Re: elementary? [7:6359]
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] Hhh... 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:
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 FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=6425t=6359 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: elementary? [7:6359]
your GE x-connect, in this instance, is basically a serial line - see the TX and RX fibres in the GBIC? conversations would occur one at a time, and be multuplexed (statistically Mux-ed). The conversations would be queued and transmitted one frame at a time, but that frames from the conversations would traverse the link in a FIFO manner (First In, First Out). hope that makes sense (as opposed to hth) Andy - Original Message - From: Vijay Ramcharan To: Sent: Wednesday, May 30, 2001 5:05 AM 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 FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=6427t=6359 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: elementary? [7:6359]
N. 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 FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=6437t=6359 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: elementary? [7:6359]
Hhh... 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] N. 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 FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=6450t=6359 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: elementary? [7:6359]
I believe it was Priscilla that found a link explaining all that in a white paper a couple months ago. I believe it backed up what you're saying...but I've slept (occasionally) since then. - Original Message - From: Chuck Larrieu To: Sent: Wednesday, May 30, 2001 10:14 AM Subject: RE: elementary? [7:6359] Hhh... 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] N. 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 FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=6459t=6359 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: elementary? [7:6359]
not on a switch, and hubs arent full duplex. -peter slow - Original Message - From: Chuck Larrieu To: Sent: Wednesday, May 30, 2001 11:14 AM Subject: RE: elementary? [7:6359] Hhh... 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] N. 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 FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=6462t=6359 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: elementary? [7:6359]
They would be multiplexed. Ethernet allows many conversations between many hosts on the same wire. -Original Message- From: Vijay Ramcharan [mailto:[EMAIL PROTECTED]] 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 FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=6463t=6359 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: elementary? [7:6359]
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] Hhh... 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] N. 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 FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] FAQ, list archives, and subscription info: http
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] Hhh... 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] N. 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 o
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] Hhh... 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] N. 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
RE: elementary? [7:6359]
It's interesting to see how things that we take for granted (ie. A switch allows for multiple conversations while a hub can't) turn out to be so complicated when you try to understand what's taking place behind the scenes. To sum up what has been uncovered thus far (and maybe put an end to this thread)- The issue in question was whether/how a 1 gig uplink can be filled by 100 meg attached stations on two switches. I think that since the uplink is serial by nature (but full duplex) only packets from one station can be sent and at the same point in time only packets from one station can be received. The packets sent and received may or may not be from the same station. Essentially, as Chuck said only one packet is on the wire per direction at any given time. The switch will buffer all packets and treat each session between any two stations individually. Multiple data streams between different stations in the same direction cannot exist at the same point in time on the wire. (think of a twisted pair cable which has 4 pairs encased in the same sheath /pipe). Data from multiple stations (represented by the pairs)cannot travel over the uplink (represented by the sheath) at the same time, resulting in 4 concurrent flows. Instead, one conversation occurs per direction at any point in time. Now about filling up that 1 gig link even though only two conversations can exist on the wire at any given time- I guess that the switch can switch between conversations fast enough and send packets over the uplink at a much greater rate than what any attached client can send. Put enough busy clients together sending requests out the uplink and I can see how that 1gig uplink could become saturated. The switch just increases the rate at which packets are sent out of the Gb uplink. Does this make sense? Vijay Ramcharan Vijay Ramcharan -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of Chuck Larrieu 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 v
RE: elementary? [7:6359]
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] Hhh... 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] N. 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 wi
Re: elementary? [7:6359]
A switch port definitely delineates collision domains. Stations reachable on different ports don't share the media and are not concerned with each other's collisions. That answers part of the question. The link that I found before (and can't find now) confirmed that this is true even with cut-through switching. The switch caches the frame even when doing cut-through and if it encounters a collision while outputting, it backs off and retransmits. It does not send a collision enforcement jam to the original sender. If the Gigabit Ethernet link between the switches is set to full-duplex, the switches can send to and receive from either at the same time. But they can still only output one frame at a time. The Ethernet port outputs bits serially. It's not a parallel port. On the other hand, at 1,000 Mbps those bits are whipping out so fast, that the question is pretty irrelevant. The serialization delay isn't significant. On the wire, the bits are whipping by at about 2/3 the speed of light in a vacuum. (Yes, even fiber-optic cabling still provides a speed that is a fraction of speed of light in a vacuum.) Theoretically on a long cable, there could be more than one frame on the wire at a time. The math is making my head hurt, but this is logical, if possibly not real-world. Ten stations outputting 100 Mbps all destined to the other switch will cause the switch to queue packets. But stations don't output that fast. They wait for ACKs coming back in the other direction, etc. Also, they probably sometimes talk to other stations on their same switch. All your traffic probably won't go across the Gigabit Ethernet link. How much queuing will occur is hard to predict, but could be estimated with a good analysis of traffic patterns. Or you could throw money at the problem and group multiple Gigabit Ethernet ports together in an EtherChannel. I think this was a good question (not elementary after all!) Answers could vary from my off-the-cuff answer to a scientific and mathematical answer that gets into the different types of delay (serialization, propagation, queuing) and switch architectures. Priscilla At 11:42 AM 5/30/01, Allen May wrote: I believe it was Priscilla that found a link explaining all that in a white paper a couple months ago. I believe it backed up what you're saying...but I've slept (occasionally) since then. - Original Message - From: Chuck Larrieu To: Sent: Wednesday, May 30, 2001 10:14 AM Subject: RE: elementary? [7:6359] Hhh... 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] N. 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
