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Home > Archive > CCNA > December 2000 > Multilink PPP
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| Hi all. I found this definition in the Wendell Odom book:
Multilink PPP is a function that allows multiple links between a router and some other device, over which traffic is balanced."
My question is...why would you want to use multilink and what are it's advantages? Thanx in advance. | |
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| MultiLink PPP is a method of doubling your connect rates using your present analog telephone system. By using MultiLink PPP, along with two regular 56K modems and two regular telephone lines, you can double your download and upload rates. Your O/S already handles the work involved in splitting the data between your two simultaneous connections.
ISDN is extremely costly compared to MultiLink PPP. ISDN requires a special ISDN modem, approx. $400 - $500. ISDN requires a high-speed data line installed at a high cost by the telephone company. The monthly charges for a data line by the telephone company are well over $100 per month. Comparing these costs with the costs of MultiLink PPP, it shows that ISDN does not stand up as a cost-effective method of high-speed data transfer & connectivity on a byte per dollar ratio. The minor speed increase that ISDN may provide does not justify the greatly increased expense of ISDN connectivity. When using a 64K ISDN connection, a MultiLink PPP connection is actually considerably faster and CONSIDERABLY cheaper
JerryL | |
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| Thanks, Jerry, for that clarification. It's nice to have people reinforce the topics one has learnt...and that one is forgetting!!
Cheers,
Deets | |
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| Deets;
Not a prob. Just glad to put back into what I've been using.
JerryL | |
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| Thanks Jerry L.
I know what multilink from a desktop's perspective is (aka "shotgunning").
What I'm still confused about is it seems there are only a limited number of places to connect multiple modems to a router. In the Odom book, it showed six lines coming out of the router, which would indicate six multilinked modems and six phone lines.
If this is the case, how would you do it?
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| Just to throw some wood into the fire, we all know ISDN-2 is 2x64k b (yes and 1 16k d) channels. You can use Multilink PPP to bring up both lines so your using 128k as one line on your ISDN2. And yes I also know use can use the threshold command for the same thing. In fact thinking about it, you can also use for Pri ISDN and bring all 30 lines up(24 I think in the USA).
Kevin. | |
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| To firechicken: I think this is a hardware issue. You wouldn't be able to get this sort of functionality (ie. 6 B channels leading off from your router), if you were using a 2500 series router. You need to go higher up the Cisco scale, which means lots of $ (or buy from a different manufacturer). Also you need more phone lines...
I remember someone explaining the visual of 6 (8?) modems connected to a router, but I am a bit hazy on the detail. Can someone give some insight on this?
Cheers,
Deets | |
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| quote:
I remember someone explaining the visual of 6 (8?) modems connected to a router, but I am a bit hazy on the detail. Can someone give some insight on this?
Basically shows two routers, with six parallel lines drawn between one another. Above these lines it reads, "6 x B-channel".
When I read his reasoning on why multilink PPP is used, it reads, "But consider the alternative--without multilink PPP, but simply PPP on each of the six links. Six routes to subnet 10.2.2.0/24 would exist in Router A's routing table."
This makes sense (although, there is a typo in the book, because the punctuation in the first sentence is wrong).
JerryL-
Thanks again, your reply has helped me have a better understanding of all that is involved with an ISDN setup. | |
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| I believe Deets is referring to the "octopus cable" that can be attached to an Async port allowing up to 8 analog modems to be installed per physical interface. These are used to provide dialup services to remote users. The down side is that you can't get better then a 28.8k connection on a 56k modem. This is due to the 56k requirement for a digital signal blah blah blah....I hate going thru that stuff.
Yankee | |
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| Firechicken;
Your more than welcome. Sorry I didn't get back to you earlier, but it looks like you got more than enough input. I had this thing called "work" that kept me from going further.
JerryL | |
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| To Yankee:
So I guess this means I am wrong in relation to the hardware: ie. a 2500 series router would support this? In effect via its two serial interfaces using the octopus cabling?
To firechicken: Yes, I've seen the Odom diagram, I know what you mean. At first the idea of setting up multiple modems like that seemed farcical: why doesn't some company just combine them into one??
The mysteries of internetworking...
Deets
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| There are 2 common types of serial interfaces on Cisco routers. The most common is a synchronous high-speed serial port. It can ONLY handle synchronous links (i.e. not asynch dial-up modems, terminals, etc.) up to around 2 megabits/sec.
There are also asynch ports. The 2509/10 support 8 asynch ports, and are cabled with one port on the router going to 8 asynch leads on an "octal" or "octopus" cable. The 2511/12 support 16 asynch ports. These are nice for a lab setup since you can have each asynch port cabled to the console port of another device and get console connectivity around the lab from one terminal. You could also use these for multilink PPP by dropping some or all of those asynch ports onto modems (if you really wanted to do that ...)
There are also synch/asynch serial ports on some routers like, if I remember the model number right, the 2521 (8 of them along with 2 high-speed synch ports, if memory serves). These are lower speed ports (I think they max out around 64 kb/s, but memory may be faulty here), but can be used either for lower speed synchronous links, or for asynch. Rumor has it that you may well get one of these in a CCIE lab rack to set up as your frame relay switch.
To round out the picture, for links faster than 2 megabits, you get a HSSI port (not available in the 2500 series to my knowledge). These are relatively uncommon, since to get a 3 megabit circuit means having to deal with an inverse MUX (in other words, the phone company gives you 2 T1's, and a box to make them look like 1 circuit to your router. IMUXes tend to be flaky ...) It's easier to drop each T1 on its own serial port. If you really want a lot of bandwidth in just a little space, you can get a 7200 with a T3 WIC card in it and run at 45 megabits over one line.
Waiting for his very own T3 to be installed in his home at someone else's expense,
doctorcisco
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Silicon is made from sand; nothing made from sand is allowed to wreck my day! | |
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| Thanks everyone for your input!
quote:
At first the idea of setting up multiple modems like that seemed farcical: why doesn't some company just combine them into one??
This brings me to my next question I've always wondered about.
If an ISP expects 80 customers to be online simultaneously, does that mean they have to have a total of eighty modems connected to multiple routers? Or is their another way of handling this?
TIA! | |
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| Good question, firechicken. Can anyone here answer? I'm a tad out of my depth...and would like to know too.
Cheers,
Deets | |
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| quote:
Originally posted by firechicken:
[B]
If an ISP expects 80 customers to be online simultaneously, does that mean they have to have a total of eighty modems connected to multiple routers? Or is their another way of handling this?
[B]
Yes,in some for or another. 80 modems is easily handled by an AS5300. You can run 8 PRIs into it and terminate 190 calls with digital modems (imagine a dozen modems fitting onto something the size of a DIMM). This keeps things digital all the way so they can support 56k connections.
Madchef
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| Mad, I was on the understanding that a AS5300 did 120 calls, which is 4 pri here in the uk. ???
Kevin. | |
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| I put in a 5300 here in the states and it had 8 PRI ports and 192 modems. They also make a quad board, so maybe that's all you got. It makes me wonder if you can stack a few more modems in there for those 30 channel PRIs you guys have. I don't know and i feel too lazy to look it up.
MadChef | |
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| Thanks for taking the time to reply, everybloody! Now I know. |
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