CCNA Guide to Cisco Networking

1
CCNA Guide to Cisco Networking

• Chapter 11 PPP and ISDN

2
Objectives

• Describe PPP encapsulation
• Configure PPP encapsulation and its options
• Describe and enable PPP multilink
• Explain how to implement ISDN BRI on Cisco
  routers
• Configure an ISDN BRI connection

3
PPP

• Internet standard protocol
• Considered a peer technology
• Used over dial-up or leased lines
• Support for multiple Network layer protocols
• Most widely use WAN connection protocol

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PPP (continued)

• SLIP
• Supports
• Encryption
• Compression
• Error correction
• Works with synchronous and asynchronous
  connections
• Can be applied on many different physical
  interfaces
• Asynchronous serial
• ISDN synchronous
• High-Speed Serial Interface (HSSI)

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PPP In The Protocol Stack

• Link control protocol
• Data Link layer
• Establish
• Configure
• Test
• Network control protocols (NCPs)
• Allows multiple protocols to used at the same
  time
• IP control protocol (IPCP)
• IPX control protocol (IPXCP)
• AppleTalk control protocol (ATCP)

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PPP In The Protocol Stack (continued)
7
Frame Format
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Frame Format (continued)

• Frame fields of PPP
• Flag Binary sequence 01111110, which indicates
  the beginning of the frame
• Address Binary sequence 11111111 because PPP is
  used to create a point-to- point connection,
  there is no need for PPP to assign an individual
  address for each host
• Control Binary sequence 00000011, which
  indicates that the transmission of user data will
  not be sequenced and is to be delivered over a
  connectionless link
• Protocol Two bytes used to identify the protocol
  that is encapsulated

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Frame Format (continued)

• Frame fields of PPP (continued)
• LCP or Data The LCP field is also known as the
  Data field, which is the location contains the
  LCP information and the data that has been
  encapsulated from the higher layers
• Frame Check Sequence (FCS) Cyclical redundancy
  check (CRC) to verify the integrity of the frame
• Flag Binary sequence 01111110, which identifies
  the end of the data frame

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LCP

• LCP field of the PPP packet may include
• Asynchronous character map
• Maximum receive unit size
• Compression
• Authentication
• PAP
• CHAP
• Magic number
• Link quality monitoring (LQM)
• Multilink

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LCP Link Configuration

• LCP link configuration process includes
• Link establishment
• Authentication (optional)
• Link-quality determination (optional)
• Network layer protocol configuration negotiation
• Link termination

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Establishing PPP Communications

• Link establishment phase
• First phase
• Testing and configuration of the data link
• Second phase
• Optional authentication
• PAP and CHAP
• Third phase
• Network layer protocol configuration negotiation
• Data packet transfer may begin

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Establishing PPP Communications (continued)
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Configuring PPP Authentication

• Configure PPP authentication on each PPP host
• Link flapping will occur if authentication is
  only on one host
• PAP
• Two-way handshake
• Usernames and Passwords sent in clear text
• CHAP
• Three-way handshake
• Usernames and passwords are protected

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Configuring PPP Authentication (continued)
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Configuring PPP Authentication (continued)
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Configuring PPP Authentication (continued)
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Confirming PPP Communications

• show interface command
• Router show interface serial 0/0

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ISDN

• Circuit-switched service
• Existing telephone service
• Data
• Voice
• Video
• Audio transmission
• Faster than traditional modem speeds

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ISDN (continued)

• Basic Rate Interface (BRI)
• 128 kbps total data transfer bandwidth
• 2 B-channels
• Bearer channel for data transfer
• 64 kbps
• 1 D-channel
• Delta or data channel for signaling
• Out of band signaling
• Link Access Procedure-D
• 16 kbps

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ISDN (continued)

• Primary Rate Interface (PRI)
• 1.544 mbps total data transfer bandwidth
• 23 B-channels
• Bearer channel for data transfer
• 64 kbps
• 1 D-channel
• Delta or data channel for signaling
• Out of band signaling
• Link Access Procedure-D
• 64 kbps

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ISDN (continued)
23
ISDN Standards
24
ISDN Operations
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ISDN Operations (continued)

• Functions and references
• Function groups
• Terminal adapter
• Terminal equipment 1 (TE1)
• Terminal equipment 2 (TE2)
• Network termination 1 (NT1)
• Network termination 2 (NT2)

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ISDN Operations (continued)

• Functions and references (continued)
• Reference points
• U Demarc between client and telco
• R Point between non-ISDN equipment (TE2) and TA
• S Point between customers TE1 or TA and the
  network termination (NT1 or NT2)
• T Point between a NT1 and a NT2
• S/T Point between TA and NT1 in the absence of a
  NT2

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SPID

• Connect to service provider switch
• Service Profile Identifier (SPIDs)
• Dial-in access
• ISDN phone numbers
• Provide a profile
• Service level agreement
• AutoSPID

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SPID (continued)

• Service provider switch types
• dms-100 Northern Telecom DMS-100 (as previously
  described)
• ni1 National ISDN-1 used in North America
• net3 Net3 switch used in Europe and the United
  Kingdom
• ntt Switch from NTT used in Japan
• 1tr6 1TR6 switch used in Germany
• ts013TS013 Australian switch
• none Used when a switch has not been specified

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SPID (continued)
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Multilink PPP

• Combine the bandwidth of individual links or
  channels
• Multilink provides
• Load balancing
• Packet fragmentation and reassembly
• Sequencing for packets
• Creates one logical connection
• Function over synchronous or asynchronous
  connections
• Router(config-if) ppp multilink

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DDR

• Dial-on-demand routing (DDR)
• Intermittent WAN access
• Saves money on metered lines
• Used with circuit switched access
• Define interesting traffic
• Common configuration commands
• dialer-list command
• dialer-group command
• access-list command

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DDR (continued)
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DDR (continued)
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ISDN BRI Configuration Examples
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ISDN BRI Configuration Examples (continued)

• Dialer profiles
• Scalable compared to legacy DDR
• Configuration of dialer profiles involves
• Dialer interface
• Logical configuration
• Dial string for each destination subnet
• Dialer map class
• Optional commands
• Define characteristics for each call
• Dialer pool
• Identify the physical interface that will be used
  by the dialer interface

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ISDN BRI Configuration Examples (continued)
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Monitoring ISDN

• ISDN problems are often associated with
• PPP configuration
• debug ppp authentication
• debug ppp negotiation
• clear interface
• Dialer configurations
• show dialer
• show interface
• debug dialer
• ISDN monitoring commands
• show isdn status
• show interface bri 0
• debug q921

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Digital Lines

• T1 24-channel, 1.544 mbps
• T1C 48-channel, 3.152 mbps
• T2 96-channel, 6.312 mbps
• T3 672-channel, 44.376 mbps
• T4 4032-channel, 274.176 mbps
• E1 30-channel, 2.048 mbps
• Fractional T1 or E1
• Digital Subscriber Line (DSL)

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Summary

• Many WAN connectivity options are available for
  modern networks, including digital lines, Frame
  Relay, and analog modems
• WAN technologies typically define Data Link and
  Physical layer standards
• The Point-to-Point Protocol (PPP) is the most
  widely used WAN protocol today
• On Cisco routers, PPP is used mainly as a Data
  Link layer encapsulation method however, it does
  provide an interface to the Network layer via
  specific Network Control Protocols (NCPs)

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Summary (continued)

• PPP provides link establishment, quality
  determination, Network layer protocol
  encapsulation, and link termination services
• PPP is often used over Integrated Services
  Digital Network (ISDN) connections
• ISDN is a digital service provided by several
  telecommunications companies worldwide
• ISDN was developed as a faster WAN connection to
  replace analog modems, and as a cheaper
  alternative to Frame Relay and full T1
  connections
• ISDN service comes in Basic Rate Interface (BRI)
  and Primary Rate Interface (PRI)

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Summary (continued)

• BRI offers connections of up to 128 Kbps for data
  transfer, and PRI offers up to 24 channels in the
  United States, each with the ability to transfer
  data at 64 Kbps
• Connections over ISDN can take advantage of
  dial-on-demand routing (DDR) and multilink
  services offered through PPP connections
• DDR allows the router using an ISDN connection to
  dial only when there is interesting traffic and
  to add more channels as needed to support given
  traffic levels
• DDR can be implemented using dialer profiles,
  which allow more flexibility regarding the
  calling parameters
• Multilink allows ISDN to use multiple channels
  evenly by spreading the load across those channels