chapter 6 panko and panko business data networks and telecommunications, 8 th edition © 2011...
TRANSCRIPT
Chapter 6
Panko and PankoBusiness Data Networks and Telecommunications, 8th Edition© 2011 Pearson Education, Inc. Publishing as Prentice Hall
Switched Network Standards
◦ Data Link layer standards
Switch operation
Frame organization
◦ Physical layer standards
Uses UTP and optical fiber
Adds standard-specific signaling
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LAN Standards: Ethernet
◦ Dominant in wired LANs
◦ Became dominant because of its low cost and adequate performance
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青春電幻物語http://zh.wikipedia.org/wiki/%E9%9D%92%E6%98%A5%E9%9B%BB%E5%B9%BB%E7%89%A9%E8%AA%9E
Switched WANs◦ Leased line networks
Company leases lines to connects its sites
Installs switches to connect the leased lines
Manages the resulting networks
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Switched WANs◦ Public Switched Data Networks (PSDNs)
PSDN vendor manages the switching cloud.
Firm only needs to install a single leased line from each site to the vendor’s nearest point of presence (POP).
Frame Relay is the dominant PSDN standard.
Metropolitan area Ethernet is growing.
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The 802 Committee
◦ Committee of the Institute for Electrical and Electronics Engineers (IEEE).
◦ IEEE created the 802 LAN/MAN Standards Committee for LAN standards.
◦ This committee is usually called the 802 Committee.
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The 802 Committee◦ The 802 Committee creates working groups for
specific types of standards.
802.1 for general standards
802.3 for Ethernet standards
802.11 for wireless LAN standards
802.16 for WiMax wireless metropolitan area network standards
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The 802.3 Working Group
◦ This group is in charge of creating Ethernet standards.
◦ The terms 802.3 and Ethernet are interchangeable today.
◦ Figure 6-4 shows Ethernet physical layer standards.
◦ Ethernet also has data link layer standards (frame organization, switch operation, etc.).
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Ethernet Standards are OSI Standards
◦ Layer 1 and Layer 2 standards are almost universally OSI standards.
◦ Ethernet is no exception.
◦ ISO must ratify them.
◦ In practice, when the 802.3 Working Group finishes standards, vendors begin building compliant products.
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UTP and Fiber Media Standards
+ Ethernet-Specific Signaling Standards
= Ethernet Physical Layer Standards
Physical Standard
Speed Max. Run Length
Medium
4-Pair UTP
100BASE-100BASE-TXTX
100 Mbps
100 m Category 5e or higher
1000BASE-T 1 Gbps 100 m Category 5e or higher
10GBASE-T 10 Gbps 55 m Category 6
10GBASE-T 10 Gbps 100 m Category 6a orCategory 7
© 2011 Pearson Education, Inc. Publishing as Prentice Hall 15http://en.wikipedia.org/wiki/Fast_Ethernet http://en.wikipedia.org/wiki/Gigabit_Ethernet
Physical Standard
Speed Max. Run Length
Core (microns)
Modal Bandwidth
Optical fiber (850 nm)
1000BASE-SX
1 Gbps 220m 62.5 160 MHz*km
1000BASE-SX
1 Gbps 275 m 62.5 160 MHz*km
1000BASE-SX
1 Gbps 500 m 50 160 MHz*km
1000BASE-SX
1 Gbps 500 m 50 160 MHz*km
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Faster Optical Fiber◦ 1 Gbps with 1,310 nm signaling: 500 m limit
◦ 10 Gbps
◦ 40 Gbps
◦ 100 Gbps
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Since the book went to press, the 802.3 Working
Group ratified the 40 Gbps and 100 Gbps standards.
Since the book went to press, the 802.3 Working
Group ratified the 40 Gbps and 100 Gbps standards.
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In baseband transmission, the signal is injected directly into the medium.
With UTP, change voltage levels.With optical fiber, turn light on or off.
In baseband transmission, the signal is injected directly into the medium.
With UTP, change voltage levels.With optical fiber, turn light on or off.
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In broadband transmission, the signal is modulated into a radio
channel and sent in a radio channel.
In broadband transmission, the signal is modulated into a radio
channel and sent in a radio channel.
Broadband transmission can carry signals farther by using amplifiers.
However, baseband transmission is less expensive, and regeneration (which we will see next) allows long distance transmission also.
Baseband transmission is simpler, so it dominates LANs today.
So BASE is in their names.
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The first physical link is 100BASE-TX,so the maximum physical span is 100 meters.
The first physical link is 100BASE-TX,so the maximum physical span is 100 meters.
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The switch regenerates the received signal.On a 1000BASE-SX link, the clean new signal
can travel up to another 220 meters.
The switch regenerates the received signal.On a 1000BASE-SX link, the clean new signal
can travel up to another 220 meters.
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The second switch also regenerates the signal.The clean regenerated signal goes on.
The second switch also regenerates the signal.The clean regenerated signal goes on.
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Physical links have maximum distance spans, but thanks to regeneration, there is no maximum
size to Ethernet network data links.
Physical links have maximum distance spans, but thanks to regeneration, there is no maximum
size to Ethernet network data links.
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Internet Layer
TCP/IP Internet Layer Standards (IP, ARP, etc.)
Other Internet Layer Standards(IPX, etc.)
Data Link Layer
Physical Layer
100BASE-TX
1000BASE-SX
…
Non-Ethernet Layer 1
Standards(802.11,
etc.)Ethernet has many physical layer
standards.Ethernet has many physical layer
standards.
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Internet LayerTCP/IP Internet Layer Standards (IP, ARP, etc.)
Other Internet Layer Standards(IPX, etc.)
Data Link
Layer
Logical Link Control Layer
802.2
Media Access Control Layer
Ethernet 802.3 MAC Layer Standard
Non-Ethernet MAC
Standards (802.11,
802.16, etc.)
Physical Layer100BASE-
TX1000BASE
-SX… …
The 802 Committee divided the data link layer into logical link
control and media access control
layers.
The 802 Committee divided the data link layer into logical link
control and media access control
layers.
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Internet LayerTCP/IP Internet Layer Standards (IP, ARP, etc.)
Other Internet Layer Standards(IPX, etc.)
Data Link
Layer
Logical Link Control Layer
802.2
Media Access Control Layer
Ethernet 802.3 MAC Layer Standard
Non-Ethernet MAC
Standards (802.11,
802.16, etc.)
Physical Layer100BASE-
TX1000BASE
-SX… …
The logical link control layer handles general work for all 802 standards.
There is a single LLC standard, 802.2.In practice, it has no significance for
Ethernet LAN managers.
The logical link control layer handles general work for all 802 standards.
There is a single LLC standard, 802.2.In practice, it has no significance for
Ethernet LAN managers.
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Internet LayerTCP/IP Internet Layer Standards (IP, ARP, etc.)
Other Internet Layer Standards(IPX, etc.)
Data Link
Layer
Logical Link Control Layer
802.2
Media Access Control Layer
Ethernet 802.3 MAC Layer Standard
Non-Ethernet MAC
Standards (802.11,
802.16, etc.)
Physical Layer100BASE-
TX1000BASE
-SX… …
The MAC layer handles standard-specific matters.Implementers must understand MAC layer
standards.
The MAC layer handles standard-specific matters.Implementers must understand MAC layer
standards.
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Internet LayerTCP/IP Internet Layer Standards (IP, ARP, etc.)
Other Internet Layer Standards(IPX, etc.)
Data Link
Layer
Logical Link Control Layer
802.2
Media Access Control Layer
Ethernet 802.3 MAC Layer Standard
Non-Ethernet MAC
Standards (802.11,
802.16, etc.)
Physical Layer100BASE-
TX1000BASE
-SX… …Ethernet only has a single MAC layer standard.Ethernet only has a single MAC layer standard.
Field
Preamble (7 octets of 10101010 for synchronization)
Start Frame Delimiter (10101011 to end synch)
Destination MAC address (48 bits)
Source MAC address (48 bits)
Tag Protocol ID (TPID, Optional, 2 octets)
Tag Control Information (TCI, optional, 2 octets)
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The first two fields synchronize the receiver’s clock with the senders clock.
If this was not done, the receiver might read bit 1,012 when it is really bit 1,102.
The first two fields synchronize the receiver’s clock with the senders clock.
If this was not done, the receiver might read bit 1,012 when it is really bit 1,102.
Field
Preamble (7 octets of 10101010 for synchronization)
Start Frame Delimiter (10101011 to end synch)
Destination MAC address (48 bits)
Source MAC address (48 bits)
Tag Protocol ID (TPID, Optional, 2 octets)
Tag Control Information (TCI, optional, 2 octets)
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The MAC address fields are 48 bits long.They are represented for humans in
hexadecimal notation (Base 16).
The MAC address fields are 48 bits long.They are represented for humans in
hexadecimal notation (Base 16).
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4 Bits Decimal(Base 10)
Hexadecimal(Base 16)
4 Bits Decimal(Base 10)
Hexadecimal(Base 16)
0000 0 0 hex 1000 8 8 hex
0001 1 1 hex 1001 9 9 hex
0010 2 2 hex 1010 10 A hex
0011 3 3 hex 1011 11 B hex
0100 4 4 hex 1100 12 C hex
0101 5 5 hex 1101 13 D hex
0110 6 6 hex 1110 14 E hex
0111 7 7 hex 1111 15 F hex
Divide a 48-bit Ethernet address into 12 four-bit “nibbles.”
Convert each nibble into a Hex symbol.
Combine two hex symbols into pairs and place a dash between pairs.
For example, A1-36-CD-7B-DF hex begins with 10100001 for A1, followed by 00110110 for 36.
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Field
Preamble (7 octets of 10101010 for synchronization
Start Frame Delimiter (10101011 to end synch)
Destination MAC address (48 bits)
Source MAC address (48 bits)
Tag Protocol ID (TPID, Optional, 2 octets)
Tag Control Information (TCI, optional, 2 octets)
Length (2 octets)
Logical Link Control (LLC subheader, 8 octets)
Packet (variable length)
PAD (Situation-Specific)
Frame Check Sequence© 2011 Pearson Education, Inc. Publishing as Prentice Hall 36
The TPID and TCI fields are optional. They are used to add priority levels of VLAN numbers.The TPID and TCI fields are optional. They are used to add priority levels of VLAN numbers.
Field
Preamble (7 octets of 10101010 for synchronization
Start Frame Delimiter (10101011 to end synch)
Destination MAC address (48 bits)
Source MAC address (48 bits)
Tag Protocol ID (TPID, Optional, 2 octets)
Tag Control Information (TCI, optional, 2 octets)
Length (2 octets)
Logical Link Control (LLC subheader, 8 octets)
Packet (variable length)
PAD (Situation-Specific)
Frame Check Sequence© 2011 Pearson Education, Inc. Publishing as Prentice Hall 37
The length field gives the length of the data field, not the total length of the frame.
The length field gives the length of the data field, not the total length of the frame.
Field
Preamble (7 octets of 10101010 for synchronization
Start Frame Delimiter (10101011 to end synch)
Destination MAC address (48 bits)
Source MAC address (48 bits)
Tag Protocol ID (TPID, Optional, 2 octets)
Tag Control Information (TCI, optional, 2 octets)
Length (2 octets)
Logical Link Control (LLC subheader, 8 octets)
Packet (variable length)
PAD (Situation-Specific)
Frame Check Sequence© 2011 Pearson Education, Inc. Publishing as Prentice Hall 38
The data field has two fields.The LLC subheader identifies the type of
packet in the data field.The packet has variable length.
The data field has two fields.The LLC subheader identifies the type of
packet in the data field.The packet has variable length.
Field
Preamble (7 octets of 10101010 for synchronization
Start Frame Delimiter (10101011 to end synch)
Destination MAC address (48 bits)
Source MAC address (48 bits)
Length (2 octets)
Logical Link Control (LLC subheader, 8 octets)
Packet (variable length)
PAD (Situation-Specific)
Frame Check Sequence
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The PAD field is added by the sender only if the data field is less than 46 octets.
The PAD field is selected so that the total of the length field and the pad is 46 octets.
The PAD field is added by the sender only if the data field is less than 46 octets.
The PAD field is selected so that the total of the length field and the pad is 46 octets.
Field
Preamble (7 octets of 10101010 for synchronization
Start Frame Delimiter (10101011 to end synch)
Destination MAC address (48 bits)
Source MAC address (48 bits)
Length (2 octets)
Logical Link Control (LLC subheader, 8 octets)
Packet (variable length)
PAD (Situation-Specific)
Frame Check Sequence
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The Frame Check Sequence field is for error detection.If an error is found, the frame is discarded.
There is no error message or request for transmission.Ethernet is not reliable.
The Frame Check Sequence field is for error detection.If an error is found, the frame is discarded.
There is no error message or request for transmission.Ethernet is not reliable.
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A packet from A1… to E5…. Must pass through
Switches 1, 2, and 3.
A packet from A1… to E5…. Must pass through
Switches 1, 2, and 3.
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Switch 1 sees that it should send the frame to E5 out Port
5.
Switch 1 sees that it should send the frame to E5 out Port
5.
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Switch 2 sees that it should send the frame to E5 out Port
7.
Switch 2 sees that it should send the frame to E5 out Port
7.
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Switch 3 sees that it should send the frame to
E5 out Port 6.
Switch 3 sees that it should send the frame to
E5 out Port 6.
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Ethernet’s hierarchy
creates single points of failure.
Ethernet’s hierarchy
creates single points of failure.
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RSTP allows backup links to be added.These are disabled until needed.
RSTP allows backup links to be added.These are disabled until needed.
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RSTP turns backup links onautomatically when needed.
Planning backup lines is difficult.
RSTP turns backup links onautomatically when needed.
Planning backup lines is difficult.
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http://en.wikipedia.org/wiki/IEEE_802.1Qhttp://zh.wikipedia.org/wiki/IEEE_802.1Q
802.1Q
Field
Preamble (7 octets of 10101010 for synchronization
Start Frame Delimiter (10101011 to end synch)
Destination MAC address (48 bits)
Source MAC address (48 bits)
Tag Protocol ID (TPID, Optional, 2 octets)
Tag Control Information (TCI, optional, 2 octets)
Length (2 octets)
Logical Link Control (LLC subheader, 8 octets)
Packet (variable length)
PAD (Situation-Specific)
Frame Check Sequence© 2011 Pearson Education, Inc. Publishing as Prentice Hall 51
The TPID and TCI fields are optional. They are used to add priority levels of VLAN numbers.The TPID and TCI fields are optional. They are used to add priority levels of VLAN numbers.
81-0081-00
802.1pPriority
802.1qVLAN ID
Benefits of VLANs
◦ VLANs reduce traffic when hosts broadcast.
Broadcasts only go to hosts on the same VLAN.
◦ VLANs give security.
Client hosts can only access servers on the same VLAN.
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http://www.dlink.com/us/en/business-solutions/switching/managed-switches
Managed switches cost substantially more than dumb switches.
However, they reduce networking staff labor because problems can be diagnosed remotely and sometimes even fixed remotely.
Management savings far offset switch costs.
Managed switches give the whole network “visibility”.
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(啞的 ,愚笨的 )
Power over Ethernet (POE)◦ Switches can supply power to devices
connected by UTP.
◦ No need for separate power to the device.
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Latest POE Standard
◦ Provide up to 25 watts to attached devices
◦ Sufficient for most wireless access points
◦ Sufficient for VoIP phones
◦ Sufficient for surveillance cameras
◦ Not sufficient for desktop or notebook PCs
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POE Switches
◦ New switches can be purchased with POE.
◦ Companies can also add POE equipment to an existing non-POE switch.
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The Threat:◦ Someone can enter a business and plug a
computer into a wall jack.
◦ This will give access to the network without going through the firewall.
The Countermeasure:◦ Require anyone plugging into an Ethernet
switch to authenticate himself or herself before being allowed beyond the switch.
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(Port-Based Access Control)
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A client plugging into the wall jack
must authenticate itself to the
Ethernet switch.
A client plugging into the wall jack
must authenticate itself to the
Ethernet switch.
RADIUS: Remote Authentication Dial In User Service
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LANs do not have to be single switched networks.
They can be internets.Individual Ethernet
networks in an internet are called subnets.
LANs do not have to be single switched networks.
They can be internets.Individual Ethernet
networks in an internet are called subnets.
Wide Area Networks (WANs)◦ Connect different sites.
WAN Purposes◦ Provide remote access to individuals who are off
site.
◦ Link sites within the same corporation.
◦ Provide Internet access.
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Carriers◦ Beyond their physical premises, companies
must use the services of regulated carriers.
◦ Carriers have rights of way for transmission in public areas.
◦ Companies are limited to whatever services the carriers provide.
◦ Prices for carrier services change abruptly and without technological reasons.
◦ Prices and service availability vary from country to country.
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High Costs and Low Speeds
◦ High cost per bit transmitted, compared with LANs
◦ Consequently, lower speeds (most commonly 256 kbps to about 50 megabits per second)
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From Chapter 1.
Leased lines are◦ Point-to-point,
◦ High-speed,
◦ Always on,
◦ All-digital,
◦ Circuits with reserved capacity
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North American Digital Hierarchy
Line Speed Typical Transmission Medium
56 kbps or 64 kbps (rare)
56 kbps or 64 kbps 2-pair data-grade UTP
T1 1.544 Mbps 2P DG UTP
Fractional T1 128, 256, 384, 512, and 768 kbps
2-pair data-grade UTP
Bonded T1s Small multiples of 1.544 Mbps
2-pair data-grade UTP
T3 44.736 Mbps Carrier fiber
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CEPT (Europe)
Line Speed Typical Transmission Medium
64 kbps (rarely offered)
64 kbps 2-pair data-grade UTP
E1 2.048 Mbps 2P DG UTP
E3 34.368 Mbps Carrier fiber
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SONET/SDH
Line Speed (Mbps) Typical Transmission Medium
OC3/STM1 155.52 Carrier fiber
OC12/STM4 622.08 Carrier fiber
OC48/STM16 2,488.32 Carrier fiber
OC192/STM64 9,954.28 Carrier fiber
OC768/STM256 39,813.12 Carrier fiber
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ADSL HDSL HDSL2 SHDSLUses existing 1p VG access line to premises?
Yes* Yes* Yes* Yes*
Target market Residences Business Business Business
Downstream throughput
A few megabits per second
768 kbps 1.544 Mbps
384 kbps–2.3 Mbps
Upstream throughput
A few megabits per second
768 kbps 1.544 Mbps
384 kbps–2.3 Mbps
* By definition. If it did not use 1p VG UTP, it would not be DSL.
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H: High-rate, SH: Super-High-rate
ADSL HDSL HDSL2 SHDSLTarget market Residences Business Business Business
Downstream throughput
A few megabits per second
768 kbps 1.544 Mbps
384 kbps–2.3 Mbps
Upstream throughput
A few megabits per second
768 kbps 1.544 Mbps
384 kbps–2.3 Mbps
Symmetric throughput?
No Yes Yes Yes
QoS throughput guarantees?
No Yes Yes Yes
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Public Switched Data Network◦ The idea is to outsource site-to-site networking
to a PSDN carrier.
◦ PSDN core is shown as a cloud because user does not care what happens there.
◦ Economies of scale, so PSDNs usually are relatively inexpensive compared to switched leased line networks.
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You only need one leased line from each site to the PSDN carrier’s nearest point of presence (POP).
You only need one leased line from each site to the PSDN carrier’s nearest point of presence (POP).
POP: Point of Presence
If you have seventeen sites and use a PSDN, how many leased lines will you need?
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X.25◦ 1970s technology
◦ Slow and expensive
◦ Gone today
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Frame Relay◦ Started to grow in the 1990s
Inexpensive and fast compared to X.25 256 kbps to about 40 Mbps This is the range of greatest corporate
demand for WAN speeds.
◦ Grew rapidly in the 1990s thanks to low prices
◦ Carriers have raised their prices to improve profit margins. This has reduced growth
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ATM◦ Created to replace the core of the Public
Switched Telephone Network
Widely adopted for the Public Switched Telephone Network core
◦ Also provided as a PSDN service
Speeds of 1 Mbps to gigabits per second
Adoption for PSDN service has been limited because of high cost and the lack of demand for very high PSDN speeds
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Metro Ethernet◦ Metropolitan area network (MAN): a city and its
environs
◦ MANs have smaller distances than national or international WANs, so lower prices and higher speeds
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Metro Ethernet
◦ Speeds of 1 Mbps to 100 Mbps and low prices
◦ No learning is needed because all firms are familiar with Ethernet
◦ Carrier can provision or reprovision service speed rapidly to meet periods of high demand
◦ The only PSDN service growing rapidly
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PSDN switches are arranged in meshes.◦ For each incoming frame, the switch must
select between multiple outgoing ports for different data links to the destination host.
With virtual circuit operation, however, PSDNs choose the best path before data transmission begins.◦ Switches do not have to consider multiple
outgoing ports, so cost is slashed.
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The virtual circuit is the best path to be followed by all frames.
The virtual circuit is the best path to be followed by all frames.
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Frames have virtual circuit numbers instead of destination host addresses.Frames have virtual circuit numbers
instead of destination host addresses.
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The switch looks up the frame’s virtual circuit number and sends the frame out the indicated
port.
The switch looks up the frame’s virtual circuit number and sends the frame out the indicated
port.
Virtual circuits reduce costs.◦ The complex work of selecting paths is done
only once—before communication begins—rather than for each frame.
Virtual circuits permit traffic engineering.◦ All frames with the same level of priority can be
given the same virtual circuit number.
◦ The firm can conduct load balancing to avoid overloading some circuits.
© 2011 Pearson Education, Inc. Publishing as Prentice Hall 85
Single Switched Networks◦ Chapter 5: Transmission media
◦ Chapter 6: Switching
Single Wireless Networks◦ Chapter 7: 802.11 WLANs
◦ Chapter 8: More on 802.11 and other wireless local and wide area networks
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© 2011 Pearson Education, Inc. Publishing as Prentice Hall 88
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Copyright © 2011 Pearson Education, Inc. Copyright © 2011 Pearson Education, Inc. Publishing as Prentice HallPublishing as Prentice Hall