1. COS 338 Day 7

2. DAY 7 Agenda Questions? Capstone Proposal must be approved by OCT 6 Submit at any time (prior to Oct 6) using format specified in Capstone guidelines Today is Lecture on Ethernet LANS and Exam #1 (again) Chap 1-3, open book, open notes, 60 min, 25 M/c questions

3. Figure 4-8: Multiswitch 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-47-21-D3-56 Switch 3, Port 6 D4-47-55-C4-B6-9F Switch 3, Port 2 B2-CD-13-5B-E4-65 Switch 1, Port 7 The Situation: A1… Sends to E5…

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

5. Figure 4-8: Multi-Switch Ethernet LAN, Continued 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 7D4-47-55-C4-B6-9F 7E5-BB-47-21-D3-56 E5-BB-47-21-D3-56 Switch 3, Port 6 On Switch 2

6. Figure 4-8: Multi-Switch Ethernet LAN, Continued 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 2D4-47-55-C4-B6-9F 6E5-BB-47-21-D3-56 E5-BB-47-21-D3-56 Switch 3, Port 6 On Switch 3

7. 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 X

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

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

10. Advanced Ethernet Considerations STP and RSTP VLANs Momentary Traffic Peaks

11. 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

12. 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 PortStation 2A1-44-D5-1F-AA-4C 7B2-CD-13-5B-E4-65 5E5-BB-47-21-D3-56

13. Figure 4-10: Hierarchical Ethernet LAN, Continued 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

14. 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

15. 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 D4-47-55-C4-B6-9F E5-BB-47-21-D3-56

16. 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 D4-47-55-C4-B6-9F E5-BB-47-21-D3-56 Activated Deactivated Normal Operation Loop, but Spanning Tree Protocol Deactivates One Link

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

18. 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

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

20. 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) 1000000100000000 81-00 hex; 33,024 decimal. 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 802.3 MAC FrameTagged 802.3 MAC Frame Start-of-Frame Delimiter (1 Octet) Preamble (7 octets) Start-of-Frame Delimiter (1 Octet) Preamble (7 octets) Source Address (6 Octets)

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

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

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

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

25. Purchasing Switches

26. 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

27. 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%

28. Figure 4-17: Switching Matrix 1 2 3 4 100 Mbps 1234 Port 1 to Port 3 400 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

29. 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

30. 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)

31. 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)

32. 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

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

34. 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

35. 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)

36. 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

37. 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

38. 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

39. 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

40. 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

41. 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

42. 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

43. 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

44. 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

45. 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

46. 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

47. 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