Networking Essentials: LAN Topologies, Media, and Protocols

1. Networking Updated June 27, 2006Updated June 27, 2006

3. Lesson Objectives By the end of this lesson, you should be able to: Describe AMI and B8ZS Define LAN and WAN List the various LAN topologies and the media that they utilize Describe what is meant by 802.3, and X.25 Describe the characteristics of Frame Relay and ATM Describe the characteristics of an Ethernet LAN and the evolutionary stages of Ethernet Explain how CSMA/CD functions Describe the design and capabilities of ISDN, including B and D channels, Clear Channels, and 2B1Q

4. T-1, DS-1

5. Inside a DS-1 Channel

6. T-1 System Timing

7. AMI Bipolar Coding Benefits: Helps detect errors Helps in timing Overall voltage equals 0 Simple Weakness: Long strings of 0s Solution: Least significant bit = 1 Impact on data

8. B8ZS Bipolar coding Improved method to deal with string of 0s

9. B8ZS Summary Bipolar with 8 Zero Substitution All benefits of basic bipolar coding: Helps detect errors Helps in timing Overall voltage equals 0 Simple Plus: Handles strings of 0s Equally effective for data Current standard line coding for T-1

10. LANs A LAN: Is a communications network Connects a variety of devices � computers, printers, terminals, routers, etc. Spans a small geography, usually not larger than a building Is capable of very high transmission rates, at least in the Mb ranges Has three key elements: Topology, Media, Protocol

11. LAN Topology Topology refers to the configuration used to connect stations to the LAN Three main topologies are available for a LAN: Bus Ring Star

12. Bus Topology Terminator is functionally just a resistor.Terminator is functionally just a resistor.

13. Bus Topology Characteristics Oldest topology Passive topology � computers only listen for data being sent; they are not responsible for moving data from one computer to the next Only 1 computer at a time can send data Signals travel both directions on bus

14. Ring Topology

15. Ring Topology Characteristics Point-to-point links connect nodes Active topology - Each station receives signal, regenerates it, and retransmits it, through a repeater Transmitted message travels around ring until originating station removes it

16. Star Topology

17. Star Topology Characteristics Devices communicate through hub Centralized resources, management Topology allows variations: star bus, star ring, etc.

18. Combination Topologies

19. Hubs Latency � the amount of time it takes for a packet to reach its destinationLatency � the amount of time it takes for a packet to reach its destination

20. Switches

21. How Switches Handle Traffic Cut-through: reads MAC address in beginning and immediately start sending to proper destination. Fast throughput No error detection/correction Store and forward: saves entire packet in buffer. Performs error check If error is detected, it is discarded No error, looks up MAC address in table and sends it to destination

22. Switch Classes Layer 2 switch Replaces hubs Faster than hubs Multiple paths for connections Connect segments from terminals Layer 3 switch More sophisticated than layer 2 switches; also called routing switches, switching routers Faster, less complex to install than routers Provide greater level of control Helps eliminate unnecessary traffic, as in broadcast messages Can connect other switches Can be packet-by-packet or flow-based Packet-by-packet switches on per-packet basis (like a router) Flow-based identifies IP packets with same destination and source, or uses special flow label (feature of IPv6)

23. Typical LAN Configuration

24. LAN Media Fundamental choices: copper, fiber Dependencies: Capacity � needs to support expected traffic levels Reliability � availability requirements Types of data supported Environmental scope Cost Strong relationship with LAN topology Number of station connections Types of connections Volume of data that will be sent

26. Connecting LANs Practical limit to the number of stations in a single LAN Additional growth facilitated by establishing and linking multiple LANs Multiple LANs linked by 3 means: Bridges Routers Switches

27. Bridges and Routers Links LANs with same protocols for layers 1 and 2 Makes no modifications to packets � no changes, no additional headers Allows correct traffic to pass; blocks all unnecessary traffic Blocks noise, errors, malformed frames Transparent to all stations Increasingly rare Operates at layers 1, 2, 3 Has routing tables which allows them to select the destination or target network Changes formats in packets � address schemes, packet sizes � when networks have different protocols Performs control functions � path optimization, sequencing Is slower than bridges A kind of hybrid device is an adaptive or learning bridge. This, like a router, is a computer. It has 2 Ethernet interfaces, and can connect 2 Ethernets. It keeps 2 address lists � one for each network. It is not programmed; it learns what stations are on each network by receiving frames. As it receives a frame from computer A, it logs computer A�s address in the address list for that network.A kind of hybrid device is an adaptive or learning bridge. This, like a router, is a computer. It has 2 Ethernet interfaces, and can connect 2 Ethernets. It keeps 2 address lists � one for each network. It is not programmed; it learns what stations are on each network by receiving frames. As it receives a frame from computer A, it logs computer A�s address in the address list for that network.

28. Ethernet LAN 1972 Bob Metcalf (Xerox) designed a �broadcast� computer network where stations could send messages at will Originally named this an Alto Aloha Network Changed name to Ethernet, to emphasize that this concept was not restricted to Xerox�s Alto computers Ether � ancient myth claimed that ether was present in the air and was responsible for the propagation of electromagnetic waves Sent data at a rate of 2.94 Mbps Patented in 1978 Standard published 1980 by DEC-Intel-Xerox consortium IEEE published standard as 802.3 in 1985 Ethernet protocols operate at layers 1 and 2 of OSI model

29. Ethernet Media Initial Ethernet required thick coax cables; nominal rate was 10 Mbps Thin coax cables installed in mid-1980s Bus topology was the standard � vulnerable to network crashes. Topology can also be a star; never a ring/loop Late 1980s � twisted pair Ethernet introduced by SynOptics Communications (cat 3)

30. Ethernet Frame

31. Ethernet Evolution 10BaseT - IEEE standard released in 1990; nominal speed was 10 Mbps; range of 250 meters with 2 pr Cat 3 wire 100BaseT - Fast Ethernet, was approved 1996. Used 2 pr Cat 5, 4 pr Cat 3, or 2 optical fibers 1000Base Ethernet introduced 1998 � Gigabit Ethernet 10 Gigabit Ethernet approved in 2000; range of 24 miles

32. Ethernet Message Delivery Broadcast delivery system Every station transmitted is heard by all stations Minimizes the address-matching intelligence in the interfaces Allows physical medium to be as simple as possible Physical signaling and media system only has to ensure bits are transmitted accurately Ethernet interface in each device does the rest Network interfaces that do not match the destination address discard the frame Transmission management provided by CSMA/CD protocol in layer 2

33. CSMA/CD Carrier Sense Multiple Access/Collision Detect Transmission Process: Station listens to see if a carrier signal is present on network � carrier sense If carrier is present, station waits If carrier is absent, station sends data frame Every station has equal opportunity and equal priority to send data � multiple access Every station receives the transmitted frame Each interface compares destination address in frame with its own 48-bit address Only the interface with a match continues to read the frame; all others ignore it

34. When Two Stations Transmit� Two stations listen, hear no carrier, and simultaneously decide to transmit: Both stations transmit their frame Transmissions �collide�; result is garbled frames Stations recognize this as a collision � collision detect Both stations stop transmitting Each station waits a random amount of time, then retransmits Random waiting period resolves most collisions from reoccurring After each consecutive collision, likelihood of another collision is reduced Frame will not be discarded until 16 consecutive collisions have occurred CSMA/CD required a minimum frame size Without a minimum frame size, it would have been possible for a station to complete transmission of a frame before the first bit reached the far end of the cable and the transmitting end would therefore not have been able to detect a collision Based on transmission speeds and propagation speeds, a minimum size of 64 bytes was established (72 with the preamble)CSMA/CD required a minimum frame size Without a minimum frame size, it would have been possible for a station to complete transmission of a frame before the first bit reached the far end of the cable and the transmitting end would therefore not have been able to detect a collision Based on transmission speeds and propagation speeds, a minimum size of 64 bytes was established (72 with the preamble)

35. Collision Back-off Times

36. WANs Wide Area Network Appropriate when geography to be covered exceeds that of a LAN Achieves widespread geographic coverage through use of switching nodes Switches can be part of common carrier�s network (Verizon, SBC, etc.) Can utilize circuit switching or packet switching systems Virtual circuits are common � Switched VC, Permanent VC A virtual circuit is a logical circuit created within a shared network between two network devices. Two types of virtual circuits exist: switched virtual circuits (SVCs) and permanent virtual circuits (PVCs). SVCs are virtual circuits that are dynamically established on demand and terminated when transmission is complete. Communication over an SVC consists of three phases: circuit establishment, data transfer, and circuit termination. The establishment phase involves creating the virtual circuit between the source and destination devices. Data transfer involves transmitting data between the devices over the virtual circuit, and the circuit termination phase involves tearing down the virtual circuit between the source and destination devices. SVCs are used in situations in which data transmission between devices is sporadic, largely because SVCs increase bandwidth used due to the circuit establishment and termination phases, but they decrease the cost associated with constant virtual circuit availability. PVC is a permanently established virtual circuit that consists of one mode: data transfer. PVCs are used in situations in which data transfer between devices is constant. PVCs decrease the bandwidth use associated with the establishment and termination of virtual circuits, but they increase costs due to constant virtual circuit availability. PVCs are generally configured by the service provider when an order is placed for service. A virtual circuit is a logical circuit created within a shared network between two network devices. Two types of virtual circuits exist: switched virtual circuits (SVCs) and permanent virtual circuits (PVCs). SVCs are virtual circuits that are dynamically established on demand and terminated when transmission is complete. Communication over an SVC consists of three phases: circuit establishment, data transfer, and circuit termination. The establishment phase involves creating the virtual circuit between the source and destination devices. Data transfer involves transmitting data between the devices over the virtual circuit, and the circuit termination phase involves tearing down the virtual circuit between the source and destination devices. SVCs are used in situations in which data transmission between devices is sporadic, largely because SVCs increase bandwidth used due to the circuit establishment and termination phases, but they decrease the cost associated with constant virtual circuit availability. PVC is a permanently established virtual circuit that consists of one mode: data transfer. PVCs are used in situations in which data transfer between devices is constant. PVCs decrease the bandwidth use associated with the establishment and termination of virtual circuits, but they increase costs due to constant virtual circuit availability. PVCs are generally configured by the service provider when an order is placed for service.

37. MAN Intermediate size � between LAN and WAN 3 � 30 mile diameter is typical Could cover an entire city Could be a group of buildings (e.g., campus) Generally not owned by one corporation (like a WAN) Acts as a high-speed network Typically consists of a fiber optic backbone

38. Data Networks � X.25 Protocol basis for traditional packet-switching network Developed in analog era ? heavy focus on error control: every leg conducts error control Connection-oriented = packets are transmitted in order Packet size 128 � 256 bytes Network of unlike equipment worked well Robust network, invulnerable to node failures Layer 3 addressing provided robust address capabilities Heavy overhead Queuing delays

39. Data Networks � Frame Relay 2nd generation of packet switching, introduced 1991 Assumes digital network ? error checking done only at end Frames consist of up to 4,096 bytes Large variation in size of packets can lead to large variation in delays Transmits at speeds up to 44.736 Mbps Can handle multiple protocols simply by encasing them in FR shell

40. Frame Relay Structure Built on experiences of X.25 � a �lean� version of X.25 Eliminates overhead of network layer; Frame Relay is a layer 2 protocol Frame structure is similar to that of LAPB Digital transmission, utilizing DS-1, DS-3 FCS of 16 bits can detect 3 random errors or a burst of 16 errorsFCS of 16 bits can detect 3 random errors or a burst of 16 errors

41. Data Networks � ATM Asynchronous Transfer Mode Designed for multimedia � voice, data, etc. Only WAN approach with architected QoS Cell = Packet of 53 bytes Reduces queuing delay for high priority cells Can be easily switched Can interface at speeds up to 622 Mbps Provides dynamic bandwidth for bursty data No link-by-link error control Connection-oriented network

42. ATM Structure Layer 2 technology Physical layer � handles physical transport over selected medium (electrical or optical) using DS-1, DS-3, OC-x Data Link Layer � ATM layer Constructs ATM cells from data received from higher levels Error checking Switches, multiplexes, demultiplexes Provides QoS

43. ATM Key Concepts Cell Heart of the ATM concept Fixed length = 53 bytes QoS - 5 fundamental service categories Constant Bit Rate � guarantees bandwidth (for real time services: telephone, real time video) Real time variable bit rate � bandwidth can vary, but delay variation is minimized (for real time services: voice, video) Non real time variable bit rate � throughput is guaranteed, but delay can vary (file transfer, packet data) Unspecified bit rate � best effort Available bit rate � cell loss can occur, but is limited; delay can vary

44. ISDN Integrated Services Digital Network Designed to be worldwide telecom network supporting circuit switching and packet switching Two fundamental types of ISDN: B-ISDN PR-ISDN Provides �clear channels� Fully digitizes the local loop

45. Digitization with ISDN

46. Clear Channels Separate channel for signaling Prevents need to bit rob Allows each voice channel to be full 64 kbps all the time Known as 64k clear channel NOT a reference to lack of noise or lack of carrier signals Also achieved by B8ZS

47. Basic Rate ISDN B Channel � Bearer channel. Used as primary carrier of information: voice, data. 64 kbps D Channel � Delta channel. Used as primary signaling carrier. Also carries data. 16 kbps

48. ISDN BRI Configurations

49. U Interface 2B1Q Format 2 binary, 1 quaternary 2 bits/baud

50. BRI - ISDN Frame

51. Primary Rate ISDN B Channels D Channels - Delta channel. Used as primary signaling carrier. Also carries data. 64 kbps H Channel � Higher speed data channels. 384, 1536 kbps Total data rate = 1.544 Mbps 23 B Channels + 1 D channel Some combination of B, D, H channels

52. What We�ve Covered Describe AMI and B8ZS Define LAN and WAN List the various LAN topologies and the media that they utilize Describe what is meant by 802.3, and X.25 Describe the characteristics of Frame Relay and ATM Describe the characteristics of an Ethernet LAN and the evolutionary stages of Ethernet Explain how CSMA/CD function Describe the design and capabilities of ISDN, including B and D channels, Clear Channels, and 2B1Q