On Mon, 30 Apr 2001, Priscilla Oppenheimer wrote:
> >b. HDLC --> The job of HDLC is to ensure that data passed up to the next
> >layer has been received exactly as transmitted (i.e error free, without
loss
> >and in the correct order).
>
> Except Cisco's HDLC doesn't do all that, and for the CCIE test you should
> know the Cisco way. Cisco's HDLC does error detection only. It does not
> retransmit.
Not just cisco's. HDLC detects and discards mangled frames, but doesn't
retransmit. I suspect that many people say HDLC when they actually mean
LAPB. LAPB retransmits lost or mangled frames and handles duplicates and
out-of-order frames.
> Great answer otherwise!
>
> Priscilla
>
>
> >c. SDLC --> Less error control than HDLC in that it only provides link
> >integrity. Frames received correctly are acknowledged by the receiver
while
> >erroneous frames are ignored.
> >
> >d. Frame-relay --> There is no guarantee of data integrity at all. Error
> >control is sacrificed in the interest of speed. Its assumed that higher
> >layer protocols will handle all necessary error control. The network
> >delivers frames, whether the CRC check matches or not. It does not even
> >necessarily deliver all frames, discarding frames whenever there is
network
> >congestion.
> >
> >e. DLSw+ --> Error control is provided by SNA, not DLSw. DLSw only handles
> >link control. Most bridging protocols (as far as I know anyway) deal
> >strictly with getting the data from point A to point B and let the layer
3/4
> >protocols handle error control/correction.
> >
> >f. ATM --> ATM does not have error control functionality (think about what
> >goes into an ATM cell - and what doesn't). Any error control has to be
> >performed by the protocols that are encapsulated in the ATM cells.
> >
> >g. T1, E1 --> These are layer 1 protocols. T1 and E1 deals with signaling
> >and encoding. At this level, its just bits, not frames or packets. Error
> >control is generally handled at layers 2 through 4 (when its done at all).
> >
> >Hope this helps,
> > Karen
> >
> >*********** REPLY SEPARATOR ***********
> >
> >On 4/30/2001 at 12:28 AM Kuldip Singh wrote:
> >
> > >Hi,
> > >
> > >Can someone help me find out who (router or host) will
> > >retransmit the packets if they were lost in the cloud
> > >while using:
> > >a. X.25 --> guarantees data integrity by using HDLC to handle error
> control.
> > >b. HDLC --> the purpose of this protocol is to provide an error free
link
> >between two connected devices.
> > >c. SDLC --> provides link integrity. Frames received correctly are
> >acknowledged by the receiver while erroneous frames are ignored.
> > >d. Frame-relay --> Think about what makes Frame-Relay different from
X-25.
> >There is no guarantee of data integrity at all.
> > >e. DLSw+ --> Error control is provided by SNA, not DLSw.
> > >f. ATM --> ATM does not have error control functionality (think about
what
> >goes into an ATM cell - and what doesn't).
> > >g. T1, E1 --> These are layer 1 protocols. Error control is generally
> >handled at layers 2 through 4.
> > >to connect from one router to another.
> > >
> > >HostRoutercloudRouterHost
> > >
> > >Thanks
> > >
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>
> ________________________
>
> Priscilla Oppenheimer
> http://www.priscilla.com
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