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Topic 8: WAN- Chapter 11 & 12: Wide Area Networks
Business Data Communications, 4e
2
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
3
*Comparison ofNetworking Options
4
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
5
*WAN Alternatives
6
Types of WANs
7
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
8
Circuit-SwitchingDefinition: 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)
9
Circuit-Switching Stages
Circuit establishmentTransfer of information
point-to-point from endpoints to node internal switching/multiplexing among
nodes
Circuit disconnect
10
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
11
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
12
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
13
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 line2. Dedicated line
14
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
15
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
16
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
17
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
18
ISDN B ChannelBasic 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
19
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
20
ISDN H Channel
Only available over primary interface
High speed ratesUsed in ATM
21
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
22
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
23
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
24
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).
25
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.
26
Frame Relay
27
Traditional Packet Switching
28
Frame Relay Operation
29
Frame Relay Architecture
30
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.
31
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.
32
Advantages of Virtual Paths
Simplified network architecture Increased network performance
and reliabilityReduced processing and short
connection setup timeEnhanced network services
33
*ATM Cell Format
34
ATM Bit Rate Services
35
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.
36
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.
37
T Carrier System
T-Carrier Designation DS DesignationSpeed
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
38
*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.
39
*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.
40
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.
41
SONETSONET Designation SDH Designation Speed
OC-1
OC-3
OC-9
OC-12
OC-18
OC24
OC-36
OC-48
OC-192
STM-1
STM-3
STM-4
STM-6
STM-8
STM-12
STM-16
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
42
*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.
43
*SMDS Network Components
SNI: Subscriber network interfaceCPE: Customer premises equipment
44
*SMDS Interface Protocol (SIP)SIP is used for communications between CPE and SMDS carrier equipment
45
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.
46
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).
47
48
49
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 IP-VPN service in March, 1999.
50
*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
51
AT&T Network Service
52
GTE BBN Planet
53
Cable & Wireless USA
54
*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.
55
MCI UUNET
56
*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)
57Figure 9-11 Gigapops and high speed backbones of Internet 2/Abilene, vBNS, and CA*Net 3
AbilenevBNS (very high speed Backbone Network Services )CA*Net 3
58
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.
59
ISP Point-of Presence
Modem Pool
Individual Dial-up Customers
Corporate T1 Customer
T1 CSU/DSU
Corporate T3 Customer
T3 CSU/DSU
Corporate OC-3 Customer
ATM Switch
Layer-2 Switch
ISP POP
ISP POP
ISP POP
NAP/MAE
Figure 9-2 Inside an ISP Point of Presence
RemoteAccess Server
ATM Switch
60Figure 9-9 Fixed wireless architecture
Wireless Access Office
WirelessTransceiver
Customer Premises
Telephone
DSL Modem
Hub
Computer Computer
CustomerPremises
CustomerPremises
MainDistribution
Frame
VoiceTelephoneNetwork
DSL AccessMultiplexer
WirelessTransceiver
Router
Line Splitter
Individual Premise
IndividualPremise
IndividualPremise
ISP POP
61
Web Server
Web Site
WAP Proxy
WAP Gateway
Wireless Telephony Application Server
HTTP Requests
HTTP Responses(plus HTML, jpeg, etc.)
Figure 9-10 Mobile wireless architecture for WAP applications
WAEResponses
(plus WML, etc.)
WAERequests
WAP Client
WirelessTransceiver
WAEUser
AgentWAE
Requests
WAEResponses
(plus WML, etc.)
WAERequests
WAEResponses
(plus WML, etc.)
62Figure 9-12 Inside the Pacific/Northwest Gigapop
Router
High-speedRouter
Abilene
DREN
WSU
Boeing
U Idaho
High-speedRouter
Router
Router
Montana State U
U Montana
U Alaska
Portland POP
Microsoft
Router Router
Switch
U Wash
Router
Switch Switch
CA*Net 3Sprint UUNet Verio
Router
AT&T
Sprint
Router
OC-48OC-12T-3
HSCC
Switch
SCCD