Transcript Cisco Semester 4 Chapter 2

Cisco Semester 4 Chapter 2
WANS
Technologies Not Covered
in Semester 4
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DSL
Cable Modem
ATM
SONET
SMDS
WAN Services
• Layer 1
– CSU/DSU connects to WAN to CSU/DSU to
other route
• Service Providers
– POTS, X.25/Frame Relay, TDM or T1/E1, Call
setup, e.g. SS7
– Frame Relay LMI
• Allows DLCI to become unique network addresses
• DLCI value placed in frame header
DCE/DTE
• CPE – customer premises equipment
– On customer premises – owned and leased
• Demaraction – point where CPE ends and local
loop service begins, e.g. POP
• Local Loop – last mile – CAT 5 – goes from
demarc to WAN provider central office
• CO – nearest point of presence for provider’s
WAN
• Toll Network – inside WAN provider cloud
• DTE – typically router
DCE – converts user
data into WAN acceptable format
Virtual Circuits
• Pathway through a packet-switched network
that appears to be dedicated physical circuit
– Can be connection-oriented (like TCP)
– PVC - Customer and carrier negotiate end
points and characteristics of virtual circuit
• Constantly available
– SVC – virtual circuit availably only on demand
WAN Line Types and Bandwidth
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56 DSO 56b kbps
64 DSO 64 kbps
T1 DS1 1.544 Mbps
E1 ZM 2.048 Mbps
E3 M3 34.068 Mbps
J1 Yi
2.048 Mbps
T3 DS3 44.736 Mbps
OC 1-48 Sonet 51.84 to 2488.32 Mbps
WAN Devices
• Router – both LAN and WAN
• WAN Switches – connect to WAN bandwidth
– Layer 2 (but distinct); mostly in WAN cloud
– Frame Relay, X.25, SMDS
• Modems - CSU/DSU and TA/NT1 devices that
interface ISDN services
• Communication servers to concentrate dial-in and
dial-out communications
Modems
• Interprets digital and analog signals
– Enable data to be transmitted over voice-grade
telephone lines
Leased Lines
• Router Port
• CSU/DSU
• Service Provider Circuit
ISDN
• TA - device used to connect ISDN BRI
connection to other interfaces
WAN and OSI Model
• WANS focus on physical and data link
layers
– Standards describe physical-layer delivery
methods and data-link layer requirements
• Addressing, flow control, encapsulation
• Agencies
– ITU-T, ISO, IETF, EIA, TIA
WAN Physical Layer Protocols
• EIA/TIA 232
- common standard
• Supports up to 64 kbps; resembles V.24; was RS-232
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V.35 and X.21
HSSI
DTE-DCE
Modem
Standards
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EIA/TIA 449 up to 2 Mbps
EIA/TIA 612-3 HSSI
ITU-T V.24 and .35
X.21 – used in Europe and Japan
WAN Data Link Layer
• Encapsulation Protocols
– HDLC high-level data link control
• Cisco has its own proprietary version
– PPP point to point – standard
• Supports several router protocols
• Replaced SLIP
• WAN Technologies
– Frame Relay
- simplified HDLC
• Packet Switched
– ISDN – data-link signal
• Circuit Switched
WAN Data Link Layer
• Dedicated Point to Point
– Cisco HDLC, PPP, and LAPB (ISDN)
• Packet Switched
– Frame Relay (IETF)
• X.25, Frame Relay
• Circuit Switched
– ISDN D channel LAPD
– ISDN B channel
WAN Data Link Detail
• Frame Relay – simple encapsulation, no error
correction, rapid data transmission
• PPP (RFC 1661) developed by IETF – contains
field to identify network layer protocol
• ISDN – digital; uses existing telephone lines
• LAPB- used to encapsulate packets in the X.25
stack; provides reliability and flow control
• Cisco/IETF – encapsulates Frame Relay traffic
• HDLC – implemented differently by vendors
WAN FORMATS
• Common Fields
– Flag, Address, Control, Data, FCS , Flag
• Different Fields
– PPP uses Protocol field; HDLC has proprietary
field
PPP
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Described in RFC 1661
Specifies Layer 3 protocol type
Is a link control protocol
Provides Authentication
– PAP Password Authentication Protocol
– CHAP Challenge Handshake Authentication
Protocol
HDLC
• Derived from SDLC encapsulation (Synchronous
Data Link Control)
• Cisco default for serial lines
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No windowing or flow control
Allows only point to point connections
Address field set to 1s
20byte type code – not interoperable
• NOTE: Use PPP with devices not running Cisco
IOS software
Dedicated/Switched Lines
• Dedicated
– Leased Lines
• Fractional T1/E1
• T1/E1
• T3/E3
• Switched
– Circuit
• POTS, ISDN, Switched 56
– Packet/Cell Switched
• X.25, Frame Relay, SMDS, ATM
Packet Switched Connections
• Network devices share PVC – permanent
virtual circuit
– Like a point-to-point link
• Frame Relay, SMDS, and X.25
Frame Relay
• Types of Service
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DLCI (Data-Link Connections Identifier)
CIR (Committed Information Rate)
Access Rate 56, 65 kbps or 1.544 Mbps
Two topologies
• Fully meshed – every device has PVD to every other device
• Partially meshed – star topology
• LMI global addressing allows DLCIs to become
unique address for DTE device
Circuit Switched Connections
• Connection on Demand
• Relatively low bandwidth
• Uses
– Remote users
– Mobile users
– Backup lines
DDR –Dial on Demand Routing
• Router can dynamically initiate and close
circuit-switched sessions
– Used as backup link when primary fails
– Source of extra bandwidth when traffic on
primary link reaches a threshhold
– Substitute for dedicated lines when full-time
circuit availability is not required
ISDN
• Three channels – 2 64 kbps B (bearer) and 1 16
kbps D (signaling
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TE1
connects to NT (Type 1 or 2
TE2
designates device not compatible
TA
converts standard signal to ISDN
NT1
Connects 4-wire ISDN wiring
NT2
Directs traffic to and from difference
subscriber devices and NT1
– S/T defines TE1 and NT; R is TE2 and TA U is NT and
ISDN cloud