16. PPP –– PPooiinntt ttoo PPooiinntt
PPrroottooccooll
6 Fields Make Up the PPP Frame
The following descriptions summarize the PPP frame fields illustrated above:
Flag—A single byte that indicates the beginning or end of a frame. The flag field
consists of the binary sequence 01111110.
Address—A single byte that contains the binary sequence 11111111, the
standard broadcast address. PPP does not assign individual station addresses.
Control—A single byte that contains the binary sequence 00000011, which calls
for transmission of user data in an unsequenced frame. A connectionless link
service similar to that of Logical Link Control (LLC) Type 1 is provided.
17. PPP – Point ttoo PPooiinntt PPrroottooccooll
–– ((CCoonnttiinnuueedd))
6 Fields Make Up the PPP Frame
The following descriptions summarize the PPP frame fields illustrated above:
Protocol—Two bytes that identify the protocol encapsulated in the information
field of the frame. The most up-to-date values of the protocol field are specified in
the most recent Assigned Numbers Request For Comments (RFC).
Data—Zero or more bytes that contain the datagram for the protocol
specified in the protocol field. The end of the information field is found by
locating the closing flag sequence and allowing 2 bytes for the FCS field.
18. PPP – Point ttoo PPooiinntt PPrroottooccooll
–– ((CCoonnttiinnuueedd))
6 Fields Make Up the PPP Frame
The following descriptions summarize the PPP frame fields illustrated above:
The default maximum length of the information field is 1,500 bytes. By prior
agreement, consenting PPP implementations can use other values for the
maximum information field length.
Frame check sequence (FCS)—Normally 16 bits (2 bytes). By prior
agreement, consenting PPP implementations can use a 32-bit (4-byte) FCS
for improved error detection.
26. HHaannddsshhaakkiinngg
In telecommunication and microprocessor systems, the term
handshaking has the following meanings:
1. In data communications, a sequence of events governed by hardware or
software, requiring mutual agreement of the state of the operational modes
prior to information exchange
2. The process used to establish communications parameters between two
stations
Handshaking follows the eessttaabblliisshhmmeenntt ooff aa cciirrccuuiitt bbeettwweeeenn tthhee ssttaattiioonnss and
pprreecceeddeess iinnffoorrmmaattiioonn ttrraannssffeerr.. It is used to agree upon such parameters as
iinnffoorrmmaattiioonn ttrraannssffeerr rraattee,, aallpphhaabbeett,, ppaarriittyy,, iinntteerrrruupptt pprroocceedduurree,, aanndd ootthheerr
pprroottooccooll ffeeaattuurreess
41. PPoorrtt aanndd MMooddeemm
SSeettttiinnggss ((ccoonnttiinnuueedd))
CCoommmmuunniiccaattiioonn bbeettwweeeenn ttwwoo DDCCEE ddeevviicceess ((ttwwoo
mmooddeemmss)) iiss ccoonnttrroolllleedd bbyy mmooddeemm sseettttiinnggss
– PPhhoonnee lliinnee
– AAnnaalloogg
– LLiinnee ssppeeeedd
Use Rule of Thumb – If the device plugs into the computer serial port and works
normally, the device is wired as DCE (or the connection cable is a crossover type
that makes it work as a DCE). If the device connects to the computer port using a
"null modem" crossover cable, it is wired as DTE.
43. DDTTEE oorr DDCCEE DDeevviiccee
How Can I Identify DTE or DCE Type Connections?
What devices have DTE type RS-232 ports? A DTE device is "Data
Terminal Equipment", this includes Computers, Serial Printers, PLC's,
Video Cameras, Video Recorders, Video Editors, and most devices which
are not used to extend communications. Think COMPUTER for DTE.
What devices have DCE type RS-232 ports? A DCE device is "Data
Communications Equipment", this includes devices intended to plug
directly into a DTE port, PDA cables, Modems and devices that extend
communications like a modem, such as RS-422, RS-485, or Fiber Optic
converters or Radio Modems. Think MODEM for DCE.
66. SShhaarriinngg IInntteerrnneett
CCoonnnneeccttiioonnss –– ((CCoonnttiinnuueedd))
Internet Connection Sharing (ICS) enables a Windows computer
to share its Internet connection with computers on local area
networks. It's been around since WWiinnddoowwss 9988 SSEE, and with the
launch of Windows XP, it's only gotten better
Windows XP ICS has some notable advantages over the versions
of ICS in Windows 98 Second Edition and Windows Me:
It's easier to set up. There's no software to install, and it doesn't
add any network components or protocols
It's much more reliable and much less likely to cause network
problems
67. SShhaarriinngg IInntteerrnneett
CCoonnnneeccttiioonnss –– ((CCoonnttiinnuueedd))
Windows XP ICS has some notable advantages over the versions
of ICS in Windows 98 Second Edition and Windows Me:
(Continued)
You can create a Network Bridge connecting two or more local
area networks and share the Internet connection with the
computers on all of them. This is especially useful if your XP
computer is connected to both a wired and wireless network
ICS client computers can use XP's Internet Gateway to monitor
and control the server computer's Internet connection. If you
have a dial-up connection, you can connect and disconnect when
deciding whether to enable ICS
68. SShhaarriinngg IInntteerrnneett
CCoonnnneeccttiioonnss –– ((CCoonnttiinnuueedd))
Consider these points when deciding whether to enable ICS
WWAARRNNIINNGG ##11:: When you enable ICS, the network adapter connected to the
local area network is assigned a static IP address of 192.168.0.1. The client
computers are assigned other IP addresses in the 192.168.0.x range. These
addresses may not be compatible with an existing network
WWAARRNNIINNGG ##22:: Don't enable ICS if any computer in your network is configured as
a domain controller, DHCP server, or DNS server. Don't enable it if another
computer is running ICS or Network Address Translation (NAT)
WWAARRNNIINNGG ##33:: To enable ICS, you must be logged on as a user that is a
member of the Administrators group
WWAARRNNIINNGG ##44:: If you establish a Virtual Private Networking (VPN) connection
while sharing a different connection, the client computers won't be able to access
the Internet until the VPN connection is ended
69. SShhaarriinngg IInntteerrnneett
CCoonnnneeccttiioonnss –– ((CCoonnttiinnuueedd))
Preparing for ICS
The ICS server computer must have two network connections: one for the
Internet, and one for the local area network. The Internet connection may be a
dial-up (PPP or ISDN), cable modem, DSL, or other broadband Ethernet
connection. The LAN connection may be a wired, wireless, or even a USB
Ethernet connection. Before enabling ICS:
Set up your Internet connection and test it so that you know you can connect
to the Internet
Decide whether to allow client computers to control the server's Internet
connection using the Internet Gateway. This feature is automatically available
on clients running Windows XP. On clients running Windows 98, Windows 98
Second Edition, or Windows Me, you must run XP's Network Setup Wizard to
enable the gateway. If you have a Windows XP CD-ROM, you can run the
Wizard from it. Otherwise, create a network setup disk containing the Wizard files
