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

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1 Metropolitan Area Networks Bridge larger distances than a LAN, usage e.g. within the city range or on a campus. Only one or two cables, no switching elements. Thus a simple network design is achieved. All computers are attached to a broadcast medium. Distinction between LAN and MAN: The utilization of a clock pulse, geographical distance. MAN Examples: Distributed Queue Dual Bus (DQDB) Gigabit Ethernet Distributed Queue Dual Bus (DQDB) Basic principle: Two unidirectional busses (simple cables) are attached to all computers:. N Head-end Each bus is responsible for the communication into one direction Each bus has a head-end, which controls all transmission activities: a constant flow of slots of size 5 byte is produced each 5µs. Utilizable data field of each slot: 48 byte Two substantial protocol bits: Busy for marking a slot as occupied, Request for the registration of a slot inquiry Expansion to 00 km permissible Data rates up to 50 MBit/s (optical fiber; with coaxial cables only 44 MBit/s) Page Page DQDB - Transmission principle During a transmission the sending station must know whether the receiver is on the left or the right side. Before starting a transmission in one direction, a slot has to be reserved. This is made by sending a reservation request in the opposite direction. Simulation of a FIFO queue in order to consider stations in the order of their communication requests: Each station manages two counters: RC (Request Counter) and CD (Countdown Counter) RC counts the number of transmission wishes of downward located stations, which arrived before the own transmission wish. CD serves as auxiliary counter. If a station wants to send, it generates an inquiry setting a special Request bit in a slot in opposite direction. The current value of RC is copied into CD (the station may occupy only the RC+ st cell). RC is set to 0 and counts the number of further coming communication wishes. With each free slot passing in communication direction, CD is counted down by one. If CD = 0, the station may send. If it has now a new communication wish, it must again wait for RC slots. Page DQDB - Example RC = 0 RC = 0 RC = 0 RC = 0 A CD = 0 B CD = 0 C CD = 0 D CD = 0 E RC = RC = RC = RC = 0 A CD = 0 B CD = 0 C CD = 0 D CD = 0 E Req RC = RC = 0 RC = RC = 0 A CD = 0 B CD = C CD = 0 D CD = 0 E Req Communication direction in question RC = 0 CD = 0 RC = 0 CD = 0 RC = 0 CD = 0. System is in the initial state. All counters are set to zero.. D wants to initiate a communication. In the counter direction, a Req is dispatched. The stations on the way increase RC by.. B also wants to use the bus. A increases RC by, B copies RC into CD. Page 4

2 DQDB - Example RC = RC = 0 RC = 0 RC = 0 A CD = 0 B CD = 0 C CD = 0 D CD = 0 E RC = 0 RC = 0 RC = 0 RC = 0 A CD = 0 B CD = 0 C CD = 0 D CD = 0 E RC = 0 CD = 0 RC = 0 CD = 0 DATA DATA 4. The head-end of the communication bus produces slots. Each station counts down RC by one with each passing cell, stations with CD > 0 count down CD. Station D wants to send and has CD = 0, by this it has sending permission. 5. With the next slot, station B has a CD = 0 and may send. Page 5 Access Control DQDB - Slot format Bit (48 byte) Virtual Channel Identifier Payload Type Segment Priority Header Check Sequence Data Access Control Control of the access to the busses Differentiates between normal and permanently reserved slots Virtual Channel Identifier Contains the channel number of the corresponding connection Payload type Differentiates between user data (00) and control data Segment Priority Not defined yet (and thus never defined any more...) Header Check Sequence Checksum which can correct single bit errors and detect multiple bit errors (header only, data are not checked) Page 6 Access Control Wide Area Networks Bit Busy Slot Type PSR for future use Request Coordination of bus access: Busy indicates whether the slot is occupied Slot Type differentiates between normally to reserve and firmly reserved slot Previous Slot Cleared (PSR): contents of the preceding slot may be deleted. This allows Slot Reuse: if e.g. station A sends to station B, a slot would be blocked along the whole bus. Thus the receiver can set this bit to indicate that the following stations can re-use the slot. Request is used for reservations regarding the counter direction DQDB never became generally accepted, since short time later ATM was introduced. Page 7 Bridging of any distance Usually for covering of a country or a continent Topology normally is irregular due to orientation to current needs. Therefore not the shared access to a medium is the core idea, but the thought how to achieve the fast and reliable transmission of as much data as possible over a long distance. Usually quite complex interconnections of subnetworks which are owned by different operators No broadcast, but point-to-point connections Range: several 000 km WAN Examples: Frame Relay Asynchronous Transfer Mode, ATM Synchronous Digital Hierarchy, SDH Page 8

3 Transmission Technologies for WANs Point-to-Point Links Provision of a single WAN connection from a customer to a remote network Example: telephone lines. Usually communication resources are leased from the provider. Accounting bases on the leased capacity and the distance to the receiver. Circuit Switching A connection is established when required, communication resources are reserved exclusively. After the communication process, the resources are released. Example: Integrated Services Digital Network, ISDN Packet Switching Enhancement of the Circuit Switching and the Point-to-Point links. Shared usage of the resources of one provider by several users, i.e. one physical connection is used by several virtual resources. Shared usage reduces costs Packet Switching Packet Switching today is the most common communication technology in WANs. The provider of communication resources provides virtual connections (virtual circuits, circuit switching) between remote stations/networks, the data are transferred in the form of packets. Examples: Frame Relay, ATM, OSI X.5 Two types of Virtual Circuits: Switched Virtual Circuits (SVCs) Useful for senders with sporadic transmission wishes. A virtual connection is established, data are being transferred, after the transmission the connection is terminated and the ressources are being released. Permanent Virtual Circuits (PVCs) Useful for senders which need to transfer data permanently. The connection is established permanently, there exists only the phase of the data transfer. Page 9 Page 0 Frame Relay Structure of Frame Relay Based on Packet Switching, i.e. the transmission of data packets Originally designed for the use between ISDN devices, usage has spread further The packets can have variable length Statistic Multiplexing (i.e. mixing of different data streams) for controlling the network access. This enables a flexible, efficient use of the bandwidth available. A first standardization took place 984 by the CCITT. However, it did not supply a complete specification. Therefore in 990 Northern Telecom, StrataCom, Cisco, and DEC formed a consortium that build up upon the incomplete specification and developed some extensions to Frame Relay which should make a usage in the complex Internet environment possible. These extensions were called Local Management Interface (LMI). Due to their success, ANSI and CCITT standardized own LMI variants. Frame Relay finally became internationally standardized by the ITU-T, in the USA by ANSI. Purpose: simple, connection-oriented technology for economic transmission of data with acceptable speed Data transmission rates of 56 KBit/s up to 45 MBit/s can be leased Mostly used for permanent virtual connections for which no signaling for the connection establishment is necessary Two general device categories can be differentiated: Data Terminal Equipment (DTE): typically in the possession of the end user, for example PC, router, bridges, Data Circuit-Terminating Equipment (DCE): in the possession of a provider. DCEs realize the transmission process. Usually they are implemented as packet switches. DTE DCE DTE DTE Page Page

4 Communication within Frame Relay Frame Relay offers connection-oriented communication on the LLC layer: Between two DTEs a virtual connection is established. It is identified by a unique connection identifier (Data-Link Connection Identifier, DLCI). Note: DLCIs only refer to one hop, not to the entire connection; in addition they are only unique in a LAN, not globally: DLCI DLCI The virtual connection offers a bi-directional communication path. Several virtual connections can be multiplexed to a single physical connection (reduction of equipment and network complexity). Frame Relay offers the possibility to use both SVCs and PVCs. Small protocol overhead, high data transmission rates DTE DTE Page Flow Control within Frame Relay Frame Relay does not possess an own flow control mechanism for controlling the traffic of each virtual connection. Frame Relay is used typically on reliable network media, therefore flow control can be left over to higher layers. Instead : Notification mechanism (Congestion Notification) to report bottlenecks to higher protocol layers, if a control mechanism on a higher layer is implemented. There are two mechanisms for the Congestion Notification: Forward-Explicit Congestion Notification (FECN) initiated, when a DTE sends frames into the network In case of overload, the DCEs in the network set a special FECN bit to If the frame arrives at the receiver with set FECN bit, it recognizes that an overload on the virtual connection is present Backward-Explicit Congestion Notification (BECN) Similarly to FECN, but the BECN bit is set in frames which are transmitted in the opposite direction from frames with set FECN bit Page 4 ATM for the Integration of Data and Telecommunication Characteristics of ATM Telecommunication: Primary goal: Telephony Connection-oriented Firm dispatching of resources Performance guarantees Unused resources are lost Small end-to-end delay Time Division Multiplexing bandwidth allocation Data communication: Primary goal: Data transfer Connectionless Flexible dispatching of resources No performance guarantees Efficient use of resources Variable end-to-end delay Statistical Multiplexing bandwidth allocation ITU-T standard (resp. ATM forum) for cell transmission Integration of data, speech, and video transmissions Combines advantages of: - Circuit Switching (granted capacity and constant delay) - Packet Switching (flexible and efficient transmission) Cell-based Multiplexing and Switching technology Connection-oriented communication: virtual connections are established Guarantee of quality criteria for the desired connection (bandwidth, delay, ). For doing so, resources are being reserved in the switches. no flow control and error handling Supports PVCs, SVCs and connection-less transmission Data rates: 4, 55 or 6 (optical fiber) MBit/s t t Page 5 Page 6

5 ATM Cells No packet switching, but cell switching: like time division multiplexing, but without reserved time slots Firm cell size: 5 byte Cell multiplexing on an ATM connection: Payload 48 byte empty cell Cell header 5 byte Asynchronous time multiplexing of several virtual connections Continuous cell stream Unused cells are sent empty Within overload situations, cells are discarded Page 7 Cell Size: Transmission of Speech Coding audio: Pulse-code modulation (PCM) Transformation of analogous into digital signals regular scanning of the analogous signal Scanning theorem (Nyquist): Scanning rate * cutoff frequency of the original signal Cutoff frequency of a telephone:.4 khz scanning rate of 8000 Hz Each value is quantized with 8 bits (i.e. a little bit rounded). A speech data stream therefore has a data rate of 8 bits * 8000 s - = 64 kbit/s Quantization range Example (simplification: Quantization with bits) Interval number Scanning error T Origin signal Reconstructed signal Scanning Intervals Time Binary code produced pulse code Page Cell Size within ATM ATM Network t=5 µs Continuous data stream with scanning 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 an ATM cell Larger cells would cause too large delays during speech transmission Smaller cells produce too much overhead for normal data (relationship Header/Payload) i.e. 48 byte is a compromise. header overhead 00% packetisation delay 0ms Two types of components: ATM Switch Dispatching of cells through the network by switches. The cell headers of incoming cells are read and an update of the information is made. Afterwards, the cells are switched to the destination. ATM Endpoint Contains an ATM network interface adapter to connect different networks with the ATM network. ATM Endpoints Router LAN switch ATM network % 5ms cell size [bytes] Page 9 Workstation ATM switch Page 0

6 Structure of ATM cells Two header formats: Communication between switches and endpoints: User-Network Interface (UNI) Communication between two switches: Network-Network Interface (NNI) GFC - Generic Flow Control Only with UNI, for local control of the transmission of data into the network. Typically unused. With NNI these bits are used to increase the VPI field. PTI - Payload Type Identifier Describes content of the data part, e.g. user data or different control data CLP - Cell Loss Priority If the bit is, the cell can be discarded within overload situations. HEC - Header Error Control CRC for the first 4 bytes; single bit errors can be corrected. Bit Byte Byte Byte Byte 4 Byte 5 GFC/VPI VPI VCI HEC PTI VPI CLP Page Connection Establishment in ATM EC OK Establish connection to c c.c00c.0.0 EC OK OK ATM address OK c c.c00c.0.0 The sender sends a connection establishment request to its ATM switch, containing ATM address of the receiver and demands about the quality of the transmission. The ATM switch decides on the route, establishes a virtual connection (assigning a connection identifier) to the next ATM switch and forwards (using cells) the request to this next switch. When the request reaches the receiver, it sends back the established path and acknowledgement. After establishment, ATM addresses are no longer needed, only virtual Chapter connection.6: Wide identifiers Area Networks are used. Page EC EC ATM Switching Before the start of the communication a virtual connection has to established. The switches are responsible for the forwarding of arriving cells on the correct outgoing lines. For this purpose a switch has a switching table. Switching Tabelle Table Eingangsleitungen Incoming lines Switch Ausgangsleitungen Outgoing lines In Alter Old Out Neuer New n n Eingang... n Header Ausgang Header a c n n a d The header information, which are used in the switching table, are VPI (Virtual Path Identifier) and VCI (Virtual Channel Identifier). If a connection is being established via ATM, VPI and VCI are assigned to the sender. Each switch on the route fills in to where it should forward cells with this information.... b e Page Path and Channel Concept of ATM Physical connections contain Virtual Paths (VPs, a group of connections) VPs contain Virtual Channels (VCs, logical channels) VPI and VCI only have local significance and can be changed by the switches. Distinction between VPI and VCI introduces a hierarchy on the path identifiers. Thus: Reduction of the size of the switching tables. There are types of switches in the ATM network: VCI VCI VCI VCI 4 VCI 5 VCI 6 VPI VPI VPI Virtual Path Switching VP Switch VP-SWITCH VPI 4 VPI 5 VPI 6 VCI VCI 4 VCI 5 VCI 6 VCI VCI Virtual Channel Switching VPI VC Switch VCI VCI VCI 4 VCI VP/VC-SWITCH VPI VPI VCI VCI 4 Page 4

7 Layers within ATM Station Higher Layers ATM Adaptation Layer ATM Layer Physical Layer Switch ATM Layer Physical Layer Switch ATM Layer Physical Layer Station Higher Layers ATM Adaptation Layer ATM Layer Physical Layer Physical Layer Transfers ATM cells over the medium Generates checksum (sender) and verifies it (receiver); discarding of cells ATM Layer Generate header (sender) and extract contents (receiver), except checksum Responsible for connection identifiers (Virtual Path and Virtual Channel Identifier) ATM Adaptation Layer (AAL) Adapts different requirements of higher layer applications to the ATM Layer Segments larger messages and reassembles them on the side of the receiver Page 5 Service Classes of ATM Criterion Data rate Synchronization (source - destination) Negotiated maximum cell rate Service Class A B C D Yes Maximum and average Cell rate Dynamic rate adjustment to free resources Bit rate constant variable Connection Connection-oriented Mode Applications: Adaptation Layer (AAL): Moving pictures Telephony Video conferences AAL AAL No Take what you can get Connectionless Data communication File transfer Mail AAL AAL 4 AAL 5 Page 6 AAL : CBR - Constant Bit Rate, deterministic service Characterized by guaranteed fixed bit rate Parameter: Peak Cell Rate (PCR) AAL : VBR - Variable Bit Rate (real time/non real time), statistical service Characterized by guaranteed average bit rate. Thus also suited for bursty traffic. Parameter: Peak Cell Rate (PCR), Sustainable Cell Rate (SCR), Maximum Burst Size AAL : ABR - Available Bit Rate, load-sensitive service Characterized by guaranteed minimum bit rate and loadsensitive, additional bit rate (adaptive adjustment) Parameter: Peak Cell Rate, Minimum Cell Rate AAL 4: UBR - Unspecified Bit Rate, Best Effort service Characterized by no guaranteed bit rate Parameter: Peak Cell Rate Load PCR Load PCR SCR Load ABR/ UBR Other connections Time Time Time Page 7 Traffic Management Connection Admission Control (CAC) (CAC) Reservation of of resources during during the the connection establishment (signaling) Comparison between connection parameters and and available resources Traffic Traffic contract between users users and and ATM ATM network Usage Usage Parameter Control/Network Parameter Control Test Test on on conformity of of the the cell cell stream stream in in accordance with with the the parameters of of the the traffic traffic contract at at the the user-network interface (UNI) (UNI) or or network-network interface (NNI) (NNI) Generic Cell Cell Rate Rate Algorithm/Leaky Bucket Bucket Algorithm Switch Switch Congestion Control (primary for for UBR) UBR) Selective discarding of of cells cells for for the the maintenance of of performance guarantees in in the the case case of of overload Flow Flow Control for for ABR ABR Feedback of of the the network status status by by resource management cells cells to to the the ABR ABR source, for for the the adjustment of of transmission rate rate and and fair fair dispatching of of the the capacity Page 8

8 Integration of ATM into Existing Networks What does ATM provide? ATM offers an interface to higher layers (similar to TCP in the Internet protocols). ATM additionally offers QoS guarantees (Quality of Service). ATM had problems during its introduction: Very few applications which build directly upon ATM. In the interworking of networks, TCP/IP was standard. Without TCP/IP binding, ATM could not be sold! Therefore different solutions for ATM were suggested, e.g. IP over ATM (IETF) LAN emulation (LANE, ATM forum) Ethernet and ATM Fast/Gigabit Ethernet: Primary goal: Capacity No No QoS QoS guarantees Separation of of traffic traffic streams by by physical separation (router, switch, switch, links) links) No No prioritization of of data data streams No No protection against competitive traffic traffic Low Low cost cost Very Very high high capacity ATM: Primary goal: Integration, QoS QoS QoS guarantees Separation of of data data streams by by logical logical separation Prioritization of of real-time flows flows Connection Admission Control protects active active connections High High cost cost Scalable capacity Page 9 Page 0 Future of ATM Synchronous Digital Hierarchy (SDH) ATM within LAN: Too high cost of the hardware Too strong competition by established techniques like Fast Ethernet etc. ATM within WAN: often implemented between company locations Telecommunication providers prefer SDH as transport resp. core networks (better performance for telecommunications, world standard) ATM cells can be packed into SDH containers at transition points (encapsulation) resp. unpacked at the receiving network. Does ATM have still a future? probably: No! ATM was replaced to a large extent by SDH. Newest research proceeds even from a direct use of the fiber by higher protocols. ATM is only offered to users as a service, in order to be able to further use existing devices and mechanisms. All modern networks in the public area are using the SDH technology Example: the German B-WIN (ATM) was replaced by the G-WIN (Gigabit-Wissenschaftsnetz) Also used within the MAN range (Replaced by Gigabit Ethernet?) Analogous technology in the USA: Synchronous Optical Network (SONET) Core Node 0 Gbit/s,4 Gbit/s,4 Gbit 6 Mbit/s Global Upstream Essen St. Augustin Aachen Oldenburg Hannover Bielefeld Frankfurt Marburg Rostock Kiel Hamburg Göttingen Ilmenau Würzburg Braunschweig Magdeburg Heidelberg GEANT Karlsruhe Kaiserslautern Stuttgart Augsburg Erlangen Leipzig Berlin Dresden Regensburg Garching Page Page

9 SDH Structure SDH realizes higher data rates than ATM (at the moment up to about 40 GBit/s) Flexible capacity utilization and high reliability Structure: arbitrary topology, meshed networks with a switching hierarchy (exemplarily levels): Multiplexing within SDH MBit/s, 4 MBit/s, 55 MBit/s 6 MBit/s.5 GBit/s 0 GBit/s Supraregional switching Regional switching centers Local networks,5 GBit/s SDH Cross Connect 55 MBit/s 55 MBit/s Add/Drop Multiplexer 4 MBit/s MBit/s Synchronous Digital Hierarchy (SDH) Page Switching center MBit/s 4 MBit/s Switching center 55 MBit/s + control information for signaling 6 MBit/s 6 MBit/s MBit/s SDH Cross Connect Page 4 Characteristics of SDH SDH Transport Module (Frame) World-wide standardized bit rates on the hierarchy levels Synchronized, centrally clocked network Multiplexing of data streams is made byte by byte, simple multiplex pattern Suitability for speech transmission: since on each hierarchy level four data streams are mixed byte by byte and a hierarchy level has four times the data rate of the lower level, everyone of these mixed data streams has the same data rate as on the lower level. Thus the data experience a constant delay. Direct access to signals by cross connects without repeated demultiplexing Short delays in inserting and extracting signals Additional control bytes for network management, service and quality control, Substantial characteristic: Container for the transport of information Page 5 Synchronous Transport Module (STM-N, N=,4,6, 64) 9 x N columns (bytes) 6 x N columns (bytes) STM- structure: 9 lines with 70 bytes each. Basis data rate of 55 MBit/s. 4 5 Regenerator Section Overhead (RSOH) Administrative Unit Pointers Multiplex Section Overhead (MSOH) Payload 9 Administrative Unit Pointers permit the direct access to components of the Payload Section Overhead RSOH: Contains information concerning the route between two repeaters or a repeater and a multiplexer MSOH: Contains information concerning the route between two multiplexers without consideration of the repeaters in between. Payload Contains the utilizable data as well as further control data 9 lines (5 µs) Page 6

10 Creation of a STM Creation of a STM Utilizable data are packed into a container. A distinction of the containers is made by size: C- to C-4 Payload data are adapted if necessary by padding to the container size As additional information to the utilizable data, for a connection further bytes are added for controlling the data flow of a container over several multiplexers: Path Overhead (POH) Control of single sections of the transmission path Change over to alternative routes in case of an error Monitoring and recording of the transmission quality Realization of communication channels for maintenance By adding the POH bytes, a container becomes a Virtual container If several containers are transferred in a STM payload, these are multiplexed byte by byte in Tributary Unit Groups. By adding an Administrative Unit Pointer, the Tributary Unit Group becomes an Administrative Unit (AU). Then the SOH bytes are supplemented, the SDH frame is complete. RSOH and MSOH contain for example bits for Frame synchronization Error detection (parity bit) STM- identificators in larger transportation modules Control of alternative paths Service channels and some bits for future use. Page 7 Page 8 SDH Hierarchy SDH Hierarchy 55 MBit/s 6 MBit/s.5 GBit/s STM- STM-4 STM-6 6 4x6=044 4x044= x9=6 Assembled from Basis transportation module for 55 MBit/s, e.g. contains: a continuous ATM cell stream (C-4 container), a transportation group (TUG-) for three 4 MBit/s PCM systems, or a transportation group (TUG-) for three containers, which again contain TUGs 4 x STM- 4x6=44 Assembled from Assembled from 4 x STM-4 4 x STM- Higher hierarchy levels assembling STM- modules Higher data rates are assembled by multiplexing the contained signals byte by byte Each byte has a data rate suitable by 64 KBit/s, for the transmission of speech data (telephony) Except STM-, only transmission over optical fiber is specified 4 * 9 columns 9 columns 6 byte 4 * 6 byte Page 9 Page 40

11 Types of SDH Containers Types of SDH Containers C-n Container n VC-n Virtual Container n TU-n Tributary Unit n TUG-n Tributary Unit Group n C-4 H4 Payload VC-4 or Tributary Unit, n (n= to ) Contains VC-n and Tributary Unit Pointer TUG or TU- C- C-n Container n VC-n Virtual Container n TU-n Tributary Unit n TUG-n Tributary Unit Group n AU-n Administrative Unit n STM-N Synchronous Transport Module N VC-4 Path Overhead (POH) Container, C-n (n= to 4) Defined unit for payload capacity (e.g. C-4 for ATM or IP, C- for ISDN or MBit/s) Transfers all SDH bit rates Capacity can be made available for transport from broadband Chapter signals.6: not Wide yet specified Area Networks Virtual Container, VC-n (n= to 4) Consists of container and POH Lower VC (n=,): single C-n plus basis Virtual Container Path Overhead (POH) Higher VC (n=,4): single C-n, union of TUG-s/TU-s, plus basis Virtual Container POH Page 4 VC- TUG- VC- TUG- C- Administrative Unit n (AU-n) Adaptation between higher order path layer and multiplex unit Consists of payload and Administrative Unit Pointers Page 4 SDH Multiplex Structure SDH Multiplexing x N STM-N AUG AU-4 VC-4 x C kbit/s PTR Logical association Physical association Pointer VC- POH Container- Container- VC- x TUG- TU- TU- PTR VC- TU- AU- Pointer Processing x 7 Multiplexing C-n Container n VC-n Virtual container n TU-N Tributary Unit n TUG-n Tributary Unit Group n AU-n Administrative Unit n AUG Administrative Unit Group STM-N Synchronous Transport Module N C- x 7 TUG- TU- VC- C- x TU- VC- C- x 4 TU- VC- C kbit/s 4 68 kbit/s 6 kbit/s 048 kbit/s 544 kbit/s AU- PTR () PTR SOH () PTR AU- PTR AUG () PTR (4) PTR POH TUG- AU- PTR VC- () VC- () VC- () VC- (4) TUG- AUG TUG- AU- AUG STM-N Page 4 Page 44

12 What can SDH achieve? SONET SDH Electrical Optical Optical STS- OC- STM-0 STS- OC- STM- STS-9 OC-9 (STM-) STS- OC- STM-4 STS-8 OC-8 (STM-6) STS-4 OC-4 (STM-8) STS-6 OC-6 (STM-) STS-48 OC-48 STM-6 STS-96 OC-96 STM- STS-9 OC-9 STM-64 STS-768 OC-758 STM-56 Theoretically possible, but not relevant in practice Data rate (MBit/s) Brutto Netto 5,84 50, 55,5 50,6 466,56 45,008 6,08 60,44 9, 90,06 44,6 0, ,4 804,0 488, 405, ,64 480,75 995,8 96,504 98, 8486,06 Page 45