Ethernet LANs Chapter 4 Copyright 2004 Prentice-Hall Panko’s Business Data Networks and Telecommunications, 5 th edition

2 Perspective Ethernet is the dominant LAN technology You need to know it well Basic Ethernet switching is very simple However, large Ethernet networks require more advanced knowledge

3 Ethernet History Developed at Xerox Palo Alto Research Center in the 1970s After a trip to the University of Hawai`i’s Alohanet project Taken over by the IEEE 802 LAN/MAN Standards Committee is in charge of LAN Standards Working Group develops Ethernet standards Other working groups create other standards

4 Ethernet Standards are OSI Standards Ethernet standards are LAN standards LANs (and WANs) are single networks Single networks are based on Layer 1 (physical) and Layer 2 (data link) standards OSI dominates standards at these layers Ethernet standards are OSI standards Must be ratified by ISO, but this is a mere formality

5 Figure 4-1: Ethernet Physical Layer Standards Physical Layer Standard MediumMaximum Run Length Speed UTP 100Base-TX4-pair Category 5 or better 100 meters100 Mbps 1000Base-T4-pair Category 5 or better 100 meters1,000 Mbps 10Base-T4-pair Category 3 or better 100 meters10 Mbps* *With autosensing, 100Base-TX NICs and switches will slow to 10 Mbps for 10Base-T devices. Often called 10/100 Ethernet

6 Figure 4-1: Ethernet Physical Layer Standards Physical Layer Standard MediumMaximum Run Length Speed Optical Fiber 100Base-FX62.5/125 multimode, 1300 nm 2 km100 Mbps

7 Figure 4-1: Ethernet Physical Layer Standards Physical Layer Standard MediumMaximum Run Length Speed 1000Base-SX62.5/125 micron multimode, 850 nm, 200 MHz-km 275 m1 Gbps 1000Base-SX50/125 micron multimode, 850 nm, 400 MHz-km 500 m1 Gbps 1000Base-SX62.5/125 micron multimode, 850 nm, 160 MHz-km modal bandwidth 220 m1 Gbps Gigabit Ethernet, 850 nm, various core sizes and modal bandwidths 1000Base-SX50/125 micron multimode, 850 nm; 500 MHz-km 550 m1 Gbps

8 Figure 4-1: Ethernet Physical Layer Standards Physical Layer Standard MediumMaximum Run Length Speed 1000Base-LX62.5/125 micron multimode, 1300 nm 550 m1 Gbps 1000Base-LX9/125 micron single-mode, 1300 nm 5 km1 Gbps Gigabit Ethernet, 1300 nm, multimode versus single-mode

9 Perspective Access links to client stations today are dominated by 100Base-TX Trunk links today are dominated by 100Base- SX Short trunk links, however, use UTP Longer and faster trunk links use other fiber standards

10 Figure 4-1: Ethernet Physical Layer Standards Physical Layer Standard MediumMaximum Run Length Speed 10GBase-LX4 62.5/125 micron multimode, 1300 nm, WDM with 4 lambdas 300 m10 Gbps 10GBase-SR/SW62.5/125 micron multimode, 850 nm 65 m10 Gbps 10 Gbps Ethernet, multimode S = 850 nm, L = 1300 nm R=LAN, W=WAN

11 Figure 4-1: Ethernet Physical Layer Standards Physical Layer Standard MediumMaximum Run Length Speed 10GBase-LR/LW9/125 micron single mode, 1300 nm. 10 km10 Gbps 10GBase-ER/EW9/125 micron single mode, 1550 nm. 40 km10 Gbps 10 Gbps Ethernet, for wide area networks L = 1300 nm, E = 1550 nm R = LAN, W = WAN

12 Figure 4-1: Ethernet Physical Layer Standards Physical Layer Standard MediumMaximum Run Length Speed 40 Gbps Ethernet 9/125 micron single mode. Under Development 40 Gbps

13 Figure 4-1: Ethernet Physical Layer Standards Notes: For 10GBase-x, LAN versions (R) transmit at 10 Gbps. WAN versions (W) transmit at Gbps for carriage over SONET/SDH links (see Chapter 6) The 40 Gbps Ethernet standards are still under preliminary development

14 Figure 4-2: Baseband Versus Broadband Transmission Baseband Transmission Source Signal Transmitted Signal (Same) Transmission Medium Signal is injected directly into the transmission medium (wire, optical fiber) Inexpensive, so dominates wired LAN transmission technology

15 Figure 4-2: Baseband Versus Broadband Transmission Broadband Transmission Source Radio Tuner Modulated Signal Radio Channel Signal is first modulated to a higher frequency, then sent in a radio channel Expensive but needed for radio-based networks

16 Figure 4-3: Link Aggregation (Trunking) UTP Cord UTP Cord 100Base-TX Switch Two links provide 200 Mbps of trunk capacity between the switches No need to buy a more expensive Gigabit Ethernet port Switch must support link aggregation (trunking)

17 Figure 4-4: Data Link Using Multiple Switches Original Signal Received Signal Regenerated Signal Switches regenerate signals before sending them out; This removes errors

18 Figure 4-4: Data Link Using Multiple Switches Original Signal Received Signal Received Signal Received Signal Regenerated Signal Regenerated Signal Thanks to regeneration, signals can travel far across a series of switches

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

20 Figure 4-4: Data Link Using Multiple Switches Data Link Does Not Have a Maximum Distance (420 m distance spanned in this example) Original Signal Received Signal Received Signal Received Signal Regenerated Signal Regenerated Signal UTP 62.5/125 Multimode Fiber 100Base-TX (100 m maximum) Physical Link 100Base-TX (100 m maximum) Physical Link 1000Base-SX (220 m maximum) Physical Link

21 Figure 4-5: Layering in 802 Networks Governs aspects of the communication Needed by all LANs, e.g., error correction. These functions not used in practice. Governs aspects of the communication Specific to a particular LAN technology, e.g., Ethernet, wireless LANs, etc. Physical Layer Media Access Control Layer Logical Link Control Layer Data Link Layer Internet Layer

22 Figure 4-5: Layering in 802 Networks TCP/IP Internet Layer Standards (IP, ARP, etc.) Other Internet Layer Standards (IPX, etc.) Ethernet MAC Layer Standard Physical Layer Media Access Control Layer Other MAC Standards (802.5, , etc.) 10Base-T 1000 Base- SX … Logical Link Control Layer Other Physical Layer Standards (802.11, etc.) Data Link Layer Internet Layer

23 Figure 4-6: The Ethernet Frame Preamble (7 Octets) … Start-of-Frame Delimiter (1 Octet) Destination MAC Address (48 bits) Source MAC Address (48 bits) Field Computers use raw 48-bit MAC addresses; Humans use Hexadecimal notation (A1-23-9C-AB-33-53), Which is discussed Later.

24 Figure 4-6: The Ethernet Frame Length (2 Octets) PAD Field Field Packet (Variable Length) LLC Subheader (Usually 7 Octets) Data Field (Variable Length) Frame Check Sequence (4 Octets) Added if data field Is less than 46 octets; Length set to make data filed plus PAD field 46 octets; Not added if data field is greater than 46 octets long. If an error is found, the frame is discarded.

25 Figure 4-7: Hexadecimal Notation 4 Bits (Base 2)* Decimal (Base 10) Hexadecimal (Base 16) hex hex hex * 2^4=16 combinations hex hex hex hex hex Begin Counting at Zero

26 Figure 4-7: Hexadecimal Notation 4 Bits (Base 2) Decimal (Base 10) Hexadecimal (Base 16) hex hex A hex B hex C hex D hex E hex F hex After 9, Count A Through F

27 Figure 4-7: Hexadecimal Notation Converting 48-Bit MAC Addresses to Hex Start with the 48-bit MAC Address … Break the MAC address into twelve 4-bit “nibbles” … 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-BB-3C-D7-23-FF

28 Figure 4-8: Multi-Switch Ethernet LAN Switch 2 Switch 1 Switch 3 Port 5 on Switch 1 to Port 3 on Switch 2 Port 7 on Switch 2 to Port 4 on Switch 3 C3-2D-55-3B-A9-4F Switch 2, Port 5 A1-44-D5-1F-AA-4C Switch 1, Port 2 E5-BB D3-56 Switch 3, Port 6 D4-47-C4-B6-9F Switch 3, Port 2 B2-CD-13-5B-E4-65 Switch 1, Port 7 The Situation: A1… Sends to E5…

29 Figure 4-8: Multi-Switch Ethernet LAN Switching Table Switch 1 PortStation 2A1-44-D5-1F-AA-4C 7B2-CD-13-5B-E4-65 5C3-2D-55-3B-A9-4F 5D C4-B6-9F 5E5-BB D3-56 Switch 2 Switch 1 Port 5 on Switch 1 to Port 3 on Switch 2 A1-44-D5-1F-AA-4C Switch 1, Port 2 B2-CD-13-5B-E4-65 Switch 1, Port 7 E5-BB D3-56 Switch 3, Port 6 On Switch 1

30 Figure 4-8: Multi-Switch Ethernet LAN Switch 2 Switch 1 Switch 3 Port 5 on Switch 1 to Port 3 on Switch 2 Port 7 on Switch 2 to Port 4 on Switch 3 C3-2D-55-3B-A9-4F Switch 2, Port 5 Switching Table Switch 2 PortStation 3A1-44-D5-1F-AA-4C 3B2-CD-13-5B-E4-65 5C3-2D-55-3B-A9-4F 7D C4-B6-9F 7E5-BB D3-56 E5-BB D3-56 Switch 3, Port 6 On Switch 2

31 Figure 4-8: Multi-Switch Ethernet LAN Switch 2 Switch 3 Port 7 on Switch 2 to Port 4 on Switch 3 A1-44-D5-1F-AA-4C Switch 1, Port 2 D4-55-C4-B6-9F Switch 3, Port 2 Switching Table Switch 3 PortStation 4A1-44-D5-1F-AA-4C 4B2-CD-13-5B-E4-65 4C3-2D-55-3B-A9-4F 2D C4-B6-9F 6E5-BB D3-56 E5-BB D3-56 Switch 3, Port 6 On Switch 3

32 Figure 4-9: Hub Versus Switch Operation AB CD Ethernet Hub Hub Broadcasts Each Bit If A Is Transmitting to C, B Must Wait to Transmit

33 Figure 4-9: Hub Versus Switch Operation AB CD Ethernet Switch Switch Sends Frame Out One Port; If A Is Transmitting to C, Frame Only Goes Out C’s Port.

34 Figure 4-9: Hub Versus Switch Operation AB CD Ethernet Switch Switch Sends Frame Out One Port If A Is Transmitting to C, B Can Transmit to D Simultaneously

35 Figure 4-10: Hierarchical Ethernet LAN Ethernet Switch F Server Y Server X Client PC1 Single Possible Path Between Client PC 1 and Server Y Ethernet Switch E Ethernet Switch D Ethernet Switch B Ethernet Switch A Ethernet Switch C

36 Figure 4-10: Hierarchical Ethernet LAN Only one possible path between stations Therefore only one entry per MAC address in switching table The switch can find the one address quickly, with little effort This makes Ethernet switches inexpensive per frame handled Low cost has led to Ethernet’s LAN dominance PortStation 2A1-44-D5-1F-AA-4C 7B2-CD-13-5B-E4-65 5E5-BB D3-56

37 Figure 4-10: Hierarchical Ethernet LAN Workgroup Ethernet Switch F Core and Workgroup Switches Workgroup Ethernet Switch E Workgroup Ethernet Switch D Core Ethernet Switch B Core Ethernet Switch A Core Ethernet Switch C Core

38 Figure 4-10: Hierarchical Ethernet LAN Workgroup switches connect to stations via access lines Core switches higher in the hierarchy connect switches to other switches via trunk lines The core is the collection of all core switches Core switches need more capacity than workgroup switches because they have to handle the traffic of many conversations instead of just a few

39 Figure 4-11: Single Point of Failure in a Switch Hierarchy No Communication Switch 1 Switch 2 Switch 3 Switch Fails A1-44-D5-1F-AA-4C B2-CD-13-5B-E4-65 C3-2D-55-3B-A9-4F D C4-B6-9F E5-BB D3-56

40 Figure 4-12: 802.1D Spanning Tree Protocol Switch 1 Switch 2 Switch 3 A1-44-D5-1F-AA-4C B2-CD-13-5B-E4-65 C3-2D-55-3B-A9-4F D C4-B6-9F E5-BB D3-56 Activated Deactivated Normal Operation Loop, but Spanning Tree Protocol Deactivates One Link

41 Figure 4-12: 802.1D Spanning Tree Protocol Switch 1 Switch 2 Switch 3 A1-44-D5-1F-AA-4C B2-CD-13-5B-E4-65 C3-2D-55-3B-A9-4F D C4-B6-9F E5-BB D3-56 Deactivated Reactivated Switch 2 Fails

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

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

44 Figure 4-14: Tagged Ethernet Frame (Governed By 802.1Q) Destination Address (6 Octets) Destination 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) hex; 33,024 decimal, So Tagged. Larger than 1,500, So not a Length Field 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 MAC FrameTagged MAC Frame Start-of-Frame Delimiter (1 Octet) Preamble (7 octets) Start-of-Frame Delimiter (1 Octet) Preamble (7 octets) Source Address (6 Octets)

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

46 Figure 4-15: Handling Momentary Traffic Peaks with Overprovisioning and Priority Traffic Network Capacity Momentary Traffic Peak: Congestion and Latency Time Congestion and Latency

47 Figure 4-15: Handling Momentary Traffic Peaks with Overprovisioning and Priority Traffic Overprovisioned Network Capacity Momentary Peak: No Congestion Time Overprovisioned Traffic Capacity in Ethernet

48 Figure 4-15: Handling Momentary Traffic Peaks with Overprovisioning and Priority Traffic Network Capacity Momentary Peak Time Priority in Ethernet High-Priority Traffic Goes Low-Priority Waits

49 Figure 4-16: Switch Purchasing Considerations Number and Speeds of Ports Decide on the number of ports needed and the speed of each Often can by a prebuilt switch with the right configuration Modular switches can be configured with appropriate port modules before or after purchase

50 Figure 4-16: Switch Purchasing Considerations Switching Matrix Throughput (Figure 4-17) Aggregate throughput: total speed of switching matrix Nonblocking capacity: switching matrix sufficient even if there is maximum input on all ports Less than nonblocking capacity is workable For core switches, at least 80% For workgroup switches, at least 20%

51 Figure 4-17: Switching Matrix Mbps 1234 Port 1 to Port Mbps Aggregate Capacity to Be Nonblocking Input Queue(s) 100Base-TX Input Ports 100Base-TX Output Ports Any-to-Any Switching Matrix Note: Input Port 1 and Output Port 1 are the same port

52 Figure 4-16: Switch Purchasing Considerations Store-and-Forward Versus Cut-Through Switching (Figure 4-18) Store-and-forward Ethernet switches read whole frame before passing it on Cut-through Ethernet switches read only some fields before passing it on Perspective: Cut-through switches have less latency, but this is rarely important

53 Figure 4-18: Store-and-Forward Versus Cut-Through Switching Preamble Start-of-Frame Delimiter Destination Address Source Address Tag Fields if Present Length Cyclical Redundancy Check Data (and Perhaps PAD) Cut-Through Based On MAC Destination Address (14 Octets) Cut-Through for Priority or VLANs (24 Octets) Cut-Through at 64 Bytes (Not a Runt) Store-and- Forward Processing Ends Here (Often Hundreds Of Bytes)

54 Figure 4-19: Jitter Jitter Variability in latency from cell to cell. Makes voice sound jittery (Figure 4-19) High Jitter (High Variability in Latency) Low Jitter (Low Variability in Latency)

55 Figure 4-16: Switch Purchasing Considerations Manageability Manager controls many managed switches (Figure 4-20: Managed Switches) Polling to collect data and problem diagnosis Fixing switches remotely by changing their configurations Providing network administrator with summary performance data

56 Figure 4-20: Manageable Switches Manager Command to Change Configuration Get Data Data Requested Managed Switch

57 Figure 4-16: Switch Purchasing Considerations Manageability Managed switches are substantially more expensive than unmanageable switches To purchase and even more to operate However, in large networks, the savings in labor costs and rapid response are worth it

58 Figure 4-21: Physical and Electrical Features Form Factor Switches fit into standard 19 in (48 cm) wide equipment racks Sometimes, racks are built into enclosed equipment cabinets Switch heights usually are multiples of 1U (1.75 inches or 4.4 cm) 19 inches (48 cm)

59 Figure 4-21: Physical and Electrical Features Port Flexibility Fixed-port switches No flexibility: number of ports is fixed 1U or 2U tall Most workgroup switches are fixed-port switches

60 Figure 4-21: Physical and Electrical Features Port Flexibility Stackable Switches Fixed number of ports 1U or 2U tall High-speed interconnect bus connects stacked switches Ports can be added in as few as 12

61 Figure 4-21: Physical and Electrical Features Port Flexibility Modular Switches 1U or 2U tall Contain one or a few modules Each module contains 1 to 4 ports

62 Figure 4-21: Physical and Electrical Features Port Flexibility Chassis switches Several U tall Contain several expansion slots Each expansion board contains 6 to 12 slots Most core switches are chassis switches

63 Figure 4-21: Physical and Electrical Features UTP Uplink Ports Normal Ethernet RJ-45 switch ports transmit on Pins 3 and 6 and listen on Pins 1 and 2 (NICs do the reverse) If you connect two normal ports on different switches, they will not be able to communicate Most switches have an uplink port, which transmits on Pins 1 and 2. You can connect a UTP uplink port on one switch to any normal port on a parent switch

64 Figure 4-21: Physical and Electrical Features 802.3af brings electrical power over the station’s ordinary UTP cord Limited to watts (at 48 volts) Sufficient for wireless access points (Chapter 5) Sufficient for IP telephones (Chapter 6) Not sufficient for computers Automatic detection of compatible devices; will not send power to incompatible devices

65 Topics Covered Who develops Ethernet standards? Many physical layer standards (100Base-TX, 1000Base-SX, etc.) Baseband versus broadband transmission Link aggregation Switch signal regeneration allows maximum distances spanning several UTP and fiber links

66 Topics Covered MAC and LLC layers Ethernet Frame Preamble and Start of Frame Delimiter fields 48-bit Source and Destination Address fields Length field (length of data field) Data field LLC subheader Packet PAD if needed to make data field + PAD 64 bits long

67 Topics Covered Ethernet Frame Frame check sequence field Discard if detect error: unreliable Hexadecimal Notation For humans, not computers Multi-Switch LAN Operation with Switching Tables

68 Topics Covered Hubs versus Switches Hierarchical Topology Only one possible path between any two end stations Makes switching decisions easy and fast This makes the cost per frame handled low Key to Ethernet’s LAN dominance Core and Workgroup Switches

69 Topics Covered VLANs to reduce congestion due to server broadcasting Handling Momentary Traffic Peaks Overprovisioning—least expensive Ethernet choice today Priority is more efficient but more expensive to do Tagged Frames for VLANs and Priority

70 Topics Covered Switch Purchasing Decisions Number and speeds of ports Switch matrix capacity and nonblocking switches Store-and-forward versus cut-though switches Jitter Manageability Form factor (U) Port flexibility UTP uplink ports 802.3af for electrical power