3. WAN
• Provide data communications that traverse a broad
geographic area
• Utilize the transmission infrastructure provided by a third
party
• Services such as Integrated Services Digital Network
(ISDN), Digital Subscriber Line (DSL), cable modems, or
even the plain old telephone
• Point-to-point is an important concept in wide area
networking
4. WAN
• WAN is not a typical direct connection
• it’s a pre-established path from one site to another that
passes through a carrier network
5. Digital Telephone with ISDN
• To run over the existing telephone copper wiring
• ISDN allows subscribers to transmit data, voice, and
multimedia digitally
• two types of ISDN services available:
– Basic Rate Interface (BRI) 64bit /1 line
– Primary Rate Interface (PRI) 1544 bit / 24 line
6. Basic Rate Interface (BRI)
• Used for home and small office connectivity
• BRI services include two B channels and a single D
channel
• A B channel offers 64 Kbps and carries user data
• A BRI D channel operates at 16 Kbps and carries control
and signaling information
• Through these two channels, a home connection can
reach 128 Kbps of data throughput
7. Primary Rate Interface (PRI):
• Used for WANs and runs across leased lines
• The PRI service is composed of 23 B channels at 64
Kbps each for user data
• A single D channel, also operating at 64 Kbps to handle
control information
• The PRI service provides a throughput rate of 1.544
Mbps
8. ISDN Equipment
• The ISDN specification includes several types of
equipment
– Terminal adapter (TA)
– Terminal equipment type 1 (TE1)
9. Using Fiber Optics with FDDI
• Fiber optics offer great advantages over copper wiring
• As a result, fiber optics offer an enormous number of benefits to
both WAN and LAN technologies
• 100-Mbps token-passing dual ring network
• Both multimode and single mode fiber optics transmit light signals
• Single mode fiber depends on lasers
• FDDI’s dual ring structure enables traffic to flow on each ring
• One of the rings is considered primary, the other secondary
• Fiber optic cables are brittle, the secondary ring acts as a backup in
case of a break in the primary ring
• These are called single attachment stations (SAS)
• Single attachment concentrators (SAC) also connect only to the
primary ring
11. Fiber Optics with FDDI
• FDDI is a physical and data-link layer protocol
• Upper-layer protocols such as TCP/IP and IPX/SPX can
run across a FDDI ring
• The FDDI frame is similar to a token ring frame format
• The FDDI data frame can become as large as 4500
bytes in length
12. The frame fields
• Preamble: Identifies the incoming data as a new frame.
• Start delimiter: Specifies the beginning of a frame.
• Frame control: Includes control information such as the size of the
address fields.
• Destination address: A 6-byte–long physical address of the
destination device.
• Source address: A 6-byte–long physical address of the source
device.
• Data: Variable-length field containing the transmitted data.
• Frame Check Sequence (FCS): The value of the cyclic redundancy
check (CRC), which is an algorithm used to determine whether the
frame has an error. In the case of an error, the frame is discarded.
• End delimiter: Indicates that the frame is completed
13. WAN Speed with ATM
• WANs are typically slow
• They are transmitted across long distances over
networks that traditionally were unreliable
• As public networks gained in reliability, WAN
technologies became mismatched
• Demand for greater data throughput was one of the
driving forces behind Asynchronous Transfer Mode
(ATM).
• Demand for bandwidth is driven by multimedia
14. Need for Speed with ATM
• The International Telecommunications Union-
Telecommunication Standardization Sector (ITU-T) and
ANSI developed ATM for high-speed data transfer within
public networks
• ATM is a network made up of a series of ATM switches
• Any ATM node can communicate with any other ATM
node by transmitting data across the ATM network
17. Frame Relay
• Frame relay is a widely applied WAN protocol that uses
packet switching
• The frame relay protocol provides an efficient data
transmission, even though the packets vary in length
• Frame relay supplies data-link and physical layer
services
• permanent virtual circuits (PVC) and switched virtual
circuits (SVC) can be used
• Although all customer networks connect to the same
carrier network, the maximum rate of data throughput is
determined by the customer’s point-to-point link into the
frame relay cloud
20. SONET/SDH
• The Synchronous Optical Network (SONET), or
Synchronous Digital Hierarchy (SDH)
• The SONET topology can be either a dual ring
architecture or a star
• SONET is a global standard focusing on synchronous
communications that are multiplexed
21. Optical Carrier Signaling (OCx)
• The signals used to transmit across SONET are framed as
Synchronous Transport Signals
• SONET’s basic transmission rate, Synchronous Transport Signal
level 1 (STS-1), also considered Optical Carrier 1 (OC1), is 51.84
Mbps
22. T-Carrier System
• The T-carrier system is a series of data transmission
formats developed by Bell Telephone for use in the
telephone network system in North America and Japan
• The base unit of a T-carrier is DS0, which is 64 Kbps
• T1/E1
– T1 and E1 lines are each multiples of DS0 signals.
The T1 line provides 1.544 Mbps, while the E1 line
provides 2.048 Mbps
• T3/E3
– T3 lines are digital carriers, equivalent to 28 T1 lines,
that can transmit at the rate of 44.736 Mbps. E3 lines
provide 16 E1 lines, with a transmission rate of
34.368 Mbps
