Chapter_6, Local Area and Wide Area Network

Chapter Six
LAN and WAN Technologies
Data Communication and Computer
Networks

Introduction
2
 LANs do not normally operate in isolation.
 They are connected to one another or to the Internet.
 To connect LANs, or segments of LANs, we use connecting devices.
 Connecting devices can operate in different layers of the Internet model.
 LANS use Repeater, Hub, Bridge and Switch as a connection device.

Repeaters
3
A repeater receives a signal, regenerates it, and passes it on.
It can regenerate signals 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.
A repeater does not actually connect two LANs; it connects two
segments of the same LAN.The segments connected are still part of one
single LAN.
A repeater forwards every frame; it has no filtering capability.

Hub
5
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.

Types of Hubs
7
1. Passive hubs do not amplify the electrical signal of incoming packets before
broadcasting them out to the network. It connects the wires coming from different
branches. In a star-topology Ethernet LAN, a passive hub is just a point where the
signals coming from different stations collide; the hub is the collision point. Its
location in the Internet model is below the physical layer.
2. Active hubs, a type of hub that can perform amplification, as does a repeater.
3. Intelligent hubs add extra features to an active hub that are of particular importance
to businesses.
 It also typically includes remote management capabilities via SNMP and virtual
LAN (VLAN) support.

Bridges
8
Bridges are used to logically separate network segments within the same network.
They operate at the OSI physical and data link layer and are independent of higher-
layer protocols.
As a data link layer device, the bridge can check the physical (MAC) addresses (source
and destination) contained in the frame.
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 to all directions

Filtering in Bridges
9
A bridge has filtering capability. It can check the destination address of a
frame and decide if the frame should be forwarded or dropped. If the frame is
to be forwarded, the decision must specify the port.A bridge has a table that
maps addresses to ports.

Contd.
10
In the previous figure, if a frame destined for station 712B13456142 arrives
at port 1, the bridge consults its table to find the departing port.
According to its table, frames for 712B13456142 leave through port 1;
therefore, there is no need for forwarding, and the frame is dropped.
On the other hand, if a frame for 712B13456141 arrives at port 2, the
departing port is port 1 and the frame is forwarded.

MAC Address Learning
11
Bridges MAC table can be static or dynamic.
To make a table dynamic, we need a bridge that gradually learns from the
frame movements.
To do this, the bridge inspects both the destination and the source addresses.

MAC Learning Process Example
12

Contd.
13
1. When station A sends a frame to station D, the bridge does not have an entry
for either D or A.The frame goes out from all three ports; the frame floods the
network. However, by looking at the source address, the bridge learns that
station A must be located on the LAN connected to port 1. This means that
frames destined for A, in the future, must be sent out through port 1. The
bridge adds this entry to its table.The table has its first entry now.
2. When station E sends a frame to station A, the bridge has an entry for A, so it
forwards the frame only to port 1.There is no flooding. In addition, it uses the
source address of the frame, E, to add a second entry to the table.
3. When station B sends a frame to C, the bridge has no entry for C, so once again
it floods the network and adds one more entry to the table.
4. The process of learning continues as the bridge forwards frames.

Switch
Switches are Multiport Bridges.
Switches provide a unique network segment on each port,
thereby separating collision domains.
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.
14
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
Switches can be cascaded to expand the network
15
A’
B’

Two/three-layer switches
 We can have a two-layer switch or a three-layer switch.
 A three-layer switch is used at the network layer; it is a kind of router.
 The two-layer switch performs at the physical and data link layers.
 A two-layer switch is a bridge, a bridge with many ports and a design that
allows better (faster) performance.
 A bridge with a few ports can connect a few LANs together.
 A bridge with many ports may be able to allocate a unique port to each station,
with each station on its own independent entity.
 This means no competing traffic (no Collision)
16

Types of Switches
1.Cut-through switch
 Cut-through switch is a packet switch wherein the switch starts
forwarding that frame (or packet) before the whole frame has been
received, normally as soon as the destination address is processed.
 A cut-through switch can achieve the lowest forwarding delays,
 In other words, this technique reduces latency through the switch,
but decreases reliability.
2.Store and Forward Switch
 A switching device that stores a complete incoming data packet
before it is sent out. Such switches are used when incoming and
outgoing speeds differ
17

LAN Technology Options
Ethernet
Fast Ethernet
Gigabit Ethernet
10 Gig Ethernet
18
LAN Technologies

Ethernet
19
 Developed by Xerox in 1976
 Eventually became an IEEE standard (IEEE 802.3)
 Has been modified for wireless applications (IEEE 802.11)
 And for higher speeds (IEEE 802.3ae for 10 Gigabit Ethernet)
 Ethernet is based on the Datagram and functions at the physical and
data link layer

Ethernet Datagram Structure
20
8 bytes
Preamble
6 bytes
Destination
Address
6 bytes
Source
Address
2 bytes
Type Field
4 bytes
Frame
Check
Sequence
46 to 1500
bytes
Data

Ethernet Datagram Structure
21
 Preamble: Repeating Flag that ID’s the sequence as an
Ethernet datagram
 Destination Address: Unique identifier found nowhere else
but on the Network Interface Card to whom the datagram is
being sent
 Source Address: Who originated the datagram
 Type Field:Tells the recipient what kind of datagram is being
received (IP, UDP, etc)
 Data:What it is that you are trying to send (text, JEPG, MP3,
etc)
 Frame Check Sequence: Detects and corrects errors

Ethernet Tidbits
 If a message has less than 46 bytes of data,“padding” is added
 Ethernet is often referred to as 100 BaseT
 First digit is the speed of the system in Mbps
 Base refers to a cable or wire system
 T refers to the system is UTP: UnshieldedTwisted Pair
 10 Base 5 stands for 10 Mbps on a cable that can go 500 m
(multiply the last number by 100 meters)
 10 Base 2 stands for 10 Mbps for 200 m
 10 Base 5 and 10 Base 2 identifies Ethernet LANs using thick net
and thin net coax cables, respectively
22
LAN Technologies

Ethernet Address
End nodes are identified by their Ethernet Addresses (MAC Address or
HardwareAddress) which is a unique 6 Byte address.
MAC Address is represented in Hexa Decimal format e.g
00:05:5D:FE:10:0A (48 bits)
The first 3 bytes identify a vendor (also called prefix) and the last 3 bytes
are unique for every host or device
The least significant bit of the first byte defines the type of address. If the bit
is 0, the address is unicast; otherwise, it is multicast.
The broadcast destination address is a special case of the multicast address
in which all bits are 1s.
23
LAN Technologies

Quiz
 Define the type of the following destination addresses:
 a.4A:30:10:21:10:1A
 b. 47:20:1B:2E:08:E7
 c. FF:FF:FF:FF:FF:FF
24
Solution
To find the type of the address, we need to look at the second
hexadecimal digit from the left. If it is even, the address is unicast. If it
is odd, the address is multicast. If all digits are F’s, the address is
broadcast. Therefore, we have the following:
a. This is a unicast address because A in binary is 1010.
b. This is a multicast address because 7 in binary is 0111.
c. This is a broadcast address because all digits are F’s.

Standard Ethernet
10 Base 5 (Thicknet) (BusTopology)
10 Base 2 (Thinnet) (BusTopology)
10 BaseT (UTP) (Star/TreeTopology)
10 Base FL (Fiber) (Star/TreeTopology)
25
LAN Technologies

Ethernet
Physical Media :-
10 Base5 - Thick Co-axial Cable with BusTopology
10 Base2 - Thin Co-axial Cable with BusTopology
10 BaseT - UTP Cat 3/5 withTreeTopology
10 BaseFL - Multimode/Singlemode Fiber withTreeTopology
Maximum Segment Length
10 Base5 - 500 m with at most 4 repeaters (Use Bridge to extend
the network)
10 Base2 - 185 m with at most 4 repeaters (Use Bridge to extend
the network)
10 BaseT - 100 m with at most 4 hubs (Use Switch to extend the
network)
26
LAN Technologies

Fast Ethernet
100 Mbps bandwidth
Uses same CSMA/CD media access protocol and packet
format as in Ethernet.
100BaseTX (UTP) and 100BaseFX (Fiber) standards
Physical media :-
100 BaseTX - UTP Cat 5e
100 BaseFX - Multimode / Singlemode Fiber
Full Duplex/Half Duplex operations.
27
LAN Technologies

Fast Ethernet
100 BaseTX - 100 m
100 Base FX - 2 Km (Multimode Fiber)
100 Base FX - 20 km (Singlemode Fiber)
28
LAN Technologies

Gigabit Ethernet
1 Gbps bandwidth.
Uses same CSMA/CD media access protocol as in Ethernet
and is backward compatible (10/100/100 modules are
available).
1000BaseT (UTP),
1000BaseSX (Multimode Fiber) and
1000BaseLX (Multimode/Singlemode Fiber) standards.
29
LAN Technologies

10 Gig Ethernet
10 Gbps bandwidth.
Uses same CSMA/CD media access protocol as in Ethernet.
10GBase-T - Not available
10GBase-LR - 10 Km (Singlemode Fiber)
10GBase-ER - 40 Km (Singlemode Fiber)
30
LAN Technologies

Part Two
WAN Devices and Technologies

WANs
Characteristics ofWANs
 Similarities to LANs
 Interconnect computers.
 Use some form of media for the interconnection.
 Support network applications.
 Differences to LANs
 Include both data networks, such as the Internet, and voice
networks, like telephone systems.
 Interconnect more workstations, so that any one workstation can
transfer data to any other workstation.
 Cover large geographic distances, including the earth.
WAN Technologies
32

Wide Area Network Basics
 A station is a device that interfaces a user to a network.
 A node is a device that allows one or more stations to access the physical
network and is a transfer point for passing information through a
network.
 A node is often a computer, a router, or a telephone switch.
 The subnet (old terminology) or physical network is the underlying
connection of nodes and telecommunication links.
WAN Technologies
33

Types of WAN Network Subnets
 A network categorized by the way it transfers information from one node to another
as
1. Circuit switched network - a network in which a dedicated circuit is established
between sender and receiver and all data passes over this circuit.The connection is
dedicated until one party or another terminates the connection.The telephone
system is a common example.
2. Packet switched network - a network in which all data messages are transmitted
using fixed-sized packages, called packets (data gram and virtual-switched network).
 Packet-switched networks can further be divided into two subcategories-virtual-
circuit networks and datagram networks
WAN Technologies
35

Circuit-switched Networks
 A circuit-switched network consists of a set of switches connected by
physical links.
 A connection between two stations is a dedicated path made of one or
more links.
 However, each connection uses only one dedicated channel on each link.
Each link is normally divided into n channels by using FDM orTDM
36

…
 As shown above, when end system A needs to communicate with end
system M, systemA needs to request a connection to M that must be
accepted by all switches as well as by M itself.
 This is called the setup phase; a circuit (channel) is reserved on each
link, and the combination of circuits or channels defines the dedicated
path.
 After the dedicated path made of connected circuits (channels) is
established, data transfer can take place.
 After all data have been transferred, the circuits are torn down.
37

Packet Switched Networks:
Datagram Networks
 If the message is going to pass through a packet-switched network, it
needs to be divided into packets of fixed or variable size.
 The size of the packet is determined by the network and the
governing protocol.
 In packet switching, there is no resource allocation for a packet.
 This means that there is no reserved bandwidth on the links, and there
is no scheduled processing time for each packet.
 Resources are allocated on demand.The allocation is done on a first-
come, first-served basis.
38

…
 When a switch receives a packet, no matter what is the source or
destination, the packet must wait if there are other packets being
processed.
 As with other systems in our daily life, this lack of reservation may
create delay.
 In a datagram network, each packet is treated independently of all
others.
 Even if a packet is part of a multipacket transmission, the network
treats it as though it existed alone.
 Packets in this approach are referred to as datagrams.
 Datagram switching is normally done at the network layer.
39

• In this example, all four packets (or datagrams) belong to the same
message, but may travel different paths to reach their destination. This is
so because the links may be involved in carrying packets from other
sources and do not have the necessary bandwidth available to carry all
the packets from A to X.
• This approach can cause the datagrams of a transmission to arrive at
their destination out of order with different delays between the packets.
Packets may also be lost or dropped because of a lack of resources. In
most protocols, it is the responsibility of an upper-layer protocol to
reorder the datagrams or ask for lost datagrams before passing them on
to the application.
40

 The datagram networks are sometimes referred to as connectionless
networks.
 The term connectionless here means that the switch (packet switch) does not
keep information about the connection state.
 There are no setup or teardown phases.
 Each packet is treated the same by a switch regardless of its source or
destination.
41

Routing Table
 If there are no setup or teardown phases, how are
the packets routed to their destinations in a
datagram network?
 In this type of network, each switch (or packet
switch) has a routing table which is based on the
destination address.
 The routing tables are dynamic and are updated
periodically.
 The destination addresses and the corresponding
forwarding output ports are recorded in the tables.
 This is different from the table of a circuit-
switched network in which each entry is created
when the setup phase is completed and deleted
when the teardown phase is over.
42

Destination Address
 Every packet in a datagram network carries a header that contains,
among other information, the destination address of the packet.
 When the switch receives the packet, this destination address is
examined; the routing table is consulted to find the corresponding
port through which the packet should be forwarded.
 This address, unlike the address in a virtual-circuit-switched
network, remains the same during the entire journey of the packet.
 Efficiency
 The efficiency of a datagram network is better than that of a circuit-switched
network; resources are allocated only when there are packets to be transferred.
 If a source sends a packet and there is a delay of a few minutes before another
packet can be sent, the resources can be reallocated during these minutes for
other packets from other sources.
43

Virtual-circuit Networks
 A virtual-circuit network is a cross between a circuit-switched network and a
datagram network. It has some characteristics of both.
1. As in a circuit-switched network, there are setup and teardown phases in
addition to the data transfer phase.
2. Resources can be allocated during the setup phase, as in a circuit-switched
network, or on demand, as in a datagram network.
3. As in a datagram network, data are packetized and each packet carries an
address in the header.
4. As in a circuit-switched network, all packets follow the same path established
during the connection.
5. A virtual-circuit network is normally implemented in the data link layer, while
a circuit-switched network is implemented in the physical layer and a datagram
network in the network layer.
44

 The above figure is an example of a virtual-circuit network.
 The network has switches that allow traffic from sources to destinations.
 A source or destination can be a computer, packet switch, bridge, or any
other device that connects other networks.
45

WAN Hardware Devices
 Switch (layer 3 switch) - A switch is a network device that selects a
path or circuit for sending a unit of data to its next destination.
 Operates at layer 2 (and 3), and uses MAC addresses/IPAddresses to
send data to correct destination. (LAN switches are not this type)
 Modem - Short for modulator/demodulator, a modem enables a
computer to communicate with other computers over telephone lines.
 Operates at layer 1, where signals are converted from digital to analogue
and vice versa for transmission and receiving.
WAN Technologies
46

 Router - An electronic device that connects a local area network (LAN) to
a wide area network (WAN) and handles the task of routing messages
between the two networks.
 Operates at layer 3, and makes decisions using IP addresses.
Gateways
 A gateway is normally a computer that operates in all five layers of the
Internet or seven layers of OSI model.
 A gateway takes an application message, reads it, and interprets it.
 This means that it can be used as a connecting device between two
internetworks that use different models.
 For example, a network designed to use the OSI model can be connected to
another network using the Internet model.
 The gateway connecting the two systems can take a frame as it arrives from
the first system, move it up to the OSI application layer, and remove the
message.
47

WAN Technology Options
Presentation
Dial-up
Leased Line
ISDN
DSL
X.25 technology
Frame relay and virtual circuit
ATMTechnology
Cable Modem
Microwave Point-to-Point Link
VSAT
WAN Technologies
48

Dial-up
Uses POTS (Plain Old Telephone System)
Provides a low cost need based access.
Bandwidth 33.6 /56 Kbps.
On the Customer End: Modem is connected to a Telephone Line
On the Service Provider End: Remote Access Server (RAS) is
connected to Telephone Lines (33.6 Kbps connectivity) or E1/R2
Line (56 Kbps connectivity)
RAS provide dial in connectivity, authentication and metering.
Achievable bandwidth depends on the line quality.
WAN Technologies
49

Dial-up
WAN Technologies
RAS
51

Leased Line
Used to provide point-to-point dedicated network connectivity.
Each side of the line permanently connected to the other,
unlike dial-up connections, a leased line is always active.
Connecting two locations in exchange for a monthly rent, the
fee for the connection is a fixed monthly rate.
Typically, leased lines are used by businesses to connect
geographically distant offices
Analog leased line can provide maximum bandwidth of 9.6
Kbps.
Digital leased lines can provide bandwidths:
64 Kbps, 2 Mbps (E1), 8 Mbps (E2), 34 Mbps (E3) ...
WAN Technologies
52

Leased Line Internet Connectivity
WAN Technologies
ISP
Broadband
Internet
Connectivit
y
ISP
Router
Interface
Converter
Modem Router
ISP PREMISES CUSTOMER PREMISES
PSTN
53

ISDN (Integrated Service Digital Network)
Another alternative to using analog telephones lines to establish a
connection is ISDN.
It is s a set of communications standards for simultaneous digital
transmission of voice, video, data, and other network services over
the traditional circuits of the public switched telephone network.
Speed is one advantage ISDN has over telephone line connections.
ISDN network is a switched digital network consisting of ISDN
Switches.
ISDN user accesses network through a set of standard interfaces
provided by ISDN User Interfaces.
WAN Technologies
54

ISDN Connection
WAN Technologies
55

ISDN
WAN Technologies
Two types of user access are defined
Basic Access - Consists of two 64Kbps user channels (B channel)
and one 16Kbps signal channel (timing and alarm channel) (D
channel) providing service at 144 Kbps.
Primary access - Consists of thirty 64Kbps user channels (B
channels) and a 64 Kbps signal channel (timing and alarm channel)
(D channel) providing service at 2.048Mbps (One 64 Kbps channel is
used for Framing and Synchronization).
Basic
B
B
D
Information 128 Kbps
(Voice & Data)
Signaling 16Kbps
Primary
B
B
D
Information 1920 Kbps
Voice & Data
Signaling 64 Kbps
56

Digital Subscriber Line (DSL)
Digital Subscriber Line (DSL) uses the Ordinary Telephone line and is an
always-on technology.This means there is no need to dial up each time to
connect to the Internet.
Because DSL is highly dependent upon noise levels, a subscriber cannot
be any more than 5.5 kilometers (2-3 miles) from the DSL Exchange
Service can be symmetric, in which downstream and upstream speeds are
identical, or asymmetric in which downstream speed is faster than
upstream speed.
DSL comes in several varieties:
Asymmetric DSL (ADSL)
High Data Rate DSL (HDSL)
Symmetric DSL (SDSL)
Very High Data Rate DSL (VDSL)
WAN Technologies
57 DSL Modem

Cable Modems
The cable modem connects a computer to the cable company
network through the same coaxial cabling that feeds cable TV
(CATV) signals to a television set.
Uses Cable Modem at Home End and CMTS (Cable Modem
Termination System) at Head End.
Characteristics:
Shared bandwidth technology
10 Mbps to 30 Mbps downstream
128Kbps-3 Mbps upstream
Maximum Distance from provider to
customer site: 30 miles
Cable modems are primarily used to deliver
broadband Internet access in the form of cable Internet, taking
advantage of the high bandwidth of a cable television network
WAN Technologies
58

Point-to-Point Microwave Link
Typically 80-100 MHz Band or 5 GHz Radio Link band
2.4 GHzWiFi links are becoming popular
Requires Line of Sight
WAN Technologies
59

VSAT
Very Small Aperture Terminal (VSAT) provide
communication between two nodes through a powerful
Earth station called a Hub.
If two terminals want to communicate, they send their
messages to the satellite, which sends it to the Hub and the
Hub then broadcasts the message through the satellite.
Typical Bandwidth offered is 9.6/19.2/32/64/128/256/512
Kbps.
WAN Technologies
60

VSAT
Each satellite sends and receives over two bands
Uplink: From the earth to the satellite
Downlink: From the satellite to the earth
Satellite frequency bands
Band Downlink Uplink
C 3.7-4.2 GHz 5.925-6.425 GHz
Ku 11.7-12.2 GHz 14-14.5 GHz
Ku-band based networks, are used primarily in Europe and
North America and utilize the smaller sizes ofVSAT antennas.
C-band, used extensively in Asia, Africa and Latin America,
require larger antenna.
WAN Technologies
61

VSAT
 VSATs are most commonly used to transmit narrowband data
(point of sale transactions such as credit card, polling or
RFID data), or broadband data (for the provision of
Satellite Internet access to remote locations, VoIP or video).
 VSATs are also used for transportable, on-the-move (utilising
phased array antennas) or mobile maritime communications.
Pag
e
62

Reading Assignment
Read about the followingWANTechnology options
and prepare your own note
X.25 technology
Frame relay and virtual circuit
ATMTechnology
WAN Technologies
64

Chapter_6, Local Area and Wide Area Network

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