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Dialups

Dialups. Access for Remote Users via Telephone lines. Dialups. Uses a remote node - typically a PC Requires phone lines, modems, and terminal servers Phone lines are typically set up in ‘hunt groups’ (a.k.a. phone rotors). Analog. Uses standard phone lines and modems Limited to < 53 Kbps

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Dialups

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  1. Dialups Access for Remote Users via Telephone lines

  2. Dialups • Uses a remote node - typically a PC • Requires phone lines, modems, and terminal servers • Phone lines are typically set up in ‘hunt groups’ (a.k.a. phone rotors)

  3. Analog • Uses standard phone lines and modems • Limited to < 53 Kbps • Line quality often limits throughput

  4. Digital • ISDN, ADSL, etc. • Requires Digital Lines and Service • Requires Digital Modems at both ends

  5. ASCII Dial-in Services • The remote node acts like (emulates) a ‘dumb’ terminal. • Requires the remote node to run terminal emulation software: • Kermit, ProComm, HyperTerminal, etc. • The terminal server provides telnet or other capabilities

  6. Dialup Networking (PPP and SLIP) • The remote node acts like a locally-attached network node. • Requires the remote node to run a TCP/IP stack • Winsock for windows 3.1 and 3.11 • Windows 95 or NT Dialup Networking • MacPPP or Apple OpenTransport

  7. PPP • Point to Point Protocol • Preferable to SLIP • Requires less setup and scripting • Negotiates MTU, IP address, subnet mask, default gateway

  8. Winsock • Windows Sockets • Standardized Interface to TCP/IP services

  9. Windows 95 • Dialup Networking is PPP • Treats Modem like any other network interface • Applications don’t know the difference

  10. MacPPP • Implements PPP on MacOSs

  11. Unices • May require recompiling kernel or kernel extensions

  12. Protocols • IP • IPX • NetBEUI • Appletalk

  13. TCP/IP • Internet Standard Protocol • End node requires an IP address, subnet mask, gateway address, MTU

  14. IPX • Novell Netware typically uses IPX packets, not IP packets • End node needs a network number and network ID

  15. Appletalk • Appletalk is used to access AppleShare disks and/or printers • End node requires an Appletalk Zone

  16. Virtual Private Tunneling Networks • Creates a private, encrypted network within a public network • Packets are encrypted, then passed over public networks • Encryption reduces the risk of ‘packet sniffing’ • Primarily used on NT

  17. Capacity • Currently one of the fastest-growing services • Typical ‘prime time’ hours are 8:00 am to midnight • Average ASCII session lasts < 20 minutes • Average PPP session lasts > 40 minutes

  18. Time Limits • A necessity unless you have unlimited resources (phone lines, modems, terminal servers) • They are never popular • They should be imposed from the beginning • They are easier to relax than to tighten, so start conservatively

  19. Time Limits • Some lines for very short sessions (< 10 minutes) to check email • The vast majority of sessions are under 2 hours. • A few lines for very long or unlimited sessions (downloads, etc.) • You can roll lesser service levels over to greater service levels

  20. Security • Authorization - who is connected to you network • RADIUS • Access Controls - Where can they connect to and what can they do • by network or per host • A ‘must’ for PPP and SLIP • A good idea for ASCII users

  21. Problem Determination • Who is on? Is the user actually connected? • Where are they connected? • What protocol are they using? • How is the connection configured?

  22. Accounting • Important as an audit trail • Begin and end date and time, user, line, protocol

  23. Routing Controls • Without a route to a given destination set on the terminal server, clients cannot send packets to that network or system. • If ASCII dial-in users are not authenticated, then they should not have routes to any unsecured systems, services, or the Internet

  24. Throughput • Modem protocols above 14.4 Kbps include data compression, so compressible data gets a bigger apparent boost

  25. Line Quality • Modems test the line quality and will ‘throttle down’ to a reliable speed • Line quality involves several segments • End user’s lines to local switch • Inter-office trunk lines • Service Provider’s lines to local switch

  26. Telephone Switching Capacity • Inter-office services - ‘trunk lines’ between local switching centers - are the most common bottleneck. • The typical telephone switching center is designed for each phone to be in use an average of 3 minutes per hour at peak load. • Widespread Internet access via dialups may require as much as 15 times the telephone switching capacity currently in place

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