Advanced Internet Technologies - Computer and Communication ...

Advanced Internet Technologies 

Chapter 2 

ATM 

Dr.-Ing. Falko Dressler 

Chair for Computer Networks & Internet 

Wilhelm-Schickard-Institute for Computer Science 

University of Tübingen 

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

dressler@informatik.uni-tuebingen.de 

Advanced Internet Technologies, SS 2004 2.1

Basics of ATM 

Introduction 

Chapter 2 

ATM 

Reference Model 

Higher Layers 

Signaling, Routing 

IP over ATM 

LAN over 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 

Therefore, ATM is part of the ITU specification of B-ISDN 


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 

in support of 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 hardware 

operations 

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 token 

techniques 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 information flow 


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 based cell adaptation 

HEC generation 

Information flow to the management and to the supervision at the 

physical layer (OAM) 


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 

SDH (Synchronous Digital Hierarchy) 

OC-3: 155,520 Mbit/s 

OC-12: 622,080 Mbit/s 

Today: OC-48, OC-192, … 


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 

connection 

Generation of ATM cell headers (but HEC) 

Negotiation of QoS parameters 

Traffic and overload control 

OAM cells (management plane) 

Meta-signaling 


ATM Cell Format 

53 Byte 

5 Byte Header 

48 Byte Payload 


ATM Cell Types 

UNI/NNI cells: data communication 

Transmission of user data 

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

VP/VC OAM cells (F4 and F5) 

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

of the transmission medium 

Empty cells: contain VPI/VCI but no payload 

OAM cells: contain control and service information 

Reserved VCI/VPI values 

Function VPI/VCI 

Meta signaling VCI=1, VPI=0 

ILMI VCI=16, VPI=0 

Point-to-point signaling VCI=5 

PNNI VCI=18, VPI=0 

…. 


Virtual Channels 

ATM Connections 

2 Hierarchies: paths and channels 

Virtual Path 

Transmission Path 


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 before a connection 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 

(ATM Forum: UNI 3.1, UNI 4.0) 

Routing Protocols (ATM-Forum: P-NNI) 

Addressing 


Traffic and Overload Control 

Traffic Management 4.0 (ATM Forum) 

Connection admission control 

Verification if connection setup would be possible 

User/network parameter control (UPC/NPC) 

Supervision of transmission bandwidth by setting a cell loss priority and 

selectively discarding of cells 

Traffic shaping 

adjustment / smoothing of the transmission rate 

Early packet discard 

discarding of complete AAL PDUs if single cells are lost 


Call Admission Control 

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

Cell delay variation tolerance (CDVT): 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 


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 traffic 

profile) 

Actions 

Cell passing 

Cell tagging (warning) 

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 into 

account), the cell is conform 


UPC/NPC II 

UPC typically at the ingress of an ATM switch 

One or two leaky buckets depending on the service category 


Traffic Shaping 

Implementation using a leaky bucket 

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

increasing the delay) 

Important note: the order of the cells is not changed 


Early Packet Discard 

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 classes (ATM-Forum) 

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 

Attribute CBR VBR-rt VBR-nrt UBR ABR 

Traffic parameters 

PCR and CDVT(pcr) 

SCR, MBS, CDVT(scr) 

MCR 

QoS parameters 

Peak-peak CDVT 

maxCTD 

CLR 

Specified 

n/a 

n/a 

Specified 

Specified 

Specified 

Specified 

Specified 

n/a 

Specified 

Specified 

Specified 

Specified 

Specified 

Advanced Internet Technologies, SS 2004 2.22 

n/a 

Unspecified 

Unspecified 

Specified 

Specified 

n/a 

n/a 

Unspecified 

Unspecified 

Unspecified 

Specified 

n/a 

Specified 

Unspecified 

Unspecified 

Flow control 

Closed loop Unspecified Unspecified Unspecified Unspecified Specified

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 


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: Signaling 


Convergence Sublayer 

Common part: to add / to remove header and trailer 

Unreliable transmission of data packets of variable length 

Connection setup between two CPCS 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 SAP PDU to transmit 

PTI informs about start and end of a SAR PDU 

Handling of overload 

Handling of cell loss priorities 

Check for ordering of SAR PDUs 


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 Specific 

Connection Oriented Protocol) 

Sequence continuity 

Error correction, retransmission 

Flow control 

Keep alive 

Connection control 

Exchange of status information between sender and receiver 


Operation, Administration and Maintenance 

Information flow for management and control 

Cells can be identified by the PT field 

Error control and localization 

Performance control 

5 hierarchies: F1-F5 

Physical layer: F1-F3 

SDH encoding: F1, F2: section overhead, F3: path overhead 

PDH encoding: using PDH internal structures 

Indication of unavailability state, transport of defect information to the 

end system, MUX problems 

ATM layer: F4, F5 

Fault management 

Transmission of defect information in both directions 

– AIS - Alarm Indication Signal: sent upstream to indicate downstream failures 

– RDI - Remote Indication Signal: sent downstream to indicate upstream failures 

Continuity check 

Loopback cells: monitoring, fault localization 

Performance management 


ATM 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 

PNNI - Private Network-to-Network Interface 

ILMI - Integrated Local Management Interface 


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 


User Network Interface III 

ATM point-to-multipoint connections 

Extensions in UNI 4.0 Signaling 

Multicast (leaf initiated join) 

Frame discard 

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


Private Network-to-Network Interface Protocol 

P-NNI: also known as Private Network Node Interface Protocol 

Setup of SVCs in networks with NSAP addressing in a multivendor 

environment 

Hierarchical routing structure, similar to OSPF 

Using topology and resource information to setup paths 

Phase 0: Inter-Switch Signaling Protocol (IISP) 

Signaling protocol for the communication between ATM switches 

(administratively configurable address prefixes) 

Phase 1: 

QoS support 

scalability and reachability 

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


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 versified using the QoS requirements (CDV, …) 

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

route 

Cranback: possibility for a rollback 


P-NNI - 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 


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 addressing) 

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 

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 

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 

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 

Classical IP, MPOA 

LAN Emulation 


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 

Avoidance of special LLC headers by using separate VCs for each 

protocol 

More efficient than LLC encapsulation 


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 

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 any 

LANE client 

All packets with a broadcast or multicast address 

Packets which cannot be delivered directly, e.g. because the 

corresponding ATM address cannot be resolved 

Sequential processing of the single messages (AAL5 does not allow the 

change 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

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