Applied Data Communictions 3rd Edition - Weber State University

Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,Wide Area Networking,Chapter 7,Halloween Version 1.0,Knowledge Checkpoints,Common carriers and the nature of competition,How to improve WAN performance,Factors in selecting WAN services,The role of common carriers in organizational WANs,Four basic categories of WAN circuits,Dialed circuit services,Dedicated circuit services,Switched circuit services,Packet network services,Important WAN Terms,Virtual Circuit (VC),The connection between two frame relay ports,Permanent Virtual Circuit (PVC),A pre-defined VC,Switched Virtual Circuit (SVC),A VC that is established dynamically,Data Link Connection Identifier (DLCI),Virtual Circuit Identification Number,More Terms to Learn,WAN,ATM,X.25,DTE/DCE,DSU/CSU,Multiplexer,Mux,Store and forward,Frame relay,PAD,VoFR,FRAD,SNA,CIR,Cell,Checking on a Network Connection,Why didnt the host respond?,Tracing the Hops,Which line is the router?,Introduction,Wide area networks (WANs) connect backbone networks and MANs across longer distances, often hundreds of miles or more,Most organizations cannot afford to build their own MANs and WANs, so they rent or lease circuits from,common carriers,such as AT&T, MCI, BellSouth, PACTEL or NYNEX,The Telephone Network,A,common carrier,is a private company that sells or leases communications services and facilities to the public,A common carrier that also provides local telephone services is called a,local exchange carrier,(LEC), while one that provides long distance services is called an,interexchange carrier,(IXC),In the United States, 90 percent of the telephone system used to be run by one common carrier, AT&T,Comparison of Telco Areas,Carrier Service Areas,DIALED CIRCUIT SERVICES,PVCs,Statically Defined at Configuration, Unless PVC Parameters Need to be Modified,Connection is Always Configured Whether There is Information to Send or Not,SVCs,Dynamically Established When There is Information to Send (Call-by-Call Basis),Connection is Released When There is No More Information to Send,Differences Between Pvcs And Svcs,Dialed Circuit Services,Dialed circuit services are the simplest and one of the most common types of MAN and WAN connection.,This type of connection uses the normal telephone network. To use dialed circuit services, the user simply leases connection points into the common carriers network, then dials the host computer using a modem, and connects to the host system.,Dialed circuit services may use different circuit paths between the two computers each time a number is dialed,Dialed Circuit Services,Direct Dialing,Direct dialing (also called dial-up) is the most commonly used direct circuit service. Every time you call your Internet service provider from your home phone, you are using direct dialing.,Charges for direct dialing are based on the distance between the two telephones (in miles) and the number of minutes the connection is used.,Wide Area Telephone Service (WATS),Wide Area Telephone Service (WATS) are a special rate service that allows direct circuit calls for,both,voice and data transmission to be purchased in large quantities.,WATS is limited to one direction only; it is either outward dialing or inward dialing. In general, inward WATS uses the toll free 800, 877 and 888 area code series in North America, and similar numbers in other countries.,DEDICATED CIRCUIT SERVICES,Dedicated Circuit Services,There are two main problems with dialed circuits.,Each connection goes through the regular telephone network on a different circuit, which may vary in quality.,The data transmission rates on these circuits are usually low 28.8 to 56 Kbps.,An alternative is to establish a private dedicated circuit, which the user leases from the common carrier for their exclusive use, 24 hrs/day, 7 days/week.,Dedicated Circuit Services,Dedicated Circuit Services,Dedicated circuits are billed at a flat fee per month and the user has unlimited use of the circuit. Dedicated circuits require more care in network design than dialed circuits.,There are five types of dedicated circuits:,Voice grade circuits,Wideband analog services,T Carrier circuits,SONET circuits,Digital subscriber line circuits,Dedicated Circuits for a WAN,Voice Grade Circuits,Voice grade circuits,are analog circuits that work in exactly the same manner as traditional telephone lines, except that you do not dial them.,Dedicated voice grade channels often have conditioning (or equalization) done on them to improve data transmission quality by reducing noise and distortion.,Wideband Analog Services,Wideband analog services are similar to voice grade circuits but they provide much greater bandwidth.,Typically wideband analog services provide one 48,000 hertz bandwidth channel for use with frequency division multiplexing or as 12 individual voice grade channels (4000 Hz each).,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.,T Carrier Circuits,A,T-1 circuit,(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.,A,T-2 circuit,(6.312 Mbps) is basically a multiplexed bundle of four T-1 circuits.,A,T-3 circuit,(44.376 Mbps) is equal to the capacity of 28 T-1 circuits.,A,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.,T Carrier System,T-Carrier DesignationDS DesignationSpeed,T-1,T-2,T-3,T-4,DS-0,DS-1,DS-2,DS-3,DS-4,64 Kbps,1.544 Mbps,6.312 Mbps,44.375 Mbps,274.176 Mbps,T-1 Frame Layout,Synchronous Optical Network (SONET),The,synchronous optical network,(SONET) has recently 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 recently standardized a version of SONET under the name of,synchronous digital hierarchy,(SDH). The two are very similar and can be easily interconnected.,Synchronous Optical Network (SONET),SONET transmission speeds begin at the OC-1 level (optical carrier level 1) of 51.84 Mbps. Each succeeding rate in the SONET fiber hierarchy is defined as a multiple of OC-1.,Several common carriers (MCI) now use OC-12 circuits at 622.08 Mbps to carry digitized voice traffic.,SONET,SONET Designation SDH DesignationSpeed,OC-1,OC-3,OC-9,OC-12,OC-18,OC-24,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,SONET Framing,NY Information Technology Center,Digital Subscriber Line (DSL),DSL services are new and not all common carriers offer them.,Two general categories of DSL services have emerged in the marketplace.,Symmetric DSL,(SDSL) provides the same transmission rates (up to 128 Kbps) in both directions on the circuits.,Asymmetric DSL,(ADSL) provides different data rates to (up to 640 Kbps) and from (up to 6.144 Mbps) the carriers end office. It includes an analog channel for voice transmissions.,Digital Subscriber Line (DSL),A new version of ADSL called,Very high rate Digital Subscriber Line,(VDSL) has been designed for use over local loops of 1000 feet or less. It uses FDM to provide three channels:,Normal analog channel,Upstream digital 1.6 Mbps channel,Downstream digital 51.84 Mbps channel.,ADSL Technology Implementation,CIRCUIT SWITCHED SERVICES,Circuit Switched Services,The major problem with dedicated circuit services it that the user must carefully plan all circuits needed.,In contrast, switched circuits work much like dialed circuits. The user buys a connection into the common carriers network from the end points of the WAN, without specifying all the interconnecting circuits needed.,The primary differences from dialed circuits is that the circuits are entirely digital and that they offer higher data transmission rates.,Circuit Switched Services,Narrowband Integrated Services Digital Network,The first generation of Integrated services digital network (ISDN), commonly called narrowband ISDN, combines voice, video, and data over the same digital circuit.,ISDN has long been more of a concept than a reliable service in North America.,Acceptance has been slowed because equipment vendors and common carriers conflicting interpretations of ISDN standards.,Narrowband Integrated Services Digital Network,Narrowband ISDN offers two types of service:,Basic rate interface,(BRI, basic access service or,2B+D,) provides two 64 Kbps bearer (B) channels and one 16 Kbps control signaling (D) channel.,One advantage of BRI is it can be installed over existing telephones lines. (if less than 3.5 miles).,Primary rate interface,(PRI, primary access service or,23B+D,) provides 23 64 Kbps B channels and one 64 Kbps D channel. (basically T-1 service),Broadband Integrated Services Digital Network,The second generation of ISDN is called Broadband ISDN (B-ISDN). B-ISDN is a circuit switched service and is backwardly compatible with ISDN.,B-ISDN is currently offered in three services:,Full duplex channel at 155.2 Mbps.,Full duplex channel at 622.08 Mbps.,Asymmetrical service with two simplex channels (Upstream at 155.2 Mbps, downstream at 622.08 Mbps).,Narrowband ISDN Architecture Information,ISDN,ISDN Technology,ISDN Architecture,ISDN Network,Multiple PVCs per Access Line,PACKET SWITCHED SERVICES,Packet Switched Services,Packet switched services,enable multiple connections to exist simultaneously between computers.,With packet switching users buy a connection into the common carrier network, and connects via a,packet assembly/ disassembly device,(PAD).,Packet switching splits messages into small segments called packets (usually 128 bytes).,Packet Switched Services,Packet Switched Services,Packets from separate messages are,interleaved,with other packets for transmission.,Although the packets from one data stream may mix (interleave) with several other data streams during their journey, it is unlikely that packets from two different data streams will travel together during the entire length of their transmission.,Packet Switched Services,There are two methods used to route packets:,A,Datagram,is a connectionless service which adds a destination and sequence number to each packet, in addition to information about the data stream to which the packet belongs. Packets may follow a different route, and are reassembled at the destination.,In a,Virtual circuit,the packet switched network establishes an end-to-end circuit between the sender and receiver. All packets for that transmission take the same route over the virtual circuit that has been set up for that transmission.,Packet Switched Services,Packet Switched Services,Packet switched services are often provided by different common carriers than the one from which organizations get their usual telephone and data services.,Therefore, organizations often lease dedicated circuits from their offices to the packet switched network,point-of-presence,(POP).,Datagram Delivery on a Packet-Switched Network,Circuit Switching vs.,Packet Switching,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.,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).,Point-to-Point vs. End-to-End Error Correction,Frame Relay Frame Layout,Leased Lines,Frame Relay,ATM,X.25,SMDS,$.167B,$1.6B,$2.6B,$6.8B,Market Forecast by WAN Technology,Public Frame,Relay,ATM,DS-3/E-3,DS-1/E-1,DS-0,X-25,International,FR,Internet,Access,IP,Management,Reports,ISDN,DS-3/E-3,Dial Access,Dial Access,FR,Access,Understanding Public Frame Relay Services,WAN Set-up,Frame Relay,Frame relay,is a newer 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 rates that are negotiated per connection and for each virtual circuit as it is established. (,Committed information rate,and,Maximum allowable rate),.,Major Components of a Wide Area Network Architecture,Frame Relay,Different common carriers offer frame relay networks with different transmission speeds: 56 Kbps to 45 Mbps.,At present, frame relay suffers from the same problems as ISDN - a lack of standards.,SVC Technical Framework,Frame,Relay,Network,A,B,Information,Information,Information,Information,Setup,Connect,Connect,Release,Release Complete,Release,Release Complete,Setup,1,4,5,7,2,3,6,7,- Denotes period of time,Call Proceeding,2,Disconnect,6,ATM,Asynchronous Transfer Mode (ATM),Asynchronous transfer mode,(ATM) is one of the fastest growing new technologies, and is similar to frame relay.,All data are packet-switched, and there is no error control at the intermediate computers within the network; error control is the responsibility of the source and destination.,Asynchronous Transfer Mode (ATM),Asynchronous Transfer Mode (ATM) (a.k.a. cell relay) is a technology originally designed for use in wide area networks that is now often used in backbone networks.,ATM backbone switches typically provide point-to-point full duplex circuits at 155 Mbps (total of 310 Mbps).,Implementation of ATM Technology,ATM Network,Asynchronous Transfer Mode (ATM),ATM has three 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 (QoS) information that enables the setting of very precise priorities among different types of transmissions (i.e., voice, video & e-mail).,ATM is scaleable. It is easy to multiplex basic ATM circuits into much faster ATM circuits.,Asynchronous Transfer Mode (ATM),ATM is a switched network but differs from switched ethernet and switched token ring in four ways:,1. ATM uses fixed-length packets of 53 bytes.,2. ATM provides no error correction on the user data.,3. ATM uses a very different type of addressing from traditional data link layer protocols such as ethernet or token ring.,4. ATM prioritizes transmissions based on Quality of Service (QoS).,Asynchronous Transfer Mode (ATM),Asynchronous Transfer Mode (ATM) is connection-oriented so all packets travel in order through the virtual circuit. A virtual circuit can either be a:,Permanent Virtual Circuit,(PVC) - defined when the network is established or modified.,Switched Virtual Circuit,(SVC) - defined temporarily for one transmission and deleted with the transmission is completed.,ATM and Traditional LANs,ATM uses a very different type of protocol than traditional LANs. It has a small 53-byte fixed length packet and is connection-oriented.Ethernet and token ring use larger variable length packets and are typically connectionless.,Translation must be done to enable the LAN packets to flow over the ATM backbones. There are two approaches LAN encapsulation (LANE) and Multiprotocol over ATM (MPOA).,ATM and Traditional LANs,Translating from Ethernet or token ring into ATM is not simple.,First the Ethernet address must be translated into an ATM virtual circuit identifier for the circuit that leads from the edge switch to the edge switch nearest the destination.,Once the virtual circuit address for the destination data link layer address has been found, it can be used to transmit the packet through the ATM backbone.,LAN Encapsulation (LANE),ATM and Traditional LANs,Once the virtual circuit is ready, the LAN packet is broken into the series of ATM cells, and transmitted over the ATM backbone using the ATM virtual circuit identifier.,Unfortunately this process can cause quite a delay (a reduction of 40 to 50 %).,Multiprotocol over ATM (MPOA) is an extension to LANE.,Switched Multimegabit Data Service (SMDS),Switched multimegabit data service,(SMDS) is 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.,SMDS is not yet a widely accepted standard.,ATM to the Desktop,ATM-25,is a low speed version of ATM which provides point-to-point full duplex circuits at 25.6 Mbps in each direction. It is an adaptation of token ring that runs over cat 3 cable and can even use token ring hardware if modified.,ATM-51,is another version designed for the desktop allowing 51.84 Mbps from computers to the switch.,ATM to the Desktop,Both of these ATMs appear to be good choices for desktop connections when ATM backbone networks are used. However, industry has been very slow to accept either and have instead moved to fast ethernet which is both cheaper and faster.,Northrop Grumman Network,Can You Describe This Network?,Addressing & Forwarding with ATM Virtual Circuits,ATM at,Carnival Cruise Lines,headquarters,IMPROVING MAN/WAN PERFORMANCE,Improving MAN/WAN Performance,Improving MAN/WAN performance is handled in the same way as improving LAN performance.,You begin by checking the devices in the network, by upgrading the circuits between computers, and by changing the demand placed on the network.,MAN/WAN Performance,Performance Checklist,Increase Computer and Device Performance,Upgrade devices,Change to a more appropriate routing protocol (either static or dynamic),Increase Circuit Capacity,Analyze message traffic and upgrade to faster circuits where needed,Check error rates,Reduce Network Demand,Change user behavior,Analyze network needs of all new systems,Move data closer to users,Improving Device Performance,One way to improve network performance is to upgrade the devices and computers that connect backbones to the WAN.,Another strategy is to examine the routing protocol, either static or dynamic. Dynamic routing will increase performance in networks which have many possible routes from one computer to another, or those in which message traffic is “bursty.,Improving Circuit Capacity,The first step is to analyze the message traffic in the network to find which dedicated point-to-point circuits are approaching capacity.,The capacity may be adequate for most traffic, but not for meeting peak demand. One solution may be to add a circuit switched or packet switched service that is only used when demand exceeds circuit capacity.,Sometimes a shortage of capacity may be caused by a faulty circuit. Before installing new circuits, monitor the existing ones to ensure that they are operating properly.,Reducing Network Demand,One step to reduce network demand is to require a network impact statement for all new application software developed or purchased by the organization.,Another approach is to shift network usage from peak or high cost times to lower demand or lower cost times.,The network can be redesigned to move data closer to the applications and people who use them.,SELECTING MAN/WAN SERVICES,Selecting MAN/WAN Services,A 1995 survey of network managers found that:,45 percent of WAN costs were for network management (primarily support staff salaries).,35 percent was spent on services (leasing data circuits from common carriers).,Only 20 percent was spent on equipment.,The most expensive part of the WAN will be the people req