Basic concept of ATM communication

Transcription

1 Lesson 3 AM Network (2days) Basic concept of AM communication Protocol structure of AM network Hardware routing OSI reference model AM network protocols Objectives : AM concepts are typical connection oriented concept. Understanding QoS control, traffic engineering and OAM are objectives of this lesson. Fixed length cell 53 bytes #j #k Label swapping / #i AM switch Application layer Presentation layer Session layer ransport layer Layer 3 Network layer Management plane (M-Plane) Control plane (C-Plane) Q.293 plane (U-Plane) SSCOP AAL4 AAL3 AAL2 AAL AAL5 AM layer Layer 2 Data link layer Virtual connection Layer Physical layer Physical layer AM : Fixed length packet = cell Virtual connection = Connection Oriented AM is Layer /2 technology Fig.3. 2 Hardware routing = Label swapping Fig Protocol stack of AM/Frame relay/packet communication systems () Protocol stack of AM/Frame relay/packet communication systems (2) Protocol stack of AM/Frame relay/packet communication systems (3) Network Node Fiber transmission line = A few bit error Layer 4~ Layer 3 Layer 2 Layer Logical channel multiplexing Out of order control Sequential number management Flow control Receive frame confirming ransmission line Packet switch Packet switch Physical layer Physical layer Logical channel multiplexing Out of order control Sequential number management Flow control Receive frame confirming Layer 4~ Layer 3 Layer 2 Layer application such as order/flow Frame relay Frame relay control switch switch Physical layer Physical layer (b) Frame relay communication system application such as order/flow control Layer 4~ Layer 3 Layer 2 Layer Order control Mux/Demux : -Network Interface : Network Node Interface AM switch AM layer Physical layer AM layer Physical layer (c)am communication system Order control Mux/Demux Fig (a) (a) Packet switch communication system (X.25 protocol) Packet switch is based on software forwarding hroughput is limited. Fig (b) Frame relax is simple transport but still need in the core network hroughput is limited. Fig (c) Basically, there is no layer 2 processing in the core network. Only cell (packet) forwarding High-speed operation.

2 AM cell format (MSB) Bit HEC P (a) In case of 5bytes Header (LSB) CLP 53byte = 5 byte header + 48 byte payload Information field (MSB) Bit (LSB) GFC P CLP HEC (b) In case of AAL type Function outline of AAL Concept Characteristic Feature AAL Protocol function AAL type AAL type 2 AAL type 3/4 AAL type 5 Channel Channel Frame Frame Frame 2 Frame 2 Channel 2 Channel 2 MID = MID =2 MID = MID =2 MID =2 (Same ) 2 structured cell Assemble and disassemble cells to/from specific by each channel. Absorbing the cell arriving time fluctuation Detecting loss of cell and bit error By building up multiple channels into the same cell, shorten the delay time to construct the cell even in low bit information. Multiplexing multiple frames into the same (length of each channel s information is variable) Absorbing the cell fluctuation Detecting loss of cell and bit error Multiplex the frames of multiple channels into the same (recognizes by MID (Multiplexing Identifier)) Error detection Below functions are realized by SSCS Resending control for error recovery Flow control Multiplexing multiple frames into the same Error correction by cell unit Assemble and disassemble the cell by frame unit Error correction by frame unit Structure and function of AAL Field (4bits) SN: Detection of loss/error insertion CSI: SN=Even: whether using a pointer or not SN=Odd: ime stamp CRC of SN and Parity of CRC (protection of SN) 4bit Boundary display of structured data 4bit Initial position of data having a boundary by 6/24/32 bytes bit 3bits 3bits bit bit 7bits CSI SC CRC P ReservedOffset SN field SNP field Pointer field SAR-PDU header (byte) SAR-PDU payload (47 bytes) AM cell 5bytes SAR-PDU: Assembling of divided cells sub-layer protocol data unit CSI: CS Indication SN: Sequential Number SC: Sequential Count CRC: Cyclic Redundancy Code P: Parity Fig HEC : Error control for header information Fig Major application field Voice and circuit switching information Low bit voice Data SMDS/AM-CL Data Control signal between network/terminal AM-CL Multimedia terminal image Voice Fig AAL is used for circuit = Circuit emulation Operation principle of SRS ransmission side CK ~ CSI CS α - CR-S CR-I CK Inserts a ~ fm Count α CK β CR-I - Receive side CR-R ~ CK Adjust so as to become 0 Structure and function of AAL2 CPS packet CID LI UUI HEC CPS packet payload (variable length) CPS packet header (3bytes) Offset value Sequential number Parity CPS-PDU OSF SN P CPS packet CPS packet CPS packet PAD 4bits 0~47bytes Start Field AM cell Structure and function of AAL3/4 SSCS data (corresponding to layer 2~4) Common Part Identifier 4bytes integer of SSCS+RAD Beginning tag Alignment: makes Buffer Allocation size trailer be 4bytes CPCS CPI Btag BA size PAD AL Etag L I (CS Common part) byte byte 2bytes 0~3bytes byte byte 2bytes Length of CS 2bytes 2bytes common part End tag: Makes the same as the beginning SAR-PDU S SN MID LI CRC tag to detect assembling error. 2bits 4bits 0bits 44bytes 6bits 0bits Bit error detection of SAR-PDU Indicates the Length of SAR payload 5bytes Fig Clock synchronization is needed. Fig.3.8 5bytes CID: Channel Identifier (8bits) LI: Payload Length Indicator (6bits) UUI: -to- Indication (5bits) HEC: Header Error Control (5bits) CPS-INFO:Information (-45/64 bytes) AAL2 is used for Voice transmission. C ted short (small packet) into one cell. Fig AM cell SSCS: Convergence Sublayer Service dependent part CPCS: Common Part CS Message identifier (identifies AAL connection or CS message) Sequential number: Detects loss/error insertion Segment type (position indication as CS frame of SAR payload) Beginning: 0 (BOM) Middle : 00 (COM) End : 0 (EOM) Single : (SSM) AAL3/4 is used for data transmission. Data packet is 4k byte long, for example. Divided into short packet. 2

3 Structure and function of AAL5 SSCS data (corresponding to layer 2~4) CPCS PDU information length (in bytes) Common Part Identifier PVC(Permanent Virtual Connection) and SVC (ed Virtual Connection) service PVC OpS Operator sets up AM network A raffic control technology in AM node 2UPC(Usage Parameter control) 4 Shaping information Padding (48 bytes integer) Error checking of CPCS B Private line CPCS Fig CPCS (CS Common Part) SAR-PDU 0+ AM cell 5bytes CPCS PDU payload 0~47 bytes PAD CPI LI CRC SAR-PDU has no Header/railer 0 or : 0:Beginning/Middle cell (identification by PI bit of AM layer) :End cell AAL5 is also used for data transmission with simple overhead. Fig.3. 4 Important SVC Connection has already been established and data is delivered to destination when user selects the (attaches it to header). Connection set up XXXX OK #3 #3 Communication is done by cell-relay AM network C Operator connects fixedly in advance. Set up connection A XXXX #7 Dynamically connects by signaling Fig Important 3Priority control 5Routing control 2Mb/s Resource information CAC(Connection admission control) raffic monitoring Congestion QoS information Fault Mechanism of Call Admission Control (CAC) X New connection 50Mb/s Unacceptable 20Mb/s Acceptable Connection-3 Connection-2 Connection- ransmission line bandwidth 50 Mb/s rest 30 Mb/s 40 Mb/s 30 Mb/s 50 Mb/s Operation of Usage Parameter Control (UPC) raffic volume raffic exceeded the threshold hreshold level ime UPC circuit Repeating AM switch UPC methods and operation mechanism UPC method () Leaky bucket method (2) Credit window algorithm Depth Mechanism Arrived cell Violation if overflowed Leaks at constant + Reset Counter ime chart Operation and feature Depth Count up when cell arrived Countdown at constant Hardware is simple Controls burst traffic by depth Count up arrived cells in hours UPC monitoring miss may exist Hardware is simple CAC CAC UPC : Usage Parameter Control AM network Subscriber AM switch (3) Sliding window algorithm (DB system) Specified value s go through ime, Number of cells on bridge is specified value. Count up the number of cells at all time phase Accu monitoring of traffic volume is possible Hardware is complex Fig Fig Fig

4 Mechanism of priority control Principle of traffic shaper Packet level transfer in AM network ransmission terminal () hreshold control (2) Sepa queue control Only priority Both priority and nonpriority cells are cells are stored stored Priority Non priority hreshold value Discarded Only non-priority cells are discarded Priority Nonpriority Distinguished by P bit, etc. Priority queue Non-priority queue ransmits only when there is no cells in priority queue raffic volume ime raffic shaper Guarantees minimum cell interval raffic volume ime Packet A AM cells OP End cell op cell AM network AM Discarded Packet A Request for resending OP Receiving terminal OP Meaningless as packet A Lost part within AM network Resend Packet reassembling completed Packet A Load within AM network increases Fig Fig Fig Mechanism of EPD(Early Packet Discard) Packet throughput control by EPD Operation of AM network when congestion occurred Operation system OpS Indicates congestion on header of user cell (FECN)... Input traffic... hreshold (H) Buffer of AM switch BECN 5UPC control Notice of UPC congestion Generation of congestion notifying cell (BECN) Priority Congestion Over traffic Notice of congestion Input ransmissionnon- priority line ransmission line Input traffic Over threshold occurred Queue length Packet throughput (throughput in packet level) EPD Conventional AM transmission CAC 2Connection Admission Control discarded 3Priority control hreshold (H) Buffer of AM switch Discard all in packet unit Abrupt decrease of throughput Invalid packets increases because of packet resending owing to congestion. 4Rerouting g control Header converter Queue length Offered load (load to be communicated) #5 #9 #24 Changes header s conversion value Fig Fig Fig CAC : Connection Admission Control UPC : Usage Parameter Control FECN : Forward Explicit Congestion Notification BECN : Backward Explicit Congestion Notification 4

5 AM services category Minimum bandwidth guarantee type best effort communication by UBR+ changing by ABR changing by ABR CBR VBR UBR UBR + ABR AB rt-vbr nrt-vbr AB-I AB-D RM cell ER raffic parameter Peak cell Peak cell Average cell Maximum burst length None Peak cell Minimum cell Peak cell ransferred traffic agging (in packet unit) AM switch raffic passing with best effort request QoS parameter (Quality assurance) ransmissio n delay Maximum delay Variation loss ransmission delay Maximum delay Variation No ransmission delay,maximum delay and Variation None Lowest packet ransmission is controlled according to state of network ransmission delay Block ratio loss (when route/bandwidth were established) MCR UPC Guaranteed MCR: Minimum Rate (ransmission side) (Receiver side) ER" Object of services Circuit switching data loss Real time Non real time Data transfer (especially CP/IP) Data transfer within/inter LANs Burst-like data ransfer Contents transfer When route is congesting, discards tagged cells When route is not congesting, passes all the packets controls node based on ER value ER" ER" ER" ransferable ransferable ransferable bandwidth bandwidth bandwidth RM cell ransferable bandwidth Variable encoding voice/image ER: Explicit Rate Feature Assumed that user knows the nature of traffic Supposed as an AM layer service to transfer data switch rewrites ER value only when bandwidth is less than the one of internal cell. able Fig Fig Mechanism of AB and image of cell transferring by AB Mechanism of AB OAM level and flow End to end F5 flow Relationship between OAM flow and equipment in physical layer and AM layer using VC VP termination (VC switch) VP cross connect VP cross connect VP termination (VC switch) using VC Segment F5 flow AB-I (AM Block ransfer with Immediate ransmission ) (ransmission side) request ( x Mb/s) Information transfer Discard Reject (No vacancy) (Receiver side) AM layer End to end F4 flow Segment F4 flow F3 flow Virtual channel level Virtual path level VC VP VC End to end F5 flow Segment F5 flow End to end F4 flow Segment F4 flow VP VP VC VC level VP level (F5) (F4) Information transfer request Release Release Resending/ request ( x ½ Mb/s) Prepare for receiving Physical layer ransmission path level Digital section level ransmission path ransmission path ransmission termination cross connect path cross connect (Example:) (Example:Cross connect ) F3 flow ransmission path termination CS-PDU CS-PDU CS-PDU CS-PDU section level ransmission path level (F3) Block Block Block : End point of each level :Connection point of each level Digital section level (F2) Fig ime Fig Fig section level (F) 5

6 Example of alarm transmission in physical layer Outline of operation of alarm transmission function in AM layer Outline of operation of continuity check function ransmission path ransmission path ransmission path ransmission path termination cross connect cross connect termination VP(VC) connection VP(VC)connection ransmission path fault occurred Signal off detected section (F) level MS-AIS sent Digital section (F2) level MS-RAI sent P-AIS sent ransmission (F3) path level Fault exists ahead :End terminal :Connection Stop transmission point or Change route :Occurrence : Fault VP(VC)AIS cell Occurred (periodically) Fault detected When fault was Returned(periodically) detected, send back RDI VP(VC)-RDI cell Fault exists ahead Continuity check cell s vacant time :End terminal :Occurrence :Connection : point cell VP(VC)-RDI cell When cells were not found for a specified time, returns RDI. P-RAI sent Fig MS-: Multiples Section P-: Path AIS: Alarm Indication Signal RAI: Remote Alarm Indication Fig Fig Outline of operation of loop-back function Outline of operation of performance monitoring function Conclusions for Lesson3 VP(VC)connection Loop-back cell Confirm connecti on Same loop-back cell as the transmitted one :End terminal :Occurrence :Connection : point ID number xx Loop back the loop-back cell of xx cell x 32 Parity Performance monitoring cell :End terminal :Connection point :Occurrence : VP(VC)connection x32 cell Reverse directionperformanc e monitoring cell Performance monitoring cell Notifies the result of monitoring to opposite side terminal cell OK or NG x K Calculate (Parity). AM protocol is one of the typical connection oriented protocol. here are three key futures included AM protocol, QoS, traffic and OAM. 2. raffic engineering is key issue. CAC, UPC and other control method are used for not only AM bt but also other protocols such as MPLS. 3. OAM is also important for network operator. Using OAM network operator can monitor and control the network. Fig Fig