Everything You Always Wanted to Know About Network Access

1. Everything You Always Wanted to Know About Network Access Chapter 5 –Layered Communication & Internet Access

2. Knowledge Checkpoints • PSTN Infrastructure • How the OSI model works • Message exchange sequence • How routers work • Cookies • HTTP protocol • DOS commands for the network

3. Student Notes • Chapter 4 & 5 give background information to understand the network that represents the Internet • The content in these chapters will be more useful when we study WANs • Most of the material in this slide set is not in the book but is necessary for you to understand using networks • Check out the web sites on the course web page for additional information

4. HTTP OSI & layers TCP/IP Cookie Router CSU DLC Compression T and E carrier SDH/SONET Frame Packet OC SS7 Architecture Header Encapsulation Router forwarding IP address DNS DHCP Domain Host Auto-configuration Adaptor Bindings HTML Tags Next hop PSTN PDH Vocabulary that is Important

5. PSTN • Infrastructure and design to support voice, only • Call length is a component of the differences between data vs voice carried on network • Channel capacity is narrow band (64 Kbps) • Backbone based on PDH (T-carrier)

6. Array of Service Providers • LEC-local exchange carrier • ILEC-incumbent local carrier (monopoly rights) • CLEC-competitive local exchange carrier • DLEC-data competitive local exchange carrier (supports data services) • IXC-inter-exchange carrier (long distance) • Who are the LEC,ILEC,CLEC,DLEC & IXC for Utah?

7. Access Services • Categories for access services include: • Trunks (2-way, DID, DOD) • Analog (POTS) or digital services (3 types) • T-1 (1.5 Mbps), J-1 (2.048 Mbps), E-1 (1.544 Mpbs) • ISDN (BRI & PRI) • DSL

8. Transport Services • Switched services • Local, long distance, toll free, international, directory assistance, operator, emergency services • Nonswitched services • Leased lines, foreign exchange • VPNs • Network where customer traffic is isolated over shared service provider facilities

9. PTSN Architecture • CPE nodes located at customer site • Switching nodes interconnect transmission facilities to route traffic • Local Exchange (CO) point of termination for customer line and location of switching equipment • Tandem Office in large metro areas connects switching offices to route local traffic • Toll office is a switching center where long distance connections are made • International gateway is where international services begin • Transmission nodes carry user traffic and control information • Service nodes handle signaling to control connections and billing

10. PDH Infrastructure • PDH is asynchronous (clocking rates of all components vary slightly) • Digital network • Offers different transmission rates • Defines the availability of channels

11. Elements of PDH Infrastructure • Transmission media • Operates on 4 wire (full-duplex) but higher bandwidths require coax or fiber • CSU-terminates each end and equalizes signal • Multiplexers consolidates voice and data channels to travel over high speed line • DLCs concentrates lines • DCS allows dynamic rerouting of network traffic

12. SDH/SONET Infrastructure • Family of transmission standards using different fiber optic products • Uses a frame format (how bits are packaged) to travel over fiber • Rapid restoration of interrupted service possible with dual ring configuration • Uses optical carrier levels of OC • Synchronous infrastructure (clocking rate from 1 source)

13. SS7 Architecture • Signaling information carried o a different path from voice and data traffic • Allows passage of information about caller (enhanced services) • SSPs are switches that begin and end calls • SS7 networks act as a backbone for AIN (service independent allows interconnects)

14. Looking Deeper into Data How Does Data Know Where to Go on a Network?

15. Layered Communication

16. The OSI Layers

17. OSI Model

18. Nested Protocol Headers Each layer adds information as it passes through

19. Under the Covers

20. Indirect Communication • Application programs on different machines cannot communicate directly--They are on different machines! HTTP Request Browser Web App Trans Trans Int Int DL DL Phy Phy User PC Webserver

21. Indirect Communication • Two processes on different machines cannot communicate directly with one another because they are physically separated • So they communicate indirectly, using cooperation with lower layers • Requests are layered on the sending machine and stripped on the host machine

22. Layer Cooperation on the Source Host • Transport layer process passes the TCP segment down to the internet layer process Application Transport TCP segment Internet Data Link User PC Physical

23. OSI Model

24. Data Structure • Data --The information to be delivered to another system Data Field Trailer Fields (if there are any) Header Fields

25. The Data Structure • Header Fields • Initial fields in a message before the data field • Source and destination address, error handling information, etc., • Like address and greeting in a written letter Header Fields Data Field Header Field

26. How Does Data Find It’s Way? IP Addresses!

27. Assigning Network Parts • An organization applies to an Internet IP address registrar • Registrar gives organization a network part • Organization assigns the local part to its hosts internally • Only large organizations and ISPs get network parts 128.171.17.13 Registrar 128.171 Firm 128.171.123.130

28. IP Addresses • Each Organization is Given a Network Part Number • For Weber, this is 137.190 • All IP Addresses in that organization’s network begin with that Network Part Network Part IP Address 128.171

29. IP Addresses • Local Part • The part of the IP address after the network part is called the local part • Total address is 32 bits, so if the network part is 8, the local part is 24 Network Part Local Part IP Address (32 bits total)

30. Assigning Parts • IP address registrar gives Weber State University the network part 137.190 • Weber State could give the College of Business Administration the subnet part 62 • College of Business Administration can give the host part 157 and a host name plogan.cba.hawaii.edu • So the computer’s IP address became 137.190.62.157

31. IP Addresses • Most Organizations Have Multiple Subnets within the Organizational Network • Usually represent each as a Subnet Part within the Local Part • Remaining Bits are the Host Part, designating a particular host on that subnet Local Part Network Part Subnet Part Host Part IP Address (32 bits total)

32. The First Router • The first router receives an IP message packet in one port (interface) • The router must make a router forwarding decision: which port to use to send it back out B B? D? Router A D Packet C? C

33. IP Addresses • Between different organization networks, routers look first at the Network Part of an arriving IP packet’s destination address • If the network part is not that of the organization, the router cannot deliver the IP packet locally • Passes the IP packet on to another router, called a next-hop router, to move the IP packet closer to the destination host Network Part

34. IP Addresses • For IP, Routers Take the Place of Post Offices • There are hundreds of millions of IP addresses on the Internet • Routers cannot store decision rules for reaching each address individually • Router simply asks if a destination IP address is that of a host on one one of the networks or subnets connected to the router or must be passed on to another router • This is the router forwarding decision

35. IP Addresses • To Simplify Router Decisions, IP Addresses are Hierarchical • The Internet is Made of Many Individual Networks Owned by Different Organizations • First route packets to a single network; only need one “sorting bin” for each network! • In the next step, route packet to host on the network

36. Layer Cooperation on the First Router • Routers only have physical, data link, and internet layer processes • So internet layer process is the highest-layer process on a router for router forwarding • Internet layer process decides where to send the packet next: another router or the destination host Internet Data Link Data Link First Router

37. Layer Cooperation on the First Router • The data link and physical layer process on the selected port sends the frame encapsulating the IP packet onto the next router (or destination host) Internet Internet Data Link Data Link Frame Selected Output Port On First Router Physical Layer Input Port On Next Router (Or Destination Host)

38. Domain Names • Internet uses hierarchical naming • A domain is a collection of resources managed by an organization • Generic top level domains by type of organization • .com for commercial organizations • .edu for educational institutions • National top level domains by country • .UK United Kingdom • .AU Australia

39. Domain Names • Organizations register second-level domain names • Microsoft.com • weber.edu • uahc.org • Whitehouse.gov

40. Domain Names • Organizations can create lower-level domain names • cba.weber.edu (for the College of Business Administration) • The lowest level domain name is the host name for an individual host or router • www.cba.weber.edu • www.microsoft.com

41. Domain Name System (DNS) • Only IP addresses are official--e.g., 137.190.62.157 • These are 32-bit binary numbers • Only they fit into the 32-bit destination and source address fields of the IP headers IP Packet 32-bit Source and Destination Addresses (110011...)

42. Domain Name System (DNS) • Users typically only know host names • Plogan.cba.weber.edu or weber.edu IP Packet NO Weber.edu

43. Domain Name System (DNS) • User’s computer sends a DNS host the target host’s host name in a DNS Request message • Sending an IP address (URL) is a request that is data • DNS host returns the target host’s IP address in DNS Response message Weber.edu User PC Internet Layer Process DNS Host 157.190.3.212

44. Domain Name System (DNS) • 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

45. Domain Name System (DNS) • 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

46. A Closer Look at HTTP HyperText Transfer Protocol

47. Protocols • A protocol is a standard for communication between peer processes, that is, processes at the same layer, but on different machines • HTTP: Browser and webserver application programs are at the same layer but on different machines Message App HTTP App

48. Protocols • A protocol is a standard for communication between peer processes, that is, processes at the same layer, but on different machines • TCP (Transmission Control Protocol) is the protocol governing communication between transport layer processes on two hosts Message Trans TCP Trans

49. HTTP: A Closer Look • World Wide Web Standards • HTTP (HyperText Transfer Protocol) governs requests and responses between the browser and the webserver application program • HTML (HyperText Markup Language) governs the structure of the HTML webpage HTTP Browser Webserver Program HTML

50. HTTP: A Closer Look • HTML Pages Contain Text to be displayed • HTML Pages Contain Tags • Some tags say “place a graphic here”, “place a JAVA applet in a box here”, etc., • For instance, the tag <img src=“big.jpg> says “Get file big.jpg and place it here in the HTML document” • Graphics, Java programs, are separate files