A slightly chauvinistic hen-pecked instructor explained simplex, half-duplex
and duplex to me about 16 years ago. It obviously worked as a memory aid as
I still remember it now.
Simplex:
When his wife talks to him - one way only
Half Duplex:
Him talking to one of his mates - One talks, then the other.
Duplex:
His wife talking to one of her friends - Both talking at the same time, but
hearing every word.
Gaz
""Hire, Ejay"" wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> With Half Duplex, It's
> Talk, Listen, Talk, Listen
>
> With Full duplex, I think its:
> Talk, Talk, Talk, Talk, Talk, Talk
> - simultaneously -
> Listen, Listen, Listen, Listen, Li
>
> Only one frame can be transmitted at a time, with the other packets
stacking
> up in the buffer in a FIFO fashion.
> The only pause would be the interface gap, and if 2 packets are sent at
the
> same time, one sits in the buffer an incredibly short amount of time (Gig
> Ethernet has a very short MTU/bps) while the other one is transmitted.
>
> -----Original Message-----
> From: Chuck Larrieu [mailto:[EMAIL PROTECTED]]
> Sent: Wednesday, May 30, 2001 3:51 PM
> To: [EMAIL PROTECTED]
> Subject: RE: elementary? [7:6359]
>
>
> I concur. I should have been a bit more clear in that I was addressing the
> issue of a gig link between two switches.
>
> For traffic that remains within a single switch, different things can be
> done with the switch fabric, thus increasing the number of packets
handled.
>
> But a single gig link between two switches, operating at full duplex, can
> have only one packet per direct on the "wire" at one time.
>
> Also, I still think that on any link between any end station and the
switch
> port, the transmitting end station still waits until it senses nothing on
> the wire fore putting the next packet out that interface. The end station,
> after all, does not know to what it is connected. Rules of the game.
Listen.
> If wire is empty, place packet onto wire, listen, if wire is busy, wait.
> Perhaps some of the newer layer two drivers do things a bit differently if
> they detect full duplex? I'm not so sure, but then I'm just an old dog.
>
> Chuck
>
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of
> Gareth Hinton
> Sent: Wednesday, May 30, 2001 10:14 AM
> To: [EMAIL PROTECTED]
> Subject: Re: elementary? [7:6359]
>
> I think everybody might be right here but arguing about different parts of
> the process, or confusing the meaning of the previous post , so just to
add
> more confusion:
> Peter said that all every station could send as much as they want, which I
> think he was referring to their own ethernet segment/(switch port). On the
> Gig link, buffering will obviously have to take place. Statistical
> multiplexing seems a good summary of what's happening.
> I'm not sure exactly what you were saying in the last post Alan, about the
> buffering. Full duplex operation will allow another station to send to you
> while you are sending to it, so no buffering required in that case.
>
> As usual, open (prone) to correction,
>
> Gaz
>
>
>
> ""W. Alan Robertson"" wrote in message
> [EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> > Chuck,
> >
> > It's pretty much an issue of semantics... Another station could send
> > to you, but the frame would be buffered by the switch until the
> > current frame had finished sending. It would be transmitted to you
> > afterward.
> >
> > Also, to confirm Peter's statement that he's never seen a full-duplex
> > hub... Such an animal does not/can not exist. This is one of the key
> > differences between hubs and switches. A hub, by it's very nature,
> > cannot provide full-duplex operation. It has no means of bufferring
> > frames, nor of providing segmentation on a per node basis. A hub is
> > layer 1 device, and the network is provides is a shared medium.
> >
> > Vijay, chances are that if it has a 1Gbps uplink, it is a switch, and
> > depending on the number of connected 100Mbps stations, and your
> > network traffic patterns, you very well might be able to saturate the
> > uplink connection, because a switch allows for multiple simultaneous
> > conversations. Under the right conditions, you could fill up
> > virtually any pipe, but unless your traffic demands are really
> > outlandish, you probably won't. If you do, you should examine the
> > reasons, and revise the design of your network accordingly.
> >
> > Alan
> >
> > ----- Original Message -----
> > From: "Chuck Larrieu"
> > To:
> > Sent: Wednesday, May 30, 2001 11:14 AM
> > Subject: RE: elementary? [7:6359]
> >
> >
> > > Hhhmmmm....... Not so sure this is exactly right......
> > >
> > > With full duplex, you have effectively created two "directions" ---
> > there
> > > and back.
> > >
> > > I believe it is accurate to say that only one packet can be on the
> > wire per
> > > direction at one time.
> > >
> > > I can send to you at the same time you are sending to me. But
> > Someone else
> > > can not send to you at the time my packet is on the wire.
> > >
> > > Correct me if I'm wrong.
> > >
> > > Chuck
> > >
> > > -----Original Message-----
> > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf
> > Of
> > > Peter I. Slow
> > > Sent: Wednesday, May 30, 2001 7:40 AM
> > > To: [EMAIL PROTECTED]
> > > Subject: Re: elementary? [7:6359]
> > >
> > > Noooooooo.
> > > nononononono.
> > > CSMA/CD only gets used when you are not in full duplex. (/me ducks)
> > ( i
> > > have NEVER seen a full-dup. hub) meaning that if i am using a switch
> > capable
> > > of full duplex (as most are) ..conversations, every station can
> > transmit as
> > > much as they want. this is what differentiates between a hub and a
> > switch.
> > > (but not the only thing)
> > > you are correct in that a 100 meg HUB with a gig uplink could never
> > fully
> > > utilize the link, but the case is completly different with a switch.
> > >
> > >
> > >
> > > ----- Original Message -----
> > > From: "Vijay Ramcharan"
> > > To:
> > > Sent: Wednesday, May 30, 2001 9:54 AM
> > > Subject: RE: elementary? [7:6359]
> > >
> > >
> > > > Thanks everyone for their replies. As I now understand it, the
> > 1Gb
> > > > uplink just moves data faster than... say, a 100Mb uplink.
> > Correct?
> > > > Conversations between hosts on each switch still take place one at
> > a
> > > > time, thereby obeying Ethernet rules of one station transmitting
> > at a
> > > > time. Correct?
> > > > Okay my next question. Is there any point at which this 1Gb uplink
> > can
> > > > become saturated, since it's only handling station to station
> > sessions-
> > > > one at a time.
> > > > If a number of stations on each switch were doing large file
> > transfers
> > > > to each other via the uplink, would there be some point at which
> > the
> > > > uplink would be maxed out- in terms of bandwidth? Or is the only
> > > > limiting factor, the workstations inability to pump data out fast
> > enough
> > > > to max out the uplink when they're only running 100Mb?
> > > >
> > > > I'm thinking that it's really not possible to max out a 1Gb uplink
> > when
> > > > stations are only running 100Mb. If this is correct then I lay
> > this
> > > > question to rest.
> > > >
> > > > Thanks.
> > > >
> > > > Vijay Ramcharan
> > > >
> > > >
> > > > -----Original Message-----
> > > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On
> > Behalf Of
> > > > Vijay Ramcharan
> > > > Sent: Wednesday, May 30, 2001 12:06 AM
> > > > To: [EMAIL PROTECTED]
> > > > Subject: elementary? [7:6359]
> > > >
> > > >
> > > > Forgive me if this sounds a little bit basic but this is what
> > happens
> > > > when you rush into things without understanding the fundamentals.
> > > > Suppose a 24 port 100Mbit switch called A is uplinked to another
> > 24 port
> > > > 100Mb switch called B via a 1Gb connnection. Suppose hosts D
> > through N
> > > > are on switch A and hosts M through X are on Switch B. Would
> > > > conversations between the hosts from Switch A to Switch B occur
> > one at a
> > > > time or are multiple conversations multiplexed over the 1Gb
> > uplink?
> > > >
> > > > I'm just trying to find out if and how that 1Gb uplink is used up.
> > > > Thanks in advance. I'd put TIA but I hate those little acronyms.
> > No
> > > > flames please.
> > > >
> > > > Vijay Ramcharan
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