Topic 8: WAN Chapter 11

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Topic 8 WAN- Chapter 11 12 Wide Area Networks

• Business Data Communications, 4e

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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

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Comparison ofNetworking Options
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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

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WAN Alternatives
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Types of WANs
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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

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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)

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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

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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

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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

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Public Switched Telephone Network (PSTN)

• Subscribers
• Local loop
• Connects subscriber to local telco exchange
• Exchanges
• Telco switching centers
• Also known as end office
• 19,000 in US

• Trunks
• Connections between exchanges
• Carry multiple voice circuits using FDM or
  synchronous TDM
• Managed by IXCs (inter-exchange carriers)

Services 1. Dial-up line 2. Dedicated line
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Integrated Service Digital Network (ISDN)

• 1st generation narrowband ISDN
• Basic Rate Interface (BRI)
• two 64Kbps bearer channels 16Kbps data channel
  (2BD) 144 Kbps
• circuit-switched
• 2nd generation broadband ISDN (B-ISDN)
• Primary Rate Interface (PRI)
• twenty-three 64Kbps bearer channels 64 data
  channel (23BD) 1.536 Mbps
• packet-switched network
• development effort led to ATM/cell relay

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Past Criticism of ISDN

• Innovations Subscribers Dont Need , It Still
  Doesnt 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.
• Didnt live up to early promises

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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

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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

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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

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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

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ISDN H Channel

• Only available over primary interface
• High speed rates
• Used in ATM

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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
• 2BD most common, but 1BD available

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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 nBD possible
• Can be used to support H channels

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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

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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).

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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.

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Frame Relay
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Traditional Packet Switching
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Frame Relay Operation
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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

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ATM Cell Format
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ATM Bit Rate Services
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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.

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T Carrier Circuits

• T-1 circuit (a.k.a. a DS-1 circuit) provides a
  data rate of 1.544 Mbps. T-1s 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.

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T Carrier System

• T-Carrier Designation DS Designation Speed

T-1 T-2 T-3 T-4
DS-0 DS-1 (24 DS-0) DS-2 (96 DS-0) DS-3 (672
DS-0) DS-4 (178 T-1)
64 Kbps 1.544 Mbps 6.312 Mbps 44.375 Mbps 274.176
Mbps
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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.
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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.

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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.

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SONET

• SONET Designation SDH Designation Speed

OC-1 OC-3 OC-9 OC-12 OC-18 OC24 OC-36 OC-48 OC-192
51.84 Mbps 155.52 Mbps 466.56 Mbps 622.08
Mbps 933.12 Mbps 1.244 Gbps 1.866 Gbps 2.488
Gbps 9.952 Gbps
STM-1 STM-3 STM-4 STM-6 STM-8 STM-12 STM-16
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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.

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SMDS Network Components
SNI Subscriber network interface CPE Customer
premises equipment
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SMDS Interface Protocol (SIP)
SIP is used for communications between CPE and
SMDS carrier equipment
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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 ATT 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.

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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).

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MPLS Services in the Market
In January 1999, ATT 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 IP-VPN
service in March, 1999.
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Internet Backbone Networks-- Major companies
ATT Network Services (http//www.ipservices.att.c
om/backbone/) BBN Planet (GTE) Cable Wireless
USA Sprintlink UUNET, a part of MCI WorldCom
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ATT Network Service
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GTE BBN Planet
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Cable Wireless USA
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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.

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MCI UUNET
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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)

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Abilene vBNS (very high speed Backbone Network
Services ) CANet 3
Figure 9-11 Gigapops and high speed backbones of
Internet 2/Abilene, vBNS, and CANet 3
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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.

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ISP POP
Individual Dial-up Customers
ISP Point-of Presence
Modem Pool
ISP POP
Corporate T1 Customer
T1 CSU/DSU
Layer-2 Switch
ATM Switch
ISP POP
Corporate T3 Customer
T3 CSU/DSU
Remote Access Server
Corporate OC-3 Customer
ATM Switch
NAP/MAE
Figure 9-2 Inside an ISP Point of Presence
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Customer Premises
Individual Premise
Main Distribution Frame
Voice Telephone Network
DSL Modem
Line Splitter
Hub
Individual Premise
Telephone
Wireless Transceiver
DSL Access Multiplexer
Individual Premise
Computer
Computer
Wireless Access Office
Customer Premises
Wireless Transceiver
Router
Customer Premises
ISP POP
Figure 9-9 Fixed wireless architecture
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Web Site
WAP Gateway
WAP Client
Web Server
WAE User Agent
Wireless Transceiver
WAE Requests
Wireless Telephony Application Server
WAE Requests
WAE Responses (plus WML, etc.)
WAE Responses (plus WML, etc.)
WAE Responses (plus WML, etc.)
WAE Requests
HTTP Requests
WAP Proxy
HTTP Responses (plus HTML, jpeg, etc.)
Figure 9-10 Mobile wireless architecture for WAP
applications
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Sprint
Abilene
UUNet
CANet 3
Verio
DREN
WSU
Router
Boeing
Router
Router
Microsoft
U Idaho
Switch
Switch
Router
Router
Montana State U
HSCC
High-speed Router
High-speed Router
Router
ATT
U Montana
Router
Switch
Switch
SCCD
Router
Sprint
U Alaska
U Wash
OC-48 OC-12 T-3
Portland POP
Figure 9-12 Inside the Pacific/Northwest Gigapop