Get documents about "OSI Model _Open System Interconnection Model_ Application
Description
One of the features of computer networks is to group the flow of information transmitted by adding control information, and send the packet to the destination correctly. Adding control information packet are two: one is used to verify whether the receiver correctly received the error control information; the other is the sender of the packet specified in the receiver's address information. Thus the network must have the error control and addressing functions. Also required when multiple nodes simultaneously send the packet, the network must also be some sort of conflict arbitration process to decide who to send, who after the delivery. All of these data packets with control information in a network nodes through a feature called the right to send forward data link control DLC.
Document Sample
Data Link Control
OSI Model (Open System Interconnection Model)
Application Layer 7 Protocol
Application Layer 7
Peer Processor
Presentation Layer 6 Protocol
Presentation Layer 6
Session Layer 5 Protocol
Session Layer 5
Transport Layer 4 Protocol
Transport Layer 4
Network Layer 3 Protocol
Network Layer 3
Data Link Layer 2 Protocol
Data Link Layer 2
Physical Layer 1 Protocol
Physical Layer 1
Peer Protocol
Data Link Control
Connectionless without reliability
Establish connection is not necessary
Acknowledgment is not need
Connectionless with reliability
Establish connection is not necessary
Acknowledgment is need
Connection-oriented with reliability
Establish connection is necessary
Acknowledgment is need
Data Link Control
Frame Synchronization
Data are sent in blocks called frames. The beginning and end of each
frame must be recognizable
Flow Control
The sending station must not send frames at a rate faster then the
receiving station can absorb them.
Error control
Any bit errors introduced by the transmission system must be corrected
Addressing
On a multipoint line, such as a local area network (LAN), the identity
of the two stations involved in a transmission must be specified
Data Link Control
Control and data on same link
It is usually not desirable to have a physically separate communications
path for control information. Accordingly, the receiver must be able to
distinguish control information from the data being transmitted.
Link management
The initiation, maintenance, and termination of a sustained data exchange
requires a fair amount of coordination and cooperation among stations.
Procedures for the management of this exchange are required
Link management
Flow Control Error Detection Error Control
Data Link Control
Flow Control
Flow control is
a technique
for assuring
that
a transmitting
entity
does not
overwhelm
a receiving
entity
with data.
Buffer Size
Data Link Control
Stop-and-Wait Flow Control simplest form of flow control.
Only one frame
Transmission Time
Transmission : The time it take for a station to transmit a frame that is normalized to one
take for a station to transmit a frame that is normalized to one
Propagation delay
Propagation delay :: The time it takes for a bit to travel from sender to receiver that is expressed as “a”
The time it takes for a bit to travel from sender to receiver that is expressed as “a”
Data Link Control
Stop-and-Wait Flow Control
propagation time less than transmission time
The frame is sufficiently long that the first bits of the frame have
arrived at the destination before the source has completed the
transmission of the frame.
propagation time greater than transmission time
The sender completes transmission of the entire frame before
the leading bits of that frame arrive at the receiver
Transmission Time
Transmission : The time it take for a station to transmit a frame that is normalized to one
take for a station to transmit a frame that is normalized to one
Propagation delay
Propagation delay :: The time it takes for a bit to travel from sender to receiver that is expressed as “a”
The time it takes for a bit to travel from sender to receiver that is expressed as “a”
Data Link Control
Sliding-windows flow control Multiple Frame Full-duplex link
3-bit field
Sequence number of the next frame
Data Link Control
Each time a frame is sent, the shade window shrinks
Each time a frame is sent, the shade window shrinks
each time an acknowledgment is received the shade window grows
each time an acknowledgment is received the shade window grows
ady 3
Next 7 Frames
Receive-Re
RNR 5 ::
RNR 5
received 4 but unable to
received 4 but unable to
accept any more
accept any more
Example of a sliding-window protocol
Data Link Control
Error Detection
Pb : Probability of a single bit error or bit error rate
P1 : Probability that a frame arrives with no bit errors.
P2 : Probability that a frame arrives with one or more undetected bit errors
P3 : Probability that a frame arrives with one or more detected bit errors
but no undetected bit errors
F : the number of bit per frame
P = (1 − Pb )
F
1
P2 = 1 − P1
Data Link Control
Error Detection and Correction
1. ใหผูรับตรวจสอบความผิดพลาดและแกไขขอมูลที่สงใหถูกตองดวยตัวเอง
2. ใชเทคนิคการสะทอนกลับ (Echoplex) โดยผูรับจะสงขอมูลที่ไดรับกลับไป
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่
3. การตรวจสอบแบบอัตโนมัติ โดยการเพิมขอมูลสําหรับใชในการตรวจสอบ
เพิ่มเขาไปในนอกเหนือจากขอมูลที่สง
Frame Check Sequence
Frame Check Sequence
(FCS)
(FCS)
Data Link Control
Error Detection
Parity Check Cyclic Redundancy Check (CRC)
Data Link Control
Parity Check
The simplest error-detection scheme is to append a parity bit to the end of
a block of data.
Synchronous transmission
XOR
Even parity G (1110001) + Odd parity
Odd parity G (11100011)
(11100011)
Asynchronous transmission G (11000011)
(11000011) ERROR
G (11000001)
(11000001) NO ERROR
Data Link Control
Block Check Character P 7 6 5 4 3 2 1 Character
1 1 0 0 0 0 0 1 1
1 1 0 0 0 0 1 0 2
XOR
0 1 0 0 0 0 1 1 3
1 1 0 0 0 1 0 0 4
0 1 0 0 0 1 0 1 5
0 1 0 0 0 1 1 0 6
1 1 0 0 0 1 1 1 7
1 1 0 0 1 0 0 0 8
0 1 0 0 1 0 0 1 9
0 1 0 0 1 0 1 0 10
1 1 0 0 1 0 1 1 11
0 1 0 0 1 1 0 0 12
1 1 0 0 1 1 0 1 13
1 1 0 0 1 1 1 0 14
1 0 0 0 1 1 1 1 BCC
Data Link Control
Cyclic Redundancy Check (CRC) or Polynomial Code
One of the most common, and one of the most powerful.
110001 1 x X55 + 1 x X44 + 0 x X33 + 0 x X22 + 0 x X11 + 1 x X00 X55 + X44 + 1
Transmitter
Frame Check Sequence)
Generate an n-bit sequence ((Frame Check Sequence) k+n bit
Modulo 2 Arithmetic Uses binary addition with no carries or XOR
1111 11001 T = (k + n)-bit frame to be transmitted with n < k
+1010 x 11 M = k-bit message, the first k bits of T
0101 101011 F = n-bit FCS, the last n bits of T
P = pattern of n + 1 bits
E = error
Data Link Control
CRC Calculating 1101010110 Q
P 110101 101000110100000 2nM
110101
111011
Message (M) = 1010001101 (10-bits) 110101
111010
110101
Pattern (P) = 110101 (6-bits) 111110
110101
To be calculated 101100
FCS (R) = 110101
(5-bits) 110010
110101
Transmitter 01110 R
Frame Check Sequence)
Generate an n-bit sequence ((Frame Check Sequence) k+n bit
Transmitter Receiver Remainder
101000110101110
101000110101110 101000110101110
101000110101110 00000
Data Link Control
Cyclic Redundancy Check (CRC)
• All single-bit errors
• All double-bit errors, as long as P(X) has at least three 1s
• Any odd number of errors, as long as P(X) contains a factor (X-1)
• Any burst error for which the length of the burst is less than the length
of the divisor polynomial; that is, less than or equal to the length of the
FCS
• Most larger burst errors
CRC-16
CRC-16 = X16
= X16 +
+ X15
X15 +
+ X2 + 1
X2 + 1
CRC-CCITT = X16
CRC-CCITT = X16 +
+ X12
X12 +
+ X5 + 1
X5 + 1
CRC-32
CRC-32 = X32
= X32 +
+ X26
X26 +
+ X25 + X23 + X22 + X16 + X12 +
X25 + X23 + X22 + X16 + X12 +
X11
X11 +
+ X10
X10 +
+ X8 + X7 + X5 + X4 + X2 + 1
X8 + X7 + X5 + X4 + X2 + 1
Data Link Control
Error Control
ERROR
Lost Frame Damaged Frame
A frame fails to arrive A recognizable frame
at the other side. does arrive, but some
of the bits are in error.
Data Link Control
Error detection
Positive acknowledgment
The destination returns a positive acknowledgment to successfully
received, error-free frames.
Retransmission after timeout
The source retransmits a frame that has not been acknowledged after
a predetermined amount of time.
Negative acknowledgment and retransmission
The destination returns a negative acknowledgment to frames in which
an error is detected. The source retransmits such frames.
Data Link Control
ARQ : Automation Repeat Request
Stop-and-Wait ARQ
Data Link Control
ARQ : Automation Repeat Request
Go-Back-N ARQ
Pipelining
Damaged Frame
Damaged RR
Data Link Control
ARQ : Automation Repeat Request
Selective-Reject ARQ
Data Link Control
HDLC : High-level Data Link Control
Basic Characteristics
Three type of stations Two link configuration Three data transfer modes
Three types of stations
Primary Station
For controlling the operation of the link called “command”
Secondary Station
Operates under the control of the primary station called “responses”
Combined Station
Two link configurations
Unbalanced configuration
One primary and one/more secondary station and supports both full-
duplex and half-duplex transmission.
Balanced configuration
Two combined stations and supports both full-duplex and half-duplex
transmission.
Data Link Control
HDLC : High-level Data Link Control
Basic Characteristics
Multidrop Line Synchronous TxRx
Three data transfer modes
Normal response mode (NRM)
Used unbalanced configuration. Primary initiate data transfer to
a secondary but a secondary may only transmit data in response to
a command from the primary
Asynchronous balanced mode (NRM)
Used with a balanced configuration. Either combined station may
initiate transmission without receiving permission from the other
combined station.
Asynchronous response mode (NRM)
Used with an unbalanced configuration. The secondary may initiate
transmission without explicit permission of the primary. The primary
still retains responsibility for the line, including initialization, error
recovery, and logical disconnection.
Data Link Control
HDLC : High-level Data Link Control : Frame Structure
Frame Format
Flag Field : unique pattern 01111110
Bit Stuffing Data transparency
Data Link Control
HDLC : High-level Data Link Control : Frame Structure
Data Link Control
HDLC : High-level Data Link Control : Frame Structure
Frame Format
Address Field : uniformity if all bit is 1, it means broadcast communication
Extended address field
Data Link Control
HDLC : High-level Data Link Control : Frame Structure
Frame Format
0 :: primary poll to secondary
0 primary poll to secondary
1 :: primary receive data
1 primary receive data
8-bit control field format Sliding-windows
Sliding-windows
Data Link Control
HDLC : High-level Data Link Control : Frame Structure
8-bit control field format Sliding-windows
Sliding-windows
00
00 RR
RR Receive ready
Receive ready
01
01 REJ
REJ Reject
Reject
10
10 RNR
RNR Receive not ready
Receive not ready
11
11 SREJ
SREJ Selective reject
Selective reject
Data Link Control
Initialization
Three phase of HDLC operation Data Transfer
Disconnect
