frame relay & Point to Point - differences and dis/advantages

[randal]

I have a pretty simple question, but I'm guessing it's a pretty lengthy answer. What is the difference between Frame Relay and point to point? afaik, we run PTP t1s here at work, and am wondering if there are any advantages or disadvantages to switching to frame relay.

I have heard that frame relay is quite a bit easier to setup in a 'failover' configuration, where if one site goes down the frame relay automagically goes to a backup place without need of a routing change.

Any info, links, things to look out would be great!
thanks,
randal

 

[spidey07]

good question.

I'll give the quick and dirty.
Frame Relay = very good performance for low cost. It is a "frame-switched" network which means you are switched with other customers traffic. Also very little overhead with frame-relay plus the ability to oversubscribe ports and do multi-point allowing you to connect many spoke sites to a single hub port. Generally the WAN of choice.

PTP - Expensive. Best performance possible as you are circuit-switched the whole distance. Generally used in same local area because of low cost. Once you go long distance you are charged mileage which can get VERY expensive.

In terms of failover that is still the responsibility of the router and it's routing protocols on both WANs. I can't really say frame is simplier because is just doesn't get any more simple than PTP. Frame-relay is pretty easy to setup and configure and monitor but a little more difficult to design because you have to take into account any oversubscription you may have and growth paths. Also different routing protocols behave differently on frame-relay, make sure you are aware of this and how you setup the router interfaces.

hope this helps. Wanna get a promotion at work? switch all those PTP T1s over to frame-relay and brag how much money you are saving them every month. Work with your carrier on design rules and how much oversubscription/burst they allow.

hope this helps,
cheers!

 

[Garion]

As always, Spidey is right on. I'll throw in a few additions, however.

Frame Relay:

Advantages:

• Very low cost, as you're not paying by the mile for a circuit
  One circuit can handle connectivity to multiple sites - Especially good for disaster recovery.
  You typically get "more than you pay for" - If you pay for a 128K CIR on a full T1 most carriers have heavily undersold their services so you usually get a lot higher than 128K.
  You can use subinterfaces with different PVC's within a single frame relay circuit which allows you to be more granular with your security policies and settings.
  Frame relay is usually easier and faster to configure than PTP circuits.

Disadvantages:

• Less reliable - You're going through the carrier's own network, depending on their frame switches and their frame routing. It's more prone to fail - Both AT&T and MCI have had spectactular frame blow-ups for multiple days. This can usually be overcome (at a reasonable financial cost) via something like ISDN backup.
  Often has a higher latency than PTP circuits.

Point-To-Point

Advantages:

• Most reliable possible circuit - It's sent through phone switches which are FAR more reliable and mature than frame relay switches.
  Can be split between different types of services - IE, eight channels of voice and sixteen channels of data.
  Works with pretty much any protocol.
  Lowest possible latency for a given distance.

Disadvantages:

1. Cost - It can be very expensive, two or more the cost of frame relay.
   Carries traffic only between two points, cannot easily handle multiple traffic destinations.

Hopes this sheds a bit more light on the matter!

- G

 

[spidey07]

randal,

how many PTP T1s to you have and how many sites? Are they all long distance? Seriously look into moving to a frame network. I got the biggest promotion and bonus of my career by saving my employer close to $250,000 a year. Just by moving to a frame-relay network.

 

[randal]

We currently only have 2 T1s; they are twisted Ts, and are just in case our 10mbit connection dies. From what I heard from the owner [who originally set it up], they are PTP to Qwest. But then I was looking at the billing, and we are billed almost nothing for it, which makes no sense -- and what originally got me thinking about Frame Relay. Well, it turns out that it *IS* frame relay, and we pay a small loop charge and then pay for bandwidth only when it's used [very rarely].

I spoke to a lead network guy at another local firm, and he told me just about everything I could handle about Frame Relay ... from what I dig, it's like the LEC aggregates all the packets from a ton of different subscribers, and then using circuit IDs, sends the packets to the right place using their own internal bandwidth. Just like on a phone call, the circuit is only live when data [voice] is being passed over it -- otherwise it's turned off and the bandwidth is used for other people's data [voice].

Now, as for Frame Relay being able to hit more places concurrently than a ptp link, I only semi-understand this. I do recognize that PTP is not a hot idea for long distances, and if it is used, if the line goes bad, the connection between the two sites is hosed completely. If they both use frame relay, then whatever path is available is taken, even if 1/2 of the LECs lines are toast, the traffic still goes over what's left. right?

heh, I think I have it down, kind of tough to explain. PTP = dedicated, Frame-Relay = Aggregate with other people on LEC's huge lines.

yes, no?
randal

 

[spidey07]

PTP - circuit switched (you have full clock all the way through network)
frame - frame switched (you are switched with other customers but are guarnteed a specific bandwidth called the commited infomration rate-CIR)

about frame being more reliable that is tough to say, generally is less reliable. But in any case 95% of all outages are not in the carriers network but are the LEC (poor wiring, misconfigured provisioning, and the list goes on and on and on)

 

[Z24]

question: is frame relay available in rural areas?

I just know people with small businesses that live in areas not serviced by DSL or cable (or even ISDN i think). Can frame relay be implemented in these spots?

Also, what is the pricing structure like?

Thanks

 

[CTR]

You can get FR over 56K leased-line, which is available where even ISDN hasn't made it. Or you could use a fractional or full T1, which is more expensive than leased-line but T1 circuits are available anywhere there is land-line based phone service. Pricing is structured by your CIR and your burst, and also take into account the recurring monthly cost of the circuit that gets you into the FR cloud.

Anyone using FR should be monitoring their equipment so that they know when their provider does not meet the SLA. It is easy to get some credit back to your account if your provider screws up. This means you can save the company even more money and finally get that really cushy leather chair you've always wanted and maybe a huge monitor for you PC so that you can more effectively monitor your SLA's.