CCNA Routing and Switching Lesson 05 - WANs - Eric Vanderburg

1. WANs
Chapter 5
Networking Essentials – Eric Vanderburg © 2005

2. DSL
DSL is layer 1
 ATM can be used on top of DSL
 PPPoE

CHAP authentication
 IP address assignment


DSLAM (DSL Access Multiplexer)
Connection at ISP for DSL. Separates
voice from data.
 Data is sent over the ISP’s data network
rather than the PSTN.


3. Cable Modem
Datalink protocol is MCNS (Multimedia
Cable Network Systems) – Identifies
each modem so shared data is only
processed by the designated modem.
 Different channels are used for upstream
& downstream data.


4. Cable Modem

Downstream data

QAM (Quadrature Amplitude Modulation)
 QAM

64 & QAM 256
Upstream data
QPSK (Quaternary Phase Shift Keying)
 QAM 16
 Same frequency range as other uses (can
collide)


5. DCE & DTE
CSU/DSU is considered DCE (Data
Communications Equipment) because it
does clocking
 Router is considered DTE (Data
Terminal Equipment)
 Connecting 2 routers directly

Use DTE to DCE cable
 One router must have clocking configured


6. HDLC (High level Data Link
Control)
Cisco uses a proprietary version with a
type field in the header.
 Default for Serial ports
 FCS in trailer. Error frames are
discarded
 Synchronous, sends receiver ready
frames when there is no data to synch
the line (keep timing for 1’s & 0’s)


7. PPP (Point to Point Protocol)
FCS in trailer
 Type field
 LCP (Link Control Protocol) - used with
dialed links to bring the connection up
 IPCP (IP Control Protocol) allows IP
addresses to be assigned over PPP
 PPP Callback - incoming connections
are disconnected & called back to verify
number and stop roaming or
unauthorized access


8. PPP (Point to Point Protocol)
Magic Number looped link detection
 Supports multilink
 PAP & CHAP support
 Synchronous or Asynchronous (used
mainly for dial-up)
 LQM (Link Quality Monitoring) – takes
down links with too many errors
 Supports compression but tasks router
processor


9. ISDN
B & D channels
 LAPD (Link Access Procedure D
channel)

used to set up and bring down circuits.
 Q.931 specifies the setup & teardown
messages

Circuit switching. Can connect to many
sites but circuits are set up by dialing.
 SPID (Service Profile Identifier) –
provided by the ISP for authenticating B
channels.


10. ISDN



B channels are digital so an analog line is
used for the DTMF (Dual Tone Multifrequency) tones
BRI for residential use (2B+D), D channel 16k
PRI for business use, D channel 64k


T1 (23B+D), uses AMI (Alternate Mark Inversion)
or B8ZS (Binary 8 with Zero Substitution) encoding
E1 (30B+D), uses HDB3 (High Density Bipolar 3)
encoding

11. ISDN DDR

DDR (Dial on Demand Routing) dials a
link if traffic is waiting to go to a site that
is not currently connected
Interesting & boring traffic (interesting traffic
“triggers the dial”)
 Dial mapping - DDR needs to be configured
with the networks on each link (static route)
& their phone numbers
 Idle timeouts allow unused connections to
be taken down.


12. Frame Relay
Frame switching service
 Leased lines from router to FR switch
 Layer 2 address – DLCI (Datalink
connection Identifier), only a place for
one DLCI number in FR frames.
Changed by switches at destination.
 Encapsulation type must be same
between routers (Cisco & IETF). Use
IETF if both routers are not Cisco.


13. Frame Relay
PVC (Permanent Virtual Circuit) – link
between 2 devices on a FR network.
PVCs are set up between the devices
you own on the FR network. (Set up by
provider)
 CIR (Committed Information Rate) –
minimum bandwidth specified


14. Frame Relay

LMI (Local Management Interface) – used for
messages sent between router & switch.
Encoding type must be same






Sends keepalive messages
Status messages can be used to find DLCI
numbers of other routers
Cisco LMI uses DLCI 1023
ANSI T1.617-D & ITU Q.933-A LMI’s use DLCI 0
LMI autosense
Inverse ARP maps IP addresses to DLCI numbers.
Routers send their IP address

15. ATM
Layer 2 protocol using fixed length cells
 Usually runs on top of SONET,
sometimes DSL
 VPI (Virtual Path Identifier) & VCI (Virtual
Channel Identifier) – used to switch cells


16. X.25
Operates on layers 2 & 3
 Reliable with high overhead
 Used in many foreign countries
