time traffic for such a period of time that none of the stations in either of chains A and B was able to gain access to the medium before their respective timers time out. Once the medium becomes idle and the various real-time stations with expired timers attempt to gain access, the head station of chain A will be the one to gain access since, as among all the stations of chains A and B, it will have been waiting the longest since its timer expired. The chain A head station then invites the other stations of its chain in the manner described above, and since the medium will not be seen by any station to be idle, none of the stations of chain B will attempt to access the medium until the tail station of chain A has completed its transmission. Thereafter the stations of chain B will each attempt to access the medium. Its head station will be the one the gain access since, as among all the stations of chain B, it will have been waiting the longest since its timer expired. The stations of chain B thereupon reconstitute themselves as well.
The maximum number of real-time stations that can be supported while ensuring that the system is unconditionally stable is at least as great as
where α=tbslot/tinter, γ=α+αmrs/rc+mrs/rc, rs is the (constant) bit rate of the sources of real-time traffic, rc is the network channel bit rate, i.e., the bit rate on medium 11, and m is the number of stations per chain—assuming for purposes of this analysis that each chain comprises the same number of stations. For example, for rs=64 kbps, taccess=25 ms, and a maximum cable length of 600 m, corresponding to a network spanning 3 hubs, we can support at least 70 stations whereas an ideal scheduling scheme would yield about 130 stations. One way to improve the performance of the system is to cause the head stations of the various chains to enforce a separation among themselves beyond the prescribed value of tinter.
The present disclosure has proceeded on the basis that all of the processing involved in controlling access to medium 11 is carried out by circuitry within the stations themselves, e.g, by a so-called network interface card, NIC1, NIC2, NIC3, NIC4, NIC5, and NIC6, installed in a personal computer or workstation. The network interface cards NIC1, NIC2, NIC3, NIC4, NIC5, and NIC6 can include, for example, inviting module IM1, IM2, IM3, IM4, IM5, and IM6, respectively, responding module RM1, RM2, RM3, RM4, RM5, and RM6, respectively, joining module JM1, JM2, JM3, JM4, JM5, and JM6, respectively, and separating module SM1, SM2, SM3, SM4, SM5, and SM6, respectively. However, it may be desirable to provide a separate outboard device, interfaced between the medium and a conventional type of network interface card so that changes to the node itself are not needed. Indeed, it is contemplated by us that the present invention can be employed in such outboard implementations. In present arrangements, delays that may be encountered by the network interface card in gaining access to the medium do not pose a problem because once access to the medium is acquired the network interface card can communicate with the application in such a way as to obtain from the application a sufficient amount of data beyond that which would normally be included within a pocket so as to compensate for the delay as though, from a throughput standpoint, the delay never occurred. An outboard implementation would in all likelihood not have the benefit of such communication back to the application so that, if nothing more were done, then, even though all the accumulated data could ultimately get transmitted, unduly large delays could occur. We believe that an advantageous solution to this problem is that the outboard device—having been delayed and having transmitted such data as was provided by the application in its standard format—will try to "buy back" some of the delay by setting its timer to a smaller value than taccess for a sufficient number of access periods to accommodate the delay that was incurred. In determining an appropriate timer setting, the device would need to be sure that the newly scheduled access time differs from those of any of the other then-active real-time stations by at least tinter in order to preclude collisions among the real-time stations.
The foregoing is merely illustrative and many variations are possible, as will now be shown by way of some examples: Although a single time interval tmin is used in the disclosed embodiment both to determine a) when chains are close enough to each other to be joined, and b) so close that they should be separated, other embodiments may use different intervals for those two activities. It may be desired to include only one of the two above-described activities of a) of joining chains together under prescribed conditions, and b) increasing their separation or forcing them to be further apart. One or both of those activities could be carried out without taking into account the lengths of the chains or any prescribed maximum chain length. Various alternative embodiments may carry out such activities whenever the prescribed criteria are met, as is the case in the present illustrative embodiment or, alternatively, carry them out only on certain occasions when the criteria are met, this being done, for example, to avoid some of the processing and signaling overhead associated with these activities. We believe, in particular, that the frequency with which linked-list chains are allowed to join should not be allowed to become unduly large since each of these events introduces some inefficiency. (We do not, at the moment, have any quantitative measure of this.) In this same vein, the criterion used in particular embodiments to determine when chains are to be joined may be stated as being that they are joined only if the separation between them becomes less than some particular amount (such as tmin). This is a sufficient, but not necessary condition, meaning that they will not be joined unless their separation is less than tmin, but also meaning that they will not necessarily be joined just because that condition is met, thereby, for example, cutting down on overhead/inefficiency as just noted.
In the disclosed illustrative embodiment, a real-time station, upon detecting a collision is assumed to, in a sense, begin new frame transmission comprising the entirety of preamble 21, followed by one or more of the black slots 24 as previously described. A slightly more efficient approach is possible, however, in which, not all of preamble 21 is transmitted but only so much of it as is needed to make the total time of transmission since the station gained access equal to the length of preamble 21 as shown.
The foregoing merely illustrates the invention. Those skilled in the art will be able to devise numerous arrangements which, although not explicitly shown or described herein, embodying the principles of the invention and are thus within their spirit and scope.
|Cited Patent
|Filing date
|Publication date
|Nov 1, 1991
|Aug 17, 1993
|Hewlett-Packard Company
|Bus contention resolution method for network devices on a computer network having network segments connected by an interconnection medium over an extended distance
|May 12, 1994
|Apr 4, 1995
|Digital Equipment Corp.
|Dynamic defer technique for traffic congestion control in a communication network bridge device
|Aug 11, 1992
|May 21, 1996
|Ncr Corporation
|Method of transmitting selected message frames without individual destination address in non-overlapping sequential time intervals from host computer to terminals via bridges and retransmitting thereafter
|Jan 14, 1993
|Nov 26, 1996
|Apple Computer, Inc.
|Communication node with a first bus configuration for arbitration and a second bus configuration for data transfer
|Dec 22, 1995
|Sep 2, 1997
|Alcatel N.V.
|Chaining arrangement between intermediate modules, particularly of repeater type, of an installation provided with terminals communicating via a packets transmission link, and an installation thus equipped
|Nov 2, 1995
|Apr 14, 1998
|Cypress Semiconductor Corp.
|Method and apparatus for performing collision detection and arbitration within an expansion bus having multiple transmission repeater units
|Sep 19, 1994
|Jun 16, 1998
|Phylon Communications, Inc.
|Real-time and non-real-time data multplexing over telephone lines
|Mar 25, 1997
|Dec 1, 1998
|International Business Machines Corporation
|Communications cell scheduler and scheduling method for providing proportional use of network bandwith
|Apr 18, 1997
|Feb 23, 1999
|3Com Corporation
|Arbitration system using linked table
|I. Chlamtac, "An Ethernet Compatible Protocol for Real-Time Voice/Data Integration," Networks and ISDN Systems 10 (1985) 81-96, Elsevier Science Publishers B.V. (North Holland).
|U.S. application Ser. No. 08/792,327, filed Mar. 8, 1996 by Krishnakumar et al., entitled "A Wireless Lan Distributed Access Procedure Providing Priority For Voice Transmissions.".
|Citing Patent
|Filing date
|Publication date
|Mar 3, 1999
|Aug 26, 2003
|Lucent Technologies Inc.
|Priority access for real-time traffic in contention-based networks
|Dec 22, 1997
|Jun 15, 2004
|Nortel Networks Limited
|Method and apparatus for communicating data between first and second pairs of transceivers communicating on a common communications link
|Dec 15, 2000
|Mar 28, 2006
|American Standard International Inc.
|Multiple device communications
|Aug 10, 1999
|May 23, 2006
|3Com Corporation
|Method and system for providing priority to a station in a congested half duplex Ethernet network
|Sep 13, 2002
|Jul 31, 2007
|Snowshore Networks, Inc.
|Selective packet processing in a packet based media processor for latency reduction
|Sep 13, 2002
|Jul 28, 2009
|Dialogic Corporation
|Methods and systems for jitter minimization in streaming media
|Feb 17, 2004
|Feb 16, 2010
|Broadcom Corporation
|Dynamic real-time quality management of packetized communications in a network environment
|May 27, 2008
|Nov 6, 2012
|Great Links G.B. Limited Liability Company
|Methods and apparatus for providing quality-of-service guarantees in computer networks
|Oct 5, 2012
|Nov 18, 2014
|Great Links G.B. Limited Liability Company
|Methods and apparatus for providing quality of service guarantees in computer networks
|Dec 15, 2000
|Jun 20, 2002
|Vanderzee Joel C.
|Multiple device communications
|Sep 13, 2002
|Mar 18, 2004
|Luis Ortiz
|Methods and systems for jitter minimization in streaming media
|Feb 17, 2004
|Jan 6, 2005
|Bye Richard A.
|Dynamic real-time quality management of packetized communications in a network environment
|Jul 31, 2006
|Feb 8, 2007
|Canon Development Americas, Inc.
|Enabling non real-time communication enabled devices to participate in real time communication scenarios
|May 27, 2008
|Aug 6, 2009
|Great Links G.B. Limited Liability Company
|Methods and apparatus for providing quality-of-service guarantees in computer networks
|Oct 5, 2012
|Mar 21, 2013
|Great Links G.B. Limited Liability Company
|Methods and apparatus for providing quality of service guarantees in computer networks
|Aug 3, 2006
|Feb 15, 2007
|Canon Development Americas, Inc.
|Enabling non real-time communication enabled devices to participate in real time communication scenarios
|Aug 3, 2006
|Jul 5, 2007
|Canon Dev Americas Inc
|Enabling non real-time communication enabled devices to participate in real time communication scenarios
|U.S. Classification
|370/444, 370/461, 370/462, 370/447
|International Classification
|Cooperative Classification
|European Classification
|Aug 26, 2005
|Fee payment
Year of fee payment: 4
|Sep 14, 2009
|Fee payment
Year of fee payment: 8
|Mar 7, 2013
Free format text: SECURITY INTEREST;ASSIGNOR:ALCATEL-LUCENT USA INC.;REEL/FRAME:030510/0627
Owner name: CREDIT SUISSE AG, NEW YORK
Effective date: 20130130
|Sep 12, 2013
|Fee payment
Year of fee payment: 12
|Oct 9, 2014
Owner name: ALCATEL-LUCENT USA INC., NEW JERSEY
Free format text: RELEASE BY SECURED PARTY;ASSIGNOR:CREDIT SUISSE AG;REEL/FRAME:033950/0261
Effective date: 20140819


text:
November 30th is written on it. Normally, when no release dates are announced apart from the period which they expect it release, they put in december 31st.
November 30th is written on it. Normally, when no release dates are announced apart from the period which they expect it release, they put in december 31st.
Man of steel was one of my most anticipated movie this year with star trek: into Darkness. It was only logical that I get the best seats in IMAX in advance to go and see it. I was worried that it wouldn't live up to my expectations. Plus, the critics have been so divisive over the movie.
Some hated the movie and the fact that it went in a more serious, The Dark knight, way. Others outright loved it. IGN's Jim Vejvoda did a great review and gave it a 9.0 while stating that this superman might be a bit too serious. Although he added that this might be one of Zack Snyder's best movies.
Snyder has made movies that divided critics a lot. Most can't seem to wrap their heads around the serious man of steel. I can understand that die hard fans don't like it when you change something they hold dear (it's a hard thing to please both new viewers and old fans). Unlike Christopher Nolan and J. J. Abrams, he doesn't seem to appeal to critics. At least he really knows how to appeal to fans (well at least new ones, plus Snyder's and nolan's fans). The audience was thrilled from the start. They even applauded when the credits finally rolled. I came out of the movie theater having been so pleased by the movie. It actually lived up to the hype, in my opinion.
The action scenes might be a bit too much for some, but it was incredible once you got used to them. The fights and confrontations are nothing short of amazing. It fits the greatness that is the Man of steel.
(I'd also like to point out that the name Superman is only used once in the entire movie. It was actually well placed. Plus, not using it gave a much more serious tone to the movie)
The soundtrack composed by Hans Zimmer is another masterpiece by this composer. It fits the superhero movie so well that it gave me chills when the theme kicked in. It's not the same as John williams' classic superman theme, but it is much more fitting given the more serious tone of the movie.
Snyder's the Man Of Steel fulfills what it set out to be: a new modern take on the classic superhero. And it does it incredibly well. The fans that have been waiting for this movie are sure to have a blast seeing this. And I definitely recommend it! Do yourself a favor and buy a ticket!
Ps. I watched the movie in IMAX 3D and it was an amazing 3D, worth it too. I do not know how it is in a regular 3D though.
I've been seeing those reviews about Oblivion for the past few weeks and it didn't make me want to see it. My family wanted to see it, so I went there thinking I'll at least enjoy the effects and scenery. I can now say that, I have been wrong for not seeing it sooner.
While some of it's story elements can be predictable, Kosinski added his own little twist an turns it. Most critics have said it was an unoriginal movie, but even though he takes big inspiration in some of the greatest sci-fis, it doesn't mean it's bad. Yes it doesn't shy away from it, but this is why I love it. Having watched 2001: a space odyssey, I have noticed so many similar looking and heavily inspired scenes form Kubrick's movies. Being a big Kubrick fan and having done a whole research paper on his work, I had to say I loved seeing his work appear in today's movies. Oblivion doesn't try to mask the fact that it is doing so. WARNING POTENTIAL SPOILERS: The famous baby in a foetus position from 2001 and HAL have both their own Kosinski updated version in oblivion. The weightlessness of space and how the character is moving through the spaceship is almost exactly as in 2001,END OF POTENTIAL SPOILERS. This actually made me smile during the movie. It was used with respect and in a way that shows Kosinski's admiration of Kubrick.
Camera movement and techniques are used and based on Kubrick's work. This is one of the reasons I see this movie as a love letter to Kubrick. The camera angles remind me so much of what Stanley's films used to have. That famous camera moving through multiple areas where various actions are taking place, or the camera following a character or a something of importance doing its actions through various areas, turning left through a corridor, going down, up, etc. It might sound dull since now almost every movie has it, but it was thanks to Kubrick that we have this amazing technique. This technique was actually first used by Max Ophüls(I don't think many people know him nowadays, but he's the one responsible for Kubrick's way of doing), Stanley took it and improved it to his taste.
What I was afraid about this movie is that it could be a heavy action packed sci-fi with nothing more to it. Thankfully it isn't. It actually has just the right amount of action. It concentrates more on the world and it's characters. This movie could be compared to Solaris, the one with George Clooney(yes the remake that failed in the box office, but I found to be actually a great movie). It takes a lot of inspiration from it.
For those who don't know about Stanley Kubrick, he is one of the greatest directors of our time. It's thanks to him that we have science fiction like today. He inspired so many directors after him: George Lucas(yes without Kubrick there would be no Star Wars), Steven Spielberg, Martin Scorsese, Quentin Tarantino(his "trunk shots" are based on the camera angles of Kubrick. The crude violence also comes from Kubrick's Clockwork orange), David Lynch(both have inspired each other), Christopher Nolan(a recent article on IGN actually has an interview where Nolan talks about Kubrick being one of his biggest influences), And I could go on, there's so much more to say, but if you want to know more, just sound off in the comment section below. I'll be happy to answer your questions.
Thanks for reading!
Trailer #1
Anti-physics vigor. Now that would be awesome. Who wouldn't love to defy the laws of physics. Defying gravity like that Wicked musical song ( or Glee if you're into that stuff). The Anti-Physics vigor would allow you to fly for a limited period of time. Forget the rails, fly over to the place you want to go. Imagine flying over Columbia ( which is pretty high itself), wouldn't that be incredible. To feel the rush of being so high would be amazing.
You could just fly over ennemies and surprise them by picking them up and dropping them from the heights of Columbia.
Another thing that vigor could do is a sort of Gravity Rush-like gravity shift. Disorient the ennemies by shifting the gravity and watch as they start to freak out. Battle them on the walls of Columbia, or on the rooftops of those huge buildings. Or just send them flying up and then watch as they crash.
This is getting actually pretty cruel. Anyways, this was my idea of an awesome vigor!
What do you guys think?
Hey guys, Disney just unveiled their new Infinity trailer. Check it out:
Disney Infinity Reveal Trailer
What do you think?

subset: commoncrawl


text:
Just wait till the "anti everything" crowd manages to get done to ammunition what was done to tobacco products.
This is a discussion on Walmart Ammo Increase within the Defensive Ammunition & Ballistics forums, part of the Defensive Carry Discussions category; I just bought a "100 Round Value Pack" of 9mm Winchester at Wally World - $15.72!!! I swear it was only $11.99 just a month ...
I just bought a "100 Round Value Pack" of 9mm Winchester at Wally World - $15.72!!! I swear it was only $11.99 just a month ago! I looked at the other Winchester white box bulk boxes and I think the 40 S&W was $25 and the 45ACp was $30.
Good lord - soon ammo costs will stop my guns from being a fun hobby to being relegated to "useful tool" status - only used when needed.
Just wait till the "anti everything" crowd manages to get done to ammunition what was done to tobacco products.
Yeah, it ain't cheap, but check the price of a movie or bowling or green fees. Nothing is as cheap as it was. Shooting is still one of the least expensive forms of recreation.
"If we loose Freedom here, there's no place to escape to. This is the Last Place on Earth!" Ronald Reagan
$15.72! ..... no wonder I am starting to resume reloads on lil' ol' 9mm!!
Last box I bought of the WWB 9mm was IIRC not even ten bucks.
Reloading .45acp too - again IIRC I used to pay just under twenty bucks for box of that. This reflects right now pretty much a 50% increase - ouch!
Chris - P95
NRA Certified Instructor & NRA Life Member.
"To own a gun and assume that you are armed
is like owning a piano and assuming that you are a musician!."
http://www.rkba-2a.com/ - a portal for 2A links, articles and some videos.
$16 for 100 is terrible but could be worse. everything that i see is $10 per 50. exept the really crappy stuff wich is MAYBE 8 per 50.
it sucks but its still cheeper
not any better online after shipping too.
im checkin out the gun show tmrw. hopefully i find somethin. if not. its off to wally world for me.
Walmart is still the cheapest place that I know of to get ammo. At the range/gun shop I pay between $14-17 for 45ACP and $10-12 for 9MM.
At walmart I can get the same box of ACP for under 12 bux. I don't buy the WWB anymore, becuase they want 28 bux. I just buy two boxes of the CCI blazer.
I went looking today for 1000 rounds of 45 for a couple of classes at the end of the month. I was told by two different stores, in different areas of the mid state that all ammo is going to go up 25% Sept 1 due to the increased cost of lead and copper, petrochemicals used for gunpowder and the fuel cost incurred by delivery
"If I was an extremist, our founding fathers would all be extremists," he said. "Without them, we wouldn't have our independence. We'd be a disarmed British system of feudal subjectivity."
I just got back from a Wally World ammo run.
Winchester White Box 100 round value packs:
.38 Special: $25.47
"I surrounded 'em"- Alvin York
"They're ain't many troubles that a man can't fix with seven hundred dollars and a thirty ought six"- Jeff Cooper
Just paid$ 43.00 for a 250 ct box of UMC 9mm at Bi Mart...bout 8.60 a box ....then paid the 15.72 over at walmart for wwb 9mm 100 ct.box!!
The ammunition woes are being driven by demand from the US military and Law enforcement supply problems. I read about this a few months ago, and since we are fighting a war on terror, the military is rapidly depleting their surplus stocks of ammunition, especially 9mm, 5.56mm .45ACP & .308 ammo. From what I understand, ammunition contractors are being stretched to the limit, with the balance being supplied through civilian contracts. These problems should continue through next year.
"Guard with jealous attention the public liberty. Suspect everyone who approaches that jewel. Unfortunately, nothing will preserve it but downright force. Whenever you give up that force, you are inevitably ruined". - Patrick Henry
Ammo's gone through the roof in the last 4-5 years. I just got my last shipment of 7.62 russian for $170+ out of Sportsmanguide. I bough my first batch of 1K out of the same outfit 3.5 years ago for $79! It is still cheaper than reloading for it but darn!
As for 9mm, it is to the point that is cheaper to reload than buying IMHO. Thank God I collected all the 9mm brass i could lay my hands on and I am the proud owner of about 10K in cases. Now I am officially scrounging for 38 special and 357 mag. And I see myself casting my own bullets soon if things keep going like this.
You have to make the shot when fire is smoking, people are screaming, dogs are barking, kids are crying and sirens are coming.
Randy Cain.
Ego will kill you. Leave it at home.
Signed: Me!
The prices you quoted are to the penny a match to my own local WalMart which out of the blue has suddenly completely restocked their shelves with everything across the board.
For six months on it was dry and they had hardly anything not even .22LR bulk packs. Now as of last week they have 30-06, multiple flavors of .17 HMR and even .17M2 (!) as well as all variants of pistol grade ammo from .38 to .45. I was stunned.
Last week I bought up four 100 rd. boxes of WWB in .45 ACP and a 550 rd. box of Federal .22LR FMJ. That cost me $130 (!!!).
I was in the same store yesterday checking supplies and found more of the same with another four boxes of 100rd. WWB in .45 ACP FMJ on the shelf. I'll be by there tomorrow to buy out that stock again and to pickup maybe two more boxes of .22LR (WWB JHP and Federal 'Match Grade' target ammo).
Definitely prices have _sky rocketed_ across the board relative to last summer which even then was expensive (never mind ~5 yrs. ago when .45 ACP ran $9.98 for a 100rd box of WWB FMJ) but I figure it's a lot cheaper than it could be and might be down the road.
Thus for now I make like a squirrel and cache as much ammo as I can secure in anticipation of a long, cold, and painfully expensive winter. :(
In fact tonight over dinner I saw an ad in the paper toward my local Ace True Value Hardware store that mentioned they have a lockable plastic trunk on sale for $13 oriented toward returning college kids. My first thought upon seeing it was hey that'll be perfect to store ammo in as my two current storage boxes are literally at capacity.
As much as I do not like WalMart they are the only game in my county unless one wants to pay high way robbery rates for same at the few local gun shops or buy crap Ultramax reload ammo from Dick's.
- Janq has now started to collect .45 ACP and 9MM brass in preparation for the inevitable
"Killers who are not deterred by laws against murder are not going to be deterred by laws against guns. " - Robert A. Levy
"A license to carry a concealed weapon does not make you a free-lance policeman." - Florida Div. of Licensing
Eric - if you were nearer I would be happy to do just that. However, if you get some books which have been referred to and accumulate brass, and some basic gear - it would not be too onerous.How about some reloading classes Chris? I really need to get onboard with the reloading thing.
Best thing is for folks starting - if they have a very specific question, beyond book info - post it here and one of us will help.
Chris - P95
NRA Certified Instructor & NRA Life Member.
"To own a gun and assume that you are armed
is like owning a piano and assuming that you are a musician!."
http://www.rkba-2a.com/ - a portal for 2A links, articles and some videos.


text:
Mazurka for Two Dead Men
€ 16,99
Besorgung - Lieferbarkeit unbestimmt
November 1992
BeschreibungMazurka for Two Dead Men represents a culmination of the 1989 Nobel Prize winner Camilo Jose Cela's literary art. The novel was originally published in Spain in 1983 and is now presented in a fine translation by Patricia Haugaard. In 1936, at the beginning of the Spanish Civil War, "Lionheart" Gamuzo is abducted and killed, an event recalled repeatedly by the widowed Adega, one of the several narrative voices. In 1939, when the war ends, Tanis Gamuzo avenges his brother. For both events, and for them only, the blind accordion player Gaudencio plays the same mazurka. Set in a backward rural community in Galicia (the author's home territory), Cela's creation is in many ways like a contrapuntal musical composition built with varying themes and moods. In alternately melancholy, humorous, lyrical, or coarse tones he portrays a reign of fools.
Untertitel: Sprache: Englisch.
Verlag: NEW DIRECTIONS
Erscheinungsdatum: November 1992
Seitenanzahl: 312 Seiten
Übersetzer/Sprecher: Übersetzt von Patricia Haugaard
Format: gebunden


text:
Asclepias welshii
|Asclepias welshii
Critically Imperiled (NatureServe)
|Scientific classification
|A. welshii
|Binomial name
|Asclepias welshii
N.H.Holmgren & P.K.Holmgren
Asclepias welshii is a rare species of milkweed known by the common name Welsh's milkweed. It is native to southern Utah and northern Arizona, where there are four known occurrences remaining.[1] Most of the plants occur in Coral Pink Sand Dunes State Park, where the habitat has been degraded in many areas by off-road vehicle use.[1][2] It is a federally listed threatened species of the United States.
This is an erect perennial herb growing up to a meter tall. It is "a rather handsome milkweed" which "is a very distinctive species with no obvious close relatives," according to Holmgren and Holmgren, who described the plant in 1979.[3] It grows from a sturdy rhizome system that anchors it in the unstable sands of its native dune habitat, with several aboveground stems arising from one rhizome system. For this reason, it is not possible to get an accurate count of how many individual plants actually exist, since several widely spaced stems may actually belong to one plant; estimates of the number of plants remaining are based on stem counts.[1] The rhizomes can penetrate very deeply into the dunes, possibly even to the bedrock at the base, and all the plants in one colony may actually be one individual with clones.[4] There are perhaps 20,000 stems, according to count data, for an unknown number of genetically separate individuals.[1] The plant colonizes empty dunes[1] and is eventually outcompeted when other plant species move into the area.[5] A pioneer species of blowouts, it often grows alongside blowout grass (Redfieldia flexuosa), a resident of this habitat type.[4]
The upright stem has several oppositely arranged pairs of leaves up to 9 centimeters long by 6 wide. The stem and leaves are covered in a dense coat of woolly hairs, especially the new leaves. The hairs may prevent the plant from losing water in its dry habitat, or protect the plant tissues from the scouring action of windblown sand.[6] The inflorescence is a dense ball of many flowers, the whole head measuring around 7 centimeters wide.[6] Each flower is just under a centimeter long and white in color with a pale pink center. The fruit is a warty follicle containing large hair-tufted seeds that measure at least 2 centimeters in length. Many plants do not produce many mature fruits and undergo vegetative reproduction, spreading via the rhizome.[6] The plant may be difficult to identify if not in its mature form; the two immature forms look very different.[5] The smallest form which emerges through the sand from the rhizome has narrow linear leaves very unlike those the mature plant, and the secondary form has leaves intermediate to the two.[4]
The largest population of the plant at Coral Pink Dunes State Park, particularly the half managed by the Bureau of Land Management, has been impacted by off-road vehicle use, but such activity in the area has not increased since the plant was listed for protection.[4] Park staff keeps track of off-road vehicle activity on the grounds.[4] ORVs are not allowed in the Paria Canyon-Vermilion Cliffs Wilderness, where there is a widespread occurrence.[7] The plant also occurs south of the Utah border in Arizona. This population is on Navajo Nation territory, which is remote, unmonitored, and not thought to be impacted by human activity.[1]
- ^ a b c d e f The Nature Conservancy
- ^ USFWS. Final rule determining Asclepias welshii (Welsh's Milkweed) to be a threatened species with critical habitat. Federal Register October 28, 1987.
- ^ Holmgren, N. H. and P. K. Holmgren. (1979). A new species of Asclepias (Asclepiadaceae) from Utah. Brittonia 31:1 110-14.
- ^ a b c d e Palmer, B. C. and L. Armstrong. Demography and monitoring of Welsh's milkweed (Asclepias welshii) at Coral Pink Sand Dunes.
- ^ a b Center for Plant Conservation Archived December 15, 2010, at the Wayback Machine.
- ^ a b c Arizona Dept. Fish and Game
- ^ Hughes, L. E. (2000). Monitoring update on four listed plants on the Arizona Strip. In: Maschinski, J. and L. Holter, Eds. Southwestern rare and endangered plants: proceedings of the third conference. USDA FS.


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We are so fortunate to live in such a wonderful community! Check out the beaver dam and the deer in our front yard! Savannah is taking a canoe ride over to see if she can spot any beavers. A tree down after the big wind storm, snowy days, and our beautiful Crystal Lake Lodge!
Doesn't get much better than this!


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|Reviews for Snapshots of a Royal Family
| Guest chapter 2 . 7/8/2013
I hope you pick this story back up and give some more insight into the lives of the other royal children. I also hope you pick back up "SP, EP", as I call it. I greatly enjoyed it, and I can't wait to see how you make it continue, whenever you decide to.
| auzziewitch chapter 2 . 2/20/2011
aww shux. Looking forward to you how you show the interim years between final chapter and epilogue of handmaid (which i loved)
| Diana Prince chapter 2 . 2/17/2011
Yeah it is so nice to see that you are going through with the story. Hope to read more soon thank you.
| Boleyn Girl13 chapter 2 . 2/16/2011
I really liked that Cecily talked to Katherine! Very clever, and I enjoyed it a lot. Good chapter.
| Aye chapter 2 . 2/15/2011
That was nice!
| Anna Taure chapter 2 . 2/15/2011
An update! That's nice. Poor Cecily, struggling with her Spanish and her distaste for her arranged marriage... Who ever said that a princess' life was easy? At least she has her step-mother to help her get through her issues and teach her the proper ways of a Spanish princess, but it won't be easy to tame the girl.
| HerMajesty85 chapter 2 . 2/14/2011
I'm happy Cecily has someone there to help her. That was a beautiful chapter.
| QueenBee10 chapter 2 . 2/14/2011
Loved it
| LeahTeirnan chapter 2 . 2/14/2011
Brilliant as always-i love seeing more of this universe, handmaid is one of my favs
more soon please
p.s. little typo-at the end of the first paragraph of mary's letter you put Edmund instead of Owen
| historyfan chapter 2 . 2/14/2011
Have you changed the names of Anne's sons?
| Robin4 chapter 2 . 2/14/2011
HAPPY DANCE! Oooh, a double update from you! I'm so delighted. As always, I love your stories, and I absolutely adore the relationship between Cecily and Katherine here. I always feel so sorry for poor Katherine, and I love that in Handmaid-and its follow-ons-that you've given her some happiness, even if it wasn't through the son she craved so much. So I really like the ending here, where she and Cecily get to spend some time together.
| unnamed visitor chapter 1 . 10/21/2010
Nice one-shot and I loved the Henry/Edward bonding and that Henry was finally able to open his heart to his son. I am already now dying for the next update. Keep up the great work and I hope to hear back from you soon.
| HerMajesty85 chapter 1 . 10/18/2010
Great one shot. I loved it. Henry finally can put the past behind him and be a father to his son.
| Vain x Life Poetess chapter 1 . 10/18/2010
| Victoria chapter 1 . 10/18/2010
So cute! I'm a huge fan of Handmiad, so of course I love Anne, Katherine, Mary, Cecily, Edmund, Elizabeth, and Owen, but I did wonder how Edward would fit into this dysfunctional family. I'll keep reading, you've started this one off really well.


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Let us know when your receive great advice so we can thank our lawyers and point others with similar questions in the right direction.Got it!
My fiancé is a legal permanent resident of the United States he holds a green card and has a stable job we are about to get married and would like for our parents to be present. His dad has a good job and can Provide ties to our country and show proof of income for him and his wife. The only promble is my mom does not work but she has ties to our country can my fiancé invite (Sponsor ) my mother to come to the US for the wedding and show proof of support for her even if his not a US Citizen yet?
Carl Shusterman, Esq.
Former INS Trial Attorney (1976-82)
Board Certified Immigration Attorney (1986 - Present)
Schedule a Legal Consultation - Telephonic, Skype or In-Person
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(213) 394-4554 x0 Mr. Shusterman is a former INS Trial Attorney (1976-82) with over 35 years of immigration experience. His response to your question is general in nature, as not all the facts are known to him. You should retain an attorney experienced in immigration law to review all the facts in your case in order to receive advice specific to your case. Mr. Shusterman's statement above does not create an attorney/client relationship.Ask a similar question
Yes your parents can file for a tourist visa.
Alexus P. Sham email@example.com (917) 498-9009. The above information is only general in nature and does not constitute legal advice. It does not create an attorney-client relationship.Ask a similar question
Sure he has every right to invite his relatives. Technically speaking, no invitation is required to get a B-2 Visa but since such visas are issued at the discretion of consular officers it is better to provide an invitation with documents supporting ties the invitee's with his/her country.Ask a similar question
Sure, family weddings are a great reason for relatives to come to the US as visitors. Just keep in mind that your parents are the applicants and will have to show sufficient ties to their home country in order to convince the Consular officer that they will return home at the conclusion of their visit.
I'm sure you have your hands full with planning for the wedding, but this might be a good time to also schedule that in-person, telephone, or Skype consultation to talk about what immigration options may be available to you once you marry even if your future husband is not a US citizen yet (permanent residents are able to sponsor their spouses for green cards right now UNDER CERTAIN CONDITIONS).
The information offered is general in nature and not meant to be relied upon as legal advice. Veronica Tunitsky offers in-person, as well as telephone and email consultations. Visit us at www.tunitskylaw.com. Call us at 713.335.5505. Follow and like us on Facebook: https://www.facebook.com/LawOfficeOfVeronicaTunitsky.Ask a similar question
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Set in the Lazio countryside, Mingone features a peaceful garden overlooking the Fibreno River. It also has a popular Italian restaurant with a wine cellar containing over 500 different labels. Mingone is 2.5 miles outside of the town of Arpino, renowned as the birthplace of the ancient Roman philosopher Cicero. It is 1.2 miles from the waterfalls of the Isola del Liri and 30 minutes' drive from the A1 motorway. All accommodation is air conditioned and features a flat-screen TV with satellite and pay-per-view channels. All have a balcony overlooking the surrounding greenery. Apartments include a kitchenette. Guests of Mingone have free parking and free Wi-Fi access. An Italian breakfast is served each morning and a packed lunch service is available.


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High TSH Value
Hi Doctor, My wife is 12 weeks into her pregnancy and TSH value showed up 8.5 and doctor suggested her to take thyronorm 75 mg . She did not had a thyroid problem before this. Can pregnancy sometime cause hypothyroidism. since she has already 12 weeks, is there any chances that it already affected baby?
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Hello, Hypothyroidism of the mother during pregnancy may result in developmental delay in the child. treatment of hypothyroidism in pregnant women is similar to that in nonpregnant women.. A synthetic form of T4 is given to replace the missing hormone. The medication dose is regularly adjusted to maintain a steady blood level of thyroid hormone within the normal range. TSH should be monitored regularly. Tell her to take medications .Pregnancy wil not cause Hypothyroidism.
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15048-15098 Broschart Road
Rockville, Maryland, 20850
Commute to Downtown Gaithersburg
Most errands require a car.
A few nearby public transportation options.
About your score
15048-15098 Broschart Road has a Walk Score of 39 out of 100. This location is a Car-Dependent neighborhood so most errands require a car.
This location is in Rockville. Nearby parks include Green Park, Malcolm King Park and Glenora Park.
Explore how far you can travel by car, bus, bike and foot from 15048-15098 Broschart Road.
15048-15098 Broschart Road has some transit which means a few nearby public transportation options.
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66 Shady Grove-Traville Transit Center
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74 Shady Grove-Germantown Transit
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43 Shady Grove-Traville Transit Center
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56 Rockville-Lakeforest
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This location is in the city of Rockville, MD. Rockville has an average Walk Score of 53 and has 61,209 residents.Learn More About Rockville


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Finally an EMR created by a physician and presented by a physician
EMR demo by local EMC physician
This Event has past- View the videos
Check back for future dates.
Special Guest Speaker: Ivor Nazareth, MD
Location: Eisenhower Medical Center Auditorium
Who better to present than one of your own colleagues who recently switched to EMR?
We are very excited to announce our upcoming event at Eisenhower Medical Center. Ivor Nazareth, MD will be our special guest speaker. Dr Nazareth has practiced medicine for 35 years and has been with Eisenhower Medical Center for 34 years. Toward the end of 2009 he changed his practice to a paperless office. Dr Nazareth chose McKesson's EMR solution- Practice Partner. At this event he will demonstrate how he uses an electronic medical record in his practice.
Before he moved to an electronic medical record he dictated his notes and used a transcriptionist. Now with EMR he continues to dictate using Dragon Naturally Speaking. Dr Nazareth explains, "I don't have a transcriptionist anymore. My transcription bill used to be between $3,000 to $3,500 a month and now that is gone." He loves that this not only saves him money but the speed and efficiency allow him to see 33% more patients a day than he was previously seeing with his paper charts! And unlike before, he no longer has to dictate the same long notes over and over again- he simply copies and pastes the information from a previous visit. He said he of course had to get to know dragon and dragon had to get to know him and his accent. "You've got to put in the effort first, then after you've put in the required amount of effort it is going to pay you back in dividens. It is a process. You have to work at it to be successful, I guess its even like a marriage- except that dragon doesn't talk back to you," he chuckles. "Now I can speak naturally, as fast as I am speaking to you, and it will pick up the text."
Dr Nazareth shared, "The jump from the old paper system to the new EMR system took a leap of faith and a little bit of training, but in the end it was worth it."
Ask him questions and hear his opinion on the software, the implementation, you name it- the floor is open for your questions.
This event is sponsored by Eisenhower Medical Center, McKesson, and AZCOMP Technologies. Find out more about this partnership and what this means for EMC physicians.
Chart the way you want to
One of the most unique things about Practice Partner EMR, Medisoft Clinical, and Lytec MD is Bright Note Technology. This allows a physician to chose whatever style of documentation they prefer. If you missed our last event we had Jaron Fischbeck, MD and Janet Mullins, MD show how they use templates with their electronic medical record. View videos


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Nightwing (Volume 2) Issue 116
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|General Information
| Nightwing
Infinite Crisis
|Issue Number:
|First Published:
|March 2006
|Previous Issue:
|Nightwing #115
|Next Issue:
|Nightwing #117
Nightwing returned to Bludhaven after its destruction, looking to help anyone he could. Superman flew in hoping to convince Dick to get out before he got radiation poisoning, but the hero refused to let his city die without taking action. As he helped a child find his mother, Chemo blew up again. He told cops the best way to get people out of the city; they were very receptive to his help. He found Sophia and placed her in the care of Captain Amy Rohrbach. Another blast struck and Nightwing was knocked unconscious.


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July 1987
Peter Balakian, Deborah Boe, Neal Bowers, Peter Cooley, James Dickey, Barry Goldensohn, Jayanta Mahapatra, Gail Mazur, Ed Ochester, Aleda Shirley, Diane Stevenson, Jon Veinberg, Susan Wood, Robert Shaw
Interested in discovering other ways to approach a poem? Have a look at the discussion guide for the May 2017 issue.
Originally appeared in Poetry magazine.
This has learning resources.
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An Introduction to DB2 for OS/390 and z/OS System Structures for DB2 Distributed Users
© 2002 International Business Machines Corporation. All rights reserved.
Editor's Note: The following article is an abbreviated version of the author's longer article, Getting Started with DB2® for z/OSTM and OS/390TM Version 7 for DB2 Distributed Platform Users (PDF, 333 KB), that discusses application development, tools, locking and concurrency, and much more.
If you understand DB2 for UNIX®, Linux and Windows®, it is not difficult for you to leverage that knowledge in understanding DB2 for OS/390TM and z/OSTM. In this article, I compare system structures on DB2 for OS/390 and z/OS with structures you probably already understand on DB2 for Linux, UNIX, and Windows.
If you are interested in learning more, an expanded version of this article called Getting Started with DB2 for z/OS and OS/390 Version 7 for DB2 Distributed Platform Users provides much more detail, including information about application development, tools, locking and concurrency, and much more.
In this article, I use DB2 ULWO to refer to DB2 Universal Database Version 7.2 for UNIX, Linux, Windows and OS/2®. I use DB2 S/390® to refer to DB2 Universal Database for z/OS and OS/390 Version 7.
Figure 1 and Figure 2 show a simplified view of the DB2 ULWO system structure and the DB2 S/390 system structure, respectively.
Figure 1. DB2 system structure on UNIX, Linux, Windows, and OS/2
Figure 2. DB2 system structure on OS/390 and z/OS
Instances and subsystems
In DB2 ULWO, an instance provides an independent environment where database objects can be created and applications can be run against them. When an instance is created, links to the DB2 code are generated. Several instances can be created in the same machine. In Windows platforms, you can install only one version of DB2 at a given fixpack level. Thus, all instances created in DB2 UDB for Windows will be linked to the same DB2 code. In UNIX platforms, you can install several versions of DB2 in the same machine because they are installed in different paths; however, only one fixpack level per version is allowed. Thus, in DB2 UDB for UNIX, you may have several instances linking to different code sets.
In DB2 S/390, a DB2 subsystem provides a separate DB2 environment similar to a DB2 ULWO instance. Several DB2 S/390 subsystems can be installed in the same machine logical partition (LPAR), and they can only communicate with each other through the Distributed Data Facility (DDF). (Data sharing provides another way that DB2 subsystems work together, but I don't cover that topic in this article.)
You can install different DB2 S/390 subsystems at different versions in the same LPAR. You can also have different DB2 S/390 subsystems at the same version but with different maintenance levels installed in the same LPAR. In both of these cases, different code sets are used. For example, you might have DB2 S/390 V6 at maintenance level 0112, DB2 S/390 V7 at maintenance level 0106, and DB2 S/390 V7 at maintenance level 0110 installed in the same machine LPAR. DB2 subsystems running with the same version and at the same maintenance level in a LPAR, are also allowed; in this case the DB2 code is shared.
In DB2 ULWO names you may need are:
- An instance name
An instance name uniquely identifies an instance in your machine. As described in Directing commands, you use the instance name to direct commands to a particular DB2 instance.
- One or many database names
Unlike DB2 S/390, a client connects to a particular database rather than a subsystem.
When connecting to a database using TCP/IP, you will also need the TCP/IP address and port for the instance. Other network protocols will need other information.
In DB2 S/390, several names are used to identify a subsystem:
- Subsystem ID (ssid)
Because DB2 is a subsystem of MVS, it will have a subsystem name or subsystem ID (ssid) that MVS can use to identify it. The default ssid is DSN1. The command prefix identifies the particular DB2 subsystem that you connect to. You do not connect to a particular database. You are automatically able to access any database in DB2 to which you are authorized.
- The location name
This is the name specified when using the CATALOG DCS DATABASE command from a DB2 Connect machine, which refers to it as the target database name. It can have from 1 to 16 characters.
- The LU name
This is the name by which VTAM can recognize the local subsystem. The unique name must be unique within the network of connected systems and can have from one to eight characters.
When connecting to a DB2 S/390 subsystem from a DB2 ULWO or DB2 S/390 client using TCP/IP, the TCP/IP address, the port for the subsystem and the location name are needed.
Directing commands
In DB2 ULWO, you can direct commands to a specific instance by setting the value of the DB2INSTANCE variable (
set DB2INSTANCE=<instance name>) or "attaching" to the instance using a node previously defined (
attach to <nodename>). In DB2 S/390 you can execute DB2 commands from different places. The
START DB2 command is the only command that is normally executed from the MVS console. Because you can have different DB2 subsystems installed, a command prefix is required for MVS to know to which DB2 should this command be applied to. This command prefix can have up to eight characters. The default is -DSN1, in which DSN1 is the default MVS subsystem name for DB2.
As an example of using a command prefix, if you want to start up a particular DB2 V7 subsystem and that subsystem has been assigned the command prefix of "#", use the command
#START DB2 from the MVS console. If you would like to start DB2 S/390 V6 subsystem that has a command prefix of '-', execute the command
-START DB2 from the MVS console. Each subsystem is running on its own address space, and can run concurrently.
The above command prefix is only required when performing DB2 commands from a place where you can access different DB2 subsystems (like the MVS console). If you are performing a DB2 command from applications that attach to only one subsystem at a time, you do not need to use specific prefixes, other than the hyphen (-), which should always be used in those cases.
Connecting a client
In DB2 ULWO, you attach to an instance to perform some administrative operations, and you connect to a database to perform database operations. In DB2 S/390 you connect to a subsystem, and perform both, administrative as well as database operations. Thus, a DB2 ULWO client connecting to DB2 S/390 (through DB2 Connect software and DDF) will not connect to a specific database, but to the entire DB2 S/390 subsystem. In DB2 ULWO you must connect to a specific database which has its own catalog. For DB2 S/390, a database does not have its own catalog, but there is one catalog for the entire DB2 subsystem; therefore, when you want to access a specific DB2 S/390 database, you actually connect to the entire DB2 subsystem.
Databases and system table spaces
This section contains information about databases and temporary work spaces. In addition, it briefly describes the different uses for directories.
In DB2 ULWO, an instance can have several databases. Each database is one closed and independent unit containing its own logs, catalog and database configuration files. You cannot perform queries that would involve tables of two different databases (unless you use Relational Connect or DataJoiner® which are out of the scope of this document). The catalog (SYSCATSPACE), temporary space (TEMPSPACE1) and the user space (USERSPACE1) are all table spaces. These are created automatically when you issue a CREATE DATABASE command.
In DB2 S/390, a DB2 subsystem can contain several databases. Databases in this subsystem interact with each other. In fact, as you can see from Figure 2, the catalog itself (DSNDB06) is a database. The work file database (DSNDB07) would correspond to the temporary space used in DB2 ULWO. The default database (DSNDB04) is used to store objects that users create without explicitly indicating the database the objects belong to. DSNDB04 would correspond to USERSPACE1 in DB2 ULWO. The catalog, directory, and other system structures are created once at DB2 subsystem installation time, not like in DB2 ULWO where a catalog and other system structures are created for every CREATE DATABASE that is executed.
The DB2 ULWO catalog tables use the schema SYSIBM. In addition, DB2 ULWO provides read-only catalog views, which use the schema SYSCAT. Updatable catalog views are in the schema SYSSTATS. DB2 S/390 catalog tables use the qualifier of SYSIBM.
Some of the DB2 S/390 catalog tables are updatable, including some of columns that hold statistics information about the data.
Under the DB2 S/390 structure, you can perform SQL operations using tables from different databases. For example, say you have table TS56692.testtbl in database MYDB1 and table DSN8710.emp in the default database DSNDB04. Then, you can execute the following query:
SELECT B.name, B.salary FROM TS56692.testtbl A, DSN8710.emp B WHERE A.id = B.edlevel
Without federation, this query would not work in DB2 ULWO because the two tables are in two different databases.
Temporary table spaces
DB2 ULWO has two types of temporary table spaces: system and user. You must always have a system temporary table space available, because this is the work area for the database manager to perform operations like joins and sorts. User temporary table space, on the other hand, are used to store declared global temporary tables. These tables are not persistent, they only "live" for a given connection or while the application that declared them is running.
Similarly, DB2 S/390 provides two types of temporary space. The work file database (DSNDB07 is the default name) corresponds to DB2 ULWO's system temporary table space. DB2 S/390's TEMP database would correspond to DB2 ULWO's user temporary table space. The TEMP database is used also for server side scrollable cursors, so client applications using this type of cursors may get an error if such a database has not been created ahead of time. The concept of global temporary table is the same in these platforms.
DB2 ULWO has a database directory, a node directory, and a dcs directory. These directories contain connectivity information and perform a similar function to DB2 S/390's communication database (CDB). Don't confuse this use of the term directory with the use of the term in DB2 S/390. The DB2 S/390 directory contains vital information about the subsystem and it is stored in an internal format. It is not intended to be used by regular end users.
DB2 ULWO uses active and archive logs for recovery purposes. It keeps track of its logs using the file SQLOGCTL.LFH, which is stored in the same directory as the database files (
<instance name>.NODE0000.SQL0000x). Version 7 allows dual logging capability. DB2 S/390 also has active and archive logs. A data set called the bootstrap data set (BSDS) is used to keep track of its logs. Dual logging has been available in DB2 S/390 for many versions of the product.
Data caching and page sizes
DB2 ULWO uses buffer pools to improve the performance of a database. In DB2 ULWO, use the command
CREATE BUFFERPOOL to create a new buffer pool. In DB2 S/390, there are predefined buffer pools, most of them starting with a size of zero. In order to "create" a buffer pool, you have to use the
ALTER BUFFERPOOL command and set a size greater than zero.
In DB2 ULWO, you specify the data page size as part of the
CREATE TABLESPACE statement. A buffer pool with the correct page size needs to be created before creating the table space that uses this page size. In DB2 S/390, there is no parameter in the
CREATE TABLESPACE statement that indicates the page size to be used; however, by specifying the buffer pool for the table space, you implicitly determine the page size.
DB2 ULWO uses Extended Storage (which can be set with the database configuration parameters ESTORE_SEG_SZ and NUM_ESTORE_SEGS) to provide a second level of caching; DB2 S/390 uses hiperpools.
Configuration parameters
DB2 ULWO has parameters at the instance level (dbm cfg) as well as at the database level (db cfg). Changes to instance level parameters currently require that you start and stop DB2. Changes to database level parameters require that all connections be terminated before the changes take place on the next connections. In DB2 S/390, these parameters are often called "zparms" (for the default name of the parameter module, which is DSNZPARM). There is only one set of parameters that would affect the entire DB2 subsystem and its databases. The job DSNTIJUZ is used to specify the desired values for these parameters. When run, this job will assemble and link-edit the DSNZPARM module as well as the application program's default module DSNHDECP. The assembled zparm module can be specified when starting DB2. If it is not specified, the module with name DSNZPARM will be used. In versions prior to V7, changes to zparms required DB2 S/390 to be recycled (stopped and started) to load the new parameter module into memory. With V7, this is still the case for some parameters but not for all. The new SET SYSPARM command allows you to load a new parameter module without recycling DB2.
Governing queries
DB2 ULWO uses the governor to monitor and limit the activity of applications against a given database. A configuration file with rules is provided, and the db2gov command is used to start the governor. Similarly, DB2 S/390 uses the Resource Limit Facility (RLF). This facility is started with the
START RLIMIT command, and the rules are stored in database DSNRLST.
Table 1, below, summarizes and compares the system structure concepts described in this article.
Table 1. Comparing DB2 S/390 and DB2 ULWO system structures
|DB2 S/390 Concept
|DB2 ULWO Analogy
|Catalog database (DSNDB06)
|SYSCATSPACE tablespace
|Directory database (DSNDB01)
|Communications database (CDB), part of the catalog
|Database directory, node Directory, DCS directory
|Active and archive logs concept
|Similar concept as in DB2 S/390
|Dual logging supported
|Dual logging supported
|Bootstrap dataset (BSDS)
|Predefined buffer pools are "created" with -ALTER BUFFERPOOL
|Buffer pools are created with CREATE BUFFERPOOL
|Extended Storage (ESTORE)
|Resource Limit Facility (DSNRLST)
|- The DB2 Governor (db2gov)
- Query Patroller
|Work file database (DSNDB07)
|TEMPSPACE1 tablespace (system temporary tablespace)
|TEMP database, for global temporary tables
|User temporary tablespace, for global temporary tables
|Default database (DSNDB04)
|USERSPACE1 tablespace
|Can execute queries involving tables of different databases
|Cannot execute queries involving tables of different databases (without federation)
|Client connects to a DB2 subsystem, not to a particular database
|Client connects to a database
|DSNZPARM (SET SYSPARM command allows DSNZPARM module to be loaded in memory while DB2 is up, but for some parameters, a -stop db2, -start db2 is still required)
|DBM CFG (db2stop, db2start required for new values to be in effect) and DB CFG (all connection need to be terminated for the new values to be in effect on next connection)