CSC 581 Communication Networks II Chapter 9 ISDN

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CSC 581 Communication Networks II Chapter 9: ISDN and ATM Dr. Cheer-Sun Yang

Topics • ISDN • BISDN • ATM 2

ISDN • • ISDN Services ISDN Architecture Protocols: SS 7 and ISDN Protocols BISDN 3

ISDN Services • Integrated voice and data applications • Example: Teleconferencing • Computer and telephone can combine. 4

ISDN Architecture • Basic rate (2 B + D): 2 D channels and 1 D channel • Prime rate (23 B + D): 23 B channels and 1 D channel 5

Signaling System No 7 • SS 7 is used for controlling the signaling of voice data communication. • X. 25 cannot support more advanced telephone services such as caller ID, 3 -way calling, call forwarding, calling card, etc. • SS 7 provides a common-channel signaling feature for supporting these advanced telephone services. Common channel signaling is an out-of band signaling technique for which signaling information is transmitted using an extra channel beyond the voice data channel. 6

SS 7 Layers 7

ATM • Asynchronous Transfer Mode • NOT the Auto-Teller Machine in a bank • Cell Switching technique using a fixed-size cell as the data unit. 8

Benefits of Small Fixed-Size Cells • Easier to program. • Faster transmission time for each cell. • Easier to overlap input and output operations. • Smaller outgoing buffer • Switches can forward multiple packets concurrently. 9

Protocol Architecture • Similarities between ATM and packet switching – Transfer of data in discrete chunks – Multiple logical connections over single physical interface • In ATM flow on each logical connection is in fixed sized packets called cells • NNI and UNI • Minimal error and flow control – Reduced overhead • Data rates (physical layer) 25. 6 Mbps to 622. 08 Mbps 10

Management plane Higher layers Plane management User plane Layer management Control plane ATM adaptation layer ATM layer Physical layer Copyright 2000 Mc. Graw-Hill Leon. Garcia and Widjaja Communication 11 Figure 9. 2

Protocol Architecture (diag) 12

Reference Model Planes • User plane – Provides for user information transfer • Control plane – Call and connection control • Management plane – Plane management • whole system functions – Layer management • Resources and parameters in protocol entities 13

Voice A/D AAL s 1 , s 2 … cells Digital voice samples Video A/D Compression … picture frames Data AAL cells compressed frames AAL Bursty variable-length packets Copyright 2000 Mc. Graw-Hill Leon. Garcia and Widjaja Communication cells 15 Figure 9. 3

Private ATM network Private UNI X X I UN c Public ATM network A li ub P X X X NNI Public UNI X B-ICI Public ATM network B X Public UNI X Copyright 2000 Mc. Graw-Hill Leon. Garcia and Widjaja Communication X Private NNI 17 Figure 9. 5

GFC (4 bits) VPI (4 bits) ATM cell header VPI (4 bits) VCI (8 bits) VCI (4 bits) PT (3 bits) CLP (1 bit) HEC (8 bits) Payload (48 bytes) Copyright 2000 Mc. Graw-Hill Leon. Garcia and Widjaja Communication 19 Figure 9. 7

Higher layer b 1 b 2 Convergence sublayer User data stream CS PDUs 47 47 47 SAR PDUs SAR sublayer 1 47 47 H H 5 H H H 1 ATM layer … b 3 48 5 1 47 ATM Cells H 48 5 48 Copyright 2000 Mc. Graw-Hill Leon. Garcia and Widjaja Communication 22 Figure 9. 10

(a) SAR PDU header CSI 1 bit SNP Seq. Count 3 bits 4 bits (b) CS PDU with pointer in structured data transfer 47 Bytes AAL 1 Pointer 1 Byte 46 Bytes Copyright 2000 Mc. Graw-Hill Leon. Garcia and Widjaja Communication 23 Figure 9. 11

Higher layer This example assumes 24 byte packets P 3 P 2 P 1 Service specific convergence sublayer Assume null Common part convergence sublayer H 3 H 24 3 24 SAR sublayer PAD 1 ATM layer Add 3 -byte header to each user packet H H 5 1 47 47 Segment into SAR PDUs H 48 5 48 Copyright 2000 Mc. Graw-Hill Leon. Garcia and Widjaja Communication 25 Figure 9. 13

(a) CPS packet structure CID (8 bits) CPS packet header PPT (2 bits) LI (6 bits) UUI (3 bits) HEC (5 bits) Payload Copyright 2000 Mc. Graw-Hill Leon. Garcia and Widjaja Communication 26 Figure 9. 14 - Part 1

Higher layer Information User message Service specific convergence sublayer Common part convergence sublayer Assume null H Information 2 44 T 4 4 SAR sublayer ATM layer PAD Pad message to multiple of 4 bytes. Add header and trailer. 2 2 44 2 … 2 44 2 Each SAR-PDU consists of 2 -byte header, 2 -byte trailer, and 44 -byte payload. … Copyright 2000 Mc. Graw-Hill Leon. Garcia and Widjaja Communication 28 Figure 9. 15

(a) CPCS-PDU format Trailer Header CPI Btag BASize 1 1 2 (bytes) CPCS - PDU Payload 1 - 65, 535 (bytes) Pad AL Etag Length 0 -3 1 1 2 (bytes) (b) SAR PDU format Trailer (2 bytes) Header (2 bytes) ST SN MID 2 4 10 (bits) SAR - PDU Payload 44 (bytes) Copyright 2000 Mc. Graw-Hill Leon. Garcia and Widjaja Communication LI CRC 6 10 (bits) 29 Figure 9. 16

Higher layer Service specific convergence sublayer Common part convergence and SAR sublayers P 1 Assume two packets from different users P 2 MID = a MID = b CPCS SAR SPDUA 2 SPDUB 2 SPDUA 1 Each packet is segmented separately. SAR PDUs identified by MID. SPDUB 1 Interleaver ATM layer Interleaved cells Copyright 2000 Mc. Graw-Hill Leon. Garcia and Widjaja Communication Cells from two packets are interleaved. 30 Figure 9. 17

Higher layer Information Service specific convergence sublayer Assume null Common part convergence sublayer Information SAR sublayer PAD T … 48 (0) 48 (1) … ATM layer PTI = 0 PTI = 1 Copyright 2000 Mc. Graw-Hill Leon. Garcia and Widjaja Communication 31 Figure 9. 18

Signaling application Message SSCF maps SSCOP service to service required by SSCF user SSCF SSCS SSCOP CSCP and SAR of AAL 5 ATM layer Message T As per Figure 9. 18 SSCOP identifies gaps in SDU sequence and requests retransmissions AAL 5 provides non-assured service … Copyright 2000 Mc. Graw-Hill Leon. Garcia and Widjaja Communication 33 Figure 9. 20

(a) DCC ATM format 1 3 13 AFI DCC HO-DSP 19 ESI IDP 20 SEL DSP IDI (b) ICD ATM format 1 AFI 3 13 ICD HO-DSP 19 ESI IDP 20 SEL DSP IDI (c) E. 164 ATM format 1 AFI 9 E. 164 IDP IDI 13 HO-DSP 19 ESI SEL DSP Copyright 2000 Mc. Graw-Hill Leon. Garcia and Widjaja Communication 20 35 Figure 9. 22

Source Switch Source A SETUP Transit Switch SETUP CALL PROCEEDING Destination B SETUP CALL PROCEEDING CONNECT CONNECT ACK RELEASE COMPLETE RELEASE COMPLETE Copyright 2000 Mc. Graw-Hill Leon. Garcia and Widjaja Communication 38 Figure 9. 25

Logical Link A B Logical Group Node Peer Group Leader PG(A) A. 2 A. 1 PG(A. 1) PG(B) PG(A. 2) B. 1 A. 2. 2 A. 1. 2 B. 3 A. 1. 1 A. 1. 3 A. 2. 1 A. 2. 3 A. 2. 4 B. 2 B. 4 Physical Link Copyright 2000 Mc. Graw-Hill Leon. Garcia and Widjaja Communication 39 Figure 9. 26

ATM Logical Connections • • Virtual channel connections (VCC) Analogous to virtual circuit in X. 25 Basic unit of switching Between two end users Full duplex Fixed size cells Data, user-network exchange (control) and network-network exchange (network management and routing) • Virtual path connection (VPC) 41 – Bundle of VCC with same end points

ATM Connection Relationships 42

Advantages of Virtual Paths • Simplified network architecture • Increased network performance and reliability • Reduced processing • Short connection setup time • Enhanced network services 43

Virtual Channel Connection Uses • Between end users – End to end user data – Control signals – VPC provides overall capacity • VCC organization done by users • Between end user and network – Control signaling • Between network entities – Network traffic management – Routing 44

VP/VC Characteristics • Quality of service • Switched and semi-permanent channel connections • Call sequence integrity • Traffic parameter negotiation and usage monitoring • VPC only – Virtual channel identifier restriction within VPC 45

Control Signaling - VCC • Done on separate connection • Semi-permanent VCC • Meta-signaling channel – Used as permanent control signal channel • User to network signaling virtual channel – For control signaling – Used to set up VCCs to carry user data • User to user signaling virtual channel – Within pre-established VPC – Used by two end users without network intervention to 46 establish and release user to user VCC

Control Signaling - VPC • Semi-permanent • Customer controlled • Network controlled 47

ATM Cells • • Fixed size 5 octet header 48 octet information field Small cells reduce queuing delay for high priority cells • Small cells can be switched more efficiently • Easier to implement switching of small cells in hardware 48

ATM Cell Format 49

Header Format • Generic flow control – Only at user to network interface – Controls flow only at this point • Virtual path identifier • Virtual channel identifier • Payload type – e. g. user info or network management • Cell loss priority • Header error control 50

Generic Flow Control (GFC) • Control traffic flow at user to network interface (UNI) to alleviate short term overload • Two sets of procedures – Uncontrolled transmission – Controlled transmission • Every connection either subject to flow control or not • Subject to flow control – May be one group (A) default – May be two groups (A and B) • Flow control is from subscriber to network – Controlled by network side 51

Single Group of Connections (1) • Terminal equipment (TE) initializes two variables – TRANSMIT flag to 1 – GO_CNTR (credit counter) to 0 • If TRANSMIT=1 cells on uncontrolled connection may be sent any time • If TRANSMIT=0 no cells may be sent (on controlled or uncontrolled connections) • If HALT received, TRANSMIT set to 0 and remains until NO_HALT 52

Header Error Control • 8 bit error control field • Calculated on remaining 32 bits of header • Allows some error correction 53

Cell Based Physical Layer • No framing imposed • Continuous stream of 53 octet cells • Cell delineation based on header error control field 54

Cell Delineation State Diagram 55

SDH Based Physical Layer • • • Imposes structure on ATM stream e. g. for 155. 52 Mbps Use STM-1 (STS-3) frame Can carry ATM and STM payloads Specific connections can be circuit switched using SDH channel • SDH multiplexing techniques can combine several ATM streams 56

STM-1 Payload for SDH-Based ATM Cell Transmission 57

ATM Service Categories • Real time – Constant bit rate (CBR) – Real time variable bit rate (rt-VBR) • Non-real time – Non-real time variable bit rate (nrt-VBR) – Available bit rate (ABR) – Unspecified bit rate (UBR) 58

Real Time Services • Amount of delay • Variation of delay (jitter) 59

CBR • Fixed data rate continuously available • Tight upper bound on delay • Uncompressed audio and video – Video conferencing – Interactive audio – A/V distribution and retrieval 60

rt-VBR • Time sensitive application – Tightly constrained delay and delay variation • rt-VBR applications transmit at a rate that varies with time • e. g. compressed video – Produces varying sized image frames – Original (uncompressed) frame rate constant – So compressed data rate varies • Can statistically multiplex connections 61

nrt-VBR • May be able to characterize expected traffic flow • Improve Qo. S in loss and delay • End system specifies: – Peak cell rate – Sustainable or average rate – Measure of how bursty traffic is • e. g. Airline reservations, banking transactions 62

UBR • May be additional capacity over and above that used by CBR and VBR traffic – Not all resources dedicated – Bursty nature of VBR • For application that can tolerate some cell loss or variable delays – e. g. TCP based traffic • Cells forwarded on FIFO basis • Best efforts service 63

ABR • Application specifies peak cell rate (PCR) and minimum cell rate (MCR) • Resources allocated to give at least MCR • Spare capacity shared among all ARB sources • e. g. LAN interconnection 64

ATM Adaptation Layer • Support for information transfer protocol not based on ATM • PCM (voice) – Assemble bits into cells – Re-assemble into constant flow • IP – Map IP packets onto ATM cells – Fragment IP packets – Use LAPF over ATM to retain all IP infrastructure 65

ATM Bit Rate Services 66

Adaptation Layer Services • • Handle transmission errors Segmentation and re-assembly Handle lost and misinserted cells Flow control and timing 67

Supported Application types • • • Circuit emulation VBR voice and video General data service IP over ATM Multiprotocol encapsulation over ATM (MPOA) – IPX, Apple. Talk, DECNET) • LAN emulation 68

AAL Protocols • Convergence sublayer (CS) – Support for specific applications – AAL user attaches at SAP • Segmentation and re-assembly sublayer (SAR) – Packages and unpacks info received from CS into cells • Four types – – Type 1 Type 2 Type 3/4 Type 5 69

AAL Protocols 70

Segmentation and Reassembly PDU 71

AAL Type 1 • CBR source • SAR packs and unpacks bits • Block accompanied by sequence number 72

AAL Type 2 • VBR • Analog applications 73

AAL Type 3/4 • Connectionless or connected • Message mode or stream mode 74

AAL Type 5 • Streamlined transport for connection oriented higher layer protocols 75

Reading • Chapter 9 • ATM Forum Web site • Frame Relay forum 76