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MIS 430 Chapter 5 – Network and Transport Layers Chapter 5 1 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 2 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 3 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 4 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 5 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 6 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 7 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 8 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 9 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 10 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 11 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 12 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 13 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 14 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 15 IV. Network Addresses Application Layer URL: misnt.indstate.edu Network Layer IP: 139.102.31.12 Data Link Layer MAC: SMC network card 00-E0-2992-24-54 (12 hex digits) at C:>type Ping misnt.indstate.edu to see if active 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 16 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/innotes/iana/assignments/country-codes Chapter 5 17 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 18 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 19 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 20 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 21 V. Routing Process of determining path through network of a message Implement via a Routing Table (for computer B) B A D E C F How many paths from A to G? ABCG, ADEFCG, ADEBCG, ABEFCG, Chapter 5 G Destinat. Route A A C C D A E E F E G C 22 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 23 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 24 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 25 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 26 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 27 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 28 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 29 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 30 Resolving Addresses Known Address, Same Subnet Known Address, Different Subnet Search IP address table, find Hand to Data Link layer, send packet 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 31 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 32