updated 12/20011 Asynchronous Transfer Mode Networks Nirmala Shenoy Information Technology Department Rochester Institute of Technology

updated 12/20012 Asynchronous Transfer Mode Scope –Purpose –Cells vs packets –Topology –Virtual connections –VP and VPC switching –ATM layers

updated 12/20013 Asynchronous Transfer Mode Scope –Delays in ATM networks –Service & QoS –Traffic control –UNI –B-ICI –Switch fabric –ATM addressing

updated 12/20014 Asynchronous Transfer Mode Purpose –Cells over frames –Optimal use of transmission and equipment technology –Interface with various packet switching networks –WAN connectivity

updated 12/20015 Asynchronous Transfer Mode Purpose –Easy and inexpensive implementation –Support exiting telecommunication hierarchies Local loops, local providers, long distance carriers –Connection oriented – reliable and predictable delivery especially for real-time application –protocol functions from sw to hw –High-speed low delay packet switching for all types of traffic

updated 12/20016 Asynchronous Transfer Mode Cell vs Frames Frames - Packets Current packet sizes- 200bytes to 64kbytes Elaborate software at intermediate nodes to accommodate variable size packets Variable header evaluations Packets to be checked for integrity Non-uniformity of service for different types of packet networks

updated 12/20017 Asynchronous Transfer Mode Packets Consistent data rate delivery not possible In-time delivery for some packets –Real-time packets may be smaller compared to data packets Cells Predictable processing Uniformity guaranteed

updated 12/20018 Asynchronous Transfer Mode Cells Deterministic delays = n*cell transmission High speed + small cell size = continuous stream effect Cells handled as cells not as bit stream – faster Fixed cells – more hardware implementable

updated 12/20019 Asynchronous Transfer Mode Asynchronous TDM

updated 12/ Asynchronous Transfer Mode Topology

updated 12/ Asynchronous Transfer Mode Topology –Similar to ISDN has all reference points and functional groupings (b tag) – Public and private UNI may use different different interfaces & schemes –ATM can be used as a LAN, WAN, hub –interconnecting networks, backbone

updated 12/ Asynchronous Transfer Mode Virtual connections Transmission Path –Physical connection between two points –Switches and end points or between switches Virtual Path –Transmission path is divided into several virtual paths

updated 12/ Asynchronous Transfer Mode Virtual connections –The set of all virtual path = transmission path Virtual circuit –A single message flow circuit –A number of virtual circuits make a virtual path

updated 12/ Asynchronous Transfer Mode Virtual connections – relationship

updated 12/ Asynchronous Transfer Mode Virtual connections – relationship

updated 12/ Asynchronous Transfer Mode Virtual connections – relationship VPI & VCI

updated 12/ Asynchronous Transfer Mode Virtual connections set-up PVC – permanent virtual circuit –Negotiated with the network on long term basis SVC – switched virtual circuit –On per call basis

updated 12/ Asynchronous Transfer Mode Virtual connections set-up

updated 12/ Asynchronous Transfer Mode VP switching

updated 12/ Asynchronous Transfer Mode VPC switching – VP & VC switching

updated 12/ Asynchronous Transfer Mode ATM layers –ATM Adaptation Layer – AAL Convergence Sub layer Segmentation and Reassembly sub layer –ATM Layer –Physical layer SONET/SDH

updated 12/ Asynchronous Transfer Mode ATM layers & the OSI layers –ATM layer performs layers 2 & 3 functions of the OSI layers –AAL combines, 2,4 and 5 of the OSI layers –Not adhering to the OSI layers OSI layers getting obsolete?

updated 12/ Asynchronous Transfer Mode ATM Planes SSCF – service specific coordination function SSCOP – service specific connection- oriented protcol

updated 12/ Asynchronous Transfer Mode ATM Adaptation Layer – at the end points ATM & Physical layer through the network

updated 12/ Asynchronous Transfer Mode ATM Adaptation Layer – application specific Classification of traffic –Class A – constant bit rate –Class B - variable bit rate, connection oriented, timing requirements –Class C- Variable Bit Rate, connection oriented, timing not required –Class D – Variable Bit Rate, connectionless, timing not required

updated 12/ Asynchronous Transfer Mode ATM Adaptation Layer –AAL1 – to support Class A –AAL2 – Class B – later for voice –AAL3/4 – connection oriented data & connectionless data, Class C & D – AAL5 – signaling – data Simple and most popular

updated 12/ Asynchronous Transfer Mode ATM Adaptation Layer- AAL1 –Convergence Sub layer –Segments PDU from upper layer to 47 byte segments –Passes to SAR

updated 12/ Asynchronous Transfer Mode ATM Adaptation Layer- AAL1 –Segmentation And Reassembly layer –SAR –adds a 1 byte header 1bit CSI – convergence sublayer id 3 bits – sequence count 3 bits – CRC on the above 1 bit parity

updated 12/ Asynchronous Transfer Mode Delays and real-time service support Transmission efficiency = Li/(Li+Lo) –Li – information field length –Lo – length of control header Variable SDU – Li can be large –Processing delays at switch Fixed SDU – predictable delays

updated 12/ Asynchronous Transfer Mode Transmission delay –To provide for time transparency Circuit emulation for some applications –Responsibility of the AAL Buffering schemes –Delay at sender end Convergence and reassembly – C/S 1 At the receiver end C/S 2 –Propagation Delay – PD 4-5  sec per Km

updated 12/ Asynchronous Transfer Mode Transmission delay –Cell loss Loss of one cell – 4-16 msec –Switching Delay – SD – fixed  sec –Delays to overcome jitter –Queuing Delay – traffic peaks

updated 12/ Asynchronous Transfer Mode Transmission delay –C/S =  sec (6000  sec at each end) –PD = 2000  sec –SD= 72  sec (24  sec for each switch –3) –QD =225  sec (total for 3 switch) Predominant PD and C/S C/S can be higher if some other layers include more mapping & convergence

updated 12/ Asynchronous Transfer Mode ATM Adaptation Layer- AAL3/4 –Convergence sub layer

updated 12/ Asynchronous Transfer Mode ATM Adaptation Layer- AAL3/4 –Convergence Sub layer bits T – type BT – Begin Tag BA – Buffer Allocation PAD- padding to proper multiple size AL – align trailer to 4 bytes ET – End Tag L – length of data unit

updated 12/ Asynchronous Transfer Mode ATM Adaptation Layer- AAL3/4 –Segmentation and Reassembly sub layer

updated 12/ Asynchronous Transfer Mode ATM Adaptation Layer- AAL3/4 –SAR sub layer bits ST – segment type CSI – convergence sublayer identifier SC - Sequence count MID – Multiplexing identifier LI – length indicator CRC -

updated 12/ Asynchronous Transfer Mode ATM Adaptation Layer- AAL5 –SEAL – Simple and Efficient Adaptation Layer –Assumes most sequencing and error control if required are provided by end system ULP –

updated 12/ Asynchronous Transfer Mode ATM Adaptation Layer- AAL5 –UU – user-to user id –T – type –L- length –CRC - checksum

updated 12/ Asynchronous Transfer Mode ATM layer –

updated 12/ Asynchronous Transfer Mode ATM layer – PT – payload type (3 bits) – 1 st bit User Data – 0 Management data – 1 –User data 2 nd bit 0- no congestion, 1 congestion 3 rd bit – 0 no signaling, 1 signaling bit

updated 12/ Asynchronous Transfer Mode ATM layer –Management data – 1 st bit = 1 00 – link associated 01 – end-to-end management 10 – resource management 11 – reserved –CLP – cell loss priority bit –HEC- header error correction/detection

updated 12/ Asynchronous Transfer Mode Services supported over ATM –CBR –VBR rt, nrt –ABR –UBR

updated 12/ Asynchronous Transfer Mode Utilization of bandwidth by Services

updated 12/ Asynchronous Transfer Mode Quality of Service QoS –User oriented –SCR – Sustained Cell Rate –PCR – Peak Cell Rate –MCR – Minimum Cell Rate –CVDT – cell variation delay tolerance

updated 12/ Asynchronous Transfer Mode Quality of Service QoS –Network oriented –CLR – cell loss ratio –CTD – cell transfer delay –CDV – cell delay variation –CER – Cell Error Ratio Traffic Descriptors

updated 12/ Asynchronous Transfer Mode Network parameters –Error Free Cells arriving before a specified time T are successfully delivered cells –Lost cells if it arrives after time T or discarded, header error –Mis-inserted cells due to wrong header –Severely damaged cells

updated 12/ Asynchronous Transfer Mode Allocation of resources

updated 12/ Asynchronous Transfer Mode Traffic control CBR – Peak cell rate – pcr VBR – pcr, scr and maximum burst size Burst tolerance - BT –BT = (MBS – 1)/(1/SCR – 1/PCR) Generic cell rate algorithm –Virtual scheduling –Continuous leaky bucket

updated 12/ Asynchronous Transfer Mode Virtual scheduling algorithm –Theoretical Arrival Time TAT is the expected arrival time –Cell arriving before TAT + L is confirming –Cell arrival time is ta, then TAT is set to ta if it was a confirming cell

updated 12/ Asynchronous Transfer Mode ATM at the UNI –Supports symmetric and asymmetric connections – bandwidth allocation independent in the 2 directions –Negotiation of QoS –

updated 12/ Asynchronous Transfer Mode ATM at the UNI –Identification of end-to-end capabilities –Client registration Address, administrative information exchange across the UNI Facilitate network administrator –A number of messages defined to facilitate the above

updated 12/ Asynchronous Transfer Mode ATM B-ICI – Inter carrier interface –Internetworking specification –ITU-T -> NNI based on SDH –ATM Forum – B-ICI based on SONET, DS3 –To accommodate Frame Relay Cell relay service as ATM cells Circuit emulation service DS1, DS3 SMDS

updated 12/ Asynchronous Transfer Mode Switch fabric – crossbar switch

updated 12/ Asynchronous Transfer Mode Switch fabric – Knockout switch

updated 12/ Asynchronous Transfer Mode Switch fabric – Knockout switch –To avoid collisions at switch Two input cells to one output –Uses distributors and queues –n 2 crossover points still required n – number of inputs/outputs

updated 12/ Asynchronous Transfer Mode Switch fabric – Banyan switch

updated 12/ Asynchronous Transfer Mode Switch fabric – Batcher Banyan switch

updated 12/ Asynchronous Transfer Mode ATM Addressing –OSI model –Initial Domain Part – IDP Authority Format Identifier –DCC ATM format –ICD ATM format –E.164 format

updated 12/ Asynchronous Transfer Mode ATM Addressing Initial Domain Identifier Domain Specific Part –DFI –AA – administrative authority –RD – routing domain id –Area –ESI – end system id –SEL – ULP entities – not used in ATM network