Matakuliah
Tahun
Versi
: H0174/Jaringan Komputer
: 2006
: 1/0
Pertemuan 15
Layer Data Link
1
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Menjelaskan peran dan fungsi data link layer
2
Outline Materi
• Flow Control
• Error Control
• Link Access
3
Data Link Layer Functions
• Provide service interface to the network layer
• Services Provided to the Network Layer
• Flow Control
• Regulating data flow
• Slow receivers not swamped by fast senders
• Error Control
• Dealing with transmission errors
• Framing
• Character Oriented
• Bit Oriented
• Line Management (Medium Access)
• Polling
• Contention
4
Frame Transmission
5
Flow Control
• Flow control refers to a set of procedures used to
restrict the amount of data that the sender can
send before waiting for acknowledgment
• Ensuring the sending entity does not overwhelm
the receiving entity
– Preventing buffer overflow
• Transmission time
– Time taken to emit all bits into medium
• Propagation time
– Time for a bit to traverse the link
6
Stop and Wait
• Source transmits frame
• Destination receives frame and replies with
acknowledgement
• Source waits for ACK before sending next frame
• Destination can stop flow by not sending ACK
• Works well for a few large frames
7
Sliding Windows Flow Control
•
•
•
•
•
•
Allow multiple frames to be in transit
Receiver has buffer W long
Transmitter can send up to W frames without ACK
Each frame is numbered
ACK includes number of next frame expected
Sequence number bounded by size of field (k)
– Frames are numbered modulo 2k
8
Sender sliding window
9
Example Sliding Window
10
Automatic Repeat Request (ARQ)
• Stop and wait
• Go back N
• Selective reject (selective
retransmission)
11
METODE KOREKSI ERROR
METODE KOREKSI ERROR
• FORWARD ERROR CORRECTION (FEC):
– DIGUNAKAN SISTEM SANDI YANG SECARA
OTOMATIS DAPAT MEMPERBAIKI
KESALAHAN YANG DITEMUKAN
• BACKWARD ERROR CORRECTION
– PENGIRIMAN ULANG DATA YANG
TERGANGGU
12
LST/FASKD/CINQ
STOP AND WAIT
13
STOP AND WAIT- NUMBERING
• Numbered acknowledgments are needed if
an acknowledgment is delayed and the next
frame is lost.
• In Stop-and-Wait ARQ, numbering frames
prevents the retaining of duplicate frames.
14
Go Back N
• If no error, ACK as usual with next frame expected
• Use window to control number of outstanding
frames
• If error, reply with rejection
– Discard that frame and all future frames until
error frame received correctly
– Transmitter must go back and retransmit that
frame and all subsequent frames
15
Go Back N - Normal
16
Selective Reject
• Also called selective retransmission
• Only rejected frames are retransmitted
• Subsequent frames are accepted by the
receiver and buffered
• Minimizes retransmission
• Receiver must maintain large enough buffer
• More complex login in transmitter
17
Selective Reject - Lost Frame
18
Selective Reject -Diagram
19
Matakuliah
Tahun
Versi
: H0174/Jaringan Komputer
: 2006
: 1/0
Pertemuan 16
Layer Data Link - Lanjutan
20
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Menjelaskan ketentuan baku dan format frame pada
data link layer
21
Outline Materi
• Standards
• Frame format
22
Frame Structure
• In synchronous transmission all transmissions are
in frames
• Single frame format for all data and control
exchanges
• Basic Structures:
– Character Oriented Protocol (COP) - BSC
(Bisynchronous)
– Bit Oriented Protocol (BOP) - HDLC, SDLC
23
Generic Frame Structure (BOP)
24
Bit stuffing and removal
Bit stuffing is the process of adding one extra 0 whenever there
are five consecutive 1s in the data so that the receiver does not
mistake the data for a flag.
25
Data Link Protocols
•
•
•
•
HDLC - High-Level Data Link Control
SDLC - Synchronous Data Link Control
PPP - Point to Point Protocol
Ethernet
HDLC can be considered as the base protocol format
26
High-Level Data Link Control
Frame format for bit-oriented protocols.
27
PPP – Point to Point Protocol
The PPP full frame format for unnumbered mode operation.
28
Protocol stack
Link Control Protocol (LCP)
Authentication Protocols
Network Control Protocol (NCP)
Bit Padding
Digital Signals (DS) Services
29
Encapsulated LCP packet
30
PPP – Point to Point Protocol
31
An example
32