Kuldip,
For most of these, a quick look at the purpose of the protocol will answer
your question. However, don't assume that error control is required,
sometimes there isn't any error control at all. However, even when a
protocol has error control functionality, don't assume that it will do
anything beyond discarding corrupted packets/frames. A good way to check if
a protocol does some form of error control is to look at the header or frame
format. If a CRC or FCS is included then it does at least minimal error
control (as in the case of SDLC). A closer look at how the protocol operates
is needed to determine what sort of error control is performed.
a. X.25 --> Guarantees data integrity by using HDLC to handle error control.
X.25 itself handles the call setup/teardown procedure, not error control
(uses the following packet types: Call Accept, Call Request, Clear
Confirmation, Clear Request, Data Packet, Diagnostic, Interrupt
Confirmation, Interrupt Request, Reject, Reset Confirmation, Reset Request,
Receive Not Ready, Receive Ready, Restart Confirmation, Restart Request,
Registration Request, Registration Confirmation).
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).
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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