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MIS 430

MIS 430. Chapter 5 – Network and Transport Layers. I. Overview. Layers are very close – move messages from end to end in a network Transport Layer – accepts outgoing messages from the application layer Packetizes them Addresses them

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MIS 430

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  1. MIS 430 Chapter 5 – Network and Transport Layers Chapter 5

  2. I. Overview • Layers are very close – move messages from end to end in a network • Transport Layer – accepts outgoing messages from the application layer • Packetizes them • Addresses them • Network layer – takes messages from the transport layer and routes them through the network • Data Link Layer – produces error-free delivery Chapter 5

  3. Introduction • See fig 5-1 p. 145 for 5 OSI layers • Note path of packets • Note additional headers added at each layer: encapsulation • Remember that each layer “talks to” its counterpart layer at the other end Chapter 5

  4. II. Transport and Network Protocols • Many similar protocols here can do the same thing: TCP/IP, IPX/SPX, X.25, etc. • Multiprotocol stacks (software) will process each protocol’s packets • must analyze the packet to determine the protocol Chapter 5

  5. TCP/IP: Internet Standard • TCP/IP originally developed for ARPANET – DoD network • Produce error-free transmissions • Compatible with variety of data link protocols • TCP/IP is world’s most popular • TCP=transmission control protocol (TL) • IP=Internet protocol (NL) Chapter 5

  6. TCP: Transport Control Protocol • Performs packetizing • Breaks message into packets • Numbers them (for reassembly later) • Assures packets are delivered reliably • Puts packets in order at destination • See figure 5-2 p. 147 for TCP packet: 192-bit header Chapter 5

  7. IP: Internet Protocol • Network layer protocol • Performs addressing and routing • IP SW must be at every node • IP packet in figure 5-3 p. 147: 192-bit header • IPv4: 32 bits=4.3B IP addresses • IPv6: 128 bits=3.4x1038 addresses! Simpler header structure but requires ALL computers be revised (Microsoft has upgrade) Chapter 5

  8. IPX/SPX: Novell • ISU still uses IPX/SPX but newer Novell Netware now uses TCP/IP • SPX: TL protocol and like TCP • IPX: NL protocol and like IP Chapter 5

  9. X.25 Packet Switching • WAN global ITU standard for packet switched networks of common carriers • Seldom used in North America • Maps to lowest 3 levels of OSI model • DTE (data terminal equipment or end devices) vs. DCE (data communications equipment or communications devices) • PAD – packet assembler/disassembler • X. means digital data carried on digital network in ITU-T notation Chapter 5

  10. System network architecture-SNA • IBM standard intended for end to end IBM network • Used only on IBM compatible mainframes • Uses proprietary protocols: important concept in open standards environment • Experts predict SNA will be replaced by TCP/IP and this will decline Chapter 5

  11. III. Transport Layer Functions • Each application layer program has a unique TCP/IP port number • 16-bit (2 byte) number up to 65536 • FTP=21, Telnet=23, HTTP=80, SMTP=25 • Can choose non standard port numbers and give application program that port # • http://someplace.com:4567/index.htm Chapter 5

  12. Packetizing • Given maximum packet size, most messages are split into >1 packet • Web browsers build page a packet at a time, especially streaming and graphics • Email clients wait until all packets have arrived and are reassembled Chapter 5

  13. Connection oriented routing • Sets up TCP connection as a virtual circuit between sender and receiver • Once established, packets flow in same order until connection is closed • Reassembling message is simple here Chapter 5

  14. Connectionless routing • Each packet is treated separately and could take different paths • May arrive out of sequence • TCP packet replaced by UDP packet • User Datagram Protocol packet is much smaller that TCP packet • Often used when entire message fits one packet (control messages) Chapter 5

  15. Quality of service (QoS) routing • Special type of connection oriented routing • Different connections are assigned different priorities • Email is low priority, videoconferencing high priority to assure smooth images Chapter 5

  16. IV. Network Addresses • Application Layer URL: misnt.indstate.edu • at C:>type Ping misnt.indstate.edu to see if active • Network Layer IP: 139.102.31.12 • Data Link Layer MAC: SMC network card 00-E0-29-92-24-54 (12 hex digits) • at C:> type winipcfg (Windows 95, 98, ME) • at C:> type ipconfig (Windows NT, 2000, XP) • Must have an approved address to attach a computer to the Internet • Servers have fixed (static) addresses, clients usually not Chapter 5

  17. Internet Addresses • Network Solutions is the agent that provides domain names (called domain registrar) • http://www.networksolutions.com • .com, .org, .net, .mil, .gov plus several new extensions (.biz, .info, .bz, and .tv) latter two were originally country codes • Country extensions: .us, .ca, .il, .jp, .de, .iq http://www.isi.edu/in-notes/iana/assignments/country-codes Chapter 5

  18. Subnets • Subnet refers to logical group of computers, often same physical network • ISU uses 139.102.x.y Class B addresses • X is the subnet and y is the computer • SB 403 and servers: 139.102.31.y • SB faculty and staff: 139.102.67.y and 139.102.69.y • Subnet mask: 255.255.255.0 vs 255.255.0.0 – parts refer to clients on the same subnet • Partial-byte subnets: 255.255.255.240 allows for 16 computers per subnet: 11111111 11111111 11111111 11110000 Chapter 5

  19. Static vs. Dynamic Addresses • Static IP address: always same, coded into the Network TCP/IP properties • DHCP and bootp give out dynamic addresses at client boot up time • Can reuse dynamic IP addresses • In TCP/IP Properties, Obtain an IP address automatically • Cannot assign a dynamic address to a server! • At ISU, even though we use bootp you always get the same IP address; (ISU is replacing bootp with DHCP for roaming) • Register: http://ithelp.indstate.edu/forms/bootp.html Chapter 5

  20. IP Address Lease • Client is given an IP address for a certain length of time • After that time expires, the IP address lease expires and someone else can use that IP address • At C> prompt, type ipconfig /all to see IP address lease information. (In Windows 9x, type winipcfg) Chapter 5

  21. Address Resolution • Server name resolution: DNS stands for Domain Name Service • Any time your computer does not know the IP address of a server, it calls the DNS to get it • DNS may have to go to root DNS to get IP • 139.102.48.35, 139.102.7.102, 139.102.1.10 are ISU DNS • Once learned, this address is stored inside your computer until you shut down. Hint: you may need to do a DNS Flush if your computer is acting up. Ask about this in class! • DNS name is associated with domain name: www.indstate.edu=139.102.15.15 • DNS servers replicate automatically Chapter 5

  22. V. Routing • Process of determining path through network of a message • Implement via a Routing Table (for computer B) • How many paths from A to G? ABCG, ADEFCG, ADEBCG, ABEFCG, C B A G D F E Chapter 5

  23. Routing - 2 • Router points in the general direction of destination • Ex: for all IP 126.x.x.x addresses, go here • Ex: for all Texas destinations go here, otherwise go there • Router contains software and builds routing tables dynamically to accommodate congestion, cuts, etc. • Cisco – has best dynamic routing software Chapter 5

  24. Tracing Your Route(rs) C:\WINDOWS\Desktop>tracert www.kelley.indiana.edu Tracing route to kelley.iu.edu [129.79.121.231] over a maximum of 30 hops: 1 27 ms 26 ms 38 ms 139.102.180.1 (this was from my home!) 2 26 ms 33 ms 28 ms 139.102.7.3 3 30 ms 2981 ms 29 ms 139.102.1.254 4 45 ms 2971 ms 54 ms ind-ag-2-atm6-0-1-12m.ind.net [157.91.9.174] 5 1982 ms 2965 ms 69 ms ihets-gw-1-atm-ind-ag-2.ind.net [199.8.76.250] 6 1970 ms * 59 ms iupui-atm6-0-100.ind.net [157.91.6.34] 7 1818 ms 2976 ms 56 ms 156.56.249.13 8 156 ms 2952 ms 148 ms wcc6-gw.ucs.indiana.edu [129.79.8.6] 9 1969 ms 182 ms 140 ms kelley.iu.edu [129.79.121.231] Trace complete. Chapter 5

  25. Types of Routing • Centralized routing: all decisions made by central computer • Static routing: all decisions made are fixed. If break in network, messages are held until routes refigured. Good for small networks with few alternative paths. • Dynamic: adapts to network conditions in decentralized fashion. Default mode with many paths, but requires lots of calculations by routers including network coordination traffic between routers. Chapter 5

  26. Routing Protocols • How routers exchange information to build, maintain routing tables • Autonomous system – network operated by one organization • Routing protocols inside such systems are interior routing protocols • Routing protocols between autonomous systems are exterior routing protocols Chapter 5

  27. Internet Routing Protocols • ICMP-Internet Control Message Protocol • RIP-Routing Information Protocol • BGP-Border Gateway Protocol • OSPF-Open Shortest Path First • EIGRP-Enhanced Interior Gateway Routing Protocol • For the test: know ICMP and RIP  Chapter 5

  28. Multicasting • Unicast message: sent from one client to another client • Multicast message: sent from one node to a group of computers at same time • Ex: Ghost for imaging hard drives; rebuild all computers with same packets • Ex: hearing a broadcast on the Internet – like a seminar or workshop Chapter 5

  29. VI. TCP/IP Example • A computer needs four TCP/IP settings: • Its IP address • Subnet mask • IP address of DNS server • IP address of gateway leading outside subnet • Can get these values • automatically or • they can be static values typed into TCP/IP Properties in Network control panel Chapter 5

  30. Example Network: fig 5-14 • Four subnets: 98, 95, 50, 75 • DNS server: 128.192.254.4 • 4 Gateways, each with at least two IP addresses (internal/external) • Bldg A: 128.192.98.1 129.192.254.3 (error) • Router: 128.192.254.7 next to Internet cloud Chapter 5

  31. Resolving Addresses • Known Address, Same Subnet • Search IP address table, find • Hand to Data Link layer, send packet • Known Address, Different Subnet • Search IP address table, find • Go through gateway to other subnet • Unknown Addresses • Search IP address table, not found • Perform DNS request, return address to table • May go through gateway or out via router Chapter 5

  32. Bruce’s Router • My home network has a Belkin wireless router: http://139.102.180.53 with a special TCP port number • It has the following ports: • WAN (connects to DSL modem) • 4 wired LAN ports – inside firewall • Wireless LAN ports – inside firewall • More in chapters 6-7 with LANs Chapter 5

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