Frame Relay and Leased Lines

persona

Sorry for this stupid question, but from what i had been reading, a leased line is reserved circuit between two points..is this PVC as in frame relay?

please clarify the matter.

Thank you.

kafifi13

Leased line is really the local loop from the CO to your site. It's the actual physical line you pay for as a customer monthly. PVC is not an actual line or leased line. It's the theory or path that a framy relay can take. Hence the name virtual. the actual routing is down at the Frame relay switch. You need to config the routers with the correct DLCI's so that something from one site can route to another.

persona

thx for ur answer mate,

But is not a frame-relay a real connection we purchase from a local telco as well? we also have to agree on the CIR and so on..

Need to understand the difference btwn frame-relay and leased line if possible.

thanks in advance.

james_

A leased Line is a dedicated, point-to-point connection between two routers that pass through a WAN switch. No-one else shares that line, there is no Frame-Relay Cloud, you (the company) have sole rights to all the bandwidth on that line.

A PVC logically resembles a leased line, ie there is an always up connection between the two routers, but physically the router connects to a FR Switch which sits on the outside of the Frame Cloud. It passes this data to another FR Switch on the other side of the cloud, which then passes it on to the end router. Inside the cloud, ATM is usually used as the Layer 2 protocol, and the network is shared between all users that have contracts with the FR provider.

FR is a lot more complex, as you noted CIR's and access rates, there are also DLCIs which are used for addressing and things like DE, FECN and BECN that provide information on congestion.

Good luck with you studies.

James.

tech-airman

persona wrote:

Sorry for this stupid question, but from what i had been reading, a leased line is reserved circuit between two points..is this PVC as in frame relay?

please clarify the matter.

Thank you.

persona,

Sounds like you're confused by the classic difference between a "Circuit Switched" WAN link and a "Packet Switched" WAN link.

A "leased line" is a "Circuit Switched" WAN technology. It's in the same family of WAN networking as dialup, ISDN, and "leased line." The physical copper cabling and WAN switches belongs to the network service provider. Kinda like an apartment is owned by the landlord/landlady/management company. So you're "leasing the line" for your personal use and no one else's traffic should be travelling across the circuit that you're leasing. A way to visualize this is to imagine a crossover cable between two computers.

Frame Relay is a "Packet Switched" WAN technology. The virtual link between your local router and destination router is called a "Permanent Virtual Circuit" or PVC for short. What that means is that the FRAMES (hint, Data Link layer Protocol Data Unit) are Relayed from the first Frame Relay switch that your local router is connected to and the last Frame Relay switch that the destination router is connected to. The Frame Relay "cloud" between the first Frame Relay switch and the last Frame Relay switch is both shared by other customers of the internet service provider as well as your frames are switched and routed around by the internet service provider's networking devices until the frame reaches the destination router. A way to visualize this is to imagine multiple computers plugged into an ethernet hub.

I know that it could be confusing when "frame" is a Data Link layer PDU and "packet" is a Network layer PDU. Just remember that like a flashlight circuit, a "circuit switched" link is mostly a Physical layer connection from end to end. A "packet switched" link involves decapsulation from the Physical layer to Data Link layer, the Frame Relay switch makes a forwarding decision, encapsulates the frame and sends it out the appropriate WAN switch port. Say, what does this sound like? LAN Switching!

I hope this helps.

persona

tech-airman thx bro. You must have praticed teaching b4. Your explanation helped a lot.
Thx goes 2 james as well.

/respect

Aquabat [banned]

persona wrote:

thx for ur answer mate,

But is not a frame-relay a real connection we purchase from a local telco as well? we also have to agree on the CIR and so on..

Need to understand the difference btwn frame-relay and leased line if possible.

thanks in advance.

yes! The big difference here is cost. Telco's don't expect all customers on the shared line to transmit data at the same time, that's why you get to share a little and save alot.

" Ever try to call your mother on valentine's day and get an 'all circuit's busy' message?"
-Todd Lammle