Topic 8: WAN
- Chapter 11 & 12: Wide Area Networks
Business Data Communications,
4e
1
LANs, WANs, and MANs
 Ownership


WANs can be either public or private
LANs are usually privately owned
 Capacity

LANs are usually higher capacity, to carry greater
internal communications load
 Coverage



LANs are typically limited to a single location
WANs interconnect locations
MANs occupy a middle ground
2
*Comparison of
Networking Options
3
Network Services Available for
MAN and WAN
 Dialed Circuit Services

Direct Dialing (DD) & Wide Area Telephone Services (WATS)
 Dedicated Circuit Services




Voice-grade circuits
Wideband Analog Services
T-Carrier Circuits
Synchronous Optical Network (SONET)
 Circuit-Switched Services

Integrated Services Digital Network (Narrowband & Broadband)
 Packet-Switched Services

X.25, Frame Relay, ATM, SMDS, and Ethernet/IP
4
*WAN Alternatives
5
Types of WANs
6
Switching Methods
 Circuit Switching: Requires a dedicated
communication path for duration of
transmission; wastes bandwidth, but
minimizes delays
 Message Switching: Entire path is not
dedicated, but long delays result from
intermediate storage and repetition of
message
 Packet Switching: Specialized message
switching, with very little delay
7
Circuit-Switching
 Definition: Communication in which a
dedicated communications path is
established between two devices through
one or more intermediate switching nodes
 Dominant in both voice and data
communications today

e.g. PSTN is a circuit-switched network
 Relatively inefficient (100% dedication
even without 100% utilization)
8
Circuit-Switching Stages
 Circuit establishment
 Transfer of information


point-to-point from endpoints to node
internal switching/multiplexing among
nodes
 Circuit disconnect
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Circuit Establishment
 Station requests connection from node
 Node determines best route, sends message
to next link
 Each subsequent node continues the
establishment of a path
 Once nodes have established connection, test
message is sent to determine if receiver is
ready/able to accept message
10
Information Transfer
 Point-to-point transfer from source to
node
 Internal switching and multiplexed
transfer from node to node
 Point-to-point transfer from node to
receiver
 Usually a full-duplex connection
throughout
11
Circuit Disconnect
 When transfer is complete, one station
initiates termination
 Signals must be propagated to all nodes
used in transit in order to free up
resources
12
Public Switched Telephone
Network (PSTN)
 Subscribers
 Local loop

Connects subscriber to
local telco exchange
 Trunks


 Exchanges



Telco switching centers
Also known as end office
>19,000 in US

Connections between
exchanges
Carry multiple voice
circuits using FDM or
synchronous TDM
Managed by IXCs (interexchange carriers)
Services:
1. Dial-up line
2. Dedicated line
13
Integrated Service Digital
Network (ISDN)
 1st generation: narrowband ISDN



Basic Rate Interface (BRI)
two 64Kbps bearer channels + 16Kbps data channel
(2B+D) = 144 Kbps
circuit-switched
 2nd generation: broadband ISDN (B-ISDN)




Primary Rate Interface (PRI)
twenty-three 64Kbps bearer channels + 64 data
channel (23B+D) = 1.536 Mbps
packet-switched network
development effort led to ATM/cell relay
14
Past Criticism of ISDN
 “Innovations Subscribers Don’t Need” , “It
Still Doesn’t Network” , “It Still Does Nothing”
 Why so much criticism?




overhyping of services before delivery
high price of equipment
delay in implementing infrastructure
incompatibility between providers' equipment.
 Didn’t live up to early promises
15
ISDN Principles
 Support of voice and nonvoice using limited





set of standard facilities
Support for switched and nonswitched
applications
Reliance on 64kbps connections
Intelligence in the networks
Layered protocol architecture (can be
mapped onto OSI model)
Variety of configurations
16
ISDN Network Architecture
 Physical path from user to office



subscriber loop, a.k.a. local loop
full-duplex
primarily twisted pair, but fiber use growing
 Central office connecting subscriber loops



B channels: 64kbps
D channels: 16 or 64kbps
H channels: 384, 1536, or 1920 kbps
17
ISDN B Channel
 Basic user channel (aka “bearer channel”)
 Can carry digital voice, data, or mixture

Mixed data must have same destination
 Four kinds of connections possible




Circuit-switched
Packet-switched
Frame mode
Semipermanent
18
ISDN D Channel
 Carries signaling information using
common-channel signaling


call management
billing data
 Allows B channels to be used more
efficiently
 Can be used for packet switching
19
ISDN H Channel
 Only available over primary interface
 High speed rates
 Used in ATM
20
ISDN Basic Access
 Basic Rate Interface (BRI)
 Two full-duplex 64kbps B channels
 One full-duplex 16kbps D channel
 Framing, synchronization, and overhead bring
total data rate to 192kbps
 Can be supported by existing twisted pair
local loops
 2B+D most common, but 1B+D available
21
ISDN Primary Access
 Primary Rate Interface (PRI)
 Used when greater capacity required
 No international agreement on rates


US, Canada, Japan: 1.544mbps (= to T1)
Europe: 2.048mbps
 Typically 23 64kbps B + 1 64kbps D
 Fractional use of nB+D possible
 Can be used to support H channels
22
Wide Area Networking Issues
 Trend towards distributed processing
architectures to support applications
and organizational needs.
 Expansion of wide area networking
technologies and services available to
meet those needs.
 Dedicated vs. Switched WAN Services
23
X.25
The oldest packet switched service is X.25, a standard
developed by ITU-T. X.25 offers datagram, switched
virtual circuit, and permanent virtual circuit services
(Data link layer protocol: LAPB (Link Access
Procedure-Balanced), network layer protocol PLP).
Although widely used in Europe, X.25 is not widespread
in North America. The primary reason is transmission
speed, now 2.048 Mbps (up from 64 Kbps).
24
Frame Relay Characteristics
 Frame relay is a packet switching technology that
transmits data faster than X.25. It differs from X.25
and traditional networks in three important ways:
1. Frame relay only operates at the data link layer.
2. Frame relay networks do not perform error control.
3. Frame relay defines two connection data rate that are negotiated
per connection and for each virtual circuit as it is established:
Committed information rate (CIR) and Maximum allowable rate
(MAR).
 Transmission speeds: 56 Kbps to 45 Mbps.
 Frame relay lacks of standards.
25
Frame Relay
26
Traditional Packet Switching
27
Frame Relay Operation
28
Frame Relay Architecture
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Asynchronous Transfer Mode
(ATM)
ATM has four important differences from frame relay:




ATM uses fixed packet lengths of 53 bytes (5 bytes of
overhead and 48 bytes of user data), which is more suitable
for voice transmissions.
ATM provides extensive quality of service information that
enables the setting of very precise priorities among different
types of transmissions (i.e. voice, video & e-mail; services
include CBR, VBR, ABR & UBR).
ATM is scaleable. It is easy to multiplex basic ATM circuits
into much faster ATM circuits.
ATM provides connection-oriented services only.
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Virtual Channels & Virtual
Paths
 Logical connections in ATM are virtual
channels


analogous to a virtual circuit in X.25 or a frame
relay logical connection
used for connections between two end users,
user-network exchange (control signaling), and
network-network exchange (network management
and routing)
 A virtual path is a bundle of virtual channels
that have the same endpoints.
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Advantages of Virtual Paths
 Simplified network architecture
 Increased network performance and
reliability
 Reduced processing and short
connection setup time
 Enhanced network services
32
*ATM Cell Format
33
ATM Bit Rate Services
34
T Carrier Circuits
T Carrier circuits are dedicated digital circuits
and are the most commonly used form of
dedicated circuit services in North America
today.
Instead of a modem, a channel service unit
(CSU) or data service unit (DSU) are used to
connect the circuit into the network.
35
T Carrier Circuits
T-1 circuit (a.k.a. a DS-1 circuit) provides a data rate of 1.544 Mbps. T-1’s
allow 24 simultaneous 64 Kbps channels (with TDM) which transport
data, or voice messages using pulse code modulation. (64Kbps x 24
= 1.536Mbps)
T-2 circuit (6.312 Mbps) is basically a multiplexed bundle of four T-1 circuits.
T-3 circuit (44.376 Mbps) is equal to the capacity of 28 T-1 circuits (672
64Kbps channels).
T-4 circuit (274.176 Mbps) is equal to the capacity of 178 T-1s.
Fractional T-1, (FT-1) offers portions of a 1.544 Mbps T-1 for a fraction of its
full costs.
36
T Carrier System
T-Carrier Designation
DS Designation
Speed
DS-0
64 Kbps
T-1
DS-1 (24 DS-0)
1.544 Mbps
T-2
DS-2 (96 DS-0)
6.312 Mbps
T-3
DS-3 (672 DS-0) 44.375 Mbps
T-4
DS-4 (178 T-1)
274.176 Mbps
37
*Digital signal X (DS-x)
A term for the series of standard digital
transmission rates or levels based on DS0, a
transmission rate of 64 Kbps, the bandwidth normally
used for one telephone voice channel.
Both the North American T-carrier system and the European
E-carrier systems of transmission operate using the DS series
as a base multiple. The digital signal is what is carried inside
the carrier system.
38
*E Carrier Circuits (European
Standard)
 E1 - 2.048 Mbps (32 DS-0). E1 carries at a higher




data rate than T-1 because, unlike T-1, it does not do
bit-robbing and all eight bits per channel are used to
code the signal. E1 and T-1 can be interconnected for
international use.
E2 - 8.448 Mbps.
E3 - 16 E1 signals, 34.368 Mbps.
E4 - four E3 channels, 139.264 Mbps.
E5 - four E4 channels, 565.148 Mbps.
39
Synchronous Optical Network
(SONET)
 An Optical Network for Dedicated Connection Services.
 SONET has been accepted by the U.S. Standards Agency
(ANSI) as a standard for optical (fiber) transmission at
gigabits per second speed.
 The International Telecommunications Standards Agency
(ITU-T) also standardized a version of SONET under the
name of synchronous digital hierarchy (SDH). The two
are very similar and can be easily interconnected.
40
SONET
SONET Designation
SDH Designation
OC-1
Speed
51.84 Mbps
OC-3
STM-1
155.52 Mbps
OC-9
STM-3
466.56 Mbps
OC-12
STM-4
622.08 Mbps
OC-18
STM-6
933.12 Mbps
OC24
STM-8
1.244 Gbps
OC-36
STM-12
1.866 Gbps
OC-48
STM-16
2.488 Gbps
OC-192
9.952 Gbps
41
*Switched Multimegabit Data
Service (SMDS)
Characteristics of SMDS:
 Uses ATM-like 53-byte cells, but a different address format.
 Provides datagram-based transmission services. So, it is a





connectionless service.
Data unit is large enough to encapsulate frames of Ethernet,
token ring and FDDI.
An unreliable packet service like ATM and frame relay. Like ATM
and frame relay, SMDS does not perform error checking; the
user is responsible for error checking.
Speed ranging 56kbps - 44.375Mbps.
Not yet a widely accepted standard.
Its future is uncertain.
42
*SMDS Network Components
SNI: Subscriber network interface
CPE: Customer premises equipment
43
*SMDS Interface Protocol
(SIP)
SIP is used for communications between CPE and SMDS carrier equipment
44
Ethernet/IP Packet Network
 A MAN/WAN service started in 2000
 X.25, ATM, frame relay and SMDS use
traditional PSTN and thus provided by the
common carrier such as AT&T and BellSouth.
ISP with Ethernet/IP packet service laid their
own gigabit Ethernet fiber-optic networks in
large cities.
 All traffic entering the network must be
Ethernet using IP.
45
Multiprotocol Label Switching
(MPLS)
 MPLS is a standards-approved technology for speeding up




network traffic flow and making it easier to manage.
MPLS sets up a specific path for a given sequence of packets,
identified by a label put in each packet, thus saving the time
needed for a router to look up the address to the next node to
forward the packet to.
MPLS is called multiprotocol because it works with the IP, ATM,
and frame relay network protocols.
MPLS allows most packets to be forwarded at the layer 2
(switching) level rather than at the layer 3 (routing) level.
In addition to moving traffic faster overall, MPLS makes it easy
to manage a network for quality of service (QoS).
46
47
48
MPLS Services in the Market
In January 1999, AT&T announced the first VPN
services to be based on MPLS --- its IP-Enabled
Frame Relay service.
Cable & Wireless and Cisco Systems conducted a
trial of IP-VPN service based on MPLS with
Hongkong Telecom in March, 1999.
MCI/Worldcom Started to offer MPLS-based IPVPN service in March, 1999.
49
*Internet Backbone Networks-Major companies
AT&T Network Services
(http://www.ipservices.att.com/backbone/)
BBN Planet (GTE)
Cable & Wireless USA
Sprintlink
UUNET, a part of MCI WorldCom
50
AT&T Network Service
51
GTE BBN Planet
52
Cable & Wireless USA
53
*Cable & Wireless USA
 Offers a world-wide voice, data, Internet and
messaging services.
 Its Internet backbones connects to 70+ countries.
 Service area includes switched services from most of
US cities to all 50 states, Puerto Rico, the Virgin
Islands and more than 200 countries.
 Private line and managed data services are available
between most major US metropolitan areas and key
business centers around the world.
54
MCI UUNET
55
*More WAN Protocols
 ATM Encapsulation Methods (LANE)
 CDPD
 FUNI (to provide users with the ability to connect between ATM
networks and existing frame-based equipment (e.g., routers)
 GPRS (allows GSM networks to be truly compatible with the
Internet)
 IP Switching Protocols
 SS7 Suite (Signaling System 7 by CCITT)
 Tag Switching Protocols (e.g. TDP - Tag Distribution Protocol)
 UMTS (a protocol for cellular network)
 Telephony
 Voice over IP (VoIP, enables users to carry voice traffic over an IP
network)
56
Abilene
vBNS (very high speed Backbone Network Services )
CA*Net 3
Figure 9-11 Gigapops and high speed backbones of Internet 2/Abilene, vBNS, and CA*Net 3
57
Abilene
 Abilene is an advanced backbone network
that supports the development and
deployment of the new applications being
developed within the Internet2 community.
Abilene connects regional network
aggregation points, called gigaPoPs, to
support the work of Internet2 universities as
they develop advanced Internet applications.
Abilene complements other high-performance
research networks.
58
Individual
Dial-up Customers
ISP POP
ISP Point-of Presence
Modem Pool
ISP POP
Corporate
T1 Customer
T1 CSU/DSU
Layer-2
Switch
Corporate
T3 Customer
ATM
Switch
ISP POP
T3 CSU/DSU
Remote
Access
Server
Corporate
OC-3 Customer
ATM Switch
Figure 9-2 Inside an ISP Point of Presence
NAP/MAE
59
Customer Premises
Individual Premise
DSL Modem
Main
Distribution
Frame
Line Splitter
Voice
Telephone
Network
Hub
Telephone
Individual
Premise
Wireless
Transceiver
Individual
Premise
DSL Access
Multiplexer
Computer Computer
Wireless Access Office
Customer
Premises
Wireless
Transceiver
Customer
Premises
Figure 9-9 Fixed wireless architecture
Router
ISP POP
60
WAP Client
WAE
User
Agent
WAP Gateway
Web Site
Web Server
WAE
Requests
WAE
Responses
(plus WML, etc.)
Wireless
Transceiver
WAE
Requests
Wireless Telephony
Application Server
WAE
Responses
(plus WML, etc.)
WAE
Requests
WAE
Responses
(plus WML, etc.)
HTTP Requests
WAP Proxy
HTTP Responses
(plus HTML, jpeg, etc.)
Figure 9-10 Mobile wireless architecture for WAP applications
61
Sprint
Abilene
CA*Net 3
UUNet
Verio
DREN
WSU
Router
Boeing
Router
Router
U Idaho
Microsoft
Switch
Switch
Router
Router
Montana
State U
HSCC
Router
High-speed
Router
High-speed
Router
AT&T
U Montana
Router
Switch
Switch
SCCD
Router
Sprint
U Alaska
Portland
POP
U Wash
Figure 9-12 Inside the Pacific/Northwest Gigapop
OC-48
OC-12
T-3
62