Chapter 9 ATM Networks Why ATM? BISDN Reference Model ATM Layer ATM Adaptation Layer ATM Signaling PNNI Routing Classical IP over ATM
Chapter 9 ATM Networks Why ATM?
The Integrated Services Vision l l Initially telephone network all-analog l Transmission & Switching Gradual transition to all-digital core l 1960’s: transmission in backbone became digital l 1970’s: switching became digital l Subscriber loop from customer to network remained analog Integrated Services Vision: l Network should be digital end-to-end l Network should support all services: telephone, data, video Three attempts at achieving Integrated Services Network l ISDN in 1980 s l ATM/BISDN in 1990’s l Internet in 2000’s
Integrated Services Digital Network (ISDN) l l ISDN: l Integrated access l to end-to-end digital communication services l through a standard set of user-to-network interfaces Network consisted of separate networks for voice, data, signaling Circuitswitched network BRI Private channelswitched network Packetswitched networks Signaling network B=64 kbps D=16 kbps Basic rate interface (BRI): 2 B+D BRI Primary rate interface (PRI): 23 B+D
Broadband ISDN l BISDN: A single universal network that is flexible enough to provide all user services in a uniform manner l l l ISDN not enough: Needed 10 s to 100 s Mbps for LAN interconnect and for digital TV Synchronous Transfer Mode (connections at nx 64 kbps) was initial candidate for BISDN, but Asynchronous Transfer Mode (ATM) chosen l l l Multiplexing & switching framework connection-oriented virtual circuits fixed-length packets, “cells”, with short headers
Benefits of ATM l Network infrastructure and management simplified by using a single transfer mode for the network l l Extensive bandwidth management capabilities l l SONET-like grooming capabilities, but at arbitrary bandwidth granularities ATM is not limited by speed or distance limitations l l Expected to cover LAN, MAN, and WAN 50 -600 Mbps the sweet spot for ATM Qo. S attributes of ATM allow it to carry voice, data, and video thus making it suitable for an integrated services network.
ATM Anticipated Scope l l l All information transferred by network that handles 53 -byte cells Scalable in terms of speed Switched approach operates in LAN, MAN, or WAN 5 bytes Network header local area network (LAN) wireless interface 48 bytes User information multimedia terminal data base ATM fibre backbone Wide Area Network (WAN) video server wireless interface supercomputer
ATM Networking Voice Video Packet ATM Adaptation Layer ATM Network
AAL converts Info into Cells Voice A/D AAL s 1 , s 2 … cells Digital voice samples Video A/D Compression … picture frames Data AAL Bursty variable-length packets cells compressed frames cells
Cell-Switching – Virtual Circuit Cells Source Cells Switches l l l Destination Connection setup establishes virtual circuit by setting pointers in tables in path across network All cells for a connection follow the same path Abbreviated header identifies connection Cells queue for transmission at ATM switches & multiplexers Fixed and Variable bit rates possible, negotiated during call set-up Delay and loss performance negotiated prior to connection setup
ATM Switching Switch carries out table translation and routing 1 1 … Switch … 6 data 32 N voice 32 video 61 N 1 75 32 61 3 2 video 67 2 data 39 3 39 67 67 … 5 video 25 25 32 voice 67 video 75 ATM switches can be implemented using shared memory, shared backplanes, or self-routing multi-stage fabrics N
Multiplexing in ATM Switches l l l Packet traffic multiplexed onto input lines Demultiplexed at input port Forwarded to output port 1 1 2 2 N N
ATM Support for Multiple Qo. S Levels VCs with different TDs & different Qo. S reqts l l l Call Admission Control based on Traffic Descriptors & Qo. S Reqts Cell streams policed at User Network Interface Cell Enqueueing Policy, Cell Transmission Scheduling, Flow Control Generalized Processor Sharing, Weighted Fair Queueing, etc. Multiplexing Gain Cell Multiplexing implies Delay, Jitter, Loss
Chapter 9 ATM Networks BISDN Reference Model
BISDN Reference Model Management Planes Higher Layers ATM Adaptation Layer ATM Layer Physical Layer Plane Management Layer Management Control Plane User Plane: transfer of user information; flow control; error recovery Control Plane: setting up, management, and release of connections Layer Management Plane: management of layer entities & OAM Plane Management: management of all the planes
Planes Explained l Three types of logical networks are involved in delivering communication services l l User Network: transfers user information Control (Signaling) Network: carries signaling messages to establish, maintain, terminate connections Management Network: carries management information: monitoring information, alarms and usage statistics A separate protocol stack, “plane”, is defined for each of these three networks
ATM Layered Architecture Higher Layers ATM Adaptation Layer (AAL) ATM Network Layer Physical Layer USER NETWORK USER
ATM Layered Architecture Higher Layers ATM Adaptation Layer (AAL) ATM Network Layer Physical Layer ATM Adaptation Layer l standard interface to higher layers l adaptation functions l end-to-end between end systems l segmentation into cells and reassembly ATM Layer l Transfer of Cells l Cell-Header Generation/Extraction l VPI/VCI Translation l Cell multiplexing/demultiplexing l Flow and congestion control Physical Layer l Cell stream / bit stream conversion l Digital transmission
ATM Interfaces X Public ATM network A li b Pu X X Public UNI X NNI B-ICI X X I N c. U Public ATM network B X X Private NNI UNI: User-Network Interface NNI: Network-Network Interface B-ICI: Broadband Inter-carrier i/f X Private UNI Private ATM network Public UNI
The ATM Physical Layer TC Sublayer: l Transmission convergence sublayer Physical medium dependent sublayer l l l Cell Delineation Header Error Checking Cell Rate Decoupling (Insertion of Idle Cells) Specific to PMD Sublayer: l l l Line code Connectors Re-use of existing physical layer standards
Private UNI Physical Layers Frame format Bit rate Media Cell stream 25. 6 Mbps UTP-3 STS-1 51. 84 Mbps UTP-3 FDDI 100 Mbps MMF STS-3 c, STM-1 155. 52 Mbps UTP-3, UTP-5, STP, SMF, MMF coaxial pair Cell stream 155. 52 Mbps MMF, STP STS-12, STM-4 622. 08 Mbps SMF, MMF UTP = Unshielded twisted pair MMF = Multimode fiber STP = Shielded twisted pair SMF = Single-mode pair
Public UNI Physical Layers Frame format Bit rate Media DS-1 1. 655 Mbps Twisted pair DS-3 44. 736 Mbps Coaxial STS-3 c, STM-1 155. 52 Mbps SMF E-1 2. 048 Mbps Twisted pair Coaxial E 3 34. 368 Mbps Coaxial J 2 6. 312 Mbps Coaxial
Chapter 9 ATM Networks ATM Layer
The ATM Layer l l Concerned with sequenced transfer of cells across network connections ATM Connections l l Point-to-Point: unidirectional or bidirectional Point-to-Multipoint: unidirectional Permanent Virtual Connections (PVC): long-term connections to provision bandwidth between endpoints in an ATM network Switched Virtual Connections (SVC): shorter-term connections established in response to customer requests
ATM Virtual Connections l l l Virtual Channel Connections: virtual circuit Virtual Path Connections: bundle of virtual connections ATM Header contains virtual connection information: l 8 -bit Virtual Path Identifier Virtual paths l 16 -bit Virtual Channel Identifier Virtual channels
Why 53 Bytes? l l l The effect of delay on packet voice influenced selection of cell size The packetization delay grows with the cell size l @64 kbps: packetization delay = cell size * 125 sec If delay is too long, echo cancellation equipment needs to be introduced Europe has short transmission lines and no echo cancellers so it proposed 32 byte payload U. S. has long transmission lines and echo cancellers in place, so it proposed 64 byte payload Compromise: 48 byte payload
ATM cell header The ATM Cell GFC (4 bits) VPI (4 bits) VCI (4 bits) Virtual Path Identifier l VCI (8 bits) VCI (4 bits) PT (3 bits) HEC (8 bits) CLP (1 bit) 8 -bits: 256 VC bundles Virtual Channel Identifier l 16 bits: 65, 536 VCs/VP Payload Type Indicator l l Payload (48 bytes) l Bit 3: data vs. OAM cell Bit 2: Congestion indication in data cells Bit 1: Carried transparently end -to-end; Used in AAL 5 Cell Loss Priority l GFC-undefined UNI cells has GFC field NNI cells allocate these 4 bits to VPI; 4096 VPs if 1, cell can be discarded by network
Header Error Check l l l l The HEC only covers the 5 bytes of the header to protect against cell misdelivery Since VPI/VCI changes at every switch, HEC must be recomputed HEC used for cell delineation Two modes: Header Error Detection / Correction Generating Polynomial: g(x)=x 8+ x 2+ x+ 1 The pattern 0101 is XORed to r(x); keeps idle cells from having HEC=0 and preventing cell delineation The pattern 0101 is XORed to r(x) in received header prior to error checking
ATM Permanent Virtual Connections Operator at Network Control Center ATM Switch l l ATM Switch Operator “manually” sets up VPI/VCI tables at switches and terminals Long set-up time, long-lived connections
ATM Switched Virtual Connections ATM Switch l l ATM Switch Terminals and switches use pre-defined VPI/VCI to setup connections dynamically, on-demand Signalling protocol used to communicate with callprocessing system
Traffic Contract l l During connection setup the user and the network negotiate two sets of parameters for a connection Traffic descriptor: the user specifies the traffic that it will expect the network to transfer on its behalf Qo. S requirements: the user specifies the type of network performance that is required by its cells Traffic Contract l l The user is expected to conform to traffic descriptor The network is expected to deliver on its Qo. S commitments
Quality of Service Parameters l l l Six Qo. S parameters are defined Three are intrinsic to network performance and are not negotiated during connection setup: Cell error ratio: fraction of delivered cells that contain bit errors Cell mis-insertion ratio: average number of cells/second that are misdelivered Severely errored cell block ratio: M or more out of N cells are lost, in error, or misdelivered
Negotiable Qo. S Parameters l Cell Loss Ratio (CLR): fraction of cells that are lost l l Cell Transfer Delay (CTD): negotiate “maximum delay” Dmax: 1 - of cells have delay less than Dmax l Determined by cell scheduling Cell Delay Variation (CDV): Peak-to-Peak variation: Dmax-D 0 probability density of cell delay l Determined by buffer priority D 0 Peak-to-Peak CDV Dmax
Traffic Descriptors l l l Peak Cell Rate: rate in cells/second that a source is never allowed to exceed Sustainable Cell Rate: average cell rate produced by the source over a long time interval Maximum Burst Size: maximum number of consecutive cells that may be transmitted by a source at the peak cell rate (PCR) Minimum Cell Rate: minimum average cell rate, in cells per second, that the source is always allowed to send Cell Delay Variation Tolerance: cell delay variation that must be tolerated for in a given connection.
ATM Service Categories Cell transfer services provided by ATM Network CBR VBR real-time non-real-time Cell Loss Rate Cell Transfer Delay Cell Delay Variation Traffic Descriptors specified PCR/CDVT SCR/BT PCR/CDVT Constant Bit Rate Variable Bit Rate Available Bit Rate Unspecified Bit Rate UBR unspecified Flow Control CBR = VBR = ABR = UBR = ABR no PCR = CDVT = SCR = BT = PCR/CDVT & others yes PCR/CDVT no Peak Cell Rate Cell Delay Variation Tolerance Sustainable Cell Rate Burst Tolerance
Multiplexing & Qo. S Guarantees l l l ATM provides per-connection Qo. S guarantees l Many cell flows are multiplexed onto a common stream, so how are guarantees delivered? CBR: scheduler must ensure transmission opportunities are regularly available for each connection Real-time VBR: expect some multiplexing gain from combining VBR flows; however need to meet delay and loss requirements Non-real-time VBR: can attempt higher multiplexing gains, subject only to loss requirement UBR: no guarantees, but excellent performance at light traffic ABR: some degree of guarantee: low CLR if source responds to network feedback; MCR can be negotiated
Traffic Contract & Call Admission Control l l Traffic contract: includes the ATM service category, the traffic descriptors, and the Qo. S requirements Connection admission control (CAC) determines whether request for a connection should be accepted or rejected l l Each switch in path must determine whether it can accommodate new flow and still meet commitments to existing flows; if yes, resources allocated CAC is not standardized, each operator is free to select own procedures l l Different degrees of overbooking possible to attain different multiplexing gains Different types of tariffs for service offerings
Policing, Traffic Shaping, and Congestion Control l l Qo. S guarantees are valid only if the user traffic conforms to the connection contract Usage parameter control (UPC) is the process of enforcing the traffic agreement at the UNI l l l Traffic shaping can be used by source to ensure that its traffic complies to the connection contract l l Token bucket can be used for shaping Congestion control l Generic Cell Rate Algorithm can be used for UPC; related to the leakybucket algorithm Non-conforming cells can be tagged (CLP=1) or dropped CLP=1 cells are dropped first when congestion occurs ABR connections must respond to congestion feedback information that is received from the network These topics were discussed in Chapter 7
Chapter 9 ATM Networks ATM Adaptation Layer
ATM Adaptation Layer l l l AAL: end-to-end protocol to adapt the cell transfer service provided by ATM network to the requirements of specific application classes Includes conversion to cells and back, and additional adaptation functions, e. g. timing recovery, reliable transfer ITU defined the following service classes Class End-to-End Timing Bit Rate Connection Mode B A required constant D C not required variable connection-oriented Class A = circuit emulation Class B = variable bit-rate video Class C & D = packet transmission connectionless
AAL Protocol Structure Higher Layers Service Specific Convergence Sublayer AAL Layer Convergence Sublayer Common Part Segmentation and Reassembly Sublayer ATM AAL has two sublayers: l Segmentation & Reassembly l l Segments PDUs into cell payloads; Reassembles PDUs from received cell payloads Convergence l l Common Part: packet framing and error detection functions required by all AAL users Specific Part: functions that depend on specific requirements of AAL user classes
AAL 1 l Provides constant bit rate transfer Higher layer b 1 b 2 Convergence sublayer CS PDUs 47 47 47 SAR PDUs SAR sublayer 1 47 47 H H 5 H H H 1 ATM layer … b 3 User data stream 48 5 1 47 ATM Cells H 48 5 48
AAL 1 4 bits SN l l 4 bits SNP 8 bits Pointer optional 46 or 47 octets Payload Convergence Sublayer: l Adaptation to cell-delay variation, constant bit rate delivery AALSDUs l Detection of lost or out-of-sequence cells l Source clock recovery l Forward error correction on user data l Forward error correction on Sequence Number (SN) l 1 -bit CS to indicate pointer (used for partially-filled cells) l 3 -bit sequence count l Time-stamp option uses 4 consecutive CS bits for residual TS SAR: Add 1 -byte header to 47 -byte payload
AAL 1 services Structured & Unstructured Transfer l l l Unstructured: take bits from T 1 and group into 8 bit bytes; since T 1 frame has 193 bits, bytes are never aligned to frame Structured: take 24 T 1 bytes and map into CS PDUs; use CS PDU pointer to indicate beginning of T 1 frame Forward error control options: l 1. 2. Insert parity cell every 15 cells, correct lost cell Interleaving of 124 cells, correct up to 4 cell losses
AAL 1 PDUs SAR PDU header CSI 1 bit SNP Seq. Count 3 bit 4 bits SN SNP 4 bits 46 or 47 octets Pointer optional 8 bits AAL 1 Pointer 1 Byte Payload 46 Bytes CS PDU with pointer in structured data transfer
AAL 2 l l New AAL 2 intended for bandwidth-efficient transfer of low-bit rate, short-packet traffic with low-delay requirement Adds third level of multiplexing to the VP/VC hierarchy of ATM, so low-bit-rate users can share an ATM connection. AAL 2 Low bit rate Short voice packets ATM cells Mobile switching office
AAL 2 Higher layer P 3 P 2 P 1 This example assumes 24 byte packets Service specific convergence sublayer Assume null Common part convergence sublayer H 3 H 24 3 SAR sublayer 24 PAD 1 ATM layer Add 3 -byte header to each user packet H 5 1 47 47 H 48 5 48 Segment into SAR PDUs
AAL 2 Common Part CS PDU l Max length CPCS PDU l CID (8 bits) CPS packet header PPT (2 bits) LI (6 bits) UUI (3 bits) l Channel ID l l HEC (5 bits) l l 3: OAM cell ≠ 3: application cell User-to-user indication l l l Payload length – 1 Packet payload type l Payload Identifies user Length Indicator l l 64 bytes End-to-end info for application cells End-to-end for AAL mgmt when OAM cell Error detection l g(x)=x 5+x 2+1
Packing ATM SDU in AAL 2 l l CPCS PDU’s concatenated, segmented into 48 byte chunks, and packed into ATM SDU’s ATM SDU format: l Offset Field (6 bits) l Cell Header Start field (STF) OSF (6 bits) SN P (1 bit) l l Sequence Number l l l CPS-PDU payload 0 or 1 Parity bit PAD l PAD From end of the field to start of first CPCS PDU or to start of PAD Max CPCS PDU may span 2 SDUs 0 -47 bytes
AAL 3/4 l Why 3 / 4 ? l AAL 3: For connection-oriented transfer of data l AAL 4: For connectionless transfer of data l l All connectionless packets use the same VPI/VCI at the UNI Multiplexing ID (MID) introduced to distinguish connectionless packets AAL 3 and AAL 4 combined into AAL that can be used for connection-oriented or connectionless transfer AAL 3/4 allows multiple users to be multiplexed and interleaved in the same ATM VC l Message mode: single user message segmented into ATM payloads l Stream mode: one or more messages segmented into ATM payloads and delivered without indication of boundaries l Assured mode: error-free delivery of messages l Non-Assured mode: messages may be delivered in error, or not at all
AAL 3/4 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.
AAL 3/4 Common Part CS PDU User Data Trailer Header CPI Btag BASize 1 1 l 2 (bytes) 1 - 65, 535 (bytes) Common Part Indicator l l CPCS - PDU Payload How subsequent fields are to be interpreted Beginning Tag & Ending Tag l Used to match header & trailer at destination l 0 -3 1 l l 1 2 (bytes) Buffer Allocation size: l l Pad AL Etag Length Buffer size required at destination Length: of payload PAD: aligns trailer to 32 -bit boundary Alignment: byte of 0 s to make trailer 32 bits long
AAL 3/4 SAR PDU Trailer (2 bytes) Header (2 bytes) ST SN MID 2 4 (bits) l 44 (bytes) Segment Type l l l 10 10 Beginning of Message 00 Continuation 01 End of Message 11 Single segment Message Sequence Number l LI CRC SAR - PDU Payload Of SAR PDU within CPCS PDU 6 10 (bits) l MID allows SAR sublayer multiplexing l l Length Indicator: size of payload l l l Up to 210 AAL users on 1 ATM VC Except for last cell, all cells have LI=44 Last cell has LI = 4 to 44 Each cell payload has 10 -bit CRC
Multiplexing in AAL 3/4 Higher layer Service specific convergence sublayer Common part convergence and SAR sublayers P 1 Assume two packets from different users P 2 MID = b MID = a CPCS SAR SPDUA 2 SPDUB 2 SPDUA 1 SPDUB 1 Interleaver ATM layer Each packet is segmented separately. SAR PDUs identified by MID. Interleaved cells Cells from two packets are interleaved.
AAL 3/4 Overhead l l l 8 bytes added to each message at CPCS sublayer Each ATM payload has 4 out of 48 bytes additional overhead 9 bytes out of 53 ATM cell bytes overhead Too much overhead! Let to development of AAL 5
AAL 5 Higher layer Information l Service specific convergence sublayer l l Common part convergence sublayer Information PAD T l SAR sublayer … 48 (0) 48 (1) … ATM layer PTI = 0 PTI = 1 Simpler than AAL 3/4 48 bytes payload Single packet at a time per VCI PTI in ATM header indicates last cell for a given packet
AAL 5 Common Part CS PDU Information 0 - 65, 535 (bytes) l l Pad UU CPI Length CRC 0 -47 1 1 (bytes) 2 4 User-to-User: 1 byte CPI aligns trailer to 8 bytes Length: 2 bytes to indicate length of CPCS PDU payload 40 -byte CRC
Signaling AAL l l AAL standard for BISDN control plane Provides reliable transport for signaling messages exchanged among endsystems and switches to set up ATM VCs. SAAL: common part & a service-specific part Service specific part: l l l service-specific connection-oriented protocol (SSCOP) Service-Specific Coordination Function (SSCF). SSCF supports the signaling applications (UNI and NNI).
SAAL Process 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 AAL 5 … SSCOP identifies gaps in SDU sequence and requests retransmissions (Selective Repeat ARQ) AAL 5 provides nonassured service
SSCOP PDU Information 0 - 65, 535 (bytes) l l l SN Type 0 -3 2 2 4 24 (bytes)(bits) Padding: 0 -3 bytes Pad Length Indicator Reserved (unassigned) PDU type l l Pad PL RSVD PDU Sequenced data message; poll and control messages 24 -bit sequence number for large delay-bandwidth product Depends on error detection provided by AAL 5
Applications, AALs, and ATM Service Categories l Applications impose requirements l l AALs provide segmentation & reassembly, and possibly additional adaptation functions l l AAL 1, AAL 2, AAL 3/4, AAL 5, SAAL ATM service category provides cell transfer with certain Qo. S attributes l l Voice, video, connectionless data CBR, rt-VBR, nrt-VBR, UBR, ABR Overall system requirements determine what combination of AAL and ATM service category is used
Application Requirements Feature transfer granularity stream message bit rate constant variable reliability non-assured accuracy error tolerant error intolerant delay sensitivity delay/jitter sensitive delay/jitter insensitive multiplexing single user multiple users payload efficiency bandwidth inexpensive bandwidth expensive
Summary of AAL Capabilities Sublayer Feature AAL 1 AAL 2 AAL 3/4 AAL 5 SAAL SSCS Forward Error Control optional no ARQ no no optional SSCOP Timing Recovery optional no Multiplexing no 8 -bit CID 10 -bit MID no no Framing Structure yes no no Message Delimiting no yes PTI Advance Buffer Alloc no no yes no no User-to-User Indication no 3 bits no 1 byte no Overhead 0 3 bytes 8 bytes 4 bytes Padding 0 0 4 bytes 0 -44 byte 0 -47 byte Checksum no no no 32 bit Sequence Numbers no no 24 -bit Payload/Overhead 46 -47 bytes 44 bytes 48 bytes Overhead 1 -2 bytes 1 byte 4 bytes 0 Checksum no no 10 bits no no Timing Information optional no no Sequence Numbers 3 -bit 1 bit 4 bit no no CPCS SAR
Examples: Voice and Video l Voice l l AAL 1 for individual PCM voice calls AAL 1 with structured transfer for nx 64 kbps AAL 2 for low-bit-rate cellular voice AAL 5 for inexpensive voice l CBR MPEG 2 Video l l l Timing recovery at AAL or at MPEG systems layer? Error detection & correction at which layer? Timing recovery at MPEG 2 systems level and AAL 5 over CBR ATM was selected
Example: ATM & ADSL Central Office User Premise splitter ATM Subscriber loop ADSL IP PPPo. E AAL 5 ATM ADSL Telephone Switch splitter Telephone Network ATM Network ISP DSL Access Mux l l IP over PPPo. E frames segmented by AAL 5 into ATM cells at ADSL modem ATM cells flow through DSLAM and ATM network to Internet Service Provider
Chapter 9 ATM Networks ATM Signaling
ATM Signaling l l Signaling: means for dynamically setting up and releasing virtual connections in ATM Signaling involves message exchange across: l l User-Network-Interface Network-Network Interface Broadband Inter-Carrier Interface Signaling requires: l l Network addressing framework Protocols
ATM Addressing l Telephony E-164 Addresses l l For public networks Up to 15 -digit E-164 (telephone) numbers In North America, 1 -NPA-NXX-ABCD, ATM End-System Addresses (AESAs) l l l For private networks ISO Network Service Access Point (NSAP) format 20 bytes long Data Country Code (DCC) International Code Designator (ICD) E. 164 (contained within the AESA format)
AESA Address Format (a) Data Country Code ATM format 1 3 13 AFI DCC 19 HO-DSP ESI IDP 20 SEL Domain Specific Part IDI (b) International Code Designator ATM format 1 AFI 3 13 ICD 19 HO-DSP ESI IDP 20 SEL DSP IDI (c) E. 164 ATM format 1 AFI 9 E. 164 Initial Domain Part Initial Domain Identifier 13 19 HO-DSP ESI DSP 20 SEL
ATM Signaling l Telephone Signaling l l l ISDN signaling (Q. 931) used in call setup messages at the user-network-interface Within the network, ISUP protocol of Signaling System #7 used to establish a connection from a source switch to a destination switch For ATM, need UNI, NNI, & B-ICI signalling l l l UNI: Q. 2931 & ATMF UNI 4. 0 NNI: ATMF PNNI based on UNI 4. 0 B-ICI based on B-ISUP
UNI 4. 0 l l ATM connections involve many more parameters than narrowband ISDN Signaling messages carry Information Elements, that describe the user requests Signaling messages transferred across the UNI using the services of the SAAL layer in the control plane The signaling cells that are produced by AAL 5 use the default virtual channel identified by VPI=0 and VCI=5.
Capabilities of UNI 4. 0
Signaling Messages Meaning (when sent by host) Meaning (when sent by network) SETUP Requests that a call be established Indicates an incoming call CALL PROCEEDING Acknowledges the incoming call Indicates the call request will be attempted CONNECT Indicates acceptance of the call Indicates the call was accepted CONNECT ACK Acknowledges acceptance of the call Acknowledges making the call RELEASE Requests that the call be terminated Terminates the call RELEASE ACK Acknowledges releasing the call
UNI Signaling Example UNI Destination Network Source SETUP CALL PROCEEDING CONNECT ACK RELEASE COMPLETE
PNNI Signaling l ATM Forum developed PNNI for use l l between private ATM switches (Private Network Node Interface) between group of private ATM switches (Private Network-to-Network Interface) Network A Network B PNNI
PNNI Protocols l A routing protocol that provides for the selection of routes that can meet Qo. S requirements l A signaling protocol for the exchange of messages between switches and between private networks. l Based on UNI 4. 0 with extensions for: l l source routing crankback (a feature of the routing protocol) alternate routing of connection requests in the case of connection setup failure. Also includes modifications in the Information Elements to carry routing information.
PNNI Signaling Example Source Switch Source A SETUP CALL PROCEEDING Transit Switch SETUP Destination B SETUP CALL PROCEEDING CONNECT CONNECT ACK RELEASE COMPLETE RELEASE COMPLETE
Chapter 9 ATM Networks PNNI Routing
PNNI Routing Protocol l l A routing protocol for the selection of routes that can meet Qo. S requirements For intra-domain and inter-domain routing Link-state approach: each node has network topology Introduces hierarchy in the ATM network that provides a switch: l l Detailed routing information in its immediate vicinity Summary information about distant destinations
PNNI Terminology l l l Peer Group: collection of nodes that maintain an identical view of the group Logical Group Node: abstract representation of a peer group at a higher level in the routing hierarchy Peer Group Leader: node in peer group that executes functions of LGN for the PG l l Summarizes topology info within the PG Injects summary info into higher order groups and into the PG
PNNI Routing Hierarchy l l PGL passes topology summary upward in hierarchy and downwards to its PG Multiple levels of hierarchy allowed Logical Link A B Logical Group Node Peer Group Leader PG(A) A. 2 A. 1 PG(A. 1) A. 2. 2 A. 1. 1 PG(B) PG(A. 2) B. 1 B. 3 A. 2. 1 A. 1. 3 Physical Link A. 2. 3 A. 2. 4 B. 2 B. 4
PNNI Source Routing l l PNNI source node specifies entire path across its PG using designated transit list (DTL) Rest of path specified using higher levels in the hierarchy Example: station in A. 1. 1 requests path to B. 3 Path: (A. 1. 1, A. 1. 2, A. 2, B) Logical Link A B Logical Group Node Peer Group Leader PG(A) A. 2 A. 1 PG(A. 1) A. 2. 2 A. 1. 1 PG(B) PG(A. 2) B. 1 B. 3 A. 2. 1 A. 1. 3 A. 2. 4 B. 2 B. 4
DTL Stacks & Pointers l l DTLs organized in a stack according to level A pointer indicates current level From node A. 1. 2 From node A. 2. 1 DTL: [A. 1, A. 2] pointer-2 DTL: [A. 2. 1, A. 2. 3, A. 2. 4] pointer-2 DTL: [A, B] pointer-1 DTL: [A. 1, A. 2] pointer-2 From node A. 1. 1 From node A. 2. 4 DTL: [A, B] pointer-1 DTL: [A. 1. 1, A. 1. 2] pointer-2 DTL: [A, B] pointer-1 DTL: [A. 1, A. 2] pointer-1 A B DTL: [A, B] pointer-1 From node B. 1 DTL: [B. 1, B. 3] pointer-2 DTL: [A, B] pointer-1 PG(A) A. 2 A. 1 PG(A. 1) A. 1. 1 PG(B) PG(A. 2) A. 2. 2 A. 1. 2 From B. 3 null B. 1 B. 3 A. 2. 1 A. 1. 3 A. 2. 4 B. 2 B. 4
PNNI Features l Call setup involves connection admission control at each node l l l PNNI uses Generic Connection Admission Control (GCAC) to select path Call request can be blocked from lack of resources PNNI provides for crankback & alternate routing l Upon blocking, call setup is “cranked back” to creator of DTL, which considers alternate routes from that point onwards
Chapter 9 ATM Networks Classical IP over ATM
Classical IP over ATM l Classical IP over ATM (RFC 2255) l l IP treats ATM as subnetwork Logical IP subnetwork (LIS) is part of ATM network that belongs to same IP subnetwork l l All members of a LIS use same IP address prefix (network # & subnetwork #) Members in same LIS communicate using ATM VC Each LIS in an ATM network operates independently of other LIS’s in the same ATM network LIS’s communicate via routers
Logical IP Subnetworks (LIS’s) ATM network LIS 1 LIS 2 LIS 3 LIS 4 LIS 5 LIS 6 Router Router
Address Resolution l Suppose host S want to send packet to host D in same LIS l l Host S sends message to ATM ARP server in the LIS, requesting ATM address corresponding to IP address of host D (All hosts in LIS know ATM address of ATM ARP server) ATM ARP replies with ATM address, and Host S sets up ATM connection to Host D If host D is in another LIS, host S sets up ATM connection to the router in its LIS l l Router determines next hop router & sets up VC to it Packets between hosts in different LIS’s always use intermediate routers, even if hosts are in the same ATM network
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