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

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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 4

*WAN Alternatives

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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 9

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 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 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.

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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 32

*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-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.

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T Carrier System

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

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SONET

SONET Designation OC-1 OC-3 OC-9 OC-12 OC-18 OC24 OC-36 OC-48 OC-192 SDH Designation STM-1 STM-3 STM-4 STM-6 STM-8 STM-12 STM-16 Speed 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 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

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*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.

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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). 46

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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.

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*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 .

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Individual Dial-up Customers Corporate T1 Customer Corporate T3 Customer Corporate OC-3 Customer ISP Point-of Presence Modem Pool ISP POP T1 CSU/DSU T3 CSU/DSU Layer-2 Switch ATM Switch Remote Access Server ATM Switch ISP POP ISP POP NAP/MAE

Figure 9-2 Inside an ISP Point of Presence 59

Customer Premises Individual Premise DSL Modem Line Splitter Hub Telephone Individual Premise Main Distribution Frame Voice Telephone Network Wireless Transceiver DSL Access Multiplexer Individual Premise Computer Computer Customer Premises Customer Premises

Figure 9-9 Fixed wireless architecture

Wireless Access Office Wireless Transceiver Router ISP POP

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WAP Client WAE User Agent WAE Requests WAP Gateway Wireless Transceiver WAE Requests Wireless Telephony Application Server WAE Responses (plus WML, etc.) WAE Responses (plus WML, etc.) WAE Requests WAE Responses (plus WML, etc.) HTTP Requests WAP Proxy Web Site Web Server HTTP Responses (plus HTML, jpeg, etc.)

Figure 9-10 Mobile wireless architecture for WAP applications 61

CA*Net 3 Abilene Sprint UUNet Verio DREN WSU Boeing U Idaho Montana State U U Montana Router Router Router Switch High-speed Router Router Switch High-speed Router Switch Switch SCCD U Alaska Portland POP U Wash

Figure 9-12 Inside the Pacific/Northwest Gigapop

Router Router Router Router Microsoft HSCC AT&T Sprint OC-48 OC-12 T-3

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