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Ethernet LANs

Ethernet LANs. Chapter 4. Figure 4-1: A Short History of Ethernet Standards. Ethernet The dominant wired LAN technology today Only “competitor” is wireless LANs (which actually are supplementary) The IEEE 802 Committee

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Ethernet LANs

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  1. Ethernet LANs Chapter 4

  2. Figure 4-1: A Short History of Ethernet Standards • Ethernet • The dominant wired LAN technology today • Only “competitor” is wireless LANs (which actually are supplementary) • The IEEE 802 Committee • LAN standards development is done primarily by the Institute for Electrical and Electronics Engineers (IEEE) • IEEE created the 802 LAN/MAN Standards Committee for LAN standards (the 802 Committee)

  3. Figure 4-1: A Short History of Ethernet Standards • The 802 Committee creates working groups for specific types of standards • 802.1 for general standards • 802.3 for Ethernet standards • The terms 802.3 and Ethernet are interchangeable • 802.11 for wireless LAN standards • 802.16 for WiMax wireless metropolitan area network standards

  4. Figure 4-1: A Short History of Ethernet Standards • Ethernet Standards are OSI Standards • Single networks, including LANs, are governed by physical and data link layer standards • Layer 1 and Layer 2 standards are almost universally OSI standards • Ethernet is no exception • The IEEE makes 802.3 standards; ISO ratifies them • In practice, when 802.3 finishes standards, vendors begin building compliant products

  5. Ethernet Physical Layer Standards

  6. Figure 4-3: Baseband Versus Broadband Transmission Baseband Transmission Signal Transmitted Signal (Same) Source Transmission Medium Signal is injected directly into the transmission medium (wire, optical fiber) Inexpensive, so dominates wired LAN transmission technology BASE in standard names means baseband

  7. Figure 4-3: Baseband Versus Broadband Transmission, Continued Broadband Transmission Modulated Signal Radio Channel Source Radio Tuner The radio tuner modulates the signal to a higher frequency. The transceiver then sends the signal in a radio channel. Expensive but needed for radio-based networks. Not used in Ethernet, but is used in wireless LANs (discussed in Chapter 5).

  8. Figure 4-2: Ethernet Physical Layer Standards UTP Physical Layer Standards Speed Maximum Run Length Medium Required 10BASE-T 10 Mbps 100 meters 4-pair Category 3 or higher 100BASE-TX 100 Mbps 100 meters 4-pair Category 5 or higher 1000BASE-T (Gigabit Ethernet) 1,000 Mbps 100 meters 4-pair Category 5 or higher 100BASE-TX dominates access links today, Although 1000BASE-T is growing in access links today

  9. Figure 4-2: Ethernet Physical Layer Standards, Continued Fiber Physical Layer Standards Speed Maximum Run Length Medium 850 nm light (inexpensive) Multimode fiber 1000BASE-SX 1 Gbps 220 m 62.5 microns 160 MHz-km 1000BASE-SX 1 Gbps 275 m 62.5 200 1000BASE-SX 1 Gbps 500 m 50 400 1000BASE-SX 1 Gbps 550 m 50 500 The 1000BASE-SX standard dominates trunk links today. Carriers use 1310 and 1550 nm light and single-mode fiber.

  10. 10 Gbps Ethernet Revised • 10 Gbps Ethernet usage is small but growing • Several 10 Gbps fiber standards are defined, but none is dominant

  11. 10 Gbps Ethernet Revised • 10 Gbps Ethernet usage is small but growing • Several 10 Gbps 10GBASE-x fiber standards are defined, but none is dominant • Copper is cheaper than fiber but cannot go as far • 10GBASE-CX4 (shielded Infiniband cable) up to 15 m • UTP • Category 6: 55 meters maximum (UTP) • Category 6A: 100 meters (UTP) • Category 7: 100 meters (shielded twisted pair, STP, which has metal shielding around each pair and around the cord)

  12. 100 Gbps Ethernet New Information • 100 Gbps has been selected as the next Ethernet speed • Chosen over 40 Gbps • 100 Gbps Ethernet standards development is just getting underway

  13. Figure 4-4: Link Aggregation (Trunking or Bonding) 1000BASE-SX Switch We have been looking at single cords Link aggregation or bonding allows you to bond two or more cords between two switches In this example, if you need 1.6 Gbps, two bonded 1 Gbps links will meet your need at lower cost than moving to a 10 Gbps switch. Link aggregation allows incremental growth in speed and cost 1 Gbps Cord 1 Gbps Cord 1000BASE-SX Switch

  14. Figure 4-5: Data Link Using Multiple Switches Original Signal Received Signal Regenerated Signal Switches regenerate signals before sending them out; this removes propagation effects. It therefore allows signals to travel farther.

  15. Figure 4-5: Data Link Using Multiple Switches, Continued Received Signal Original Signal Received Signal Received Signal Regenerated Signal Regenerated Signal Thanks to regeneration, signals can travel far acrossa series of switches

  16. Figure 4-5: Data Link Using Multiple Switches, Continued Received Signal Received Signal Original Signal Received Signal Regenerated Signal Regenerated Signal 62.5/125 Multimode Fiber UTP UTP 100BASE-TX (100 m maximum) Physical Link 1000BASE-SX (220 m maximum) Physical Link 100BASE-TX (100 m maximum) Physical Link Each trunk line along the way has a distance limit

  17. Station-to-station data link does not have a maximum distance (420 m maximum distance in this example) Figure 4-5: Data Link Using Multiple Switches, Continued Received Signal Original Signal Received Signal Received Signal Regenerated Signal Regenerated Signal 62.5/125 Multimode Fiber UTP UTP 100BASE-TX (100 m maximum) Physical Link 1000BASE-SX (220 m maximum) Physical Link 100BASE-TX (100 m maximum) Physical Link

  18. Ethernet Data Link (MAC) Layer Standards 802 Layering Frame Syntax Switch Operation

  19. Figure 4-6: Layering in 802 Networks, Continued InternetLayer TCP/IP Internet Layer Standards (IP, ARP, etc.) Other Internet Layer Standards (IPX, etc.) The 802 LAN/MAN Standards Committee subdivided the data link layer The media access control (MAC) layer handles details specific to a particular technology (Ethernet 802.3, 802.11 for wireless LANs, etc.) The logical link control layer handles some general functions: Connection to the internet layer, etc.; Not important to corporate networking professionals Data Link Layer Logical Link Control Layer 802.2 Media Access Control Layer Ethernet 802.3 MAC Layer Standard Non-Ethernet MAC Standards (802.5, 802.11, etc.) Physical Layer 100BASE- TX 1000 Base- SX … Non-Ethernet Physical Layer Standards (802.11, etc.)

  20. Figure 4-6: Layering in 802 Networks, Continued InternetLayer TCP/IP Internet Layer Standards (IP, ARP, etc.) Other Internet Layer Standards (IPX, etc.) Ethernet only has a single MAC standard (The 802.3 MAC Layer Standard) Ethernet has many physical layer standards (Fig. 4-2) Data Link Layer Logical Link Control Layer 802.2 Media Access Control Layer Ethernet 802.3 MAC Layer Standard Non-Ethernet MAC Standards (802.5, 802.11, etc.) Physical Layer 100BASE- TX 1000 BASE- SX … Non-Ethernet Physical Layer Standards (802.11, etc.)

  21. Figure 4-7: The Ethernet MAC Layer Frame Field Preamble and Start of Frame Delimiter Strong repeating 10… pattern. Synchronizes receiver’s clock with sender’s clock Like quarterback calling out “Hut 1, Hut 2, Hut 3 …” to synchronize the team Preamble (7 Octets) 10101010 … Start of Frame Delimiter (1 Octet) 10101011 Destination MAC Address (48 bits) Source MAC Address (48 bits)

  22. Figure 4-7: The Ethernet MAC-Layer Frame, Continued Field Preamble (7 Octets) 10101010 … Start of Frame Delimiter (1 Octet) 10101011 Computers use raw 48-bit MAC addresses; Humans use Hexadecimal notation (A1-23-9C-AB-33-53), which is discussed next. Destination MAC Address (48 bits) Source MAC Address (48 bits)

  23. Figure 4-8: Hexadecimal Notation 4 Bits (Base 2)* Decimal (Base 10) Hexadecimal (Base 16) Symbol Begin Counting at Zero 0000 0 0 hex 0001 1 1 hex 0010 2 2 hex 0011 3 3 hex 0100 4 4 hex 0101 5 5 hex 0110 6 6 hex 0111 7 7 hex • With 4 bits, there are 24=16 possible symbols. • For example, 01-34-CD-7B-DF hex begins with 00000001 for 01.

  24. Figure 4-8: Hexadecimal Notation, Continued 4 Bits (Base 2) Decimal (Base 10) Hexadecimal (Base 16) Symbol 1000 8 8 hex 1001 9 9 hex 1010 10 A hex 1011 11 B hex After 9, Count A Through F 1100 12 C hex 1101 13 D hex 1110 14 E hex 1111 15 F hex

  25. Figure 4-8: Hexadecimal Notation, Continued • Converting 48-Bit MAC Addresses to Hex • Start with the 48-bit MAC Address • 1010000110111011 … • Break the MAC address into twelve 4-bit “nibbles” • 1010 0001 1101 1101 … • Convert each nibble to a hex symbol • A 1 D D • Write the hex symbols in pairs (each pair is an octet) and put a dash between each pair • A1-DD-3C-D7-23-FF

  26. Figure 4-7: The Ethernet MAC Layer Frame, Continued Field Length field gives the length of the data field in octets Length (2 Octets) Data Field (Variable Length) LLC Subheader (Usually 8 Octets) Data field contains A packet of variable length Packet is preceded in the data field by an LLC subheader that describes the type of packet (IP, IPX, etc.) Packet (Variable Length) PAD Frame Check Sequence (4 Octets)

  27. Figure 4-7: The Ethernet MAC Layer Frame, Continued Field Length (2 Octets) A PAD is added if the data field is less than 46 octets; length is set to make the data field plus PAD field 46 octets; A PAD field is not added if data field is greater than 46 octets long. Data Field (Variable Length) LLC Subheader (Usually 8 Octets) Packet (Variable Length) PAD Frame Check Sequence (4 Octets)

  28. Figure 4-7: The Ethernet MAC Layer Frame, Continued Field Sender computes the frame check sequence field value based on the bits in the other fields. The receiver redoes the computation. If it gets a different results, the frame must have a transmission error. The receiver discards the frame. There is no error correction.Ethernet is not reliable. Length (2 Octets) Data Field (Variable Length) LLC Subheader (Usually 8 Octets) Packet (Variable Length) PAD Frame Check Sequence (4 Octets)

  29. Figure 4-9: Multiswitch Ethernet LAN Switch 2 Port 7 on Switch 2 to Port 4 on Switch 3 Port 5 on Switch 1 to Port 3 on Switch 2 The Situation:A1… Sends to E5… Frame must go through3 switches along the way(1, 2, and then 3) Switch 1 Switch 3 B2-CD-13-5B-E4-65 Switch 1, Port 7 E5-BB-47-21-D3-56 Switch 3, Port 6 A1-44-D5-1F-AA-4C Switch 1, Port 2 D5-47-55-C4-B6-9F Switch 3, Port 2

  30. Figure 4-9: Multiswitch Ethernet LAN, Continued On Switch 1 Switch 2 Switching Table Switch 1 PortStation 2 A1-45-D5-1F-AA-4C 7 B2-CD-13-5B-E4-65 5 D5-47-55-C4-B6-9F 5 E5-BB-47-21-D3-56 Port 5 on Switch 1 to Port 3 on Switch 2 Switch 1 B2-CD-13-5B-E4-65 Switch 1, Port 7 A1-44-D5-1F-AA-4C Switch 1, Port 2 E5-BB-47-21-D3-56 Switch 3, Port 6

  31. Figure 4-9: Multiswitch Ethernet LAN, Continued On Switch 2 Switch 2 Port 5 on Switch 1 to Port 3 on Switch 2 Port 7 on Switch 2 to Port 4 on Switch 3 Switch 1 Switch 3 • Switching Table Switch 2 • PortStation • A1-44-D5-1F-AA-4C • 3 B2-CD-13-5B-E4-65 • D5-47-55-C4-B6-9F • 7 E5-BB-47-21-D3-56 E5-BB-47-21-D3-56 Switch 3, Port 6

  32. Figure 4-9: Multiswitch Ethernet LAN, Continued Switch 2 • Switching Table Switch 3 • PortStation • 4 A1-44-D5-1F-AA-4C • B2-CD-13-5B-E4-65 • 2 D5-47-55-C4-B6-9F • 6 E5-BB-47-21-D3-56 Port 7 on Switch 2 to Port 4 on Switch 3 Switch 3 On Switch 3 A1-44-D5-1F-AA-4C Switch 1, Port 2 D5-47-55-C4-B6-9F Switch 3, Port 2 E5-BB-47-21-D3-56 Switch 3, Port 6

  33. Figure 4-10: Hierarchical Ethernet LAN Single Possible Path Between Client PC 1 and Server Y Ethernet Switch A Ethernet Switch C Ethernet Switch B Ethernet Switch F Ethernet Switch D Ethernet Switch E Server X Server Y Client PC 1

  34. Figure 4-10: Hierarchical Ethernet LAN, Continued • With only one possible path between stations… • Therefore there is only one possible port on a switch to send the frame back out • Therefore only one row per MAC address in switching table • Switch can find the one row quickly • This makes Ethernet switches inexpensive per frame • Low cost has ledto Ethernet’sLAN dominance PortStation 2 A1-44-D5-1F-AA-4C 7 B2-CD-13-5B-E4-65 5 E5-BB-47-21-D3-56

  35. Figure 4-10: Hierarchical Ethernet LAN, Continued Core Core Switches Core Ethernet Switch A Workgroup Ethernet Switch D Core Ethernet Switch C Core Ethernet Switch B Workgroup Ethernet Switch F Workgroup Ethernet Switch E As noted in Chapter 3, there are workgroup and core switches. Core switches need more capacity. Workgroup Switch

  36. Figure 4-11: Single Point of Failure in a Switch Hierarchy Switch Fails Switch 2 No Communication No Communication Switch 1 Switch 3 B2-CD-13-5B-E4-65 D4-47-55-C4-B6-9F E5-BB-47-21-D3-56 A1-44-D5-1F-AA-4C

  37. Figure 4-12: 802.1D Spanning Tree Protocol (STP) Loop, but Spanning Tree Protocol Deactivates One Link Normal Operation Activated Switch 2 Activated Deactivated Switch 1 Switch 3 B2-CD-13-5B-E4-65 D4-47-55-C4-B6-9F E5-BB-47-21-D3-56 A1-44-D5-1F-AA-4C

  38. Figure 4-12: 802.1D Spanning Tree Protocol (STP), Continued Switch 2 Fails Deactivated Switch 2 Deactivated Reactivated Switch 1 Switch 3 C3-2D-55-3B-A9-4F B2-CD-13-5B-E4-65 D4-47-55-C4-B6-9F A1-44-D5-1F-AA-4C E5-BB-47-21-D3-56

  39. Figure 4-12: 802.1D (STP), Continued • Spanning Tree Protocol (STP) • Works but when there is a break in the hierarchy, the network converges to a new hierarchy too slowly • Rapid Spanning Tree Protocol (RSTP) • Newer algorithm that converges very quickly

  40. Virtual LANs (VLANs)

  41. Figure 4-13: Virtual LAN (VLAN) with Ethernet Switches Server Broadcasting without VLANS Servers Sometimes Broadcast; Goes To All Stations; Latency Results Server Broadcast Client C Client B Client A Server D Server E

  42. Figure 4-13: Virtual LAN (VLAN) with Ethernet Switches, Continued Server Broadcasting with VLANS With VLANs, Broadcasts Only Go To a Server’s VLAN Clients; Less Latency Server Broadcast No No Client C on VLAN1 Client B on VLAN2 Client A on VLAN1 Server D on VLAN2 Server E on VLAN1

  43. Figure 4-13: Virtual LAN (VLAN) with Ethernet Switches, Continued • VLANs primarily reduce congestion due to latency • They can also be used for security • Only people on a server’s VLAN can reach it • This provides some degree of security • Not sufficient by itself, but it can help • Wireless LANs • In wireless LANs, wireless clients may be initially placed in a VLAN that only has a single server—a server that authenticates the clients • After authentication, clients are allowed beyond the initial VLAN

  44. Figure 4-14: Tagged Ethernet Frame (Governed By 802.1Q) By looking at the value in the 2 octets after the addresses, the switch can tell if this frame is a basic frame (value less than 1,500) or a tagged (value is 33,024). Basic 802.3 MAC Frame Tagged 802.3 MAC Frame Preamble (7 octets) Preamble (7 octets) Start-of-Frame Delimiter (1 Octet) Start-of-Frame Delimiter (1 Octet) Destination Address (6 Octets) Destination Address (6 Octets) Source Address (6 Octets) Source Address (6 Octets) Length (2 Octets) Length of Data Field in Octets 1,500 (Decimal) Maximum Tag Protocol ID (2 Octets) 1000000100000000 81-00 hex; 33,024 decimal. Larger than 1,500, So not a Length Field

  45. Figure 4-14: Tagged Ethernet Frame (Governed By 802.1Q), Continued Basic 802.3 MAC Frame Tagged 802.3 MAC Frame Data Field (variable) Tag Control Information (2 Octets) Priority Level (0-7) (3 bits); VLAN ID (12 bits) 1 other bit PAD (If Needed) Length (2 Octets) Frame Check Sequence (4 Octets) Data Field (variable) PAD (If Needed) Frame Check Sequence (4 Octets)

  46. Figure 4-15: Handling Momentary Traffic Peaks with Overprovisioning and Priority Momentary Traffic Peak:Congestion and Latency Traffic Momentary Traffic Peak: Congestion and Latency Network Capacity Momentary traffic peaks usually last only a fraction of a second; They occasionally exceed the network’s capacity. When they do, frames will be delayed, even dropped. Time

  47. Figure 4-15: Handling Momentary Traffic Peaks with Overprovisioning and Priority, Continued Overprovisioned Traffic Capacity in Ethernet Traffic Overprovisioned Network Capacity Momentary Peak: No Congestion Overprovisioning: Build high capacity than will rarely if ever be exceeded. This wastes capacity. But cheaper than using priority (next) Time

  48. Figure 4-15: Handling Momentary Traffic Peaks with Overprovisioning and Priority, Continued Priority in Ethernet Traffic Momentary Peak High-Priority Traffic Goes Low-Priority Waits Network Capacity Priority: During momentary peaks, give priority to traffic that is intolerant of latency (delay), such as voice. No need to overprovision, but expensive to implement. Ongoing management is very expensive. Time

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