Local Area Networks
a data communication system that allows a
number of independent devices to
communicate directly with each other in a
limited geographic area
dominated by




Ethernet
Token Bus
Token Ring
Fiber Distributed Data Interface (FDDI)
IEEE Project 802
covers the first two layers of the OSI model
and part of the third layer
the data link layer is subdivided into

logical link control (LLC)


non-architecture specific
medium access control (MAC)

specific to LAN technology
adapted HDLC
IEEE Project 802
also contains a section governing
internetworking – assures the compatibility of different
LANs and MANs across protocols and allows data to be
exchanged across otherwise incompatible networks
modularity – standardizes
those that can be generalized
and isolate those that must
remain specific
IEEE Project
IEEE 802.1 – Internetworking


meant for internetworking in LANs and MANs
not fully implemented
IEEE 802.2 – LLC

takes the structure of
HDLC frame (protocol data
unit – PDU)

DSAP/SSAP – identify
higher layer protocol stacks
IEEE Project
IEEE 802.2 – LLC (cont)

control (like in HDLC)
can be I-frames,
S-frame, U-frames
IEEE 802.3/4/5/… - MAC



resolves the contention for the shared media
synchronization, flag, flow, error control
MAC protocol is specific to LAN (Ethernet, Token Bus, Token
Ring, etc)
Ethernet
IEEE 802.3


baseband – digital signal
(Manchester encoding)
broadband – analog signal
(PSK encoding)
Ethernet
Access Method – CSMA/CD (carrier sense
multiple access with collision detection)

MA – every workstation
has equal right to access
the link

CSMA – any workstation
wishing to transmit must
first listen for existing
traffic on the line; only transmit
when the line is idle

CSMA/CD – listen, transmit, listen again; if collided, quit
current transmission, wait and try to resubmit
Ethernet
Addressing

Each station (PC, workstation, printer) has its own
network interface card (NIC) with unique 6-byte
physical address
Signaling

baseband (Manchester encoding), broadband
(PSK encoding)
Data Rate

1 - 100 Mbps, 1 Gbps
Ethernet
Frame format


Length/type of PDU - number of bytes or the type of protocol
carried
CRC - CRC-32
Ethernet
Implementation

10base5: Thick Ethernet (Thicknet)
Ethernet
Implementation

10base5: Thick Ethernet (cont)
Ethernet
Implementation

10base5: Thick Ethernet (cont)
Ethernet
Implementation

10Base5: Thick Ethernet (cont)
Ethernet
Implementation

10Base2: Thin Ethernet (Thinnet, cheapnet,
cheapernet)
Ethernet
Implementation

10Base2: Thin Ethernet (Thinnet, cheapnet,
cheapernet)
Ethernet
Implementation

10BaseT: Twisted-Pair Ethernet
Ethernet
Implementation

10BaseT: Twisted-Pair Ethernet
Ethernet
Implementation

1Base5: StarLAN
Ethernet
Other Implementations

Switched Ethernet


replacing the hub with a switch - a device that recognize
the destination address and can route the frame to the
port to which the destination
station is connected.
theoretically no collision –
increase capacity
Ethernet
Other Implementations

Fast Ethernet

100Base-T4
3 x 33.66 Mbps
< 100m

100Base-TX
< 100m

100Base-FX
< 2000m
Ethernet
Other Implementations (cont)

Gigabit Ethernet


usually serves as a backbone to connect fast Ethernet
networks
1000Base-SX
Fiber (multimode) 550m

1000Base-LX
Fiber (multimode) 550m
Fiber(single mode) 5000m

1000Base-CX
STP 25m

1000Base-T
UTP 25m
Token Bus
IEEE 802.4
combines features of Ethernet and Token Ring

a physical bus that operates as a logical ring using token
limited to factory automation and process control and
has no commercial application in data communication
Token Ring
IEEE 802.5
stations take turns sending data and may
send one frame during
each turn
no collision
Token Ring
Access Method




a three-byte free token circulates from NIC to NIC
if a station with the free token has something to send, it may
done so, and passes the frame to its neighboring station
the data frame proceeds around the ring until it reaches the
destination station where the destination station copies the
data frame, indicates received and passes back to the
sender
the sender, upon receiving the notified received frame,
discard the used data frame and release the token back to
the ring for other station to utilize
Token Ring
Access Method (cont)
Token Ring
Access Method (cont)

Priority and reservation


In general, once token has been released the next
station on the ring with data to send has the right to take
charge but the busy token can be reserved by station
with highest priority by entering priority code in AC field
Time limits

a time limit is imposed on any station wanting to use the
ring
Token Ring
Access Method (cont)

Monitor stations


one station is designated as a monitor station by setting
a timer each time the token is passed
the function of a station monitor to handle



damaged token due to noise – create a new one
a sending station may not release the token once its turn
ended
If the monitor fails, another station takes over as a
backup
Token Ring
Addressing

a six-byte address
Electrical Specifications

Signaling


differential Manchester encoding
Data Rate

4 Mbps, 16 Mbps
Frame Format

data/command, token, abort
Token Ring
Frame Format
Token Ring
Implementation

uses shielded twisted pair (STP)
Token Ring
Implementation (cont)

Switch


a ring introduces a
potential problem
(if a node disabled or
disconnected, the
entire network down)
automatic switch can
bypass an inactive
station
Token Ring
Implementation (cont)

Multistation Access Unit (MAU)

a hub for manageable network (each MAU can support
up to 8 stations and several MAUs can be connected to
one another to form star-ring)
FDDI
Fiber distributed data interface
an ANSI and ITU-T (ITU-T X.3) standard
data rates at 100 Mbps
originally fiber-based,
currently available
using copper cable
(CDDI)
unlike Token Ring,
FDDI uses dual ring
FDDI
Access Method – Token Passing


a station may sends as many frames as it can
within its allocated access period
each station that captures token is required to
send synchronous frame (S-frame) followed by
several asynchronous frames (A-frames) during
remaining time
Addressing

a six-byte address
FDDI
Electrical Specifications


Signaling – 4B/5B and NRZ-I (refer table 12.3 in
text book)
Five-bit codes that have not been assigned to
represent a four-bit counterpart are used for
control (refer table 12.4 in text book)
FDDI
FDDI layers
FDDI
Frame Types
FDDI
Implementation

Dual Ring
FDDI
Implementation

data transmission is confined to primary while
secondary is for healing after failure
FDDI
Implementation


MIC – connecting the node to the ring
DAS – connect
to both ring

SAS – connect
only to primary
ring

DAC – connect
SAS to dual
ring