CS-09 – Data Communications and Networks
Quiz
Sliding Window Protocol
HDLC
SLIP/PPP
ATM – CELL TRANSMISSION/RECEPTION
Quiz
1.
Framing at Data-Link Layer Helps in
a)
Peer to Peer Connection.
b)
Error Control and Recovery.
c)
Easy Network Layer Connectivity
d)
Both (a) and (c) above.
2.
Using DLE,STX at start and DLE,ETX at frame end is a good framing method for
bit oriented protocols.
TRUE/FALSE
3.
Identify the correct bit stuffing pattern for ‘FC’ (Hex)
a)
1 1 1 1 1 1 0 0 0
b)
1 1 1 1 1 0 1 0 0
c)
0 1 1 1 1 1 0 1 0
d)
1 1 1 1 0 1 1 0 0
4.
Cyclic Buffers can help in Error Correction.
TRUE/FALSE
5.
Hamming distance between ‘A0’ (hex) and ‘0A’ (hex) is
a) 4 b) 3 c) 2 d)
0
6. CRC stands for
a)
Correct Reproduction of Code.
b)
Cyclic Retention Code.
c)
Cyclic Redundancy Code.
d)
Corrected Redundancy Code.
7. Putting Seq. No. in a
Protocol Frame solves the problem of.
a)
Flow Control.
b)
Lost Acknowledgement.
c)
Frame Repetition.
d)
Time-out.
8. Acknowledgement Wait Timer
should be
a)
Less than Channel Delay.
b)
More than Channel Delay.
c)
Equal to Channel Delay.
d)
Not Related to Channel Delay.
Sliding Window Protocol
· Efficient Channel Utilisation By Interleaving Data and Control Frame.
· Control Frame can be piggybacked over subsequent frame.
· Control Frame can be independently sent if data frame availability times out.
· n bit sequence number with 2n – 1 maximum number used for used for frame sequencing.
· Sender Maintains sequence numbers of frames permitted to send.
· Receiver Maintains another sequence number it is permitted to receive.
· Same window limit at sender and Receiver.
· When New Packet Available to send Upper Edge of Window is Advanced.
· When Frame is Acknowledge lower edge of window is advanced.
· All frames in window are buffered for retransmission.
· Protocol Options
o 1 Bit Sliding Window
o Go back ‘n’ (Acknowledgement May Come after ‘n’ frames – if not retransmit all frames after negative acknowledgement)
o Selective Repeat (Frames after bad frame are also buffered and only selected frames are repeated)
·
Protocols are specified and verified by
Mathematical models like
HDLC – High Level Data Link Control
· ISO standard (original IBM version known as SDLC – Synchronous Data-Link Control)
· CCITT based LAP and LAPB on this model.
· Bit Oriented Protocol
· Typical Frame Format is
|
01111110 |
Address |
Control |
Data |
Checksum |
01111110 |
· Control Field is used for sequence number, acknowledgement etc.
· Checksum is a CRC polynomial.
· Idle line transmit flags continously.
· Information, Supervisory and Unnumbered frames are defined.
Data Link Layer On Internet
SLIP:
· Serial Line Interface Protocol.
· Special byte 0xC0 used for Frame ending.
· If this byte occurs in Data 0xDB,0xDC is sent in its place. 0xDB is also stuffed.
· Recent Version include TCP and IP Header compression.
· No Error Detection or Correction.
· Suitable for Fixed IP Addresses.
· No Authentication.
PPP:
· Point to Point Protocol.
· Designed by IETF (Internet Engineering Task Force).
· Start and End of frame unamibiguously detected.
· Frame format handles Error Detection.
· Link Control Procedure (LCP) for connection setup and disconnection standardised.
· Negotiable Network Layer Options (for Upper Layer Peer to Peer Connectivity) NCP – Network Control Protocol.
· IP address assignment can be dynamic.
· PPP frame format is HDLC like but it is Byte Oriented.
· Authentication Procedure.
Data Link Layer in ATM
CELL TRANSMISSION:
· 4 Byte Virtual Circuit and control Information, 1 byte Checksum (HEC-Header Error Control).
· Payload is not checksummed – Error Control on this left to higher layers.
· Cells are inserted on to ASYNC or SYNC medium as required.
· Idle Cells may be required on SYNC transmission medium.
· OAM (Operation and Maintainence) cells are defined for control purposes between ATM switches.
· Underlying Physical Medium – SONET.
CELL RECEPTION:
· Frame boundary detection is done by checking the valid frame header using a 40 bit shift register.
· HEC is used find frame boudary condition.