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Chapter 11

Chapter 11. Network Fundamentals. Network Classifications. Topology Star, hierarchical, mesh, bus, ring, hybrid Ownership Private, public Purpose or transmission type E-mail, value-added networks, packed data networks Geography WAN, MAN, LAN. Topology - Star.

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Chapter 11

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  1. Chapter 11 Network Fundamentals

  2. Network Classifications • Topology • Star, hierarchical, mesh, bus, ring, hybrid • Ownership • Private, public • Purpose or transmission type • E-mail, value-added networks, packed data networks • Geography • WAN, MAN, LAN

  3. Topology - Star • Circuits radiate from central node • Advantages • Easy to control and expand network • Disadvantages • Central node is single point of failure • Central node can get overloaded • Examples • PBX, Computer cluster, some Ethernets • Question to consider: • How do you control/manage the network?

  4. Star Network

  5. Topology - Hierarchical (Tree) • Top node is root, or head-end • Advantage • No single point of failure • Lower levels can communicate even if host is lost • Example • Cable TV network

  6. Hierarchical Network

  7. Topology - Mesh • Nodes highly interconnected • Fully-connected mesh - each node connects to all others • Advantage • Redundant connections • Disadvantage • Lots of interconnects • Example • Public telephone network

  8. Mesh Network

  9. Topology - Bus • Nodes tap into a bus cable • All stations independent • Advantage • No single point of failure • Typically run at high speed • Disadvantage • Limited distance and number of attached devices • Faults hard to find • Example • Old Ethernet was logical and physical bus • New Ethernet is logical bus, physical star

  10. Bus Network

  11. Topology - Ring • Devices tap into closed ring • Signals move around ring from source to destination • Each node reads message address and either copies message or passes it on • Advantage • Each node checks for errors • Disadvantage • Single point of failure in unidirectional ring • Bi-directional ring more robust

  12. Unidirectional Ring Network

  13. Bi-directional Ring

  14. Topology - Hybrid Networks • Larger networks tend to be hybrids, or combinations of topologies

  15. Hybrid Network

  16. Classification by Geography • WAN - wide area network • Large geographical area • Typically star topology, but also mesh or tree • MAN - metropolitan area network • City-wide network • Standardized by 802.6 • High bandwidth • LAN - local area network • Most common type • Small area

  17. Classification by Transmission Technology - Circuit Switched • When two sites are connected, a dedicated line exists between them • Line may be temporary • Developed for public telephone network • Can handle data • Not efficient - Why?

  18. Circuit-Switched Network

  19. Classification by Transmission Technology - Packet Switched • Also called packet data network (PDN) • Example: ARPANET, Internet • Messages in digital form, broken up into fixed-length pieces (packets) • Packets contain (among other things) • Source and destination address • Location code to tell where it is in message • Packets can travel different routes • Reassembled at destination

  20. Classification by Transmission Technology - Packet Switched • PDN connection types • Switched virtual circuit • Source and destination establish fixed route that exists for the duration of session • Permanent virtual circuit • Virtual circuit is long-term • Example: leased circuit • Datagram • Message packets are sent along most efficient routes at that time • Packets can arrive out of order • Example: X.25 is a ITU-T standard for PDN

  21. Packet-Switched Network

  22. Classification by Transmission Technology - Frame Relay • Designed to reduce overhead in X.25 networks • Also, PDNs use ACK after each packet before sending next • Message divided into variable-length frames (layer 2) • Reassembled at destination • Circuit congestion drops throughput considerably • Customer guaranteed a CIR (Committed Information Rate) • Speed may be greater than CIR (port speed) • Compare to EIR (Excess Information Rate) • Network discards frames during congestion • Reduces throughput until CIR reached

  23. Asynchronous Transfer Mode • Evolution of frame relay • Reverts back to using packets called cells • 53 octets long, fixed length • More efficient to assemble and disassemble • WANs use it in T-3 (44.7 Mbps) or higher speed circuits • LANs use ATM in fiber-optic backbones • LAN Emulation (LANE) • OC-1 (51.84 Mbps) is minimum speed • Most services minimize delays in transmission • Good for synchronized audio and video • Realtime Services • Constant Bit Rate (CBR) • Realtime Variable Bit Rate (rt-VBR) • Non-Realtime Services • Non-Realtime Variable Bit Rate (nrt-VBR) • Available Bit Rate (ABR) • Unspecified Bit Rate (UBR) (delays and cell loss possible)

  24. Interconnecting Networks • Networks have different characteristics • Users want transparency • Do not want to worry about how messages are transmitted • LANs, MANs, WANs connected with an internet • Terminology • End system - computer or other device • Subnetwork - networks of end systems, part of an internet • Intermediate system - interface subnets to main communication links • Example: bridges and routers

  25. TCP/IP • Transmission Control Protocol / Internet Protocol • Developed as part of ARPANET • Now it is the protocol used for Internet traffic • Provides packet data transfer between incompatible computer operating systems

  26. 7 - Application 6 - Presentation 5 - Application 5 - Session 4 - Transport 4 - Transport 3 - Network 3 - Internet 2 - Data Link 2 - Network Access 1 - Physical 1 - Physical Comparing OSI Model and TCP/IP OSI TCP/IP

  27. Some TCP/IP Protocols • W. Stallings, Data and Computer Communications, 6 ed., Upper Saddle River, NJ, Prentice Hall, 2000

  28. Some TCP/IP Process Layer Protocols • Telnet • Virtual terminal utility enabling access to remote hosts • FTP - File Transfer Protocol • File transfer utility • SMTP - Simple Mail Transfer Protocol • Main protocol responsible for transmission and distribution of e-mail • SNMP - Simple Network Management Protocol • Main protocol responsible for transmission of vital network and system statistics and commands • HTTP - Hypertext Transfer Protocol • Main protocol responsible for transmission of information throughout the World Wide Web • TFTP – Trivial File Transfer Protocol • Uses UDP • Inherently unsecure

  29. Some TCP/IP Host-to-Host Layer Protocols • TCP • Connection oriented • Reliable • “Connection” established between both ends before data transfer begins • Creates a virtual circuit between end-user applications • Responsible for • Breaking messages into segments (segmentation) • Reassembling messages at destination (reassembly) • Handles retransmitting dropped packets

  30. Some TCP/IP Host-to-Host Layer Protocols • UDP - User Datagram Protocol • Connectionless protocol • No acknowledgements • Unreliable • No checking for segment delivery and sequencing • Depends on higher layers for reliability

  31. Some TCP/IP Internet Layer Protocols • IP - Internet Protocol • Main protocol of the entire TCP/IP protocol suite responsible primarily for addressing and routing of packets • Connectionless, best-effort delivery

  32. Some TCP/IP Internet Layer Protocols • RIP - Routing Information Protocol • Interior routing protocol used to disseminate routing information within an autonomous system • Autonomous system • Group of routers exchanging information via a common routing protocol • Group of routers and networks managed by a single organization • Always a connection between any two nodes (except during failure) • Distance-vector protocol • Hop count determines shortest path • Often used in LANs

  33. Bit 0 Bit 31 Bit 0 Bit 31 Header Length 4 5 00 00 28 Service Packet Length Version E0 01 0000000(2) Identification 0 1 0 Fragment Offset B L D M Transport Protocol 20 06 4F 2A TTL Header Checksum Source IP Address C0 09 55 C8 Destination IP Address C0 09 55 C9 IP Options IP Options Padding Padding IP Header

  34. Some IP Header Fields • Minimum IP header size is 20 octets • More if options are used • Version • Presently Version 6 (replaced Version 4) • TTL (Time To Live) • Time in seconds that a packet can remain valid • Internet nodes must decrease by 1 second • When TTL reaches zero, packet is discarded • Device discarding sends packet back ICMP message saying packet was dropped • Since internet nodes process packets in less than 1 second, TTL is essentially the maximum hop count • Used by TRACEROUTE utility

  35. Some IP Header Fields • Transport protocol • Number identifying the TCP protocol in the payload • Source IP address • 32-bit source IP address • Destination IP address • 32-bit destination address • Data • Host-to-Host (TCP) layer protocol data follows IP header

  36. TCP Header

  37. TCP Header Fields • Minimum TCP header size is 20 bytes • More if options are used • Source port • Number of calling port • Initiator of request is client process • Generally not significant • Destination port • Number of called port • Grantor of request is the server process • Identifies one of the destination processes such as HTTP • Data • Process (Application) layer protocol data follows TCP header

  38. Popular Port Numbers

  39. TCP/IP Transmit & Receiver Process • Transmission process • Host-to-Host (TCP) layer receives data from Process (Application) layer and adds TCP header • Sends this segment to Internet (IP) layer • Internet layer receives segment from TCP layer and adds IP header • Sends this packet to Network Access (Data Link + Physical) layer • Network Access layer receives packet from Internet layer and adds its own header and trailer • Sends this frame out over network • Receive process • Process reverses • Each layer strips off its header and / or trailer as information moves up the protocol stack

  40. Host 2 Host 1 Application Application TCP TCP Router IP IP IP Network Interface Network Interface Network Interface Network Interface End-to-End Delivery

  41. Message Routing • Connection-oriented • Network switches or routers set up data path before transmission • Virtual circuit • Packets arrive in order • Connectionless • Datagram • Packets can take different paths to destination • Destination host must put packets in order • Intermediate routers decide on paths • Routers communicate with each other to determine “best” path for packet to travel

  42. Intranets • Intranet - internal company network • Used for sharing information • Usually access the Internet through firewalls • Restricts access of company network from Internet side

  43. Internet

  44. Software for Network Management • Functions • Monitor network status and display status conditions • Log pertinent network operational data for storage • Example: statistics, errors, and alarms • Provide operator with control functions to optimize network performance

  45. Protocol Analyzers • Protocol analyzers are used to analyze traffic on networks (WAN and LAN) • Interpret the protocol fields • Workstation-based analyzers are software packages that use the workstation’s NIC to capture frames on the network • Ethernet card programmed to respond to all MAC addresses, not just its own (and broadcasts) • Strips off MAC framing and passes IP information up to Internet (Network) layer • Called “promiscuous” mode

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