Lesson 3 Network technologies - Controlling

Transcription

1 Lesson 3 Network technologies - Controlling Objectives : Network control or traffic engineering is one of the important techniques in the network. Understanding QoS control, traffic engineering and OAM are objectives of this lesson. 1

2 Basic concept of ATM communication Hardware routing Fixed length cell 53 bytes #j #k ATM switch VCI/VPI Label swapping #i Virtual connection ATM : Fixed length packet = cell Virtual connection = Connection Oriented 2 Fig.3.1 Hardware routing = Label swapping

3 Protocol stack of ATM/Frame relay/packet communication systems (1) Terminal Network Node Terminal NNI Layer 4~ Terminal Upper layer Packet switch Transmission line Packet switch Terminal Upper layer Layer 3 Layer 2 Logical channel multiplexing Out of order control Sequential number management Flow control Receive frame confirming Frame Mux/Demux Transmission error control Logical channel multiplexing Out of order control Sequential number management Flow control Receive frame confirming Frame Mux/Demux Transmission error control Layer 1 Physical/Electrical conditions UNI Physical layer NNI Physical layer UNI Physical/Electrical conditions (a) Packet switch communication system (X.25 protocol) Fig (a) Packet switch is based on software forwarding Throughput is limited.

4 Protocol stack of ATM/Frame relay/packet communication systems (3) Terminal Fiber transmission line = A few bit error Terminal Layer 4~ Layer 3 Upper layer Upper layer Layer 2 Order control Transmission error control ATM switch Order control Transmission error control Layer 1 Cell Mux/Demux ATM layer ATM layer Cell Mux/Demux Physical/Electrical conditions UNI Physical layer NNI Physical layer UNI Physical/Electrical conditions (c)atm communication system UNI : User-Network Interface NNI : Network Node Interface Basically, there is no layer 2 processing in the core network. Fig (c) Only cell (packet) forwarding High-speed operation.

5 ATM cell format 53byte = 5 byte header + 48 byte payload 5bytes 48bytes Header Information field UNI NNI (MSB) VPI VCI Bit VPI VCI HEC PT VCI (LSB) CLP (MSB) GFC VPI VCI Bit VCI HEC PT (b) In case of UNI VPI VCI (LSB) CLP (a) In case of NNI HEC : Error control for header information Fig.3.4 5

6 6 Relationship between packet size and quality Header P byte t sec Payload H byte

7 Function outline of AAL AAL type AAL type 1 AAL type 2 AAL type 3/4 AAL type 5 Channel 1 Channel 1 Frame 1 Frame 1 Concept Channel 2 Cell VCI1 VCI2 Channel 2 VCI structured cell Frame 2 Cell MID =1 MID MID =2 =1 MID =2 MID =2 (Same VCI) Cell VCI1 VCI1 VCI2 Frame 2 VCI2 VCI2 Characteristic Feature Assemble and disassemble cells to/from specific VCI by each channel. By building up multiple channels into the same cell, shorten the delay time to construct the cell even in low bit rate information. Multiplex the frames of multiple channels into the same VCI (recognizes by MID (Multiplexing Identifier)) Assemble and disassemble the cell by frame unit AAL Protocol function Absorbing the cell arriving time fluctuation Detecting loss of cell and bit error Multiplexing multiple frames into the same VCI (length of each channel s information is variable) Absorbing the cell fluctuation Detecting loss of cell and bit error Error detection Below functions are realized by SSCS Resending control for error recovery Flow control Multiplexing multiple frames into the same VCI Error correction by cell unit Error correction by frame unit Fig Major application field Voice and circuit switching information Low bit rate voice Data SMDS/ATM-CL Data Control signal between network/terminal ATM-CL Multimedia terminal image Voice

8 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 1 1 0~47bytes Start Field ATM cell 5bytes 48bytes CID: Channel Identifier (8bits) LI: Payload Length Indicator (6bits) UUI: User-to-User Indication (5bits) HEC: Header Error Control (5bits) CPS-INFO:Information (1-45/64 bytes) AAL2 is used for Voice transmission. Fig.3.8 8

9 Structure and function of AAL3/4 SSCS Upper layer data (corresponding to layer 2~4)(4byte~256Kbyte) Common Part Identifier Beginning tag Buffer Allocation size 4bytes integer of SSCS+PAD Alignment: makes trailer be 4bytes CPCS CPI Btag BA size PAD AL Etag L I (CS Common part) 1byte 1byte 2bytes 0~3bytes 1byte 1byte 2bytes SAR-PDU 2bytes ST SN MID LI 2bytes CRC Length of CS common part(4byte ~256Kbyte) End tag: Makes the same as the beginning tag to detect assembling error. 2bits 4bits 10bits 44bytes 6bits 10bits Bit error detection of SAR-PDU 5bytes 48bytes Indicates the Length of SAR payload Fig ATM cell SSCS: Convergence Sublayer Service dependent part CPCS: Common Part CS Message identifier (identifies AAL connection or CS message) Sequential number: Detects Cell loss/error insertion Segment type (position indication as CS frame of SAR payload) Beginning: 10 (BOM) Middle : 00 (COM) End : 01 (EOM) Single : 11 (SSM) AAL3/4 is used for data transmission. Data packet is 4k byte long, for example. Divided into short packet.

10 PVC(Permanent Virtual Connection) and SVC (Switched Virtual Connection) service PVC User OpS Operator sets up ATM network A B Private line Connection has already been established and data is delivered to destination when user selects the VCI (attaches it to header). C Operator connects fixedly in advance. SVC Connection set up XXXX VCI#3 ATM network Set up connection Fig Important User OK #3 Communication is done by cell-relay #7 A XXXX Dynamically connects by signaling

11 Soft PVC, virtual high-speed path set-up Controller A ATM NW User VCI-A PVC-A table PVC-B B VCI-A VCI-B PVC-A PVC-B 11

12 Traffic control technology in ATM node 2UPC(Usage Parameter control) 4 Shaping 3Priority control 2Mb/s 5Routing control Resource information 1 CAC(Connection admission control) Traffic monitoring Important Congestion QoS information Fault 12 Fig.3.12

13 Mechanism of Call Admission Control (CAC) New connection 50Mb/s X Unacceptable Transmission line bandwidth 150 Mb/s 20Mb/s Acceptable Connection-3 rest 30 Mb/s 40 Mb/s Connection-2 30 Mb/s Connection-1 50 Mb/s CAC device CAC device Fig.3.13

14 Adaptive CAC method 150M 100M 50M Numbers ((time) (a) 50M 100M 150M (bps) (b) Total, S New connection Overload, O Expected packet loss = O S 30M 50M 100M (c) 150M (bps) 14

15 Operation of Usage Parameter Control (UPC) Traffic exceeded the threshold Traffic volume Threshold level Time UPC circuit Repeating ATM switch UPC : Usage Parameter Control ATM network Subscriber ATM switch Fig

16 UPC methods and operation mechanism UPC method Mechanism Time chart Operation and feature (1) Leaky bucket method Depth Arrived cell Violation if overflowed Depth Count up when cell arrived Countdown at constant rate Hardware is simple Controls burst traffic by depth Leaks at constant rate (2) Credit window algorithm Counter + Reset T Count up arrived cells in T hours UPC monitoring miss may exist Hardware is simple T T Specified value (3) Sliding window algorithm (DB system) Cells go through Time, T Number of cells on bridge is specified value. T T T Count up the number of cells at all time phase Accurate monitoring of traffic volume is possible Hardware is complex Fig

17 Mechanism of priority control (1) Threshold control (2) Separate queue control Only priority cells are stored Both priority and nonpriority cells are stored Priority Priority queue Priority Non priority Threshold value Nonpriority Non-priority queue Discarded Only non-priority cells are discarded Distinguished by PT bit, etc. Transmits only when there is no cells in priority queue Fig

18 Principle of traffic shaper Traffic shaper Guarantees minimum cell interval Traffic volume Traffic volume Time Time Fig

19 Packet level transfer in ATM network Transmission terminal Packet A ATM cells EOP TOP End cell Top cell ATM network ATM Discarded EOP Receiving terminal TOP Packet A Request for resending EOP TOP Meaningless as packet A Lost part within ATM network Resend Packet reassembling completed Packet A Load within ATM network increases Fig

20 Mechanism of EPD(Early Packet Discard) Input traffic EOP... EOP... Threshold (TH) Buffer of ATM switch Input Queue length Input traffic Over threshold occurred EOP... EOP... Threshold (TH) Buffer of ATM switch Discard all in packet unit Queue length Fig

21 Packet throughput control by EPD 1 Packet throughput (throughput in packet level) EPD Conventional ATM transmission Abrupt decrease of throughput Invalid packets increases because of packet resending owing to congestion. 1 Offered load (load to be communicated) Fig

22 Operation of ATM network when congestion occurred Operation system OpS Indicates congestion on header of user cell (FECN) BECN 5UPC control Generation of congestion notifying cell (BECN) Congestion 1Notice of congestion Switch 1Notice of congestion UPC Priority Over traffic TransmissionNon- priority line Transmission line CAC 2Connection Admission Control 3Priority control Cell discarded 4Rerouting control Header converter #5 #9 #24 Changes header s conversion value Fig CAC : Connection Admission Control UPC : Usage Parameter Control FECN : Forward Explicit Congestion Notification BECN : Backward Explicit Congestion Notification

23 OAM level and flow End to end F5 flow Segment F5 flow ATM layer End to end F4 flow Segment F4 flow Virtual channel level Virtual path level F3 flow Physical layer Transmission path level F2 flow Digital section level F1 flow Repeater section level : End point of each level :Connection point of each level Fig

24 Relationship between OAM flow and equipment in physical layer and ATM layer Terminal using VC VP termination device (VC switch) VP cross connect VP cross connect VP termination device (VC switch) Terminal using VC VC VP VP VC VC End to end F5 flow VP Segment F5 flow VC level (F5) End to end F4 flow Segment F4 flow VP level (F4) Transmission path termination device Transmission path cross connect Repeater Transmission path cross connect Repeater Transmission path termination device (Example:Switch) (Example:Cross connect device) F3 flow Transmission path level (F3) F2 flow F2 flow F2 flow Digital section level (F2) Fig F1 flow F1 flow F1 flow Repeater section level (F1)

25 Example of alarm transmission in physical layer Transmission path termination device Transmission path cross connect Transmission path cross connect Transmission path termination device Repeater Repeater Transmission path fault occurred Signal off detected Repeater section level (F1) Detected MS-AIS sent MS-RAI sent Detected Digital section level (F2) Detected P-AIS sent P-RAI sent Detected Transmission (F3) path level Fig MS-: Multiples Section P-: Path AIS: Alarm Indication Signal RAI: Remote Alarm Indication

26 Outline of operation of alarm transmission function in ATM layer VP(VC) connection Fault exists ahead Stop transmission or Change route Detected :End terminal :Connection point :Occurrence :Detected Fault VP(VC)AIS cell Occurred (periodically) Fault detected When fault was Returned(periodically) detected, send back RDI VP(VC)-RDI cell Fig

27 Outline of operation of continuity check function VP(VC)connection Continuity check cell User cell Fault exists ahead Detected User s vacant time :End terminal :Connection point :Occurrence :Detected VP(VC)-RDI cell When cells were not found for a specified time, returns RDI. Fig

28 Outline of operation of loop-back function VP(VC)connection ID number xx Loop-back cell :End terminal :Connection point :Occurrence :Detected Confirm connecti on Same loop-back cell as the transmitted one Loop back the loop-back cell of xx Fig

29 Outline of operation of performance monitoring function VP(VC)connection User cell Performance monitoring cell User cell Performance monitoring cell User cell x 32 Parity Detected :End terminal :Connection point :Occurrence :Detected x32 Reverse directionperformanc e monitoring cell Notifies the result of monitoring to opposite side terminal OK or NG x K Calculate (Parity) Fig

30 Conclusions for Lesson3 1. ATM protocol is one of the typical connection oriented protocol. There are three key futures included ATM protocol, QoS, traffic and OAM. 2. Traffic engineering is key issue. CAC, UPC and other control method are used for not only ATM 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. 30

31 1 Background (Simple) 2, Motivation --Conventional approach --Problems 3, Key point --Originality --Ideas (with Figure.) 4, Effectiveness -- Merit, graph.. 5 Conclusions -- future study issue --show your idea