ATM networks. C. Pham Université de Pau et des Pays de l Adour LIUPPA Laboratory

Transcription

1 ATM networks C. Pham Université de Pau et des Pays de l Adour LIUPPA Laboratory Congduc.Pham@univ-pau.fr

2 Issues Driving LAN Changes Traffic Integration Voice, video and data traffic Multimedia became the buzz word Quality of Service guarantees not possible with the IP/Ethernet model (e.g. limited jitter, non-blocking streams) LAN Interoperability Mobile and Wireless nodes

3 High-speed interconnection Interconnection of distant LANs must be flexible to provide «bandwidth on demand» Frame Relay was a first step to remove network overheads and put most of the processing into endhosts SMDS & DQDB was 2 technologies that offer a flexible multi-service interconnection infrastructure SONET/SDH not flexible enough ATM is the continuation of these work Multi-service/multimedia network: voice, video, data Hundred s of Mbits/s rate Quality of Service adapted to end applications ATM standard (defined by CCITT) is widely accepted by common carriers as mode of operation for communication particularly BISDN.

4 Asynchronous Transfer Mode Voice Data packets Images ATM (Asynchronous Transfer Mode) Simplicity and performance of circuit switching Flexibility of packet switching Telco operator technology MUX Wasted bandwidth TDM ATM `

5 Limitation of datagram packet switching A With IP datagram mode, difficult to provide quality of service (no sequence, no ressource provisioning) R3 R1 R4 D D B C D D R2 Destination D D Next Hop R3 R5 F E E R3 F R5

6 Reliability of circuit switching SW SW Trunk lines SW SW SW SW PABX PABX SW

7 Traditional circuit in telephony Simple, efficient, but low flexibility and wastes resources 1 23 N MUX Fixed bandwitdh N De- MUX 1 sample every 125us gives a 64Kbits/s channel 1 23 N ATM: take advantages of both worlds Packet-switching with virtual circuit!

8 Virtual Circuit Connections & Virtual circuits table Label IN Link IN Label OUT Link OUT label 23 R Link 1 Link 2 45 Link 3 Link 4 34 Virtual Circuit: X.25 & Frame Relay. ATM: same principle but much smaller packet size A B C R1 R2 R3 R4 R5 D E

9 ATM Conceptual Model, 4 assumptions ATM network will be organized as a hierarchy. User s equipment connects to networks via a UNI (User- Network Interface). Connections between provided networks are made through NNI (Network-Network Interface). ATM will be connection-oriented. A connection (an ATM channel) must be established before any cells are sent. Vast majority of ATM networks will run on optical fiber networks with extremely low error rates. ATM must supports low cost attachments This decision lead to a significant decision to prohibit cell reordering in ATM networks.

10 ATM, reference model Management plane Control plane Higher layers ATM adaptation layer User plane Higher layers Layer management Plane management ATM layer Physical layer

11 Adaptation in end-host Voice A/D s 1, s 2 Digital voice samples AAL cells Video A/D picture frames Compression compressed frames AAL cells Data Bursty variable-length packets AAL cells

12 OSI vs ATM

13 An ATM network with hierarchy Admission control Traffic control

14 Hop-by-hop cell forwarding Use labels to forward cells Label in Label out Output port

15 Which size for a cell? European et japanese telcos 32 bytes makes a packetization delay of 4ms avoiding echo cancellation devices Computer scientists 64 bytes to reduce the header overhead US telcos had no problems with 64 bytes because of an already large deployed infrastructure of echo cancellation devices. The trade-off 53 bytes! (DQDB packet was also 53 bytes) 90.57% of efficiency at the maximum with 5 bytes for header

16 The ATM cell : 53 bytes label GFC: Generic Flow Control (UNI), VPI & VCI: Virtual Path Identifier, Virtual Channel Identifier PTI: Payload Type Identifier CLP: Cell Loss Priority HEC: Header Error Checksum

17 Pros & Cons of small size cells Pros Better management of buffers in ATM switches, Make easier the building of large parallel switches, Smaller switching delays. Cons Size of header is significant when compared to data, segmentation & reassembly is costly, At 622Mbits/s it s a cell every 700ns! ATM switch design is more difficult.

18 The physical layer Cell rate adaptation, HEC generation and verification,

19 Supported throughput Multimode Fiber: 100 Mbps using 4b/5b, 155 Mbps SONET STS-3c, 155 Mbps 8b/10b Single-mode Fiber: 155 Mbps STS-3c, 622 Mbps Plastic Optical Fiber: 155 Mbps Shielded Twisted Pair (STP): 155 Mbps 8b/10b Coax: 45 Mbps, DS3, 155 Mbps Unshielded Twisted Pair (UTP) UTP-3 (phone wire) at 25.6, 51.84, 155 Mbps UTP-5 (Data grade UTP) at 155 Mbps DS1, DS3, STS-3c, STM-1, E1, E3, J2, n T1

20 ATM over SONET/SDH

21 The ATM layer multiplexing & demultiplexing of cells, generation & extraction of headers, processing of VPs & VCs, Generic flow control (GFC). Virtual Circuit Virtual Path Transmission Path

22 VP & VC Virtual Circuit Virtual Path Transmission Path A VPC = 1 VP or a concatenation of several VPs. A VCC = 1 VC or a concatenation of several VCs. A VP contains several VCs Avantages Simple connection setup for most used paths Easy definition of Virtual Private Networks (VPN), Simplier traffic management: traffics with different constraints can be transported in different VPs for isolation.

23 Virtual Path a b c d e ATM Sw 1 VP3 ATM DCC VP5 ATM Sw 2 a ATM Sw 3 b c VP2 VP1 Sw = switch ATM Sw 4 d e Digital Cross Connect Only switches virtual paths

24 Virtual Channels

25 Advantages of VP and VC hierarchy Re-routing a VP automatically re-routes all VCs of the VP

26 QoS,, PVC, and SVC Quality of Service (QoS) requirements are handled at connection time and viewed as part of signaling. ATM provides permanent virtual connections and switched virtual connections. Permanent Virtual Connections (PVC) Permanent connections set up manually by network manager. Switched Virtual Connections (SVC) set up and released on demand by the end user via signaling procedures.

27 ATM switches & interface Optical fiber for longdistance Twisted copper possible for small distance High-speed connection matrix Fore ASX 200

28 Review: : crossbarc rossbar, general design Simplest possible spacedivision switch Crosspoints can be turned on or off, long enough to transfer a packet from an input to an output Expensive need N2 crosspoints time to set each crosspoint grows quadratically Data In configuration Data Out

29 Switch Fabrics: Buffered crossbar (packets) What happens if packets at two inputs both want to go to same output? Can defer one at an input buffer Or, buffer cross-points: complex arbiter

30 Switch fabric element Goal: towards building self-routing fabrics Can build complicated fabrics from a simple element data 10 0 data 00 1 Routing rule: if 0, send packet to upper output, else to lower output If both packets to same output, buffer or drop

31 Banyan element (1 possible configuration) 110 data 10 data ATM has boosted research on high-performance switches

32 Buffer management Input buffers Output buffer

33 Knockout switch Too costly!

34 Batcher-Banyan switch a same direction than arrow if a > b, a opposite direction if a is alone

35 ATM Protocol Architecture ATM Adaptation Layer (AAL) the protocol for packaging data into cells is collectively referred to as AAL. Must efficiently package higher level data such as voice samples, video frames and datagram packets into a series of cells. Design Issue: How many adaptation layers should there be? CCITT envisioned four classes of applications (A-D) requiring four distinct adaptation layers (1-4) which would be optimized for an application class: Constant bit-rate applications CBR Variable bit-rate applications VBR Connection-oriented data applications Connectionless data application

36 AAL Architecture First end-to-end layer in the ATM network model An AAL is further divided into: The Convergence Sublayer (CS) manages the flow of data to and from SAR sublayer. The Segmentation and Reassembly Sublayer (SAR) breaks data into cells at the sender and reassembles cells into larger data units at the receiver.

37 Original ATM Architecture The AAL interface was initially defined as classes A-D with SAP (service access points) for AAL1-4. AAL3 and AAL4 were so similar that they were merged into AAL3/4. The data communications community concluded that AAL3/4 was not suitable for data communications applications. They pushed for standardization of AAL5 (also referred to as SEAL the Simple and Efficient Adaptation Layer). AAL2 was not initially deployed.

38 Revised ATM Service Categories Class Description Example CBR Constant Bit Rate T1 circuit RT-VBR NRT-VBR Real Time Variable Bit Rate Non-real-time Variable Bit Rate Real-time videoconferencing Multimedia ABR Available Bit Rate Browsing the Web UBR Unspecified Bit Rate Background file transfer

39 Generic AALs Segmentation and Reassembly Each AAL is divided in 2 parts: SAR (Segmentation and Reassembly) and CS (Convergence Sublayer). CS makes the specific adaptation required by enduser/application.

40 AAL 1 Payload (b) CS PDU with pointer in structured data transfer 47 Bytes AAL 1 Pointer 1 Byte 46 Bytes optional (a) SAR PDU header CSI Seq. Count SNP 1 bit 3 bits 4 bits Copyright 2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks Figure 9.11

41 AAL 1 Higher layer b 1 b 2 b 3 User data stream Convergence sublayer CS PDUs SAR sublayer H H H SAR PDUs ATM layer H 5 48 H 5 48 H 5 48 ATM Cells Copyright 2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks Figure 9.10

42 AAL 3/4 CS and SAR PDUs (a) CPCS-PDU format Header Trailer CPI Btag BASize CPCS - PDU Payload Pad AL Etag Length , (bytes) (bytes) (bytes) (b) SAR PDU format Header (2 bytes) Trailer (2 bytes) ST SN MID SAR - PDU Payload LI CRC (bits) (bytes) (bits) Copyright 2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks Figure 9.16

43 AAL 3/4 Higher layer Service specific convergence sublayer Information User message Assume null Common part convergence sublayer H Information PAD 4 4 T Pad message to multiple of 4 bytes. Add header and trailer. SAR sublayer Each SAR-PDU consists of 2-byte header, 2-byte trailer, and 44-byte payload. ATM layer Copyright 2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks Figure 9.15

44 AAL 5 Convergent Sublayer Format Information Pad UU CPI Length CRC 0-65, (bytes) (bytes) SAR Format ATM Header 48 bytes of Data Copyright 2000 The McGraw Hill Companies 1-bit end-of-datagram field (PTI) Leon-Garcia & Widjaja: Communication Networks Figure 9.19

45 AAL 5 Higher layer Information Service specific convergence sublayer Assume null Common part convergence sublayer Information PAD T SAR sublayer 48 (0) 48 (0) 48 (1) ATM layer Figure 9.18 Copyright 2000 The McGraw Hill Companies PTI = 0 PTI = 0 PTI = 1 Leon-Garcia & Widjaja: Communication Networks

46 Example: : AAL 1, jitter compensation for audio restitution buffering Variable jitter not suitable for audio AAL1 Fixed-spacing for audio restitution

47 ATM LAN (obsolete) ATM switches as hub E t h e r n e t bridge Station ATM Station ATM Switch ATM Bridge H U B Station ATM Station ATM Station ATM source G. Beuchot Ethernet

48 ATM in the backbone Voice VPN IP Leased Lines Layer 3 Aggregation Layer 2 QoS VOICE FR ATM C IP ATM Layer 1 Restoration Layer 0 Transport SONET/SDH WDM FIBER source alcatel

49 ATM and ADSL Customer POTS Local Loop D< 3,5 Kms Central Office CAA PSTN Copper Wire Splitte r ATU-R Downstream 500 Kbps ou 1 Mbps ATM Network DSLAM (DSL Access Multiplexer) BAS (Broadband Access sever) Upstream 128 ou 256 Kbps BROADBAND Source FT NETWORK

50 ATM for ADSL BAS splitter DSLAM IP Routeur for ISP ATU-R ATM Network DSLAM Turbo IP splitter 1 VC ATM for flow 1 1 VC ATM for flow 2 DSLAM - BAS ATU-R 1 VP ATM LAN Netissimo 1 VC ATM / Customer Netissimo 1 (128 kbit/s, 500 kbit/s Netisimo 2 (256 kbit/s, 1000 kbit/s) Source FT

51 ATM in the telco s network BAS ATM Switch INTERNET DSLAM ADM ADM SDH/SONET ADM DSLAM DSLAM Source FT

52 Summary: ATM s curriculum Reduce overhead in core networks, push processing into end-host (Frame Relay philosophy) Software components (AALs) adapt the network service for end applications Several (and complex) quality of service Fixed and small size packet=cell, suitable for audio Connection-oriented at the network layer Packet switching philosophy with virtual circuits VP & VC hierarchy