[ Pobierz całość w formacie PDF ]

FC-2) form what is known as the Fibre Channel physical standard
(FC-PH). This defines all the physical transmission characteristics of
Fibre Channel. The remaining layers (FC-3 and FC-4) handle inter-
faces with other network protocols and applications.
Unlike local area network (LAN) technologies such as Ethernet
and Token Ring, Fibre Channel keeps the various functional layers
of the stack physically separate. This enables vendors to build prod-
ucts from discrete functional components, such as chip sets and bus
interfaces, that handle specific portions of the protocol stack. It also
enables them to implement some stack functions in hardware and
others in software or firmware.
FC-0 Layer: Physical Layer
FC-0 defines the basic physical link, including the fiber, connectors,
and optical/electrical parameters for a variety of data rates. Fibre
Channel offers a basic rate of 133 MBd, the most commonly used
speed of 266 MBd, and 531 MBd and 1.062 GBd. It is important to
note that these signaling rates include the overhead involved in
establishing and maintaining connections. The actual data through-
put is somewhat lower: 100 Mbps for 133 MBd, 200 Mbps for 266
MBd, 400 Mbps for 531 MBd, and 800 Mbps for 1.062 GBd.
Data rates are expected to go well beyond today s 1.062-GBd ceil-
ing. In most cases, including switched environments, users will be
able to upgrade simply by swapping in an adapter card. Specifica-
tions for 2.134 and 4.268 GBd are already in place.
FC-1 Layer: Transmission Encode/Decode Layer
FC-1 defines the transmission protocol, including serial encoding
and decoding rules, special characters, timing recovery, and error
control. The information transmitted over a fiber is encoded 8 bits at
a time into a 10-bit transmission character (8B/10B transmission
coding scheme licensed from IBM). The two extra bits are used for
Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.
Fibre Channel
Fibre Channel
93
error detection and correction, known as disparity control. The
8B/10B scheme supplies sufficient error detection and correction to
permit use of low-cost transceivers, as well as timing recovery meth-
ods to reduce the risk of radiofrequency interference and ensure bal-
anced, synchronized transmissions.
FC-2 Layer: Framing and Signaling Layer
The FC-2 layer performs the basic signaling and framing functions
and defines the transport mechanism for data from the upper layers
of the stack.
FC-2 frames and sequences data from the upper layers for trans-
mission via the FC-0 layer. It also accepts transmissions from the
FC-0 layer and reframes and resequences them for use by the upper
layers. Fibre Channel frame sizes can vary and must be negotiated
by the transmitter-receiver pair for each connection. Frame sizes
typically range from 36 bytes to 2 kilobytes but may be larger in
some cases. Fibre Channel is making the biggest impact in the stor-
age arena particularly using SCSI as the ULP. Compared with tra-
ditional SCSI, the benefits of mapping SCSI command set onto Fibre
Channel include
 % Faster speed
 % More device connections
 % Larger distances allowable between devices
Fibre Channel using arbitrated-loop topology is simply a replace-
ment for SCSI. Many companies are moving toward SCSI adapter
cards for several platforms and operating systems in addition to disk
drives and storage devices with Fibre Channel interfaces. SCSI com-
panies are selling Fibre Channel devices that run IP. Although ULP
is an independent topology, IP is found more commonly in switched
fabric environments. At the present time, SCSI and IP are pretty
much the only two ULPs used commercially on Fibre Channel.
FC-0 layer features include
 % Signaling
 % Media specifications
 % Receiver-transmitter specifications
Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.
Fibre Channel
Chapter 5
94
FC-2 signaling defines the connection between at least two Fibre
Channel node ports (or N_Ports). One of these acts as originator of
outbound traffic, and one other acts as a responder receiving
inbound traffic and sending traffic back. Connections between
N_Ports are in full duplex. The FC-2 layer provides traffic manage-
ment functions, including flow control, link management, and buffer
memory management, in addition to error detection and correction.
The FC-2 layer supplies additional flow control and error correc-
tion mechanisms. For flow control, it employs sliding-window
schemes similar to that of Transmission Control Protocol (TCP)/
Internet Protocol (IP). Flow control functionality varies somewhat
according to class of service defined. Error detection is performed
using a 32-bit CRC. A link control facility (LCF) manages the Fibre
Channel connection and maintains the information needed to [ Pobierz całość w formacie PDF ]