faq_nway

-Nway Switch-

General Questions

Q16: What is the major difference between a switch and hub?
Q15: What is “MAC Address”?
Q14: What's the difference between MAC-based VLAN and 802.1Q VLAN?
Q13: Why can't I use the Uplink port and its next port simultaneously?
Q12: How can you use a switch to the current network installation?
Q11: What is the difference between "cut-through" and "store-and-forward" switches?
Q10: What is a collision domain?
Q09: Why my Ethernet network is slow?
Q08: What is back-pressure?
Q07: What is Web-based Management switch?
Q06: Is Nway Auto-Negotiation a standard?
Q05: What is Flow Control regarding of a switch?
Q04: How can I get two HUBs to link up using a straight cable?
Q03: What kind of security of switches provided or supported?
Q02: What is a "stackable switch" and what are its advantages?
Q01: What is a “Stackable Management Switch”?

Q16: What is the major difference between a switch and hub?

A switch operates at layer 2 and just transmits the packets to the port which the destination address exist so that it separates each port into several collision domains. The port-to-port bandwidth is dedicated. On the other hand, a hub transmits packets to all ports. The port-to-port bandwidth is shared.

Q15: What is “MAC Address”?

Media Access Control Address is a unique hex number assigned by the manufacturer to any Ethernet networking device, such as a network adapter, that allows the network to identify it at the hardware level.

Q14: What's 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 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 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.

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Q13: Why can't I use the Uplink port and its next port simultaneously?

For most of products, there is an Uplink port (MDI-II port) on them, You can link two hubs or switches to each other using any of normal twisted-pair ports or the Uplink port. Linking hubs or switches using normal twisted-pair ports requires crossover twisted-pair cables; linking using one normal twisted-pair port and the Uplink port requires an ordinary straight-through twisted-pair cable. The Uplink port is shared with the next port and they cannot be use at the same time.

Q12: How can you use a switch to the current network installation?

A Switch can be installed up-stream from existing hubs, routers, and servers. It isn't necessary to remove or replace any existing equipment. In doing this, you will create dedicated bandwidth for each device at each port:
--- No NIC change is necessary for stations or servers.
--- No cable or software driver changes are necessary anywhere.

Q11: What is the difference between "cut-through" and "store-and-forward" switches?

Cut-Through: The switch will begin forwarding data after it receives the DA (destination address) of the frame, 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 DA, 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.

Advantages of Cut-Through:
+ Cut-Through is faster because the packet is sent as soon as the first eight bytes are received.
+ Cut-Through requires less memory since the switch only reads the address but does not store the entire message.

Disadvantages of Cut-Through:
+ Bad packets are perpetuated, taking up bandwidth.
+ Benefits diminish in the high traffic networks.
+ Cut-Through cannot be used on networks that use both Ethernet and Fast Ethernet. The network must be one or the other.

Store-and-Forward: The switch will wait until the entire frame has arrived prior to forwarding it. This process ensures that the destination network is not affected by corrupted or truncated frames, but is a slower method than cut-through.

Advantages of Store-and-Forward:
+ Store-and-forward only sends out valid data packets. Bad packets created by collisions on the network or other problems are not sent.
+ Use Store-and-Forward when some devices on the network run at 10Mbps and other run at 100Mbps.

Disadvantages of Store-and-Forward:
+ Store-and-Forward requires more time because it receives the whole packet before sending it out. Every byte buffered is an additional 8 microseconds of delay.
+ More memory is required to store the data packet before sending it out.

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Q10: What is a collision domain?

The collision domain is defined by IEEE 802.3 Standard:
A single CSMA/CD network. If two or more MACs are within the same collision domain and both transmit at the same time, a collision will occur. MACs separated by a repeater are within the same collision domain. MACs separated by a bridge (switch) are within different collision domains.

Q09: Why my Ethernet network is slow?

If you think it is problem from network hardware, please:
1. Check your network if it is connected in a loop. Remove the link cause loop.
2. Check the cables connected with the switch if follows EIA/TIA-568B standard.
3. Check the duplex mode between switch and connected devices. Please force the speed and duplex mode to match with each other. Normally it is matches automatically.

Q08: What is back-pressure?

A non-standard but popular scheme called back-pressure was used in half-duplex flow control. If a port is operating at half-duplex, the switch sends a collision to make the transmitting device to wait.

So when a half-duplex device wasn't able to handle the amount of data it was receiving from an end station, it collided with it (faked a collision by sourcing JAM). Thus all devices on the shared LAN would have to back-off, and then try to re-transmit. The device could keep on colliding, so the other end stations will keep backing off.

Q07: What is Web-based Management switch?

A device (Hub, Switch or Router) embedded web-based (hypertext) interface allows users to manage the device from anywhere on the network through a standard browser such as Netscape Navigator/Communicator or Microsoft Internet Explorer. The web-browser acts as a universal access tool and can communicate directly with the device using HTTP protocol.

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Q06: Is Nway Auto-Negotiation a standard?

Auto-Negotiation is a technology standard that defined by the IEEE 802.3u 100BASE-T Working Group for a mechanism to adapt multi-speed network devices. Currently, the Auto-Negotiation mechanism is defined in Clause 28 of the D5 draft of the ANSI/IEEE Std 802.3 MAC Parameters, Physical Layer, Medium Attachment Units and Repeater for 100 Mbps Operation. The draft has been approved by the IEEE802.3 working group.

Q05: What is Flow Control regarding of a switch?

During times of heavy network activity, the switch's port buffers receive too much traffic and fill up faster than the switch can send the information.

In cases like this, the switch tells the transmitting device to wait so the information in the buffer can be sent. This intervention is called flow control.

The method of flow control depends on whether the ports are set to full- or half- duplex. A non-standard but popular scheme called Back-pressure was used in half-duplex links. The IEEE 802.3 committee established a standard called 802.3x flow control was used in full-duplex links.

Q04: How can I get two HUBs to link up using a straight cable?

The MDI-II (Uplink) port is for the connection using a straight cable between hubs/switches. Plug one end of UTP cable into MDI-II (Uplink) port of one device, and plug the other end into a normal port of another device. You don't need to have a crossover cable.

Q03: What kind of security of switches provided or supported?

There are two ways to use a switch to improve network security:
VLAN: A network administrator can define several VLANs and block access to each VLAN to prevent users from accessing servers for which they don't have access permission.

Mac address filtering: A network administrator can define a DA (Destination Address) so that packets can only be received from port A (a hub) and only allow those same packets to be forwarded to port B (a server connection, for example). Using MAC address filtering, only users that are connected to port A can access the server connected to port B, other packets from other ports, even those whose DA is for the server on port B, will be dropped.

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Q02: What is a "stackable switch" and what are its advantages?

A stackable switch is a switch design which enables more than one switch to stacked together using stackable cables, instead of connecting with each other using TP cables through data ports.

Q01: What is a “Stackable Management Switch”?

A “stackable management switch” is a switch design which enables more than one switches can be “stacked” together for management. When managing these switches from management user interface, they are stacked together, but physically they can be separated in different locations and linked by “stackable” cables. Note that the stackable TP cable is for management information flow, not the same as “stackable switch” for data flow. Meanwhile, the “stackable management” switches can be or not necessary to be cascaded by data links.

EUSSO Technologies, Inc. is a dedicated data communication and networking company. With professional experiences in design, production, marketing and service support, we deliver the full range networking products including Gigabit Ethernet, Fiber Optic, Wireless LAN, Switches, Hubs, LAN cards, PCMCIA adapters, Converter, Transceivers. As well as Internet Telephony Gateway, Print Servers, Broadband Router and many others.