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

Topics ISDN BISDN ATM

ISDN ISDN Services ISDN Architecture Protocols: SS7 and ISDN Protocols BISDN

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

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

Signaling System No 7 SS7 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. SS7 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.

SS7 Layers

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

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.

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) 25.6Mbps to 622.08Mbps

Management plane Plane management Control plane User plane Layer management Higher layers Higher layers ATM adaptation layer ATM layer Physical layer Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.2

Protocol Architecture (diag)

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

5 Bytes 48 Bytes Header Payload Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.1

Bursty variable-length packets Voice A/D AAL cells s1 , s2 … Digital voice samples Video A/D … Compression AAL cells compressed frames picture frames Data AAL cells Bursty variable-length packets Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.3

… User information User information End system Network End system AAL ATM ATM ATM ATM PHY PHY PHY PHY … End system Network End system Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.4

X X X X X X X X X Private ATM network Private UNI Private NNI Public UNI Public ATM network A X X NNI Public UNI X B-ICI Public ATM network B X Public UNI X X Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.5

ATM layer Physical layer Physical medium Transmission convergence sublayer Physical layer Physical medium dependent sublayer Physical medium Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.6

GFC (4 bits) VPI (4 bits) VPI (4 bits) VCI (4 bits) ATM cell header PT (3 bits) CLP (1 bit) HEC (8 bits) Payload (48 bytes) Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.7

 probability density D0 Peak-to-Peak CDV Dmax Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.8

AAL Layer Service Specific Convergence Sublayer Convergence Sublayer Common Part AAL Layer Segmentation and Reassembly Sublayer Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.9

Higher layer User data stream … Convergence sublayer CS PDUs SAR PDUs b1 b2 b3 … Convergence sublayer CS PDUs 47 47 47 SAR PDUs SAR sublayer H 1 47 H 1 47 H 1 47 ATM Cells 5 48 H 5 48 H ATM layer 5 48 H Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.10

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

Mobile switching office AAL 2 Mobile switching office ATM cells Low bit rate Short voice packets Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.12

This example assumes 24 byte packets Higher layer This example assumes 24 byte packets P1 P2 P3 Service specific convergence sublayer Assume null Common part convergence sublayer H H Add 3-byte header to each user packet H 3 24 3 24 3 24 SAR sublayer Segment into SAR PDUs 1 47 1 47 PAD H ATM layer H 5 48 5 48 Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks 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 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.14 - Part 1

(b) ATM SDU Cell Header Start field (STF) OSF (6 bits) CPS-PDU payload SN (1 bit) P (1 bit) Start field (STF) OSF (6 bits) CPS-PDU payload PAD Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.14 - Part 2

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

1 1 2 1 - 65,535 0-3 1 1 2 (bytes) (bytes) (bytes) (a) CPCS-PDU format Header Trailer CPI Btag BASize CPCS - PDU Payload Pad AL Etag Length 1 1 2 1 - 65,535 0-3 1 1 2 (bytes) (bytes) (bytes) (b) SAR PDU format Trailer (2 bytes) Header (2 bytes) ST SN MID SAR - PDU Payload LI CRC 2 4 10 44 6 10 (bits) (bytes) (bits) Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.16

Service specific convergence sublayer Higher layer Assume two packets from different users P1 P2 Service specific convergence sublayer MID = a MID = b Common part convergence and SAR sublayers Each packet is segmented separately. SAR PDUs identified by MID. CPCS SAR CPCS SAR  SPDUA2 SPDUA1  SPDUB2 SPDUB1 Interleaver Interleaved cells Cells from two packets are interleaved. ATM layer Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.17

… … Higher layer Service specific convergence sublayer Information Service specific convergence sublayer Assume null Common part convergence sublayer Information PAD T SAR sublayer … 48 (0) 48 (0) 48 (1) … ATM layer PTI = 0 PTI = 0 PTI = 1 Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.18

Information UU CPI Length CRC 0 - 65,535 0-47 1 1 2 4 (bytes) (bytes) Pad UU CPI Length CRC 0 - 65,535 0-47 1 1 2 4 (bytes) (bytes) Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.19

Signaling application Message Message SSCF maps SSCOP service to service required by SSCF user SSCF SSCS SSCOP identifies gaps in SDU sequence and requests retransmissions SSCOP Message T AAL 5 provides non-assured service CSCP and SAR of AAL 5 As per Figure 9.18 … ATM layer Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.20

0 - 65,535 0-3 2 2 4 24 (bytes) (bytes)(bits)(bits) (bits) (bits) PL RSVD PDU SN Type Information Pad 0 - 65,535 0-3 2 2 4 24 (bytes) (bytes)(bits)(bits) (bits) (bits) Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.21

(a) DCC ATM format AFI DCC HO-DSP ESI SEL IDP DSP IDI 1 3 13 19 20 AFI DCC HO-DSP ESI SEL IDP DSP IDI (b) ICD ATM format 1 3 13 19 20 AFI ICD HO-DSP ESI SEL IDP DSP IDI (c) E.164 ATM format 1 9 13 19 20 AFI E.164 HO-DSP ESI SEL IDP DSP IDI Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.22

Source Network Destination UNI UNI SETUP CALL PROCEEDING SETUP CALL PROCEEDING CONNECT CONNECT CONNECT ACK CONNECT ACK RELEASE RELEASE COMPLETE RELEASE RELEASE COMPLETE Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.23

Network A Network B PNNI PNNI Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.24

Source Switch Transit Switch Destination Switch Source A Destination B SETUP SETUP SETUP CALL PROCEEDING SETUP CALL PROCEEDING CALL PROCEEDING CALL PROCEEDING CONNECT CONNECT CONNECT CONNECT CONNECT ACK CONNECT ACK CONNECT ACK CONNECT ACK RELEASE RELEASE RELEASE COMPLETE RELEASE RELEASE COMPLETE RELEASE RELEASE COMPLETE RELEASE COMPLETE Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.25

Logical Link A B Logical Group Node Peer Group Leader PG(A) A.2 A.1 PG(B) PG(A.2) PG(A.1) A.2.2 B.1 A.1.2 B.3 A.2.3 A.2.1 A.1.3 A.2.4 B.2 A.1.1 B.4 Physical Link Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.26

A.2 B A.1.2 A.1.1 A.1.3 Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks Figure 9.27

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) Bundle of VCC with same end points

ATM Connection Relationships

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

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

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

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 establish and release user to user VCC

Control Signaling - VPC Semi-permanent Customer controlled Network controlled

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

ATM Cell Format

Header Format Generic flow control Virtual path identifier 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

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

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

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

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

Cell Delineation State Diagram

SDH Based Physical Layer Imposes structure on ATM stream e.g. for 155.52Mbps 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

STM-1 Payload for SDH-Based ATM Cell Transmission

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)

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

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

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

nrt-VBR May be able to characterize expected traffic flow Improve QoS 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

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

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

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

ATM Bit Rate Services

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

Supported Application types Circuit emulation VBR voice and video General data service IP over ATM Multiprotocol encapsulation over ATM (MPOA) IPX, AppleTalk, DECNET) LAN emulation

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

AAL Protocols

Segmentation and Reassembly PDU

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

AAL Type 2 VBR Analog applications

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

AAL Type 5 Streamlined transport for connection oriented higher layer protocols

Reading Chapter 9 ATM Forum Web site Frame Relay forum