Ethernet LANs Chapter 4 Panko’s Business Data Networks and Telecommunications, 5th edition Copyright 2005 Prentice-Hall

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

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 802.3 Working Group develops Ethernet standards Other working groups create other standards

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

Ethernet Physical Layer Standards

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

Figure 4-1: Ethernet Physical Layer Standards, Continued Speed Maximum Run Length Medium Optical Fiber 100Base-FX 100 Mbps 2 km 62.5/125 multimode, 1300 nm, switch

Figure 4-1: Ethernet Physical Layer Standards, Continued Speed Maximum Run Length Medium 1000Base-SX 1 Gbps 220 m 62.5/125 micron multimode, 850 nm, 160 MHz-km modal bandwidth 1000Base-SX 1 Gbps 275 m 62.5/125 micron multimode, 850 nm, 200 MHz-km 1000Base-SX 1 Gbps 500 m 50/125 micron multimode, 850 nm, 400 MHz-km 1000Base-SX 1 Gbps 550 m 50/125 micron multimode, 850 nm; 500 MHz-km Gigabit Ethernet, 850 nm, various core sizes and modal bandwidths

Figure 4-1: Ethernet Physical Layer Standards, Continued Speed Maximum Run Length Medium 1000Base-LX 1 Gbps 550 m 62.5/125 micron multimode, 1310 nm 1000Base-LX 1 Gbps 5 km 9/125 micron single mode, 1310 nm Gigabit Ethernet, 1300 nm, multimode versus single mode

Perspective Access links to client stations today are dominated by 100Base-TX Trunk links today are dominated by 1000Base-SX Short trunk links, however, use UTP Longer and faster trunk links use other fiber standards

Figure 4-1: Ethernet Physical Layer Standards, Continued Speed Maximum Run Length Medium 10GBase-SR/SW 10 Gbps 65 m 62.5/125 micron multimode, 850 nm 10GBase-LX4 10 Gbps 300 m 62.5/125 micron multimode, 1300 nm, WDM with 4 lambdas 10 Gbps Ethernet, multimode S = 850 nm, L = 1300 nm R=LAN, W=WAN

Figure 4-1: Ethernet Physical Layer Standards, Continued Speed Maximum Run Length Medium 10GBase-LR/LW 10 Gbps 10 km 9/125 micron single mode, 1300 nm. 10GBase-ER/EW 10 Gbps 40 km 9/125 micron single mode, 1550 nm. 10 Gbps Ethernet, for wide area networks L = 1300 nm, E = 1550 nm R = LAN, W = WAN

Figure 4-1: Ethernet Physical Layer Standards, Continued Speed Maximum Run Length Medium 40 Gbps Ethernet 40 Gbps Under Development 9/125 micron single mode.

Figure 4-1: Ethernet Physical Layer Standards, Continued Notes: For 10GBase-x, LAN versions (R) transmit at 10 Gbps. WAN versions (W) transmit at 9.95328 Gbps for carriage over SONET/SDH links (see Chapter 6) The 40 Gbps Ethernet standards are still under preliminary development

Figure 4-2: 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

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

Figure 4-3: Link Aggregation (Trunking) 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) UTP Cord UTP Cord 100Base-TX Switch

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

Figure 4-4: 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 across a series of switches

Figure 4-4: 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 Each transmission line along the way has a distance limit.

Figure 4-4: 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 Data Link Does Not Have a Maximum Distance (420 m distance spanned in this example)

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

Figure 4-5: Layering in 802 Networks Internet Layer Data Link Layer Logical Link Control Layer Governs aspects of the communication needed by all LANs, e.g., error correction. These functions not used in practice. Media Access Control Layer Governs aspects of the communication specific to a particular LAN technology, e.g., Ethernet, 802.11 wireless LANs, etc. Physical Layer

Figure 4-5: Layering in 802 Networks, Continued 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 Other MAC Standards (802.5, 802.11, etc.) Physical Layer 10Base-T 1000 Base- SX … Other Physical Layer Standards (802.11, etc.)

Figure 4-6: The Ethernet Frame 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), Destination MAC Address (48 bits) Source MAC Address (48 bits)

Figure 4-6: The Ethernet Frame, Continued Field Length (2 Octets) Added if data field is less than 46 octets; length set to make data field plus PAD field 46 octets; Not added if data field is greater than 46 octets long. Data Field (Variable Length) LLC Subheader (Usually 8 Octets) Packet (Variable Length) PAD Field If an error is found, the frame is discarded. Frame Check Sequence (4 Octets)

Figure 4-7: Hexadecimal Notation 4 Bits (Base 2)* Decimal (Base 10) Hexadecimal (Base 16) Begin Counting at Zero 0000 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 * 2^4=16 combinations

Figure 4-7: Hexadecimal Notation, Continued 4 Bits (Base 2) Decimal (Base 10) Hexadecimal (Base 16) 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

Figure 4-7: 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-BB-3C-D7-23-FF

Figure 4-8: Multiswitch Ethernet LAN The Situation: A1… Sends to E5… 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 C3-2D-55-3B-A9-4F Switch 2, Port 5 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 D4-47-55-C4-B6-9F Switch 3, Port 2

Figure 4-8: Multi-Switch Ethernet LAN, Continued On Switch 1 Switch 2 Switching Table Switch 1 Port Station 2 A1-44-D5-1F-AA-4C 7 B2-CD-13-5B-E4-65 C3-2D-55-3B-A9-4F 5 D4-47-55-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

Figure 4-8: Multi-Switch Ethernet LAN, Continued On Switch 2 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 Switch 1 Switch 3 Switching Table Switch 2 Port Station A1-44-D5-1F-AA-4C 3 B2-CD-13-5B-E4-65 C3-2D-55-3B-A9-4F D4-47-55-C4-B6-9F 7 E5-BB-47-21-D3-56 E5-BB-47-21-D3-56 Switch 3, Port 6

Figure 4-8: Multi-Switch Ethernet LAN, Continued On Switch 3 Switch 2 Port 7 on Switch 2 to Port 4 on Switch 3 Switching Table Switch 3 Port Station 4 A1-44-D5-1F-AA-4C B2-CD-13-5B-E4-65 4 C3-2D-55-3B-A9-4F 2 D4-47-55-C4-B6-9F 6 E5-BB-47-21-D3-56 Switch 3 A1-44-D5-1F-AA-4C Switch 1, Port 2 D4-55-C4-B6-9F Switch 3, Port 2 E5-BB-47-21-D3-56 Switch 3, Port 6

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

Figure 4-9: Hub Versus Switch Operation, Continued Ethernet Switch Switch Sends Frame Out One Port. If A Is Transmitting to C, Frame Only Goes Out C’s Port. C D A B

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

Advanced Ethernet Considerations STP and RSTP VLANs Momentary Traffic Peaks

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 PC1

Figure 4-10: Hierarchical Ethernet LAN, Continued 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 Port Station 2 A1-44-D5-1F-AA-4C 7 B2-CD-13-5B-E4-65 5 E5-BB-47-21-D3-56

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

Figure 4-10: Hierarchical Ethernet LAN, Continued 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

Figure 4-11: Single Point of Failure in a Switch Hierarchy Switch Fails Switch 2 No Communication No Communication C3-2D-55-3B-A9-4F 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

Figure 4-12: 802.1D Spanning Tree Protocol Normal Operation Loop, but Spanning Tree Protocol Deactivates One Link Activated Switch 2 Activated Deactivated C3-2D-55-3B-A9-4F 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

Figure 4-12: 802.1D Spanning Tree Protocol, Continued Switch 2 Fails Deactivated Deactivated Switch 2 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

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

Figure 4-13: Virtual LAN (VLAN) with Ethernet Switches, Continued 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

Figure 4-14: Tagged Ethernet Frame (Governed By 802.1Q) Basic 802.3 MAC Frame 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). 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

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)

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

Overprovisioned Traffic Capacity in Ethernet 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 Time

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 Time

Purchasing Switches

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 buy a prebuilt switch with the right configuration Modular switches can be configured with appropriate port modules before or after purchase

Figure 4-16: Switch Purchasing Considerations, Continued 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%

Figure 4-17: Switching Matrix 100 Mbps 1 Port 1 to Port 3 100 Mbps 400 Mbps Aggregate Capacity to Be Nonblocking 2 Any-to-Any Switching Matrix 100 Mbps 3 100 Mbps 4 100Base-TX Input Ports Input Queue(s) 100Base-TX Output Ports 1 2 3 4 Note: Input Port 1 and Output Port 1 are the same port

Figure 4-16: Switch Purchasing Considerations, Continued 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

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

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

Figure 4-16: Switch Purchasing Considerations, Continued 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

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

Figure 4-16: Switch Purchasing Considerations, Continued 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

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)

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

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

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

Figure 4-21: Physical and Electrical Features, Continued 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

Figure 4-21: Physical and Electrical Features, Continued 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

Figure 4-21: Physical and Electrical Features, Continued 802.3af brings electrical power over the station’s ordinary UTP cord Limited to 12.95 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

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

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

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

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

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

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