Erwin Craps
Erwin.Craps at ithelps.be
Tue Nov 4 01:07:10 CST 2003
Thats not totaly true. Switches prevent collisions and resends to happen on the OTHER virtual connections. On A point to point connection you also have collisions. Because all trafic all goes to one link to the server that link will have all collisions to, thus taking bandwith of others connections. Simply because you have a single bottleneck. Erwin -----Oorspronkelijk bericht----- Van: dba-tech-bounces at databaseadvisors.com [mailto:dba-tech-bounces at databaseadvisors.com] Namens John Colby Verzonden: maandag 3 november 2003 23:33 Aan: Discussion of Hardware and Software issues Onderwerp: RE: [dba-Tech] Re: [] Wireless network (sort of) Erwin, But none of that takes into account collisions and retransmissions due to collisions. Hubs have that to deal with, switches don't. John W. Colby www.colbyconsulting.com -----Original Message----- From: dba-tech-bounces at databaseadvisors.com [mailto:dba-tech-bounces at databaseadvisors.com]On Behalf Of Erwin Craps Sent: Monday, November 03, 2003 5:21 PM To: Discussion of Hardware and Software issues Subject: RE: [dba-Tech] Re: [] Wireless network (sort of) OK, it's me again. I still stand with my remarks. I'm implemented a lot of switch several years ago and am very much aware how layer 2 and 3 switches work. Layer 4 don't know. Not in to that business anymore. As I already commented it is wrong to say that switches will always will improve your bandwith. A switch will only be able to do his thing when some condtions are true. These coditions are most of the time present but not always. But generaly you could conclude a switch will have network performance effect when 1) 2 servers/hosts or more with each his own direct link to the switch 2) When having only one server the server link bandwith MUST be higher than the (single) client bandwith. It all turns about the slowest link principle. With a switch you create dynamic virtual connections. The slowest link at that time will decide the bandwith for that connection. Small example. You have: 1x client A at 100Mbps 1x client B at 100Mbps 1x x-port switch all 100Mbps 1x server S at 100Mbps Both clients starts sending large data to the server at maximum speed (let's say each 100Mbps to make an easy calc). Question: What will be the maximum network bandwith obtained to the server? A) 100Mbps B) 200Mbps C) 300Mbps Right, a) 100 Mbps, why? Because the server has only one 100Mbps link. Will this go faster than a hub. No. Infact, a switch has to make a decision based on MAC or IP address and this takes time. So, I would like to believe it will be slightly slower than a hub... If a was talking about speed in my previous mails I could have mixed speed and bandwith. You have the network speed (should be bandwith), and you have speed (or performance) of the switch. Speed of a switch is the delay (lack of) and the quantity of ethernet packets it can manipulate per second. I remember me some figures (delay times) but I supose they will be much lower now. A router takes about 600 to 800µsec to make a decision (and change) to forward a packet to a port based on IP or other layer 3 routable protocol. A switch took (in 1996 or so) around 180µsec based on Mac. A hub none... Because it doesn't take a look inside the pakket.. It justs repeats stupidly. A hub is nothing more than a stupid (bon-intelligent but active) repeater. So if you wanna see bandwith improvement on a single server network you must have a 1Gb connection to the server (thats what I would suggest) or use dual link between server and switch. Both server and switch must support dual links (teamed links?). By this you would have 200Mb between server and switch and you could now have 2 clients running at full speed (100Mb). I'm not sure about this dual link if both are full duplex, maybe it depends on the brand but I believe I read somewhere that with a dual link you have 100Mb upstream and 100mb downstream. Which would result that when both clients are sending they only would have 50 Mb each. If one would send other receive they would have each 100Mbps. This is the theoricatal best situation because, if you don't have a heavely loaded network, you will have more bandwith, but not used. It's like having a east-west coast pipeline and you only send a drop of water trough it... The switch is of no use due to lack of trafic. You would better put your money in a good server or applications or new pc's... But hey, don't get me wrong. I'm 100% pro switches. If you are having doubts for buying a switch or a hub, buy a switch. You gonna need it someday. Prices are down, but I'm not that sure if performance of those cheap ones are good. But don't say switches will always improve speed. It really depends on your network configuration. Erwin -----Original Message----- From: dba-tech-bounces at databaseadvisors.com [mailto:dba-tech-bounces at databaseadvisors.com] On Behalf Of Francisco H Tapia Sent: Monday, November 03, 2003 8:11 PM To: Discussion of Hardware and Software issues; jimdettman at earthlink.net Subject: [dba-Tech] Re: [] Wireless network (sort of) Jim, I'm replying to the dba-tech list as that is the proper list for this topic :). On that note, some of your more recent Switches also come w/ somthing called spanning trees. Jim Dettman wrote: >Drew/Erwin, > > One minor correction. Switches don't use NAT tables. They use MAC >Address lists and ARP tables. NAT is something done only in a router. > >Jim Dettman >President, >Online Computer Services of WNY, Inc. >(315) 699-3443 >jimdettman at earthlink.net > >-----Original Message----- >From: accessd-bounces at databaseadvisors.com >[mailto:accessd-bounces at databaseadvisors.com]On Behalf Of Drew Wutka >Sent: Monday, November 03, 2003 11:59 AM >To: 'Access Developers discussion and problem solving' >Subject: RE: [AccessD] OT: Wireless network (sort of) > > >Read Erwins post a little while ago, was waiting for your's before I >replied! <grin> > >Erwin, switches also use NAT tables. Because of this, they don't have >to broadcast everything in all directions. They're 'smart', when a >packet comes in, they can properly direct it. The downside to the NAT >tables is that if you blow the NAT table away, it has to be rebuilt, so >sometimes on an initial powerup, a switch may seem slower, which is >simply the time it is using to build the NAT tables. > >Drew > >-----Original Message----- >From: Frank Tanner III [mailto:pctech at mybellybutton.com] >Sent: Sunday, November 02, 2003 8:35 AM >To: Access Developers discussion and problem solving >Subject: RE: [AccessD] OT: Wireless network (sort of) > > >And they improve speed. > >Because they do not SHARE the bandwidth amongst the >ports. A 10-BaseT hub SHARES that speed amongst the >available ports. This dividing the individual >bandwidth per port. > >A switch allocates all available bandwidth on a PER >PORT basis. > >Maybe you need to learn what you are talking about >before you give out false information. > >--- Erwin Craps <Erwin.Craps at ithelps.be> wrote: > > >>And to be correct, switches don't improve speed >>(compared to hub's) they >>improve bandwith and reduce collisions!!! >>Switches create virtual point to point connections. >> >>Switches do improve speed compared to routers. >> >>Erwin >> >>-----Oorspronkelijk bericht----- >>Van: accessd-bounces at databaseadvisors.com >>[mailto:accessd-bounces at databaseadvisors.com] Namens >>Frank Tanner III >>Verzonden: zaterdag 1 november 2003 16:23 >>Aan: Access Developers discussion and problem >>solving >>Onderwerp: RE: [AccessD] OT: Wireless network (sort >>of) >> >> >>Switches will ALWAYS improve your speed over hubs. >>Period. >> >>Hubs SHARE the same bandwidth on all ports. >>Switches >>allocate the max bandwidth per port. >> >>You are incorrect. >> >>--- Erwin Craps <Erwin.Craps at ithelps.be> wrote: >> >> >>>But switches have no sense in a 1 server >>> >>> >>environment >> >> >>>because all of the >>>trafic goes and comes from one point. >>>Unless your clients are 100Mb and the uplink to >>> >>> >>the >> >> >>>server is 1Gb. >>> >>>People often believe switches will improve their >>>network speed, but that >>>is not always the case. >>>But indeed the prices of the switches have dropped >>>that you buy a switch >>>at the price of a good hub these days. >>> >>>Erwin >>> >>>-----Original Message----- >>>From: accessd-bounces at databaseadvisors.com >>>[mailto:accessd-bounces at databaseadvisors.com] On >>>Behalf Of Rocky Smolin >>>- Beach Access Software >>>Sent: Saturday, November 01, 2003 1:55 AM >>>To: Access Developers discussion and problem >>> >>> >>solving >> >> >>>Subject: Re: [AccessD] OT: Wireless network (sort >>>of) >>> >>> >>>Got it. I think. Switch can route packet based on >>>IP address but can't >>>generate an IP address. Yes? >>> >>>Rocky >>> >>> >>>Rocky >>> >>>----- Original Message ----- >>>From: "Frank Tanner III" >>> >>> >><pctech at mybellybutton.com> >> >> >>>To: "Access Developers discussion and problem >>>solving" >>><accessd at databaseadvisors.com> >>>Sent: Friday, October 31, 2003 10:29 AM >>>Subject: Re: [AccessD] OT: Wireless network (sort >>>of) >>> >>> >>> >>> >>>>It is sort of half-way, but not really. >>>> >>>>Switches are a "generation" better. Hubs and >>>>switches, on their most basic level perform the >>>> >>>> >>>same function. They >>> >>> >>>>distribute network traffic. But HOW they >>>> >>>> >>>distribute that traffic is >>> >>> >>>>fundimentally different. >>>> >>>>Unless they're one of the newer layer 3 or layer >>>> >>>> >>4 switches, they >> >> >>>>cannot perform routing functions. >>>> >>>> >>>They >>> >>> >>>>just hand packets off from point A to point B. >>>> >>>> >>>Think >>> >>> >>>>of them as sort of a postman. They have an >>>> >>>> >>>address >>> >>> >>>>for each device on the network and they hand off >>>> >>>> >>>each >>> >>> >>>>piece of mail to the appropriate address. A >>>> >>>> >>hub, >> >> >>>>using this sama analagy would deliver the same >>>> >>>> >>>piece >>> >>> >>>>of mail to every house and the one that it >>>> >>>> >>>belonged to >>> >>> >>>>would be the one that actually reads it. >>>> >>>>--- Rocky Smolin - Beach Access Software >>>> >>>> >><bchacc at san.rr.com> wrote: >> >> >>>>>"but it's as close as I could think of without >>>>>getting too technical." >>>>> >>>>>Thank you. Much appreciated. So a switch is >>>>> >>>>> >>>like >>> >>> >>>>>halfway between a hub and >>>>>a router? >>>>> >>>>>Rocky >>>>> >>>>>----- Original Message ----- >>>>>From: "Frank Tanner III" >>>>> >>>>> >>><pctech at mybellybutton.com> >>> >>> >>>>>To: "Access Developers discussion and problem >>>>>solving" >>>>><accessd at databaseadvisors.com> >>>>>Sent: Friday, October 31, 2003 7:36 AM >>>>>Subject: Re: [AccessD] OT: Wireless network >>>>> >>>>> >>>(sort >>> >>> >>>>>of) >>>>> >>>>> >>>>> >>>>> >>>>>>A router and a switch are fundimentall >>>>>> >>>>>> >>>different >>> >>> >>>>>>things. >>>>>> >>>>>>A router does just that. It routes network >>>>>> >>>>>> >>>>>traffic. >>>>> >>>>> >>>>>>A switch plays "traffic cop" for a network. >>>>>> >>>>>>Newer switches, especially the layer 3 and >>>>>> >>>>>> >>>layer 4 >>> >>> >>>>>>ones can perform both functions.This isn't >>>>>> >>>>>> >>an >> >> >>>>>exact >>>>> >>>>> >>>>>>definition, but it's as close as I could >>>>>> >>>>>> >>think >> >> >>>of >>> >>> >>>>>>without getting too technical. >>>>>> >>>>>>--- Rocky Smolin - Beach Access Software >>>>>> >>>>>> >>><bchacc at san.rr.com> >>> >>> >>>>>>wrote: >>>>>> >>>>>> >>>>>>>Is there a difference between a switch and >>>>>>> >>>>>>> >>a >> >> >>>>>router? >>>>> >>>>> >>>>>>>Rocky >>>>>>> >>>>>>>----- Original Message ----- >>>>>>>From: "Frank Tanner III" >>>>>>> >>>>>>> >>>>><pctech at mybellybutton.com> >>>>> >>>>> >>>>>>>To: "Access Developers discussion and >>>>>>> >>>>>>> >>>problem >>> >>> >>>>>>>solving" >>>>>>><accessd at databaseadvisors.com> >>>>>>>Sent: Friday, October 31, 2003 6:54 AM >>>>>>>Subject: RE: [AccessD] OT: Wireless >>>>>>> >>>>>>> >>network >> >> >>>>>(sort >>>>> >>>>> >>>>>>>of) >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>>>I recommend "hardwiring" the IP address >>>>>>>> >>>>>>>> >>of >> >> >>>any >>> >>> >>>>>>>device >>>>>>> >>>>>>> >>>>>>>>or server connected to your LAN that's >>>>>>>> >>>>>>>> >>not >> >> >>>a workstation and >>> >>> >>>>>>>>is virtually always on. >>>>>>>> >>>>>>>>For the price, I would also highly >>>>>>>> >>>>>>>> >>>recommend >>> >>> >>>>>>>removing >>>>>>> >>>>>>> >>>>>>>>all hubs from your network and using >>>>>>>> >>>>>>>> >>them >> >> >>>as doorstops. >>> >>> >>>>>>>>Switches have come way down in >>>>>>>> >>>>>>>> >>>>>price >>>>> >>>>> >>>>>>>and >>>>>>> >>>>>>> >>>>>>>>have many benifits over hubs. >>>>>>>> >>>>>>>>Hubs divide the bandwidth across all >>>>>>>> >>>>>>>> >>>ports. >>> >>> >>>>>Thus >>>>> >>>>> >>>>>>>if >>>>>>> >>>>>>> >>>>>>>>you have an 8-port 10-BaseT hub, all >>>>>>>> >>>>>>>> >>ports >> >> >>>>>that >>>>> >>>>> >>>>>>>are >>>>>>> >>>>>>> >>>>>>>>processing data split that 10Mbit. A >>>>>>>> >>>>>>>> >=== message truncated === > >_______________________________________________ >AccessD mailing list >AccessD at databaseadvisors.com >http://databaseadvisors.com/mailman/listinfo/accessd >Website: http://www.databaseadvisors.com >_______________________________________________ >AccessD mailing list >AccessD at databaseadvisors.com >http://databaseadvisors.com/mailman/listinfo/accessd >Website: http://www.databaseadvisors.com > > >_______________________________________________ >AccessD mailing list >AccessD at databaseadvisors.com >http://databaseadvisors.com/mailman/listinfo/accessd >Website: http://www.databaseadvisors.com > > > -- -Francisco _______________________________________________ dba-Tech mailing list dba-Tech at databaseadvisors.com http://databaseadvisors.com/mailman/listinfo/dba-tech Website: http://www.databaseadvisors.com _______________________________________________ dba-Tech mailing list dba-Tech at databaseadvisors.com http://databaseadvisors.com/mailman/listinfo/dba-tech Website: http://www.databaseadvisors.com _______________________________________________ dba-Tech mailing list dba-Tech at databaseadvisors.com http://databaseadvisors.com/mailman/listinfo/dba-tech Website: http://www.databaseadvisors.com