DSL is layer 1
ATM can be used on top of DSL
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.
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.
QAM (Quadrature Amplitude Modulation)
64 & QAM 256
QPSK (Quaternary Phase Shift Keying)
Same frequency range as other uses (can
DCE & DTE
CSU/DSU is considered DCE (Data
Communications Equipment) because it
Router is considered DTE (Data
Connecting 2 routers directly
Use DTE to DCE cable
One router must have clocking configured
HDLC (High level Data Link
Cisco uses a proprietary version with a
type field in the header.
Default for Serial ports
FCS in trailer. Error frames are
Synchronous, sends receiver ready
frames when there is no data to synch
the line (keep timing for 1’s & 0’s)
PPP (Point to Point Protocol)
FCS in trailer
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
PPP (Point to Point Protocol)
Magic Number looped link detection
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
B & D channels
LAPD (Link Access Procedure D
used to set up and bring down circuits.
Q.931 specifies the setup & teardown
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
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)
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.
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.
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
CIR (Committed Information Rate) –
minimum bandwidth specified
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
Inverse ARP maps IP addresses to DLCI numbers.
Routers send their IP address
Layer 2 protocol using fixed length cells
Usually runs on top of SONET,
VPI (Virtual Path Identifier) & VCI (Virtual
Channel Identifier) – used to switch cells
Operates on layers 2 & 3
Reliable with high overhead
Used in many foreign countries
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