Distributed Queue Dual Bus (DQDB) Metropolitan Area Networks. DQDB - Transmission principle. DQDB - Example MAN

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1 Metropolita Area Networks Bridge larger distaces tha a LAN, usage e.g. withi the city rage or o a campus. Oly oe or two cables, o switchig elemets. Thus a simple etwork desig is achieved. All computers are attached to a broadcast medium. Distictio betwee LAN ad MAN: The utilizatio of a clock pulse, geographical distace. MAN Examples: Distributed Queue Dual Bus (DQDB) Gigabit Etheret Distributed Queue Dual Bus (DQDB) Basic priciple: Two uidirectioal busses (simple cables) are attached to all computers: 3. N Head-ed Each bus is resposible for the commuicatio ito oe directio Each bus has a head-ed, which cotrols all trasmissio activities: a costat flow of slots of size 53 byte is produced each 5µs. Utilizable data field of each slot: 48 byte Two substatial protocol bits: Busy for markig a slot as occupied, Request for the registratio of a slot iquiry Expasio to 00 km permissible Data rates up to 50 MBit/s (optical fiber; with coaxial cables oly 44 MBit/s) Page Page DQDB - Trasmissio priciple Durig a trasmissio the sedig statio must kow whether the receiver is o the left or the right side. Before startig a trasmissio i oe directio, a slot has to be reserved. This is made by sedig a reservatio request i the opposite directio. Simulatio of a FIFO queue i order to cosider statios i the order of their commuicatio requests: Each statio maages two couters: RC (Request Couter) ad CD (Coutdow Couter) RC couts the umber of trasmissio wishes of dowward located statios, which arrived before the ow trasmissio wish. CD serves as auxiliary couter. If a statio wats to sed, it geerates a iquiry settig a special Request bit i a slot i opposite directio. The curret value of RC is copied ito CD (the statio may occupy oly the RC+ st cell). RC is set to 0 ad couts the umber of further comig commuicatio wishes. With each free slot passig i commuicatio directio, CD is couted dow by oe. If, the statio may sed. If it has ow a ew commuicatio wish, it must agai wait for RC slots. Page 3 DQDB - Example A B C D E RC = RC = RC = A B C D E Req RC = RC = A B CD = C D E Req Commuicatio directio i questio. System is i the iitial state. All couters are set to zero.. D wats to iitiate a commuicatio. I the couter directio, a Req is dispatched. The statios o the way icrease RC by. 3. B also wats to use the bus. A icreases RC by, B copies RC ito CD. Page 4

2 DQDB - Example RC = A B C D E A B C D E DATA DATA 4. The head-ed of the commuicatio bus produces slots. Each statio couts dow RC by oe with each passig cell, statios with CD > 0 cout dow CD. Statio D wats to sed ad has, by this it has sedig permissio. 5. With the ext slot, statio B has a ad may sed. Wide Area Networks Bridgig of ay distace Usually for coverig of a coutry or a cotiet Topology ormally is irregular due to orietatio to curret eeds. Therefore ot the shared access to a medium is the core idea, but the thought how to achieve the fast ad reliable trasmissio of as much data as possible over a log distace. Usually quite complex itercoectios of subetworks which are owed by differet operators No broadcast, but poit-to-poit coectios Rage: several 000 km WAN Examples: Asychroous Trasfer Mode, ATM Sychroous Digital Hierarchy, SDH DQDB ever became geerally accepted, sice short time later ATM was itroduced. Page 5 Page 6 Trasmissio Techologies for WANs Packet Switchig Poit-to-Poit Liks Provisio of a sigle WAN coectio from a customer to a remote etwork Example: telephoe lies. Usually commuicatio resources are leased from the provider. Accoutig bases o the leased capacity ad the distace to the receiver. Circuit Switchig A coectio is established whe required, commuicatio resources are reserved exclusively. After the commuicatio process, the resources are released. Example: Itegrated Services Digital Network, ISDN Packet Switchig Ehacemet of the Circuit Switchig ad the Poit-to-Poit liks. Shared usage of the resources of oe provider by several users, i.e. oe physical coectio is used by several virtual resources. Shared usage reduces costs Packet Switchig today is the most commo commuicatio techology i WANs. The provider of commuicatio resources provides virtual coectios (virtual circuits, circuit switchig) betwee remote statios/etworks, the data are trasferred i the form of packets. Examples: Frame Relay, ATM, OSI X.5 Two types of Virtual Circuits: Switched Virtual Circuits (SVCs) Useful for seders with sporadic trasmissio wishes. A virtual coectio is established, data are beig trasferred, after the trasmissio the coectio is termiated ad the ressources are beig released. Permaet Virtual Circuits (PVCs) Useful for seders which eed to trasfer data permaetly. The coectio is established permaetly, there exists oly the phase of the data trasfer. Page 7 Page 8

3 ATM for the Itegratio of Data ad Telecommuicatio Characteristics of ATM Telecommuicatio: Primary goal: Telephoy Circuit-switched Firm dispatchig of resources Performace guaratees Uused resources are lost Small ed-to-ed delay Time Divisio Multiplexig badwidth allocatio Data commuicatio: Primary goal: Data trasfer Packet-switched Flexible dispatchig of resources No performace guaratees Efficiet use of resources Variable ed-to-ed delay Statistical Multiplexig badwidth allocatio ITU-T stadard (resp. ATM forum) for cell trasmissio Itegratio of data, speech, ad video trasmissios Combies advatages of: - Circuit Switchig (grated capacity ad costat delay) - Packet Switchig (flexible ad efficiet trasmissio) Cell-based Multiplexig ad Switchig techology Coectio-orieted commuicatio: virtual coectios are established Guaratee of quality criteria for the desired coectio (badwidth, delay, ). For doig so, resources are beig reserved i the switches. o flow cotrol ad error hadlig Supports PVCs, SVCs ad coectio-less trasmissio Data rates: 34, 55 or 6 (optical fiber) MBit/s t t Page 9 Page 0 ATM Cells Cell Size: Trasmissio of Speech No packet switchig, but cell switchig: like time divisio multiplexig, but without reserved time slots Firm cell size: 53 byte Cell multiplexig o a ATM coectio: 3 3 Payload 48 byte 3 empty cell 3 Cell header 5 byte Asychroous time multiplexig of several virtual coectios Cotiuous cell stream Uused cells are set empty Withi overload situatios, cells are discarded Page Codig audio: Pulse-code modulatio (PCM) Trasformatio of aalogous ito digital sigals regular scaig of the aalogous sigal Scaig theorem (Nyquist): Scaig rate * cutoff frequecy of the origial sigal Cutoff frequecy of a telephoe: 3.4 khz scaig rate of 8000 Hz Each value is quatized with 8 bits (i.e. a little bit rouded). A speech data stream therefore has a data rate of 8 bits * 8000 s - = 64 kbit/s Quatizatio rage Example (simplificatio: Quatizatio with 3 bits) Iterval umber Scaig error T Origial sigal Recostructed sigal Scaig Itervals Time Biary code produced pulse code Page 0 00

4 Cell Size withi ATM ATM Network t=5 µs Cotiuous data stream with scaig rate /5 µs T D = 6 ms Problem: Delay of the cell stream for speech is 6 ms: 48 samples with 8 bits each = 48 byte = Payload for a ATM cell Larger cells would cause too large delays durig speech trasmissio Smaller cells produce too much overhead for ormal data (relatioship Header/Payload) i.e. 48 byte is a compromise. header overhead 00% packetisatio delay 0ms Two types of compoets: ATM Switch Dispatchig of cells through the etwork by switches. The cell headers of icomig cells are read ad a update of the iformatio is made. Afterwards, the cells are switched to the destiatio. ATM Edpoit Cotais a ATM etwork iterface adapter to coect differet etworks with the ATM etwork. ATM Edpoits Router LAN switch ATM etwork % 5ms cell size [bytes] Page 3 Workstatio ATM switch Page 4 ATM Switchig Before the start of the commuicatio a virtual coectio has to established. The switches are resposible for the forwardig of arrivig cells o the correct outgoig lies. For this purpose a switch has a switchig table. Switchig Tabelle Table Eigagsleituge Icomig lies Switch Ausgagsleituge Outgoig lies I Alter Old Out Neuer New Eigag Header Ausgag Header a c a d The header iformatio, which are used i the switchig table, are VPI (Virtual Path Idetifier) ad VCI (Virtual Chael Idetifier). If a coectio is beig established via ATM, VPI ad VCI are assiged to the seder. Each switch o the route fills i to where it should forward cells with this iformatio. b e Page 5 Path ad Chael Cocept of ATM Physical coectios cotai Virtual Paths (VPs, a group of coectios) VPs cotai Virtual Chaels (VCs, logical chaels) VPI ad VCI oly have local sigificace ad ca be chaged by the switches. Distictio betwee VPI ad VCI itroduces a hierarchy o the path idetifiers. Thus: Reductio of the size of the switchig tables. There are types of switches i the ATM etwork: VCI VCI VCI 3 VCI 4 VCI 5 VCI 6 VPI VPI VPI 3 Virtual Path Switchig VP Switch VP-SWITCH VPI 4 VPI 5 VPI 6 VCI 3 VCI 4 VCI 5 VCI 6 VCI VCI Virtual Chael Switchig VPI VC Switch VCI VCI 3 VCI 4 VCI VP/VC-SWITCH VPI VPI 3 VCI VCI 4 Page 6

5 Structure of ATM cells Two header formats: Commuicatio betwee switches ad edpoits: User-Network Iterface (UNI) Commuicatio betwee two switches: Network-Network Iterface (NNI) GFC - Geeric Flow Cotrol Oly with UNI, for local cotrol of the trasmissio of data ito the etwork. Typically uused. With NNI these bits are used to icrease the VPI field. PTI - Payload Type Idetifier Describes cotet of the data part, e.g. user data or differet cotrol data CLP - Cell Loss Priority If the bit is, the cell ca be discarded withi overload situatios. HEC - Header Error Cotrol CRC for the first 4 bytes; sigle bit errors ca be corrected. Bit Byte Byte Byte 3 Byte 4 Byte 5 GFC/VPI VPI VCI HEC PTI VPI CLP Page 7 Layers withi ATM Statio Higher Layers ATM Adaptatio Layer Switch Switch Statio Higher Layers ATM Adaptatio Layer Trasfers ATM cells over the medium Geerates checksum (seder) ad verifies it (receiver); discardig of cells Geerate header (seder) ad extract cotets (receiver), except checksum Resposible for coectio idetifiers (Virtual Path ad Virtual Chael Idetifier) ATM Adaptatio Layer (AAL) Adapts differet requiremets of higher layer applicatios to the Segmets larger messages ad reassembles them o the side of the receiver Page 8 Service Classes of ATM Criterio Data rate Sychroizatio (source - destiatio) Negotiated maximum cell rate Service Class A B C D Yes Maximum ad average Cell rate Dyamic rate adjustmet to free resources Bit rate costat variable Coectio Coectio-orieted Mode Applicatios: Adaptatio Layer (AAL): Movig pictures Telephoy Video cofereces AAL AAL No Take what you ca get Coectioless Data commuicatio File trasfer Mail AAL 3 AAL 4 AAL 5 Page 9 AAL : CBR - Costat Bit Rate, determiistic service Characterized by guarateed fixed bit rate Parameter: Peak Cell Rate (PCR) AAL : VBR - Variable Bit Rate (real time/o real time), statistical service Characterized by guarateed average bit rate. Thus also suited for bursty traffic. Parameter: Peak Cell Rate (PCR), Sustaiable Cell Rate (SCR), Maximum Burst Size AAL 3: ABR - Available Bit Rate, load-sesitive service Characterized by guarateed miimum bit rate ad loadsesitive, additioal bit rate (adaptive adjustmet) Parameter: Peak Cell Rate, Miimum Cell Rate AAL 4: UBR - Uspecified Bit Rate, Best Effort service Characterized by o guarateed bit rate Parameter: Peak Cell Rate Load PCR Load PCR SCR Load ABR/ UBR Other coectios Time Time Time Page 0

6 Traffic Maagemet Coectio Admissio Cotrol Reservatio of of resources durig durig the the coectio establishmet (sigalig) Compariso betwee coectio parameters ad ad available resources Traffic Traffic cotract betwee users users ad ad ATM ATM etwork Usage Usage Parameter Cotrol/Network Parameter Cotrol Test Test o o coformity of of the the cell cell stream stream i i accordace with with the the parameters of of the the traffic traffic cotract at at the the user-etwork iterface or or etwork-etwork iterface Geeric Cell Cell Rate Rate Algorithm/Leaky Bucket Bucket Algorithm Switch Switch Cogestio Cotrol (primary for for UBR) UBR) Selective discardig of of cells cells for for the the maiteace of of performace guaratees i i the the case case of of overload Flow Flow Cotrol for for ABR ABR Feedback of of the the etwork status status by by resource maagemet cells cells to to the the ABR ABR source, for for the the adjustmet of of trasmissio rate rate ad ad fair fair dispatchig of of the the capacity Page Status of ATM ATM withi LAN: Too high cost of the hardware Too strog competitio by established techiques like Fast Etheret etc. ATM withi WAN: ofte implemeted betwee compay locatios Telecommuicatio providers prefer SDH as trasport resp. core etworks (better performace for telecommuicatios, world stadard) ATM cells ca be packed ito SDH cotaiers at trasitio poits (ecapsulatio) resp. upacked at the receivig etwork ATM was replaced to a large extet by SDH ATM is today mostly oly offered to users as a service, i order to be able to further use existig devices ad mechaisms Page Sychroous Digital Hierarchy (SDH) All moder etworks i the public area are usig the SDH techology Example: the Germa B-WIN (ATM) was replaced by the G-WIN (Gigabit-Wisseschaftsetz) o basis of SDH Sice 006: X-WIN complete redesig of topology, additioally itegratio of DWDM (dese wavelegth divisio multiplexig): up to 60 parallel trasmissios over a fiber, givig.6 TBit/s capacity! Surfet Also used withi the MAN rage (Replaced by Gigabit Etheret?) Aalogous techology i the USA: Reater Sychroous Optical Network (SONET) AAC DUI FZJ Geat SAA EWE MUE BIR GSI FZK AWI BRE BIE KEH MAR HAM KAS GIE FRA WUE HEI STU DES KIE HAN BRA GOE ILM ERL AUG Switch/GARR Dark Fiber reted wavelegth LEI ROS POT MAG JEN BAY ESF GAR ZIB CHE REG GRE TUB FFO HUB ADH DRE GÉANT Europea scietific etwork GÉANT Coects more tha 30 coutries I Germay: coectio by a cetral ode i Frakfurt Also i Frakfurt ad Hamburg: itercotietal coectios. Page 3 Page 4

7 SDH Structure SDH realizes higher data rates tha ATM (at the momet up to about 40 GBit/s) Flexible capacity utilizatio ad high reliability Structure: arbitrary topology, meshed etworks with a switchig hierarchy (exemplarily 3 levels): Multiplexig withi SDH MBit/s, 34 MBit/s, 55 MBit/s 6 MBit/s.5 GBit/s 0 GBit/s Supraregioal switchig Regioal switchig ceters Local etworks,5 GBit/s SDH Cross Coect 55 MBit/s 55 MBit/s Add/Drop Multiplexer 34 MBit/s MBit/s Sychroous Digital Hierarchy (SDH) Page 5 Switchig ceter MBit/s 34 MBit/s Switchig ceter 55 MBit/s + cotrol iformatio for sigalig 6 MBit/s 6 MBit/s MBit/s SDH Cross Coect Page 6 Characteristics of SDH SDH Trasport Module (Frame) World-wide stadardized bit rates o the hierarchy levels Sychroized, cetrally clocked etwork Multiplexig of data streams is made byte by byte, simple multiplex patter Suitability for speech trasmissio: sice o each hierarchy level four data streams are mixed byte by byte ad a hierarchy level has four times the data rate of the lower level, everyoe of these mixed data streams has the same data rate as o the lower level. Thus the data experiece a costat delay. Direct access to sigals by cross coects without repeated demultiplexig Short delays i isertig ad extractig sigals Additioal cotrol bytes for etwork maagemet, service ad quality cotrol, Substatial characteristic: Cotaier for the trasport of iformatio Page 7 Sychroous Trasport Module (STM-N, N=,4,6, 64) 9 x N colums (bytes) 6 x N colums (bytes) STM- structure: 9 lies with 70 bytes each. Basis data rate of 55 MBit/s Regeerator Sectio Overhead (RSOH) Admiistrative Uit Poiters Multiplex Sectio Overhead (MSOH) Payload 9 Admiistrative Uit Poiters permit the direct access to compoets of the Payload Sectio Overhead RSOH: Cotais iformatio cocerig the route betwee two repeaters or a repeater ad a multiplexer MSOH: Cotais iformatio cocerig the route betwee two multiplexers without cosideratio of the repeaters i betwee. Payload Cotais the utilizable data as well as further cotrol data 9 lies (5 µs) Page 8

8 Creatio of a STM Creatio of a STM Utilizable data are packed ito a cotaier. A distictio of the cotaiers is made by size: C- to C-4 Payload data are adapted if ecessary by paddig to the cotaier size As additioal iformatio to the utilizable data, for a coectio further bytes are added for cotrollig the data flow of a cotaier over several multiplexers: Path Overhead (POH) Cotrol of sigle sectios of the trasmissio path Chage over to alterative routes i case of a error Moitorig ad recordig of the trasmissio quality Realizatio of commuicatio chaels for maiteace By addig the POH bytes, a cotaier becomes a Virtual cotaier If several cotaiers are trasferred i a STM payload, these are multiplexed byte by byte i Tributary Uit Groups. By addig a Admiistrative Uit Poiter, the Tributary Uit Group becomes a Admiistrative Uit (AU). The the SOH bytes are supplemeted, the SDH frame is complete. RSOH ad MSOH cotai for example bits for Frame sychroizatio Error detectio (parity bit) STM- idetificators i larger trasportatio modules Cotrol of alterative paths Service chaels ad some bits for future use. Page 9 Page 30 SDH Hierarchy SDH Hierarchy Higher hierarchy levels assemblig STM- modules Higher data rates are assembled by multiplexig the cotaied sigals byte by byte Each byte has a data rate suitable by 64 KBit/s, for the trasmissio of speech data (telephoy) Except STM-, oly trasmissio over optical fiber is specified 4 * 9 colums 9 colums 6 byte 4 * 6 byte 55 MBit/s 6 MBit/s.5 GBit/s STM- STM-4 STM-6 6 4x6=044 4x044= x9=36 Assembled from Basis trasportatio module for 55 MBit/s, e.g. cotais: a cotiuous ATM cell stream (C-4 cotaier), a trasportatio group (TUG-3) for three 34 MBit/s PCM systems, or a trasportatio group (TUG-3) for three cotaiers, which agai cotai TUGs 4 x STM- 4x36=44 Assembled from Assembled from 4 x STM-4 4 x STM- Page 3 Page 3

9 SDH Multiplex Structure x N STM-N AUG AU-4 VC-4 x 3 C kbit/s x 3 TUG-3 TU-3 VC-3 AU-3 VC-3 Poiter Processig x 7 Multiplexig C- Cotaier VC- Virtual cotaier TU-N Tributary Uit TUG- Tributary Uit Group AU- Admiistrative Uit AUG Admiistrative Uit Group STM-N Sychroous Trasport Module N C-3 x 7 TUG- TU- VC- C- x 3 TU- VC- C- x 4 TU- VC- C kbit/s kbit/s 63 kbit/s 048 kbit/s 544 kbit/s Page 33