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Understanding WAN Technologies | CCNA HUB
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Understand WAN Standards and Protocols
Understanding WAN Technologies Article covers the following CCNA/ICND1 Exam Topics:
Under Operation of IP Data Networks:
1. Recognize the purpose and functions of various network devices such as Routers, Switches, Bridges,
and Hubs.
2. Select the components required to meet a given network specification.
3. Predict the data flow between two hosts across a network.
Recommended Study Plan:
1. Download the ICND1v2 Exam Topics Sheet from Cisco Website.
2. Follow the Steps and the Articles under “IP Networking Fundamentals” by order.
Average Time Required Studying this Article: 1 Hour
Two Primary Networks Exist Today
Local Area Network (LAN) Wide Area Network (WAN)
Inside Our Home and Office Network called LAN, and outside called Internet or WAN. Internet for
instance, is basically a combination of Multi different WANs locations. ISPs WANs connected together
with other ISPs WANs.
WANs and LANs technologies service TCP/IP layer 1 and 2 standards; therefore, they have many
similarities. Both connections standards define:
Cabling details
Transmission speeds
Encoding
How to send data over physical link
Data link frame
And Forwarding Logic
Briefly, WAN is mainly used to connect 2 apart locations, could be campus buildings, or another state
office. One of the main differences between home LAN and WAN, that you don’t need to pay for your
inside home LAN a monthly fee since you own the switch and the cables inside your home, but you
http://www.ccnahub.com/ip-fundamentals/understanding-wan-technologies/
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Understanding WAN Technologies | CCNA HUB
23/01/15 5:51 pm
need to pay to lease a WAN connection – similar to your internet fee at home but of course more
money when it comes to business leased line such T1 or T3. The cables that run between the buildings
and under the ground as infrastructure are owned by the ISP provider (The Telco Company), hence, we
lease and pay a fee to use it.
Most Known WAN connection Type or Form
The most known type since long time, starting by:
Leased Line (DS1 or T1) physical circuit (Old style and limited)
Virtual Circuit (New style unlimited Virtual Connections) through Frame Relay Cloud, started on late
90’s.
And recently, because of the Fiber-Optic’s longer cable length used today, Ethernet through EoMPLS
can provide us with WAN connection as well.
Leased lines have been around for almost 20 years. Leased Line has too many names:
Leased Circuit, Virtual Circuit
Serial Link or Line
Point to Point Link or Line
T1 or T3
WAN Link or Line
However, many people today use the generic term Service Provider or Internet Service Provider (ISP)
to refer to company (Telco Company– Old Term) that provides a form of WAN, including Internet
services.
WAN’s Leased Line
Lease Line between 2 routers is just a Crossover Cable similar to an Ethernet Crossover cable but with
few distance limitations, rather, a lease line can go for miles. Each router can send any time – FullDuplex – over a leased Line, for tens, hundreds, or even thousands of miles. The speed is Symmetric,
meaning that both routers send and receive bits at the same speed. Synchronous, meaning the
Upstream and the Downstream is the same, which is good for businesses especially if they have WebServers in-house, and not like home Cable or DSL where it is Asymmetric and Asynchronous, meaning
the Downstream is more than the Upstream.
How leased Lines can be used by Routers?
http://www.ccnahub.com/ip-fundamentals/understanding-wan-technologies/
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Understanding WAN Technologies | CCNA HUB
23/01/15 5:51 pm
The main goal for a WAN is to move data between LANs. In 1990’s and before the internet boosts,
companies used WAN to connect Main office with branch offices and different locations. From a
networking perspective, think of each site as being one or more LANS that need to communicate with
each other, and to communicate, those LANs need to be connected to each other using a WAN type
connection. Usually the router connected to LAN at one interface port and another at WAN link which
is between 2 routers. (Note: most of business these days use DSL, Cable, or T1 for Internet instead of
dedicated private Lease Lines, and if they are looking for secure connection between their sites, they
use VPN connections which equivalent to private lease line and much cheaper), the following figure
shows a small Network with one Leased Line.
The world of WAN technologies includes many different options and types of WAN can be used, in
addition to the leased line shown in the figure. WAN technologies include a large number of options for
physical links, as well as the Data Link protocols that control these links. If you have to compare WAN
technologies with LAN technologies, the wired LAN world basically has one major option today –
which is Ethernet – because Ethernet won the home and office wired battle in the marketplace back in
the 1980’s and 1990’s.
The physical component of T1 Leased Line
Long time ago in the 1990’s and when the WAN started, there was special component to run the leased
line. We can compare this component to a Cable Modem or DSL modem now days. The following
summarizes what was needed in terms of component in order to connect to a Leased Line from the
customer’s end.
Customer premise equipment (CPE): This Telco term refers to the gear that sits at their
customer’s sites. (This is the Router owned by the customer.)
Channel service unit/data service unit (CSU/DSU): This device provides a function called
Clocking, in which it physically controls the speed and timing at which the router serial interface sends
and receives each bit over the serial cable. (Very similar to a Cable or DSL modem box that connects
to our Router these days)
http://www.ccnahub.com/ip-fundamentals/understanding-wan-technologies/
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Understanding WAN Technologies | CCNA HUB
23/01/15 5:51 pm
Serial Cable: This is a short cable that connects the CSU and the router serial interface. (Similar to
an Ethernet cable that connects the Cable or DSL modem to our Netgear or Linksys Router)
Now days, many routers use serial interfaces usually exist as part of a removable card on the router,
called WAN interface cards, and the CSU/DSU became built in inside these removable interface cards.
The following figures show how the CSU used to be a separate box and how later it evolved to be part of
the card itself.
As shown in the above figure how the router connects through a v.35 serial cable and that’s why it’s
called serial port.
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Understanding WAN Technologies | CCNA HUB
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This figure shows the serial card interface with 2 serial ports; serial ports are used to connect to
CSU/DSU.
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Understanding WAN Technologies | CCNA HUB
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And as you can see from this figure, there is no need for a Modem any more. Rather, will be RJ-45
cable comes straight from the wall (the Telco connection) and plugged in the T1 DSU/CSU port as
shown in the figure WIC-1DSU-T1. It has Built-In CSU/DSU.
Leased Line and its variety of speed
Telco companies offer a wide variety of speeds for leased lines. However, a Telco customer cannot pick
just any speed. Instead, the speeds follow the standards of an age-old technology called the T-carrier
system.
Back in 1950’s and 1960’s, the US based Bell companies developed and deployed digital voice and the
T-carrier system. As part of that work, they standardized different transmission speeds, including 64
Kbps, 1.544 Mbps, and 44.736 Mbps. (64 Kbps is the minimum required for one voice over IP call)
Bell companies also developed time-division multiplexing (TDM) technology that let them combine
multiple of these base speeds onto a single line. For Example, one popular standard, a Digital Signal
Level 1 (DS1, or known by T1, combines 24 DS0s which is equal to 64Kbps each plus 8Kbps overhead
into one physical line that runs at 1.544Mbps.
And you can get faster speed of multiples of T1 as well (Up to 28 T1 lines), which became T3 at speed of
http://www.ccnahub.com/ip-fundamentals/understanding-wan-technologies/
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Understanding WAN Technologies | CCNA HUB
23/01/15 5:51 pm
44.736Mbps. (T1 and T3 are Symmetric/Synchronous connections that provide upstream and
downstream at the same rate with same speed both ends.
So the various speeds can be broken down as follows:
Minimum is DS0=64Kbps (Probably the Dialup Connection goes here)
Multiples of DS0 (up to 24 DS0 lines)=1.544Mbps – called DS1 or T1 Line (Mostly used by small
businesses)
Multiples of DS1 or T1 Lines (up to 28 T1 lines)=44.736Mbps (Mostly used by large businesses,
colleges, and government)
A good advantage of a Leased Line or T1/T3 is the dedicated bandwidth you gain when you sign for
such service since it is a symmetric. The Internet Cable modem and most DSL are asymmetric
connections that share the bandwidth among the customers. It is worth to mention that some Telco
companies these days provide a Fiber Optic service such Verizon FIOS which is very similar to a Leased
line in terms of speed and bandwidth, for instance you can subscribe for 20Mbps as Upstream and
Downstream from FIOS and available to home and businesses.
CSU/DSU role and its relation to speed
The CSU controls the speed; either it is separate box or built-in Interface card that plays a big role in
the leased line speed. If the customer subscribed for a fractional T1 which could be 256Kbps, and
rather than giving the customer T1 speed, the CSU controls the speed at a fractional rate through
something called Clocking. Tells the router when to send and receives bits, and at which rate of
impulse or Clock.
Similar to the Wall Clock that ticks every second at certain rate. The clocking in this case is measured
by an electrical impulse, meaning, if a customer subscribed for a fractional T1 than the rate of the clock
is slower than fully 1.544Mbos T1 rate. Which means, the router won’t be able to send or receive data
unless it sense the clock rate, slower clock impulse=fractional T1, Faster Impulse=T1 and so on. The
clock rate is measured and configured by the Telco Company Engineer based on or per Lease Lines
Packages.
How to simulate T1 Leased Line using 2 Routers
You can create your own WAN at home equivalent of leased line using a cabling trick. In reality dealing
with CSU, the serial cable that connects from CSU to the router has two different ends:
The end that connects to CSU Box called Data Circuit-terminating Equipment (DCE) which controls
http://www.ccnahub.com/ip-fundamentals/understanding-wan-technologies/
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Understanding WAN Technologies | CCNA HUB
23/01/15 5:51 pm
the speed.
Other end called Data Terminal Equipment (DTE) connects to the router.
Basically, we are connecting 2 routers in here, but what’s happening: instead of leasing a Line to study,
we are simulating a Leased Line. One end acts as ISP CSU equipment that provides Clocking (Rate
Control) and another router’s end acts as our Router in the office. By connecting 2 routers as shown
below, you can create a WAN link for testing using serial interfaces using one DTE and DCE combined
cable. The DCE/DTE cable does the same thing as Ethernet crossover cable between like type devices
(switch connected to switch).
The router with the DCE cable installed must provide clocking rate. A router serial interface can
provide clocking, but it can do so only if a DCE cable is connected to the interface and by the
configuration of clock rate command. Note, that the more recent version of IOS, when the router
notices a DCE cable connected to a serial interface, even with no clock rate command configured, the
router automatically add a clock rate command automatically so the link can be used.
Next: Understanding Data Link Layer Encapsulation
Print
PDF
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Understanding WAN Technologies | CCNA HUB
23/01/15 5:51 pm
About Imad Daou
Founder of CCNA HUB. Imad has more than 10 years of experience as Field Service and Consulting IT
Engineer. A+, Network+, Server+, Security+, Storage+, HP, Dell, and IBM Hardware Certified. Follow
Imad by one of your favorite social Networks below.
Facebook • Twitter • Linkedin • Google •
http://www.ccnahub.com/ip-fundamentals/understanding-wan-technologies/
Page 9 of 9
23/01/15 5:51 pm
Understand WAN Standards and Protocols
Understanding WAN Technologies Article covers the following CCNA/ICND1 Exam Topics:
Under Operation of IP Data Networks:
1. Recognize the purpose and functions of various network devices such as Routers, Switches, Bridges,
and Hubs.
2. Select the components required to meet a given network specification.
3. Predict the data flow between two hosts across a network.
Recommended Study Plan:
1. Download the ICND1v2 Exam Topics Sheet from Cisco Website.
2. Follow the Steps and the Articles under “IP Networking Fundamentals” by order.
Average Time Required Studying this Article: 1 Hour
Two Primary Networks Exist Today
Local Area Network (LAN) Wide Area Network (WAN)
Inside Our Home and Office Network called LAN, and outside called Internet or WAN. Internet for
instance, is basically a combination of Multi different WANs locations. ISPs WANs connected together
with other ISPs WANs.
WANs and LANs technologies service TCP/IP layer 1 and 2 standards; therefore, they have many
similarities. Both connections standards define:
Cabling details
Transmission speeds
Encoding
How to send data over physical link
Data link frame
And Forwarding Logic
Briefly, WAN is mainly used to connect 2 apart locations, could be campus buildings, or another state
office. One of the main differences between home LAN and WAN, that you don’t need to pay for your
inside home LAN a monthly fee since you own the switch and the cables inside your home, but you
http://www.ccnahub.com/ip-fundamentals/understanding-wan-technologies/
Page 1 of 9
Understanding WAN Technologies | CCNA HUB
23/01/15 5:51 pm
need to pay to lease a WAN connection – similar to your internet fee at home but of course more
money when it comes to business leased line such T1 or T3. The cables that run between the buildings
and under the ground as infrastructure are owned by the ISP provider (The Telco Company), hence, we
lease and pay a fee to use it.
Most Known WAN connection Type or Form
The most known type since long time, starting by:
Leased Line (DS1 or T1) physical circuit (Old style and limited)
Virtual Circuit (New style unlimited Virtual Connections) through Frame Relay Cloud, started on late
90’s.
And recently, because of the Fiber-Optic’s longer cable length used today, Ethernet through EoMPLS
can provide us with WAN connection as well.
Leased lines have been around for almost 20 years. Leased Line has too many names:
Leased Circuit, Virtual Circuit
Serial Link or Line
Point to Point Link or Line
T1 or T3
WAN Link or Line
However, many people today use the generic term Service Provider or Internet Service Provider (ISP)
to refer to company (Telco Company– Old Term) that provides a form of WAN, including Internet
services.
WAN’s Leased Line
Lease Line between 2 routers is just a Crossover Cable similar to an Ethernet Crossover cable but with
few distance limitations, rather, a lease line can go for miles. Each router can send any time – FullDuplex – over a leased Line, for tens, hundreds, or even thousands of miles. The speed is Symmetric,
meaning that both routers send and receive bits at the same speed. Synchronous, meaning the
Upstream and the Downstream is the same, which is good for businesses especially if they have WebServers in-house, and not like home Cable or DSL where it is Asymmetric and Asynchronous, meaning
the Downstream is more than the Upstream.
How leased Lines can be used by Routers?
http://www.ccnahub.com/ip-fundamentals/understanding-wan-technologies/
Page 2 of 9
Understanding WAN Technologies | CCNA HUB
23/01/15 5:51 pm
The main goal for a WAN is to move data between LANs. In 1990’s and before the internet boosts,
companies used WAN to connect Main office with branch offices and different locations. From a
networking perspective, think of each site as being one or more LANS that need to communicate with
each other, and to communicate, those LANs need to be connected to each other using a WAN type
connection. Usually the router connected to LAN at one interface port and another at WAN link which
is between 2 routers. (Note: most of business these days use DSL, Cable, or T1 for Internet instead of
dedicated private Lease Lines, and if they are looking for secure connection between their sites, they
use VPN connections which equivalent to private lease line and much cheaper), the following figure
shows a small Network with one Leased Line.
The world of WAN technologies includes many different options and types of WAN can be used, in
addition to the leased line shown in the figure. WAN technologies include a large number of options for
physical links, as well as the Data Link protocols that control these links. If you have to compare WAN
technologies with LAN technologies, the wired LAN world basically has one major option today –
which is Ethernet – because Ethernet won the home and office wired battle in the marketplace back in
the 1980’s and 1990’s.
The physical component of T1 Leased Line
Long time ago in the 1990’s and when the WAN started, there was special component to run the leased
line. We can compare this component to a Cable Modem or DSL modem now days. The following
summarizes what was needed in terms of component in order to connect to a Leased Line from the
customer’s end.
Customer premise equipment (CPE): This Telco term refers to the gear that sits at their
customer’s sites. (This is the Router owned by the customer.)
Channel service unit/data service unit (CSU/DSU): This device provides a function called
Clocking, in which it physically controls the speed and timing at which the router serial interface sends
and receives each bit over the serial cable. (Very similar to a Cable or DSL modem box that connects
to our Router these days)
http://www.ccnahub.com/ip-fundamentals/understanding-wan-technologies/
Page 3 of 9
Understanding WAN Technologies | CCNA HUB
23/01/15 5:51 pm
Serial Cable: This is a short cable that connects the CSU and the router serial interface. (Similar to
an Ethernet cable that connects the Cable or DSL modem to our Netgear or Linksys Router)
Now days, many routers use serial interfaces usually exist as part of a removable card on the router,
called WAN interface cards, and the CSU/DSU became built in inside these removable interface cards.
The following figures show how the CSU used to be a separate box and how later it evolved to be part of
the card itself.
As shown in the above figure how the router connects through a v.35 serial cable and that’s why it’s
called serial port.
http://www.ccnahub.com/ip-fundamentals/understanding-wan-technologies/
Page 4 of 9
Understanding WAN Technologies | CCNA HUB
23/01/15 5:51 pm
This figure shows the serial card interface with 2 serial ports; serial ports are used to connect to
CSU/DSU.
http://www.ccnahub.com/ip-fundamentals/understanding-wan-technologies/
Page 5 of 9
Understanding WAN Technologies | CCNA HUB
23/01/15 5:51 pm
And as you can see from this figure, there is no need for a Modem any more. Rather, will be RJ-45
cable comes straight from the wall (the Telco connection) and plugged in the T1 DSU/CSU port as
shown in the figure WIC-1DSU-T1. It has Built-In CSU/DSU.
Leased Line and its variety of speed
Telco companies offer a wide variety of speeds for leased lines. However, a Telco customer cannot pick
just any speed. Instead, the speeds follow the standards of an age-old technology called the T-carrier
system.
Back in 1950’s and 1960’s, the US based Bell companies developed and deployed digital voice and the
T-carrier system. As part of that work, they standardized different transmission speeds, including 64
Kbps, 1.544 Mbps, and 44.736 Mbps. (64 Kbps is the minimum required for one voice over IP call)
Bell companies also developed time-division multiplexing (TDM) technology that let them combine
multiple of these base speeds onto a single line. For Example, one popular standard, a Digital Signal
Level 1 (DS1, or known by T1, combines 24 DS0s which is equal to 64Kbps each plus 8Kbps overhead
into one physical line that runs at 1.544Mbps.
And you can get faster speed of multiples of T1 as well (Up to 28 T1 lines), which became T3 at speed of
http://www.ccnahub.com/ip-fundamentals/understanding-wan-technologies/
Page 6 of 9
Understanding WAN Technologies | CCNA HUB
23/01/15 5:51 pm
44.736Mbps. (T1 and T3 are Symmetric/Synchronous connections that provide upstream and
downstream at the same rate with same speed both ends.
So the various speeds can be broken down as follows:
Minimum is DS0=64Kbps (Probably the Dialup Connection goes here)
Multiples of DS0 (up to 24 DS0 lines)=1.544Mbps – called DS1 or T1 Line (Mostly used by small
businesses)
Multiples of DS1 or T1 Lines (up to 28 T1 lines)=44.736Mbps (Mostly used by large businesses,
colleges, and government)
A good advantage of a Leased Line or T1/T3 is the dedicated bandwidth you gain when you sign for
such service since it is a symmetric. The Internet Cable modem and most DSL are asymmetric
connections that share the bandwidth among the customers. It is worth to mention that some Telco
companies these days provide a Fiber Optic service such Verizon FIOS which is very similar to a Leased
line in terms of speed and bandwidth, for instance you can subscribe for 20Mbps as Upstream and
Downstream from FIOS and available to home and businesses.
CSU/DSU role and its relation to speed
The CSU controls the speed; either it is separate box or built-in Interface card that plays a big role in
the leased line speed. If the customer subscribed for a fractional T1 which could be 256Kbps, and
rather than giving the customer T1 speed, the CSU controls the speed at a fractional rate through
something called Clocking. Tells the router when to send and receives bits, and at which rate of
impulse or Clock.
Similar to the Wall Clock that ticks every second at certain rate. The clocking in this case is measured
by an electrical impulse, meaning, if a customer subscribed for a fractional T1 than the rate of the clock
is slower than fully 1.544Mbos T1 rate. Which means, the router won’t be able to send or receive data
unless it sense the clock rate, slower clock impulse=fractional T1, Faster Impulse=T1 and so on. The
clock rate is measured and configured by the Telco Company Engineer based on or per Lease Lines
Packages.
How to simulate T1 Leased Line using 2 Routers
You can create your own WAN at home equivalent of leased line using a cabling trick. In reality dealing
with CSU, the serial cable that connects from CSU to the router has two different ends:
The end that connects to CSU Box called Data Circuit-terminating Equipment (DCE) which controls
http://www.ccnahub.com/ip-fundamentals/understanding-wan-technologies/
Page 7 of 9
Understanding WAN Technologies | CCNA HUB
23/01/15 5:51 pm
the speed.
Other end called Data Terminal Equipment (DTE) connects to the router.
Basically, we are connecting 2 routers in here, but what’s happening: instead of leasing a Line to study,
we are simulating a Leased Line. One end acts as ISP CSU equipment that provides Clocking (Rate
Control) and another router’s end acts as our Router in the office. By connecting 2 routers as shown
below, you can create a WAN link for testing using serial interfaces using one DTE and DCE combined
cable. The DCE/DTE cable does the same thing as Ethernet crossover cable between like type devices
(switch connected to switch).
The router with the DCE cable installed must provide clocking rate. A router serial interface can
provide clocking, but it can do so only if a DCE cable is connected to the interface and by the
configuration of clock rate command. Note, that the more recent version of IOS, when the router
notices a DCE cable connected to a serial interface, even with no clock rate command configured, the
router automatically add a clock rate command automatically so the link can be used.
Next: Understanding Data Link Layer Encapsulation
http://www.ccnahub.com/ip-fundamentals/understanding-wan-technologies/
Page 8 of 9
Understanding WAN Technologies | CCNA HUB
23/01/15 5:51 pm
About Imad Daou
Founder of CCNA HUB. Imad has more than 10 years of experience as Field Service and Consulting IT
Engineer. A+, Network+, Server+, Security+, Storage+, HP, Dell, and IBM Hardware Certified. Follow
Imad by one of your favorite social Networks below.
Facebook • Twitter • Linkedin • Google •
http://www.ccnahub.com/ip-fundamentals/understanding-wan-technologies/
Page 9 of 9
