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US8135024B2 - Method and system to reduce interconnect latency - Google PatentsMethod and system to reduce interconnect latency Download PDF
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- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L45/00—Routing or path finding of packets in data switching networks
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L45/00—Routing or path finding of packets in data switching networks
- H04L45/62—Wavelength based
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L47/00—Traffic regulation in packet switching networks
- H04L47/50—Queue scheduling
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L47/00—Traffic regulation in packet switching networks
- H04L47/50—Queue scheduling
- H04L47/58—Changing or combining different scheduling modes, e.g. multimode scheduling
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L49/00—Packet switching elements
- H04L49/25—Routing or path finding through a switch fabric
- H04L49/253—Connections establishment or release between ports
- H04L49/254—Centralized controller, i.e. arbitration or scheduling
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/28—Data switching networks characterised by path configuration, e.g. local area networks [LAN], wide area networks [WAN]
- H04L12/40—Bus networks
- H04L12/407—Bus networks with decentralised control
- H04L12/417—Bus networks with decentralised control with deterministic access, e.g. token passing
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L43/00—Arrangements for monitoring or testing packet switching networks
- H04L43/08—Monitoring based on specific metrics
- H04L43/0852—Delays
- H04L43/087—Jitter
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L49/00—Packet switching elements
- H04L49/30—Peripheral units, e.g. input or output ports
- H04L49/3027—Output queuing
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L49/00—Packet switching elements
- H04L49/50—Overload detection; Overload protection
- H04L49/505—Corrective Measures, e.g. backpressure
- H04L49/508—Head of Line Blocking Avoidance
This application claims the benefit of U.S. Provisional Application No. 60/736,779, filed Nov. 14, 2005, entitled "METHOD AND SYSTEM TO REDUCE INTERCONNECT LATENCY."
This invention was made with Government support under Contract No. W-7405-ENG-48 awarded by DOE/NNSA. The Government has certain rights in this invention.
1. Field of the Invention
The present invention relates to the field of packet switching, and more particularly to the field of input-queued packet-switch architectures, with particular applicability to computer interconnection networks.
2. Description of the Related Art
Advances in transmission technologies and parallelism in communications and computing are constantly pushing the envelope of bandwidth available to transfer information data. For instance, advances such as wavelength-division multiplexing (WDM) and dense WDM (DWDM) greatly increase available bandwidth by multiplexing large numbers of channels onto a single fiber. Each individual channel operates at the Optical Carrier (OC-x) rates OC-48 (2.5 Gb/s), OC-192 (10 Gb/s), or OC-768 (40 Gb/s). Using state-of-the-art DWDM techniques, a single fiber can carry over 5 terabit of data per second.
At the same time, the gap is widening between the increasingly high speeds provided by such advances and the speeds at which available switches are capable of switching. While optical switches provide such theoretical advantages of routing through free space, minimal signal attenuation over large distances, and the elimination of conversion between the optical domain to the electrical domain and back again, current all-optical type switches are relatively slow or prohibitively expensive. In addition, optical storage of information is very cumbersome and often impractical. Until the shortcomings of optical switching are overcome, electronic switches will continue to play a dominant role in packet switching schemes.
Typically, a backplane switch, or more generally a routing fabric is used to interconnect boards. In networking systems, these boards are called line cards, and in computing and storage, they are often called adapters or blades. An increasingly broad set of systems uses backplanes to connect boards, such as telecommunication switches, multiservice provisioning platforms, add/drop multiplexers, digital cross connects, storage switches, routers, large enterprise scale switches, embedded platforms, multiprocessor systems and blade servers.
When information data is transmitted from a source to a destination through an interconnect system, the information often is first segmented into data packets. Each data packet typically includes a header, payload and tail sections, and is further segmented into smaller units. A data packet is switched through a routing fabric simultaneously with other data packets originating from other sources. Many current packet switch systems, including those employed in interconnects for parallel computers, Internet routers, S(t)AN networks, Asynchronous Transfer Mode (ATM) networks, and especially in optical networks, use an input-queuing arrangement, include queues sorted per output at every line card (such an arrangement, often called virtual output queuing (VOQ), eliminates head-of-line blocking inherent to the use of FIFO queues), a crossbar routing fabric, and a centralized scheduler (e.g., arbiter or arbitration unit), that allocates switching resources and arbitrates among the queues.
The arbiter 107 performs processes involving allocating input ports and output ports in a non-conflicting manner to packets waiting in the buffers of the buffer groups 121. These processes include allocation and arbitration. Allocation determines a matching between the inputs 2 b 1 to 2 b N and the outputs 3 1 to 3 N of the routing fabric 106 such that at most one packet from each buffer group 121 is selected for output to at most one output resource. Arbitration resolves multiple requests for a single output resource 3 1 to 3 N and assigns a single one of the outputs to one of a group of requesters. In the conventional arrangement of
As can be seen, there are two basic paths of communication in such input-queuing systems: control paths, which include flow of control information from the line cards to the arbiter (e.g. requests) and back to the line cards (e.g. grants), and data paths, which include flow of data packets from the input line cards through the crossbar and to the output line cards.
While the conventional packet switching arrangement illustrated in
With increasing capacity, the physical size of packet switches also is growing. At the same time, the duration of a single packet or cell (T=L/B, where L is the length of a packet in bits, and B the link rate in bits per second) is shrinking because although the line rate increases, packet sizes remain substantially constant. These trends directly imply a significant jump in the switch-internal round trip (RT) measured in packet times. This effect hits centrally-arbitrated input-queued switches doubly hard, because the minimum transit latency in such a switch is composed of two latencies: (1) the latency of submitting a request to the arbiter and waiting until the corresponding grant arrives, which includes the time-of-flight to and from the arbiter and the time to arbitrate; and (2) the latency of serialization/deserialization (SerDes), transmission, and time-of-flight to send the packet through the switch. Roughly speaking, these latencies amount to a minimum latency of 2 (RT) packet times, which is double that of a similar switch, but one having a buffered routing fabric.
Because these latencies have become a relevant issue only recently, they have received very little attention. In practice, a preferred solution has been to physically locate boards, such as line cards having input queues (typically organized in a VOQ fashion), close to the routing fabric (e.g., a switch core including a crossbar and arbiter). However, current packaging and power constraints prohibit placing a large number of line cards close to the switch core. As a result, such conventional arrangements cannot address ever-increasing demands for more bandwidth by simply increasing the number of line cards located at the routing fabric.
U.S. Pat. No. 6,647,019 to McKeown et al. attempts to increase the number of line cards, and thus the aggregate system bandwidth, by physically separating the line cards from the routing fabric. The bulk of buffering and processing is implemented on the physically remote line cards.
As shown in
The main drawback of the McKeown et al. approach is that both the line cards 202 and the switch ports 280 contain buffers, even though only a small amount of buffering, namely, enough packets to cover one RT, is required in the switch ports 280. These buffered switch ports add cost, card space, electrical power, as well as latency (e.g., additional SerDes and buffering). They also duplicate functionality already present in the line cards 202.
Even using the approach described in the McKeown et al. patent, it would be difficult in practice to achieve a round-trip time between the switch ports 280 and the arbiter module 207 that is shorter than one cell time. Moreover, in the specific case of a switch fabric that comprises optical links from line cards to switch core (to cover the long distance from line cards to switch core) and an optical routing fabric, the switch ports 280 would require additional electrical-to-optical and optical-to-electrical conversions for buffering in electrical/CMOS chips because optical buffers are currently not practically or economically feasible. Such added conversion circuitry would significantly increase the cost and complexity of the system.
Another approach to reducing interconnection network latency, presented in W. J. Daily et al., "Principles and Practices of Interconnection Networks," Morgan Kaufman, 2004, pages 316-318, involves "speculation with lookahead." As described in Dally et al., a router's matching arbiter uses speculation with lookahead to look deeper into an ingress VOQ queue than the first member (head of line, or HoL) and allocate ahead of time some switch resources with the expectation (hope) that grants will be offered for those subsequent packets. This approach attempts to reduce the pipeline to as few stages as possible by enabling the router to perform some matching and setup tasks in parallel. While speculation with lookahead benefits queued packets that dwell in the ingress VOQ, and packets that have already made transmission requests that cannot be served immediately by the arbiter, it does not speed the transmission of packets whose transmission requests have not yet been received by the arbiter for consideration and/or packets that have just arrived at the ingress VOQ.
Further, speculation with lookahead addresses latency mostly in the arbiter algorithms and does not address the usually larger transmission time latency from the transmitter to the switch fabric. Earlier concepts of double and even triple speculation (e.g., see page 317 of Dally et al.), which rely on internal switch speedup and light switch loading to speculatively allocate even more of the switch's resources, fail in most applications. In many conventional strictly non-blocking switch fabrics, the internal fabric is internally partitioned into several successive switching stages. In double and triple speculation, those stages are incrementally set (allocated) for the speculative load. Only when the speedup is extreme or the load is light do speculations in these schemes regularly succeed in granting transmission through the entire multistage fabric. As the load increases, this approach to speculative allocation can hurt performance because it wastefully reserves resources that would be better allocated to successfully arbitrated requests.
Additionally, all of the above-described systems still suffer from the first RT latency in which the line card must wait until a grant arrives after submitting a request for an output resource.
Thus, there remains a need in the art for more efficient, less complex and lower cost ways to reduce latencies associated with routing fabrics in interconnect systems.
Accordingly, the present invention is directed to a method and apparatus that substantially obviates one or more of the shortcomings or problems due to the limitations and disadvantages of the related art.
The present invention includes both a system and a method for transmitting information units that reduces overall latency incurred by scheduled arbitration in systems employing routing fabrics. The method is particularly suited in systems including switched fabrics in which data packets are sent with or without scheduled arbitration from a plurality of sources to inputs of a routing fabric, which switches the input packets to specified routing fabric outputs.
In an aspect of the present invention, a method includes a step of sending at least one data packet according to the result of the prior arbitration (i.e., the scheduled arbitration) if a result of a scheduled arbitration is present, and if no scheduled arbitration result is present, selecting a data packet to transmit speculatively. The method also includes simultaneously issuing a speculative request that includes an output identifier of the selected data packet and sending the selected packet to the routing fabric.
In another aspect of the invention, a system for transmitting data packets with or without scheduled (prior) arbitration from a plurality of inputs to a plurality of outputs of a routing fabric includes a mechanism for sending at least one data packet according to the result of a scheduled arbitration, if a result of a prior arbitration is present, and a mechanism for selecting a data packet to transmit speculatively, and simultaneously issuing a speculative request that includes an output identifier of the selected data packet and sending the selected packet to the routing fabric, if no scheduled arbitration result is present.
Another aspect of the invention involves a system for managing the flow of information units among plural locations. The system includes a plurality of inputs for receiving requests for access to a switching fabric to transmit information units from source locations to destination locations. The requests for access include requests for scheduled arbitrated grant of access and requests for speculative access without prior arbitrated grant. Each request also includes an indication of a destination location to which to transfer an associated information unit. The system includes an arbiter for determining a conflict-free allocation of the switching fabric resources for a group or subgroup of the requests for scheduled arbitration grant of access. The system includes a speculative arbiter for receiving the speculative access requests at a time in which the determined group of requests is to be next applied to the switching fabric, and granting or denying the received speculative requests based on the determined allocation.
Yet another aspect of the invention is facilitating an increase in speed of transmission of data packets just arriving at an ingress queue without the need to pre-allocate or reserve switching resources, which otherwise would be wasted if a grant ultimately is denied.
Another aspect of the invention involves reducing average latency by way of reducing an amount of roundtrip transmissions between packet source and routing fabric. For instance, each successful speculative transmission of a packet saves at least one round trip (i.e., from transmission of request until reception of grant) that would otherwise be required to send the packet through a routing fabric.
Additional aspects and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned from practice of the invention. The aspects and advantages of the invention will be realized and attained by the system and method particularly pointed out in the written description and claims hereof as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and exemplary only and are not restrictive of the invention, as claimed.
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention that together with the description serve to explain the principles of the invention. In the drawings:
These and other aspects of the invention will now be described in greater detail in connection with examples that are illustrated in the accompanying drawings.
As described above in connection with the related art, central arbitration arrangements achieve high maximum throughput, but incur the penalty of the arbitration latency, especially at low to medium utilization. The present invention addresses such latencies using a novel kind of speculation called speculative transmission (STX). The concept of STX described herein is related to the basic concept behind ALOHA and Ethernet, in which packets are transmitted without prior arbitration (i.e., there is speculation on the success of a given transmission) over a shared medium. However, in the present invention, this concept is applied in the context of a switched medium to eliminate the arbitration latency. Because operating a packet switch using only speculative transmissions would lead to frequent packet collisions, resulting in catastrophic performance at medium to high utilization, the present invention combines speculative transmission and arbitration to obtain the advantages of both concepts, i.e., high maximum throughput and lower latency at low to medium utilization.
The present invention reduces arbitration latency by employing STX without prior arbitration in combination with routing fabric arbitration without implementing an additional stage of buffering close to the routing fabric. Moreover, the present invention allows very deep pipelining of the speculative operations, such that round trips that are (much) larger than the packet duration can be dealt with effectively. The present invention substantially reduces or eliminates the average latency incurred by arbitration in switching fabrics, thereby achieving a 50% or lower decrease in overall latency.
In contrast to the speculation schemes of the prior art, which involve pre-allocations of switch resources that often are wasted, the efficient non-blocking single-stage broadcast nature of the routing fabric described herein does not pre-allocate such resources. In other words, the present invention implements a single-stage selector in the switching fabrics, and thus avoids wasting switch resources because fabric resources are not actually speculatively set.
The present invention addresses issues related to STX selection policy, collisions, retransmission, out-of-order delivery, resequencing, duplicate delivery, retransmission and resequencing window sizing. However, it should be understood that other issues and particularities related to switching fabrics that would be pertinent to any particular application of the present invention would be readily appreciated by those skilled in the art.
The present invention may be utilized with other types of routing fabrics. It is, however, especially suited for crossbar-based switches. Thus, while the system illustrated in
A property of a crossbar-type switch is that, at any time, an input can only be connected to one output, and vice versa. That is, there is a one-to-one matching between inputs and outputs of the switch. To obtain good performance in terms of latency and throughput, a matching is typically computed by a centralized allocation and arbitration unit. Additionally, the allocation and arbitration unit resolves contentions for a single output resource of the switch. In the exemplary system shown in
The arbiter 307 receives requests for output resources from the line cards 302. A request includes an output port identifier, which indicates that the line card 302 that originated the request wishes to transmit a packet to a specific output port. Based on the received requests, the arbiter 307 computes a suitable one-to-one matching between input and output ports, which is equivalent to a bipartite graph-matching problem. Based on the computed matching, the arbiter 307 returns the corresponding grants to the line cards 302, where a grant comprises an output port identifier meaning that the line card 302 receiving this grant is allowed to transmit a packet to this specific output port. Optionally, when no output resource is available for a particular request, the arbiter 307 may return an acknowledgment corresponding to a denied request. When a line card 302 receives a grant, it dequeues a packet from the corresponding VOQ of ingress buffer unit 321 and transmits it on data link 303 to the crossbar 306. The crossbar 306 routes the incoming packets to the data links 303 according to the configuration (i.e., the matching) computed by the arbiter 307 and applied via the configuration link 312.
In operation, packets arrive on input data link 301 connected to the ingress buffer unit 321 and the demultiplexer 410 routes incoming packets to the corresponding VOQ 411 in accordance with their respective destinations (output ports). The arrival of the packet also is communicated to the control unit 416. The control unit 416 sends requests to the arbiter unit 307 and receives grants from the arbiter unit 307 via control channel 304. When sequence numbers are required for the reliable delivery scheme, the control unit 416 assigns subsequent sequence numbers to subsequent packets destined to the same output. Requests for scheduled arbitration and speculative requests, and grants and acknowledgments, all comprise an output identifier. Speculative requests, grants, and acknowledgments may additionally include a sequence number. For example, certain types of reliable delivery (RD) methods, some of which are described later, may require that data packets transmitted as a result of a scheduled arbitration and data packets speculatively transmitted each have a sequence number.
The system comprises two modes of transmission, namely, arbitrated transmission (i.e., transmission resulting from scheduled arbitration) and speculative transmission (STX). The scheduled arbitration mode of transmission is known from the prior art. For instance, see C. Minkenberg et al., IP.com, Jun. 3, 2004, article number IPCOM000028815D, the entire contents of which is incorporated herein by reference. The present invention addresses the speculative transmission mode and the interaction between the scheduled arbitration and speculative transmission modes. This is accomplished by distinguishing between requests for scheduled arbitration and the corresponding grants on one side, and speculative requests and the corresponding positive and negative acknowledgements on the other.
Returning to
The selected packet is stored in the retransmission buffer 412 via mux 413 and transmitted towards the crossbar 306 on data link 303 via muxes 413, 414, 415. Simultaneously, control section 416 sends a corresponding speculative transmission request comprising the output identifier via control link 304 to the arbiter 307. The purpose of storing the packet in retransmission buffer 412 is to allow a retransmission of the packet in case the speculative transmission fails. A line card 302 also may issue a request for scheduled arbitration seeking a grant and a speculative request simultaneously. In a preferred embodiment, packets stored in a retransmission queue 412 would not be eligible for speculative transmission, because they have already been transmitted speculatively once. That is, little or no advantage would be gained in resending failed STX packets speculatively because it would be highly likely that the potential latency advantage has already been lost.
If a line card 302 receives a grant by way of scheduled arbitration for a given output in a given time slot, this line card 302 would be eligible to transmit a packet for this output in the current time slot. The control unit first checks the occupancy of the corresponding retransmission queue 412. If it is not empty, one packet is dequeued from this retransmission queue 412 and is retransmitted on data link 303 to the crossbar 306 via muxes 414 and 415. If the retransmission queue 412 is empty, the control unit checks the occupancy of the corresponding VOQ 411. If retransmission queue 411 is not empty, one packet is dequeued from this VOQ 411 and transmitted on data link 303 to the crossbar 306 via the multiplexers 413, 414 and 415. It is to be understood that packets waiting in the RTX queue 412 usually would have priority over the packets in the corresponding VOQ 411 when a grant arrives. This is to ensure that failed STX packets are quickly delivered to their destination. However, priority also may depend on other factors, such as the nature of data (e.g., incoming latency-sensitive data such as speech and video) waiting or arriving in the queues 411. Owing to the speculative mode of operation, it may happen that a grant arrives for an empty VOQ 411. Such a grant is referred to as wasted. In a preferred embodiment, a line card 302 is eligible to send a speculative packet in any time slot in which it received a wasted grant.
In exemplary embodiments of the invention described below, if a line card 302 receives an acknowledgment, it checks whether the packet with the sequence number included in the acknowledgment is present in the retransmission queue 412 indicated by the output identifier also included in the acknowledgment. If this packet is not present, the acknowledgment is ignored. If it is present, an action is taken that may depend on a specific application of the present invention, for example, one integrating a reliable delivery scheme (see section "Reliable Delivery"). For instance, in an exemplary embodiment utilizing Selective Retry (SR), the acknowledged packet (if present) is dequeued from any position in the retransmission queue 412. In alternative exemplary embodiments (e.g., Go-Back-In (GBN), Stop & Wait (S&W)), the acknowledged packet would only be dequeued if it were at the head of a retransmission queue (GBN) or VOQ (S&W).
No Resequencing at Egress
In operation, packets arrive at the egress buffer unit 322 a along data link 303. The control section 528 inspects the packet header and decides whether enqueuing unit 521 should store the packet in output queue 526 or drop the packet. When a Stop & Wait or a Go-Back-N RD scheme is used, packets are only accepted in the correct order. It is to be understood, however, that even with Stop & Wait duplicate deliveries may occur, whereas with GBN duplicate and out-of-order deliveries may occur. Therefore, the control unit 528 maintains the next expected sequence number for every input. The control unit 528 checks whether the sequence number of the packet received equals the next expected sequence number for the corresponding input (e.g., the sequence number of the last successfully received packet plus one). If this is the case (i.e., the expected and received sequence numbers are equal), the packet is enqueued in the output queue 526. Otherwise, the packet is dropped because it is either a duplicate (e.g., sequence number too low) or out of order (e.g., sequence number too high).
The dequeuing unit 527 dequeues a packet, if present, from output queue 526 and transmits it on the external data link 301.
With Resequencing at Egress
In operation, egress buffer unit 322 b receives packets on data link 303. The control unit 628 checks whether an arriving packet is in order (i.e., whether its sequence number is equal to the next expected sequence number for the corresponding input). If this is the case, the packet is routed via demux 621 and mux 625 and enqueued directly in the output queue 626 and the expected next sequence number is incremented. It is to be understood that a value of a next expected number depends on a particular type of sequencing scheme chosen. For example, in one exemplary embodiment described below, packet sequence numbers are numbered using integers incremented by one for each next packet in an expected order. Of course, resequencing may be performed using any one of a number of other sequencing schemes, such as one in which numbers decrement in a sequence order, and/or ones in which a packet sequence number increments or decrements by a value other than one. If the packet arrives out of order (e.g., its sequence number is larger than the next expected sequence number for the corresponding input), it is routed via demux 621 and demux 622 to the resequencing queue 623 corresponding to its input. Therefore, the resequencing queues 625 store all packets that arrive out of order. These packets are only allowed to proceed to the output queue 626 when all preceding packets have been correctly received. If the packet is a duplicate (e.g., its sequence number is smaller than the next expected sequence number for the corresponding input) it is dropped. Duplicates of packets in the resequencing queues are not dropped according to this policy and will simply overwrite the copy already stored.
Whenever an in-order packet arrives, the control section 628 checks whether this in-order arrival enables packets to be dequeued from the corresponding resequencing queue 623. If this is the case, one or more of such packets are dequeued from the resequencing queue 623, routed via mux 624 and mux 625, and enqueued in the output queue 626 and the next expected sequence number for the corresponding input is updated.
The dequeuing unit 627 dequeues a packet, if present, from the output queue 626 and transmits it on the external data link 301.
As shown in
The speculative request arbitration unit 764 receives as inputs the current matching of the scheduled arbitration transmission requests to be applied to the crossbar and the current speculative requests. It denies all speculative requests corresponding to an output already matched in the current matching, i.e., scheduled arbitration transmissions always take precedence over speculative ones to ensure high maximum throughput. For every unmatched output for which there is at least one speculative request, speculative request arbitration unit 764 selects one to grant according to some policy (e.g., round robin) and denies all others. It sends an acknowledgment (ACK) corresponding to every successful speculative transmission request to the control message transmission unit 765 corresponding to the input that sent the request. Optionally, speculative request arbitration unit 764 sends a negative acknowledgment (NAK) corresponding to each denied speculative transmission request. The successful speculative transmission requests are added to the matching and the result is applied to the crossbar via crossbar configuration links 312.
Each control message transmission unit 765 assembles a control message for its corresponding line card 302 and sends it to the line card 302 via control link 304 b. The control message may include new arbitrated grants (if present) and acknowledgments for successful speculative transmissions (if present)
In general, the use of speculative transmission can cause out-of-order arrival of packets at the egress buffer unit 322, because out of a sequence of in-flight speculative packets, one or more may be lost due to collisions. Therefore, depending on the specific RD scheme, the egress buffer unit 322 may need to perform a sequence check and/or resequencing.
Reliable Delivery
The STX mode of operation implies that packets transmitted by speculative arbitration may collide with either other speculative packets or with packets transmitted by way of scheduled arbitration. If a collision occurs, one or more packets must be dropped, resulting in lossy switching operation even in the absence of errors. Additional measures can be taken to ensure reliable, correct, single-copy, in-order delivery. For instance, the present invention may be integrated with a number of reliable delivery (RD) schemes to increase system reliability. In general, such schemes operate by keeping packets stored at the sender until an acknowledgment (ACK) is received indicating that the receiver has correctly received a specific packet. Retransmissions are generally triggered either implicitly by timeouts or explicitly by negative acknowledgements (NAKs). Depending on the specific implementation, sequence numbers are needed to identify specific packets and/or resequencing buffers are needed at the egress to restore the correct packet order.
For example, STX arbitration in combination with scheduled arbitration may be integrated with known Stop & Wait (S&W), Go-Back-N (GBN), and Selective Retry (SR) RD schemes to increase reliable, in-order delivery in the presence of speculative transmission. These exemplary schemes are now described:
Stop & Wait
In the case of Stop & Wait (S&W), only one unacknowledged packet per output is allowed to be outstanding at each input at any given time. The next packet for this input-output pair can only be transmitted when either a grant for the corresponding output arrives at the input, or the corresponding acknowledgment arrives. In this case, the packets, the speculative transmission requests, and acknowledgments carry an indicator, for example, a one-bit sequence number, to allow detection of duplicates. For example, an egress buffer unit can check the sequence number (e.g., sequence numbers that are in sequence must alternate) and enqueue the packet if OK (i.e., in sequence), and otherwise drop the packet.
S&W is simple to implement and low in overhead. For instance, the physical implementation of a separate RTX queue is not necessary because the packet can remain at the head-of-line of the VOQ until acknowledged or granted. However, when the round-trip time is larger than one packet time, the expected latency improvement will be low because speculative transmission cannot be pipelined. This can be especially disadvantageous when traffic is bursty.
In the case of Go-Back-N (GBN), a predetermined maximum number of packets per output are allowed to be unacknowledged at each input at any given time. This number depends on the maximum allowed length of the retransmission queue 412. In GBN, the egress buffer unit can be implemented without resequencing, for example, according to egress buffer unit 322 a of
This implies that when the first in a sequence of (pipelined) STX requests fails, causing a gap in the corresponding sequence of ACKs, all subsequent ACKs must be ignored until the failed packet has been successfully delivered. Consequently, all packets in the RTX queue must be retransmitted when an ACK is missing, hence the name Go-Back-N. A new STX request can only be issued when the RTX queue is not full.
GBN is more complex to implement than S&W. The additional complexity arises in part from an RTX queue having a first-in-first-out (FIFO) organization. The extra overhead may include longer sequence numbers on the packets, the STX requests and acknowledgments. The ingress buffer also can be implemented in a different fashion (e.g., a shift-register RTX queue plus additional NAK queue).
On the other hand, use of GBN may be better suited than S&W in systems that have a large round trip. For instance, GBN allows many packets to be sent speculatively back-to-back, which is not possible with an S&W scheme.
Selective Retry
Selective Retry (SR) allows a predetermined maximum number of packets per output to be unacknowledged at each input at any given time. This number depends on the maximum allowed length of the retransmission queue 412 and the maximum allowed length of the resequencing queue 623. The egress buffer unit may be implemented according to the egress buffer unit 322 b shown in
SR is significantly more complex to implement than GBN because of the added complexity of a plurality of resequencing queues at the egress buffer unit 322. Additionally, an RTX queue in SR requires a random-access organization because packets can be dequeued from any point in the queue and not just from the head of line.
Retransmission and Resequencing Buffer Sizing
In general, it is advantageous to dimension the retransmission buffer such that at least a full round-trip's worth of packets can be transmitted speculatively in order to obtain the maximum advantage in terms of latency reduction. In this case, the links can be utilized at 100% with speculative transmissions.
To achieve optimal advantage, a preferred embodiment dimensions every resequencing queue (RSQ) such that it can store at least a number of packets equal to the RTX queue corresponding to the RSQ buffer. For example, the size of RSQ 623 may be determined based on the difference between the sequence number of the head-of-line packet of the RTX queue, for example, the RTX queue 412 corresponding to the RSQ 623 and sequence number of the tail packet of the RTX queue 412 corresponding to the RSQ 623.
Speculation in Asymmetric Routing Fabrics
The above examples of the invention generally show a "square" crossbar-like routing fabric (i.e., a fabric having the same number of inputs and outputs). While it is typical for boards, such as line cards and the like, to be connected to one fabric input and one fabric output, the present invention also may be implemented with switch fabrics featuring more outputs than inputs. For instance, assuming that there are K times as many outputs than inputs, with K integer and greater than one, exactly K routing fabric outputs can be assigned to every egress line card. This enables every egress line card to receive up to K packets in every time slot.
Switch core 810 includes the routing fabric 806 and an arbiter 807 for determining a conflict-free allocation of the switching fabric resources for a group or subgroup of requests for scheduled and/or speculative arbitration to provide a suitable matching between input and output ports. A configuration link 812 provides a switching configuration determined by the arbiter 807 to the routing fabric 806. As noted above, each egress 822 is provided with K times as many outputs from the routing fabric than the number of inputs from the line cards 802. For example, in a system implementing asymmetry with K=2, the egress buffer 822 would have one additional data link (output from the switching fabric) that can receive a packet from any one of the switching fabric inputs. To handle the increase in data packets received in any time period or cycle, queues in egress buffer 822 are dimensioned according to the load and/or various constraints. Also, the egress buffers 822 preferably have K times the write bandwidth.
In the exemplary system of
This feature can be advantageously utilized to either allow multiple scheduled arbitration transmissions, multiple speculative transmissions, or a combination of both to be accepted by every egress in any time slot. In an embodiment of the invention, for example, this feature can be exploited to great advantage of the speculative transmission scheme. For instance, in a given time slot, if there is no scheduled arbitration transmission, every egress 822 can accept up to K speculative transmissions. If there is one scheduled arbitration transmission, every egress 822 can accept up to K−1 speculative transmissions. In this example, scheduled arbitration transmissions can still form a one-to-one matching between inputs and outputs, and speculative arbitration transmissions can take advantage of all remaining fabric output bandwidth. In this way, it can be ensured that speculative transmissions have a significantly higher probability of being successful, thus achieving considerably higher latency reductions (depending on the load).
Existing one-to-one matching algorithms would require minimal or no modifications to implement the asymmetric example of present invention. However, it is to be understood that a number of schemes may be employed to match routing fabric inputs to outputs with respect to types of transmitted packets and/or a number of each type of transmitted packets.
To handle up to K speculative requests/acknowledgments per output per time slot, the speculative request arbitration unit 764 of
The present invention finds application in interconnection networks, such as parallel computing applications, including high-performance computing systems, clusters, and IO networks, where low latency is desired or required, as it has a direct impact on the computing performance of the system as a whole. The invention may be used with routing fabrics that include electrically controlled electrical switches, electrically controlled optical switches, and optically controlled optical switches.
To facilitate an understanding of the invention, many aspects of the invention have been described in terms of sequences of actions to be performed by elements of an interconnection system. It will be recognized that, in each of the exemplary embodiments, the various actions could be performed by specialized circuits (e.g., discrete logic gates interconnected to perform a specialized function), by program instructions being executed by one or more processors, or by a combination of both. Moreover, the invention can additionally be considered to be embodied within any form of computer readable carrier, such as solid-state memory, magnetic disk, optical disk or carrier wave (such as radio frequency, audio frequency or optical frequency carrier waves) containing an appropriate set of computer instructions that would cause a processor to carry out the techniques described herein. Thus, the various aspects of the invention may be embodied in many different forms, and all such forms are contemplated to be within the scope of the invention.
In the examples described above, a board (e.g., a line card) is eligible to perform speculative transmission only when it does not receive a grant for a given time slot. However, in applications where the effective capacity of the link to the crossbar exceeds that of the external link such that multiple packets can be sent in one time slot, the spare capacity could be used to perform speculative and granted transmissions in the same time slot.
The invention has been described with reference to particular embodiments. However, it will be apparent to those skilled in the art that various changes and modifications can be made in the present invention without departing from the spirit and scope thereof. Thus, it is intended that the present invention cover the modifications of this invention provided they come within the scope of the appended claims and their equivalents.
Claims (19)
Priority Applications (2)
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- 2006-11-14 KR KR1020087014427A patent/KR20080077189A/en not_active Application Discontinuation
- 2006-11-14 DE DE602006013180T patent/DE602006013180D1/en active Active
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Also Published As
|Publication number
|Publication date
|WO2007120209A2 (en)
|DE602006013180D1 (en)
|JP4796149B2 (en)
|JP2009516478A (en)
|EP1949622B1 (en)
|US20070110087A1 (en)
|KR20080077189A (en)
|CN101341698B (en)
|CN101341698A (en)
|EP1949622A2 (en)
|WO2007120209A3 (en)
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Who are we?
Certus Solutions is an award-winning global implementation partner for Oracle Cloud Applications. We were the first UK partner to specialise solely on the Cloud in 2012; the first to deliver a combined ERP and HCM project in Europe; the first dedicated Oracle Cloud support service and the first to tailor an Oracle Cloud solution for the Public Sector on G-Cloud. Certus is proud to be the first name in Oracle Cloud. Certus has been awarded Oracle Specialized Partner for HCM Cloud EMEA and Oracle Cloud Excellence (CEI) Implementer.
Certus has delivered over 30 Cloud projects in over 100 countries and understand the different challenges posed by Cloud-based implementation and support. We are an Oracle Platinum partner, delivering Enterprise Resource Planning, Human Capital, Payroll and Talent Management solutions to a wide range of corporate and public sector clients. We are trusted by the UK's central government to deliver and support their systems professionally and securely.
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Certus will provide you with a host of added value services to enhance your business operations and we will also enhance the user experience, maximising return on investment whilst maintaining a low cost of ownership.
Certus is 100% focussed on Cloud applications, without any on-premise baggage. Our business model has been built around Cloud services right from the off. Our consultants are the most experienced in the industry and they joined the company to focus 100% on Software as a Service (SaaS) implementations. Our approaches and tools are designed exclusively to support SaaS projects encapsulated in our engage™ service offerings. Our services include our knowledge transfer service that gives you the right guidance, best practice, learning and knowledge to successfully deliver and manage the right solution for you.
This partner has demonstrated ongoing expertise, a successful track record, and superior customer satisfaction in Oracle Cloud implementations.
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Certus Solutions Certus is an Oracle® Platinum Partner and specialises in the end-to-end delivery of Oracle Cloud based business change programmes for Finance, HR, Payroll and Talent Management. Certus will provide you with a host of added value services to enhance your business operations and we will also enhance user experience.
Certus Solutions' Engage Service Wrap for Taleo Enterprise Cloud Service, An Oracle Accelerate Solution
Certus Solutions' Engage® Service Wrap for Taleo Enterprise Cloud Service has been specifically designed for cloud services delivery for Oracle® Taleo, focusing on high levels of client collaboration to ensure all opportunities for knowledge transfer are taken advantage of. As an Oracle Cloud Services Specialised Partner in Fusion Applications & Taleo our level of expertise is second-to-none and industry recognised. This has culminated in Oracle Corporation recognising Engage® as an Oracle Accelerate solution for midsize companies.
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In today's knowledge economy, up to 70 percent of an organization's value is based upon the skills and experiences of its employees. Yet for most businesses, there is simply no visibility into how well the company's biggest asset is being managed. Without a unified approach to talent data, real intelligence on a company's most valuable asset – its workforce – is not immediately available.
Leading organizations worldwide use Oracle Taleo Enterprise Cloud Service to hire the best people, align them to corporate objectives, and develop their skills to drive superior business results. Oracle Taleo Enterprise Cloud Service meets the talent management needs of the largest and most demanding enterprises with global consistency and local flexibility.
This Oracle Accelerate Solution delivered by Certus Solutions for Professional Service sector is implemented using the Certus Solutions accelerated implementation methodology to get you up and running on Taleo Enterprise Cloud Service quickly and reliably by adopting Modern Best Practices for Talent Management to align common processes, stay compliant and always be productive.
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Certus Engage - an Oracle Accelerate Solution for Oracle Human Capital Management Cloud for Financial Services Industry
The Oracle Accelerate Solution for Human Capital Management Cloud delivered by Certus Solutions for Financial Services industry is built around a licensed methodology that has been designed specifically to facilitate the delivery of the Oracle HCM Cloud Applications product set (Global Human Capital Management, Talent Management, Compensation, Benefits, Payroll, Workforce Lifecycle, Oracle Taleo Recruitment, and Oracle Taleo Learn) and a professional services offering overseeing the deployed solution in either as Software as a Service (SaaS) offering in a public or private cloud, or on a customer's premises. This solution integrates Modern Best Practices, to align all your business processes, stay compliant and be more productive.
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The 2002 Protocol to the 1974 Athens Convention ("The 2002 Protocol ") and the EU Passenger Liability Regulation No. 329/2009 ("PLR") an update on the status of the legislation and the International Group response to consequent certification
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Do I Have to Use PayPal with Your Text to Donate Service?By Eric Bryant,
One question we often get is, "Do I have to use PayPal as my payment processor when I sign up to use your service?" We address this question on our F.A.Q. page, but the short answer is no. In this post we will explain the pros and cons of using PayPal, Gnosis Media Group, or an alternate third-party donation processor.
Pros of Using PayPal
While you do not have to use PayPal as your payment processor, there are some advantages to using PayPal:
PayPal's fulfillment rates are typically higher than other processors.
PayPal is the most widely used digital wallet in the U.S., which means more of your prospective donors will already be using it. This makes PayPal checkout faster than most other processors.
When you use PayPal, we can track which donations come in through our shortcode. We cannot do this with all payment processors.
PayPal has the lowest transaction fees for nonprofits, at 2.2% +$0.30 per donation.
Cons of Using PayPal
There are a few areas where PayPal lacks:
PayPal only gives donors the option to input the amount they want to donate or pre-populate the amount. It does not, for example, give you the option to show multiple payment amounts. UPDATE 12/16/2018: PayPal now does offer the option to offer multiple donation amounts to your donors.
PayPal offers limited customization. You cannot easily ask for additional information such as address or mobile phone number through a donate button or link. Often PayPal requires complex development to customize the checkout experience. Many nonprofits don't have these development resources on staff.
You cannot customize the email notifications or receipts that come from PayPal very easily.
What About Using GMG as a Payment Processor?
You always have the option of using us as your payment processor. Some advantages of using us (as opposed to PayPal) include:
We offer a high level of customization. With us, you can customize your entire checkout experience. You can add your logo to your checkout page, customize the form copy, customize the amounts, and even customize the confirmation emails that are sent to the donor on successful completion.
You can request pretty much any donor info you would like, such as mobile phone number, city, state, or address.
Since you can request mobile phone number, using us means we can match the donor receipt to the donor's mobile phone number. With PayPal, we can only give you the donor mobile phone number, but we have no way of knowing which phone number goes to which donor, as donations do not pass through us.
When you use us as a payment processor, your donations pass through us. This means that, not only can we tell you how many subscribers you've received, we can also tell you how much in donations you've received through our platform. We cannot do this when you use PayPal or another processor.
As with all payment processors, there are some disadvantages to using us:
We charge a 6% transaction fee on all donations processed. This is to offset the merchant fees associated with processing donor credit/debit card payments.
Donors must use a debit/credit card to donate, unlike Paypal, where they can often sign in and draw from their existing PayPal balance, never having to enter card details.
Our payment form is longer and requires more steps to complete than PayPal's. This may increase abandonment rates.
It will generally take longer to get your funds using us than it will if you use PayPal. We disburse funds via check within 15 days of receipt, whereas PayPal deposits your funds usually within 5 business days.
The main draw with us is customization and availability. Nonprofits use us when they require a higher level of customization than what PayPal provides. Also, newer nonprofits who do not yet have their own payment processor can get up and running fast with us, without having to set up their own merchant account.
What About Using A Processor Other than PayPal or GMG?
There are a plethora of donation payment processors on the market. One great feature of our service is that you are free to use pretty much any payment processor you like; we can integrate with any of them. Additionally, other payment processors may offer features that PayPal or we don't, such as integration with your CRM. However, there are some downsides to using a processor other than PayPal or us:
We cannot tell you which donations came through our system. With PayPal, we can embed a unique ID into each donation receipt. This shows you which donations came through your keyword and short code. But with other payment processors, we cannot do this.
Most other payment processors (including us) have higher fees than PayPal.
Customization: You will have varying degrees of customization with other third-party processors. Some will give you no customization at all.
Mobile friendliness: Not all payment processors are as mobile friendly as PayPal or us. You need to ensure that the checkout experience you provide to donors is mobile-friendly, easy to navigate, fast-loading, and easy to read. Nothing kills conversion rate more than a poor mobile experience.
There is a lot to consider when choosing your donation payment processor. You will want to determine which features are "must-haves" and which are "nice-to-haves" when making this decision. Each payment processor has its pros and cons, and in the end you'll have to decide which one best meets your fundraising needs.


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The Japanese are known for two things around these parts: Amazing stationery and terrible naming conventions. Luckily for my sanity, the former outweighs the latter by a large margin, but sometimes I have to post the full product name solely for the humor it provides.
While the name leaves a lot to be desired, the pen does not. The Tombow Mono Graph Multi Pen - yes, I'm shortening the name - is a great choice in the 2+1 multi pen category.
What is a 2+1? I'm so glad you asked! It may not be the textbook definition of describing multi pens, but I refer to any multi pen with a pencil component as a +1. This Tombow has two ink cartridges and one pencil cartridge, therefore it is a 2+1. I like that designation because it saves me from writing "multi pen and pencil" over and over again. These are multi pens, with a pencil component.
Uni-ball, Pilot, and other Japanese brands make multi pens up to a 4+1 size, which requires a wide barrel, as you can imagine. One of them made a 1+1 in the past - I'm thinking Uni-ball or Zebra - but I don't see it as available right now on JetPens.
When thinking about buying a multi pen, I consider barrel diameter first. How many components can I jam into one barrel and still feel comfortable writing with it? Secondly, I consider the refill choices. If the first part doesn't satisfy my needs, the second part doesn't matter, does it?
This Tombow multi pen fits three components in just a slightly larger diameter barrel than most standard gel ink pens. That's a great thing, primarily for one rarely talked about reason. More components and a wider barrel lead to the refills being deployed at a less-than-vertical angle. That means the tip of the refill looks like it comes out of the front of the barrel crooked. Rotate the barrel in your hands, look at the tip, and you will see.
This isn't always avoidable from a design perspective, but some companies do it better, and some do it worse. Another thing to keep in mind when shopping for multi pens.
In lieu of a knock mechanism, this Tombow uses a twist to engage the component you want. Rotate the clip around the barrel in any direction (there is no hard stop at any point) to line it up with the component name you wish to use. This one has black and red 0.5 mm ballpoint refills plus an 0.5 mm mechanical pencil.
Unlike other multi pens with a +1, this one has an eraser, and a killer one at that. Tombow makes some of the best quality erasers on the market, and this one has a jumbo twist eraser built right in. No dinky mechanical pencil eraser here!
From a writing perspective, I love the 0.5 mm tip sizes, but they aren't for everyone. That is especially true for ballpoints, because an 0.5 mm tip gets you a line finer than 0.4 mm, or even finer, gel ink pens. And it's not completely smooth due to the ink type. Know the fineness of this pen before diving into it.
I had zero issue diving into this one personally. In fact, if I worked at Tombow, this is a pen I would have designed for myself. Two extra fine refills, a fine pencil refill, a large, high quality eraser, as narrow of a barrel as I could fit it all into, and a killer paint job. All for under $10? Count me in.
I've been putting this one to good use over the last few weeks, and I can see myself carrying it for some time to come.
(JetPens provided this product at no charge to The Pen Addict for review purposes.)
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Membership starts at just $5/month, with a discounted annual option available. To find out more about membership click here and join us!


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MAP of FALKLANDS ISLANDS
J, Lodge
Map shows the coastlines with limited interior detail. Nine ship-based views with distance to surrounding islands indicated. Map of Falkland islands five years after first settlement during brief conflict between Spain and Britain over control.
Map of Falklands Islands, located just east of the Southern Tip of South America. Prime Meridian is unknown due to lack of information and graticul; however, at bottom right corner it states "51º 22' South Latitude and 64º30' West Longitude from latest Observatories". There is one scale bar on the map, represented in Miles. There are 9 Cross maps throughout the map.
Sylvanus Urban
1 map ; 16 x 24 cm
South America
Falkland Islands
-61.569; -57.454; -52.516; -50.988
W. K. Morrison Special Collection
Gentleman's Magazine
v.40, September 1770, opposite pg. 480
D. Henry and R. Cave
This material is provided for research, education and private use only. Commercial use of this work is strictly prohibited. Attribution for use must be provided as follows: "Digital reproduction from the W. K. Morrison Special Collection of the J. B. Hall Library at the NSCC Centre of Geographic Sciences" and link to the original record. For use other than research, education or private uses please contact the J. B. Hall Library at the NSCC Centre of Geographic Sciences.


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Saturday, 15 Oct. 2011.Me and group of 20 odd blogger escape temporarily from hectic city of KL to Pulau Ketam "Crab Island" which is a small island located off Port Klang, Selangor,Malaysia thanks to Tourism Selangor which is organizing the #TSDayOut to explore part of Selangor thru Social Media and at same time I am able to meet some of my friend from MSS Selangor 2010 and blogging community.
Founded circa 1880. Its a fishing village inhabited by Malaysian Chinese and yet at same time a tourist attraction for both domestic or foreign tourist alike. To reach Pulau Ketam, U must take the ferry/speed boat (Rm7 for the ticket) from Jetty at Port Klang (accessible from KTM Port Klang) ETA 40 minutes . Arriving at Pulau Ketam Jetty, the floating house perching casually on long wooden stilts and suspended merely about one to ten (1-10) metre above the sea level was a breathtaking view . We quickly ushered to community hall for simple briefing before starting exploring the island on small group by walking or rented bicycle which is the island main and only means of transport. Despite it size, Pulau Ketam has own school, clinic, police station, community hall, volunteer fire station, electric generator plus Motel, shop and restaurant to cater to tourist beside the thriving fishing community dotted by boat and supporting industry.
Thanks to Tourism Selangor for organizing #TSDAYOUT outing, me and group of nearly 20 blogger are able to explore Pulau Ketam on foot, bike and able take photo using our DLSR, Digital Camera and of course, my La Sardina Camera!
|Norah posing using my La Sardina Camera
For more facebook picture . Press Here. For Lomography Picture, Press here.Register now at Lomography and win yourself some piggies to start your lomo adventure!
Source: cakapniagaPS: One of my picture is selected by Tourism Selangor to Promote Pulau Ketam and won myself RM250 cash prize too!


text: A possible apparition at Mercy Medical Center in Springfield, MA. The hospital's mission leader was quoted in the paper: "Sister Kathleen Sullivan, senior vice president at Mercy, said an image was observed on the window of a vacant office at the 300 Stafford St. medical building late this morning. "What it is I don't know, but it was certainly humbling to see the faith of the people. It was so beautiful," she said." Crowds again gather to pray before image in window - MassLive.com (via) Whispers Michael Miller, Jr.October 1, 2008 Facebook0 Twitter LinkedIn0 Tumblr


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2018's new thrift stores: Los Angeles
May 24, 2018 | By Lourdes Linares
Jul 16, 2009
Looking very WAC-ish in her 1940's, militaristic dress and hat, this Berlin native was attending an underground fashion show during Berlin fashion week. One of our editors caught her as she was about to jump on the train where the show was held. Trains were transformed into runways as they drove around the city and, of course, our '40s vintage vixen had a front row seat. I salute you, Fräulein, and your fantastic vintage outfit!
Know what's next. Become a WGSN member today to benefit from our daily trend intelligence, retail analytics, consumer insights and bespoke consultancy services.


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NYCC '17: DC MASTER CLASS Artists Eye 'New Age of DC Heroes'
DC's top artists are assembling for the "DC Master Class" panel Saturday at New York Comic Con. DC Co-Publisher Jim Lee is scheduled to be joined by Frank Miller, Greg Capullo, Tony S. Daniel, Andy Kubert, John Romita Jr., and more. This group is the lead artists on the upcoming "New Age of DC Heroes" imprint, spinning out of Dark Nights: Metal.
And as part of Newsarama's live coverage of New York Comic Con, you can follow along live with the below play-by-play. Give our widget a little to load, and follow along.
Twitter activity Tweets by @Newsarama


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Legend: The Newest and Best Nurse Kits in the Industry ?
We are a small company and therefore care for the school we are working with as well as the students. And what everyone to have the best experience possible. We will work with every school individually to meet their exact needs. We customize kits like no one else in the business. YOU decide what goes in your kit, YOU decide the style of your bag, YOU decide who pays and how the kits are delivered. And YOU decide if changes are needed even in between shipments. We ask schools to make a one year commitment however we will only ship you the kits you need per semester, keeping your space free and clear of any unnecessary bulk. We can even customize the inside of your kit. We can label certain items for certain classes or make different kits for different classes and programs.
Every one of our kits comes with your school name and logo and NO additional charge. And every facility gets the personalized attention of Maribeth Hollern, current RN as well as a nursing educator. See her profile for more information (enter link for profile). She is always up to date on what is current in the field and as well in the classroom.
We make sure to go always go out of our way for our customers. If you need a product please let us know. We are the leader in sourcing hard to find products. And we can customize anything from our clinical nurse kits to bedside kits to diagnostics packs. Whatever you need, we can make it happen and in a timely fashion! Don't ever assume there isn't enough time. We have assembled and shipped kits inside of just a couple weeks. We can always make something work for you. If you have a request PLEASE call us. We would love to help!
Maribeth Hollern ?
My name is Maribeth Hollern and I am currently an Adjunct Clinical Nursing Faculty Member for two Michigan universities as well as an active SICU RN. Both of these roles have served me well, and have led me to my third role, as creator and product specialist for Legend Medical.
We tailor make to your specifications Clinical Lab Student Nurse Skills Kits utilizing supplies that reflect current practice thereby benefiting the students and the program alike.
Students are allowed and encouraged to practice their skills before, during and after lab which is an incredible advantage related to skills that require remediation. The students have ownership of their supplies thus mindful of being prepared and responsible.
The Schools of Nursing benefit by significantly reducing lab costs. Yearly inventory and re-ordering becomes unnecessary. Lab set-up time and the need for storage are all but eliminated.
Our kits were highly received at the NLN Education Summit this past September, and what we learned there, is that Student Nurse Skill's kits are the future. Ours are economic, current and customized.
Therefore, I would love to come and show you a sample kit, give you an estimate on what we can do for your program, or just speak with you regarding the features and benefits of skills kits.
Philosophy Statement
My nursing philosophy is dynamic and unique to my belief system.
"Every clinical teacher has a philosophy of clinical teaching, whether they know it or not."
(Gaberson & Oermann, 1999).
- I believe that statement to be true. Continuous self-reflection is essential to my philosophy of being a clinical educator.
- I believe that learning is an active process that takes time and varies from learner to learner.
- I also believe that the learning environment must be supported by a climate of mutual trust and respect to enhance a student's confidence.
- I believe I have a responsibility to create a link between the classroom and clinical environment.
- I know my philosophy will continue to evolve as I progress throughout this educational process.
Professional Certifications
Trauma Nurse Core Course and Certification (T.N.C.C)
Advanced Cardiac Life Support (A.C.L.S.)
5 Year
Presently I am a staff RN in the Surgical Intensive Care Unit (SICU) at Spectrum Health Meijer Heart Center and an adjunct clinical faculty member for local university nursing programs. I have taught in many areas; pediatrics, medical-surgical, oncology, woman's health and Psych. I am actively pursuing my goal of obtaining my Master's of Science in Nursing (MSN) degree from Ferris State University. My plan is to grow as an educator throughout this process and continue my clinical teaching.
10 Year
After receiving my MSN degree I will continue to pursue my Doctorate in nursing. A PhD. in Nursing will enable me to reach my ultimate goal of obtaining a full time faculty position at the university level.
Sample Quotes ?
Click each item to view more information.
|Unit Price
|360 ea
|Custom Skills Lab Nursing Student Kit
|$149.99 ea
|Nursing Student Skills Lab Kit
|$135.00 ea
|125 ea
|Custom Skills Lab Nursing Student Kit
|$97.75 ea
|120 ea
|Custom LPN Nursing Student Kit
|$79.00 ea
|50 ea
|Nurse Practitioner Kit
|$215.00 ea
These quotes are just samples and are based off quantity and other factors. Please contact us for an official, up to date, accurate quote for your facility.
Bookstores We Work With ?
Local School Bookstores
Barnes and Noble
Events ?
National League for Nursing (NLN)
International Nursing Association for Clinical Simulation and Learning (INACSL)
INACSL 13th Annual Conference Lanyard Sponsor
Sponsorships ?
INACSL 13th Annual Conference Lanyard Sponsor
Kent State - 5K "Race into Finals" Benefiting Nursing Students
2013 Davenport University Excellence in Business Dinner Gala Silver Partner Sponsor
News ?
2014 NLN Education Summit Exhibitor – Booth # 321 – September 17-19 – Phoenix Arizona
Customer Reviews and References ?
Please contact us for references.
"Maribeth, We are so pleased with the skills kits and messenger bags."
"Everyone LOVES the kits that you put together for us this year—thanks again for all of your help and your prompt responses. Your great customer service is truly appreciated!"
"Hi Maribeth, We just love the new PA kit bags!!!"
...Early delivery, wow – what a change from our last vendor. I've cc'd the bookstore to let them know they will be arriving. Thank you so much for all your help, Maribeth –I look forward to a long partnership."
"I received the sample bag and faculty love it. Students can make use of this well into their practice."
"Our estimates (really rough right now) are that by utilizing the supply bags, our bulk supply costs will decrease by approximately $30,000.00/year.""
"So far your price has beat everyone."
How to Purchase ?
At Legend we try to be extremely easy to work with. There are a number of different ways to purchase from us. Start by contacting Maribeth Hollern to get a quote on your custom nurse kit. Then we can discuss how you would like them delivered and how they will be purchased. Here are the options:
Who can purchase:
- The facility bookstore
- The Nursing program (with lab fees for example)
- The individual student (with credit card by calling Legend or going to our website)
After the program decides who will pay for the kits they then decide how the kits will be shipped, either to the bookstore the nursing program or the student's home. We will be with you every step of the way to help you make these decisions so that it works out best for everyone.
Gallery ?
Specials and Products Unique to Legend ?
We can customize any kits from RN to FNP to Nurse Practioner as well as Bedside kits and Diagnostic Packs. Don't see what you are looking for? Just call us, we are leader in sourcing products!
Custom 14fr Foley Tray with Benzalkonium swabsticks instead of iodine to protect your manikins from staining.
- Stop staining your mannequins with iodine/PVP swab sticks!
- These custom foley trays have a 3 pack of Benzalkonium swab sticks.
- An innovative manufacturing process provides the maximum amount of silicone coating available.
- Latex catheter coated internally and externally to resist encrustation and bacterial colonization.
- Each of the Foley trays contains: compartmentalized prep tray, wrapped Aloetouch 3G gloves, 3 pre-saturated Benzalkonium Chrloide swabsticks, moisture-proof underpad, fenestrated drape, 10ml sterile water syringe, water soluble lube jelly, specimen container with ID label, CSR wrap, and a Silicone-Elastomer coated latex Foley catheter pre-connected to a 400 ml urine meter and 2500 ml drain bag.
- Mock - Sterile.
- Available in 14 Fr.
Injection pad by Wallcur. The perfect size for students to practice on (Practi-SimSkin with an epidermis, dermis and subcutaneous layer also now available!)
Teach a variety of injection techniques using just one innovative simulation aid. Wallcur's Practi-Mini Injecta Pad™ is a more compact (smaller and lighter weight) version of the original Practi-Injecta Pad™.
This compact injection simulator is perfect to include in individual skills packs for students of nursing, EMT, and other allied health classes. With Practi-Mini Injecta Pad™, now each student can practice intradermal, subcutaneous, intramuscular, z-track, and many other injection techniques with their very own injection simulator.
The Practi-Mini Injecta Pad™ measures 5"x5" providing plenty of surface area for students to practice skin puncture resistance and tissue displacement on both the top, and bottom of the pad. At 2-1/2" thick, and plump with Wallcur's exclusive filling, your students will experience the "feeling" of aspiration tension, so vital when mastering I.M. injection techniques. In addition, this thickness provides the opportunity for practice with a variety of different needle lengths.
Help your students overcome the natural fears associated with giving injections. Building muscle memory and mastering injection techniques go hand-in-hand as the more opportunities they have to practice, the more confident they will become.
Watch your students' confidence, and competence, improve as they hone their injection technique skills, safely, with Practi-Mini Injecta Pad™.
Add Wallcur's Practi-Mini Templates™ to increase student skill competency. A perfect accompaniment to the Practi-Mini-Injecta-Pad.
Wallur's new Practi-SimSkin consists of an epidermis, dermis and subcutaneous layer and behaves and feels like real skin. Designed for intradermal injection and handcrafted to produce a "bleb" or "wheel" with either liquid or air injections. Ideal for use with Wallcur's patented Practi-Injecta Pad.
The size of this injection simulator is 3"x3", giving your students plenty of practice area and the option of using multiple needle lengths.
Nurse and educator tested and approved!
For simulation practice only.
Bulk Supplies ?
At Legend we just don't supply kits, we supply everything your program needs. Including anything in your kit in bulk for instructors or testing. As well as furniture for the lab, refurbished items, pumps and accessories and anything else you may need! We will source any hard to find items and give you a fair competitive price…we guarantee it!
Medical Equipment/Repair Parts
- Hospital beds, furniture, patient lifts, scales, IV poles, rollators, and wheelchairs.
- Mattresses, pressure prevention products, cushions, repair parts and accessories, and bed pendants.
Medical Supply Kits
- Custom student kits.
Wound Management
- Dessings/trays, tape, irrigation solutions, bandages, and casting materials.
- Irrigation solutions, applicators, antiseptics, and med surg products.
Urological Care
- Urethral and foley insertion trays/catheters.
- Collection systems and accessories.
IV Supplies
- IV starter kits, venous dressing change trays, IV dressings, labels, catheters, and solutions.
- Administration sets - standard and needle systems.
Respiratory Supplies
- Respiratory diagnosis and oxygen delivery, suction catheter, and trach trays.
- Resuscitators, laryngoscopes, and airways.
- Blood collection systems, training pharmaceuticals, and blood collection systems.
- Syringes, needles, injectables, sharps containers, and test strips.
Infection Control/Protection
- Exam/surgical gloves, protective wear, Glo-Germ, and BioHazard.
Nursing Services
- Nutrition/feeding supplies, bathing/grooming, and admissions.
- Ostomy, urinary and bowel management, scrubs/lab coats, and maternity.
- Patient exam and exam room and supplies.
- Stethoscopes, IDs, blood pressure sets, penlights, organizers, and eye charts.
- Thermometers and batteries, measuring devices, forks, and hammers.
- Forceps, scissors, otoscopes, and ophthalmoscopes.
Linens and Patient Safety
- Linens, gait belts, restraints, alarms, and pad systems.
Headwalls and Accessories
- Headwalls and accessories.
Rehabilitation Theraphy
- Exercise bands, balls, tubing, putty, casting tape, splints, and supports.
- PTA student kits, posters, charts, mobility aids/transfer devices, toileting and bathing aids, and grab bars.
CPR Training and Manikins
- CPR supplies, manikins, and educational simulators.


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Concrete Hanging Star
Out of stock
Product Details
Simple statement piece. Little concrete carved star made from smooth concrete complete with a tan leather tie to hang on drawer handles or walls for a timeless chic addition to your home.
Measurements – 10 x 1 x 2 cm
Shipping And Returns
STANDARD DELIVERY for all items excluding large items weighing over 5kg is £4.95 per delivery to UK mainland.
We dispatch orders Monday to Friday. Please allow 5 working days for your delivery. If for any reason an item is out of stock, we will let you know immediately with an expected due date. You will have the option to cancel your order.
Express or Next Day Delivery.
If you need a special or urgent delivery service then please call us and we will do our best to provide you with the best postal option for your needs. Please contact us on 07595251452 or email firstname.lastname@example.com before 12pm in order to request this service so that we can guarantee delivery. Unfortunately we cannot provide this service on larger items.


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Southern Magnolia
Angled Eyebrow Cosmetic Brush
An angled brush that is perfect for eyebrows. It places powder into the brow, and also blends pencils softly. I have found this is also a great eyeliner brush for creating that smokey eye effect that is so popular!
The flat shaped with angled tip is perfect for shading and shaping the eye or eyebrow. It will firmly distribute colors over the eyelid and into the corners easily. It can also be used to apply creams, liquids, or powders. It is a must have to get an arched brow and to acheive a professional look!
The name of the brush style is embossed on the birch wood handle. The ferrule is a silver alloy making it very durable for many years of use! Excellent quality!


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Open Kitchen Shelving: Is it For You?
Considering open kitchen shelving? The look is becoming a major trend in kitchen design, but before you take the leap and forgo upper cabinets, it's important to consider the practical implications of open kitchen shelving as well. Here are a few questions to ask yourself first.
Does dust bother you?
One of the major advantages to closed cabinetry is that it prevents dust, dirt, and cooking grease from settling into dishes and appliances, a benefit that open shelving doesn't provide. While dust may not have time to accumulate in dishes you use regularly, you can anticipate having to rinse out some of your lesser-used pieces before setting them on the table.
Do you own nice dishes?
True, this is a matter of aesthetics, but it is also a practical consideration because anything you put on your open shelves will essentially be on display. Open shelving can be a benefit or a drawback to the look of your kitchen, and the determining factor will be how nice your dishes are and how well they complement your space. If you don't currently have a kitchen full of matching dishes, glasses, serving pieces, and appliances, you'll want to add that into you budget for open shelving. Otherwise, the space will quickly feel cluttered and messy.
Do you have ample cabinet storage?
Certain items aren't meant for open shelving. Things like you slow cooker, your frying pans, and your vitamix are not only bulky and awkward (meaning they likely won't tuck away neatly on a shelf), but they're also an eyesore. Before you get rid of closed cabinetry, make sure you have enough room for everything that won't fit on the shelves in the lower-level drawers and cabinets.
For more kitchen design inspiration, visit our Pinterest page or our Houzz Profile.


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The Pulitzer Project: Coming Soon!
This series will be an ongoing attempt to read and reflect on each work that has been a finalist or winner in the fiction, general nonfiction, or drama categories for the Pulitzer Prize. I certainly don't believe that the Pulitzer is the be-all-end-all stamp of quality—I don't even expect all these works to be good—but they captured something in the zeitgeist, and I'm interested in exploring and examining that quality.