Matakuliah : H0484/Jaringan Komputer
Tahun
: 2007
Data Link Layer - Ethernet
Pertemuan 14
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Menggunakan Ethernet
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Outline Materi
• Standards
• Frame format
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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
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Generic Frame Structure (BOP)
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Data Link Protocols
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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
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Ethernet Frame Format
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Ethernet Frame
The frame can be any number of bytes in length,
depending on the specific technology used
Ethernet frame can be as long as 1522 bytes.
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Ethernet Layers
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Logical Link Control
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Interface to higher levels
Flow and error control
Transmission of link level PDUs between two stations
Must support multiaccess, shared medium
Relieved of some link access details by MAC layer
Addressing involves specifying source and destination
LLC users
– Referred to as service access points (SAP)
– Typically higher level protocol
MAC Control Packet
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MAC Frame Format
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MAC control
Destination MAC address
Source MAC address
LLC
– MAC layer receives data from LLC layer
• CRC
– MAC layer detects errors and discards frames
LLC optionally retransmits unsuccessful frames
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Media Access Control
• Assembly of data into frame with address and error
detection fields
• Disassembly of frame
– Address recognition
– Error detection
• Govern access to transmission medium
– Not found in traditional layer 2 data link control
• For the same LLC, several MAC options may be
available
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Media Access Control (MAC)
• Shared-media broadcast technology.
• Ethernet’s MAC performs three functions:
 Transmitting and receiving data packets
 Decoding data packets and checking them for valid addresses
before passing them to the upper layers of the OSI model
 Detecting errors within data packets or on the network
• Specified by the technology being used.
• Dictates who can transmit and when (Only one station may transmit at
a time; otherwise, their signals would be scrambled)
• Two types:
 Deterministic (Token Ring)
 Opportunistic (First come, first served - Ethernet)
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Ethernet and IEEE 802.3
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Specify similar technologies.
Broadcast network.
Using CSMA/CD algorithm.
Hardware implementation.
Differences:
– Ethernet provides services corresponding to
physical and datalink layer.
– IEEE 802.3 specifies the physical layer and the
channel-access portion of the data link layer but
does not define a LLC protocol.
Protocol stack
Link Control Protocol (LCP)
Authentication Protocols
Network Control Protocol (NCP)
Bit Padding
Digital Signals (DS) Services
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Encapsulated LCP packet
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An example
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