Fibre Channel (FC) - the fiber channel

In Russian-speaking literature the term is used without transfer.

History

The history Fibre Channel began in 1985, and in 1994 ANSI as the standard simplifying the HIPPI interface to which the massive 50-paired cable with bulky connectors was used was approved. Originally the Fibre Channel interface had to increase range and simplify connection of transmission lines, but not increase speed.

Fibre Channel topology

Topology of FC defines mutual connection of devices, namely transmitters (transmitters) and receivers (receivers) of devices. There are three types of topology of FC:

• Point-to-point (point-to-point)

Devices are connected directly — the transmitter of one device is connected to a receiver of the second and vice versa. All personnel sent by one device is intended for the second device.

• The managed loop (arbitrated loop)

Devices are united in a loop — the transmitter of each device is connected to a following receiver. Before the loop is able to serve for data transmission, devices agree about the addresses. For data transmission on a loop the device should take control of "relay" (token). Adding of the device in a loop leads to suspension of data transmission and recollecting of a loop. For creation of the managed loop use hubs which are capable to disconnect or close a loop during the adding of the new device or the output of the device from a loop.

• The switched coherent architecture (switched fabric)

It is based on use of switches. Allows to connect the bigger number of devices, than in the managed loop, at the same time adding of new devices does not influence data transmission between already attached devices. As on the basis of switches it is possible to build complex networks, on switches the distributed services of network management (fabric services) which are responsible for data transmission routes, registration in networks and assignment of the network addresses and so forth are supported.

Sometimes mistakenly mean data storage network topology by topology of FC, i.e., mutual connection of the equipment of infrastructure and terminal units.

Levels

The Fibre Channel consists of five levels:

• FC-0 Physical Describes a transmission medium, transceivers, connectors and types of the used cables. Includes determination of electric and optical characteristics, data transfer rates and other physical components. Both the optical, and electric environment (the twisted pair cable, coaxial or twinaxial cables and also multimode or single-mode fiber), at data transfer rate from 133 megabits / with up to 10 gigabits / with on distances up to 50 kilometers is supported.
• FC-1 Coding Describes process 8b/10b Codings (every the 8th data bit are coded in the 10-bit character (Transmission Character)), special characters and error control. For 10GFC coding 64b/66b thereof 10GFC it is incompatible with 1/2/4/8GFC is used.
• FC-2 Framing and signaling Describes signal protocols. At this level there is determination of words, splitting a data stream into the personnel. Defines rules of data transmission between two ports, classes of services).
• FC-3 of the services, General for a node, Defines basic and expanded services for the transport layer and also such features as: splitting of a data stream (striping) (A possibility of transfer of a data stream through several connections (routes), display of a set of ports to one device.
• FC-4 of Display of protocols Gives an opportunity to encapsulation of other protocols (SCSI ATM IP HIPPI AV VI IBM SBCCS and many others.)

Logical types of ports

Depending on the supported topology and type of the device ports are separated into several types:

• Ports of nodes:
  • N_Port (Node port), port of the device with support of topology of FC-P2P ("Point-to-point") or FC-SW (with the switch).
  • NL_Port (Node Loop port), port of the device with support of topology of FC-AL (arbitrated loop is the managed loop).

• Ports of the switch/router (only for FC-SW topology):
  • F_Port (Fabric port), tkani port. It is used for connection of ports like N_Port to the switch. Does not support loop topology.
  • FL_Port (Fabric Loop port), tkani port with support of a loop. It is used for connection of ports like NL_Port to the switch.
  • E_Port (Expansion port), port of expansion. It is used for connection of switches. It can be connected only to port like E_Port.
  • EX_port port for connection of the FC router and the FC switch. From the switch it looks as normal E_port, and from the router it is EX_port.
  • TE_port (Trunking Expansion port (E_port)) is entered to the Fibre Channel by CISCO company, now is accepted as the standard. It is expanded with ISL or EISL. TE_port provides in addition to standard opportunities of E_port routing mnozhestvennyykh to VSANs (Virtual SANs). It is implemented by application of a non-standard frame of the Fibre Channel (vsan tagging).

• General case:
  • L_Port (Loop port), any port of the device with support of topology Loop - NL_port or FL_port.
  • G_port (Generic port), port with auto detection. Can automatically be defined as port like E_Port, N_Port, NL_Port.

Options of optical medium of data transmission

Fibre Channel infrastructure

The equipment for infrastructure of the Fibre Channel is subdivided into several classes.

• Directors — multiport modular switches with high degree of availability.
• The selected switches (standalone switches) are switches with the fixed number of ports.
• Stekiruyemy switches (stackable switches) are the switches having additional high-performance ports for communication of independent chassis among themselves.
• The built-in switches (embedded switches) are the switches which are built in a blade basket (blade enclosure) where there is separation of ports for function (the ports intended for connection of blade servers cannot be used for interswitch connections).
• Hubs (hubs) are the devices providing communication in the managed loop (Arbitrated Loop).
• Hubs switches (loop-switches) are the switches providing communication in the managed loop (Arbitrated Loop). Hubs and hubs switches are practically not used for connection of terminal units; are used for connection of disks to controllers in disk arrays.

For increase in range of connection use the additional transmission hardware, such as multiplexers on the basis of WDM, etc.

The main equipment manufacturers for Fibre Channel infrastructure: Brocade, Cisco, QLogic, Emulex.

Logic gates of a data stream

At data transmission select the following logical sequences:

Ordered sets (Ordered Sets)

Four-byte words (Transmission Words) containing data and special characters. Splitting a data stream into ordered sets allows to save synchronization between the transmitter and a receiver at the level of bits and words. Ordered sets always begin with the character of K28.5. The main types of sets are defined by the signal protocol.

Dividers of the personnel

Dividers of the personnel are used for separation of one frame from another. There are two such sets:

• Beginning of a frame (Start Of Frame, SOF)
• End of a frame (End Of Frame, EOF)

Basic signals

• Signal of failure to act (Idle). It is transferred for designation of readiness to accept and send the personnel.
• Receiver ready signal (Receiver Ready, R_RDY). It is used at dataflow control (see Service Classes) for indication of existence of the place in the receiver buffer.
• Basic sequences. Are transferred for the notification about a non-standard status of port. When obtaining such sequence the corresponding sequence or a signal of failure to act is in reply sent. The standard maintains four sequences:

1. Offline (OLS)
2. Not Operational (NOS)
3. Link Reset (LR)
4. Link Reset Response (LRR)

Protocols

Addressing

Unique address of the device

Each device has the unique 8-byte address, the called NWWN (Node World Wide Name) consisting of several components: A0:00:BB:BB:BB:CC:CC:CC || | | |||±------Are appointed the producer of the device. || ±--------------- IEEE for each producer Are appointed. |±--------------------Always 0:00 a.m. (It is reserved by the standard) ±---------------------the Number is randomly selected by the producer.

Classes of services (CoS)

The Fibre Channel supports the following classes of services (Classes of service, CoS).

The FC-PH standard defines Classes 1-3, Class 4 is defined in FC-PH-2 standard (in FC-FS-2 it is set obsolete), Class 5 is offered for the isochronous mode, but insufficiently standardized, Class 6 is defined in FC-PH-3 standard, Class F — in the FC-SW and FC-SW2 standards.

• Class 1 — Acknowledged Connection Service (allocated channels with confirmation). Between two devices via the switch or factory dedicated connection is established. The accepting device sends to the sending device of receipt acknowledgment of each frame. Connection remains open until data transmission is not complete. Transient time of connection makes several microseconds. Usually duplex though the organization simplex (for example is as necessary possible if it is necessary to transfer at the same time data to one node and to accept the provided channel from another). All its capacity is available to devices. End-to-end flow control is used. The high exchange rate and the correct order of acceptance of the personnel is guaranteed. Is ideal for the applications working with large volumes of data — for example, the systems of modeling or processing of video. If capacity is not used by completely this application, it is all the same unavailable to other applications until connection is closed as attempts of connection with such port will be rejected with signal output "is busy". Therefore, in the standard it is recommended to close connections in the absence of data for transfer. In this case the maximum capacity is available. The main shortcoming - impossibility of work among themselves ports with a different speed of work. The unidirectional broadcast standardized in FC-PH-2, buffering of class 1 and Camp on, since FC-FS, are considered as obsolete.
• Class 2 — Acknowledged Connectionless Service (transfers without the organization of connection with confirmation). Each frame is switched irrespective of the others, the final port can transfer and accept at the same time data from several nodes, at the same time the channel between two interacting is not selected (in fact, there is a multiplexing by the traffic switch). Each frame is confirmed by the accepting device. The personnel can be brought along different routes, i.e. ordered delivery of the personnel in this class is not guaranteed, ordering of the sequence of the personnel is performed at the FC-2 level. Utilization of available bandwidth is lower, than in Class 1 as mechanisms of regulation of a flow on a frame basis turn on.
• Class 3 — Unacknowledged Connectionless Service, sometimes is called Datagram Connectionless Service (transfers without the organization of connection and without confirmation). It is similar to class 2 except that there is no delivery confirmation. Capacity for lack of errors, due to the lack of confirmations, slightly (from 0% in most cases in the worst case for class 2) increases to 3% in comparison with class 2, but there are no guarantees of delivery, ordered delivery of the personnel is not guaranteed. Ordering of the sequence of the personnel is performed at the FC-2 level, and the request for repeated transfer of lost frames is performed by protocols of top levels. Respectively, in case of transmission errors and also if the frame deviates or the resource is occupied, then the frame is lost, and protocols of top levels are connected. Capacity falls as at protocols of top levels the response time and timeouts are significantly higher, than at the FC-2 level. At the same time, for protocols of real time, the delay with repetition can be such that the transmitted data became already outdated. It is used for the organization multi-address and multicastings, it is applied also in the systems of mass memory. The most widespread class of the switched FC networks as it is simplest in implementation and as the most widespread protocols of top levels of SCSI and IP work in this class.
• Class 4 — Fractional Bandwidth Connection-oriented Service (connection with fractional bandwidth) between N_Ports. It is similar to Class 1 as too assumes connection establishment, delivery confirmation, the fixed delay, observance of an order of the personnel. Connection between ports is established in the form of a virtual channel with the bandwidth sufficient for provision of services with predictable quality (QoS including the guaranteed bandwidth and the maximum delay). Such virtual bidirectional channel consists two unidirectional virtual connections (Virtual Circuit, VC), and on each VC different QoS can be provided. Each N_port can set several such connections (up to 254). It is used for data, critical by the time of delivery — for example, video and audio streams.
• Class 5 — Isochronous Service (isochronous connection). It is not standardized. It is intended for the applications demanding immediate delivery of data without intermediate buffering.
• Class 6 — Unidirectional Connection Service (the unidirectional connection). It is similar to Class 1, but is exclusively unidirectional. It is used for broadcasting and multi-address mailings via the corresponding server. N_port can request connection of Class 6 on one or several devices (ports). The set connection exists until the initiator in an explicit form closes it. It is developed for delivery of traffic of real time (for example, audio and video).
• The mixed class — Intermix — is class 1 subspecies. Allows to transfer the personnel of class 2 or 3 to those moments when the application of the first class does not occupy the channel, and the personnel of classes 2 or 3 should be optional addressed to the same receiver, as at class 1. Was specially developed to eliminate on purpose partially blocking of factory with transfers of the first class.
• Class F — is used by switches for management and transfer of the service information, transfer goes without connection establishment on Inter Switch Links (ISL) between E_ports.

Scopes of the Fibre Channel

The Fibre Channel is widely applied to creation Storage area networks (Storage Area Networks). Thanks to high data transfer rate, short delay and expansibility has practically no analogs in this area. However, in recent years, the field of its application gradually moves to a segment of the high-performance systems and solutions, and the budget segment with success accustoms inexpensive solutions iSCSI based on Gigabit Ethernet and 10G of Ethernet. Also the tendency to transfer of the transport layer of the FC protocol in the same Gigabit and 10G of Ethernet by means of protocols was outlined FCoE and FCIP.

Links

# Fibre Channel Industry Association # Technical Committee T11 # Jon Tate, Brian Cartwright, John Cronin, Christian Dapprich. IBM SAN Survival Guide. IBM RedBooks, SG24-6143-01, August 2003

1. All about Fibre Channel protocols and FCoE in Russian
2. Transfers of FC-PH, FC-FG and FC-FS and others into Russian

Notes