CS 635 Lecture 6, Part 1
Designed to combine the speed of I/O channel communication with the flexibility
and interconnectivity of protocol-based network connection.
I/O Channel oriented facilities
Data type qualifiers for routing frame payload into particular interface
Link-level constructs associated with individual I/O operations
Protocol interface spec to allow support of existing I/O channel architecture,
such as SCSI
Network oriented facilities
Fibre Channel is 1 Gbps transfer interface technology that maps several
common transport protocols including IP and SCSI allowing it to merge high-speed
I/O and internetworking functionality in a single connectivity technology.
Full multiplexing of traffic between multiple destinations
Peer-to-peer connectivity between any pair of ports on a fibre channel
Capabilities for internetworking to other connection techniques
Fibre channel is a open standard as defined by ANSI and OSI standards
and operates over copper and fiber optic cabling at distances up to 10
It supports multiple interoperable topologies including point-to-point,
arbitrated loop and switching and it offers several qualities of service
Fibre Channel Architecture
Full duplex with two fibers per link
Performance from 100 to 800 Mbps on a single link (200 to 1600 Mbps per
Support for distances up to 10 km
Fibre Channel Elements
The network consists of nodes and one or more switching elements. The collection
of switching elements is called a fabric. These elements are interconnected
by point-to-point links between ports on the individual nodes and switches.
Communication consists of the transmission of frames across the point-to-point
XXX picture 9.2
Each node includes three or more ports, called N_Ports, for interconnection.
Each fabric switching element includes one or more ports, called F_Ports.
Any node can communicate with any other node connected to the same
fabric using the services of the fabric. All routing of frames between
N_Ports is done by the fabric. Data may be buffered within the fabric,
making it possible for different nodes to connect to the fabric at different
data rates. Fabric is responsible for buffering and routing frames between
source and destination nodes.
Fibre channel fabric is not a shared medium, therefore there are no
MAC related issues. Fibre Channel scales easily in terms of N_Ports, data
rates, and distance covered.
Fibre Channel Protocol Architecture
XXXX picture 9.3
The Fibre Channel standard is organized into five levels.
FC-0 Physical media
Currently, data rates ranging from 100 to 800 Mbps per fiber are defined.
Depending on the data rate and medium involved, max distances for individual
point-to-point links range from 50 meters to 10 km.
Optical cable with laser or LED transmitters
Copper coaxial cable for highest speed over short distances
Shielded twisted pair for lower speeds over short distances
FC-1 Byte synchronization and encoding
8B/10B encoding/decoding scheme provides balance, is simple to implement,
and provides useful error-detection capability. 8 bits of data from level
FC-2 is converted into 10 bits for transmission. The 8B/10B scheme was
patented by IBM.
Special code character maintains byte and word alignment
FC-2 Actual transport mechanism
This level deals with the transmission of data between N_Ports in the form
of frames. Among the concepts defined at this level:
Framing protocol and flow control between N_Ports
Tree classes of service between ports
Node and N_Port and their identifiers
Classes of service provided by the fabric
Segmentation of data into frames and reassembly
Grouping of frames into logical entities called sequences and exchanges
Sequencing, flow control, and error control.
FC-3 Common service layer
FC-3 provides a set of services that are common across multiple N_Ports
of a node. The functions include
Port related services
Services across two or more ports in a node
Striping: makes use of multiple N_Ports in parallel to transmit a single
information unit across multiple links simultaneously. This achieves higher
aggregated throughput. For transferring large data sets in real time, as
in video-imaging applications
Hunt groups: a set of associated N_Ports at a single node. This set is
assigned an alias identifier that allows any frame set to this alias to
be routed to any available N_Port within the set. This may decrease latency
by decreasing the chance of waiting for busy N_Port.
Multicast: delivers a transmission to multiple destinations. This includes
sending to all N_Ports on a fabric (broadcast) or to a subset of the N_Ports
on a fabric.
FC-4 Upper layer protocols
FC-4 defines the mapping of various channel and network protocols to FC-PH.
I/O channel interfaces include:
Supports a variety of channel and network protocols
Network interfaces include:
Small computer system interface (SCSI)
High-performance parallel interface (HIPPI)
IEEE 802: frames map onto Fibre Channel frames
Asynchronous Transfer Mode (ATM)
Physical Media and Topologies
Optical Fiber Transmission Media
The standard specifies both single-mode and multimode optical fiber alternatives.
Optical fiber will operate up to 1.0625 Gbps and distances up to
10 km. S
Coaxial Cable Transmission Media
Lower cost alternative to optical fiber. Supports up to 1.0625 Gbps up
to 24m., and 266 Mbps up to 47m.
Shielded Twisted Pair
Used only over very short distances.
Fabric or switched topology is the most common. Includes at least
one switch to interconnect a number of N_Ports. (figure 9.5). The fabric
topology may include a number of switches forming a switched network.
Routing in the fabric topology is transparent to the nodes. Each node
in the configuration has a unique address. When data from a node are transmitted
into the fabric, the edge switch to which the node is attached uses the
destination port address in the incoming data frame to determine the destination
port location. The switch then either delivers the frame to another node
attached to the same switch or transfer the frame to an adjacent switch
to begin the routing of the frame to a remote destination.
Point-to-point topology includes two N_Port nodes connected to each
other with no fabric switch. There is no routing
additional nodes increase aggregate capacity of the network
the fabric is protocol independent and largely distance insensitive
the switch maybe changed without affecting the overall configuration
burden on nodes is minimized: each node is only responsible for managing
a point-to-point connection between itself and the fabric
Arbitrated loop topology is low cost topology for connecting
up to 126 nodes in a loop. The ports on the arbitrated loop must contain
the functions of both N_Ports and F_Ports; these are called NL_Ports. Roughly
equivalent to the token ring protocol. This topology was developed with
peripheral connectivity in mind. It natively maps SCSI.
The FC-2 framing protocol defines the rules for the exchange of higher-layer
information between nodes. FC-2 specifies types of frames, procedures for
their exchange, and formats. FC-2 is similar to the data link layer
Classes of Service
Fibre Channel provides a logical system of communication called Class of
Service. Five different Classes of Services are available:
Class 1 Service
Class 1 - Acknowledged connection service
Class 2 - Acknowledged connectionless service
Class 3 - Unacknowledged connectionless service
Class 4 - Fractional bandwidth connection oriented service
Class 6 - Simplex connection service
Provides dedicated path though the fabric, similar to circuit-switched
network. Provides guaranteed data rate between two communicating ports
and guaranteed delivery of frames in the order in which they are transmitted.
To initiate class 1 service, a N_Port transmits a frame with a special
start-of-frame delimiter SOFc1. This alerts the fabric that a connection
is requested. The fabric allocates a circuit between the requesting N_Port
and the destination N_Port. The destination N_Port can then transmit an
ACK indicating its acceptance of the connection to the requesting N_Port.
Class_1 is used for large files and absolute quality of service.
Class 2 Service
Connectionless service, independently switching each frame and providing
guaranteed delivery with an acknowledgment of each receipt. The path between
two interconnected devices is not dedicated. The switch multiplexes traffic
from N_Ports and NL_Ports without dedicating a path through the switch.
Class 2 credit-based flow control eliminates congestion that is found
in many connectionless networks. If no buffer space is available, a "Busy"
is sent to the originating N_Port. The N_Port will then re-send the message.
This way no data is arbitrarily discarded just because the switch is busy
at the time.
Typical Class 2 frame latency is less than one microsecond, making it
ideal for shorter data transfers like those in most business applications.
Class 3 Service
Class 3 is a connectionless service, similar to Class 2, but no confirmation
of receipt is given. This unacknowledged transfer is used for multicast
and broadcasts on networks and for storage interface on Fibre Channel loop.
The loop establishes a logical point-to-point conniption and reliably moves
data to and from storage.
Class 3 arbitrated loop transfers are also used for IP networks. Some
applications use logical point-to-point connections without using a network
layer protocol, taking advantage of Fibre Channel's reliable data
Class 4 Service
Class 4 is fractional bandwidth, connection-oriented service. Virtual
connections are established with bandwidth reservation for a predictable
quality of service (Qos). A class 4 connection is bi-directional with one
virtual circuit operation in each direction and supports a different set
of QoS parameters for each VC (guaranteed bandwidth and latency). A node
may reserve up to 256 concurrent Class 4 connections.
Class 4 flow control is end-to-end and provides guaranteed delivery.
Class 4 is ideal for time-criticial applications like video.
Class 6 Service
Class 6 is similar to class 1, providing simplex connection service.
However, class 6 also provides multicast and preemption. Class 6 is ideal
for video broadcast application and real-time systems that move large quantities
Intermix mode allows the reservation of full Fibre Channel bandwidth
for a dedicated (class 1) connection but also allows connectionless traffic
within the switch to share the link during idle Class 1 transmission.
An ideal application for Intermix is linking multiple large file transfers
during system backup. During a Class 1 file transfer, a Class 2 or 3 message
can be sent to the server to set up the next transfer. Upon completion
of one transfer, the next will immediately start, increasing efficiency.