Cover Image

Not for Sale



View/Hide Left Panel
Click for next page ( 205


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 204
A.~.5 Communication Networks and Protocols Traditionally, communications networks have been based on two general techniques: 1) Circuit switched for voice, video, etc., signals which require controlled delay time from source to destination and exact ordering of transmission data. These networks are implemented by He telecommunications industry. Technologies include TI, SONET, and related multiplexing, cross-connect, etc., products. These networks are isochronous meaning "equal delay." 2) Packet switched for data (especially E-mail, computer networks, Internet access, etc.) which can tolerate random (but reasonable) time delays and resulting occasional out-of-order packet reception. These networks are implemented by the computer, LANJ~AN/WAN, data services (e.g., Compuserve, AOL, etc.) industries. Current ITS-related systems have been implemented using equipment and technologies of bow techniques: I) Field infrastructures typically employ circuit switched techniques, with simple end-to-end protocols to support real-tune requirements. 2) TOC computer networks employ packet-switched techniques (e.g., L`ANS) to interconnect large screen displays, workstations, printers, servers, etc. A clear industry trend has been an evolution of these techniques to support transport of multimedia voice, data, and video over He public telecotnmunicabons network and LAN/MANIWAN packet networks. This section will discuss the network protocols and systems that are available to support He emerging ITS multimedia requirements. L:~ - c2~t N~3-51. P~2F~Re~n A1-196

OCR for page 204
A.~.5.1 Packet Networks, OS! Stack, and Standards In the 19SOs and 1960s as computers emerged and were commercialized, We need for interconnected computer networks also emerged to share data In the early 1970s, more formal computer networks and products began emerging. Researchers quickly discovered that data networks had different characteristics Ran He widely deployed c~rcuit-switched voice networks and required different methodologies. The solution was He packet network which partitioned longer data messages at the source into smaller packets, transmitted He packets over He communication network, and reassembled the packets back to the ong~nal data message at He destination. This concept is illustrated in Figure A.~.S.~-~. Much effort has been focused on "Store and Forward" (sometimes denoted "Hold") packet networks. The unique characteristics and factors of the data networks Hat favor packet technology include: 1) Random interarrival times of source data 2) Random message lengths (pnor to packetization). 3) CaB (or connection) setup for short bursty data messages creates significant inefficiencies in c~rcu~t-sw~tched networks which are best suited for voice cans urge durations of minutes as opposed to fractions of seconds. Packet technologies handle this more efficiently. 4) Data networks can accommodate random delays of packet reception at He destination and can handle out-of-order reception sequences if Hey occur. 5) Modern digital error detection and correction technologies can be efficiently applied as required at bow He packet and message level. L::\NCHRP`Phase2. ~NCHRP3-51e Phase2FmalReport A1-197

OCR for page 204
,-: o o a) o a) a) i ~ D cn a) >a D - a' cn cn a' a' D U) 1 or) Cat D a) cn E: In _ - a) Q O I-\ -~196 /L o a) 01 ~ ~ .6 1 1 O 1 ' no" o o In' a) o A i\ ~ I, ~ 1 C) _ cn 1 1 Q I ~ FEZ \ o J L: J To r ~ z o y ~: o 3 z ~ Y ~C C! 3 er: o ~o ~n tY .

OCR for page 204
6) Network performance, in terms of average delay and throughput, is better in packet networks. The performance of a packet network is typ~caRy measured in terms of average throughput and delay. Models based on "Queuing Theory" are available to simulate the performance of packet networks. Figure A.~.5.~-2 illustrates how packet links and networks generally perform by plotting average delay versus percent throughput capacity. As We figure illustrates, if a network is lightly loaded, Me average delay is largely fixed and a function of propagation time and processing delays. But, as the load approaches 80-90% of capacity, Me delay detenorates rapidly. Thus, network managers strive to maintain percent link and network loading wed below 80-90% capacity by: I) Simulations in network design to predict performance. (Computer s~mulabon tools exist.) 2) Use of network management to collect statistics on actual network and link loadings during actual operation. 3) Plan rather than react to Increase capacity before problems emerge. In 1983, the International Standards Organization aso' released the Open Systems Interconnect fOS ~ Reference Mode! (often caned the OST Stack) Mat is shown in the block diagram in Figure A.~.5.~-3. The OST reference mode! is for packet networks generally performing Me functions described In Table A.~.5.~-~. Much like ITS-related systems today, Me private and public packet networks (e.g., LANIMAN/WAN, X.25, and Intemet data networks) of Me 83 era were experiencing problems urge multivendor interoperability and modulanty to support multiple physical media and multiple application layers. The 7-layer OS] reference mode! provides a methodology to address these problems by applying Me following principles: I) Each layer should perform well defined functions Mat are reasonably cohesive (i.e., naturally related). L::`NCHRP`Phasc2rp ~NCHRP3-51 Phace2FmalReport Al-199 1

OCR for page 204
- - >- a) . - a' or a) Q o LO . _ U) o CL _' U) o lo o o 00 rat . -1 - +, O _ ~ cn A\ ~ U) 0 au CO '-! O ~ A ~ O CL o o lo lo - O in \ in 1 ~ D cn Q D as Anew by 3 fir lo IL at, - o In lo: lo: lo: >a ~ -, ,,,

OCR for page 204
~E.~ E - ,, O ~= ~tL Al ~_ ~He O ~E X I i | | | | i . ~ W ~A, ~ ~ 9lUC ~ con ~E ' o' , , 3 ~O cut _ _O ~O l O ' O. 8 =- E am ~I, ~ ' O ' ~ ' ~_ cat Ji =1 . it, ~ ~Age ~- WO l O. = ' -= ' ~o i,, o _ ~'A ~ ~ ~ ~ ~ a) O ~ E. [_ Oos , I ~, ~ 0 ,_ ~_ Z 1 1 1 1 1 1 1 _. 1 1 1 1 1 1 1 I I I I ~1 ~ ~%_ 1 1 . ~ 1 1 1 1 1 1 ~, 1 1 1 1 1 1 1 - _ ~ ~. , ~ W j j j j jj j ~ ce ~ I=1oIol-=cI-=cI=5 e~ c ~ ~ ~ ~ ~ ~ co c~ c o

OCR for page 204
- ' ca ~ ~ - 0 5? c#o Q cent CD x al o ._ 3 _ U. ~ _ J In O O - o o Q C1S E - ; a, Cal - a, ._ - ._ CO LL X _ ~ o _ 3 ~ a, a, Cal ~ ' 0 ~ I,` 0 CtS c a) a) ~ CO ~ E ~ r a) Q . ~.0= c, `, Q at: O _ 1 1M 2 o 2 ~ ~ 8 ~ ~ , ~ ~ o ~ ~ g ~ ~. 1 11 2 ~ ~Q~ ~ == ~oh ~ z c: CO ~CO Cal O C~ ~t c~ a) 1 ~ ~ O _ m . 1- 1 1. 1. ~ o Q cn ~ C~ s- Ct ~ =: ,= Ce 0 ~.O S S ~ Q rL ~ ~ .. .O cn s Q <: m u, cn cn co _ 1 1 J J I I o ._ ._ cn a CO ~ 0 C o ~ - o U) - U) CtS 0 o ~ ~ ._ ~ Q cD Ct ~ a,- _ ~ CtS .= C' O C~ S Q Q c~ o - Cd L) - Q Q ~0 - e~ C o o ~: o

OCR for page 204
2) The functionality of We layers should be sufficiently self contained so that information flow across the interface to other layers is reasonably minimized. 3) The functions of each layer should be conceived to support development of international standards for the layer. These standards define services provided by each layer as well as protocols for the Interfaces between layers. 4) The resulting standards for each layer should define services, functions, and interfaces to adjacent layers but not dictate how they must be implemented in hardware or software. 5) The stack should be modular so each layer may be changed without affecting adjacent layers and interfaces. Thus, new operational requirements can be accommodated as weD as advances in architecture, communication, hardware, software, and related technologies. 6) It should be possible to bypass (or consolidate) a layer when not needed. As examples, many implemented protocol stacks consolidate layers 5 Trough 7 as done in NEMA's NTCIP ITS protocol stack. The OS] stack is not a communication protocol standard, but a reference model standard to facilitate consistent, modular, and flexible protocol standards development. Although each layer is often referred to as a protocol, application protocol stacks, or profiles, such as NEMA's NICIP Signal System protocol, require definitions of Be individual layer protocols, services, and interfaces. With the OST reference model, Me assignment of funchonality to individual layers has achieved significantly better standardization. However, of necessity, some variability still exists for a variety of reasons. These include: I) Technology improvements (e.g., x.25 to frame relay, TCP/IP., etch 2) Different applications requirements (e.g., LAN versus MAN versus WAN). L:~h~.~t NC~ 3-51 Pee 2 Fee Re"n A1-203

OCR for page 204
3) Implementation requirements (e.g., high speed LAN versus lower speed Internet protocols). 4) Complexity of (even supple) protocols makes nerd standardization bow undesirable and virtually impossible. 5) Different preferences, interpretations, arid priorities of the individual standards defining organizations. Thus, a protocol stack requires Me integration of public standard protocols (e.g., TCP/IP) and application-specific protocols (e.g., NTCIP) and the definition/ selection of many required ~mplementabon profiles and parameters. In Figure A.~.5.~-3, a communication infrastructure is identified Nat includes (I) the physical layer, (2) He link layer, and (3) We network layer. This cormnunicabon infrastructure is He distnbuted communication public and/or private infrastructure of a packet network. End users/equipment are physically located at He required source or destination of data and are provided end-to-end communication services by the communications infrastructure consisting of mediums, modes, hubs, terminals, etc. Commercial public communication services (and private networks) provide protocols for the lower Free layers only. Layers ~ Croup 7 are provided in end user equipment such as field equipment terminals and network/TOC communication servers and related equipment. ITS-related field communication infrastructure has not traditionalRy employed OSI-based standard protocols; however, NTCIP initiates an evolution within ITS toward this goal. Many public protocol standards are suitable for 11 S-related applications. Figure A.~.5.~-4 presents an overview of currently deployed or anticipated LAN/WAN standards with potential AS application. This figure illustrates the various OSI layers addressed by He standards. Users implementing a complete application stack must define and implement undefined higher and lower layers. ITS systems have many options and choices that include: :`NCHRP`Phasc2~pr NCHRP3-51e Phase2FmalRepoIt A1-204

OCR for page 204
f l Q) au ~ u) c:) ~ Q O CL) C~ ~ C~ ~ ~C C~ Q C~ - r, _ ~n U) ~ ~ o `~ _ kE 0 >, ~ a 11 ~ _` cn L~ .C l~ O Q) -~ ~ o `_ C3_~ - I I ~ ~ 0 _ ~ U' _ ~ C: _ ~ ~ . .~ C'-m U) 6) Q J O y g~ . ~ - U) - O O _% Q ' O c' o 00 ~ O `_ C Q _Q) 0' Q ct' ._ J Q) ~ C~ O . O O 3 ._ ~ I' Z _ 1 1 . 1 mm 0= _ C~ o~ CD O -T-- '~ I < . I ---1---- C~ I I ~ --- 1 --- J ~ 1 C_ _ Q) m 0 ~' ~J <: :5 J ~) I _' a' _ a, c =) ~ C) {' ~ - ~ .c C) J oo O l_ ~ s ~ O > ~ cn _ I C] CL 1 o7 1 {,o, 1 c~ 1 I ~ I 1 1 1 1 [L I CL 1 1 ~n tn_ ~ . ~o ~ ~ . > C~ CN ~ Ln r~ c~ ~ 0 C > N ___ - > ~hJ ~ D cn a' ._ au _ o ~n 0 a' ~O ._ ~c cn ._ cn 1 .' I J `_ Z C - cn a) o C Q Q) C a) _ ,_ ~ C' ~ C ~ C~ J ~ ~ ._ ._ _ ~ - ~ Q, , >%z x c e: ~n o I O 1 o ~c cn ._ _ ._ _ u) _ c dIC -= O z ~ l - c ~ c) a' ~ c~ ~ o c .c Q ~ c' ~ tn _ U) {y o CL" C - ~ ~ C ~ a' '' c) 1 ^, Z c Lf) U] I X Q ~ _ 3 Q Q Q Q c C~ - _ a 0 ~ ~ ~ _ ~ C ~ ~) a 0 cn C cO ~n ~ a) J ~ C c' .= . 'Cn~ J J J ~ - ~ . cn cn ~ m 0 ~ ~ ~ C) CD < OCR for page 204
I) The LAN 802.x standards only define the physical and link layers as LANs have tradidonaBy provided only shared bus, point-to-point, links of a few hundred meters. Higher layers have traditionally been implemented in Network Operating Systems (NOS), TCP/IP, etc. 2) TCP/IP are intemetworking protocols for MAN/WAN applications and only address He transport (TCP or 4~) layer and network (IT' or 3rd) layer. Typically, the employed lower layers are HDLC win dialup modems or, more recently, ISDN circuits. These are integrated in LAN systems (e.g., 802.x). 3) ElA-232, 422, 485, X.2l, etc., are physical (~) layer only protocols and multivendor interoperability requires specification of at least link (2) and often network (3) and higher layer protocols. 4) X.25 is a legacy protocol (70s, 80s) stack for layers 1, 2, and 3 that was conceived for networks interconnected by error-proof lower quality links. Thus, each layer of He protocol stack has significant overhead for error protection/control which makes X.25 unsuitable for higher speed links. TCP/IP addressed this problem by minimizing layers I, 2, and 3 error checking overheads and performing much of these functions in layer 4 ~CP) which is resident only in end user equipment and not the network infrastructure. Modern communication links are less error prone and can operate efficiency win these overhead error control functions on He periphery of the communications infrastructure. Lower overhead in layers I, 2, and 3 of He infrastructure is essential for higher link bit rates. 5) SONET and the T} hierarchy are physical (~) layer protocols that were developed to accommodate high speed transmission for the telephone industry. Bow public arid private Implementations have been extensively used for MAN/WAN intemetworkir~g of LAN networks. These win be discussed in more detail in Section A.1.2.3. 6) ATM is a telephone switching technology to support "On Demand" multimedia voice, data (LAN), and video. Standards are embryonic (1995) win many gaps and emerging end user products. Eventually, as standards and products evolve, ATM should prove cost-effective and valuable for lids applications. :\NCHR~Phasc:.'p ~NCHRP 3-51 Phase 2 Anal Report A1-206

OCR for page 204
Point to Point Protocol which as the name implies, assumes a "one-on-one" sort of exchange. This class is targeted toward major "center to center'' exchanges of information, supporting interactive exchanges (Telnet) and file transfer ~P). Both of these application layer protocols provide a degree of security through user authentication procedures. Conformance Statements and Testing As even common protocols are complex, implementation developed solely from a common specification by multiple suppliers would not guarantee interoperability. To maximize We potential of interoperability, standards organ~zabons, including NEMA's NTCIP, require manufacturers (for certified ~mplementions) to complete a Protocol Implementation Conformance Statement (PICS) Cat answers detailed questions about mandatory and optional features provided. A PICS provides: 1) Verification of features implemented; 2) Checklist for conformance testing by independent test organizations; and 3) Detailed listens) of requirements for procurers. Even PICS do not provide 100% guarantee of interoperability on multivendor implementations, especially early releases; however, vendors conforming to standards will usually accept contractual statements requiring minor warrantee modifications to achieve interoperability. A list of Dublished standards and documents providing more details on NTCIP are contained in Table A.1.5.2-7. A.1.5.3 Circuit-switched Technology Packet networks are based on the concept of disassembly of messages into smaller packets for transmission store-and-forward at intermediate nodes in a network. No direct connection between origin and destination is established although virtual connection may be employed. This ~;\NCH~Phase2.rp: NCHRP 3-51 Phase 2 Final Report A1-227

OCR for page 204
pre-establishes addressing/routing parameters so Mat actual transmissions are more efficient and can support higher throughput. Table A.~.5.2~7 NTCIP Standards and Supporting Documents Standards 1 ) NTCIP Steering Group - Point to Mulfi-point Protocol (PMPPJ 2) NEMA Standards Publication TS3.1 - 1996 National Transportation Communication for ITS Protocol- Overview 3) NEMA Standards Publication TS3.2 - 1996 National Transportation Communication for ITS Protocol - Simple Transportation Management Framework 4) NEMA Standards Publication TS3.3 - 1996 National Transportation Communication for ITS Protocol - Class B Profile 5) NEMA Standards Publication TS3.5 - 1996 National Transportation Communication for ITS Protocol Object Definition for actuated Traffic Signal Controller Units 6) National Electrical Manufacturers Association, Draft Standard - NTCIP Object Definitions for Ramp Meter Controllers 7) National Electrical Manufacturers Association, Draft Standard - NTCIP Object Definitions for Variable Message Signs 8) National Electrical Manufacturers Association, Draft Standard - NTCIP Object Definitions for Camera Controllers Supporting Documents (Ge! Complete Titles) 1 ) NEMA Standards Publication, How to Use NTCIP 2) NEMA Standards Publication, NTCIP Systems Developers Guide 3) NEMA Standards Publication, Hows and Whys of NTCIP 4) NTCIP Steering Group 1996 Draft - Class A Profile 5) NTCIP Steering Group 1996 Draft- C/ass B Profile 6) NTCIP Steering Group 1996 Draft- C/ass C Profile 7) NTCIP Steering Group 1996 Draft - Class E Profile Circuit switching establishes a permanent connection between origin and destination. It is We memos used by me telephone industry for switching voice. In its infancy, c~rcuit-sw~tch technology was analog win stepper relays. Since the 19SOs, digital switching has been replacing analog switching, due to me availability of low cost digital components aIld computer technology to control and manage circuit-switched networks. Key requirements for voice and video L:\NCHRP\Phase2.rpt NCHRP3-51 e Phase2FmalReport Al-228

OCR for page 204
networks are controlled time delay of the digitized signals and an intolerance to random ordering of data at the destination. Table A.~.5.3-1 summarizes and contrasts packet-switched and c~rcuit-switched technologies. More information on digital c~rcuit-switched technologies is in Section A.~.5.3 which discusses T} and SONET multiplex~ng/transmission hierarchies. Modern technology advances have blurred He use of packet technology for data and circuit switched technology for voice and video. V~rtual connections in packet networks and Asynchronous Transfer Mode (ATM) are defining packet capabilities for circuit-switched telephone service providers. A.~.5.4 LANs Local Area Networks ~ANs) are being deployed in TOCs in ITS-related systems within TOCs to link operator workstations with venous servers, and to integrate field data. AS presented in Figure A.~.5.~, L`AN protocol stacks typically define Be physical (1) layer and link (2) layer protocols. The physical layer specifies a medium (e.g., TWP, coaxial cable, fiber, etc.~. The hardware elements of an LAN consist of: I) Network Interface Cards Tics) Mat interface PCs, pnnters, workstations, etc., to the medium; 2) Servers which are computers, such as file servers, communication servers, or application servers; and 3) Communication devices such as hubs, repeaters, bndges, routers/brouters, and gateways. :\NCHRP\Phase~p ~NCHRP 3-51 Phase 2 Fmal Report A1-229

OCR for page 204
cn cn os e~ cn eQe Q cn _ O e~ O C~ ~_ e~. ~ ,a " _ CO C, O O~ e_ ~: e~ O e ~a) ~ O e~ C, ~ ~_ 0I _, 3 ~a) e" S ._ 3 ~ e O a e~ .O cn g O CLS CO U) c_ ~8 ~e aC ~ _ eO ~ e ~ C~ ~ ~ C~ ~ O ~ .O ~ CL e~ C~ 0 e~ G) eO 2' 0 ~ ~ .` g D _ e~ E ~t O e ~C\S .O t.) ee ~CtS e ~Q ~e 03 ~ e cn ~ O J ~' ma, ~ eY C' O Oe _ g _ ~ ~ e~ eO . '~ Q ,U) 0 Ct Ce O _ ~ _ U) ~ a) ce cn ~e G C' ___ ~ ~ ~ ~ ~ _ ,= a) ~ .O ~ g Q _ O) O ,~ _ ~ ~ ~e E s - cn . eC (8 tt e c 0 _ Q ,U) o Q E ~ ' E ~ o^ _ 0 =] et5 _ (D ~ Oc ~ ~ Q tl5 Q CC ~e g a Q CO cn o Q - - 8 ~n eQ o C, ~ ~_ 3 ._ el_ - - Oe CtS ~e ._ 0 52 eTe ~ e~e `,~ e ~e CO a~ ~S ~ CtS e" 4, Pt C3 co cn oo Ce C15 Q Q CIS ~ ~ ._ o ._ C as- O _ cn o CO C~ C~ - ~S O ~Q~ C~ a, C, ~ ,0 0.m . `' E- ,cn cO ~ _ Q U) Q O O ~ ~ ~ ~ m ~n Ct Y ._ CO C' ._ ~- - C :~ ~ CD - CO ~ a, C~ C 0 ~ U) 0 ,cn c E ._ cn C' ~ Ct ~ $ o S Z ~ ~ CS ~ m ~ ~ O o' O Q 0 {55 0 0 ~ ~ E ~ ~ C, ~ Q O ~ ~- a, 2 ~s ~ ~ s ~ ~ C) 0 I ~ ~ ~ ._ cn ._ ._ a Cd c o .g c o C~ - ~n ~ - a) - cd s c) cs - cn o ~o s ~ol. ^u, o 2 - Ct s o o U, - D

OCR for page 204
Figure A.~.5.4-l presents an overview of a typical LAN environment in the popular star topology. LANs employ several network topologies: bus, star, ring. The topologies are presented as Figure A.15.4-2. The most widely deployed Ethernet (' ME 802.3) LAN ong~naDy used a 10 Mbps bit rate on a shared coaxial cable bus with ad devices employing Catner Sense Multiple Access wad Collision Detect (CSMA/CD). This essentially says, before access: listen, Den talk, and if two or more messages collide, then (each Ones wait random and try again. This worked well in small fixed systems, but users encountered He following problems: ~ Reconfigurations for moves, addidons, and deletions were difficult; and 2) Network throughput was detenruned poorly as numbers of devices and network traffic increased. The star topology provides an alternative that substantially reduces these problems. Each device is provided win a dedicated TWP connection from its NIC to a hub at Be full lO Mbps data rate. The hub implements Be bus and experiences the collision. Like telephone circuits to Be desk, LANs also employ TWP wide parallel installation. Premise TWP standards for design, installation, configuration, and maintenance are defined by EIA/IIA, NEMA, and Bellcore. Additionally, this star arrangement permitted more natural segmentation of LAN networks to nary workgroups using bridges or routers. By proper segmentation of workgroups, collision only occur within shared segments undess a remote segment device is addressed. Thus, ovemll network capacity is increased. Many additional extensions to He E~emet standards are emerging Hat include 100 Mbps operations and fiber medium. These are summarized in Table A.1.5.4-1. A competing, but less popular, LAN configuration is the Token Ring ~ FIEF. Standard ~ lid it 802.5. Access to the shared ring is permitted only when an authorizing token is received by a device. This eliminates He collision problem of Ethernet and allows the network to operate at a throughput capacity close to He link bit rates of 4 and 16 Mbps, regardless of total system c:~t New 3-51 Pie 2 Fig Rein A1-23 1

OCR for page 204
l - m c/) am _ 1~ mm _ == O Im Q _ _ in O LL _ I o - J llJ ~5 llJ m \ 111 Z Q Q m, '' :::: - ! lelll Ut! . no :: a:: nil' ~3 1 1 ~ Z O o TO O. _ MU ~- en A: LLI o OCR for page 204
l - ~ '-'l ::c5 CY > L,J CC CY llJ A CY c . . / En m _ \ \ \ \ CY En m' am ''n' - :~:: m m' Inn am MU C) o i a/ _ tY ret llJ (a LY Let 'a - ~u' US - : UlBl U) o o O O CNJ F 1~ ~ LO echo o - lo: lo: l- ~: ~-

OCR for page 204
load. For reasons similar to Ethernet, token ring systems rapidly adapted the star configuration. The key features of token ring LANs are summarized in Table A.~.5.4-~. The Fiber Distributed Data Interface (FDDI) was developed in the early 1980s to support an emerging need for high capacity 100 Mbps LANs using fiber as the transmission medium. More recently, a filll 100 Mbps (shielded) 1-WP FDDI standard, suitable for shorter distances, has been developed. Early applications of FDD! were motivated by three requirements: I) Him speed backbones for Token Ring or Ethernet LANs; 2) Distance extensions provided by the bandy and low attenuation of fiber (see Table A.~.5.4-~; and 3) Internetworking for LANs and WANs. FDD! employs a token ring access mechanism like 802.5. Additionally, FDD] specifies dual rings which potentially could support 200 Mbps operation, although most implementations employ the second ring to provide fault tolerant backup. A more recent development is FDDI-H which provides isochronous (i.e., equal delay) capabilities for multimedia voice, video, and data transmission. Some commercial FDD] services are available, but not on a widespread basis. The overall features and capabilities of FDDI are summarized in Table A.~.5.4-~. Frame relay is a fast packet switching technology that provides end users a high-speed virtual private network (VPN) over public and private facilities. It provides bit rates ranging from 64 Kbps, DSO, to 1.544 Mbps, DS-1 (or 2.048 Mbps internationally). Frame relay is suitable for MAN/WAN applications. Frame relay is based on modern transmission systems that are far less error-prone than lower speed transmission systems that traditional data networks such as X.25 employed 1970s-80s. Thus, network (3) and link (2) layer services can be consolidated and simplified and generally accomplished in end-user equipment instead of the network infrastructure. Specifically, time consuming, expensive error-correction and retransmissions are not implemented in He network infrastructure. Thus, higher bit rates can be transmitted/ switched by the infrastructure. By using VPN, public service providers can offer lower cost L:~b=~t NC~ 3-51 PI 2 Few Ream A1-234

OCR for page 204
c`i o Q A no _ ~ ~ _ ? z ~ - 8 A ' ~I C] to ~I to ~ ~ ~ ~ O Q Y E =Q !1 ~o ~o=0D ~ ~ ~ ~ ~ ~ ! ~1 1 1 E | to ~ ~ ~ o | = 5 | ~ | ~ x | 5 | e n = ~5 1: 55 n 5 5 0 5 = ~ lomiB lo) .. ~ In 8~ 1 ~15050 ID ATE 15 1a' _ At 0 a, ~ ~ a, Qua CO ~ CO C, ~ _ O a, ma_ cr (D.ce O ~ ~ ~ Cal ~ ~ ffl ~ 1: ~ ~ . O LO ~ C e_ ~ ~ O ~O ~ ~ Q CD ~ C~ CD ~ ~QO I~0 Q O ~ o ` ~ m 2 -, sO t - ~ ffl .,2. o C] ~_ . ~O 2 ; ~"o - ~o co ~ u, c' ~ _ - N ._ 0 0 U' cn ~ ~ffl ~ .- C~ .= o~ - ~n Ct Q ~ cn - 1_ ~ _ <: ~ - 0 eS ~ Q _ ._ UJ ~ cn ~ ~ U' i~ ~ ~ Ul C' ~ CO Ct ._ c - cn a, ~._ O ~ ~ C, - C,~ ~ ~S ._ C Y CO

OCR for page 204
c~ - o c~ Q - o ~ ~ s ., cn ce o o o o C~ o cn o - ~q ~ ' a) _ 1 ~C,9 Q 0~ ~ ~ O q) O ~ Q ~ o ~ Ce a) =.') 3 ~ ~o ~o ~ o o o o C~ ~ ~ ~n ~ L ~: 4, ~ Y _ ~ o ., Q 3 Q Q `: 3 U) cn C~ 2 =3 I 2 s x 1 m8 o 2 N C _ ~ N O ~ _ ~ o Q z C~ ~2 o o - t: C CO ~ 0 o,,, o o. ~. CO as ,<~) 5O 3 e~ ~IL o o E ~ CL o o , o o ~ o _ ~ C~ CO ~ C O ~ O ~ C1S ~ ~ ~ ~ ~ 3 ~ ~ _ m ~ U.' - _ ~ Q ~_ ~ -_ ~ CL _ $ ~ t ~g ~D ~ ,= .- c~ _ t~s Q- Z ~ O._ o UJ Z . - ~o ~ cn o Z Z ~ c5 ~C] _ x ~D Q C] o ._ ~0 _ Q o _ _ Q ~ ._ ~ Q o Q cn o - - ~ CtS ~ ._ o 52 - C,~ Y o

OCR for page 204
. services than is possible win the development of a comparable private network with leased DS-O/DS-1 circuits. The standards bodies for frame relay are lTU-T (~.233), ANS! (T! .606), and BelIcore (TR-TSV-001369 and TR-TSV-001370~. Standard UNIs (user-to-network interfaces) are defined under the auspices of the frame relay forum. Fiber channel is a networking standard that has been developed by several supercomputer, mainframe, workstation, networking, and peripheral companies. The purpose is to provide high speed (100 Mbps to 2 Gbps) networking. Media supported include Single Mode Fiber Optics (SMFO), Multimode Mode Fiber Optic (MMFO), coaxial cable, and shielded twisted pair (STP). Fiber channel networking transparently supports several LAN protocols plus TCP/IP. The overall characteristics are presented in Table 1.5.4-~. Fiber channel key characteristics include: ~ Low latency (end-to-end delay); 2) Full complement of bit rates including rates greater than those supported by ATM; and 3) Efficient support of short and long message transmission and long me transfers. L:\NCHRP\Phase2.rpt NCHRP3-51e Phase2FmalReport A1-237