Glossary

BHS: Basic Header Segment - The 48-byte header of an iSCSI packet.

CDB: Command Descriptor Block - The standard format for SCSI commands. CDBs are commonly 6, 10, or 12 bytes long, though they can be 16 bytes or of variable length.

CHAP: Challenge Handshake Authentication Protocol - An authentication technique for confirming the identity of one computer to another. Described in RFC 1994.

CID: Connection Identifier - A 16-bit number, generated by the initiator, that uniquely identifies a connection between two iSCSI devices. This number is presented during the login phase.

Data Digest - a code used to insure data integrity of a block of data. Checksums and CRCs are common types of digests.

Domain Name - A unique name assigned by an Internet authority that identifies a business or group of computers, e.g. "diskdrive.com", "csu.edu", "usgs.org".

EUI: Extended Unique Identifier - A 64-bit number that uniquely identifies every device in the world. The format consists of 24 bits that are unique to a given company, and 40 bits assigned by the company to each device it builds.

Fabric - A general term meaning a network of interconnected devices. Common use refers to a "Fibre Channel fabric" as opposed to a "Fibre Channel network."

FCP: Fibre Channel Protocol - despite the seemingly generic name, this protocol is specifically for transporting SCSI commands and data across a Fibre Channel network.

Fibre Channel - a standard for connecting computing devices into a network. The predominant usage is for Storage Area Networks.

HBA: Host Bus Adapter - A hardware card that plugs into a computer and provides a given interface. The term HBA is commonly used for SCSI adapters and Fibre Channel adapters. Ethernet adapters are called NICs.

IANA (eye-anna): Internet Assigned Number Authority - The organization responsible for assigning various names and numbers to Internet users. Does not deal with Domain Names.

Initiator - The originating end of a SCSI conversation. Typically a controlling device such as a computer.

Inquiry - A SCSI command that reads generic information from a target device. The information returned includes device type, manufacturer, model number, and version.

IP: Internet Protocol - The standard Internet protocol for moving packets of information from one computer to another. Commonly combined with TCP in the phrase TCP/IP.

IPS: Internet Protocol Storage - The class of protocols or devices that use the IP protocol to move data in a storage network. FCIP, iFCP, and iSCSI are all examples of IPS protocols.

IQN: iSCSI Qualified Name - A name format for iSCSI that uniquely identifies every device in the world (e.g. iqn.5886.com.acme.tapedrive.sn-a12345678).

iSCSI (eye-scuzzy): Internet Small Computer System Interface - a protocol for transporting SCSI commands and data across an IP network.

ISID: Initiator Session Identifier - A 48-bit number, generated by the initiator, that uniquely identifies a session between the initiator and the target. This value is created during the login process, and is sent to the target with a Login PDU.

ITT: Initiator Task Tag - A 32-bit number that is unique to every outstanding command at the target. A given value of ITT can be reused once that command is complete and status has been received from the target.

Kerberos - In mythology, a three-headed dog that guards the gates of hell. In computers, an authentication technique that allows one server to administer all passwords and access permissions. Described in RFC 1510.

LAN (rhymes with "tan"): Local Area Network - a network of interconnected computers, usually consisting of clients and servers. Ethernet is the most common LAN.

LUN (rhymes with "run"): Logical Unit Number - Technically, the LUN is the number that identifies a sub-element within a SCSI target device. In common usage, LUN is used to refer to the device itself, although LU (Logical Unit) is the more proper term.

Mode Select - A SCSI command that sets operating parameters on a target.

Mode Sense - A SCSI command that reads operating parameters from a target.

NAS (rhymes with "grass"): Network Attached Storage - a storage device that is attached to a LAN and provides file-oriented storage to clients.

NFS: Network File System - An Internet standard way of making a disk on a remote machine appear to be attached to a local machine. Commonly used in Unix systems.

NIC (nick): Network Interface Card - A hardware card that plugs into a computer and provides a network interface. NIC is almost exclusively used to describe Ethernet interface cards.

NPU: Network Processing Unit - A microprocessor designed specifically to handle network traffic.

Request Sense - A SCSI command that tells a target to return sense data (error details) back to the initiator.

SAM: SCSI Architectural Model - A document that describes the behavior of SCSI in general terms, allowing for different types of devices communicating over various media.

SAN (rhymes with "tan"): Storage Area Network - a network of host computers and mass storage devices. Used to share disks and tapes with multiple hosts. SANs move stored data at the block level and have no awareness of file structure.

Socket - A TCP connection established between two computers. A socket is uniquely identified by the source IP address, source port number, destination IP address, and destination port number.

SRP: Secure Remote Password - An authentication technique developed at Stanford University and described in RFC 2945.

Target - The receiving end of a SCSI conversation, typically a device such as a disk drive, tape drive, or scanner. See also "Initiator."

TCP: Transmission Control Protocol - A common Internet protocol that insures packets arrive at the end point in order, acknowledged, and error-free. Usually combined with IP in the phrase TCP/IP.

Test Unit Ready - A SCSI command that checks to see if the target device is ready to read or write data to the medium.

TOE: TCP/IP Offload Engine - A piece of hardware that implements the TCP/IP stack, and thereby "offloading" this task from the main processor. This hardware may be a custom ASIC or a network processor with firmware.

TSID: Target Session Identifier: A 16-bit number, generated by the target, that uniquely identifies a session between the initiator and the target. This value is created during the login process, and is sent to the initiator with a Login Response PDU.

URL: Uniform Resource Locator - A standard way of writing an Internet address that describes both the location of the resource, and its type. The best known URL type is for web pages (e.g. http://www.acme.com), but URLs are used for other resources also, such as FTP sites and iSCSI nodes (e.g. ftp://ftp.acme.com, iSCSI://tapedrive.acme.com).

UTF-8 - A clever way of putting Unicode characters into a byte stream. If the MSB is zero, then the remaining 7 bits are interpreted as a standard ACSII character. If the MSB is one, then the lower 7 bits are combined with the next byte to create a 14-bit Unicode character.