General
Questions
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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?
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
Copyright
EUSSO Technologies, Inc. 2003
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