| Author |
Frame Relay; connection-oriented communication
|
|
|
| Does Frame Relay provide connection-oriented data link layer communication? Can anybody explain this? | |
|
| Frame Relay operates at the data-link layer and is connectionless. It relies on the upper layer protocols to ensure the delivery of packets. Hope this helps. | |
|
| quote:
Originally posted by greatgonzos:
It relies on the upper layer protocols to ensure the delivery of packets.
Hmm. Can you elaborate on this?!
Cheers!
| |
|
| Before people jump all over me, allow me to retract my original answer. Frame Relay in fact does provide connection-oriented communication. A communication exists between DTE's and these connections are what is associated with a DLCI.
Sorry for any confusion. I was thinking of another WAN technology and more along the lines of error correction rather than whether or not it is connectionless or not.
It is error correction that is left to the upper layer protocols. | |
|
| Just to add:
Connection oriented means that in order for data transfers to begin, there first must be an establishment of a virtual circuit. In this case, as mentioned in the previous post, the virtual circuit is the DLCI.
Hope this helps. | |
|
| quote:
Originally posted by firechicken:
In this case, as mentioned in the previous post, the virtual circuit is the DLCI.
I wouldn't say that. A virtual circuit is an abstract entity (that happens to map to a certain physical circuit at a certain moment), while a DLCI is an identifier for the virtual circuit. Quite different things, don't you agree?
Cheers!
| |
|
| I see what you're sayin', dmaftei! Thanks again for keeping me on my toes.
Note to self: watch what you post as long as this guy is a member of the exam notes forum. 
BTW, if a virtual circuit is abstract, how can it map to a physical circuit?
| |
|
| At least by my understanding, frame relay is NOT connection-oriented.
It seems like we had a thread like this one not long ago. I think people get confused by the term "virtual circuit" in the definition of "connection-oriented." These "virtual circuits" are NOT the same thing as frame relay PVC's or SVC's. Connection oriented means:
1) An end-to-end virtual circuit is established (provided in TCP, for instance, with port numbers), and is torn down when the task is completed.
2) Delivery of PDU's is verified; PDU's are retransmitted if there is an error or if delivery fails.
Frame relay does NOT request retransmission of bad frames; it just trashes the bad frame and relies on upper layer protocols (like TCP) to notice the missing data and retransmit. It is, therefore, not connection oriented.
Corrections welcome,
doctorcisco
------------------
Silicon is made from sand; nothing made from sand is allowed to wreck my day! | |
|
| When you see the term "virtual" it means whatever function is done in software. That's why you have that swap file on your Windows and other OSs machine.
There is however, a person that links the DLCI to a specific circuit ID via software in the DSLAM (talking ADSL here) and PVC at the other end.
DLCIs are not unique. And if someone could explain where the circuit ID comes in, I would appreciate it.
| |
|
| Hi guys.
Here's a quote from the Cisco site (gee, I'm actually starting to use this resource!!):
quote:
Access to Frame Relay networks is made through private leased lines at speeds ranging from 56 kbps to 45 Mbps. Frame Relay is a connection-oriented, packet-transfer mechanism that establishes virtual circuits between endpoints.
This comes from:
>>>> http://www.cisco.com/univercd/cc/td..._c/wcfrelay.htm
The reference also has details on configuring PVCs and SVCs.
Hope this helps,
Deets
| |
|
| quote:
Originally posted by Bernie:
Does Frame Relay provide connection-oriented data link layer communication? Can anybody explain this?
Unfortunately the term "connection oriented" is not uniformly defined within the data communication community. That is one reason why this thread and other threads on this subject are prone to excessive growing without firm conclusions. Let me describe two definitions of connection oriented:
1) "Data communications, computer networks and open systems" by Fred Halshall, ISBN 0-201-56506-4 says: "Connectionless: which treats each information frame as a self-contained entity that is transferred using a best-try approach; that is, if errors are detected in a frame then the frame is simply discarded.
connection oriented, which endeavours to provide an error-free information transfer facility."
This and variants thereof is probably the most widely used view on what constitutes connection oriented. With this definition Frame Relay would NOT be considered connection oriented (its lesser known sibling Frame Switching on the other hand is still connection oriented).
But there are other views and I will let our friend Wendel Odom speak for one of them:
2) In his book "Cisco CCNA Exam #640-507 Certification Guide", ISBN 0-7357-0971-8" he says: "connection-oriented protocol: A protocol that either requires an exchange of messages before data transfer begins or has a required pre-established correlation between two endpoints.
Connectionless protocol:A protocol that does not require exchange of messages and that does not require a pre-established correlation between two endpoints."
Given this definition Frame Relay as well as ATM becomes connection oriented due to their reliance on a pre-established virtual circuit (VC).
There are also other variants that does not fit into any of the two abovementioned.
Which definition does Cisco use? I am sorry to say that Cisco is not consistent in its use. In fact I have seen books that are not consistent within themselves, the ICND book beeing an example.
Which definition should you use? For Real Life it's wise to know that there are inconsistent definitions circulating.
For the exam you might be prepared to choose one or the other. Have your choice :/
Sorry for adding to the confusion and not giving a firm answer. I have been tearing my hair myself for a long time over this question.
Terje
| |
|
| Glad to see I wasnt the only one confused on this issue. But for test purposes, I would answer that it is connection oriented,because thats what it says on the Cisco site. An argument can be made that it doesnt provide all the services that a true connection-oriented protocol, but like I said, for testing purposes, go with what Cisco says is your best bet. |
|
|
|