Addition of this functionality will enable HP servers and storage resources to be shared between StorageWorks 8/20q based SANs and HP B-series fabrics. It also lets businesses start with an 8-port 8/20q fibre channel switch and add TR ports for more storage capacity without impacting their existing Storage Area Network (SAN).

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The term “repeater” originated with telegraphy and referred to an electromechanical device used to regenerate telegraph signals. Use of the term has continued in telephony and data communications.

In telecommunication, the term repeater has the following standardized meanings:

1. An analog device that amplifies an input signal.
2. A digital device that amplifies, reshapes, retimes, or performs a combination of any of these functions on a digital input signal for retransmission.

Repeaters are often used in trans-continental and trans-oceanic cables, because the attenuation (signal loss) over such distances would be completely unacceptable without them. Repeaters are used in both copper-wire cables carrying electrical signals, and in fibre optics carrying light.

In optical communications the term repeater is used to describe a piece of equipment that receives an optical signal, converts that signal into an electrical one, regenerates it, and then retransmits an optical signal. Since such a device converts the optical signal into an electrical one, and then back to an optical signal, they are often known as Optical-Electrical-Optical (OEO) repeaters.

A router can be used to either connect at least two networks, or to form a mobile ad-hoc network. A special variety of router is the one-armed router used to route packets in a virtual LAN environment. In the case of a one-armed router the multiple attachments to different networks are all over the same physical link.

A router that connects clients to the Internet is called an Edge Router. A router that serves to transmit data between other routers is called a Core Router.

A router creates and/or maintains a table, called a routing table that stores the best routes to certain network destinations and the “routing metrics” associated with those routes. In recent times many routing functions have been added to LAN switches, creating “Layer 2/3 Switches” which route traffic at near wire speed.

Routers are also now being implemented as Internet gateways, primarily for small networks like those used in homes and small offices. This application is mainly where the Internet connection is an always-on broadband connection like cable modem or DSL. These are not “routers” in the true sense, but the terminology has been confused with network address translation.

There are several manufacturers of routers including:

• 3Com
• Alcatel
• Belkin
• Cisco Systems, Inc
• D-Link Systems
• Juniper Networks
• Linksys
• Mikrotik
• NETGEAR
• Nortel
• Pivotal Networking
• Siemens AG
• SMC Networks
• Tellabs
• MRV Communications
• Zoom Telephonics

How switches work?

A switch can connect Ethernet, Token Ring, or other types of packet switched network segments together to form a heterogeneous network operating at OSI Layer 2.

As a frame comes into a switch, the switch saves the originating MAC address and the originating port in the switch’s MAC address table. The switch then selectively transmits the frame from specific ports based on the frame’s destination MAC address and previous entries in the MAC address table. If the MAC address is unknown, or a broadcast or multicast address, the switch simply floods the frame out of all of the connected interfaces except the incoming port. If the destination MAC address is known, the frame is forwarded only to the corresponding port in the MAC address table. If the destination port is the same as the originating port, the frame is filtered out and not forwarded.

Switches, unlike hubs, use microsegmentation to divide collision domains, one per connected segment. This way, only the NICs which are directly connected via a point-to-point link, or directly connected hubs are contending for the medium.

By eliminating the possibility of collisions, full-duplex point-to-point connections on the switch become possible. Virtual LANs can be used in switches to reduce the size of the broadcast domains and at the same time increase security. In redundant architectures, Spanning Tree Protocol (STP) can be used in switches to prevent loops.

Forwarding Methods used by a Switch

1. Cut through
2. Store and forward – the switch, unlike cut through, buffers and typically, performs a checksum on each frame before forwarding it on.
3. Fragment free
4. Adaptive switching

Hub can also be called a multi-port repeater. This is due to the fact that a hub will repeat the signals received from one port to all other ports excluding the port it received the signals from. For example, in a 10 port hub, if signal is sent from port # 10 then hub will repeat the signal to all other ports except port # 10.

In a hub every device connected to it will receive the broadcast traffic and thus makes it inefficient for larger networks. But for small networks with less than 20 computers, using a hub can be cost effective. All the devices connected to the hub are part of the same broadcast domain and also collision domain. That means, only one device can transmit the data at any given point of time and other system when try to transmit will result in a collision.

A ethernet network utilizing a hub behaves like a shared-medium, that is only one device can successfully transmit at a time and each host remains responsible for collision detection and retransmission.

Advantages of a Hub

1. A protocol analyzer connected to a hub allows it to see all the traffic on the segment but not when it comes to a switch as it will separate the ports into different segments.
2. Some computer clusters require each member computer to receive all of the traffic going to the cluster. A hub will do this naturally; using a switch requires implementing special tricks.
3. A cheap hub with a 10BASE2 port is probably the cheapest and easiest way to connect devices that only support 10BASE2 to a modern network. (Cheap switches don’t tend to come with 10BASE2 ports.)

Disadvantages of a Hub

1. The need for hosts to be able to detect collisions limits the number of hubs and the total size of the network.
2. For 10 Mbit/s networks, up to 5 segments (4 hubs) are allowed between any two end stations.
3. For 100 Mbit/s networks, the limit is reduced to 3 segments (2 hubs) between any two end stations, and even that is only allowed if the hubs are of the low delay variety.
4. Some hubs have special (and generally manufacturer specific) stack ports allowing them to be combined in a way that allows more hubs than simple chaining through Ethernet cables, but even so a large Fast Ethernet network is likely to require switches to avoid the chaining limits of hubs.

Modems are generally classified by the amount of data they can send in a given time, normally measured in bits per second, or “bps”.

Various standards of a modem

v.32

Normally the phone system sends a small amount of the outgoing signal, called sidetone, back to the earphone, in order to give the user some feedback that their voice is indeed being sent. However this same signal can confuse the modem, is the signal it is “hearing” from the remote modem, or its own signal being sent back to itself?

Echo cancellation was a way around this problem. By using the sidetone’s well-known timing, a slight delay, it was possible for the modem to tell if the received signal was from itself or the remote modem. As soon as this happened the modems were able to send at “full speed” in both directions at the same time, leading to the development of the 9600 bps v.32 standard.

v.34

It is also known as 28,800 bps v.34 standard. Eventually, the manufacturers were forced to use more “flexible” parts, generally a DSP and micro controller, as opposed to purpose-designed “modem chips”.

v.90

Also known as 56k standard, systems use in-band signaling for command data, inserting one bit of command data per byte of signal.

Every network card has a unique 48-bit serial number called a MAC address. Every computer on a network must have a card with a unique MAC address. The IEEE is responsible for assigning MAC addresses to the vendors of network interface cards. No two cards ever manufactured should share the same address.

The card implements the electronic circuitry required to communicate using a specific physical layer and data link layer standard such as ethernet or token ring. This provides a base for a full network protocol stack, allowing communication among small groups of computers on the same LAN and large-scale network communications through routable protocols, such as IP.

There are four techniques used for transfer of data, the NIC may use one or more of these techniques.

1. Polling is where the microprocessor examines the status of the peripheral under program control.
2. Programmed I/O is where the microprocessor alerts the designated peripheral by applying its address to the system’s address bus.
3. Interrupt-driven I/O is where the peripheral alerts the microprocessor that it’s ready to transfer data.
4. DMA is where the intelligent peripheral assumes control of the system bus to access memory directly. This removes load from the CPU but requires a separate processor on the card.

A network card typically has a twisted pair, BNC, or AUI socket where the network cable is connected, and a few LEDs to inform the user of whether the network is active, and whether or not there is data being transmitted on it. The Network Cards are typically available in 10/100/1000 Mbits/s(Mbps). This means they can support a transfer rate of 10 or 100 or 1000 Megabit per second.

Introduction to networking hardware

On a very high level, there are two types of transmission technology that are in use as of today.

1. Broadcast based transmission, and
2. Point-Point links

In broadcast based network, computers send packets on the network that every other connected computer will receive and process. Such computer networks that are based on the broadcast transmission are usually slower and with ever increasing number of computers on the network, it becomes difficult to provide faster transmission speed.

Thanks to some of the network devices which makes our life easy by cutting down on broadcast and provide unicast based transmission. In unicast based transmission, there is only one sender and one receiver, often termed as point-to-point links at a very high level.

The network devices that are most commonly used are as follows:

• NIC
• Modem
• Hub
• Switch
• Router and
• Repeater