Network+ Oct 22 08

N003
[Q254]

Hub has number of ports .

Each port is connected to one workstation

So, one Hub can connect few workstations together.

This group of workstations is considered as One Segment

So, we can say that , HUB is used to connect multiple workstations to
create one segment ; or we call it as single logical segment .


[Q255]

Intermittent Connectivity means sometime the connection is ok ,
but sometime there is no connection.

That’s mean the connection / connectivity is not stable.

If we have intermittent connectivity problem to internet , it could be
high traffic of router ( the router experience high traffic or high utilization)

Because Router is used to connect LAN and Internet . The Router is act
as Gateway. If Gateway is experience high traffic , this will cause Intermittent
Connectivity .

If the Web Server traffic is heavy , it wouldn’t cause intermittent connectivity
problem , instead of , it will cause the access to Web Server very slow .

High traffic on Web Server will cause slow access to the Server

[Q256]

From this diagram , you can see there is 2 segments ( 2 group of workstations)

Each group is connected to one HUB ( there is 2 HUBs to create 2 segments )

Now , once we swap the group of workstations to difference Hub , we find
out that there is ONE workstation cannot connect to network .

Since it is only affect ONE workstation , it couldn’t be the HUB because
If HUB has problem , few workstations will be affected at the same time .

The most possible cause is the factor that can affect only ONE workstation
, that’s could be PATCH CABLE ( UTP Cable / Coaxial Cable / Fiber Optic Cable)

[Q257]

Switch / Bridge carry/forward [ MAC Address + Frame ]. This happen in Layer 2

Router carry/forward [ IP Address + Packet ]. This happen in Layer 3


Hub , never carry Frame or MAC Address .

Hub , only forward SIGNAL . Hub is at Layer 1


[Q258]

ISDN has 2 types of services
(a) BRI ( Basic Rate Interface )
(b) PRI ( Primary Rate Interface )

For BRI services :
ISDN use 2 channels B ”bearer channel “ + One D Channel ( delta channel )
B Channel carry voice + data
D Channel carry control signal such as call forwarding & conference call

B channel speed is 64 Kbps . If 2 B channels , it become 64+64 Kbps = 128 Kbps
D channel speed is 16 Kbps

If ( 2B+D) , we call it a “bonding” and the total rate is 128Kbps.
This speed is 4X of normal analog modem ( V.34 modem = 28.8Kbps)

For PRI service :-

It become ( 23B + D ). It become 24 channels of A T1 line .
It can combine 6 channels together and become 384Kbps . This speed
Is used for VIDEO CONFERENCING


ISDN calls are dialed much faster than regular telephone calls.


Connecting an ISDN Device
Connecting ISDN to a personal computer requires a network terminator (NT1) and ISDN terminal adapter (TA).

The NT1 plugs into the two-wire line from the telephone company with an RJ-11 connector and provides four-wire output to the TA.

Within the U.S., the NT1 is typically built into the TA; but in Europe and Japan, they are separate devices.

The TA , often called an "ISDN modem" because the device may support an analog telephone or fax machine,.

The TA itself is technically not a modem, because it provides a digital to digital connection.

External TAs plug into the serial port while internal TAs plug into an expansion slot.

Some TAs hook into the parallel port for higher speed.

The TA may also include an analog modem and automatically switch between analog and digital depending on the type of call.

TAs support bonding for Internet operation, which links the channels together for higher speed, but the ISP must provide the Multilink PPP protocol (MPPP) to support this operation.