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

2. Perspective Ethernet (802.3)Ethernet physical layer standardsEthernet data link layer (MAC) StandardsAdvanced Ethernet conceptsSwitched Wide Area Networks (WANs) © 2011 Pearson Education, Inc. Publishing as Prentice Hall 2

3.  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

4.  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

5.  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

6.  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

7. Perspective Ethernet (802.3) Ethernet physical layer standardsEthernet data link layer (MAC) StandardsAdvanced Ethernet conceptsSwitched Wide Area Networks (WANs) © 2011 Pearson Education, Inc. Publishing as Prentice Hall 7

8.  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

9.  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

10.  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

11.  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

12. PerspectiveEthernet (802.3) Ethernet physical layer standards Ethernet data link layer (MAC) StandardsAdvanced Ethernet conceptsSwitched Wide Area Networks (WANs) © 2011 Pearson Education, Inc. Publishing as Prentice Hall 12

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

14. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 14 UTP and Fiber Media Standards + Ethernet-Specific Signaling Standards = Ethernet Physical Layer Standards

15. Physical Standard SpeedMax. Run Length Medium 4-Pair UTP 100BASE-TX100 Mbps 100 mCategory 5e or higher 1000BASE-T1 Gbps100 mCategory 5e or higher 10GBASE-T10 Gbps55 mCategory 6 10GBASE-T10 Gbps100 mCategory 6a or Category 7 © 2011 Pearson Education, Inc. Publishing as Prentice Hall 15 http://en.wikipedia.org/wiki/Fast_Ethernethttp://en.wikipedia.org/wiki/Gigabit_Ethernet

16. Physical Standard SpeedMax. Run Length Core (microns) Modal Bandwidth Optical fiber (850 nm) 1000BASE-SX1 Gbps220m62.5160 MHz*km 1000BASE-SX1 Gbps275 m62.5160 MHz*km 1000BASE-SX1 Gbps500 m50160 MHz*km 1000BASE-SX1 Gbps500 m50160 MHz*km © 2011 Pearson Education, Inc. Publishing as Prentice Hall 16

17.  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.

18. © 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.

19. © 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.

20.  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

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

22. © 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.

23. © 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.

24. © 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.

25. © 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.

26. PerspectiveEthernet (802.3)Ethernet physical layer standardsEthernet data link layer (MAC) StandardsAdvanced Ethernet conceptsSwitched Wide Area Networks (WANs) © 2011 Pearson Education, Inc. Publishing as Prentice Hall 26

27. © 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 1000BAS E-SX … Non- Ethernet Layer 1 Standards (802.11, etc.) Ethernet has many physical layer standards.

28. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 28 Internet Layer TCP/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 Layer 100BASE- TX 1000BASE -SX …… The 802 Committee divided the data link layer into logical link control and media access control layers.

29. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 29 Internet Layer TCP/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 Layer 100BASE- TX 1000BASE -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.

30. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 30 Internet Layer TCP/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 Layer 100BASE- TX 1000BASE -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.

31. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 31 Internet Layer TCP/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 Layer 100BASE- TX 1000BASE -SX …… Ethernet only has a single MAC layer standard.

32. 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.

33. 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).

34. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 34 4 BitsDecimal (Base 10) Hexadecimal (Base 16) 4 BitsDecimal (Base 10) Hexadecimal (Base 16) 000000 hex100088 hex 000111 hex100199 hex 001022 hex101010A hex 001133 hex101111B hex 010044 hex110012C hex 010155 hex110113D hex 011066 hex111014E hex 011177 hex111115F hex

35.  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

36. 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.

37. 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.

38. 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.

39. 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.

40. 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.

41. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 41 A packet from A1… to E5…. Must pass through Switches 1, 2, and 3.

42. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 42 Switch 1 sees that it should send the frame to E5 out Port 5.

43. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 43 Switch 2 sees that it should send the frame to E5 out Port 7.

44. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 44 Switch 3 sees that it should send the frame to E5 out Port 6.

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

46. PerspectiveEthernet (802.3)Ethernet physical layer standardsEthernet data link layer (MAC) Standards Advanced Ethernet concepts Switched Wide Area Networks (WANs) © 2011 Pearson Education, Inc. Publishing as Prentice Hall 46

47. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 47 Ethernet’s hierarchy creates single points of failure.

48. © 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.

49. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 49 RSTP turns backup links on automatically when needed. Planning backup lines is difficult. RSTP turns backup links on automatically when needed. Planning backup lines is difficult.

50. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 50 http://en.wikipedia.org/wiki/IEEE_802.1Q http://zh.wikipedia.org/wiki/IEEE_802.1Q 802.1Q

51. 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. 81-00 802.1p Priority 802.1q VLAN ID

52.  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

53. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 53 http://www.dlink.com/us/en/business-solutions/switching/managed-switches

54.  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 )

55.  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

56.  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

57.  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

58.  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)

59. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 59 A client plugging into the wall jack must authenticate itself to the Ethernet switch. RADIUS: Remote Authentication Dial In User Service

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

61. © 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.

62. PerspectiveEthernet (802.3)Ethernet physical layer standardsEthernet data link layer (MAC) StandardsAdvanced Ethernet conceptsSwitched Wide Area Networks (WANs) © 2011 Pearson Education, Inc. Publishing as Prentice Hall 62

63.  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

64.  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

65.  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

66.  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

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

68. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 68  North American Digital Hierarchy LineSpeedTypical Transmission Medium 56 kbps or 64 kbps (rare) 56 kbps or 64 kbps2-pair data-grade UTP T11.544 Mbps2P DG UTP Fractional T1128, 256, 384, 512, and 768 kbps 2-pair data-grade UTP Bonded T1sSmall multiples of 1.544 Mbps 2-pair data-grade UTP T344.736 MbpsCarrier fiber

69. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 69  CEPT (Europe) LineSpeedTypical Transmission Medium 64 kbps (rarely offered) 64 kbps2-pair data-grade UTP E12.048 Mbps2P DG UTP E334.368 MbpsCarrier fiber

70. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 70  SONET/SDH LineSpeed (Mbps)Typical Transmission Medium OC3/STM1155.52Carrier fiber OC12/STM4622.08Carrier fiber OC48/STM162,488.32Carrier fiber OC192/STM649,954.28Carrier fiber OC768/STM25639,813.12Carrier fiber Page 263

71. ADSLHDSLHDSL2SHDSL Uses existing 1p VG access line to premises? Yes* Target marketResidencesBusiness Downstream throughput A few megabits per second 768 kbps1.544 Mbps 384 kbps–2.3 Mbps Upstream throughput A few megabits per second 768 kbps1.544 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

72. ADSLHDSLHDSL2SHDSL Target marketResidencesBusiness Downstream throughput A few megabits per second 768 kbps1.544 Mbps 384 kbps–2.3 Mbps Upstream throughput A few megabits per second 768 kbps1.544 Mbps 384 kbps–2.3 Mbps Symmetric throughput? NoYes QoS throughput guarantees? NoYes © 2011 Pearson Education, Inc. Publishing as Prentice Hall 72

73.  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

74. © 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). POP: Point of Presence

75.  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

76.  X.25 ◦ 1970s technology ◦ Slow and expensive ◦ Gone today © 2011 Pearson Education, Inc. Publishing as Prentice Hall 76

77.  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

78.  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

79.  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

80.  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

81.  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

82. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 82 The virtual circuit is the best path to be followed by all frames.

83. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 83 Frames have virtual circuit numbers instead of destination host addresses.

84. © 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.

85.  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

86. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 86 PerspectiveEthernet (802.3)Ethernet physical layer standardsEthernet data link layer (MAC) StandardsAdvanced Ethernet conceptsSwitched Wide Area Networks (WANs)

87.  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

88. © 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 Hall