Patent Description:
The present invention relates generally to communication systems, and particularly to methods and systems for transporting fibre channel (FC) traffic over packet-switched communication networks.

Fibre channel (FC) is a high-speed serial interconnection interface, which is used in various storage and networking applications. FC has been standardized by working group T11 of the International Committee for Information Technology Standards (INCITS). FC standards are available at www.

Some FC standards and drafts define the transport of FC traffic over different backbone networks. For example, the<NPL>, defines the functions and mappings necessary to tunnel fibre channel links, or bridge fibre channel networks, across wide area networks (WAN). This document describes mapping models of FC to Asynchronous Transfer Mode (ATM), Synchronous Optical Network (SONET), Transmission Control Protocol/Internet Protocol (TCP/IP) and Transparent Generic Framing Procedure (GFP-T).

Methods for carrying FC traffic over IP networks are also described by <NPL>. The FCIP mechanisms allow the interconnection of islands of FC storage area networks over IP-based networks to form a unified storage area network in a single FC fabric. This RFC, as well as other IETF RFCs cited hereinbelow, is available at www.

A system for combining multiple FC frames and compressing them to form a single IP datagram for tunnelling transmission over an IP network is described in <CIT>. Incoming host frames are stored in a buffer, then batched together, compressed and converted into an IP datagram. The network layer fragments the datagram into data link level frames. Once the datagram is at its final destination, the segmented datagram is reconstructed, decompressed and the multiple host frames are extracted.

Embodiments of the present invention provide improved methods and systems for transporting fibre channel (FC) traffic over packet-switched networks. FC translators located at the edge of a packet-switched network perform transparent transport of FC traffic between source and destination FC devices.

An ingress FC translator accepts a sequence of FC words, typically comprising FC data frames and ordered sets, from the source FC device. The FC words are translated into packets of a communication protocol used by the packet-switched network, such as the multiprotocol label switching (MPLS) protocol. Typically, the translation comprises encapsulating the FC data frames and/or ordered sets in data packets of the communication protocol. The packets are transported over the packet-switched network, and the sequence of FC words is reproduced from the transported packets by an egress FC translator connected to the destination FC device.

In order to reduce the traffic sent over the packet-switched network, the ingress FC translator identifies in the sequence of FC words repetitive signals, such as primitive sequences and IDLE sequences. The ingress FC translator refrains from sending the repetitive signals over the packet-switched network, and instead sends a repetition indication packet identifying the repetitive signal. The egress FC translator re-generates the repetitive signal sequence responsively to the repetition indication packet, thus providing legitimate FC traffic sequence to the destination FC device without sending superfluous data over the packet-switched network.

In some embodiments, the communication path used for transporting the packets between the ingress and egress FC translators has a certain packet loss probability. For example, statistical multiplexing may be used when allocating bandwidth to the communication path, to increase the efficiency of use of network resources. In these embodiments, the ingress and egress FC translators selectively retransmit lost packets. Additionally or alternatively, the ingress FC translator may adaptively adjust the packet transmission rate based on the packet loss performance of the communication path.

Thus, the methods and systems described herein enable reliable, efficient and transparent transport of FC traffic over packet-switched networks. Additionally, since only a single, non-terminated FC link is defined between the source and destination FC devices, the methods and systems described herein enable logical and operational separation between the FC domain and the packet domain, which are often operated by different organizations.

There is therefore provided, in accordance with an example of the present invention, a method for transporting fibre channel (FC) traffic over a packet-switched communication network, the method including:.

The method may further include receiving the transported data packets from the packet-switched communication network, reproducing the first sequence of the FC words by re-generating the sub-sequence of repetitive FC signals responsively to the repetition indication packet, and providing the reproduced FC words to a destination FC device.

In an example, receiving the transported data packets includes identifying a lost data packet, and transporting the second sequence includes retransmitting the lost data packet. Additionally or alternatively, receiving the transported data packets includes monitoring a packet loss performance of the transported data packets, and transporting the second sequence includes adjusting a transmission rate of the data packets responsively to the monitored packet loss performance.

In another example, providing the reproduced FC words to the destination FC device includes providing data for storage in a remote storage device.

In yet another example, the communication protocol includes a multiprotocol label switching (MPLS) protocol, and transporting the second sequence includes sending the data packets via an MPLS label switched path (LSP) established through the packet-switched communication network.

In still another example the first sequence includes FC data frames and ordered sets, and translating the first sequence into the second sequence includes encapsulating at least one of the FC data frames and the ordered sets in accordance with the communication protocol to produce the data packets.

In an example, translating the first sequence into the second sequence includes sending the repetition indication packet while refraining from sending the sub-sequence of repetitive FC signals over the packet-switched communication network.

In another example, the method includes establishing a FC connection between the source and destination FC devices via the packet-switched communication network that is not terminated between the source and destination FC devices by:.

In yet another example, transporting the second sequence of data packets includes at least one of communicating with a shared resource, accessing shared content and communicating with a server in a server cluster.

There is additionally provided, in accordance with an example of the present invention, a method for transporting fibre channel (FC) traffic over a packet-switched communication network, the method including:.

There is further provided, in accordance with an example of the present invention, a system for transporting fibre channel (FC) traffic between source and destination FC devices over a packet-switched communication network, including:.

There is also provided, in accordance with an example of the present invention, apparatus for transporting fibre channel (FC) traffic over a packet-switched communication network, including:.

There is additionally provided, in accordance with an example of the present invention, apparatus for transporting fibre channel (FC) traffic over a packet-switched communication network, including:.

<FIG> is a block diagram that schematically illustrates a communication system <NUM>, in accordance with an embodiment of the present invention. System <NUM> comprises two or more fibre channel (FC) devices <NUM>, which communicate with one another over a packet-switched network <NUM>. For example, system <NUM> may be used in a remote storage application in which data produced at a primary computing site is sent for storage in a remote storage device. Alternatively, system <NUM> may comprise any other system or application that uses FC communication, such as mirroring of data in secondary backup sites and recovery of remotely-stored data.

FC devices <NUM> may comprise computing platforms, storage devices or any other device capable of communicating using FC traffic. Network <NUM> may comprise a wide area network (WAN) such as the Internet, a metropolitan area network (MAN), a local area network (LAN) or any other suitable packet-switched network. Typically, network <NUM> comprises an IP network. In the exemplary embodiment of <FIG>, the network is configured for multiprotocol label switching (MPLS). MPLS is described by <NPL>.

The FC devices are connected to network <NUM> using FC translators <NUM>, which are located at the edge of the packet-switched network. The translators perform transparent bidirectional translation of FC traffic into the communication protocol used by the packet network, the MPLS protocol in the present example. In <FIG>, system <NUM> comprises two FC devices, denoted 24A and 24B. Two translators, denoted 32A and 32B, connect FC devices 24A and 24B, respectively, to the MPLS network. A label switched path (LSP) <NUM>, also referred to as an MPLS tunnel, is established between translators 32A and 32B.

Translators <NUM> perform both ingress and egress processing of traffic. The term "ingress processing" refers to the process of accepting FC traffic from a source FC device connected locally to the translator, processing the traffic and sending it over network <NUM> to a remote destination FC device. The term "egress processing" refers to the process of accepting data packets originating from a remote source FC device over network <NUM>, reproducing the FC traffic and providing it to a destination FC device connected locally to the translator. A translator performing ingress processing is referred to as an ingress translator, and a translator performing egress processing is referred to as an egress translator. Typically, each translator <NUM> performs both ingress and egress processing simultaneously. Each FC device <NUM> typically acts as a source FC device for some FC frames, and as a destination FC device for others.

In principle, the ingress translator accepts a sequence of FC words from the source FC device. The sequence typically comprises FC data frames and ordered sets. (The term "ordered set" collectively refers to FC primitive signals and primitive sequences, as defined in the FC standard. ) The ingress translator encapsulates the data frames and ordered sets in MPLS packets. The ingress translator then sends the MPLS packets via MPLS tunnel <NUM> to the destination translator. The destination translator decapsulates the MPLS packets, reproduces the encapsulated FC data frames and ordered sets, and provides the reproduced traffic to the destination FC device.

Unlike some known FC transport methods in which the FC link is terminated at the edge of the packet network, in the methods and systems described herein the translator is not defined as a FC entity, i.e., it does not have a FC address. The methods and systems described herein provide full logical and operational separation between the FC domain and the packet domain, which are often operated by different organizations. In a storage area network (SAN) application, for example, the SAN and the packet network can be managed as separate and independent administrative domains.

Moreover, the methods and systems described herein comprise mechanisms that reduce the bandwidth allocation in network <NUM> needed for transporting the FC traffic. FC traffic often includes repetitive data patterns and commands, referred to herein as repetitive signals. For example, when a FC link is idle, the source FC device periodically sends IDLE signals to the destination FC device. Sequences of IDLE signals are also transmitted in the inter-frame gaps (IFG) between successive FC frames. Additional examples of repetitive signals, i.e., periodic repetitive transmission of the same primitive at regular intervals, may comprise primitive sequences such as off-line (OLS), not operational (NOS), link reset (LR) and link reset response (LRR).

In order to reduce the amount of traffic sent over the packet network, the ingress translator identifies repetitive signals produced by the source FC device. The ingress translator suppresses the repetitive signals and refrains from sending them over network <NUM>. Instead, the ingress translator sends only a repetition indication packet identifying the repetitive signal over network <NUM> to the egress translator. The egress translator re-generates the repetitive signal responsively to the received repetition indication packet, and provides the repetitive signal to the destination FC device. Using this process, the source and destination FC devices exchange repetitive signals as defined in the FC standard, without having to transport superfluous data over the packet network.

Additionally, since the FC traffic is transported over network <NUM> using MPLS, the communication path between the ingress and egress translators can use the MPLS traffic engineering (TE) and quality of service (QoS) mechanisms. For example, in MPLS, network resources (e.g., bandwidth of network segments or links) are typically reserved along MPLS tunnel <NUM> in accordance with a predetermined class of service. Bandwidth requirements may be defined statistically, such as using committed information rate (CIR) and/or peak information rate (PIR) specifications.

Resource reservation in MPLS networks is often performed in accordance with a reservation protocol called RSVP-TE, described by <NPL>). RSVP-TE extends the well-known Resource Reservation Protocol (RSVP), allowing the establishment of explicitly-routed LSP using RSVP as a signaling protocol. RSVP itself is described by <NPL>).

Since the bandwidth that is actually used by a particular tunnel may vary over time, a certain amount of statistical oversubscription is often allowed when reserving network resources to MPLS tunnels. Oversubscription significantly increases the efficient use of network resources. On the other hand, oversubscription means that there is a finite probability of packet loss, when the actually used bandwidth exceeds the reserved bandwidth.

In order to ensure that all FC traffic produced by the source FC device reaches the destination FC device, even though the traffic passes through a communication path having a finite packet loss probability, the methods and systems described herein use selective retransmission and packet rate adaptation. These mechanisms are described in detail below. It should be noted that the methods and systems described herein preserve the original order of the FC traffic produced by the source FC device, as required by the FC standard.

Thus, the methods and systems described herein enable reliable, efficient and transparent transport of FC traffic over packet-switched networks. The system configuration of <FIG> is an exemplary configuration, chosen purely for the sake of conceptual clarity. In alternative embodiments, system <NUM> may comprise any number of FC devices, translators and MPLS tunnels. Each translator may serve one or more FC devices. For example, the methods and systems described herein can be used to interconnect two or more remote FC "islands" using a packet-switched network. Although <FIG> shows a point-to-point configuration, the methods and systems described herein can be used in any other FC topology, such as node-to-fabric and fabric-to-fabric connections.

Alternatively to using MPLS, network <NUM> may use any other suitable communication standard or protocol that provides control over the network resources allocated to the communication path between the translators, such as the asynchronous transfer mode (ATM) protocol.

<FIG> is a block diagram that schematically illustrates FC translator <NUM>, in accordance with an embodiment of the present invention. Translator <NUM> connects to one or more FC devices via optical fibers and optical transceivers <NUM>. Transceivers <NUM> convert optical FC signals to electric signals, and vice versa.

In the ingress direction (i.e., from the FC device to the packet network), the high-speed serial electrical signals produced by transceivers <NUM> are converted to parallel data using a serializer-deserializer (SERDES) <NUM>. A FC controller <NUM> performs media access control (MAC) functions, such as byte, word and frame synchronization. The FC controller detects and identifies FC primitive signals and other ordered sets (four-byte words used to encode FC data and commands). In particular, FC controller <NUM> classifies the FC traffic, identifies repetitive signals and suppresses them in order to conserve network bandwidth, as described in <FIG> below.

The FC traffic produced by FC controller <NUM> (which may comprise FC data frames and/or ordered sets) is queued in an ingress queue <NUM> and provided to a packet processor <NUM>. The packet processor encapsulates the FC traffic in MPLS packets. The MPLS packets are then sent over network <NUM>, to be accepted by a remote egress translator. An exemplary method for ingress processing is described in <FIG> below.

A protocol management module <NUM> controls the transmission of MPLS packets over network <NUM>. Module <NUM> performs a selective retransmission process, in which lost (dropped) MPLS packets are retransmitted over the packet network. Additionally, module <NUM> adaptively adjusts the packet transmission rate to ensure a tolerable packet loss probability. Exemplary selective retransmission and packet rate adaptation methods are described in <FIG> below.

FC data frames and primitives produced by FC controller <NUM> are typically numbered with successive sequence numbers and cached in a buffer memory <NUM>, as part of the selective retransmission process. If a particular MPLS data packet is dropped by the packet network, a corresponding cached FC data frame or primitive can be read from memory <NUM> and retransmitted. The size of buffer memory <NUM> is typically determined based on factors such as the maximum time window defined for the selective retransmission mechanism, the expected delays over tunnel <NUM> and/or the expected packet rate.

In the egress direction (i.e., from the packet network to the FC device), MPLS data packets are accepted by packet processor <NUM>. The packet processor decapsulates the MPLS packets to extract the FC traffic. The FC traffic is queued in an egress queue <NUM> and provided to FC controller <NUM>. The FC controller sends the FC traffic via SERDES <NUM> and optical transceivers <NUM> to the locally connected destination FC device. In particular, the FC controller re-generates repetitive signals suppressed by the ingress translator and sends the re-generated signals to the destination FC device. An exemplary method for egress processing is described in <FIG> below.

Translator <NUM> may be implemented using dedicated hardware or firmware, such as in a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC). Some functions of the translator, such as, for example, the functions of protocol management module <NUM>, can be implemented using software, or as a combination of hardware and software elements. The translator may be implemented as a standalone provider edge (PE) unit, or as a user interface module (UIM) in a network element (NE) that connects different types of users and services to the packet network.

<FIG> is a flow chart that schematically illustrates a method for ingress processing, in accordance with an embodiment of the present invention. The method is carried out by a FC translator acting as an ingress translator. The method begins with translator <NUM> accepting FC traffic from a locally connected source FC device, at an ingress input step <NUM>. FC controller <NUM> of the ingress translator classifies the FC traffic, at an ingress classification step <NUM>. In general, FC traffic may comprise data frames, primitive signals or primitive sequences.

When the FC controller identifies a FC data frame, packet processor <NUM> of the ingress translator encapsulates the frame in an MPLS data packet, at a data encapsulation step <NUM>. An exemplary FC data frame encapsulated in an MPLS packet is described in <FIG> below. The packet processor then sends the MPLS packet via MPLS tunnel <NUM> to the egress translator, at an ingress transmission step <NUM>.

When the FC controller identifies a FC primitive signal, packet processor <NUM> of the ingress translator encapsulates the primitive signal in an MPLS data packet, at a primitive signal encapsulation step <NUM>. An exemplary primitive signal encapsulated in an MPLS packet is described in <FIG> below. (In some embodiments, IDLE and receiver ready (R_RDY) primitives are processed in a different manner, as will be described further below. ) The packet processor then sends the MPLS packet via MPLS tunnel <NUM> to the egress translator at ingress transmission step <NUM>.

When the FC controller identifies a repetitive signal, it suppresses the repetitive signal, at a suppression step <NUM>. Repetitive signals may comprise, for example, sequences of IDLE frames and other primitive sequences, as described above. Typically, the FC controller considers a particular sequence of frames to be a repetitive sequence when three successive identical primitive signals are identified.

When the FC controller identifies a repetitive signal at step <NUM> above, it produces a single repetition indication frame that identifies the repetitive signal. The repetition indication frame is encapsulated by packet processor <NUM> in an MPLS packet, at step <NUM>. The packet is transmitted over network <NUM> to the egress translator, at step <NUM>. The FC controller of the egress translator subsequently uses the repetition indication frame to re-generate the repetitive signal, as will be described in <FIG> below.

In some cases, different repetitive signals may be suppressed in different ways. For example, during the initialization of the FC link, the source and destination FC devices send IDLE sequences to one another. These IDLE sequences are typically replaced by the ingress translator with repetition indication frames, as described above. During normal operation of the FC connection, the source FC device produces sequences of IDLE signals in the IFG, i.e., between successive data frames. In some embodiments, the IDLE sequences in the IFG are suppressed by the ingress translator without transmitting a repetition indication frame. The egress translator automatically generates repetitive IDLE signals in the IFG.

As another example, FC devices exchange R_RDY signals to indicate that the receiver is ready to accept traffic. In some embodiments, the ingress and egress translators terminate the R_RDY signals locally without transmitting them over network <NUM>. The translators count the number of R_RDY signals and use them for buffer and credit management.

Additionally or alternatively, the FC controller may identify particular primitive signals or other ordered sets, and apply special processing to these signals. For example, the FC controller can identify the beginning and end of an FC data frame by identifying start-of-frame (SOF) and end-of-frame (EOF) primitives, as defined in the FC standard.

<FIG> is a flow chart that schematically illustrates a method for egress processing, in accordance with an embodiment of the present invention. The method is carried out by a FC translator acting as an egress translator. The method begins with translator <NUM> accepting MPLS packets from MPLS tunnel <NUM>, at an egress input step <NUM>. The MPLS packets comprise encapsulated FC traffic, as described above. Packet processor <NUM> of the egress translator decapsulates the MPLS packets to extract the FC traffic, at a decapsulation step <NUM>. The FC traffic is provided to FC controller <NUM> of the egress processor.

The FC controller classifies the FC traffic, at an egress classification step <NUM>. When the FC controller identifies a FC data frame, it transmits the FC data frame to the locally connected destination FC device, at an egress transmission step <NUM>. Otherwise, the FC controller checks whether the classified traffic comprises a repetition indication frame that indicates a repetitive signal, at a repetition checking step <NUM>. If the classified traffic comprises a primitive signal that does not represent a repetitive signal, the FC controller transmits the primitive signal to the destination FC device at step <NUM> above.

If the classified traffic comprises a repetition indication frame, such as produced by the ingress translator at step <NUM> of <FIG> above, the FC controller of the egress translator re-generates a repetitive signal similar to the suppressed signal, at a re-generation step <NUM>. The FC controller identifies the type of repetitive signal from the repetition indication frame, and produces a corresponding repetitive signal. The re-generated repetitive signal is sent to the destination FC device at step <NUM>. The FC controller of the egress translator typically continues to transmit the repetitive signal until a different FC frame or primitive is identified.

Note that according to the FC standard, the source FC device should login with the destination FC device before exchanging FC traffic. In the login process, the destination FC device provides its address (possibly along with additional operating characteristics of the destination FC device) to the source FC device. The source FC device uses the provided address as the destination address of subsequent FC frames. In some embodiments, the ingress and egress translators encapsulate and transport the signaling frames exchanged between the source and destination FC devices during the login process. The encapsulation and transport are transparent to the FC devices, and the resulting FC connection is an end-to-end non-terminated connection between the source and destination FC devices, which traverses the packet-switched network.

<FIG> is a diagram showing an exemplary MPLS data packet <NUM>, which encapsulates a FC data frame <NUM>, in accordance with an embodiment of the present invention. The FC data frame comprises a <NUM>-byte start-of-frame (SOF) delimiter <NUM>, and a <NUM>-byte frame header <NUM>. A payload field <NUM> carries the data of the FC frame. The payload is typically up to <NUM> bytes in size and is made of <NUM>-byte FC words. The payload is followed by a <NUM>-byte cyclic redundancy check (CRC) <NUM> and a <NUM>-byte end-of-frame (EOF) delimiter.

The MPLS packet that encapsulates the FC data frame comprises an MPLS label <NUM>, a virtual circuit (VC) label <NUM>, a control word (CW) <NUM> and an <NUM>-byte encapsulation header <NUM>. The control word typically encodes the length of the packet, and may encode a sequence number used for selective retransmission. The encapsulation header may comprise flags that identify the FC frame type (e.g., primitive signal or data frame) and other control information, such as sequence numbers used for selective retransmission.

In some embodiments, the sequence number in CW <NUM> is not used. Instead, the encapsulation header comprises two different sequence numbers: a sequence number of the current packet and a sequence number indicating the last properly received packet. The egress translator uses these numbers to determine which frames should be retransmitted.

<FIG> is a diagram showing an exemplary MPLS data packet <NUM>, which encapsulates FC ordered sets, in accordance with an embodiment of the present invention. Packet <NUM> comprises an MPLS header <NUM>, which comprises an MPLS label, VC label and control word, similar to the respective fields in frame <NUM> of <FIG> above. The MPLS header is followed by an <NUM>-byte encapsulation header <NUM>, similar to encapsulation header <NUM> of <FIG> above. The headers are followed by a control payload <NUM>, which comprises the encapsulated ordered sets, typically up to <NUM> bytes in size.

<FIG> is a flow chart that schematically illustrates a method for controlling the packet transmission over network <NUM>, in accordance with an embodiment of the present invention. The method combines two separate processes, a selective retransmission process and a packet rate adaptation process, in order to ensure a reliable transport of MPLS packets via tunnel <NUM>.

The method begins with protocol management module <NUM> of the egress translator monitoring and detecting lost MPLS packets, at a monitoring step <NUM>. As MPLS packets are accepted by the packet processor of the egress translator, module <NUM> tracks the sequence numbers in the received packets. Using the sequence numbers, module <NUM> checks whether packets are missing, at a dropped packet checking step <NUM>. If a packet is found to be missing, the packet is retransmitted, at a retransmission step <NUM>. Module <NUM> of the egress translator reports (over network <NUM>) the sequence number of the missing packet to the ingress translator. The ingress translator reads the corresponding FC frame or primitive signal from buffer memory <NUM>, encapsulates it in an MPLS packet, and retransmits the packet.

Module <NUM> of the ingress translator uses the information regarding dropped packets reported by the egress translator to monitor the rate of packet loss at monitoring step <NUM> above. An exceedingly high packet loss rate typically increases the rate of retransmitted packets, thus increasing the communication and computation overhead and reducing network efficiency. The communication latency may also increase with the higher retransmission rate. Module <NUM> of the ingress translator controls the packet transmission rate based on the monitored packet loss rate. Typically, module <NUM> of the ingress translator attempts to maximize the packet transmission rate while minimizing packet loss. In alternative embodiments, the rate adaptation process may adjust the packet transmission rate so as to maintain the packet loss rate within a predetermined range.

If the packet loss rate is higher than a predetermined upper bound, as checked by an upper bound checking step <NUM>, module <NUM> of the ingress translator reduces the packet transmission rate through tunnel <NUM>, at a rate reduction step <NUM>. If, on the other hand, the packet loss rate is tolerable, module <NUM> attempts to increase the packet transmission rate, at a rate increasing step <NUM>.

Typically, dropped packets are detected and reported by the egress translator. The ingress translator calculates the dropped packet rate, compares it to the upper bound and performs the appropriate packet transmission rate modifications. In alternative embodiments, these functions can be partitioned differently between the ingress and egress translators.

Claim 1:
A system for transporting between first (24A) and second (24B) devices a traffic, that is according to a protocol that use continuous transmission of frames for synchronization and includes data frames and idle frames, over an Internet Protocol, IP, based packet-switched network (<NUM>), the system comprising:
a first translator (32A) connected between the first device and the packet-switched network and operative to receive (<NUM>) a first traffic according to the protocol from the first device, to encapsulate (<NUM>) a second traffic from the first traffic in packets suitable for transporting over the packet-switched network, and to transmit the packets to the packet-switched network; and
a second translator (32B) connected between the second device and the packet-switched network and operative to receive (<NUM>) the packets from the first packet-switched network, to decapsulate (<NUM>) the first traffic from the second traffic in the received packets; and to transmit the generated first traffic to the second device;
characterized in that:
the first translator is further operative to identify (<NUM>) a repetitive signal that is made of successive idle frames in the first traffic and to generate (<NUM>) the second traffic by replacing the identified repetitive signal in the first traffic with an indicator; and
the second translator is further operative to identify (<NUM>, <NUM>) the indicator in the second traffic and to reproducing (<NUM>) in response to the indicator the first traffic from the second traffic,
wherein the protocol is compatible to Fibre Channel, FC, the idle frames are IDLE frames according to the FC protocol, the traffic is FC traffic, and the first and second devices are respectively first and second FC devices.