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IMPORTANT MATERIAL

IMPORTANT MATERIAL. Chapters 8-11. Topology. Topology is the basic geometric layout of the network -- the way in which the computers on the network are interconnected.

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IMPORTANT MATERIAL

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  1. IMPORTANT MATERIAL Chapters 8-11

  2. Topology Topology is the basic geometric layout of the network -- the way in which the computers on the network are interconnected. • Ethernet uses a bus topology (a high speed circuit and a limited distance between the computers, such as within one building).

  3. Bus Topology Terminators required on each end

  4. Ring Topology Data Flow

  5. Token Ring

  6. Star Topology Preferred method for today’s LANs Wiring Hub

  7. Media Access Control • Ethernet uses a contention-based technique called Carrier Sense Multiple Access with Collision Detection (CSMA/CD) • If two computers attempt to transmit at the same time, they detect the collision, send a jamming signal, wait a random amount of time, then re-broadcast.

  8. Ethernet Tree Topology • Each hub broadcasts to own segment • Misbehaving nodes will be shut off by the hub

  9. Network Servers: Everything You Wanted to Know But Were Afraid to Ask! • Servers use multiple processors • Very important to access-intensive operations • Multiple processors provide 50% improvement • Buses provide backbone internal support for data transfer • RAM provides a buffer for operations

  10. It’s a RAID! • Disk arrays improve performance and redundancy • RAID (Redundant Array of Inexpensive Disks) is a method used to write across (stripe) multiple disks to improve performance and fault tolerance • RAID 1 and 5 most popular but all have problems

  11. RAID File Disk 1 Disk 2 RAID 0--Stripes data between disks RAID 1--Mirrors data between disks

  12. Mirrored Disk Drives Duplexed Controllers Controller 1 Controller 2 File 1 File 1 File 2 File 2 2 1

  13. Raid Level 5 Technology Server File 1 Part 1 File 1 Part 2 File 1 Parity File 1 Part 3 File 2 Part 2 File 2 Part 3 File 2 Part 1 File 1 Parity 1 2 3 4

  14. A Fault-Tolerant Duplexed Server Duplexed Servers Dedicated High-Speed Connection Disk Drive Disk Drive Mirrored Disk Drives

  15. Immediate and Recurring Costs of a LAN Immediate Costs Equipment upgrades Documentation Installation of cabling System software installation Creating user environments Space required for new equipment LAN management—personnel costs Consumable supplies—toner, paper, etc. Training users, operators, administrators Site preparation Hardware installation Installing applications Testing Supplies and spares Hardware and software maintenance Training new users, administrators Recurring Costs

  16. Basic LAN Management Tasks User/Group Oriented Add, delete users and groups Set user environment Install/remove printers Maintain printers Add/change/delete hardware Add/change/delete hardware Plan and implement changes Make backups Carry out recovery as necessary Plan capacity needs Serve as liaison with other network administrators Set user/group security Solve user problems Setup user/printer environment Manage print jobs Establish connections with other networks Diagnose problems Maintain operating procedures Educate users Monitor the network for problems and to gather statistics for capacity planning Printer Oriented Hardware/Software Oriented General

  17. Backup Devices • Removable Disk Drives • Manual intervention is necessary for changing disk cartridges, whereas some tape backup system provide tapes with much higher storage capacity and with automatic tape changing. • Hard-Disk Drives • The arguments for and against this alternative are much the same as those for diskettes. The major difference is that the capacity of hard-disk drives is greater than that of diskettes.

  18. Backup Devices (cont.) • Optical Disk Drives • Optical disk drives are gaining popularity as input, output, and backup devices. The reasons for this are their decreasing costs and large storage capacity. • Magnetic Tape Drives • A magnetic tape drive is the usual choice for a backup device. Magnetic tapes are less expensive than the other options. They hold large volumes of data, are easy to use and store, and generally provide good performance.

  19. Gateways • Gateways operate at the network layer and use network layer addresses in processing messages. • Gateways connect two or more LANs that use the same or different (usually different) data link and network protocols. They may connect the same or different kinds of cable. • Gateways process only those messages explicitly addressed to them.

  20. Gateways • One of the most common uses of gateways is to enable LANs that use TCP/IP and Ethernet to communicate with IBM mainframes that use SNA. • The gateway provides both the basic system interconnection and the necessary translation between the protocols in both directions.

  21. Gateways

  22. Classic SNA Architecture

  23. Standalone PC 3270 Terminal Emulation

  24. LAN-based SNA Gateways

  25. Full Duplex Ethernet

  26. Switched Ethernet Switched Ethernet at Fish & Richardson

  27. Hierarchies Vulnerable to Single Points of Failure • Switch or Link (trunk line between switches) • Divide the network into pieces X X Ethernet Switch

  28. Switch Learning Every Few Minutes, Switch Erases Switch Forwarding Table • To eliminate obsolete information • Relearning is very fast Ethernet Switch Address Port Erased A1 BF C9

  29. Routing Types

  30. Standards for Web Server Access

  31. OSI Networking Model Provide network services To OS through network client Layer 7 Application Application & OS Network Client Application & OS Data compression & decompression; data Encryption/decryption Layer 6 Presentation 54321 12345 Connection between Client & server Layer 5 Session Session Packet control & sequencing error control Layer 4 Transport Packets Packet construction, Transmission, & reception Layer 3 Network Data Packet with Header & Trailer Bit stream connection protocol Layer 2 Data Link Network card & drivers Network Wiring & specifications Layer 1 Physical

  32. Domain Name System (DNS) • Subtlety • Organizations or ISPs have local DNS hosts • These hosts must know only local host names and IP addresses • For other host names, local DNS host passes request to another DNS host User PC Internet Layer Process Local DNS Host Remote DNS Host

  33. Domain Name System (DNS) • Subtlety • Remote DNS host passes information back to the local DNS host • Local DNS host passes information back to user PC • Browser only talks to local DNS host User PC Internet Layer Process Local DNS Host Remote DNS Host

  34. Autoconfiguration • Every computer attached to the Internet is a host • Including desktop PCs • Every host must have an IP address • Some hosts, such as routers and webservers, get permanent IP addresses • So that they can be found easily

  35. Autoconfiguration • User PCs do not need permanent IP addresses • They only need to be found within a use session • They usually are given temporary IP addresses each time they use the Internet • They may get a different IP address each time they use the Internet

  36. Autoconfiguration • Request-Response Cycle • User software requests IP address for the user PC in Autoconfiguration Request message • Autoconfiguration Response message contains temporary IP address to use in current session Autoconfiguration Request User PC Autoconfiguration Host Temporary IP Address in Autoconfiguration Response

  37. Autoconfiguration • Most popular autoconfiguration protocol is DHCP • Dynamic Host Configuration Protocol • Built into Windows after Win 3.1 • Supplies host with temporary IP address • DHCP can give more information too • Usually gives IP address of a default gateway (Microsoft terminology for router) • Can give IP address of a local DNS host • Can give other information

  38. The Peak Load Problem • Capacity Sufficient Most of the Time • Otherwise, get bigger switches and trunk lines! • BriefTraffic Peaks can Exceed Capacity • Frames will be delayed in queues or even lost if queue gets full Traffic Peak Capacity

  39. Overprovisioning Overprovisioning: Install More Capacity than Will be Needed Nearly All of the Time Wasteful of capacity Still, usually the cheapest solution today because of its simplicity Overprovisioned Capacity Traffic Peak

  40. Priority Assign Priorities to Frames • High priority for time-sensitive applications (voice) • Low priority for time-insensitive applications (e-mail) • In traffic peaks, high-priority frames still get through • Low-priority applications do not care about a brief delay for their frames Low-Priority Frame Waits Briefly High-Priority Frame Goes

  41. Bridges • A bridge can be used to connect two similar LANs, such as two CSMA/CD LANs. • A bridge can also be used to connect two closely similar LANs, such as a CSMA/CD LAN and a token ring LAN. • The bridge examines the destination address in a frame and either forwards this frame onto the next LAN or does not. • The bridge examines the source address in a frame and places this address in a routing table, to be used for future routing decisions.

  42. Bridges Interconnect

  43. Connecting LANs

  44. Frames Are Converted

  45. Storage Area Network

  46. Relationship Between the OSI Model and Internetworking Devices

  47. Internet Protocols • UDP • Layer 4 • Operates over IP • End-to-end connectionless, unreliable datagram service • Used for query based applications, multicasting and VoIP • ICMP • Provides error-handling • Messages related to network management • IGMP • Layer 3 • Allows Internet hosts to participate in multi-casting

  48. TCP/IP • TCP performs the packetizing function • Breaking data into smaller packets • Numbering packets • Ensuring reliable delivery of packets • Ordering packets at the destination

  49. Linking to the Application Layer • Each type of application has a unique port address • Application software sends both source and destination port addresses to the transport layer • Standard port addresses • Port 80 - web server • Port 21 – FTP (also port 20) • Port 23 - telnet • Port 25 - SMTP

  50. Packetizing • Breaking large data messages into smaller packets for transmission through the network • Size is dependent of data link layer protocol • Default size without protocol is 536 bits • Size can be negotiated between sender and receiver • Numbering packets (sequencing) when needed • Ensuring reliable delivery of every packet • Delivered one at a time or held until all have arrived at the destination • Reassembling and ordering packets at the destination

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