Re: difference between Repeater,hub,bridge, switch,router, gateway


annalissa wrote:

Hi all

as far as i understand the difference between Repeater,hub,bridge,
switch,router, gateway are as follows , how correct is my
understanding ?

You've made a good list of features already. I'll add some suggested
differences.


Repeater

Forwards every frame it receives
it is a generator,not an amplifier(i.e it removes noise &
regenerates signal )
Bi-directional in nature
Useful in increasing ethernet size/length
Maximum of 5 Repeaters in an Ethernet

Yes - a repeater repeats frames at the electrical level, layer 1. Is
part of a collision domain. I cannot remember a rule of thumb for how
many repeaters can be had in sequence but I think it is really
governed by the timing budget. There has to be enough time for the two
most widely separated hosts to mutually detect a collision (and
respond with a jamming signal) within the collision period which I
think for Ethernet is 64 bit times after the preamble. Maybe someone
can correct that if necessary.


Hub

basically a multiport repeater
can be used to divide a single LAN into multiple levels of Hierarchy


A hub is a repeater, certainly. I wouldn't say that a hub divides a
network in any way - since it is just a repeater. Still operates at
layer 1 only. Still a component of a single collision domain.

The term hub at one time was split into

repeating hub - what we now call a hub
switching hub - what we now call a switch


Bridge

connect similar/dissimilar LANS
Designed to store and forward frame
Protocol independent
Transparent to End Stations
Operates in Layer-1 & Layer-2
uses a table for filtering/routing
does not change the Mac address in the frame
two types of bridges are there Transparent/source routing

A bridge is/was a device for connecting networks into separate
collision domains. As you say it operates at layers 1 and 2 and it was
originally a 2-port device. Normal bridging is transparent - e.g.
Ethernet to Ethernet. If you are masochistic and have stuff like token
ring or even FDDI I believe some translational bridges were made to
convert the frames as best as was possible between one and the other.
Better, IMHO, to keep each lan technology separated by routers.

Either way a bridge, while splitting the network into collision
domains, is a component of a broadcast domain. Collisions stop at its
ports but broadcasts pass through. It won't protect the network from
broadcast storms and the like.


Switch

A fast Bridge.
Common forwarding approaches used include Cut through,collission
free & Fully buffered

Yes, a switch is normally much faster than a bridge. Bridges tended to
have CPUs to handle the frame forwarding and table management.
Switches, on the other hand, tend to have ASICs to do what they do and
switches normally have multiple ports as befits their original name of
a switching hub.

Cisco support (at least on some switches) a choice between cut-through
(start to transmit as soon as the frame starts to come in and the
output port is free - same speed ports only), collision-free (wait for
at least the collision period before starting to transmit) and store-
and-forward. More modern Cisco switches may not support all three
approaches. LANs are generally so reliable that cut-through is best if
in and out port speeds are the same.

Note that for full duplex Ethernet which is the most common LAN
technology and mode used with switches there is no possibility of a
collision.



Routers

Links dissimilar n/ws
not transparent to end stations
acts on a network layer frame
isolates LAN to subnets to manage & control traffic

Well, routers focus on work at layer 3. They _can_ link layer 2
network technologies which are different but are just as happy working
between ones which are alike. The protocol data units (PDUs) they work
on are traditionally called packets. (PDUs at layer 2 are called
frames.) Routers terminate broadcast domains. Yes, routers do separate
LANs but that can be incidental to their primary functions which
include getting sending packets in the right direction based on their
routing tables. They can usually apply a range of traffic control
measures including filtering, traffic shaping and reporting.



Gateway

uses Layer -7 Relay

The meaning of "gateway" has changed over the years and tends to
depend on context. They generally convert one protocol to another or
provide a conversion of packets between one system and a dissimilar
one. A voice gateway may translate between VoIP and normal phone
lines, for example.

The term originally was used for routers (but is not used that way any
longer). The hangover from the old days is that end stations are
configured with a default router which we still call the default
gateway.

A final point on your Layer 7 comment. You are right that the highest
level of the ISO model protocol stack is 7 for applications but bear
in mind that the TCP/IP suite works on a reduced stack something like
the following.

1. Physical - electrical and timing (and connectors)
2. Data link - basically the LAN technology - works on frames
3. Network - works on packets using IP addresses
4. Session & transport mixed together - works on end-to-end
connections or transactions using in nearly all cases TCP and UDP

Above that there is only the applications. There is no presentation
layer at all unless the applications include it within themselves.

HTH,
James
.

Relevant Pages

  • Re: Physical wavelength vs relative wavelength
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    (sci.physics)
  • Re: Light Postulate Invalidated
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    (sci.physics.relativity)
  • Re: Wrapper & Tables
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    (microsoft.public.frontpage.programming)
  • Re: Physical wavelength vs relative wavelength
    ... After collision they will rebound ... at 50 mph each in that frame. ... all we know is the relative speeds to each other.. ...
    (sci.physics)
  • Re: Light Postulate Invalidated
    ... >> Consider any two entities which are on a collision course, ... >> frame A's clocks at the given points). ... Now suppose that after one such collision point is ... >> Eis an inertial observer, and entity Eis a light ray. ...
    (sci.physics.relativity)