1. The Building Blocks: LAN Shared and Switched Ethernet Connecting Devices Ethernet Access Methods Network Operating Systems Best Practice LAN Designs

2. Review Layered communication: OSI model

3. Ethernet Frame Layout

4. Shared Ethernet Topology Shared Ethernet’s logical topology is a bus topology. This means all computers on the network receive messages from all other computers, whether the message is intended for those computers or not. When a frame is received by a computer, the first task is to read the frame’s destination address to see if the message is meant for it or not.

5. Shared Ethernet Topology

6. If the message is not intended for a computer, the computer discards the message. If the message is intended for a computer, the computer processes the message and move it up to the next layer of the OSI model. Ethernets today use a physical star topology, with the network’s computers linked into hubs. It is also common to link use multiple hubs to form more complex physical topologies, enabling the networks to span longer distances.

8. Switched Ethernet Topology Switched Ethernet uses switches instead of hubs. Switches that make switching decisions based on data link layer addresses are called workgroup or layer-2 switches. While a hub broadcasts frames to all ports, the switch reads the destination address of the frame and only sends it to the corresponding port. The effect is to turn the network into a group of point-to-point circuits and to change the logical topology of the network from a bus to a star.

9. Ethernet Physical Layer Standards The three most commonly used forms of Ethernet today are: 10BaseT (10 = 10Mbps, T = twisted pair and base = baseband, meaning one channel) Fast Ethernet which includes 100BaseT and 100BaseF (F = fiber) Gigabit Ethernet which includes 1 Gigabit Ethernet (1 GbE) and 10 GbE (10 Gbps). Even faster versions are being developed.

10. The 10BaseT Ethernet Standard 10BaseT uses twisted-pair cable. By far the most common form today is using 8-wire, category 5 cables with RJ-45 connectors (similar to phone jacks but larger). Twisted pair cables can be either unshielded (UTP) or shielded (STP). Shielding reduces interference from outside sources that may cause transmission errors. The maximum possible cable length is 100 meters.

11. Fast Ethernet There are two forms of fast Ethernet, 100BaseT and 100BaseF. 100BaseT uses twisted-pair cable. 100BaseF uses fiber optic cable. Light created by an LED (light-emitting diode) or laser is sent down a thin glass or plastic fiber.

12. Gigabit Ethernet (1GbE) Gigabit Ethernet is the newest family of Ethernet protocols running at speeds of 1 Gbps and above. Can use either twisted pair or fiber. 1000BaseT uses CAT-5e UTP, using all four wire pairs operating in parallel. Two types of Gigabit Ethernet use fiber optic cables:  1000BaseSX uses MMF and has a maximum segment length of 220 or 550 meters depending on the cable  1000BaseLX which uses MMF or SMF which can have a segment length of up to 5 kilometers for SMF.

13. 10GbE A 10 gigabit version of Ethernet is now being developed. 10GbE now has two forms, one for LANs and one for WANs. Interconnect LAN/WAN networks will be possible using 10GbE. The LAN form of 10GbE runs over four parallel MMF or SMF fibers.

14. Connecting Devices Hubs Switches Routers Repeaters Bridges

15. Hubs Physical layer (Layer 1) devices When hubs receive a signal from one device, it broadcasts the signal out all ports All devices attached to the hub receive the signal Collisions need to be handled Disadvantage Shared bandwidth Latency grows as the number of station grows

16. Hub Operation D4-47-55-C4-B6-9F A1-44-D5-1F-AA-4C B2-CD-13-5B-E4-65 C3-2D-55-3B-A9-4F Ethernet Hub Station A1-44-D5-1F-AA-4C transmits a bit.

17. Hub Operation D4-47-55-C4-B6-9F A1-44-D5-1F-AA-4C B2-CD-13-5B-E4-65 C3-2D-55-3B-A9-4F Ethernet Hub Hub broadcasts the bit out all ports.

18. Switches Data link layer (Layer 2) devices Provide a set of separate point-to-point circuits Send received frame out a single port Small latency Can use the maximum bandwidth Perform format convention between different physical layer standards, i.e., copper and optical fiber Maintain a switching table

19. Switch Operation D4-47-55-C4-B6-9F On Switch Port 13 A1-44-D5-1F-AA-4C On Switch Port 10 B2-CD-13-5B-E4-65 On Switch Port 11 C3-2D-55-3B-A9-4F On Switch Port 13 Ethernet Switch Station A1-44-D5-1F-AA-4C transmits a bit.

20. Switch Operation D4-47-55-C4-B6-9F On Switch Port 13 A1-44-D5-1F-AA-4C On Switch Port 10 B2-CD-13-5B-E4-65 On Switch Port 11 C3-2D-55-3B-A9-4F On Switch Port 13 Ethernet Switch A switch sends a frame out a single port— the one to the receiver

21. Other Switches Layer 3 switches Work at the network layer Forward packets based upon IP addresses Usually only support Ethernet at Layer 2 and limited Layer 3 protocols Dominant within the site Layer 4 switches Examine the port number field of a packet; therefore switch packets based on the application they contain Give priority to or deny forwarding to IP packets from certain applications

22. Routers Connect different types of networks that have different physical and data link layer standards (Layer 3 device) i.e., internal Ethernet LAN, internal Token- ring network, a leased T1 line Usually are organized into a mesh topology Identify all possible routes and then select the best route Slower and more expensive than switches

23. Ethernet LAN 3 Internetworking with Routers Ethernet LAN 1 Ethernet LAN 2 Token-Ring Network Router W Router Y Router X Router Z T1 Leased Line T1 Leased Line Frame Relay Network Site C Site A Site B Routers Connect Different Types of Networks

24. Router Operation When a frame arrives at a router The data link layer of the interface of that port removes the frame of the packet and passes the packet up to the router’s network layer The network layer makes a routing decision using routing tables and selects a interface The data link layer of the selected interface put the packet in a frame suitable for that network and then passes it down to the physical layer The physical layer of the interface translate the frame to bits and transmit

25. Format Conversion IP Packet IP Packet PPP T PPP H 1.Frame arriving at a router through Physical Layer User PCRouter 3.The data link layer process the PPP frame and passes the IP packet to the router’s network layer 2.The Physical passes it on to the Data Link layer

26. Format Conversion 1.The router decides the route (and port) and then passes the IP packet to the port attached to the selected network. User PCRouter IP Packet IP Packet PPP T PPP H 3.The data link places the packet in a frame suitable for that network and passes down to the physical layer. IP Packet IP Packet DL T DL H 4.The physical layer of the port convert the frame to signals and send them out. 2.The network layer passes it down to the data link layer of the port.

27. Layer 3 Switches and Routers in Site Internets Layer 3 switches switch IP packets rather than Ethernet frames. Based on IP addresses instead of MAC addresses Router To Other Sites Layer 3 Switch Ethernet Switch Ethernet Switch

28. Layer 3 Switches and Routers in Site Internets Router To Other Sites Layer 3 Switch Ethernet Switch Ethernet Switch However, they are usually limited to IP and perhaps IPX routing. Also, they rarely have WAN interfaces or non-Ethernet LAN ports.

29. Other Connecting Devices Repeaters Layer 1 devices Used to extend the distance of a physical link Regenerate and transmit signals Bridges Data link (Layer 2) devices Connect two or more network segments that use the same data link layer protocols and addresses Slower than switches Not commonly used now

30. Media Access Control Collisions occur when two computers on the same circuit transmit at the same time Media access control prevents or recover from collisions

31. Carrier Sense Multiple Access with Collision Detection (CSMA/CD) 1. Carrier Sense Multiple Access (CSMA) If a NIC wishes to transmit, it must listen for traffic  If there is no traffic, the NIC may transmit  If there is traffic, the NIC must wait until the transmission is finished  When the transmitting station finishes transmitting, the NIC listens for other stations transmitting before it transmits; if others are transmitting, it must wait until they are finished too

32. CSMA/CD 2. Collision Detection (CD) If there is a collision (by two or more stations transmitting at the same time),  All NICs stop transmitting and wait for a random amount of time  The first NIC that finishes its wait my transmit but only if there is no traffic! If there is traffic, the NIC must wait until there is no traffic

33. CSMA/CD 3. Collision Detection (CD) If there are multiple collisions,  The random wait is increased each time  After 16 collisions, the sending NIC discards the frame

34. Network Operating Systems Connects all machines and peripherals on a network into an interactive whole Coordinates and controls the functions of machines and peripherals across the network Supports security and privacy for both the network and the individual users Controls access to resources on a user authentication basis Advertises and manages resources from a centralized directory Gives the ability to share resources such as printers, files, and Internet access

35. Popular Network Operating Systems Microsoft Windows Server NT server 2000 server, 2000 Advanced Server, 2000 Datacenter Server.NET server Linux Many distributions Free, open-source Novell NetWare Once dominated the NOS market IPX/SPX protocol

36. Popular Network Operating Systems Microsoft Windows LINUXNovell NetWare Ease of Learning Very Good PoorGood Ease of UseVery Good PoorGood Reliability Very Good for recent versions ExcellentVery Good Standardization Availability of Device Drivers Purchase Price Excellent Moderate Poor (Many Distributions) Poor Low or Free Excellent Very Good Higher than Windows Management Labor ModerateHigh Higher than Windows

37. The Best Practice LAN Design

38. Effective Data Rates The effective data rate is the maximum practical speed hardware layers can expect to provide. It depends on 4 factors: nominal data rate (e.g., 10Mbps for 10BaseT) error rate, since this determines the frame retransmission rate efficiency of the data link protocol which depends on the percentage of the transmission devoted to overhead efficiency of the media access control protocol meaning how effective is the protocol at making use of the nominal data rate.

39. Media Access Control Protocol Efficiency Shared and switched Ethernet differ in their MAC protocols. Shared Ethernet is very sensitive to network traffic levels Shared Ethernet network capacity is effectively limited to just under 50% of capacity At 97% data link protocol efficiency, 10BaseT can carry 0.97 x 0.5 x 10mbps = 4.85Mbps In a low traffic environment with only two active users on a network, this would correspond to 2.5 Mbps/user In moderate traffic, with 10 users, this would mean only 500 kbps/user

40. Eff. Data Rates for Switched Ethernet Switched Ethernet dramatically improves performance since each computer appears to have its own dedicated circuit and collisions and congestion are no longer a problem. Experts believe switched Ethernet users can effective utilize 95% of network capacity. For a 10BaseT switched LAN, each computer would have an effective capacity = 0.97 x 0.95 x 10Mbps ~ 9 Mbps. For 100BaseT switched LAN, each computer would have an effective capacity = 0.97 x 0.95 x 100Mbps ~ 92Mbps.

41. Eff. Data Rates for Gigabit Ethernet Gigabit Ethernet is typically implemented in a full-duplex switched environment. This means it provides 1 Gbps in both directions at once. This makes the effective data rate for sending data in one direction is 0.97 x 0.95 x 1 Gbps ~ 900 Mbps Since 1GbE is implemented as a full-duplex network, traffic can be sent simultaneously in both directions, so the effective capacity is really double this value or 1.8 Gbps.

42. 1. Technology Low Traffic Moderate Traffic High Traffic Shared 10BaseT2.5 Mbps1 Mbps500 kbps Shared 100BaseT37.5 Mbps15 Mbps7.5 Mbps Switched 10BaseT9 Mbps Switched 100BaseT90 Mbps Full Duplex 1 GbE1.8 Gbps Full Duplex 10 GbE18 Gbps Effective Data Rate per User Assumptions: 1.Most frames are 1500 bytes or larger 2.No transmission errors occur 3.Low traffic means 2 active users, moderate traffic means 5 active users, high traffic means 10 active users

43. LAN Recommendations Since network traffic almost always increase, the best practice design is for the worst case. For most networks, switched 10/100BaseT is the best option For networks with high traffic levels, switched 100BaseT or 1 GbE over MMF is best. In most LANs, the circuit to and from the server is the network bottleneck. The solution for this is to use a 10/100 switch and then connect the server using a 100Mbps or higher circuit.