ATM Overview Shorthand

7/29/2019 ATM Overview Shorthand

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Advanced Internet Technologies, SS 2005 2.1

Advanced Internet Technologies

Chapter 2

ATM

Prof. Dr. Georg Carle

Chair for Computer Networks & Internet

Wilhelm-Schickard-Institute for Computer Science

University of Tübingen

http://net.informatik.uni-tuebingen.de/

[email protected]




Basics of ATM

Introduction

Reference Model Higher Layers

Signaling, Routing

IP over ATM

LAN over ATM

Chapter 2

ATM




B-ISDN and ATM

The goal of broadband ISDN (1990)

Worldwide consistently build high-performance network

Transmission of data, audio, video

Standardization via ITU (CCITT)

ATM (Asynchronous Transfer Mode) was selected as the base

technology for B-ISDN

ATM is part of the ITU specification of B-ISDN Additional specifications have been published by the ATM Forum




Introduction

ATM: Asynchronous Transfer Mode

Based on standardized protocols

Integrated technology for multiple services

Data

Speech / Audio

Video

Usable in LAN and WAN areas

Highly scalable

Support for different connection qualities -> real-time!

Employment of asynchronous time multiplex technologies for flexibility,supporting various transmission bandwidths




Properties

Data packets of fixed size, named cells

ATM cells have a length of 53 byte (5 byte header, 48 byte payload)

This allows a high speed processing including massive parallel hardwareoperations

At a payload length of 48 byte, the packetisation delay (time to fill a cellwith 64 Kbit/s digitized voice samples)

Connection oriented

point-to-point

point-to-multipoint Connections may have a fixed (reserved) bandwidth and guaranteed

quality of service characteristics

Centralized coordination of permissions to send (in contrast to tokentechniques or CSMA/CD)

No shared medium Dedicated bandwidth




Standardization

ITU-T: International Telecommunications Union – Telecommunications

Standards Section (formerly CCITT)

http://www.itu.ch/

ETSI: European Telecommunications Standards Institute

http://www.etsi.fr/

ANSI: American National Standards Institute

http://web.ansi.org/

ATM-Forum

Development of industry standards allowing a fest development of new

products

http://www.atmforum.com/




ATM Layer Model

User plane: information flow between the layers

Control plane: connection setup, maintenance and termination

Management plane: meta-signaling and OAM (Operation and Maintenance)

information flow

AAL Type

ATM Layer

Service Class /

Service Category

(CBR, nrt-VBR,rt-VBR, UBR, ABR)

AAL Service Class

(Class A / B / C / D )




Physical Layer

Physical medium sends and receives a bit stream

Bit timing

Transmission convergence

The physical layer adopts the ATM cells received from the ATM layer

to the bit stream required by the physical layer (cell coding)

Direct cell transmission

Cell adaptation to existing transmission frames PLCP (Physical Layer Convergence Protocol) based cell adaptation

HEC (Header Error Correction) generation – an element of the ATM layer

Information flow to the management and to the supervision at thephysical layer (OAM, Operation and Maintenance)




Physical Layer II

Transmission speeds

PDH (Plesiochronous Digital Hierarchy)

Europe: 2,048 Mbit/s, 8,448 Mbit/s, 34,368 Mbit/s, 139,264 Mbit/s

USA: 1,544 Mbit/s, 6,312 Mbit/s, 44,736 Mbit/s, 254,176 Mbit/s

SONET (Synchronous Optical NETwork) - USA

SDH (Synchronous Digital Hierarchy) - Europe

OC-3/STM-1: 155,520 Mbit/s

OC-12/STM-4: 622,080 Mbit/s

OC-48/STM-16: 2.48832 Gbit/s

OC-192/STM-64: 9.953280 Gbit/s

OC-768/STM-256: 39.813120 Gbit/s




ATM Layer

Transport of ATM cells between the communication end points

Tasks of the user and control plane

Connection setup, multiplexing/de-multiplexing and maintaining ATM

connections

Generation of ATM cell headers (exception: HEC)

Negotiation of QoS (Quality of Service) parameters

Traffic and overload control

OAM cells

cells of the management plane

Meta-signalling

initial signalling to set up signalling VCs (Virtual Channels)




ATM Cell Format

53 Byte

5 Byte Header

48 Byte Payload




ATM Cell Types

UNI/NNI (User-Network-Interface / Network-Network-Interface) cells:data communication

Transmission of user data

Transmission of signalling data (connection setup, maintenance, tear down)

Idle cells: decoupling of the cell rate at the sender and the available bandwidth of

the transmission medium

Empty cells: contain VPI/VCI (Virtual Path Identifier / Virtual Channel Identifier) but

no payload

OAM cells: contain control and service information

VP/VC (Virtual Path/Virtual Channel) OAM cells: fault management, loopback, and

continuity check (CC) cells; F4: used in VPs, F5: used in VCs

Reserved VCI/VPI values

….

VCI=18, VPI=0PNNI (Private Network-to-Network Interface)

VCI=5Point-to-point signaling

VCI=16, VPI=0ILMI (Interim Local Management Interface)

VCI=1, VPI=0Meta signaling

VPI/VCIFunction




ATM Connections

2 Hierarchies: paths and channels

Transmission Path

Virtual Path

V i r t u a l C h a n n e l s




Properties of ATM Connections

Start and end at higher layer functions

Have associated service parameters (e.g. cell loss ratio, latency)

Negotiation of transmission parameters by signalling before aconnection is set up (provision of QoS)

Preservation of the transmission order

Unidirectional or bidirectional

Symmetric or asymmetric bandwidth

Permanent

PVC: Permanent Virtual Channel

Dynamic

SVC: Switched Virtual Channel

Signaling: connection setup and tear down

(Two signalling variants specified by ATM Forum: UNI 3.1, UNI 4.0) Routing Protocols (ATM-Forum: P-NNI)

Addressing of end points using E.164 addresses




Traffic and Overload Control

Six ATM service categories

Constant bit rate (CBR)

Real time variable bit rate (rt-VBR)

Non-real-time variable bit rate (nrt-VBR)

Unspecified bit rate (UBR) Available bit rate (ABR)

Guaranteed frame rate (GFR)

Traffic Management 4.0 (ATM Forum)

Connection admission controlVerification if connection setup would be possible

User/network parameter control (UPC/NPC)Supervision of transmission bandwidth by setting a cell loss priority and selectivelydiscarding of cells

Traffic shapingadjustment / smoothing of the transmission rate

Early Packet Discard (EPD)discarding of complete AAL PDUs if single cells are lost




Call Admission Control (CAC)

Exchange of information during the connection setup

Source traffic descriptor

Peak cell rate (PCR): upper bound for the maximum cell transmission rate [c/s]

Sustainable cell rate (SCR): upper bound for the average cell transmission

rate [c/s] Maximum burst size (MBS): size of a buffer used for short bursts [c]

Minimum cell rate (MCR): lower bound for the cell transmission rate [c/s]

Cell delay variation tolerance (CDVT)

provides upper bound for the cell jitter

specifies lower bound for the minimum distance between two cells(generated by multiplexing, OAM cells, …)

QoS of the connection (QoS parameters)

Successful completion of the CAC

Traffic agreement is negotiated between the network and the end systems




Effects of Network Congestion

Throughput and delay for increasing load




Cell Transfer Delay PDF

Probability Density Function (PDF) of Cell Transfer Delay




UPC/NPC

Usage Parameter Control / Network Parameter Control

Verification of

Correctness of the VP/VC identifiers in the cell header

Conformance of the cell stream (compliance with the negotiated trafficprofile): the observation whether the measured variable is withinpredefined boundaries.

Actions

Cell passing Cell tagging (warning: CLP bit set to 1)

Cell discarding (in overload situations)

Generic cell rate algorithm (GCRA)

For every cell, a theoretical arrival time (TAT) is calculated based on the

assumption that the distance between all cells is equal

If the actual arrival time corresponds with the TAT (taking a tolerance intoaccount), the cell is conformant (otherwise it is violating the traffic contract)




UPC/NPC II

UPC typically at the ingress of an ATM switch

One or two leaky buckets depending on the service category

Processing of cells according to Cell Loss Priority (CLP)

Cells with a CLP bit setting of 1 are discarded before cells with a CLP bitsetting of 0.

Generic cell rate algorithm (GCRA)




Traffic Shaping

Different implementation alternatives

leaky bucket / token bucket

virtual scheduling (GCRA)

Reduction of the burst size and removal of the cell delay variation (by

increasing of the delay)

Important note: the order of the cells is not changed

Token Bucket shaper:




Early Packet Discard (EPD)

EPD buffer threshold to prevent overload situations

If threshold is exceeded, complete AAL5 PDUs are dropped

→ performance enhancement




Quality of Service

Parameter are negotiated at connection setup (ITU I.356/UNI4.0) Cell error ratio

Severely errored blocks

Cell loss ratio*

Cell misinsertion ratio

Cell transfer delay* Mean cell transfer delay

Cell delay variation*

*: currently unused

Different traffic classes (ATM Service Classes) Constant bit-rate (CBR)

Delay sensitive CBR cell stream

Variable bit rate - real time (VBR-rt)

Delay sensitive VBR cell stream

Variable bit rate - non real time (VBR-nrt)

Delay insensitive VBR cell stream

Unspecified bit rate (UBR)

Best effort

Available bit rate (ABR)

Dynamic bandwidth allocation if available




Quality of Service II

SpecifiedUnspecifiedUnspecifiedUnspecifiedUnspecified

Flow control

Closed loop

Unspecified

Unspecified

Unspecified

Unspecified

Unspecified

Unspecified

Unspecified

Specified

Specified

Specified

Specified

Specified

Specified

Specified

QoS parameters

Peak-to-peak CDV

maxCTD

CLR

Specified

n/a

Specified

Specified

n/a

n/a

Specified

Specified

n/a

Specified

Specified

n/a

Specified

n/a

n/a

Traffic parameters

PCR and CDVT(pcr)

SCR, MBS, CDVT(scr)MCR

ABRUBRVBR-nrtVBR-rtCBR Attribute

PCR Peak Cell Rate

CDVT Cell Delay Variation ToleranceSCR Sustainable Cell Rate

MBS Maximum Burst Size

MCR Minimum Cell Rate

maxCTD maximum Cell Transfer Delay

CLR Cell Loss Rate




ATM Adaptation Layer

AAL (ATM Adaptation Layer): mapping data structures between higher layers and ATM cells

Criteria:

Time constraints

Bit rate (constant, variable) Connection type (connection oriented / connection less)

Convergence Sublayer (CS)

Building CS-PDUs out of an application generated byte stream

Segmentation and Reassembly Sublayer (SAR) Convert CS-PDUs into 48 byte fragments which fit in the payload of ATM cells




ATM Adaptation Layer II

Example: AAL 3/4




ATM Adaptation Layer III

AAL0: “native” ATM

AAL1: constant bit rate (circuit emulation)

AAL2: transmission of data streams with variable bit rates and well defined

time constraints between sender and receiver

AAL3/4: Variable bit rate without any time constraints

AAL5: simplified AAL3/4 (no multiplexing of cells)

SAAL: Signalling AAL,

SSCOP (Service-Specific Connection-oriented Protocol)

and SSCF (Service-Specific Convergence Fuction)over AAL5




ATM Adaptation Layer IV

AAL Service Classes and AAL Types

Connectionless

Date Transfer

Bit Rate

Connection

Mode

Examples

of

Services

Circuit

Emulation

Constant BitRate Video

and Audio

Constant Variable

Connection Oriented Connectionless

Variable Bit

Rate Video

and Audio

Connection-

oriented

DataTransfer

AAL

TYPEAAL 1 AAL 2

AAL 3/4

AAL 5

Class A Class B Class C Class D

Related Not Related

AAL ServiceClass

Timingbetween

Source and

Destination

AAL3/4AAL 5




Convergence Sublayer

Common part: to add / to remove header and trailer

Unreliable transmission of data packets of variable length

Connection setup between two CPCS (Common Part Convergence

Sublayer) end points

Preservation of the order within a single CPCS connection

Error detection and handling

Handling of overload information

Handling of cell loss priorities

Dropping of incomplete CPCS PDUs

Service specific:

Q.SAAL (SSCS: specification for signaling channels)




Segmentation and Reassembly Sublyaer

Identification of the next SAR PDU to transmit

PTI (Payload Type Indication) informs about start and end of a SAR PDU

AAL5: Last cell of an AAL frame: PTI=1

Handling of overload

Handling of cell loss priorities

Check for ordering of SAR PDUs







AAL 5 Protocol

CPCS-PDU Payload PAD CPI Length

1 2 40 - 47

CPCS

UU

1

CRC-32

AAL5 is a simple and efficient AAL (SEAL) to perform a subset of the functions

of AAL3/4

The CPCS-PDU payload length can be up to 65,535 octets and must use PAD

(0 to 47 octets) to align CPCS-PDU length to a multiple of 48 octets

PAD Padding

CPCS-UU CPCS User-to-User Indicator

CPI Common Part Indicator

Length CPCS-PDU Payload LengthCRC-32 Cyclic Redundancy Chuck




Higher layer

Common part

convergence

sublayer

SAR sublayer

ATM layer

PTI = 0

Service specific

convergence

sublayer

Assume null

48

(1)

Information

TPAD

…

…

Information

48

(0)

48

(0)

PTI = 0 PTI = 1

AAL 5 Layering




SAAL

SAAL: Adaptation layer for signaling meta signaling

signaling AAL

ITU Q.2100

Offers a reliable service for the higher layer signaling (Q.2931) Q.2931 has no error correction mechanisms

SSCS sublayer: realizes SSCOP protocol (Service SpecificConnection Oriented Protocol)

Sequence continuity Error correction, retransmission

Flow control

Keep alive

Connection control

Exchange of status information between sender and receiver




ATM Network Components

ATM Hosts

ATM Switches

ATM Edge Devices

Interconnection of ATM networks and non-ATM networks

ATM Interfaces (public/private) UNI (User Network Interface): defines protocols for the communication between

hosts and switches

NNI (Network to Network Interface): defines the interface between two network

components




Higher Layers

Signaling, Routing UNI – User Network Interface

Signalling Interface at ATM end systems

PNNI - Private Network-to-Network Interface

Routing Interface ILMI - Integrated Local Management Interface

Management Interface, using SNMP messages without UDP and IP

Addressing

NSAP (Network Service Access Point) addressing

Three NSAP-like address formats

DCC (Data Country Code) ATM Format

ICD (International Code Designator) ATM Format

E.164 ATM Format.

Procedure E.164 number is filled with leading zeros to make 15 digits.

A F16 is padded to make 8 bytes.

AFI and DSP are added.




User Network Interface – Connection Setup

Host A: specification of bandwidth, QoS and destination address

Within the network:

Verification of the available resources

Acceptance / rejection of the request

Reservation of the required resources

Maintenance of the routing tables

Host B: acceptance / rejection of the connection request




User Network Interface – Connection Release

Host A: connection release message

Within the network:

Release of resources belonging to the connection

Acknowledgement of the connection release message

Host B: acknowledgement of the connection release message

U N t k I t f III




User Network Interface III

ATM point-to-multipoint connections

Extensions in UNI 4.0 Signaling Multicast (leaf initiated join)

Frame discard

Signalling of more QoS parameters (CLR, meanCTD, maxCTD, CDV, ....)

ATM M t d R ti P t l




ATM Management and Routing Protocols

Defined by ATM Forum

PNNI (Private Network-to-Network Interface)

a hierarchical, dynamic link-state routing protocol

ILMI (Interim Local Management Interface)

a protocol defined by the ATM Forum for setting and capturing physical layer, ATMlayer, virtual path, and virtual circuit parameters on ATM interfaces.

ILMI uses simple network management protocol (SNMP) messages without User

Datagram Protocol (UDP) and IP

ILMI organizes managed objects into the following four management information

bases (MIBs): Textual Conventions MIB - Defines textual conventions and object IDs

Link Management MIB - Physical layer, ATM layer, Virtual path connection,

Virtual channel connection

Address Registration MIB - address registration mechanism to automatically

configure network prefixes in end-systems.

Service Registry MIB - general-purpose service registry for locating ATM

network services such as a LAN Emulation Configuration Server (LECS) in

LANE.

P i t N t k t N t k I t f P t l




Private Network-to-Network Interface Protocol

PNNI: also known as Private Network Node Interface Protocol Setup of SVCs in networks with NSAP (Network Service Access Point)

addressing in a multivendor environment

Hierarchical routing structure, similar to OSPF

Using topology and resource information to setup paths

PNNI Phase 0: Inter-Switch Signaling Protocol (IISP)

Signalling protocol for the communication between ATM switches(administratively configurable address prefixes)

PNNI Phase 1:

QoS support

scalability and reachability

Signaling is based on UNI3.1/4.0 with some extensions

P NNI QoS




P-NNI - QoS

CAC (connection admission control) Admission control at each node along the path

Topology state protocol

GCAC (generic CAC) Determination of the shortest path over all nodes which comply with the

ABR and CLR Additionally, the path is verified using the QoS requirements (CDV, …)

Source node creates a “Designated Transit List“ containing the complete

route

Crankback - possibility for a rollback

Crankback:

PNNI Hierarchy




PNNI - Hierarchy

Scalability: hierarchical routing protocol

Summary of the reachability information at each hierarchy

Identification using NSAP addresses

Problems:

internetworking with

other networks

Complexity in route

aggregation

ILMI Integrated Local Management Interface




ILMI - Integrated Local Management Interface

Protocol for the bidirectional exchange of management information

Monitoring of systems

Management of systems

Using SNMP (simple network management protocol) for the

communication (without UDP/IP)

Fundamentals: data base (ATM-UNI-MIB) with well defined commands

for accessing the data base: AAL encapsulated SNMP messages,

community name ILMI

ILMI Address Registration




ILMI - Address Registration

Bidirectional address registration

Dynamic exchange of address information between end systems and

the network at the UNI

The ATM host informs the switch about its ESI address

esiAddress: end system ID portion of the ATM NSAP address in the

format xxxxxxxxxxxx.xx

The ATM switch provides the address prefix to the host

Protocol for automatic address registration

Benefits:

There is no need to configure the prefix at each host

There is no need for an additional address resolution protocol in the

switches (all hosts register first)

Applications




Applications

Multimedia Video over ATM

Benefits:

guaranteed QoS parameters

Low latency Resource sharing between multiple applications

Drawbacks:

Complexity in the maintenance of ATM networks

Examples:

M-JPEG codecs: 15Mbit/s, TV quality

MPEG2 codecs: 3-40Mbit/s, DVD up to studio quality

Lossless SDI: 270Mbit/s, uncompressed studio signals

IP/LAN over ATM CLIP (Classical IP over ATM / Classical IP)

MPOA (Multi-Protocol over ATM)

LANE (LAN Emulation)

Multiprotocol Encapsulation over AAL5 (RFC2684)




Multiprotocol Encapsulation over AAL5 (RFC2684)

RFC2684

LLC/SNAP encapsulation

LLC data packets are encapsulated into AAL5 CPCS PDUs

Transmission of a complete data stream in a single VC A special header informs about the encapsulated protocol

All protocols based on Ethernet, FDDI, … can be transported

VC based multiplexing

Communication end point in layer 3

Avoiding special LLC headers by using separate VCs for each

protocol

More efficient than LLC encapsulation

Classical IP




Classical IP

Specification of a complete IP implementation for ATM Allows unicast communication only

Very efficient Support for large MTU sizes

Direct encapsulation of IP packets into AAL PDUs

LIS: logical IP subnet ATMARP/InATMARP: protocol similar to ARP to resolve IP to ATM addresses

InATMARP functions are provided by an ATMARP server

There must be an ATMARP server in each LIS

Classical IP II




Classical IP II

Each ARP client must register its IP/ATM address information at the ATMARP server or request an IP address from the ATMARP server

LANE




LAN Emulation: connecting LANs over ATM networks

The properties of ATM are completely hidden

Complete emulation of the LAN MAC layer

Thus, no need to modify existing LAN software

But, no special ATM features can be used, e.g. QoS

Provisioning of a special broadcast mechanism, which is also used for

multicast

Translation of MAC to ATM addresses

Transmission of LAN packets using AAL5 PDUs

Modules:

LANE client (LEC)

LANE server (LES)

LANE configuration server (LECS)

Broadcast and unknown server (BUS)

LANE II




LEC (LANE client) Control functions

Data exchange using the ATM interface

Interface to the application as a standard LAN MAC interface

LES (LANE server) Control and maintenance of an E-LAN (emulated LAN)

Registration of LECs

Mapping of MAC to ATM addresses

BUS (broadcast and unknown server)

Delivery of broadcast, multicast and unknown packets received from anyLANE client

All packets with a broadcast or multicast address

Packets which cannot be delivered directly, e.g. because thecorresponding ATM address cannot be resolved

Sequential processing of the single messages (AAL5 does not allow thechange of the order of PDUs)

LANE III




LECS (LANE configuration server) Management of the different emulated LANs and the associated LANE

servers

Configuration database allowing a LANE client to find the appropriate

LANE server for a specific emulated LAN LECS address

Statically configured in LES and LEC

Well known address

via ILMI

LANE IV




Documents

ATM Overview Shorthand