Ethernet is the most widely-installed local area network technology. Specified in a standard, IEEE 802.3, Ethernet was originally developed by Xerox and then developed further by Xerox, DEC, and Intel. An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. The most commonly installed Ethernet systems are called 10BASE-T and provide transmission speeds up to 10 Mbps. Devices are connected to the cable and compete for access using a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol.
Fast Ethernet or 100BASE-T provides transmission speeds up to 100 megabits per second and is typically used for LAN backbone systems, supporting workstations with 10BASE-T cards. Gigabit Ethernet provides an even higher level of backbone support at 1000 megabits per second (1 gigabit or 1 billion bits per second).
Fibre Channel is a technology for transmitting data between computer devices at a data rate of up to 1 Gbps (one billion bits per second). (A data rate of 4 Gbps is proposed.) Fibre Channel is especially suited for connecting computer server to shared storage devices and for interconnecting storage controllers and drives. Since it is three times as fast, Fibre Channel is expected to replace the Small Computer System Interface as the transmission interface between servers and clustered storage devices. It is also more flexible; devices can be as far as ten kilometers (about six miles) apart. The longer distance requires optical fiber as the physical medium. However, Fibre Channel also works using coaxial cable and ordinary telephone twisted pair.
Fibre Channel offers point-to-point, switched, and loop interfaces and interoperates with SCSI, the Internet Protocol, and other protocols.
Manufacturers and early customers plan to use Fibre Channel to interconnect a number of servers with a common pool of storage devices (possibly including redundant arrays of independent disks (redundant array of independent disks). Vendors that offer or plan to offer Fibre Channel storage devices, switch, hub, and subsystems include Compaq, Data General, Dell, EMC, IBM, Storage Technologies, StorageTek, and Sun Microsystems.
Fibre Channel is specified by a set of standards, but mainly the Fibre Channel Physical and Signalling standard, American National Standards Institute X3.230-1994, which is also International Organization for Standardization 14165-1.
The Merlin DL core is a cost-effective Fibre Channel protocol controller which delivers the highest available Fibre Channel data rate to your storage applications. Combined with other LSI Logic CoreWare® cores and customer-specific logic blocks, designers can create high-performance, single chip disk controllers, RAID disk array controllers and Fibre Channel host adapters.
The Merlin DL core complies with the ANSI Fibre Channel Standard providing Class-3 service and support for the Fibre Channel Arbitrated Loop (FC-AL) Topology, the Fibre Channel protocol for SCSI (FCP SCSI), the Private Loop Direct Attach (PLDA) Profile and the Public Loop Profile (PLP).
At the heart of the Merlin DL core's flexible architecture is a high-performance Fibre Channel protocol engine which manages all Fibre Channel interface functions on two separate arbitrated loops. Once programmed with control information for a Fibre Channel exchange, the Merlin DL core automates the exchange from start to finish. The Merlin DL core also provides hardware assistance for FCP SCSI operations. It provides notification of incoming SCSI commands and completes the FCP SCSI operation unassisted.
The Merlin DL core is architected for scalability, enabling both high performance and low cost Fibre Channel implementations. Frame buffer sizes can be chosen to maintain Fibre Channel performance with a wide range of back-end bus structures. The Merlin DL core-based designs require as little as 48 bytes of total frame buffering in systems using a fast drain bus model. The number of exchanges supported concurrently on chip can also be tuned to meet varying performance requirements. The Merlin DL core has seven high speed bus interfaces which eliminate bottlenecks in the Fibre Channel datapath. Four 10 bit datapaths service two independent gigabit transceivers. Two 32-bit interfaces handle frame delivery between the Merlin DL core and downstream logic. A 32-bit local bus is provided for designs requiring a local microprocessor, such as LSI Logic's MiniRISC® core, or RAM. End-to-end parity protection is provided on all Merlin DL core datapaths. The Merlin DL core simplifies the design debug process by providing extensive core visibility through a dedicated debug bus.
The CoreWare® design program enables system-on-a-chip design integration, delivering unmatched market advantages. It is proven and complete, offering the technology and application know-how to put an entire system on a single chip. Industry-standard functions, or cores, are combined with on-chip memory and user-defined logic to create market-leading, one-of-a-kind designs efficiently and rapidly.
Also see stackable hub.
In general, a hub is the central part of a wheel where the spokes come together. The term is familiar to frequent fliers who travel through airport "hubs" to make connecting flights from one point to another. In data communications, a hub is a place of convergence where data arrives from one or more directions and is forwarded out in one or more other directions. A hub usually includes a switch of some kind. (And a product that is called a "switch" could usually be considered a hub as well.) The distinction seems to be that the hub is the place where data comes together and the switch is what determines how and where data is forwarded from the place where data comes together. Regarded in its switching aspects, a hub can also include a router.
1) In describing network topologies, a hub topology consists of a (main circuit) to which a number of outgoing lines can be attached ("dropped"), each providing one or more connection port for device to attach to. For Internet users not connected to a local area network, this is the general topology used by your access provider. Other common network topologies are the bus network and the ring network. (Either of these could possibly feed into a hub network, using a bridge.)
2) As a network product, a hub may include a group of modem cards for dial-in users, a gateway card for connections to a local area network (for example, an Ethernet or a token ring), and a connection to a line (the main line in this example).
Also see bridge, gateway, hub, and router.
In telecommunications, a switch is a network device that selects a path or circuit for sending a unit of data to its next destination. A switch may also include the function of the router, a device or program that can determine the route and specifically what adjacent network point the data should be sent to. In general, a switch is a simpler and faster mechanism than a router, which requires knowledge about the network and how to determine the route.
Relative to the layered Open Systems Interconnection (OSI) communication model, a switch is usually associated with layer 2, the data link layer. However, some newer switches also perform the routing functions of layer 3, the Network layer. Layer 3 switches are also sometimes called IP switches.
On larger networks, the trip from one switch point to another in the network is called a hop. The time a switch takes to figure out where to forward a data unit is called its latency. The price paid for having the flexibility that switches provide in a network is this latency. Switches are found at the backbone and gateway levels of a network where one network connects with another and at the sub-network level where data is being forwarded close to its destination or origin. The former are often known as core switches and the latter as desktop switches.
In the simplest networks, a switch is not required. Many local area networks are organized as token ring or bus in which all destinations inspect each message and read only those intended for that destination.
Most data today is sent, using digital signals, over networks that use packet-switching. Using packet-switching, all network users can share the same paths at the same time and the route a data unit travels can be varied as conditions change. In packet-switching, a message is divided into packets, which are units of a certain number of bytes. The network addresses of the sender and of the destination are added to the packet. Each network point looks at the packet to see where to send it next. Packets in the same message may travel different routes and may not arrive in the same order that they were sent. At the destination, the packets in a message are collected and reassembled into the original message.
A RAID appears to the operating system to be a single logical hard disk. RAID employs the technique of striping, which involves partitioning each drive's storage space into units ranging from a sector (512 bytes) up to several megabytes. The stripes of all the disks are interleaved and addressed in order.
In a single-user system where large records, such as medical or other scientific images, are stored, the stripes are typically set up to be small (perhaps 512 bytes) so that a single record spans all disks and can be accessed quickly by reading all disks at the same time.
In a multi-user system, better performance requires establishing a stripe wide enough to hold the typical or maximum size record. This allows overlapped disk I/O across drives.
There are at least nine types of RAID plus a non-redundant array (RAID-0):
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RAID-0. This technique has striping but no redundancy of data. It offers the best performance but no fault-tolerance. |
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RAID-1. This type is also known as disk mirroring and consists of at least two drives that duplicate the storage of data. There is no striping. Read performance is improved since either disk can be read at the same time. Write performance is the same as for single disk storage. RAID-1 provides the best performance and the best fault-tolerance in a multi-user system. |
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RAID-2. This type uses striping across disks with some disks storing error checking and correcting (ECC) information. It has no advantage over RAID-3. |
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RAID-3. This type uses striping and dedicates one drive to storing parity information. The embedded error checking (ECC) information is used to detect errors. Data recovery is accomplished by calculating the exclusive OR (XOR) of the information recorded on the other drives. Since an I/O operation addresses all drives at the same time, RAID-3 cannot overlap I/O. For this reason, RAID-3 is best for single-user systems with long record applications. |
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RAID-4. This type uses large stripes, which means you can read records from any single drive. This allows you to take advantage of overlapped I/O for read operations. Since all write operations have to update the parity drive, no I/O overlapping is possible. RAID-4 offers no advantage over RAID-5. |
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RAID-5. This type includes a rotating parity array, thus addressing the write limitation in RAID-4. Thus, all read and write operations can be overlapped. RAID-5 stores parity information but not redundant data (but parity information can be used to reconstruct data). RAID-5 requires at least three and usually five disks for the array. It's best for multi-user systems in which performance is not critical or which do few write operations. |
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RAID-6. This type is similar to RAID-5 but includes a second parity scheme that is distributed across different drives and thus offers extremely high fault- and drive-failure tolerance. There are few or no commercial examples currently. |
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RAID-7. This type includes a real-time embedded operating system as a controller, caching via a high-speed bus, and other characteristics of a stand-alone computer. One vendor offers this system. |
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RAID-10. This type offers an array of stripes in which each stripe is a RAID-1 array of drives. This offers higher performance than RAID-1 but at much higher cost. |
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RAID-53. This type offers an array of stripes in which each stripe is a RAID-3 array of disks. This offers higher performance than RAID-3 but at much higher cost. |
A token ring network is a local area network () in which all computers are connected in a ring or star topology and a binary digit- or token-passing scheme is used in order to prevent the collision of data between two computers that want to send messages at the same time. The token ring protocol is the second most widely-used protocol on local area networks after Ethernet. The IBM Token Ring protocol led to a standard version, specified as IEEE 802.5. Both protocols are used and are very similar. The IEEE 802.5 token ring technology provides for data transfer rates of either 4 or 16 megabits per second. Very briefly, here is how it works:
The token scheme can also be used with bus topology LANs.
The standard for the token ring protocol is Institute of Electrical and Electronics Engineers 802.5. The Fiber Distributed-Data Interface also uses a token ring protocol.
This information came from many different sources. The definitions came from http://www.webopedia.com/
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