Black Box Explains...Layer 2, 3, and 4 switches.
... more/see it now
E-Mail, Diagnostics, Word Processing, Database
Shells and Gateway Workstation Software
TR=Token Ring; A=ARCNET®; P=PhoneNET®
With the rapid development of computer networks over the last decade, high-end switching has become one of the most important functions on a network for moving data efficiently and quickly from one place to another.
Here’s how a switch works: As data passes through the switch, it examines addressing information attached to each data packet. From this information, the switch determines the packet’s destination on the network. It then creates a virtual link to the destination and sends the packet there.
The efficiency and speed of a switch depends on its algorithms, its switching fabric, and its processor. Its complexity is determined by the layer at which the switch operates in the OSI (Open Systems Interconnection) Reference Model (see above).
OSI is a layered network design framework that establishes a standard so that devices from different vendors work together. Network addresses are based on this OSI Model and are hierarchical. The more details that are included, the more specific the address becomes and the easier it is to find.
The Layer at which the switch operates is determined by how much addressing detail the switch reads as data passes through.
Switches can also be considered low end or high end. A low-end switch operates in Layer 2 of the OSI Model and can also operate in a combination of Layers 2 and 3. High-end switches operate in Layer 3, Layer 4, or a combination of the two.
Layer 2 Switches (The Data-Link Layer)
Layer 2 switches operate using physical network addresses. Physical addresses, also known as link-layer, hardware, or MAC-layer addresses, identify individual devices. Most hardware devices are permanently assigned this number during the manufacturing process.
Switches operating at Layer 2 are very fast because they’re just sorting physical addresses, but they usually aren’t very smart—that is, they don’t look at the data packet very closely to learn anything more about where it’s headed.
Layer 3 Switches (The Network Layer)
Layer 3 switches use network or IP addresses that identify locations on the network. They read network addresses more closely than Layer 2 switches—they identify network locations as well as the physical device. A location can be a LAN workstation, a location in a computer’s memory, or even a different packet of data traveling through a network.
Switches operating at Layer 3 are smarter than Layer 2 devices and incorporate routing functions to actively calculate the best way to send a packet to its destination. But although they’re smarter, they may not be as fast if their algorithms, fabric, and processor don’t support high speeds.
Layer 4 Switches (The Transport Layer)
Layer 4 of the OSI Model coordinates communications between systems. Layer 4 switches are capable of identifying which application protocols (HTTP, SNTP, FTP, and so forth) are included with each packet, and they use this information to hand off the packet to the appropriate higher-layer software. Layer 4 switches make packet-forwarding decisions based not only on the MAC address and IP address, but also on the application to which a packet belongs.
Because Layer 4 devices enable you to establish priorities for network traffic based on application, you can assign a high priority to packets belonging to vital in-house applications such as Peoplesoft, with different forwarding rules for low-priority packets such as generic HTTP-based Internet traffic.
Layer 4 switches also provide an effective wire-speed security shield for your network because any company- or industry-specific protocols can be confined to only authorized switched ports or users. This security feature is often reinforced with traffic filtering and forwarding features. collapse
Black Box Explains...Remote Access Servers.
Remote access servers (RASs) are high-level intelligent devices with multiple asynchronous communication ports that connect to modems and provide remote users with dial-in access to a central site network.
You... more/see it nowcan configure your RAS to operate via remote control or remote node access.
Remote control operation enables remote users to send keystroke data and receive screen output from the central site. The actual processing takes place inside the communication server. Remote node access enables the remote user to become a network node and all remote workstations to function as if they were connected locally.
A fixed-port remote access server has a network connection to your LAN and one or more asynchronous RS-232 ports that connect to external modems. It usually comes equipped with 4, 8, or 16 async ports and is easy to install, support, and maintain. These devices are ideal for traveling workers who dont have a remote office but who need connections to the corporate network for short periods of time.
For configuration flexibility, scalability, and remote wide-area connection options, choose a modular remote-access server that you can change as your network grows. Most modular RASs accept a variety of modules, including:
• High-density async RS-232 modules that connect to external modems or ISDN terminal adapters. These modules typically have eight or more ports.
• High-density modem modules that usually incorporate eight modems on a single card, enabling you to consolidate equipment costs, increase reliability, and simplify management.
• Digital modules that enable you to make direct connections to high-speed digital lines. Instead of using multiple dialup lines, you can use these devices to bring a single high-speed digital phone line—known as a channelized T1— to your equipment.
The best way to determine what type of RAS you need—or whether you need a router or a RAS—is to identify what remote solution will meet your connectivity requirements. If you’re not sure what you need, contact our FREE Tech Support. collapse
Black Box Explains...How fiber is insulated for use in harsh environments.
Fiber optic cable not only gives you immunity to interference and greater signal security, but it’s also constructed to insulate the fiber’s core from the stress associated with use in... more/see it nowharsh environments.
The core is a very delicate channel that’s used to transport data signals from an optical transmitter to an optical receiver. To help reinforce the core, absorb shock, and provide extra protection against cable bends, fiber cable contains a coating of acrylate plastic.
In an environment free from the stress of external forces such as temperature, bends, and splices, fiber optic cable can transmit light pulses with minimal attenuation. And although there will always be some attenuation from external forces and other conditions, there are two methods of cable construction to help isolate the core: loose-tube and tight-buffer construction.
In a loose-tube construction, the fiber core literally floats within a plastic gel-filled sleeve. Surrounded by this protective layer, the core is insulated from temperature extremes, as well as from damaging external forces such as cutting and crushing.
In a tight-core construction, the plastic extrusion method is used to apply a protective coating directly over the fiber coating. This helps the cable withstand even greater crushing forces. But while the tight-buffer design offers greater protection from core breakage, it’s more susceptible to stress from temperature variations. Conversely, while it’s more flexible than loose-tube cable, the tight-buffer design offers less protection from sharp bends or twists. collapse
Black Box Explains... Multiplatform cabling environments.
When using a ServSwitch™ with multiple computer platforms, choosing which peripherals to use to control your diverse group of CPUs can be confusing. Because of the wide variation in connector... more/see it nowtypes and compatibilities, there is a hierarchy to follow when choosing your user station keyboard, monitor, and mouse.
1. If you have at least one Sun® computer in your application, you should use a Sun keyboard and mouse to control your CPUs.
2. If you have a mixture of PCs and Mac® computers, use your PC-style keyboard and mouse to control your CPUs. collapse
Black Box Explains... Manual switch chassis styles.
There are five manual switch chassis styles: three for standalone switches (Styles A, B, and C) and two for rackmount switches (Styles D and E). Below are the specifications for... more/see it noweach style.
Chassis Style A
Size — 2.5"H x 6"W x 6.3"D (6.4 x 15.2 x 16 cm
Weight — 1.5 lb. (0.7 kg)
Chassis Style B
Size — 3.5"H x 6"W x 6.3"D (8.9 x 15.2 x 16 cm)
Weight — 1.5 lb. (0.7 kg)
Chassis Style C
Size — 3.5"H x 17"W x 5.9"D (8.9 x 43.2 x 15 cm)
Weight — 8.4 lb. (3.8 kg)
Chassis Style D (Mini Chassis)
Size — 3.5"H x 19"W x 5.9"D (8.9 x 48.3 x 15 cm)
Chassis Style E (Standard Chassis)
Size — 7"H x 19"W x 5.9"D (17.8 x 48.3 x 15 cm) collapse
Cold aisle containment.
Cold aisle containment (CAC) is a cooling method that increases cooling efficiency and reduces energy costs in data centers.
This cooling method relies on the fact that most network equipment... more/see it nowand servers are designed to cool themselves by drawing air in through the front and exhausting it out the rear. To implement cold aisle containment, rows of cabinets or racks are arranged facing each other to form aisles, and cool air is routed between the rows. Equipment takes the cool air in at the front of the cabinet and exhausts it out the back into the room.
To keep cool air from mixing with warm air, row ends are closed off with an air-flow barrier. This barrier can range from makeshift arrangements of plastic strips to doors made expressly for this purpose.
Because cold aisle containment concentrates cool air at the front of equipment where it’s most needed, it’s an exceptionally effective cooling method. Cold aisle containment significantly reduces energy costs, lowering power bills as well as reducing data centers’ carbon footprints.
Black Box Explains…Remote monitoring.
Beyond virus protection.
It has become almost automatic to protect your data center by backing up your servers, installing firewalls and virus protection, and keeping the protection up-to-date.
But what about... more/see it nowmore tangible threats? Do you have hot spots in your racks? If the cooling system shuts down, how will you know when temperatures climb out of control? Are you
alerted to humidity changes or water leaks
that threaten your equipment?
Planning for the unexpected is a critical task because there are more systems performing mission-critical functions than ever before. These systems are often deployed without the proper environmental infrastructure to support them. Equipment density is increasing constantly, which is creating more stress on ventilation and power.
The top three IT risks:
1. Environmental disruption.
The number one cause of downtime for remote locations, environmental problems go beyond fires and floods and affect as much as 30% of a company’s mission-critical infrastructure. Cooling and power are key points of exposure and increase as equipment density does.
2. Unnecessary risk.
When systems are housed in less-than-optimal settings, or are in remote and unsupervised locations, any error causes downtime. Yet, it’s not practical to have someone babysitting the servers.
Regardless of the probability, terrorism is
now something each of us must plan for. Your systems can also be brought down from within if the proper security safeguards are not in place.
What’s an environmental
Environmental monitoring products enable you to actively monitor the conditions in your rack, server room, data center, or anywhere else you need to protect critical assets. Conditions
monitored include extreme temperatures, humidity, power spikes and surges, water leaks, smoke,
and chemical materials. With proper environmental monitoring, you’re alerted to any conditions that could have an adverse effect on your mission-critical equipment. These products can also
alert you to potential damage from human error, hacking, or prying fingers.
Environmental monitors consist of three main elements: a base unit, probes or sensors, and
network connectivity and integration. The base units may contain one or more built-in sensors,
as well as ports for hooking up external probes. Additionally, they include an Ethernet port and have software for remote configuration and graphing. This software may also work with
existing network management software,
such as SNMP systems.
An environmental monitoring appliance
displays the values measured by the attached probes, e.g. temperature, humidity, airflow,
status of dry contact, door, motion detector,
and other sensors.
Data collecting and graphing.
Measurements are periodically stored in the internal memory or external storage media and displayed as graphs.
When the measured value exceeds the
predefined threshold, it triggers an alert: a blinking LED on the front panel, an audible alarm, SNMP trap, e-mail, etc. The environmental monitoring appliance can also activate an external alarm
system like a siren or strobe light.
Benefits of environmental monitoring:
Reduced downtime—When things go wrong, you’re the first to know. Minimize downtime by being alerted about conditions that cause damage to servers and other network devices.
Increased profits—Environmental monitoring systems are easy to implement. Also, they help you cut replacement equipment costs and redistribute your workforce more effectively.
Increased employee satisfaction—With built-in notification features like e-mail, SMS, and SNMP traps, a remote monitoring system enables employees to better manage their work.
Envornmental and security monitoring systems can be used for a variety of applications, including:
Data center monitoring
Computer room monitoring
Rackmount industrial equipment
Food and beverage applications
Air conditioner/refrigerants/freezer monitoring
Black Box Explains...Digital Visual Interface (DVI) connectors.
The DVI (Digital Video Interface) technology is the standard digital transfer medium for computers while the HDMI interface is more commonly found on HDTVs, and other high-end displays.
The Digital... more/see it nowVisual Interface (DVI) standard is based on transition-minimized differential signaling (TMDS). There are two DVI formats: Single-Link and Dual-Link. Single-link cables use one TMDS-165 MHz transmitter and dual-link cables use two. The dual-link cables double the power of the transmission. A single-link cable can transmit a resolution ?of 1920 x 1200 vs. 2560 x 1600 for a dual-link cable.
There are several types of connectors: ?DVI-D, DVI-I, DVI-A, DFP, and EVC.
- DVI-D is a digital-only connector for use between a digital video source and monitors. DVI-D eliminates analog conversion and improves the display. It can be used when one or both connections are DVI-D.
- DVI-I (integrated) supports both digital and analog RGB connections. It can transmit either a digital-to-digital signals or an analog-to-analog signal. It is used by some manufacturers on products instead of separate analog and digital connectors. If both connectors are DVI-I, you can use any DVI cable, but a DVI-I is recommended.
- DVI-A (analog) is used to carry an DVI signal from a computer to an analog VGA device, such as a display. If one or both of your connections are DVI-A, use this cable. ?If one connection is DVI and the other is ?VGA HD15, you need a cable or adapter ?with both connectors.
- DFP (Digital Flat Panel) was an early digital-only connector used on some displays.
- EVC (also known as P&D, for ?Plug & Display), another older connector, handles digital and analog connections.