WIRED LANS: ETHERNET
13.3 CHANGES IN THE
Presented by : Malik S.Abeisat
- From 10-Mbps Standard Ethernet until it’s moving
to higher data rate , it passes through through
- These changes actually opened the road to the
evolution of the Ethernet to become compatible
with other high-data-rate LANs.
- Here we’ll talk about some of them :
WHAT EXACTLY IS A BRIDGE IN
A Bridge is a device that filters data traffic at a network
boundary. Bridges reduce the amount of traffic on a LAN by
dividing it into two segments. It connects on the data-link
layer, (layer 2) of the OSI model.
In the picture to the right, the data is
coming from the database server.
The bridge filters the data, sending
the data to the correct locations.
The first step in the Ethernet evolution was the division of a LAN by bridges.
The term bridge was coined in the early 1980s.
Today, the terms LAN switch or (in the context of Ethernet) Ethernet switch
Bridges have two effects on an Ethernet LAN:
1- They raise the bandwidth.
2- they separate collision domains.
Bridges are intermediate systems that forward MAC frames to
destinations based on MAC addresses.
Q. Is an Ethernet hub a bridge or a repeater ? What’s the difference ?
A. It can be either a bridge or a repeater. “hub” is a product name, not an
architecture name. Modern hubs are bridges. Old ones are repeaters.The
difference is: a repeater is a layer 1 intermediate system (acts on bits)
whereas a bridge is a layer 2 intermediate system (acts on entire MAC
frames). Also: a bridge separates collision domains, a repeater does not
HOW DOES A BRIDGE WORK?
Bridges are similar to repeaters and network hubs, devices that connect at the
physical layer, however, with bridging, traffic from one network is managed
rather than simply rebroadcast to adjacent network segments.
Bridges tend to be more complex than hubs or repeaters. Bridges can analyze
incoming data packets to determine if the bridge is able to send the given
packet to another segment of the network.
Since bridging takes place at the data-link layer of the OSI model, a bridge
processes the information from each frame of data it receives. In an
Ethernet frame, this provides the MAC address of the frame's source and
destination. Bridges use two methods to resolve the network segment that
a MAC address belongs to.
Raising the Bandwidth
Stations shares the total bandwidth they are provided with. When we have more
than one station they share the provided bandwidth hence we can put the bridge
we can spilt the stations so that they can share the same bandwidth but the
number of stations are less as it’s divided between stations. For example, We
have 10 stations sharing 10 mbps now if we bridge them over 5-5 stations ,we
will have 5 stations sharing the same 10mbps bandwidth, hence bridged
connection can increase the bandwidth by above mentioned method.
Separating Collision Domains
The collision domain becomes much smaller and the
probability of collision is reduced tremendously. Without
bridging, 12 stations contend for access to the medium;
with bridging only 3 stations contend for access to the
Consists of a several
segments, each of which is
shared by NICs attached to it.
(Network interface controller “NIC”)
The network is segmented
into several collision domains.
Bridges, switches, and routers
create the segment and
collision domain boundaries.
Segments may contain hubs
There is switch table and it’s build by
(media access control address “MAC”) for
Switch - 1 port per hub
Full-duplex is a data communications term that
refers to the ability to send and receive data at the
The full-duplex mode increases the capacity of
each domain (ex. from 10 to 20 Mbps).
instead of using one link between the station and
the switch, the configuration uses two links:
one to transmit and one to receive.
In full-duplex mode, both devices can transmit and
receive to and from each other at the same time, and
there is no collision domain. This doubles the
aggregate bandwidth of the link and is sometimes
advertised as double the link speed (e.g., 200 Mbit/s).
o The elimination of the
collision domain for these
connections also means
that all the link's
bandwidth can be used by
the two devices on that
segment and that segment
length is not limited by the
need for correct collision
Carrier Sense Multiple Access With Collision Detection
Collision: two transmissions interfere with each
Station that wants to transmit first listens to check if
another transmission is in progress (carrier sense).
If medium is in use, station waits; else, it transmits.
Collisions can still occur.
Transmitter waits for ACK; if no ACKs, retransmits.
(CARRIER SENSE MULTIPLE ACCESS
WITH COLLISION DETECTION)
Access method: method of controlling how network
nodes access communications channels
CSMA/CD: Ethernet’s access method
Ethernet NICs listen on network
Wait until no nodes transmitting data over the signal on the
communications channel before transmission
Several Ethernet nodes can be connected to a network and can
monitor traffic simultaneously
(Network interface controller “NIC”)
In a full-duplex switched Ethernet, each station is
connected to the switch via two separate links.
Each station or switch can send and receive
independently without worrying about collision.
Each link is a point-to-point dedicated path between the
station and the switch.
There is no longer a need for carrier sensing; there is no
longer a need for collision detection. The job of the MAC
layer becomes much easier.
The carrier sensing and collision detection functionalities
of the MAC sublayer can be turned off.
Specified by the technology being used.
Determine who can transmit and when.
Deterministic: “Let’s take turns”.
Non-deterministic: “First come, first serve”.
Ethernet : CSMA/CD.