Lecture Computer Networks

Transcription

1 Lecture Computer Networks Prof. Dr. Hans Peter Großmann mit M. Rabel sowie H. Hutschenreiter und T. Nau Sommersemester 2012 Institut für Organisation und Management von Informationssystemen Asynchronous Transfer Mode (ATM)

2 Page 2 ATM The Idea Provision of network capabilities for handling all current and future applications independently of their bandwidth requirements. The main goal was a unification of telecommunication with data communication.

3 Page 3 ATM The Idea (II) Computer and Application Software ATM Interface Video Video Disks Audio Network

4 Page 4 B-ISDN Telecommunication Radio and Television Data Communication Telecommunication Data Communication ISDN (Integrated Services Digital Network) B-ISDN (Broadband Integrated Services Digital Network)

5 Page 5 Todays Communication Infrastructure T C P u b l i c S T N T C M U X M U X... R o u t e r c o n n e c t i o n o r i e n t e d p a c k e t s w i t c h e d R o u t e r R o u t e r X. 2 5 F r a m e - R e l a y H U B R o u t e r

6 Page 6 B-ISDN / ATM Infrastructure B-ISDN IBCN Services Server

7 Page 7 Asynchronous Transfer Mode (ATM) Strategic B-ISDN direction since 1988 Standards of ITU and the ATM Forum Technology Fast packet switching Variable bandwidth channel assignment ATM can handle different bit rates and traffic parameters with data rates Mbps / Mbps at UNI Transmission interface SONET / SDH up to 2.4 Gbps Culmination of all developments in circuit and packet switching over the past 20 years ATM-Forum founded in 1991

8 Page 8 ATM II

9 Page 9 ATM Drafts Packet switching no linkwise error protection connection-oriented small packet (cells) of fixed length Time division multiplexing method time slot method time relations are not supported time slots are not marked by their position (asynchronous)

10 Page 10 STM / ATM

11 Page 11 Synchronous Transfer Mode (STM) Based on time division multiplexing Disadvantages Fixed data rates Fixed bandwidth for connection

12 Page 12 ATM Transmission Efficiency

13 1 Byte Page 13 Cell Structure 5 Bytes 48 Bytes Header Payload GFC VPI VPI VCI VCI VCI PTI CLP HEC GFC: GFC: VPI: VPI: VCI: VCI: PTI: PT: CLP: CLP: HEC: HEC: Generic Flow Control (used only with UNI) Generic Flow Control (used only with UNI) Virtual Path Identifier Virtual Channel Identifier Virtual Path Identifier Virtual Channel Identifier Payload Type Identifier Payload Type Identifier Cell Loss Priority Cell Loss Priority Header Error Control Header Error Control

14 Page 14 ATM Bandwidth NNI (network-network interface) 155 Mb/s, 622 Mb/s, 2.4 Gb/s UNI (user-network interface) 25 Mb/s Mb/s bandwidth allocation for an application on demand

15 Page 15 Modes of Connection Permanent Virtual Circuit (PVC) VCI/VPI tables are created manually by administrator PVCs exist permanent, even when there is no data traffic Switched Virtual Circuits (SVC) connections are established and closed dynamically by ATM signalling SVCs normally are closed when no data traffic occurs

16 Page 16 ATM Switch Matrix

17 Page 17

18 Page 18 ATM - Classes of Services I Class A Class B Class C Class D Time Reference time-continuous not time-continuous Bit rate constant variable Connection Mode connection-oriented connectionless Services Audio / Video Audio / Video Services for data Services for data Adaption Layer AAL 1 AAL 2 AAL 5, AAL 3/4

19 Page 19 ATM - Classes of Services II Class A Circuit emulation Intended for constant bitrate voice and video applications Timing relationship between source and destination Class B Variable bit rate services Intended for isochronous voice and video traffic with variable bitrate information Timing relationship between connection endpoints (connectionoriented)

20 Page 20 ATM - Classes of Services III Class C Connection-oriented data transfer Intended for traditional data traffic as known e.g. in X.25 message mode : transfer of single frames streaming mode : transport for multiple fixed length frames Class D Connectionless data transfer Intended to carry e.g. TCP/IP or LAN interconnection traffic

21 Page 21 ATM Architecture OSI Model Higher Layers Control Plane Signalling & Controlling Management Plane User Plane Class 1 Class 2 Class 3 Class 4 Layer 2 Layer 1 ATM Adaptation Layer (AAL) ATM Layer Physical Layer

22 Page 22 ATM Layers Control User Higher Layers Signalling Class A Class B Class C Class D ATM Adaptation Layer Sign. AAL AAL1 AAL2 AAL3/4 or AAL5 ATM Layer Convergence Sublayer CS Segmentation and Reassembly Physical Layer Transmission Convergence TC Physical Medium PM

23 Page 23 Encapsulation the general scheme Data from Application Header CS Convergence Layer Data Trailer CS Sublayer CS Data Data Data CS ATM cells: ATM ATM ATM Layer CS Data Data Data CS ATM (Not each adaption layer uses CS and header and trailer)