chapter 6 panko and panko business data networks and telecommunications, 8 th edition © 2011...

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Chapter 6 Panko and Panko Business Data Networks and Telecommunications, 8 th Edition © 2011 Pearson Education, Inc. Publishing as Prentice Hall

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Chapter 6

Panko and PankoBusiness Data Networks and Telecommunications, 8th Edition© 2011 Pearson Education, Inc. Publishing as Prentice Hall

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 2

Switched Network Standards

◦ Data Link layer standards

Switch operation

Frame organization

◦ Physical layer standards

Uses UTP and optical fiber

Adds standard-specific signaling

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 3

LAN Standards: Ethernet

◦ Dominant in wired LANs

◦ Became dominant because of its low cost and adequate performance

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 4

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

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 5

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 6

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 7

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 8

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

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 9

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.).

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 10

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 11

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 12

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 13

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 14

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

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 16

Faster Optical Fiber◦ 1 Gbps with 1,310 nm signaling: 500 m limit

◦ 10 Gbps

◦ 40 Gbps

◦ 100 Gbps

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 17

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 18

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 19

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 20

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 21

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 22

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 23

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 24

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 25

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 26

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 27

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 28

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 29

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 30

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 31

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)

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 32

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)

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 33

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).

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 34

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 35

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

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 39

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

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 40

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 41

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 42

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 43

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 44

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 45

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 46

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 47

Ethernet’s hierarchy

creates single points of failure.

Ethernet’s hierarchy

creates single points of failure.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 48

RSTP allows backup links to be added.These are disabled until needed.

RSTP allows backup links to be added.These are disabled until needed.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 49

RSTP turns backup links onautomatically when needed.

Planning backup lines is difficult.

RSTP turns backup links onautomatically when needed.

Planning backup lines is difficult.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 50

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 52

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 53

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”.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 54

(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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 55

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

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 56

POE Switches

◦ New switches can be purchased with POE.

◦ Companies can also add POE equipment to an existing non-POE switch.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 57

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 58

(Port-Based Access Control)

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 59

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

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 60

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 61

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.

© 2011 Pearson Education, Inc.  Publishing as Prentice Hall 62

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 63

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 64

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)

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 65

From Chapter 1.

Leased lines are◦ Point-to-point,

◦ High-speed,

◦ Always on,

◦ All-digital,

◦ Circuits with reserved capacity

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 66

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 67

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 68

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

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 69

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

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 70

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

Page 263

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 71

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

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 72

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 73

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 74

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?

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 75

X.25◦ 1970s technology

◦ Slow and expensive

◦ Gone today

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 76

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

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 77

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

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 78

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

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 79

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

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 80

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 81

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 82

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.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 83

Frames have virtual circuit numbers instead of destination host addresses.Frames have virtual circuit numbers

instead of destination host addresses.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 84

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

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 86

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

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 87

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 88

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any

means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. Printed in the

United States of America.

Copyright © 2011 Pearson Education, Inc.  Copyright © 2011 Pearson Education, Inc.  Publishing as Prentice HallPublishing as Prentice Hall