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Point to Point Protocol - Computer Network - Lecture Slides, Slides of Computer Networks

Chhattisgarh Swami Vivekanand Technical UniversityComputer Networks

Point to Point Protocol, Serial Communication, Time Division Multiplexing, Demarcation Point, Data Terminal Equipment, Data Communications Equipment, HDLC Encapsulation and many other topics of Computer Network can be find in my documents.

Typology: Slides

2011/2012

Uploaded on 11/09/2012

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Point-to-Point Protocol
(PPP)
Semester 4 – Module 3
Students completing this module should be able to:
Describe and give an example of TDM
Identify the demarcation point in a WAN
Describe the functions of the DTE and DCE
Discuss the development of HDLC encapsulation
Use the encapsulation hdlc command to configure HDLC
Troubleshoot a serial interface using the show interface and show controllers commands
Identify the advantages of using PPP
Explain the functions of the Link Control Protocol (LCP) and the Network Control Protocol (NCP)
components of PPP
Describe the parts of a PPP frame
Identify the three phases of a PPP session
Explain the difference between PAP and CHAP
List the steps in the PPP authentication process
Identify the various PPP configuration options
Configure PPP encapsulation
Configure CHAP and PAP authentication
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Point-to-Point Protocol

(PPP)

Semester 4 – Module 3

Students completing this module should be able to:  Describe and give an example of TDM  Identify the demarcation point in a WAN  Describe the functions of the DTE and DCE  Discuss the development of HDLC encapsulation  Use the encapsulation hdlc command to configure HDLC  Troubleshoot a serial interface using the show interface and show controllers commands  Identify the advantages of using PPP  Explain the functions of the Link Control Protocol (LCP) and the Network Control Protocol (NCP) components of PPP  Describe the parts of a PPP frame  Identify the three phases of a PPP session  Explain the difference between PAP and CHAP  List the steps in the PPP authentication process  Identify the various PPP configuration options  Configure PPP encapsulation  Configure CHAP and PAP authentication Docsity.com

Overview

  • This module is an overview of WAN Technologies
  • PPP is the protocol of choice to implement over WAN

connections

  • Point-to-Point Protocol (PPP) is the protocol of choice to

implement over a serial WAN switched connection.

  • It can handle both synchronous and asynchronous communication and includes error detection.
  • Most importantly it incorporates an authentication process using either CHAP or PAP.
  • PPP can be used on various physical media, including

twisted pair, fiber optic lines, and satellite transmission.

Time-Division Multiplexing

• Transmits several sources of information using

one common channel, or signal

• Reconstructs the original streams at the remote

end

• The output timeslot is always present whether or

not the TDM input has any information to

transmit

• TDM is a physical layer concept, it has no regard

for the nature of the information that is being

multiplexed onto the output channel

• TDM is independent of the Layer 2 protocol that

has been used by the input channels

Demarcation Point

• The demarcation point, or "demarc" as it is

commonly known, is the point in the network

where the responsibility of the service provider

or "telco" ends.

Data Terminal Equipment (DTE)

• The CPE, which is generally a router, is the DTE

• If two DTEs must be connected together, such

as two computers or two routers, a special cable

called a null-modem is necessary to eliminate

the need for a DCE

• For synchronous connections, where a clock

signal is needed, either an external device or

one of the DCEs must generate the clock signal

• Other DTE examples could be a terminal,

computer, printer, or fax machine

Data Communications Equipment (DCE)

  • The DCE, commonly a modem or

CSU/DSU, is the device used to convert

the user data from the DTE into a form

acceptable to the WAN service provider

transmission link

  • The connection between the two DCEs is

the WAN service provider transmission

network

HDLC Frame Types

• HDLC defines the following three types of

frames, each with a different control field format:

  • Information frames (I-frames) - Carry the data to be

transmitted for the station. There is additional flow

and error control, and data may be piggybacked on

an information frame.

  • Supervisory frames (S-frames) - Provide

request/response mechanisms when piggybacking is

not used.

  • Unnumbered frames (U-frames) - Provide

supplemental link control functions, such as

connection setup. The code field identifies the U-

frame type.

Configuring HDLC Encap

• Default encapsulation method used by Cisco

devices on synchronous serial lines

• If the serial interface is configured with another

encapsulation protocol, and the encapsulation

must be changed back to HDLC, enter the

interface configuration mode of the serial

interface.

  • encapsulation hdlc

• Cisco HDLC is a point-to-point protocol that can

be used on leased lines between two Cisco

devices

• When communicating with a non-Cisco device,

synchronous PPP is a more viable option

PPP Layered Architecture

  • A layered Design that provides a method for encapsulating

multi-protocol datagrams over a point-to-point link

  • Load balancing possibilities
  • PPP is made up of two sub-protocols:
  • Link Control Protocol (LCP) - sits on top of the physical layer and is used to establish, configure, and test the data-link connection
  • Network Control Protocol (NCP) - encapsulates and negotiates options for multiple network layer protocols
  • PPP can be configured on the following types of physical

interfaces:

  • Asynchronous serial
  • Synchronous serial
  • High-Speed Serial Interface (HSSI)
  • Integrated Services Digital Network (ISDN)

Link Control Protocol (LCP)

  • PPP also uses LCP to automatically agree upon

encapsulation format options such as:

  • Authentication
    • PAP or CHAP are used to ensure the caller has the network administrator's permission to make the call.
  • Compression
    • Two compression protocols available in Cisco routers are Stacker and Predictor
  • Error detection
    • Error detection enables a process to identify fault conditions
  • Multilink
    • Cisco IOS Release 11.1 and later supports multilink PPP
    • Provides load balancing
  • PPP Callback
    • Cisco IOS Release 11.1 offers callback over PPP
    • Cisco router can act as a callback client or as a callback server Docsity.com

Establishing a PPP Session

  • Link-establishment phase
    • PPP device sends LCP frames to configure and test the data link
    • Before any network layer packets can be exchanged, LCP must first open the connection and negotiate the configuration parameters
    • A configuration acknowledgment frame is sent and received
  • Authentication phase (optional)
    • Takes place before the network layer protocol phase is entered
    • LCP also allows for an optional link-quality determination test to determine whether the link quality is good enough to bring up network layer protocols
  • Network layer protocol phase
    • NCP packets are sent to choose and configure one or more network layer protocols, such as IP.
    • Once each of the chosen network layer protocols has been configured, packets from each network layer protocol can be sent over the link.
    • If LCP closes the link, it informs the network layer protocols so that they can take appropriate action.
  • The show interfaces command reveals the LCP and NCP states under PPP configuration.

Password Authentication Protocol (PAP)

  • PAP provides a simple method for a remote node to establish its identity, using a two-way handshake
  • After the PPP link establishment phase is complete, a username/password pair is repeatedly sent by the remote node across the link until authentication is acknowledged or the connection is terminated
  • PAP is not a strong authentication protocol.
    • Passwords are sent across the link in clear text and

can be easily spoofed to allow playback or repeated

trial-and-error attacks.

  • The remote node is in control of the frequency and

timing of the login attempts.

Intro to Configuring PPP

• Configurable aspects of PPP include the

following:

  • authentication
  • Compression
  • error detection
  • whether or not multilink is supported.

• When the encapsulation ppp command is

used, either PAP or CHAP authentication can be

optionally added

• If no authentication is specified the PPP session

starts immediately

Configuring PPP

  • The following example enables PPP encapsulation on serial interface 0/0: - Router# configure terminal - Router(config)# interface serial 0/ - Router(config-if)# encapsulation ppp
  • To configure compression over PPP, enter the following commands:
    • Router(config)# interface serial 0/
    • Router(config-if)# encapsulation ppp
    • Router(config-if)# compress [predictor | stac]
  • Enter the following to monitor the data dropped on the link, and avoid frame looping: - Router(config)# interface serial 0/ - Router(config-if)# encapsulation ppp - Router(config-if)# ppp quality percentage
  • The following commands perform load balancing across multiple links:
    • Router(config)# interface serial 0/
    • Router(config-if)# encapsulation ppp
    • Router(config-if)# ppp multilink Docsity.com