This document discusses networking concepts related to expanding networks, modems, digital modems, carriers, remote access services (RRAS), virtual private networks (VPN), virtual local area networks (VLAN), routing, brouters, and gateways. Key points include the evolution of modem standards to support higher speeds, differences between asynchronous and synchronous communication, digital modem technologies like ISDN and DSL, remote access protocols like PPP, and VPNs as a more secure and cost-effective alternative to modem pools.

1. Chapter 11
Enterprise & Distributed Networks
Networking Concepts – Eric Vanderburg ©2005

2. Expanding Networks
 Modem
(Modulator/Demodulator)
 RJ11
phone port
 External modems use RS-232
(Recommended Standard 232) serial port
 Hayes-compatible – works with software
designed for the original Hayes modems in
the early 80’s
Networking Concepts – Eric
Vanderburg ©2005

3. Modems
Baud – number of sound wave oscillations per second
– old modems transferred 1 bit/baud
 ITU (International Telecommunications Union) –
created the V-series standards

•
•
•
•
•
V.22bis* – 2400baud, 2.4kbps
V.32 – 2400baud, 9.6kbps
V.32bis – 2400baud, 13.4kbps
V.32ter – 2400baud, 19.2kbps
V.FC (Fast Class) – 9600baud,
28.8kbps
•
•
•
•
•
V.34 – 9600baud, 28.8kbps
V.34bis – 9600baud, 33.6kbps
V.42bis – uses compression &
error correction, 28.8kbps
V.90 – 56k d/l, 22.6k u/l
V.92 – modem on hold, 56k
Networking respectively
*Bis & ter mean 2nd & 3rd revisionsConcepts – Eric
Vanderburg ©2005

4. Modems
Asynchronous – start and stop bits are placed before and after each byte
(8 bits + parity bit). More check data and more overhead.
 PCM (Pulse Code Modulation) – digitizing an analog signal on a modem



33.6 Kbps from modem to ISP
56 Kbps from ISP to modem
MNP Class 5 compression
 Synchronous – devices agree on a timing scheme utilizing sync bits and
transfer blocks of data (frames) accordingly. Less overhead, leased line
use. Also provide error checking.

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

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SDLC (Synchronous Data Link Control)
HDLC (High-level Data Link Control)
Bisync (Binary Synchronous)
Transfer rates depend on



Line conditions
V standard
FCC regulations (max is 54kbps)
Networking Concepts – Eric
Vanderburg ©2005

5. Digital Modems

ISDN (Integrated Services Digital Network)





Cable


NT (Network Termination)
TA (Terminal Adapter)
BRI (Basic Rate Interface) – 2 B channels (64k) & 1 D channel (16k),
$50-$70
PRI (Primary Rate Interface) – 23 B channels, 1 D channel
(H10=1472 kb/s *see ch.7), $300-$1500
DOCSIS encrypts each connection to increase security.
DSL



Distance limitation between user and CO (17,500-23,000ft)
ADSL (Asymmetric Digital Subscriber Line) - 8 Mbps d/l, 1 Mbps u/l
SDSL (Symmetric Digital Subscriber Line) - equal d/l and u/l speeds
Networking Concepts – Eric
Vanderburg ©2005

6. Carriers
 Throughput
– how much data can be
sent over the line per second
 Distance
 Cost
Networking Concepts – Eric
Vanderburg ©2005

7. RRAS
 RRAS
Authentication
 Wizard
Networking Concepts – Eric
Vanderburg ©2005

8. RRAS & terms

RRAS




DUN (Dial-up Networking)
SLIP (Serial Line Internet Protocol)



Layer 1
Works with TCP/IP only
CSLIP (Compressed Serial Line Internet Protocol)


Max concurrent clients: 256
Called RAS (Remote Access Service) in NT
Same as SLIP but can compress data to increase speed
PPP (Point-to-Point Protocol)




Layers 1 & 2
Works with IP, IPX, & NetBEUI
Can compress & check for errors
Supports DHCP
Networking Concepts – Eric
Vanderburg ©2005

9. Other Vendors

Novell NetWare provides VPN server connections




Able to form VPN WAN by connecting corporate LANs over
VPN connections through the Internet
Mac OS version 9 and above support VPN client
connections to Windows servers using PPTP or IPSec
Mac OS X Server provides a VPN server service that
permits Mac OS, Windows, and Linux/Unix clients to
connect to the corporate LAN
Linux versions using L2TP may not be compatible with
Windows VPN solutions
Networking Concepts – Eric
Vanderburg ©2005

10. VPN
 Linux
supports VPN client and server
applications
 Not
compatible with Windows L2TP
 More difficult to use; may require a patch to
the kernel
 VPNs
are Less expensive than a modem
pool. Internet connection replaces direct
modem connection
Networking Concepts – Eric
Vanderburg ©2005

11. VLAN
 Implemented
on switches
 Requires a router also
 Divides ports into logical
sections
 Usually separated by
subnet
Networking Concepts – Eric
Vanderburg ©2005

12. Routing
 Static
routing – each path must be
manually entered – same path is used
each time
 Dynamic routing – router determines the
best route based on available info
Networking Concepts – Eric
Vanderburg ©2005

13. Brouters
 Routes
packets that use routable
protocols
 Forwards packets that are not routable
 Useful in hybrid network with mixture of
routable and nonroutable protocols
 May be identified as router with bridging
capabilities
Networking Concepts – Eric
Vanderburg ©2005

14. Gateway
 Operates
at layer 7
 Translates between most dissimilar
networks
 GSNW…
Networking Concepts – Eric
Vanderburg ©2005