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Understanding Dial-Up Access for Remote Users: A Comprehensive Guide

This guide explores dial-up access for remote users via telephone lines, detailing both analog and digital connections. It includes discussions on remote nodes, the necessary hardware, terminal emulation software, and the significance of protocols like PPP and SLIP. The differences between various protocols, time limits, security measures using RADIUS, and the importance of throughput and line quality are also covered. This resource serves as a foundational overview for anyone looking to understand the dynamics of dial-up networking.

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Understanding Dial-Up Access for Remote Users: A Comprehensive Guide

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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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