HDLC - Sliding window full duplex point to point question
Posted on 2004-10-03
Hi, just have a fairly nuf nuf question im sure, but im hopeless @ this stuff! :)
A point to point full duplex comm link has been established bw stations A & B capable of using HDLC (ABM) protocol. The protocol (software) is configured so that each I-fram can carry 1000 data bytes. The line speed is such that each full I-fram is transmitted in 10ms, each U fram in 5ms and each S-fram in 3ms.
Following parameters "n" = 7 "m" = 8 and "p" = 0
Following events occur (in milliseconds)
a. At T=0 HDLC driver in B initiates the establishment of a connection with A
b. At time T = 10 + n the hDLC driver program in A is requested to transmit 4000 data bytes to B
c. At time T = 20 +m the HDLC driver in B is requested to transmit 3000 data bytes to A
d. At time T= 20+m+p an error occurs on the data link which corrupts several bits of the transmission from A to B
e. Third I-fram from B also has an error corrupting one or more bits the first time the fram is sent
f. 50ms after the satisfactory completion of all data transfer, station A initiates the disconnection of the connection.
Need to produce a message - exchange diagram showing all frames being sent in each direction to achieve the successful transmission of the 7000 bytes of data.
- need to be made clear the time the transmission begins, & the time reception is completed
- frame type and contents of its control bye
- contents of the V(R) V(S) and value of the retransmission counter in each station resulting from the transmission or reception of the frame. (there is no need to repeat it for every clock tick of the frame.)
- propagation is zero
- processing time is negligible
- "ack timer" is set to 50 ms the ack timer begins at the time when the I frames start to be transmitted
- window soze is large enough to allow all I frames to be sent without waiting for ack
- ack, either piggy backed via an I frame or cia an RR frame, are sent as soon as possible after the acceptance of an incoming I frame.