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Home > Archive > CCNA > May 2001 > Ppp&hdlc
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| two Qs,please help.
Is the ppp a connectionless protocol? and hdlc?
Does the RIP use the service of UDP?
thanks. | |
| strikeattack 2001-05-21, 6:31 pm |
| Because PPP and HDLC are layer-2 "Line" protocols, I am unsure as to what you mean when you say "connectionless". If you mean the term in the sense that UDP is connectionless and TCP is connection-oriented, I would have to say that they are connection-oriented because they are Point-to-point protocols working over a PVC.
RIP uses UDP, port 520 | |
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| Hi,layer 2 protocol such as Frame-relay,ATM,X.25 are connect-oreinted.LLC type 1,PPP are connectionless.Cisco press book,p551.
but I think ppp is connect-oriented protocol. | |
| Trouble Man 2001-05-21, 11:26 pm |
| PPP is a conection-oriented protocol, because it uses LCP (Link Control Protocol) to "establish, configure, maintain, and terminate the point-to-point connection." That's a quote from Todd Lammle in the Sybex CCNA Study Guide Second Edition, page 483.
For LLC I'll quote him again:
LLC Logical Link Control: Defined by the IEEE, the higher of two Data Link Layer sublayers. LLC is responsible for error detection (but not error correction), flow control, framing, and software sublayer addressing. The predominant LLC protocol, IEEE 802.2, defines both connectionless and connection-oriented operations. (Sybex, page 687)
LLC can be either (just like the transport layer with TCP and UDP).
HDLC is also connection-oriented. (Sybex, page 481)
Strike Attack is right on about RIP.
If you need me to elaborate more, please let me know. | |
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| Thank you,Trouble Man!I think you are right.
Is Wendell Odom rong? In his book,CCNA EXAM Certification Guide, p551,and I 've done some practices in the CD with the book.I remembered that a Qs about this says that ppp is a connectionless protocol. | |
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| quote:
Originally posted by ppp
Is the ppp a connectionless protocol? and hdlc?
Unfortunately the term connection oriented is not universily well definded. Most sources would agree that HDLC is connection oriented, but there would be different opinions on PPP.
For more on this confusion look at my post in this thread:
http://www.examnotes.net/forums/sho...p?threadid=9016
Terje | |
| Trouble Man 2001-05-22, 10:12 am |
| Interesting. I'm gonna have to go with Lammle, though, because PPP is a protocol stack, not just a single protocol. Within PPP are NCP, LCP, HDLC, and EIA/TIA-232-C. Now if mostly everyone agrees that HDLC is connection-oriented then they would have to agree that PPP is too, because every PPP protocol stack contains it's own proprietary HDLC. Not to mention that the whole purpose of LCP is to make a connection, and it is encased within PPP, too. | |
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| quote:
Originally posted by Trouble Man
Interesting. I'm gonna have to go with Lammle, though, because PPP is a protocol stack, not just a single protocol. Within PPP are NCP, LCP, HDLC, and EIA/TIA-232-C. Now if mostly everyone agrees that HDLC is connection-oriented then they would have to agree that PPP is too, because every PPP protocol stack contains it's own proprietary HDLC. Not to mention that the whole purpose of LCP is to make a connection, and it is encased within PPP, too.
NCP and LCP are parts of the PPP specification and transmitted within PPP frames. So far I do not disagree.
But: PPP does not contain HDLC. PPP frame format is based on the HDLC frame format. This is in fact true for lots of other protocols too (LAP, LAPB, LAPD, AX.25, Frame Relay and lots of others).
On the physical layer almost anything can be used. EIA/TIA-232C can be part of it, but the PPP specs says nothing about that. In fact it is quite common to use PPP on ISDN.
Although NCP and LCP frames are encapsulated within PPP frames, PPP is generally considered a data link layer protocol, not a multilayer protocol. This is similar to the way ICMP is encapsulated in IP but still generally considered part of the same layer.
LCP does indeed exchange some frames before actual data transfer takes place, thus qualifying as connection oriented by Odoms definition. Using the more common definition used by Halshal (see link in previous post) PPP is not connection oriented. Although its frame format is based on HDLC it does not use all of the HDLC syntax. Especially it does not use error correction and flow control.
Yes I know this is confusing. The main point is not beeing able to classify protocols as connection oriented or not (although that is sometimes usefull) but to know how all of the above interrelate.
Terje | |
| strikeattack 2001-05-23, 9:29 am |
| I agree with Terje's reply. Good explanation. | |
| Trouble Man 2001-05-23, 10:46 am |
| quote:
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."
So Hashal is saying that connection oriented and reliable are the same thing. It doesn't look that by his definition that you could have an unreliable connection-oriented protocol, which is possible by everybody else's definition.
Is this definition used a lot or is the other applied more often? Lammle seems to agree with Odom. Also, Lammle defines PPP as a protocol stack specified at the Data Link and Physical layers. | |
| Terje 2001-05-24, 10:54 am |
| quote:
Originally posted by Trouble Man
So Hashal is saying that connection oriented and reliable are the same thing. It doesn't look that by his definition that you could have an unreliable connection-oriented protocol, which is possible by everybody else's definition.
Is this definition used a lot or is the other applied more often?
It is my impression that Halshall is more main stream than Odom in this case, but I have not read all data communication litterature. Far from. It is worth noting that even Cisco is inconsistent.
I wouldn't worry to much about it.
quote:
Also, Lammle defines PPP as a protocol stack specified at the Data Link and Physical layers.
That is obviously wrong. PPP is data link layer only and can run on different physical layers.
Terje |
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