CEN-444
Networks Structure And Protocols
LAN TECHNOLOGIES
Mohammed Saleem Bhat
m.bhat@mu.edu.sa
Computer Engineering and Networks, College of Engineering , Majmaah University
Technology Options-Ethernet
Ethernet
Fast Ethernet
Gigabit Ethernet
10 Gig Ethernet
WLAN
Computer Engineering and Networks, College of Engineering , Majmaah University
Media Access
Ethernet and Wi-Fi are both “multi-access” technologies
Broadcast medium, shared by many hosts
Simultaneous transmissions will result in collisions
Media Access Control (MAC) protocol required
Rules on how to share medium
The Data Link Layer is divided into two Part MAC Media
Access Control) Sublayer and LLC (Logic Link Control)
Sublayer
Computer Engineering and Networks, College of Engineering , Majmaah University
802.3 Ethernet
Carrier-sense multiple access with collision detection
(CSMA/CD).
CS = carrier sense
MA = multiple access
CD = collision detection
Base Ethernet standard is 10 Mbps.
100Mbps, 1Gbps, 10Gbps standards came later
Computer Engineering and Networks, College of Engineering , Majmaah University
Ethernet CSMA/CD
CSMA/CD (carrier sense multiple access with collision
detection) media access protocol is used.
Data is transmitted in the form of packets.
Sense channel prior to actual packet transmission.
Transmit packet only if channel is sensed idle; else, defer
the transmission until channel becomes idle.
After packet transmission is started, the node monitors its
own transmission to see if the packet has experienced a
collision.
If the packet is observed to be undergoing a collision, the
transmission is aborted and the packet is retransmitted
after a random interval of time using Binary Exponential
Backoff algorithm.
Computer Engineering and Networks, College of Engineering , Majmaah University
Ethernet Address
End nodes are identified by their Ethernet Addresses
(MAC Address or Hardware Address) which is a unique 6
Byte address.
MAC Address is represented in Hexa Decimal format e.g
00:05:5D:FE:10:0A
The first 3 bytes identify a vendor (also called prefix) and
the last 3 bytes are unique for every host or device
Computer Engineering and Networks, College of Engineering , Majmaah University
LAN Technologies
Ethernet Frame Structure
Preamble:
7 bytes with pattern 10101010 followed by one byte with
pattern 10101011
Used to synchronize receiver, sender clock rates
Addresses: 6 bytes, frame is received by all adapters on a
LAN and dropped if address does not match
Length: 2 bytes, length of Data field
CRC: 4 bytes generated using CR-32, checked at receiver, if
error is detected, the frame is simply dropped
Data Payload: Maximum 1500 bytes, minimum 46 bytes
If data is less than 46 bytes, pad with zeros to 46 bytes
Computer Engineering and Networks, College
Length of Engineering , Majmaah University
LAN Technologies
Ethernet
10 Base 5 (Thicknet) (Bus Topology)
10 Base 2 (Thinnet) (Bus Topology)
10 Base T (UTP) (Star/Tree Topology)
10 Base FL (Fiber) (Star/Tree Topology)
Computer Engineering and Networks, College of Engineering , Majmaah University
LAN Technologies
802.11 Wireless LAN
Network
connectivity
to the
legacy
wired LAN
Desktop
with PCI 802.11 LAN card
Access Point
Laptop
with PCMCIA 802.11 LAN card
Provides network connectivity over wireless media
An Access Point (AP) is installed to act as Bridge between
Wireless and Wired Network
The AP is connected to wired network and is equipped
with antennae to provide wireless connectivity
Computer Engineering and Networks, College of Engineering , Majmaah University
LAN Technologies
802.11 Wireless LAN
Range ( Distance between Access Point and WLAN client)
depends on structural hindrances and RF gain of the
antenna at the Access Point
To service larger areas, multiple APs may be installed with
a 20-30% overlap
A client is always associated with one AP and when the
client moves closer to another AP, it associates with the
new AP (Hand-Off)
Three flavors:
802.11b
802.11a
Computer
Engineering and Networks,
802.11g
College of Engineering , Majmaah University
LAN Technologies
Multiple Access with Collision
Avoidance (MACA)
other node in
sender’s range
sender
RTS
receiver
other node in
receiver’s range
CTS
data
ACK
Before every data transmission
Sender sends a Request to Send (RTS) frame containing
the length of the transmission
Receiver respond with a Clear to Send (CTS) frame
Sender sends data
Receiver sends an ACK; now another sender can send data
When sender doesn’t get a CTS back, it assumes collision
Computer Engineering and Networks, College of Engineering , Majmaah University
LAN Technologies
WLAN : 802.11b
The most popular
deployment.
802.11
standard
currently
in
Supports 1, 2, 5.5 and 11 Mbps data rates in the 2.4 GHz
ISM (Industrial-Scientific-Medical) band
Computer Engineering and Networks, College of Engineering , Majmaah University
LAN Technologies
WLAN : 802.11a
Operates in the 5 GHz UNII (Unlicensed National
Information Infrastructure) band
Incompatible with devices operating in 2.4GHz
Supports Data rates up to 54 Mbps.
Computer Engineering and Networks, College of Engineering , Majmaah University
LAN Technologies
WLAN : 802.11g
Supports data rates as high as 54 Mbps on the 2.4 GHz
band
Provides backward compatibility with 802.11b equipment
Computer Engineering and Networks, College of Engineering , Majmaah University
Repeater, HUB, Bridge & Switch
REPEATER, HUB, BRIDGE AND
SWITCH
Computer Engineering and Networks, College of Engineering , Majmaah University
Repeater, Hub, Bridge & Switch
Repeater
A repeater receives a signal, regenerates it, and passes it
on.
It can regenerate and retime network signals at the bit
level to allow them to travel a longer distance on the
media.
It operates at Physical Layer of OSI
The Four Repeater Rule for 10-Mbps Ethernet should be
used as a standard when extending LAN segments.
This rule states that no more than four repeaters can be
used between hosts on a LAN.
This rule is used to limit latency added to frame travel by
each repeater.
Computer Engineering and Networks, College of Engineering , Majmaah University
Repeater, Hub, Bridge & Switch
Hub
Hubs are used to connect
multiple nodes to a single
physical device, which connects
to the network.
Hubs are actually multiport
repeaters.
Using a hub changes the network
topology from a linear bus, to a
star.
With hubs, data arriving over
the cables to a hub port is
electrically repeated on all the
other ports connected to the
same network segment, except
for the port on which the data
Computer
Engineering and Networks, College of Engineering , Majmaah University
was sent.
Repeater, Hub, Bridge & Switch
Bridge
Bridges are used to logically separate
network segments within the same network.
They operate at the OSI data link layer
(Layer 2) and are independent of higherlayer protocols.
The function of the bridge is to make
intelligent decisions about whether or not to
pass signals on to the next segment of a
network.
When a bridge receives a frame on the
network, the destination MAC address is
looked up in the bridge table to determine
whether to filter, flood, or copy the frame
onto another segment
Broadcast Packets are forwarded
Computer Engineering and Networks, College of Engineering , Majmaah University
Repeater, Hub, Bridge & Switch
Switch
Switches are Multiport Bridges.
Switches provide a unique network segment on each port,
thereby separating collision domains.
Today, network designers are replacing hubs in their wiring
closets with switches to increase their network performance
and bandwidth while protecting their existing wiring
investments.
Like bridges, switches learn certain information about the
data packets that are received from various computers on the
network.
Switches use this information to build forwarding tables to
determine the destination of data being sent by one computer
to another computer on the network.
Computer Engineering and Networks, College of Engineering , Majmaah University
Repeater, Hub, Bridge & Switch
Switches: Dedicated Access
Hosts have direct connection to
switch
Full Duplex: No collisions
Switching: A-to-A’ and B-to-B’
simultaneously, no collisions
A
C’
B
switch
Switches can be cascaded to
expand the network
C
B’
A’
Computer Engineering and Networks, College of Engineering , Majmaah University