Transcript WANs

WANs
Semester 4, Chapter 2
Allan Johnson
Table of Contents
Go There!
WAN Technology & Devices
Go There!
WANs & The OSI Model
Go There!
WAN Encapsulation Formats
Go There!
WAN Link Options
WAN Technology &
Devices
Table of Contents
WAN Services
A WAN is the communications network that connects LANs
through a WAN Service Provider (e.g. RBOC)
WANs operate at the first three layers of the OSI, but focus
mainly on the physical and data link layers.
Examples of WAN Services include….
Call-setup
 SS7 used for telephone calls
ISDN
 A circuit-switched service using TDM, which allocates bandwidth to different
sources on the same media
Frame Relay
 A packet-switched service using statistical multiplexing
WAN Physical Structure
Toll Network – collection of
switches/trunks in WAN cloud
CO Switch – nearest point of
presence for the WSP’s service
Local loop – extends from the
CPE (at the demarc) to the CO
CPE – devices located on
premises, either owned or leased
DTE/DCE Interface
The transfer of responsibility for service between
the ISP and the customer occurs at the DTE/DCE
interface.
The customer’s gateway router is always the DTE.
The ISP’s modem or CSU/DSU is the DCE and
sets the clock rate.
In our standard lab, we must make one router on our WAN
links be the DCE since we are not attaching to an ISP
WAN Virtual Circuits
Switched Virtual Circuits (SVCs) are WAN paths to the
destination established and terminated on demand.
Three phases:
 Circuit establishment – creates the virtual circuit
 Data transfer – sending and receiving user data
 Circuit termination – tearing down the virtual circuit
Telephone service and ATM use SVCs
Increased use of bandwidth but decreased cost
Permanent Virtual Circuits (PVCs) are permanently
established circuits with one mode: data transfer
X.25 and Frame Relay use PVCs
Decreased use of bandwidth but increased cost
Link Types & Bandwidth
Line Type
56
64
T1
E1
E3
J1
T3
OC-1
OC-3
OC-9
OC-12
OC-18
OC-24
OC-36
OC-48
Signal Standard
DS0
DS0
DS1
ZM
M3
Y1
DS3
SONET
SONET
SONET
SONET
SONET
SONET
SONET
SONET
Bit Rate Capacity
56 kbps
64 kbps
1.544 Mbps
2.048 Mbps
34.064 Mbps
2.048 Mbps
44.736 Mbps
51.84 Mbps
155.54 Mbps
466.56 Mbps
622.08 Mbps
933.12 Mbps
1.21 Gbps
1.82 Gbps
2.43 Gbps
WAN Devices
In order to connect to a leased line, the customer
must have…
Access to the service provider’s circuit
An appropriate router port available
An a CSU/DSU, modem or ISDN Terminal Adapter
Routers
Routers offer many services including:
Internetworking
WAN serial interfaces
Routers can operate as...
Internal Routers
Backbone Routers
Area Border Routers
Autonomous System Boundary Routers
Modems
Also called CSU/DSUs (channel service
units/digital service units)
Interface with voice-grade connection in order to
convert analog signal to digital.
Represents the DCE side of the DTE/DCE
connection.
Leased line
Router
CSU/DSU
CSU/DSU
Router
WANs & The OSI Model
Table of Contents
WAN Standards
What layers of the OSI model do WAN standards
describe?
Physical and Data Link Layers
WAN Physical Layer
Protocols that describe how to provide electrical,
mechanical, operational, and functional
connections for WAN services.
These services are most often obtained from WAN
service providers such as RBOCs, alternate
carriers, post-telephone, and telegraph (PTT)
agencies.
Describes the interface between the data terminal
equipment (DTE) and the data circuit-terminating
equipment (DCE).
WAN Physical Layer
Typically, the DCE is the service provider and the
DTE is the attached device.
In this model, the services offered to the DTE are
made available through a modem or a CSU/DSU.
WAN Physical Layer
Several physical layer standards specifying this
interface between the DTE & DCE are...
EIA/TIA-232
EIA/TIA-449
V.24
V.35
X.21
G.703
EIA-530
WAN Data-Link Layer
WAN data link protocols describe how frames are
carried between systems on a single data link.
They include protocols designed to operate over
dedicated point-to-point, multipoint, and multiaccess switched services.
WAN standards are defined and managed by a
number of recognized authorities, including the
following agencies: ITU-T, ISO, IETF, & EIA
WAN Encapsulation
Formats
Table of Contents
WAN Data-Link Encapsulations
PPP (Point-to-Point Protocol)
Developed by IETF; replacing SLIP
Contains a field to identify the network layer protocol
PPP can check for link quality during connection
establishment
Supports PAP (Password Authentication Protocol) & CHAP
(Challenge Handshake Authentication Protocol)
WAN Data-Link Encapsulations
High-Level Data Link Control (HDLC)
Cisco default encapsulation; typically used between routers
running Cisco IOS; replacing SDLC
Streamlined: no windowing or flow control
may not be compatible with different vendors because of
the way each vendor has chosen to implement it.
HDLC supports both point-to-point and multipoint
configurations with minimal overhead
WAN Data-Link Encapsulations
Frame Relay
uses high-quality digital facilities;
uses simplified framing with no error correction
mechanisms (connectionless!!);
it can send Layer 2 information much more rapidly than
other WAN protocols
WAN Link Options
Table of Contents
WAN Link Options
Switched
Dedicated
• T1, E1, T3, E3
• xDSL
• SONET
Circuit
Switched
• POTS
• ISDN
Packet/Cell
Switched
• X.25
• Frame Relay
• ATM (cell)
• SMDS (cell)
WAN Link Options
Switched
Dedicated
• T1, E1, T3, E3
• xDSL
• SONET
Circuit
Switched
• POTS
• ISDN
Packet/Cell
Switched
• X.25
• Frame Relay
• ATM (cell)
• SMDS (cell)
Dedicated Digital Services
Dedicated Digital Services provide full-time
connectivity through a point-to-point link
T series in U.S. and E series in Europe
Uses time division multiplexing to “slice up” data and
assign time slots for transmissions
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T1 = 1.544 Mbps
T3 = 44.736 Mbps
E1 = 2.048 Mbps
E3 = 34.368 Mbps
•Uses twisted pair & fiber
•Extremely popular
•Moderate cost
Dedicated Digital Services
Digital Subscriber Lines (xDSL); the x stands for
a family of technologies
WAN Technology for home use; decreasing bandwidth
with increasing distance from the phone companies CO.
Data rates as high as 51.84 Mbps but more common to
be in the 100s of Kbps
Varieties include HDSL, SDSL, ADSL, & VDSL
Moderate expense and getting cheaper
Dedicated Digital Services
Synchronous Optical Network (SONET)
Specialized high bandwidth technology for use at various
Optical Carrier speeds (OC) ranging from 51.84 Mbps
(OC-1) to 9,952 Mbps (OC-192)
Uses lasers to divide the wavelength of the light into
sections that can carry large amounts of data (Wave
Division Multiplexing)
Very expensive; used by large ISPs and other Internet
backbone entities.
WAN Link Options
Switched
Dedicated
• T1, E1, T3, E3
• xDSL
• SONET
Circuit
Switched
• POTS
• ISDN
Packet/Cell
Switched
• X.25
• Frame Relay
• ATM (cell)
• SMDS (cell)
Circuit Switched Services
Plain Old Telephone System (POTS)
Not a computer data service but...
 POTS is an important component of our communication
infrastructure and
 It is still the standard for designing reliable networks
Circuit Switched Services
Integrated Services Digital Network (ISDN)
Historically important--first dial-up digital service
Provides both voice & data transmission over existing
phone lines
Cost is moderate; max. bandwidth = 128 kbps for BRI
(Basic Rate Interface)
 2 B channels @ 64kps and 1 D channel @ 16kps
 B channels are voice/data channels; D for signaling
B
D
B
WAN Link Options
Switched
Dedicated
• T1, E1, T3, E3
• xDSL
• SONET
Circuit
Switched
• POTS
• ISDN
Packet/Cell
Switched
• X.25
• Frame Relay
• ATM (cell)
• SMDS (cell)
Packet Switched Services
X.25 (Connection-oriented)
Older WAN technology developed in 1970s
Reliable--X.25 has been extensively debugged and is now
very stable--literally no errors in modern X.25 networks
Store & Forward--Since X.25 stores the whole frame to
error check it before forwarding it on to the destination, it
has an inherent delay (unlike Frame Relay) and requires
large, expensive memory buffering capabilities.
Packet Switched Services
Frame Relay (Connectionless)
More efficient and much faster than X.25
Packet switched version of ISDN (which is circuit
switched); data rates up to 44.736Mbps with 56kbps and
384kbps being the most popular
Used mostly to forward LAN IP and IPX packets but can
be used to forward other types of traffic
Primary competitive advantage is its low cost
Cell Switched Services
Asynchronous Transfer Mode (ATM)
Relatively new WAN Technology related to broadband
ISDN; max. bandwidth = 622 Mbps
Developed in order to provide one technology for both
WANs and LANs to transport data, video, and voice.
(High Cost)
Key Benefits:
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One network for all traffic--voice, data, video
Compatible with current wiring infrastructure (cable plant)
Very flexible and scalable
Simplifies network management
Cell Switched Services
Switched Multimegabit Data Service (SMDS)
Closely related to ATM; SMDS is the MAN (Metropolitan
Area Network) implementation of ATM
High Cost with max. bandwidth 44.736 Mbps
WAN Link Options Review
Acronym
Name
Dedicated Digital Services
T1, T3
T1, T3
xDSL
Digital Subscriber Line
Synchronous Optical
SONET
Network
Circuit Switched Services
Plain Old Telephone
POTS
Service
Integrated Services
ISDN
Digital Network
Packet Switched Services
X.25
X.25
Frame Relay
Frame Relay
Cell Switched Services
Asynchronous
ATM
Transfer Mode
Switched Multimegabit
SMDS
Data Service
Max. Bandwidth
Comments
1.544 & 44.736 Mbps Widely used telecommunications
384 kbps
New technology over phone lines
9,992 Mbps
Very fast optical fiber transmission
4 kHz Analog
The Standard for Reliability
128 kbps
Data and Voice Together
up to 44.736 Mbps
An Old Reliable, Workhorse
A flexible new workhorse; son of ISDN
622 Mbps
High powered Networks
1.544 & 44.736 Mbps MAN variant of ATM
Table of Contents
End Slide Show