333: DISCUSS THE FUNDAMENTALS OF
NETWORKING
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1. Discuss networking concepts (20 hrs)
2. Discuss hardware & software requirement
to setup a Local Area Network (20 hrs)
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PERFORMANCE STANDARD
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Objectives:
◦ Given a scenario, identify correctly the hardware and
services required for a Network
◦ Define a Node/Host
◦ Discuss functional & geographical relationship among
nodes
◦ Discuss services provided by a common carrier such as
 Leased line
 Switched line
◦ Describe switching techniques
 Circuit
 Message
 Packet
◦ Discuss ISO/OSl reference model
◦ Explain network communication protocols
Discuss services
provided by a common
carrier
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You can only install wires on your own property
◦ Called your customer premises
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To send signals between sites or to customers, you
must use a carrier
Carriers transport data and voice traffic between
customer premises, charging a price for their
services
Receive rights of way from the government to lay
wires and radio links
Customer
Premises
Carrier
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In data communication, a physical network
node may either be a data circuit-terminating
equipment
(DCE)
such
as
a modem, hub, bridge or switch or a data
terminal equipment (DTE) such as a digital
telephone handset, a printer or a host
computer,
for example
a router,
a
workstation or a server.
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Dial-Up Service (Any-to-Any)
Leased Lines
◦ Point-to-point only
◦ Cheaper for high volumes of use
Switched
Dial-Up
Service
Brunei
Leased Line
Miri
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Uses POTS (Plain Old Telephone System)
Dial up networking technology provides PCs and
other network devices access to a LAN or WAN
via standard telephone lines.
Dial up Internet service providers offer
subscription plans for home computer users.
Provides a low cost need based access.
Bandwidth 33.6 /56 Kbps.
Types of dial up services include V.34 and
V.90 modem as well as Integrated Services Digital
Network (ISDN). Dial up systems utilize specialpurpose network protocols like Point-to-Point
Protocol (PPP).
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To use a dial up Internet connection, a client modem calls
another modem located at the Internet Service Provider
(ISP). The modems transfer network information over the
telephone until one modem or the other disconnects.
When the popularity of the Internet exploded in the 1990s,
dial up was the most common form of Internet access due
mainly to its low cost to setup. However, the performance
of dial up networking is relatively poor due to the
limitations of traditional modem technology. V.90 modem
dial up supports less than 56 Kbps bandwidth and ISDN
handles approximately 128Kbps.
Many home users are currently replacing their dial up
services with high-speed broadband technologies that
operate at much higher speeds.
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A leased line connects two locations for private voice
and/or data telecommunication service.
It is not a dedicated cable, a leased line is actually a
reserved circuit between two points.
Permanent telephone connection between two points
Organization ‘owns’ the leased line – not shared with
anyone else.
Leased lines can span short or long distances.
Quality of service is assured
Line access is assured
Line is always active
Fixed monthly fee
Fees based on distance and speed of connection
Switching
Office
Leased Lines
May Pass Through
Multiple Switches,
Even Multiple
Carriers
Trunk
Line
Switching
Office
Local
Loop
Customer Premises A
Trunk
Line
Switching
Office
Local
Loop
Customer Premises B
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Leased Lines are Circuits
◦ Often goes through multiple switches and trunk lines
◦ Looks to user like a simple direct link
◦ Limited to point-to-point communication
 Limits who you can talk to
◦ Carriers offer leased lines at an attractive price per bit sent
to keep high-volume customers
Switch
Trunk Line
Leased Line
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If you have several sites, you need a mesh of
leased lines among sites
Mesh
Leased Line
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Largest Demand is 56 kbps to a few Mbps
56 kbps (sometimes 64 kbps) digital leased
lines
◦ DS0 signaling
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T1 (1.544 Mbps) digital leased lines
◦ 24 times effective capacity of 56 kbps
◦ Only about 3-5 times cost of 56 kbps
◦ DS1 signaling
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Fractional T1
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T3: is the next step
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Europe has E Series
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SONET/SDH lines offer very high speeds
◦ Fraction of T1’s speed and price
◦ Often 128, 256, 384 kbps
◦ 44.7 Mbps in U.S.
◦ E1: 2.048 Mbps
◦ E3: 34 Mbps
◦ 156 Mbps, 622 Mbps, 2.5 Gbps, 10 Gbps
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Flexible level of connection based upon
your business requirements
Synchronous service where upstream and
downstream speeds are the same
Private network offers reduced security
risks as it does not use the public network
Service Level Agreement provides peace of
mind
Managed service
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Increased threats of Internet misuse has
prompted companies to add firewalls to
private leased lines to filter traffic coming
into their network
The firewall filters traffic based on rules
Can block several types of attacks
Can monitor network traffic
Can not protect against virus attacks
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Can Use Instead of Traditional Leased Lines
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HDSL (High-Speed DSL)
◦ Less expensive
◦ Symmetrical: Same speed in each direction
◦ HDSL: 768 kbps (Half a T1) on a single twisted
pair
◦ HDSL2: 1.544 Mbps (T1) on a single twisted pair
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Normal Leased Lines Used Data Grade Wires
◦ High-quality, high-cost
◦ Two pairs (one in each direction)
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DSLs Normally Use Voice Grade Copper
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Not designed for high-speed data
So sometimes works poorly
Usually one pair (ADSL, HDSL)
Sometimes two pairs (HDSL2)
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With many sites, meshes are expensive and difficult
to manage
With N sites, N*(N-1)/2 leased lines for a mesh
◦ May not need all links, but usually use many
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User firm must handle switching and ongoing
management
◦ Expensive because this requires planning and the hiring,
training, and retention of a WAN staff
Sites
5
10
25
Lines
10
45
300
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Voice Requirements
◦ Analog voice signal is encoded as a 64 kbps data
stream
◦ 8 bits per sample
◦ 8,000 samples per second
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T1 lines are designed to multiplex 24 voice
channels of 64 kbps each
T1 lines use time division multiplexing
(TDM)
◦ Time is divided into 8,000 frames per second
 One frame for each sampling period
◦ Each frame is divided into 24 8-bit slots
 One for each channel’s sample in that time period
 (24 x 8) 192 bits
 Plus one framing bit for 193 bits per frame
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Speed Calculation
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Framing Bit
◦ 193 bits per frame
◦ 8,000 frames per second
◦ 1.544 Mbps
◦ One per frame
◦ 8,000 per second
◦ Used to carry supervisory information (in groups
of 12 or 24 framing bits)
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Public Switched Data Networks
◦ Designed for data rather than voice
◦ Site-to-site switching is handled for you
◦ You merely connect each site to the PSDN “cloud”
(No need to know internal details)
PSDN
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Connect each site to the PSDN using one
leased line
◦ Only one leased line per site
◦ With N sites, you only need N leased lines, not N*
(N-1)/2 as with a full mesh
1 Leased
Line
PSDN
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Access Device Needed at Each Site
◦ Connects each site to access line
◦ Often a router
◦ Sometimes a device specific to a particular PSDN
Technology
Access
Device
PSDN
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Point of Presence (POP)
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Place where you connect to the cloud
May be several in a city
May not have any POP close
Need leased line to POP
Separate from PSDN charges
POP
Leased
Line
PSDN
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Simpler than Networks of Leased Lines
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Less Expensive than Networks of Leased
◦ Less staffing
◦ Fewer leased lines to support
Lines
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Less staffing
PSDN prices are very low
PSDN is less expensive overall
PSDNs are replacing many leased line mesh
networks
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End-to-End Capacity is Guaranteed
◦ If you need it, it is always there
◦ When you don’t need it, you still pay for it
◦ Expensive for data traffic, which usually has short
bursts and long silences
A
bcd
efg
PSDN
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Messages are divided into small units called
packets
◦ Short packets load switches more effectively than
fewer long messages
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Packet-Switched PSDNs Usually Operate at
Layer 2 (Data Link Layer for Single Subnets)
◦ Should be called frame-switched networks
◦ Still called packet-switched networks
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Packets are multiplexed on trunk lines
◦ Cost of trunk lines is shared
◦ Packet switching lowers transmission costs
◦ Dominates PSDN service today
Multiplexed
Trunk Line
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All commercial packet switched PSDNs use
virtual circuits
◦ Eliminates forwarding decisions for individual packets
◦ Reduces switching load, so reduces switching costs
Virtual
Circuit
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Most commercial PSDNs are Unreliable
◦ (Only obsolete X.25 PSDN technology was reliable)
◦ No error correction at each hop between switches
◦ Reduces costs of switching
◦ Note that both virtual circuits and unreliable service
reduce switching costs
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Packet Switching
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Virtual Circuits
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Unreliability
◦ Reduces costs of transmission lines through
multiplexing
◦ Reduces costs of switches because they do not
have to make decisions for each frame
◦ Reduces costs of switches because they do not
have to do error correction
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Question?