1. Broadband ISDN and ATM 발표자 : 박종민 Jmpark@cs.chonbuk.ac.kr

2. Contents 1.Introduction to B-ISDN and ATM –The B-ISDN ATM Reference Model 2.Physical Layer in ATM –Virtual Circuits versus Circuit Switching –Transmission in ATM Networks –ATM Switches ( Knockout, Batcher-Banyan ) 3.Data Link Layer in ATM

3. 4.Network Layer in ATM –Cell Formats –Connection Setup –Routing and Switching –Service Categories –Quality of Service –Congestion Control –ATM LANs 5.ATM AAL Layer Protocols –Structure of the ATM Adaptation Layer –AAL 1, AAL 2, AAL 3 / 4, AAL 5 –Comparison of AAL Protocols –Service Specific Connection-Oriented Protocol(SSCOP)

4. 1. Introduction to B-ISDN & ATM B-ISDN(Broadband Integrated Services Digital Network) –A single physical network integrates variety of services –Problems QoS Requirements for services widely different –Voice : Real time(low delay jitter), tolerates occasional losses –Data : Usually no real-time requirements, error-free, guaranteed delivery –Video : High bandwidth, low delay and jitter Traffic characteristics also widely different Certain applications require synchronization among multiple traffic streams

5. ATM(Asynchronous Transfer Mode) –Underlying technology that makes B-ISDN possible –Transmit all information in small, fixed size packet (ATM cell) –Cell switching technology Flexible and handle both constant(audio, video) and variable(data) rate traffic Easier than traditional multiplexing techniques using fiber optics Broadcasting(television distribution) –Connection-oriented : Cell order is guaranteed –Intended speed : 155 Mbps, 622 Mbps, gigabit speeds later 155 Mbps(exact choice) : made for compatibility with AT&T’s SONET

6. B-ISDN ATM Reference Model

7. Physical Layer(deals with physical medium) –Voltage, bit timing, various other issues. –Designed to be independent of the transmission medium ATM Layer(deals with cells and cell transport) –Defines the layout of a cell –Establishment and release of virtual circuits –Congestion control AAL Layer(ATM Adaptation Layer) –Allows users to send packets larger than a cell –Segments packets, transmits the cells individually, and reassembles then at the other end User plane –Deals with data transport, flow control, error correction, and other user functions Control plane is concerned with connection management

9. 2. Physical Layer in ATM B-ISDN service : Compromise between circuit and packet switching Virtual Circuits –Connection oriented –Implemented internally with packet switching –Connection Types Permanent virtual circuits (No setup time) Switched virtual circuits (Like telephone call) –Circuit establishment The route is chosen from source to destination All switch along the way make table entries so they can route any packet on that virtual circuit

11. Transmission in ATM Network Synchronous transmission mode Asynchronous transmission mode –Not required that the stream of cells coming out of a computer be continuous(Gaps between the data cells are filled by idle cells) –Does not standardize the format for transmitting cells –All ATM links are point-to-point(unidirectional) –Multicasting : Enter a switch on one line and exit it on multiple lines

12. ATM Switches General Model for an ATM cell switch ATM switches are generally synchronous –Cell arrive on the input lines asynchronously –Master clock marks the beginning of a cycle Common goal –Switch all cells with as low a discard rate as possible –Never reorder the cells on a virtual circuit

13. Input queueing : head-of-line blocking Output queueing

14. The Knockout Switch Output queueing

15. Batcher-Banyan Switch

19. 3. Data Link Layer in ATM TC(Transmission Convergence) sublayer Cell Transmission –takes a sequence of cells –add HEC to each one ( HEC : Header Error Control ) –convert the result to bit stream –match the bit stream to the speed of the underlying physical transmission system by inserting OAM cells as filler –OAM : Operation And Maintenance Cell Reception –takes an incoming bit stream –locates cell boundaries –verifies the header –processes the OAM cells –passes the data cell up to the ATM layer

20. Locating the cell boundaries –HUNT : Shifting bits into the shift registers one at a time looking for a valid HEC –PRESYNCH : shifts in the next 424 bits(5-bytes) without examining them

21. 4. Network Layer in ATM Network Connection-oriented layer –Basic element : virtual circuit(virtual channel) –Unusual for a connection-oriented protocol Does not provide any acknowledgements Used for real-time traffic(audio, video) –Guarantee : cells sent will never arrive out of order Supports a two-level connection hierarchy

22. Cell Formats UNI(User-Network Interface) –Define boundary between a host and an ATM network (between the customer and the carrier) NNI(Network-Network Interface) –Define boundary between two ATM switches GFC : General Flow ControlPTI : Payload Type VPI : Virtual Path IdentifierCLP : Cell Loss Priority VCI : Virtual Channel IdentificationHEC : Header Error Check 40 bits

23. GFC : flow control or priority VPI : select a particular virtual path VCI : select a particular virtual circuit PTI : define the type of payload CLP : set by host to differentiate between high-priority traffic and low-priority traffic HEC : checksum over the header Payload typeMeaning 000User data cell, no congestion, cell type 0 001User data cell, no congestion, cell type 1 010User data cell, congestion experienced, cell type 0 011User data cell, congestion experienced, cell type 1 100Maintenance information between adjacent switches 101Maintenance information between source and destination switch 110Resource Management cell(used for ABR congestion control) 111Reserved for future function

24. Connection Setup Messages used for connection establishment and release ATM address –20 bytes(based on OSI addresses) Byte 1 : indicate which of three formats the address is in Bytes 2-3 : country(alternatively, international organization) Bytes 4 : format of the rest of the address 3-byte(authority), 2-byte(domain), 2-byte(area), 6-byte(address) –15 digit decimal ISDN telephone number MessageMeaning when sent by hostMeaning when sent by network SETUPPlease establish a circuitIncoming call CALL PROCEEDINGI saw the incoming callYour call request will be attempted CONNECTI accept the incoming callYour call request was accepted CONNECT ACKThanks for acceptingThanks for making the call RELEASEPlease terminate the callThe other side has had enough RELEASE COMPLETEAck for release

25. Connection setup in an ATM network Connection release

26. Routing and Switching Route on VPI field, but not VCI field –Exception : route on VCI at the final hop in each direction Advantage –No new routing decisions have to be made –Routing of individual cells is easier when all VCs for a given path are always in the same bundles –Easier to switch a whole group of VCs –Easier for carriers to offer closed user groups(private network) to corporate customers

27. Examples : Rerouting a VP reroutes all of its VCs

29. Service Categories The ATM service categories Characteristics of the ATM service categories ClassDescriptionExample CBRConstant bit rateT1 circuit RT-VBRVariable bit rate : real time Real-time videoconference NRT-VBRVariable bit rate : non-real timeMultimedia email ABRAvailable bit rateBrowsing the Web UBRUnspecified bit rateBackground file transfer Service characteristicCBRRT-VBRNRT-VBRABRUBR Bandwidth guaranteeYes Optional No Suitable for real-time trafficYes No Suitable for bursty trafficNo Yes Feedback about congestionNo YesNo

30. Quality of Service Some of the quality of service parameters ParameterAcronymMeaning Peak cell ratePCRMaximum rate at which cells will be sent Sustained cell rateSCRThe long-term average cell rate Minimum cell rateMCRThe minimum acceptable cell rate Cell delay variation toleranceCDVTThe maximum acceptable cell jitter Cell loss ratioCLRFraction of cells lost or delivered too late Cell transfer delayCTDHow long delivery takes(mean and maximum) Cell delay variationCDVThe variance in cell delivery times Cell error rateCERFraction of cells delivered without error Severely-errored cell block ratioSECBRFraction of blocks garbled Cell misinsertion rateCMRFraction of cells delivered to wrong destination

31. The probability density function for cell arrival times

32. Congestion Control Admission Control. –Must describe the traffic to be offered and the service expected. –Check to see if it is possible to handle this connection. –If no route can be located, the call is rejected. –Denying admission should be done fairly. Resource Reservation. –Reserving resources in advance, usually at call setup time. –Bandwidth can be reserved by having the SETUP message along each line it traverses. Rate-Based Congestion Control. –CBR and VBR : No dynamic congestion control are possible( real-time ). –UBR : Nobody cares. –ABR : How congestion should be detected, signaled, and controlled ?

33. Rate-based solution –After every k data cells, transmits a special RM cell –RM(Resource Management) cell Travels along the same path as the data cells Contains ER(Explicit Rate). When it gets the destination, it is examined, updated, and sent back –Congestion control mechanism Overloaded switches generate RM cells and ship them back to the sender Overloaded switches set the middle PTI bit

34. ATM LANs How to provide connectionless LAN service over the ATM network –Introduce a connectionless server into the network –Every host has a (potential) ATM virtual circuit to every other host LES : LAN Emulation Server BUS : Broadcast/Unknown Server

35. 5. ATM ALL Layer Protocol AAL : ATM Adaptation Layer Goal –Provide useful services to application programs –Shield application programs from the mechanical processing Original service classes supported by AAL(now obsolete) Defined four protocols to handle services(AAL 1 ~ AAL4)

36. Structure of the ATM Adaptation Layer ATM adaptation layer Convergence sublayer –Provide the interface to the application –Service specific part –Common part SAR(Segmentation And Reassembly) sublayer –Sender : add header and trailers to the data –Receiver : reassemble the cells into message Convergence sublayer (service specific part) Convergence sublayer (common part) Segmentation reassembly sublayer

38. AAL 1 Used for transmitting class A traffic –Simple, connection-oriented, real-time constant bit rate –Ex. Uncompressed audio and video CS sublayer –Break up the input message or stream into 46- or 47- byte unit –Does not have any protocol header Cell format –SN(Sequence Number), SNP(Sequence Number Protection: checksum) –P cell : used when message boundaries must be preserved

39. AAL 2 Used for transmitting class B traffic –Rate can vary strongly in time –Message boundary preserved –Ex. Compressed audio or video As in AAL1, the CS sublayer does not have a protocol header Cell format –1-byte header, 2-byte trailer, 45-byte data bytes –IT(Information Type) : indicate that cell is the start, middle, or end –LI(Length Indicator) : tells how big the payload is

40. AAL 3/4 Protocols for classes C and D Stream or message mode –Message mode : Boundaries are preserved –Stream mode : Boundaries are not preserved Multiplexing of several sessions onto one virtual circuit

41. AAL 3 / 4 CS sublayer message format –CPI(Common Part Indicator) : Message type –Btag, Etag : Used to frame message –BA size, Length : Payload length Cell format : ST(Segment Type), MID(Multiplexing ID)

42. AAL 5 SEAL(Simple Efficient Adaptation Layer) Service –Reliable service, Unreliable service –Unicast and Multicast(not guaranteed) are supported –Supports message mode and stream mode CS sublayer –UU(User to User) : available for a higher layer for its own purpose Sequencing, multiplexing –Length : Payload length(not counting padding) SAR sublayer : does not add headers or trailers

43. Some difference between the various AAL protocols Comparison of AAL Protocols ItemAAL 1AAL 2AAL 3/4AAL 5 Service classABC/D MultiplexingNo YesNo Message delimitingNone Btag/EtagBit in PTI Advance buffer allocationNo YesNo User bytes available0001 CS padding0032-Bit word0-47 bytes CS protocol overhead(bytes)0088 CS checksumNone 32 Bits SAR payload bytes46-47454448 SAR protocol overhead(bytes)1-2340 SAR checksumNone 10 BitsNone

44. SSCOP AAL protocols does not provide for simple end-to-end reliable transport connections SSCOP –Service Specific Connection-Oriented Protocol –Used for control, not for data transmission –Fundamentally a dynamic sliding window protocol No piggybacking Periodically, sender asks to send back the bit map giving the window status