What is the difference between Store-and-Forward switching and Cut-Through switching?

Store-and-Forward: Store-and-Forward switching will wait until the entire frame has arrived prior to forwarding it. This method stores the entire frame in memory. Once the frame is in memory, the switch checks the destination address, source address, and the CRC. If no errors are present, the frame is forwarded to the appropriate port. This process ensures that the destination network is not affected by corrupted or truncated frames.

Cut-Through: Cut-Through switching will begin forwarding the frame as soon as the destination address is identified. The difference between this and Store-and-Forward is that Store-and-Forward receives the whole frame before forwarding. Since frame errors cannot be detected by reading only the destination address, Cut-Through may impact network performance by forwarding corrupted or truncated frames. These bad frames can create broadcast storms wherein several devices on the network respond to the corrupted frames simultaneously.

What is Blocking Vs. Non-Blocking switch architecture?

A switch has a backplane bandwidth and an number of ports running at the highest speed in full duplex. If the total bandwidth for all the ports is less than the switches backplane, it would be a non-blocking switch because there is enough bandwidth to carry all packets without delay. If the backplane is less than the total port bandwidth, it would be a blocking architecture.

What is a VLAN?

Virtual Local Area Networks (VLANs) are a logical grouping of network users and resources connected to defined ports on the switch. A VLAN looks like, and is treated like, its own subnet. By using virtual LANs, you're no longer confirmed to physical locations. A VLAN can be created by location, function, and department regardless of where the resources or users are located.

What is the difference between MAC-based VLAN and 802.1Q VLAN?

There are two major differences between MAC-based and 802.1Q VLAN:

The first point of difference is that a MAC-based VLAN is configured using MAC address, but 802.1Q VLAN uses assigned tag address to distinguish VLAN information.

The second difference is that a MAC-based VLAN is a traditional and proprietary-based VLAN, so interoperability is a problem. On the other hand 802.1Q VLAN, is an industry standard-based VLAN, which helps resolve any interoperability problems between difference vendors of LAN switches.

What is Spanning-Tree Protocol 802.1d?

Spanning Tree Protocol was developed to prevent routing loops in a network. If a router, bridge, or switch has more than one path to the same destination, a routing problem could occur. STP achieves this by running the Spanning Tree algorithm, detecting the presence of multiple physical paths and logically disabling (blocking-stand by mode) one ore more of the redundant links. This guarantees that only one path between network devices will be active at given time. STP uses BPDU (Bridge Protocol Data Units), which are special multicast frames that are broadcast out by all the switches on the network. These frames contain all the of the vital topology information about each sender that is needed by the switch to maintain the Spanning Tree

What is IGMP Snooping?

Internet Group Membership Protocol Snooping (IGMP Snooping) is a protocol that operates on switches that allows them to dynamically learn about multicast traffic. IGMP Snooping, an industry standard, does what it implies: it snoops all traffic listening for IGMP packets. Once it sees an IGMP packet, it dynamically learns what MAC address the traffic is destined for, and what MAC address the traffic comes from. Once the switch knows the MAC address, it can look up in its table on what port to send the traffic to.

What is Web-based Management?

A device (hubs, switches, routers, or wireless access points) with an embedded web-based (hypertext) interface allows users to manage the hub from anywhere on the network through a standard browser such as Netscape Navigator or Microsoft Internet Explorer. The web-browser acts as a universal access tool and can communicate directly with the device using HTTP protocol.

To access your device, open your web browser and enter the IP address of the device

What is the difference between multimode and single-mode fiber? Which fiber and equipment type should I choose for particular applications?

The terms multimode and single-mode pertain to certain optical transmission properties. Multimode optical fiber is suitable for shorter distances 2-5 kilometers, common in for instance security projects.

Single-mode fiber, which exhibits lower attenuation, is generally used for medium to very long distances and for carrying high-bandwidth signals.

What is link alarm (LLF)

Link Alarm provides central office an indication regarding the status of the remote devices.

With Link Alarm when remote site's TP link is down, the remote converter will send a trap back to central site (Network Management Station) to report a link failure status.

Link ALARM function back to network administrator by:

Hardware Alarm: LED indication of both central (slide-in modules on Converter chassis ARG1600) and remote (stand-alone media converters) sites.

Software Alarm: User can also get the notice by SNMP Management Screens

What is in Band Management?

With "IN-BAND" management functions, network administrators can manage control and monitor each port of the remote devices from central office. Management information is being transferred secured over data channel with no need for a parallel network to transfer management information.

What is CCTV?

Closed Circuit Television (CCTV) is a television system that operates on a "closed loop" basis. Unlike broadcast television which is available to anyone with a suitable receiver, CCTV pictures are only available to those directly connected to the loop, which in Caerphilly county borough's case is the central monitoring control room. The loop is a physical link consisting of a fibre optic cable that carries the picture from the camera to a monitor.

What is Signal-to-Noise Ratio (SNR)?

The ratio of the total signal to the total noise which shows how much higher the signal level is than the level of the noise. A measure of signal quality

What is a video server?

The term "video server" refers to a network-attached server for video that is connected to a computer network like a LAN. A video server can deliver live video, automatically or on request, to a browser or other professional security applications. Security systems have traditionally been based on analog CCTV (closed-circuit television) technology. Video servers digitize analog video sources and distribute digital video over an IP network - turning analog cameras into IP cameras. A video server can also be connected via a modem for access over a phone or ISDN line.

What's the advantage using MPEG-4?

MPEG-4 provides DVD quality video, but uses lower bit rate so that it's feasible to transmit digitized video streams in LAN, and also in WAN, where bandwidth is more critical, and hard to guarantee. MJPEG's bandwidth requirement is a little bit more than MPEG-4, while its resolution and frame rate are much worse. MPEG-2 can provide DVD-like video, just like MPEG-4. However, MPEG-2's bandwidth requirement is so high that it's not possible to use in a LAN or WAN environment.

What is the difference between RS-422 and RS-485?

RS-422 provides a balanced, full-duplex, 4-wire serial interface for point-to-point links. RS-485 offers balanced, serial 2-wire (half-duplex) or 4-wire interfacing (full-duplex) suitable for constructing a data bus. RS-485 outputs can be individually set to a high-impedance, inactive state ('tristate') and can therefore be wired in parallel.

Two-wire and four-wire serial interfacing: which one is better?

Conventional copper-wire systems often utilize 2-wire configurations; with optical fibre modems, 4-wire connections are preferred

Aren't fiber solutions more expensive than UTP copper solutions?

Not any more. Recent cost modeling completed by the Fiber Optics LAN Section and Pearson Technologies shows that when centralized cabling or fiber-to-the-zone designs are used, all fiber systems are actually less expensive than networks using fiber in the backbone and UTP copper in the horizontal.

Is fiber more difficult to install than copper?

No. Fiber is just as easy, and sometimes easier, to install than copper. Remember, since fiber is accepted as the standard choice for communications backbones for many years, today's installers are comfortable with the technology. In fact, new generation high-speed copper networks. such as Category 5e and Category 6 Unshielded Twisted Pair (UTP) cable -- require more stringent and time-consuming installation techniques than those of fiber. Compared to newer grades of copper cable, fewer regulations exist on the methods by which optical cable is pulled and terminated. In addition, there is no need to worry about the location of EMI/RFI sources during installation. Furthermore, optical fiber cables are stronger, lighter and smaller than comparable copper cable designs, and there are few routing restrictions, particularly in areas with other electrical power cables.

I have an existing copper infrastructure, what's the most cost-effective way to upgrade to copper?

For companies that want to leverage their legacy electronics, need to upgrade only a portion of their network, or do not have the resources to upgrade their entire network at once, fiber can be installed incrementally. For these users, media conversion technology offers them a controlled migration strategy. Media converters do just what their name implies -- the devices convert the signal from one type of media to another, allowing seamless links between different media and supporting incremental upgrades to fiber. Media converters also allow users to continue to use their existing electronics, leveraging their existing investment.

What's the difference between 62.5 micron and 50 micron fibers?

Physically the two fiber types differ in the diameter of their cores, the light-carrying region of the fiber. This is signified by the numeric nomenclature. In 62.5/125 fiber, for example, the core has a diameter of 62.5 microns and the cladding diameter is 125 microns. In terms of performance, the difference lies in the fibers' bandwidth, or information-carrying capacity. Bandwidth is actually specified as a bandwidth-distance product with units of MHz·km. The bandwidth needed to support an application depends on the data rate. As the data rate goes up [MHz], the distance that rate can be transmitted [km], goes down. Thus, a higher fiber bandwidth enables you to transmit at higher data rates or for longer distances. 50 mm multimode fiber offers nearly three times more bandwidth (500 MHz·km) than FDDI-grade 62.5 mm fiber (160 MHz·km) at 850 nm. Network planners often choose 50 micron fiber when they know the network will need to carry high bandwidth applications over longer link distances, or when they anticipate running higher speed protocols in the future.

Techaya Inc.
P.O Box 1500
Pardes Hana, 37100
Phone: +972 (4) 6377741
Fax: +972 (4) 6377761
Email: info@techaya.com