RS -Curs Electronica

8/12/2019 RS -Curs Electronica

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Prof. E.Borcoci- UPB -2013-2014 2

Retele si Servicii

Sem II licenta spec. RST

(English version)

Network and Services

E. Borcoci, UPB

2013-2014


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CONTENTS

1 INTRODUCTION-ARCHITECTURE REVISION 6

1.1 NETWORKS LAYERED ARCHITECTURES 61.1.1 General Principles and Functional Layers 61.1.2 OSI Reference Model 71.1.3 Real Stack Examples. Incomplete stacks 10

1.1.3.1 TCP/IP Stack 10

1.1.3.2 IEEE 802.x standards for LAN, MAN 141.1.3.3 Signalling System No.7 141.1.3.4 MPLS architecture 15

1.1.3.4.1 MPLS IP stack 151.2 MULTIPLE PLANES ARCHITECTURES 16

1.2.1 Principles 161.2.2 Signalling Issues 171.2.3 Next Generation Networks Architecture- high level view 18

1.3 BUSINESS MODELS FOR (MULTIMEDIA)COMMUNICATION ARCHITECTURES 211.3.1 Customers and Users 211.3.2 Providers (PR) 211.3.3 Multiple Plane Architecture and Business Actors 231.3.4 Service Level Agreements/Specifications (SLA/SLS) 23

1.4 EXAMPLES OF MULTIPLE PLANE ARCHITECTURES 25

1.4.1 IEEE 802.16 multi-plane stack 251.4.2 Generic Example of a multi-plane architecture 27

1.4.2.1 An Architecture oriented to multimedia distribution over multiple domains networks 27

1.4.3 Example: Architectural stack for wireless heterogeneous mesh network 291.4.4 Control Plane in GSM (2G) 31

2 INTERCONNECTION- REVISION 34

2.1 MODURI DE LUCRU CU I FRCONEXIUNE CO/CL 342.2 CERINELE UNUI SERVICIU DE INTERCONECTARE (LA NIVEL TREI) 342.3 MODUL DE LUCRU CO(CONEXIUNE LA NIVEL REEA) 352.4 MODUL DE LUCRU CL (FARA CONEXIUNE LA NIVEL REEA) 362.5 INTERCONECTAREA DE TIP PUNTE (BRIDGE APPROACH) 362.6 EXEMPLE DE INTERCONECTRI 37

2.6.1 Interconectarea de reele LAN prin puni (B) 392.6.1.1 Puni transparente (Transparent Bridges- TB) 412.6.1.2 Punti cu rutare de tip sursa 41

3 ROUTING PROTOCOLS 42

3.1 ALGORITMI DE RUTARE -SUMAR 423.2 ALGORITMI DE BAZA PENTRU CAUTAREA CELUI MAI SCURT DRUM 46

3.2.1 Algoritmul Dijkstra (centralizat) 473.2.2 Algoritmul Ford (Fulkerson) 50

3.3 IPROUTING PROTOCOLS 543.3.1 Internet Protocol reminder 543.3.2 Principles of IP routing 563.3.3 Network hierarchies 57

3.3.3.1 Multi-Tier hierarchy 583.3.3.2 Autonomous System Definition 593.3.3.3 ASes and Tiers 60

3.3.4 General definitions 613.3.5 Address Resolution Protocol (ARP), Reverse ARP RARP 633.3.6 Interior Gateway Protocols 64

3.3.6.1 Routing Internet Protocol (RIP) 653.3.6.2 RIP Extensions 673.3.6.3 Ad hoc On-Demand Distance Vector (AODV) 683.3.6.4 Open Shortest Path First (OSPF) 74

3.3.7 Border Gateway Protocol (BGP) 803.4 IPV6 813.5 ICMPV6 85


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4 IPQOS TECHNOLOGIES 86

4.1 INTRODUCTION 864.2 APPLICATIONS 86

4.2.1 Application 874.2.2 classes 87

4.2.2.1 Elastic applications 874.2.2.2 Streaming applications 87

4.2.3 Traffic Description 874.2.3.1 Traffic descriptors 88

4.3 ARCHITECTURAL FRAMEWORK FOR QOSIN IPNETWORKS 884.3.1 IP Services 904.3.2 Data Plane Mechanisms 92

4.3.2.1 Traffic Classification (TCl) 934.3.2.2 Packet Marking 934.3.2.3 Traffic policing (TP) 934.3.2.4 Traffic Shaping (TS) 944.3.2.5 Buffer (Queue) Management (QM) 944.3.2.6 Queuing and Scheduling Q&S 944.3.2.7 Congestion Avoidance (CA) 95

4.3.3 Control Plane 954.3.3.1 Admission Control (AC) 954.3.3.2 QoS Signalling 96

4.3.3.3 QoS Routing 964.3.3.4 Resource Reservation (RR) 96

4.4 BASIC IPQOSAND TRAFFIC CONTROL MECHANISMS-DATA PLANE 974.4.1 QoS Guarantees (I) 97

4.4.1.1 Types of guarantees 974.4.1.1.1 Bandwidth Guarantees 974.4.1.1.2 Other guarantees 97

4.4.1.2 Level of guarantees 984.4.2 Classical Routers, Qos Capable Routers 984.4.3 IP Level services 99

4.4.3.1 Besteffort (BE) service 994.4.3.1.1 Fairness problem 99

4.4.3.2 Buffer (queue) management 100

4.4.3.2.1 Tail drop 1004.4.3.2.2 Random Early Detection 1004.4.3.2.3 Weighted RED 102

4.4.3.3 Maximum bandwidth service 1024.4.3.4 Minimum bandwidth service 103

4.4.4 Packet Classification and Marking 1044.4.4.1 Packet Flows defined at different layers 105

4.4.4.1.1 Layer 3 Flows 1054.4.4.1.2 Layer 4 Flows 1054.4.4.1.3 Upper layer Flows 105

4.4.4.2 IP Packet Marking 1074.4.5 Policing and Shaping 108

4.4.5.1 Measuring the Rate of Incoming Flows 108

4.4.5.1.1 General Measuring Algorithms of Flow Rate 1094.4.5.1.2 Basic Token Bucket Algorithm (TB) 1104.4.5.1.3 Extensions of Token bucket 1114.4.5.1.4 Leaky Bucket 1134.4.5.1.5 Dual Token Bucket 114

4.4.5.2 Shaping Based on Token Bucket 1144.4.6 QoS Guarantees (II) 1154.4.7 Scheduling algorithms 1164.4.8 Planificarea extragerii pachetelor 117

4.4.8.1 Functiuni de baza ale unui planificator 1174.4.8.2 Planificatoare pentru fluxuri Best Effort 117

4.4.8.2.1 Partajarea procesorului 117


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4.4.8.2.2 Planificator circular 1194.4.8.2.3 Planificator circular cu control individual de credit 120

4.4.8.3 Planificatoare pentru fluxuri cu garantii 1214.4.8.3.1 Planificator cu prioritati absolute 1224.4.8.3.2 Procesor partajat generalizat 1224.4.8.3.3 Planificator circular cu ponderi 1224.4.8.3.4 Planificator cu echitate si cozi ponderate 123

5 REFERENCES 127

5.1 GENERAL LIST OF ACRONYMS 1276 ANNEX 1 134

6.1 ETHERNET FRAME FORMATS: 1346.2 AODVDETAILS 136


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1 INTRODUCTION-ARCHITECTURE REVISION

1.1 Networks Layered Architectures

1.1.1 General Principles and Functional Layers

Architectural Model : set of functions and relations between them, independent ofimplementation

Objective:

management of high complexity: (divide et impera) - principle

interoperability among different products

Tools: definition of functional layers + interfaces

Network element: terminal, switching node, multiplexer, router, etc. = hierarchical set of

levels

-tasks:

- information transport (lower layers)- high level processing of information (upper layers)

Ta Tb

Processing

functionsNetwork

functions

Appl.

processes

Processing

functionsNetwork

functions

Appl.

processes

C1

C2

N2

N1

Ta Tb

Network(s)

User

Protocols

Physical medium

Upper layers

rotocols

Complexity/

Intelligence Future Internet?(more intelligent networks)

E.g. Content aware networks

a b

Figure 1 Simplified architectural model for communication


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a. Network and terminals b.Two level model : Ta, Tb= terminals

-application processes ( usually resident in Ta, Tb- they communicate through a set of rules

(protocol)at user level:

Protocols at different levels between:

- application processes

- higher layers processing functions (higher layers)- network transport functions (lower layers)

- set of layers =protocol stack

Layering principle is extended inside each of the two layer

1.1.2 OSI Reference Model

Classical architectural mode (1970-80)

ISO (International Standardization Organization):OSI - RM ("Open System Interconnection -Reference Model") for layered architecture networks

OSI RM defines: architectural and functional principles for open systems able to be

interconnected no matter the equipment manufacturer

- real world stack can be different of OSI-RM, but the same principles are applied

- OSI, TCP/IP model one plane architectural model

Usage examples of layered architecture networks use:

- industry, administration, business, health, military, education, research, etc.

- data and multimedia networks: local (LAN), metropolitan (MAN) wide area WAN (typical

example: INTERNET, Intranets, Extranets)

-digital telecommunication wide area networks:

- fixed communications: ISDN, BISDN, GSM ( e.g. Signalling System No.7 SS7

used to control the digital telecom networks)

- networks for mobile communications 2G, 3G,

- Integrated (convergent) networks

- TCP/IP based, 3G, 4G- for fixed or mobile communications

- Next Generation Networks ( ITU-T) ~ 1995-2000

- Future Internet: evolution/revolution for current Internet ( > 2005)

Fundamental Architectural Principles:

- layer N offers to N+1 a service set

- that can be accessed through interfaces (SAP = Service Access Point)

- service implementation is achieved by the protocol of the lower layer

-service primitives - information transport between adjacent layers

- protocols- specify the rules of comm between two peer entities

Criteria for function distribution on layers :

- homogeneity inside a layer

- minimal interactions between layers

- small number of layers

Note about word service usage


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- very general term used in a lot of contexts- much confusion out of this- OSI model defines very precise semantic for service- Adopting such semantic we distinguish among:

o Low level services , e.g: L2 service = connectivity service between two nodes L3 service = connectivity service over a network domain L4 service = E2E connectivity service

o High level services , e.g: data oriented services: FTP, e-mail, web access to info, transactional

services

multimedia-oriented services: VoIP, video conf, A/V streaming, DVB,IPTV, etc.

Curent trends:

-traditionally we want/have low coupling between layers

- today this principle is no longer considered good by all professional communities

- Cross-layer optimisation especially in wireless on L1-L3

- Content aware networks and Network Aware Applications

- pros and cons this approach still open issue

Base layers (1-3) ( network access and information transfer through network(s)

Upper layers (4-7)

- higher layer processing functions (closer to user application processes)

- usually layers 4-7 belong to terminals (endto-end ( E2E) protocols independent of:

- Network technology, Number of networks, Fixed or mobile mode

Important Notes:

o the same function name can be encountered on different layers but with differentsemantics

o Not all functions listed must be present in a layer (large variety in practical stacks)

Layer 1 (Physical- PHY); Layer 2 (Data Link Layer - DL ); Layer 3 (Network) :

Layer 4 (Transport T); Layer 5 (Terminal Session S); Layer 6 (Presentation);

Layer 7 (Applicaion) :


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Local Processes

Communication

Processes

Ta

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

Local Processes

Communication

Processes

Tb

7 Application

6 Presentation

5 Session

4 Transport

3 Retea

2 Data Link

1 Physical

Different levelProtocols

3 Network

2 Data Link

1 Physical

Transport Protocol

Network node

Physical transmission

medium

User Entities

Service AccessPoint

Service Primitives

Protocol Data

Units (PDU)

Information flow circulation

through layers

E2EProtocols

NetworkTransport

Protocols

Higher

Layer

Protocols

Network

AccesProtocols

Network

environment

OSI Environment

Real systems environment

Figure 2 OSI Reference Model


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Figure 3 Internetworking example in OSI Model

Note : Service Provider = Transport Service Provider

1.1.3 Real Stack Examples. Incomplete stacks

1.1.3.1 TCP/IP Stack

- TCP/IP stack different from OSI

- much greater success (history, simpler stack, market driven)

- WWW/Internet strengthened the usage of TCP/IP stack

Important note:

o Advances in microelectronics and huge increase of perf/cost allowed to include thefull TCP/IP stack in all terminals (including small mobile devices)

o This naturally creates the posibility to integrate all kind of high level services basedon TCP/IP stack

o That is why TCP/IP ( called Internet is accepted today as a basis for full networkand services integration

Communication models:

o Hierachy criterion

Classic model: Client/server( asymmetric one)

After 2000 Peer to peer (P2P) model

Symmetric model

huge expansion in last years ( ~70% of the total Internet traffic)

o Time criterion

Synchronous communication (usually r.t: VoIP, AVC, VoD, but also FTP,etc.)

Asynchronous communication : e-mail, publish/subscribe

o Mode to get information: push/pull


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- Original TCP/IP stack single architectural plain containing several protocols fordata transfer and control

Application services

Transport (TCP)

Internetworking (IP)

Subnetworks

Figure 4 Simplified view of TCP/IP stack

Application(communication between processes or

applications on separate hosts)

Telnet, FTP, E-mail,

SNMP, etc

Transport

(end-to-end data transfer service reliable or unreliable)

TCP, UDP

Network layer( network resources mng.,

routing the data to destination)

IP, ICMP, IGMP,

OSPF, etc.

Data link

(acces CO or CL to network layer)

(LLC) + MAC

Physical layer

Figure 5 Simplified view of the TCP/IP protocol stack

MIME

BGP(*1)

FTPTelnet HTTP SMTP RTCP

TCP (Connection oriented)

IP (Connectionless)

(LLC)+MAC (e.g.IEEE 802.x), AAL+ATM,

Physical Layer

ARPRARP


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VideoVoice

RTP SNMP

Multicast

protocols RIP

(*) BOOTP RSVP

UDP (Connectionless)

OSPF

(*1)

ICMP,

IGMP

(*2)

IP (Connectionless)

(LLC)+MAC (e.g IEEE 802.x) , AAL+ATM, etc

Physical Layer

ARP RARP

Figure 6 Example of TCP/IP stack protocols

(*1) they are not transport protocols but cooperate with IP

MIME Multipurpose Internet Mail Extensions

BGP Border Gateway Protocol

HTTP Hypertext Transfer Protocol

SMTP Simple Mail Transfer Protocol

SNMP Simple Network Management Protocol

FTP File Transfer protocol

RTP Real Time Protocol

ICMP Internet Control Messages Protocol

IGMP Internet Group Management Protocol

OSPF Open Shortest Path First Protocol

Transport:

TCP Transmission Control Protocol (connection oriented -CO)

UDP User Datagram Protocol ( connectionless CL)

Network: IP Internet Protocol + ICMP, IGMP, BGP, OSPF

Data link Layer:

LLC Logical Link Control + MAC- Medium acces Control

Example: AAL ATM Adaptation Layer + ATM Asynchronous TransferMode

Example: FTP, TCP, IP, (LLC) + MAC ( driver Ethernet)


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Multicasting:

IGMP Internet Group Management Protocol ( v.1, v.2, v.3)

Multicast routing protocols:

DVMRP Distance Vector Multicast Routing Protocol

PIM-DM Protocol Independent Multicast Dense Mode

PIM-SM Protocol Independent Multicast Sparse Mode

CBT Core based Tree

MOSPF Multicast OSPF multicast extension of OSPF

MBGP Multicast BGP extension of BGP to multicast

Multicast transport protocols:

RMTP Reliable Multicast Transport Protocol

SRM Scalable Reliable Multicast Protocol

MFTP Multicast File Transfer Protocol

PGM Pretty Good Multicast

Ping FTP

Telnet

Rlogin

SMTP

X

Trace-

route

DNS

TFTP

BOOTP

SNMP

NFS+RPC

User

process

UDPTCP

IP

IGMP

ARP RARP

ICMP

(LLC) MAC

Appl

Transport

Data link

Network

User

processes

Figure 7 Example of logical links between layers

ARP Address Resolution Protocol

RARP Reverse Address Resolution Protocol

TFTP Trivial FTP, BOOTP Bootstrap Protocol

NFS Network File Server


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1.1.3.2 IEEE 802.x standards for LAN, MAN

Figure 8 IEEE 802 LAN/MAN Standards- examples

1.1.3.3 Signalling System No.7

SS7:

- datagram virtual network for digital circuit switching network ( ex. ISDN, GSM) control

- Control planefor Telecom Digital Network containing the signaling protocols

Example for GSM - MSC:

(MSC- Message Switching Centre main switch in GSM)

- MTP 1-2-3 subsystem for message transport (layers 1-3)

- Layers 4-5-6 : void

- signaling applications : TUP, ISUP, MAP, etc

ISUP, TUP, MAP, TCAP

MTP-1

MTP-2

MTP-3

7

4-6

3

2

1

Control Plane

of Telecom

Network

SCCP

Figure 9 Example of incomplete stack: SS7 signalling stack

Signalling Connections Control Part (SCCP) optionally completes the L3 (CO mode for L3)

- applications :

TCAP-"Transaction Capabilities Application Part" - realizes a common general transaction service

offered to other applications


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Transaction : communication of type query/response (suitable for low volume of information

transfer)

Examples of signalling applications :

TUP - "Telephonic User Part"- telephonic call control

ISUP - "ISDN User Part" - ISDN call control

MAP - "Mobile Application Part" mobility control in GSM

All these applications use the message transport part MTP1-3in CL mode ( if they work directly over MTP 3)

in CO mode ( if they work directly over SCCP)

1.1.3.4 MPLS architecture

Packet Forwarding in IP Networks

IP forwarding is done independently at every hop

IP forwarding decision is made on:

o Packet header, Routing algorithm output (routing table)

o

Note: Searching in routing table- time consuming operation done for everypacket

Each IP hop runs its own instance of the routing algorithm

Each IP hop makes its own forwarding decisions

Figure 10 IP routing example (Cisco Systems)

MPLS ideas

Packet forwarding is done based on label switching (not IP addresses, no search in theforwarding table of routers) Labels are short allow indexed addressing- fast switching

Labels are assigned when the packets enter into the network (edge)

Assignment is result of classification at the ingress node in a MPLS domain (criteria:destination, VPN, QoS, TE, Multicast)

Labels are added in frontof the IP packets

1.1.3.4.1 MPLS IP stack


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Application

Transport TCP, UDP

Internet layer IP, ICMP, IGMP,

OSPF, etc.

MPLS sublayer

Data link layer (LLC) + MAC

Physical layer

Figure 11 MPLS oriented IP stack

IP-H TCP-H Application Data IP Datgram

MPLS-H IP-H TCP-H Application Data Labelled IP

Datagram

LABEL EXP S TTL Header MPLS

20 Bit 3 1 832 bit

Figure 12 MPLS label adding

1.2 Multiple Planes Architectures

1.2.1 Principles

Ongoing standardization : IETF, ITU-T ETSI, IEEE, 3GPP

Telecom originated layered architectures: more than one architectural plane

IETF (TCP/IP- Internet) stack originally only one plane

Nowadays- recognized the need of defining several cooperating architectural planes

Reasons: Real systems/networks deals with:

- user data flow transfer

- network resources ( paths, links, buffers, etc. ) should be controlled

- short time scale, long time scale

- high level services should be controlled (short and long time scale)

Architectural Planes

Data plane ( DPl)- transport of user data traffic directly:

o Examples of functions: traffic classification, packet marking traffic policing, trafficshaping, buffer management, congestion avoidance, queuing and scheduling

o transfer the user dataflows and accomplish the traffic control mechanisms to assurethe desired level of QoS

Control plane (CPl)

o controls the pathways for user data traffic: e.g. Admission control, Routing, Resourcereservation.


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o short term actions for resource and traffic engineering and control, including routing.In multi-domain environment the MPl and also CPlare logically divided in two sub-

planes: inter-domain and intra-domain. This approach allows each domain to have itsown management and control policies and mechanisms.

Management plane (MPl)

o the operation, administration, and management aspects of the resources and servicesto serve user data traffic: Monitoring, Management Policies (management based not

on fixed configuration of network elements but on set of rules), Service

Management, Service and network restoration.

o long term actions related to resource and traffic management in order to assure thedesired QoS levels for the users and also efficient utilization of the network resources

Examples of early multiple plane architectures (DPl + CPl + MPl):

ISDN , GSM, BISDN

- reason: telecom design philosophy (user data have been seen long time ago - from the

beginning of telecom systems as separate entities from signalling and management) data s

TCP/IP :

- Initially: mono-plane (data + control + management)

- Currently it becomes multi-plane (DPl + CPl + MPl)

New stacks- multiple plane: IEEE802.16, 3G, 4G

1.2.2 Signalling Issues

Signaling = actions performed in the control plane :

- convey application (or network) performance requirements

- reserve network resources across the network

- discover routes

- general control messages

- QoS related signalling

QoS signaling : in bandor out of band.

In band

- signalling info is part of the associated data traffic( typically presented in a particular header field

of the data packets. (e.g., the TOS field in IPv4 as in DiffServ and 802.1p)

- Performed in the data plane neither introduces additional traffic into the network nor incurs setup

delay for the data traffic.

- not suitable for resource reservation or QoS routing, which needs to be done a priori before data

transmission

- in-band signaling by definition is path-coupled (signaling nodes must be collocated with routers)

Out of band

- signalling info - carried by dedicated packets, separate from the associated data traffic. - introducesextra traffic into the network and incurs an overhead for delivering desired network performance

it entails the use of a signaling protocol and further processing above the network layer, which tends

to render slower responses than in-band signaling.


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- lends itself naturally to resource reservation or QoS routing.

- depending on whether the signaling path is closely tied to the associated data path, signaling ispath-coupledor decoupled

Path-coupled

- signaling nodes must be collocated with routers

signaling messages - routed only through the nodes that are potentially on the data path.

- advantage of reduced overall signaling processing cost (since it leverages network- layer routing

tasks)

- disadvantage of inflexibility in upgrading routers or in integrating control entities (e.g., policy

servers) not on the data path (or nontraditional routing methods)

If a path-coupled mechanism involves a signaling protocol, routers need to support the protocol and

be able to process related signaling messages

- Example of a path-coupled signaling protocol : RSVP

Path-decoupled

- signaling messages are routed through nodes that are not assumed to be on the data pathonly out-of-band signaling may be path-decoupled. (to date, most out-of-band QoS signaling schemesare path coupled.)

- signaling nodes should be dedicated and separate from routers

- advantage of flexibility in deploying and upgrading signaling nodes independent of routers or inintegrating control entities not on the data path

- disadvantage of added complexity and cost in overall processing and operational tasks.

Example: Session Initiation Protocol for VoIP, videoconference, etc.

Standardization Effort

NSIS ( Next Step in Signalling)

- Standards efforts underway specifically dealing with QoS signaling- e.g. IETFnsis working group

- developing a flexible signaling framework with path-coupled QoS signaling as its initial major

application

- a QoS signaling protocol defined under the framework - expected to address the limitations of RSVP

On path-decoupled signaling there seems not enough support in the IETF for a new project after

some explorative discussion

1.2.3 Next Generation Networks Architecture- high level view

Standardization Players ATIS NGN FG: Alliance for Telecommunication Industry Solutions, Next Generation Networks

Focus Group - USA

ITU-T NGN FG: International Telecommunication Union (Telecom), Next Generation NetworksFocus Group

ETSI TISPAN: European Telecommunications Standards Institute, Telecoms & Internetconverged Services & Protocols for Advanced Networks

3GPP: Third Generation Partnership standardization in Mobile 3G networks


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NGN

packet-basednetwork

able to provide Telecommunication multiple services

able to make use of multiple broadband,

QoS-enabled transporttechnologies service-related functionsare independentfrom underlying transport-related technologies.

enables unfettered accessfor users to networks and to competing service providers and/or servicesof their choice.

supports generalized mobilitywhich will allow consistent and ubiquitous provision of services tousers.

Key requirements of an NGN Architecture

Trust:Operator should be able to trust the network. User should be able to trust the operator

Reliability: Users should find it reliable

Availability: Network should always be available

Quality: Able to control Quality of the Service

Accountability: Determine usage of the Service Legal: Comply with laws in the local jurisdictions

GeneralizedMobilitysupport

Note: Classical Internet cannot respond in very controllable manner to the above requirements

NGN characteristics

NGN: new telecommunications network for broadband fixed access

facilitates convergence of networks and services

enables different business models across access, core network and service domains

it is an IP based network

IETFSession Initiation Protocol (SIP)will be used for call & session control

3GPP release 6 (2004) IMSwill be the base for NGN IP Multimedia Subsystem

enables any IP access to Operator IMS; from

Mobile domain

Home domain

Enterprise domain

enables service mobility

enables interworking towards circuit switched networks

maintains Service Operator control for IMS signaling & media traffic


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Transport Level

Applications andService Level

ManagementPlane

User (Data)Plane

ControlPlane

INTERNET

SCN

Figure 13 NGN Architecture

Design Principles Service is rendered in exchange for value

o explicitly requested and explicitly stopped, providing a basis for chargingo only delivered to authorized userso only saleable if QoS and security can be guaranteed

Note : Traditional Internet does not offer this!

Dedicated VoIP infrastructure is expensiveo Only a converged(packet) network that supports multiple services over one

infrastructure can be commercially viable NGN will be deployed in an unbundled environment

o Competition on service values other than price

o Support for value-added applications

Affordable multi-service architectureo Do not mix application and transport!

Support service for roaming users

o

Service provided from HOME service providero New Home Box concept

End user as content consumer and/or content provider

Service provider determines media route

o Service may include in-band media events

o Support for Lawful Intercept

o Call Routing follows the money

o QoS flows cost money so service providers will do least cost routing on it (providingQoS can be met)

Technologies are transient:NGN is technology independent !

Clear separation of Application/Services from Transport Serviceso Note that this concept is in discussion today!!

Provide a modular architectural framework which is easy to introduce and extend.

Use a meta-protocol to specify the technology and inter-working to all applicable protocols


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1.3 Business Models for (Multimedia) Communication Architectures

1.3.1 Customers and Users

Customer (CST) (may be a subscriber):- entity, having legal ability to subscribe to QoS-based services offered byProviders

(PR) orResellers (RS)

- target recipients of QoS-based services: CST/PR or CST/RS interaction- Examples of CS: Householders, SMEs, large corporations, universities or public

organisations Service Level Agreements(SLA)- concluded between CS and providers

CST differentiationby : size , type of business, type of services required

User (US)- entity (human or process) - named by a CST and appropriately identified by PR for

actually requesting/accessing and using the QoS-based services cf. SLAs- USs are end-users of the services, they can only exist in association with a CST- may be associated with one or several CST using services according to the agreed

SLAs of the respective CST. (e.g. Company = Customer, End User = employee)

Note: In the current public internet, the majority of users are subscribers for Connectivity servicesonly and maybe for a small subset of high level services (e.g e-mail)

- there is no SLA concluded for high level services quality; e.g for media A/Vstreaming, IPTV, etc.

- best effort access to high level services is practised but with no guarantees

1.3.2 Providers (PR)

PR types :

(High Level) Service Providers (SP)

IP Network Providers (NP)

Physical Connectivity Providers (PHYP) (or PHY infrastructure Providers)

Resellers (RS)

Content Providers (CP)

Network Providers (NPs)

- offer QoS-based plain IP connectivity services- own and administer an IP network infrastructure- may interact withAccess Network Providers'(ANP) or CS can be connected directly

to NPs

- Expanding the geographical span of NPs- Interconnected NPs - corresponding peering agreements- IP NPs differentiation: small ( e.g. for a city) , medium (region) and large ( e.g.

continental)

(High Level) Service Providers (HLSP or SPs)

- offer higher-level (possible QoS-based) services e.g. : e-mail, VoIP, VoD, IPTV,A/VC, etc.

- owns or not an IP network infrastructure- administer a logical infrastructure to provision services (e.g. VoIP gateways, IP

videoservers, content distribution servers)- may rely on the connectivity services offered by NPs (SPs Providers' interact with

NPs following a customer-provider paradigm based on SLAs

- expanding the geographical scope and augmenting the portfolio of the services

offered SP may interact with each other


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- size : small, medium and large

Physical Connectivity Providers (PHYP)

- offer physical connectivity services between determined locations- services may also be offered in higher layers (layer-3 e.g. IP), ( but only between

specific points)- distinguished by their target market:

Facilities (Infrastructure)Providers (FP)

Access Network Providers (ANP)(could be seen as distinct stakeholders)

FPs services- are mainly offered to IP NPs (link-layer connectivity , interconnect with their peers

FPs differentiation : size of technology deployment means

ANPs - connect CST premises equipment to the SPs or NPs equipment

- own and administer appropriate infrastructure

- may be differentiated by

- technology (e.g. POTS, FR, ISDN, xDSL, WLAN, Ethernet, WiMAX, hybrid)

- their deployment means and their size

- may not be present as a distinct stakeholder in the chain of QoS-service delivery

- may be distinct administrative domains, interacting at a business level with SPs /NPs and/or

CSTs

Interactions between Providers

- mainly governed by the legislations of the established legal telecom regulation framework- may follow a customer-provider and/or a consumer-producer paradigm on the basis of

SLAs

Reseller (RS)

- intermediaries in offering the QoS-based services of the PRs to the CSTs- offer market-penetration services (e.g. sales force, distribution/selling points) to PRs for

promoting and selling their QoS-based services in the market

- may promote the QoS-based services of the PRs either 'as they are' or with 'value-added',however adhering to the SLAs of the services as required by the 'Providers'

- interact with : CSTs on a customer-provider paradigm (SLA based)

PRs based upon respective commercial agreements..

Different types RSs:

- according to whether they introduce value-added or not- their market penetration means- size ( # of of points of presence and/or sales force)

RSs examples: Dealers, electronic/computers commercial chains, service portals

Content Provider (CP)

- an entity (organisation) gathering/creating, maintain, and distributing digitalinformation.

- owns/operates hosts = source of downloadable content- might not own any networking infrastructure to deliver the content- content is offered to the customers or service providers.


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- can contain : Content Manager(CM); several Content Servers (CS

New enties (in the perspective of Future Internet)

Virtual Network Provider (VNP)

- composes and configures and offer Virtual Network slices, i.e., a set of virtualresources at request of higher layers, as a consequence of its provisioning policy or

during self-healing operations- this approach avoids for the higher layers to establish direct relationships with

infrastructure providers and to take care of inter-domain connections at physical

layer.

Virtual Network Operator (VNO)

- manages and exploits the VNEt s provided by VNPs , on behalf of HLSPs or endusers

Note: the same organisational entity migh play the both roles :VNP and VNO

1.3.3 Multiple Plane Architecture and Business Actors

Service Plane

Control Plane

Mana ement Plane

Data Plane

CC ANP CP/CSSPNP

Inter-domain

manager

Figure 14 Exemplu de arh. generica generic multi-domeniu multi-plan

Actori de Business

High Level - Service Providers (SP)

Content Providers (CP) ( can own separate Content Servers- CS)

Connectivity Services - Network Providers (NP)

Content Consumers (CC)

Access Services - Network Providers (AC)

Fiecare actor poate avea una sau mai multe functionalitati- depinzand de rolul sau inarhitectura.

1.3.4 Service Level Agreements/Specifications (SLA/SLS)

SLA

it is a contract : documented result of a negotiation between a customer and aproviderof a service that specifies the levels of availability, serviceability, performance,operation or other attributes of the transport service


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SLA contains technical and non-technicalterms and conditions

May be established offline or online (using negotiation oriented-protocols)

Service Level Specification (SLS)

It is a part of SLA

SLS = set of technical parameters and their values, defining the service, offered by the provbiderto the customer

o e.g. service offered to a traffic stream by a network domain (e.g. Diffserv domain)

(HIGH LEVEL)

SERVICE

PROVIDER 1

USER

RESELLER

CUSTOMERIP NETWORK

PROVIDER 1

PHYSICAL

CONNECTIVITY

PROVIDER 1

PROVIDER/

OPERATOR 1

HIGH LEVEL

SERVICE

PROVIDER N

IP NETWORK

PROVIDER M

PHYSICAL

CONNECTIVITY

PROVIDER P

. . . . .

May be joined

within the same

entity

. . . . .

. . . . .

Content

Provider

USER

USER

Figure 15 Generic IP Business Model (I) - and business relationships (SLA)


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SERVICE

PROVIDER

USER

CUSTOMER

CONTENT

PROVIDER

CONTENT

MANAGER

CONTENT

SERVER

IP NETWORK

PROVIDER N

PROVIDER

1

3.n

3.23.1

2

5

6

IP NETWORK

PROVIDER N

PHYSICAL

CONNECTIVITY

PROVIDER

PROVIDER

PHYSICAL

CONNECTIVITY

PROVIDER

Data

4. Data pipe QoS guaranteed

established through actions 3.x

3.1

3.2 3.n

Cascade model

Hub model

Figure 16 Example: IP Business Models (II) - Hub model and Cascade model

1.4 Examples of Multiple Plane Architectures

1.4.1 IEEE 802.16 multi-plane stack

IEEE 802.16 : PHY + MAC

Multiple plane architecture: Data Plane(DPl), Control Plane (CPl), Management Plane (MPl)

Figure 17 Basic IEEE 802.16 multi-plane protocol stack


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Figure 18 (IEEE 802.16g-05/008r2, December 2005)

Figure 19 Relation IEEE802.16 vs. WiMAX NWG


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1.4.2 Generic Example of a multi-plane architecture

Stratum:Application

Stratum:Transport

DataPlane

ApplicationApplication Data flow-user

Inter-domainResources and traffic Mng.

Access & Core

Intra-domain

Resources and traffic Mng.Access & Core

Services and session Control

Control

Plan

Control ResurseInter & Intra domain

Service Mng. (Planning provisioning,

Offering, monitoring)Management

Plane

Control flow

Figure 20 Generic example of a multi-plane architecture

1.4.2.1 An Architecture oriented to multimedia distribution over multiple domains networksExample: Enthrone European FP6 research 2006-2008 project

End-to-End QoS through Integrated Management of Content, Networks and Terminals

Business Actors: Includes the complex business model: CP, SP, CC, NP, ANP

CC- Content consumer (Company, End users)o Customer ( org), End user

CP- Content Providero CPM content provider managero CS1, CS2, - Content Servers

SP- Service Provider (high level services)

NP- Network Provider (connectivity services)

ANP Access Network Providers


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NP3

SM&RM

Content

Provider

Content

Server

Service

Provider

NP1

SM&RM

NP2

SM&RM

Content

Consumers

SM&RM = Service Mgmt and

Resource Mgmt

Figure 21 Business actors and multi-domain infrastructure

General objectives:

to Offer high level services: Video on Demand (VoD), Streaming, E-learning, Multimediadistribution, IPTV (basically uni-directional)

over heterogeneous network technology and Over multiple independent domains

to manage, in an integrated way the whole chain of protected content handling transport anddelivery to user terminals across heterogeneous networks, while offering QoS-enabled

services

o methods of QoS control: provisioning(offline and online) adaptationof flows to network capabilities

NP1

ENTHRONE

NP2AN

Content

Consumers

Content

Provider

QoS provisioning

QoS adaptationloop

Figure 22 QoS assurance methods in ENTHRONE architecture

Multiple plane architecture:

DPl, CPl, MPl

NGN like prinnciples: separation of transport and services Creation of an service overlay over IP networks


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1.4.3 Example: Architectural stack for wireless heterogeneous mesh network

WLANS and Mesh networks

- Technology: 802.11, 802.16, 802.15

Figure 23 WLANs and Meshnetworks: a) WLAN-infrastructure; b) WLAN-ad hoc; c)

mixedmode; d) mesh network.

Notation: MP Mesh Point; STA Station; ESS Extended Set Services

Routing: - at Layer 2 ( 802.11s), or at Layer 3

Double role:Access Point andRouter

Figure 24 Examples of mesh network topologies:

a) 802.11 connected mesh; b) 802.11 mesh ad hoc


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Example: European Research Project, FP7, 2008-2011

SMART-antenna multimode wireless mesh Network

Vertical structure of the architectural stack:

Application and Service Macro-Layer (ASM)

Transport Macro-Layer (TM) (layers 1-4 in the OSI terminology)

ASM- contains applications (real-time or not real-time), which in their turn may use servicesoffered by the system (e.g. a given complex application may use, among others, a VoIP

service).

TM- abstraction of layers providing IP connectivity services, (any PHY and MACtechnologies)

This view offers a complete independency to the application and service providers withrespect to the transport infrastructure.

The application and service providers can be third parties using connectivity services providedby the Transport Macro-Layer based on agreed Service Level Agreements (SLA) betweenthem.

Applications &Services

PHY

Multimode MAC( 802.11, 802.16, ..)

ConvergenceSublayer

TCP/IP

Services andSession

Mng&Ctrl

PHY Mng&CtrlSmart Antennas and RAT Control

Data Plane Management and Control Plane

ResourceMng &Control

Coordinator

AccesControl

MobilityMng

QoS

Data Link Mng&CtrlQoS, Mobility, RR Control,

Scheduling

NetworkCoding

CrossLayer

Optimization

TransortMacro-Laer

Applicationand

ServiceMacro-Layer

DataFlows

Routing

Sec

RM&C

Figure 25 Multi-plane generic functional architecture

The architecture is horizontally divided into MPl, CPl, DPl.

The Data Plane (DPl) processes the data packets (e.g. traffic classification and conditioning,conversion, coding/transcoding, prioritizing, marking and queuing) and transfer the multimedia flows.


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At ASM level, the DPl may run mechanisms to adapt/transform media flows (fixed or scalablecoding/decoding, transcoding, compression, conversion, security operations) under the controlof some Media Control Middleware (MCM).

At TM level DPl runs all network level data flow mechanisms which directly operates on datatraffic

o and assure QoS if guarantees are required from the connectivity service offered by thismacro-layer

The Management Plane(MPl) performs essentially mid-long-term functions related to:

At ASM: management of high level services (e.g subscription, invocation, etc.)

At TM network, resources and traffic management operations.

The Control Plane (CPl)performs the short-term control functions including (at different layers):

At ASM: it accomplishes the service and session control.

At TM: PHY processing control, MAC processing, routing, mobility control, resource andQoS control, security, etc.

Further vertical decomposition can be seen in the TM

The lower layers covers Data Link layers and below. The upper layers cover the network

and traditional Layer 4 (transport).

A convergence layer will solve the compatibility with Layer 3. The MPL and CPl contains

all low-layer mechanisms for PHY/MAC usually defined in the 802.xstandards

but also custom/proprietary management and control methods/algorithms ((these are intentionally not specified by the standards in order to give freedom

to constructors to use their best know how for them).

The QoS will be assured with several levels of guarantee (depending on applicationrequirements), by considering two time scale approaches for resource management andcontrol:

provisioningfor those applications flows where future resource consumptionscan be forecasted (e.g. media distribution applications), done at aggregatedlevels based on Service Level Agreements/Specifications between entities;

per session/flow QoS controlfor dynamic call requests.

1.4.4 Control Plane in GSM (2G)

PLMN Public Land Mobile Network

MS Mobile Station

BTS Base Tranceiver Station

BSC Base Station Controller

MSC Mobile Switching Center

GMSC Gateway MSC

HLR/VLR Home Visitor Location Register

EIR Equipment Identity Register

AUC- Authentication Center

ISDN Integrated Services Digital Network

PSPDN Packet Switched Public Data Network


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EIRBSC

MS

HLR

GMSC

MSC

VLR

MSC

VLR

PLMN

AUC

ISDN/IN

PSTN

PSPDN Other PLMNs

MS

BTS

Figure 26 GSM Network General Architecture

Distribution

DTAPBSSMAP

BSSAP

MS BTS BSC

RIL3-CM

RIL3-

MM

DTAP

RIL3-

RR

I/F radio

LAPDm

4-5-

3

Distrib

Um Abis

RSM

LAPD

64 kb/s

4-5-6

3

RIL3_RR

SCCP

4-5-6

MTP1-3

Releu

LAPDm

I/F radio

4-5-6

3

LAPD

64 kb/s

4-5-6

3

RIL3_RR RSM

Relay

to MSC

anchor

Protocol MM

Protocol CM

PHY Conections

7 OSI-RM

2

1

BSS

MSC/VLR

Relay

A

SCCP

4-5-6

MTP1-3

Distribution

DTAPBSSMAP

BSSAP

RIL3-CM

RIL3-MM MAP/EMAP/G

TCAP

NSS

Figure 27 Control Plane in GSM

RIL3- Radio Interface Layer;

CM, MM, RR- Connection, Mobility, Radio Resource - Management;

Distrib distribution

RSM - Radio Subsystem Management;

DTAP- Data Transaction Application Part


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BSSAP - Base Station Subsystem Appl. Part;

BSS BS subsystem

NSS Network Subsystem

SS7 components:

MTP Message Transport Part ( SS7)

LAPD Link Access Protocol for D channel layer 2 for ISDN

LAPDm modification of LAPD for mobility

SCCP - Signalling connection Control Part (CO mode for L3)


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2 INTERCONNECTION- REVISION

(Romanian)

2.1 Moduri de lucru cu i frconexiune CO/CL

CO/CL

DTE-A DTE-B

ISa

SN3

SN2SN1

ISc

ISb DTE-C

14 3 2

n CO PDU

32

1

1CL PDU

Figura 2-1 Modul de lucru cu i frconexiune

IS Sistem intermediar; SN - subreea

- CO fiecare IS joncioneazntre ele dousegmente de circuit virtual ( Ex. ATM, MPLS)

- CL - fiecare IS ia pentru fiecare PDU o decizie de dirijare ( forwarding n mod independentde cele anterioare nu se garanteazpstrarea secvenei datelor

- Interneti poate baza transportul sau pe suporturi fizice ale altor reele der telecomunicatii (PSTN, ISDN, CATV, etc.) sau pe suportul unor reele publice de pachete de arie mare

- elemente interconectabile: sisteme de capt (hosts) , sisteme intermediare (puni,comutatoare de nivel doi, comutatoare MPLS, rutere), subreele

A B

P2

P3

P1

PPR

R R

A B

P2

P3

P1

PN

PN

PN

Telco

a b

Figura 2-2 a. Reea publiccu comutaie de pachete b. Reea Internet

PN Packet Network

2.2 Cerinele unui serviciu de interconectare (la nivel trei)

- sasigure link-uri ntre reele diferite

- adresare i rutare/dirijare prin reele diferite


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- contabilizarea utilizrii rersurselor pentru a ti starea fiecrui element de interconectare ( lanivel de element de reea; la nivel de domeniu administrativ)

- sfurnizeze serviciile de mai sus astfel nct sse poatinterconecta la reele de tipuri diferitefra modifica infrastructura interna fiecreia; deci trebuie rezolvate problemele:

- scheme de adresare diferite

- dimensiuni maxime diferite ale unitilor de date (este necesarsegmentatare/reasamblare)

- mecanisme de acces la reea diferite

- valori diferite de expirare pentru diverse temporizatoare ( timers )

- diferite metode (sau inexistente) de recuperare a erorilor

- rapoarte de stare

- tehnici de rutare diferite

- controlul accesului utilizatorilor mecanisme diferite

- mod de lucru CO/CL

NSAP_1

SNICP

SNDCP

SNDAP

DL

PHY

SNDCPSNDAP DL

PHY

SNDCP

SNDAPDL

PHY

Releu + rutare: SNICP

T

IS

ES/H

Nivel

N = 3

Retea 1 Retea 2

Figura 2-3 Architectura generica nivelului de reea

soluie pentru acomodarea diferitelor reele: divizarea nivelului reea n trei subnivele:SNICP, SNDCP, SNDAP

SNICP Subnetwork Independent Convergence Protocol

SNDCP - Subnetwork Dependent Convergence Protocol

SNDAP - Subnetwork Dependent Access Protocol (can be void)

Exemplu de SNICP: IP

2.3 Modul de lucru CO ( conexiune la nivel reea)

- faze: stabilire, meninere, eliberare de VC

- este nevoie ca toate subreelele sa cunoasca acelai protocol COpentru a putea construi VCmulti-reea

- deci presupunem cfiecare subreea oferacelai serviciu de conectivitate (de nivel trei) detip CO; rezultatul final este concatenarea unor segmente de VC (virtual circuits)

- Figura 2-4.a: - mod de lucru CO - accesul la subreele se face prin intermediul aceluiaiprotocol de reea nu este nevoie de mai multe subnivele


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- funciunile unui ruter CO :

o funcie de releu pentru unitile de date de la o reea la alta ( forwarding)

o selectarea iniiala rutei (nod cu nod) are loc n faza de stabilire a conexiunii

o fiecare ruter jonctioneazntre ele segmente de VC (conexiuni logice)

2.4 Modul de lucru CL (fara conexiune la nivel reea)

- tratare independenta fiecarei uniti de date n fiecare nod de reea (ruter)- este util a defini un protocol de reea comun, independent de diferite tipuri de subreeaparticulare: IP = SNICP (RFC 791) ; ISO 8473 Connectionless Network Protocol (CLNP) -

are funciuni similare

- accesul la subreele particulare se face prin subnivelul de adaptare dependent de tehnologiaspecific (SNDAP= N1, N2, N3; SNDCP poate fi necesar sau nu, depinde de caz)

- Figura 2-4.b exemplu de stiv

- Avantaje CL:

- robustete (datorittratrii independente a unitilor de date - datagrame);

- flexibilitate (poate lucra peste subreele CO sau CL);

- adaptare naturala la rutare dinamica

- ofercel mai potrivit serviciu pentru un nivel transport de tip CL

- Dezavantaje CL:

- Servicul nativ este frgaranii ( best effort ) relativ la band, pierderi, ntrzieri detransfer, fluctuaia de intrziere, secvenialitate

2.5 Interconectarea de tip punte (Bridge approach)

- Punte = bridge = releu de nivel MAC lucrnd n mod CL

- Nu se analizeazadresele de nivel trei

- Utilizate de regulpentru interconectare de LAN-uri


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A BSN2SN1 SN3

T

N

L1

P1

RN N

L1 L2

P1 P2

RN N

L2 L3

P2 P3

T

N

L3

P3

T

I

N1

L1

P1

I

N1 N2

L1 L2

P1 P2

I

N2 N3

L2 L3

P2 P3

T

I

N3

L3

P3

T

I

LLC

MAC1

P1

Relay

MAC1 MAC2

P1 P2

T

I

LLC

MAC3

P3

Relay

MAC2 MAC3

P2 P3

a

c

b

ISbISa

Figura 2-4 Arhitecturi de interconectare

a. mod CO b. mod CL c. Mod de lucru de tip punte ( Bridge operation)

2.6 Exemple de interconectri

Examplu 1: Conexiune FTP client-server

Client

FTP

TCP

IP

MAC1

ETH

PHY1

IP

MAC1

ETH

MAC2

TR

PHY1 PHY2

ServerFTP

TCP

IP

MAC2

TR

PHY2

Figura 2-5 Acces FTP acces ntre doureele LAN via un ruter

Examplu 2: IP peste o configuraie de subrutele: LAN-reea publicde pachete -LAN


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TCP

IP

LLC

MAC

P1

IP

X.25-3LLC

MAC

X.25-2

P1 P2

A BLAN1 LAN2WAN

X.25R1 R2

IP

X.25-3LLCX.25-2

MAC

P2 P3

TCP

IP

LLC

MAC

P3

12

3 4

786

5

1,6, 7 IP-H TCP-H Date

2, 5 LLC1-H IP-H TCP-H Date

MAC1-H LLC1-H IP-H TCP-H Date MAC1-T

8 P-H IP-H TCP-H Date

DL-H P-H IP-H TCP-H Date DL-T

9

3,4

9

Tunel X.25

Figura 2-6 Operarea protocolului Internet via reea publicde pachete (WAN ex.X.25)

Note:- avem acelai nivel IP ( SNICP) n toate sistemele ( A, R1, R2, B)- au loc ncapsulri/decapsulri succesive n timp ce PDU traverseaz in sus i in jos nivelele

funcionale (vezi figura)- se face segmentare/reasamblare daca e necesar- informatie de rutare: necesara in R1 i R2- R1 sau R2 ofera un serviciu de conectivitate nefiabil (best effort)- congestii posibile (deoarece banda unui VC este limitatn reeaua X.25)- intarziere de transfer variabil

Examplu 3: Interconectare de tip punte (distant) peste o reea de pachete


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\

3

LLC

MAC

P1

Releu

X.25-3MAC

X.25-2

P1 P2

A BLAN1 LAN2WAN

X.25B1 B2

Releu

X.25-3

X.25-2 MAC

P2 P3

3

LLC

MAC

P3

1

2

3 4 6

5

1 Data

2 LLC-H Data

3,4 MAC-H LLC-H Data MAC-T

5 X.25-H MAC-H P-H Data MAC-T

DL-H X.25-H MAC-H P-H Data MAC-T DL-T6

Figura 2-7Operarea protocolului Internet prin puni interconectate la nivel doi printr-o reeade pachete ( exemplu: X.25 WAN )

- presupunem cavem n LAN1 si LAN2 acelai MAC dei nu este obligatoriu

- diferena fa de interconectarea IP/WAN este ca in acest caz cadrele de nivel doi sunttransportate prin tunelul X.25 i nu datgramele IP

2.6.1 Interconectarea de reele LAN prin puni (B)

Interconectarea de nivel 1 ( prin repetor):o Permite extinderea distantei fizice

o Stiva arhitecturaleste aceeai n toate sistemele (nivel 1- nivel 7)

o Repetorul: obiect de interconectare de nivel fizic care regenereaza formatul electric alsemnalului

o Repetor: cost sczut, dar non-inteligent

o Efect general aceeai reea dar cu extindere pe dimensiuni fizice mai mari

o Exemplu clasic: reea Ethernet cu repetoare (Hub)

Interconectarea la nivel 2 a retelelor locale (LAN ): prin punti (B =Bridge)

- Interconectri pentru reele cu MAC diferit; LLC i nivele >2 aceleai


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Aplicatie

TCP/UDP

IP

(LLC)*

MAC1-ETH

PHY1

Aplicatie

TCP/UDP

IP

(LLC)*

MAC2 TR

PHY2

Releu (LLC partial)

MAC1-ETH MAC2-TR

PHY1 PHY2

LAN 1LAN 2

Figura 2-8 Arhitectura de interconectare prin puni

(*) n principiu LLC poate lipsi

Cadrele recepionate de ctre B pe un port (de la un segment de LAN) : memorate, verificateCRC, convertite la formatul noului MAC, redirijate

Are loc o filtrare a adreselor locale (adrese MAC)

Avantaje ale punilor (sunt mai importante dect dezavantajele)

o Memorare + retransmisie MAC1 poate fi diferit de MAC2. Exemplu : 802.3 802.5 posibile extensii gradate spre tehnologii diferite

o Elimin constrngerile de distanfizic (repetorul interconectare de nivel 1 nu faceasta)

o B este releu pe bazde adresMAC- transparent la nivele superioare

o Uureazgestionarea reelelor mai mari (dacn B se include SW de management)

o Crete securitatea reelelor (datoritfiltrrii traficului local/extern)

o Creste fiabilitatea /disponibilitatea segmentelor

o Conceptul de B se extinde imediat la comutatoare de nivel 2 ( Layer 2 switch)

o Permit crearea de LAN-uri virtuale (VLAN) foarte important in practic

Dezavantaje ale punilor (Problemele de principiu greu rezolvabile/netriviale)

o Lungime diferitde cadre

o Lucru diferit cu prioriti

o Incompatibilitate ntre valorile timerelor utilizate

o probleme de gestiune a configuraiei mixte

Alte probleme:

- lipsa de control de flux la nivel MAC posibilitatea suprancrcrii memoriei din B

- memorare + retransmisie ntrzieri mai mari dect la interconectarea repetoare

- probleme cu expirri de timere n MAC-uri diferite dacdistana este mare

- modificarea cadrelor la traversarea B + calculul pentru noul CRC erori eventuale n timpultranslatrii (releu) care rmn nedetectate

Concluzii : avantajele sunt mai mari dect dezavantajeleB utilizate foarte frecvent ( azi subformde comutatoare de nivel 2)

Exemple de standarde:

IEEE 802.1 - puni transparente


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IEEE 802.5 conine o parte referitoare la B cu rutare de tip surs

2.6.1.1 Puni transparente (Transparent Bridges- TB)Caracteristici generale

prezena n reea a (n>1) puni - transparena pentru staiile ce intercomunic

TB- se iniializeaz i configureaz automat la introducerea n reea (fro intervenie specialdin partea restului reelei)

reconfigurarea dinamicn timpul funcionrii

sunt prevzute cu n 2 porturi pentru n 2 LAN-uri

fiecare port are chip-set-uri MAC corespunztoare tipului de LAN i SW de gestiunecorespunztor

( SW initializeazchip-set-ul; gestioneazmemoria (buffere) alocbuffere pentru chip-setMAC dinMAC de recepie ; paseaz buffere pline spre chip-setMAC de transmisie ).

Extensie 1: comutatoare de nivel 2 ( punti cu n > 2 porturi) eventual cu tehnologii diferite

Extensie 2 : VLAN

2.6.1.2 Punti cu rutare de tip sursa Punti transparente : B participa in mod colectiv la rutare intr-un mod transparent pentru

statii . Statiile comunica intre ele ca i cum ar fi pe acelasi LAN.

Punti cu rutare sursa : statia src include in cadrele emise informatii de rutare pana ladestinatie . Info- rutare in antetul cadrului folosita de punti pentru rutare (fiecare B

determina daca acel cadru trebuie dirijat spre alt segment sau nu)

Informatia de rutare = secventa de perechi ( S- B ) unde S= segment ( adresa LAN) B= idpunte

Observatie Rutarea sursa se utilizeaza in special in IEEE 802.5 ( fiind o parte a acestuistandard) Exemplu cadru 802.5


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3 ROUTING PROTOCOLS

(Romanian + english)

Not complete

3.1 Algoritmi de rutare -sumar

Protocol de rutare = algoritm + mecanism de schimb de nesaje intre nodurile retelei

Retea-abstractizata printr-un graf orientat/neorientat

A

D

C

B2

12

1

3

1

asimetric

asimetric

Figura 3-1 Exemplu simplu de graf orientat

G(V,E); V- set de noduri; E edge set set de link-uri

Ponderi/costuri asociate link-urilor

Problema de rutare: gasirea unui arbore cu cost minim de la orice nod considerat ca sursa catre oricenod considerat ca destinatie

- costul oricarei cai = minim ( SPT = Shortest path tree)

- cost total al arborelui = minim (arbori de tip Steiner)

Clasificarea algoritmilor de rutare

- Centralizati /distribuiti/ de tip mixt

Criterii de cost/metrica:

- metrica simpla (1 criteriu)

- compusa mai multe criterii

Exemple de metrici:

- statice: nr. de noduri traversate, 1/Banda_link, cost administrativ, cost total al unui arbore,

- dinamice ( costul se modifica odata cu incrac area retelei cu trafic): grad de incarcare a unuilink, intarziere pe link/ ruta, numar mediu de erori de transmisie per link

Obs: n>1 metrici => probleme NP - complete; se cauta solutii aproximante quasi-optime

Se poate demonstra in unele cazuri particulare care este departarea (procentuala - d.p.d.v al costului

obtinut) unei solutii aproxiomative fata de optimul teoretic.


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Exemple de grafuri:

2 5 8 11

3

7

9

10

4

6

M= {1,5,6,9,11}

Cost/link =1

S

a.

Network graph

1

2 5 8 11

3

7

9

10

4

6

M= {1,5,6,9,11}

Cost/link =1

S

b.

Shortest Path Tree (SPT)

Source Specific Tree

C = 8

Dmax = 3

Dav =2.5

1

Figura 3-2 Exemplu de graf si SPT

M= submultime de noduri inregistrate la un grup de multicast

2 5 8 11

3

7

9

10

4

6

M= {1,5,6,9,11}

Cost/link =1

S

Group Shared Tree

Example of Steiner Tree

1

Figura 3-3 Arbore Steiner- exemplu


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Steiner Tree Problem in Networks (SPN) - NP-complete problem

Given: G = (V,E) undirected

M = multicast group included in V

cuv = cost of link (u,v); u,v V

Required: t = (VT, ET), which spans M so that

imumcT

uv

Evu

min),(

=

Steiner nodes = nodes u,v VT but they do not belong to M

Example

Steiner nodes= {4,7}

M = {1,5,6,9,11}

CT = 6 !! less than in SPT

DSav = (2 + 3 + 4 + 3)/4 = 12/4 = 3

Greater than for SPT!!

Constrangeri:

Constraints to a link (e.g bandwidth, available buffer, etc.). to a path or to the whole tree,

Tree constraints can be( m = metric) additive (e.g.

E2E delay on every path from source to destination number of hops 1/B_link

m(u,v) = m(u,i) + m(i,j) + m(pv), for a path P( u,i,j, ..v) Sum of the costs on all edges of the tree

multiplicative ( e.g : m= the probability that a packet will reach thedestination, being given the correctness probability on each link)

m(u,v) = m(u,i) *m(i,j) * m(pv), for a path P( u,I,j, ..v)the cost of the path could be expressed as [1- m(u,v)] concave (e.g. minimum bandwidth on a chain of links on a path)

m(u,v) = Min{ m(u,i), m(i,j), m(pv)}, for a path P( u,I,j, ..v)

Moduri de lucru ale protocolului:

- Proactiv


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o Algoritmul lucreaza in permanenta ( background) si caluleaza rute;

o Info de rutare exista in permanenta in tabelul de fwd.

o Rutele pot sa nu mai fie actuale daca intervalul temporal de calcul e mare incomparatie cu modificarile de topologie sau costuri ( ex. retele cu mobilitate)

o Daca perioada de calcul este f. Micaatunci rezulta un overhead cu trafic de control

- Reactiv ( on demand) o ruta se caluleaza la cererea unei statii

o

De ex. in retele ad-hoc- De tip mixt

o Alg. Poate rula in stil proactiv in anumite conditii si in mod reactiv in altele

Clasificare d.p.d.v cunoasterea topologiei:

- vectori de distanta (distance vector)

o un nod nu cunoaste topologia completa a retelei ci numai informatii de tip distanteintre anumite puncte

- cu stari ale link-urilor (link state)

Probleme suplimentare in calculul rutelor:

- mobilitatea;

- inteferente in radio;

- refacerea rutelor deteriorate

- problema link-urilor asimetrice

- problema cailor diferite in cele doua sensuri.

Caracteristici dorite ale protocolului: convegenta, optimalitate, complexitate redusa, robustete,extensibilitate, echitate, fiabilitate, etc. (unele sunt contradictorii)


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S2

S1

R4

R3R2

R1 R5

RP

S2

S1

R4

R3R2

R1 R5

S2

S1

R4

R3

R2

R1 R5

Unidirectional treeOne tree per source

S1 rooted tree (SPT)S2 rooted tree (SPT)

Optimised for source specific mccommunication

Unidirectional Shared(by all sources) treeComponents:

Shared tree

Data path S1RP

Data path S2RP

Bidirectional Shared TreeDistribution of S1 dataDistribution of S2 data

Figura 3-4 Exermple de tipuri de arbori

3.2 Algoritmi de baza pentru cautarea celui mai scurt drum

- Retea- echiv cu un graf- Caut drumul cel mai scurt intre doua noduri d.p.d.v cost- Cost de tip aditiv proportional cu cu : nr. Noduri/dist./t. intarziere/ inversul benzii

i

k1

k2

Figura 3-5 Cautarea drumului minim intre nodurile i si j (graf simplificat)

dij min= min { dik+ dkj}

k


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unde k este un nod oarecare prin care exista drum spre nodul j.

3.2.1 Algoritmul Dijkstra (centralizat)

Se cauta toate drumurile minime de la un nod sursa catre toate celelalte. Rezulta un arbore de

acoperire cu radacina in nodul sursa.

Se repeta alg. ptr. fiecare nod al retelei.

- date de intrare : lista nodurilor, lista interconectarilor, costurile link-urilor.

Algoritm:

Fie un nod A

Se construieste arborele drumurilor minime cu radacina in A extinzandu-l succesiv pana ce toate

nodurile apartin arborelui.

Notatii:

Fie v, w, noduri ale grafului

D(v) = distanta intre A si nodul v ( suma costurilor pe un drum intre A si v)

l (v, w) = distanta ( costul arcului) intre v si w

N = multimea nodurilor din arbore

Nota : alg se poate aplica in principiu pentru grafuri orientate sau nu.

A

D

C

B

2

12

1

3

1

Graf initial

(orientat)

A

D

C

B

2

12

3

Graf orientat pentrucalculul unui arbore cu

radacina in sursa A

Figura 3-6 Exemple de cazuri pentru grafuri neorientate sau orientate

Algoritm de baza pentru graf neorientat

1. Initializare:

N={A}

Ptr. vNse eticheteaza nodul vastfel : v(NH,D(v)), unde NHeste (next hop) nodul dinarbore prin care vare acces spre A.

In particular avem:

v(A, D(v)) pentru nodurile legate direct la A


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v(-, ) pentru nodurile care nu sunt legate direct la A

2. Se completeaza arborele cu un nod nou , astfel:

- se cauta wN, pentru care D(w)= minim

- N= N {w} se include in arbore nodul w- Se reeticheteaza fiecare vecin v(care nu apartine lui N) al lui w, prin recalcularea dist. la

Atinand seama de noul nod inclus in arbore , astfel:

D(v) = min{ D(v), D(w) + l(w, v)},

v N, v V(w)

unde V(w)este multimea vecinilor lui w. Ca urmare a reetichetarii, NHdin eticheta v(NH, D(v)):

- va ramane NH ( valoarea care era deja)

- sau va deveni w daca prin w se obtine un nou drum mai scurt spre A.

3. Se repeta etapa 2 pana ce toate nodurile apartin arborelui.

Exemplu:


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A

B(A,1)

D(A,3)

C(A,6)

E(-,)

1 1

3

6

3

1

24

Initial: N={A}

A

B(A,1)

D(B,2)

C(D,4)

E(D,5)

1 1

3

6

3

1

24

Pas (2): N= {A,B,D}

Se adauga D

A

B(A,1)

D(B,2)

C(B,5)

E(-,)

1 1

3

6

3

1

24

Pas 1: N={A,B}

Se adauga B

= dist. recalculate

V(B) C (N)C (N)= complement al

lui N

A

B(A,1)

D(B,2)

C(D,4)

E(D,5)

1 1

3

6

3

1

24

Pas (3): N= {A,B,D,C}

Se adauga C

A

B(A,1)

D(B,2)

C(D,4)

E(D,5)

1 1

3

6

3

1

24

Pas (4): N= {A,B,D,C, E}

Se adauga E

Arbore de drumuri minime

de la A la B,C,D,E

costuri

Figura 3-7 Exemplu de calcul pentru algoritmul Dijkstra

Arborele de dirijare pentru nodul A va fi cel din tabelul de mai jos :

Destinatia Nodul urmator

B B

C B

D B

E B


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3.2.2 Algoritmul Ford (Fulkerson)

- cauta drumurile de cost minim- nodul radacina ( fie A) este considerat ca destinatie- rularea algoritmului este gata

- dupa etichetarea tuturor nodurilor cu dist. fata de A si cu eticheta noduluiurmator pe drumul cu cost minim catre A

- constructia tab. rutare = repetarea alg. pentru fiecare nod destinatie.

Eticheta are aceeasi forma ca la alg Dijkstra . Ex B(5, C) este eticheta nodului B care arata cadistanta pana la A este 5, via nodul vecin C

1. Initializare

Fie nodul A = destinatie, D(A) = 0.

Se eticheteaza toate celelelte noduri cu ( -, ).

2. Etichetarea tuturor nodurilor cu distantele minime pana la A

Pentru nod v A executa:

- actualizeaza distantele D(v) pana la destinatia A, pentru fiecare nod, prin utilizarea

valorilor curente D(w) ale tuturor vecinilor w ai lui v, adica pentru toti w V(v). Se face

atribuirea:

D(v) = min{D(w) + l(w,v)}

w V(v)

- se actualizeaza eticheta de nod cu nr. nodului vecin care minimizeaza expresia demai sus si cu noua distanta D(v).

3. Repeta etapa 2 pana cand nu mai apar modificari.

v

w

t

u

A

duA

dtA

dwA

lau

lat

law

Comparatie:

(lau+ duA) < > (lat+ dtA) < > (law+ dwA)

Vv

Figure 28 Actualizarea distantelor lui v fata de A

Exemplu problema.

1.Sa se determine arborele drumurilor minime in raport cu nodul A ptr. reteaua din fig.

1. Sa se scrie tab de rutare din nodul A pentru host-urile Hi, I < > 1.2. Folosind drumurile de lungime minima sa se aloce numere de circuite virtuale pentru

conexiunile (solicitate temporal in ordinea data) H1 - H7, H3 - H7, H2 - H6, H1 H6,

H1 H5.


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B

A

C

D F

G

E

H1

`

H3`

H6`

H7

`

H2

H4

12

1

22 3

4

4

8

3

7

H4

V( B)

Figure 29 Configuratia retelei. Nodul A este destinatie.

Lista etichetelor initiale

B C D E F G

(-, ) (-, ) (-, ) (-, ) (-, ) (-, )

Pasul 1.1 : v = B

Nod w D(w) l (v,w) D(w) + l (v,w) Noua eticheta

ptr. nodul B

A 0 1 1

C 1

D 2

(A, 1)

Lista etichetelor dupa pasul 1.1

B C D E F G

(A,1) (-, ) (-, ) (-, ) (-, ) (-, )

Pasul 1.2 : v = C


ptr. nodul C

A 0 2 2 (A, 2)


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B 1 1 2

D 3 *

F 3 *

G 2 *

* = se poate inlocui cu x ( nu conteaza)


B C D E F G

(A,1) (A,2) (-, ) (-, ) (-, ) (-, )

Pasul 1.3 : v = D


ptr. nodul D

B 1 2 3

C 2 3 5

G x

(B,3)


B C D E F G

(A,1) (A,2) (B,3) (-, ) (-, ) (-, )

Pasul 1.4 : v = E


ptr. nodul E

A 0 7 7

G x

(A,7)


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B C D E F G

(A,1) (A,2) (B,3) (A,7) (-, ) (-, )

Pasul 1.5 : v = F


ptr. nodul F

C 2 3 5

G x

(C,5)


B C D E F G

(A,1) (A,2) (B,3) (A,7) (C,5 ) (-, )

Pasul 1.6 : v = G


ptr. nodul G

C 2 2 4

D 3 8 11

E 7 4 11

F 5 4 9

(C,4)


B C D E F G

(A,1) (A,2) (B,3) (A,7) (C,5) (C,4)

Repetand pasul doi se constata ca nu mai apar modificari.

Atentie: rezolvarea completa presupune si terminarea pasului 2 ( adica 2.1 2.6).


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B

A

C

D F

G

E

H1

H3

H6

H7`

H2

H4

12

1

22 3

4

4

8

3

7

H4

Figure 30 Arborele drumurilor minime pana la nodul A

Tabelul de rutare pentru nodul A este :

Destinatia Ruta ( via) Cost

H2 B 1

H3 C 2

H4 B 3

H5 E 7

H6 C 5

H7 C 4

Algoritmul se repeta pentru fiecare nod pentru care se construieste tabelul de rutare.

3.3 IP Routing Protocols

3.3.1 Internet Protocol reminder

- connectionless style, RFC 791- official specification of IP

- best effortprotocol no guarantees- problems for real time traffic- if problems appear rejection of datagrams (IP-DGs)

- functions:

- segmentation / reassembly(segmentation at the input of

first subnetwork and reassembly only at the end destination machine)

- routing hop-by-hop principle

-error reporting

IP services


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- two service primitives :send( ), deliver( )

- primitive parameters:

-sourceanddestination IP addresses ( IPa_src, IPa_dst)

-protocol ( recipient of IP-DGs)

-type of service indicator specifies data treatment

- identifier used in combination with IPa_src, IPa_dst and protocol field to uniquelyidentify data unit

-dont fragment segmentation indication

-time to livelife time of DGmeasured in network hops

- data length length of data being transmitted

-optional data option request by the IP user

- security allow a security label attached to IP-DG

- source routing list of routers

- route recordingfield allocated to record the sequence of routers

- stream identification names reserved used for stream service

- time-stamping source IP entity and some or all intermediate routers add a

timestamp ( precision - ms) to the data unit

-data data to be transmitted

IP Service quality options

- precedence eight levels of importance (3 bits)

- reliability two levels (normal / high)

- delay two levels ( normal/high)

-throughputtwo levels ( normal/high)

Note ToS has been re-defined in the DiffServ Technology as DSCP = DiffServ Code Point

showing the packet priority

IP v4 Datagram format

- version indicates version number

-Internet header length (IHL) in 32 bits words; (minimum IP-H 20 octets)

-type of service precedence, reliability, delay, throughput

-identifier ( 16 bits) together with IPa_src, IPa_dst uniquely identifies the IP-DG

-flags ( more bit, dont fragment bit) used in segmentation

-fragment offset ( measured in 64 bit units) used in segmentation

- time to live (TTL) measured in router hops


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0 4 8 16 31

Version IHL Type of service Total length ( in octets)

Identification Flags Fragment offset

Time to live (TTL) Protocol Header checksum

Source IP adress (x1.y1.z1.w1)

Destination IP adress (x2.y2.z2.w2)

Options

Information

20

oct.

Figure 31 IP datagram format

-protocol indicates the higher level protocol

- header checksum- error detecting code for header only re-verified at each router (1

complement addition of all 16 bit words in IP-H)

- options (variable) encodes the options requested by the user-padding to assure multiple of 32 bits

-data field integer multiple of 32 bits, 65 535 octets

3.3.2 Principles of IP routing

- if source and destination are on same local network then IP-DG sent arrives directly to the

destination ( broadcast medium or serial line)

- if not, the IP-DG is sent to a router charged to forward the IP-DG (based on forwarding

tables) - to another router (next hop) up to the destination

- forwarding table is consulted for each IP-DG

- routing protocolsare executed to build the routing tables

- one may have several routing tables(RT)

- one of them is selected asforwarding table(FT)

- if there is only one routing table thenthe two are the same

- usual principle of routing: hop by hop

- one machine can be configured to function as a router also ( that is to retransmit the received

IP-DGs which are not addressed to itself)

one entry in the routing table (RT/FT) :

-IPa_dst- destination IP address (machine addr. or network addr.)

- next hop routeraddress or an address of a network directly connected

-flags - indicates ifIPa_dst belongs to a machine or a network, etc.

- interface specification of the output I/F where the IP_DG must be sent

IP forwarding operation

- search best matchin RT (actually FT) of an entry corresponding to:


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- full destination address (if found then route to next hop router or to I/F directly

connected ( depending on flags)

- or,destination network address(prefix) - similar actions

- ordefault entry

UDP TCPnetstat

command

route

command

Routing

protocoldemon

packet for

this dest?

ICMP

IP process

options

forwarding

(compute

the next

hop)

Routing

table

Source routing

yes

Retransmission

(if valid)

no

update

redirection

Network interfaceIP layer

Figure 32 IP actions on the received datagrams

3.3.3 Network hierarchies


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Figure 33 Internet global view

3.3.3.1 Multi-Tier hierarchyThe Internet today operates as a hierarchy

Thousands of small, local, regional and small country ISPs operate at the bottom of an Internet

pyramid.

These operators typically have to pay for access to the networks and customers operated by largerISPs.

At the middle of the pyramid are several dozen Tier-2 ISPs that typically pay to transit the networks of

the largest ISPs.

Tier-2 ISPs seek to interconnect on a "peering" basis with other, Tier-2 ISPs.

At the top of the pyramid are a handful of Tier-1 ISPs that typically peer with other Tier-1 ISPs.


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Figure 34Hierarchical Structure of the Internet

The diversification of ISPs has increased the number of locations where ISPs exchange traffic.

When the Internet comprised a small number of Tier-1 ISPs, these ventures could exchange traffic atrelatively few locations.

Over time the number of network interconnection points has grown.

These interconnection points are commonly referred to as Internet Exchange Points (IXPs).

The increased number of IXPs results from:

The proliferation of ISPs, and

The fact that many ISPs now operate networks within only a small geographic area.

With more networks lacking complete national and international coverage, more ISPs need to

interconnect with and access the transit services of other ISPs.

IXPs enable even small, regional ISPs to offer global Internet access to their subscribers.

3.3.3.2 Autonomous System DefinitionThe current Internet is a decentralized collection of computer networks from all around the

world. Each of these networks is typically known as adomain or an autonomous system (AS)

AS = network or group of networks under a common routing policy, and managed by a single

authority.

Today, the Internet is basically the interconnection of more than 20,000 ASes [4].

Intra-domain routing:Every one of these ASes usually uses one or more interior gateway protocols

(IGPs), such as Intermediate System to Intermediate System (IS-IS) or Open Shortest Path First(OSPF), to exchange routing information within the AS.

Inter-domain routingfocuses on the exchange of routes to allow the transmission of packets betweendifferent ASes.


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Single-homed

stub AS

Multi-homed

stub AS

Transit AS

Tier-1, Tier-2Tier-3

Figure 35 A simplified inter-domain scenario

When an AS is connected to multiple different ASes, it is referred to as a multihomed AS.

Types: single-homed, multi-homed, transit AS. Note a transit AS could be sometimes considered as

multi-homed stub AS. ( e.g. AS 2).

3.3.3.3 ASes and TiersTodays Internet : hierarchy of transit ASes .

This hierarchical structure consists in two different types of relationships that could exist betweenASes ( SLA can be established between them)

- customer-provider- peer-to-peer

Thus, for each transit AS any directly connected AS is either a customer or peer.

Level 1:the top of this hierarchy we found the largest ISPs, (Tier-1 ISPs).- There are about 20 Tier-1s at present which represents less than 0.1 percent of the total

number of ASes in the Internet- Tier-1s are directly interconnected in almost a full meshand compose the Internet core. In

the core all relationships between Tier-1s are peer-to-peer, so

a Tier-1 is any ISP lacking an upstream provider.

Tier 1 ISPs key attributes of. They:

have access to the entire Internet routing table through their peering relationships.


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have one or two AS numbers per continent or, ideally, one AS worldwide.

own or lease international fiberoptic transport.

deliver packets to and from customers and to and from peers around the world.

Global tier 1 ISPs have two additional characteristics:

They peer on more than one continent.

They own or lease transoceanic fiberoptic transport

Second levelof the hierarchy is composed of

Tier-2 ISPs ( national ISPs)- A Tier-2 is any transit AS that is a customer of one or more Tier-1 ISPs

- A representative example of a Tier-2 ISP is a national service provider. Tier-2 ISPs tendto establish peer-to-peer relationships with other neighboring Tier-2s for both

economical and performance reasons

(SLA-s can be negotiated)- This is typically the case for geographically close Tier-2 ISPs that exchange large

amounts of traffic.-

Tier-3 ISPs : those transit ASes in the hierarchy that are customers of one or more Tier-2 ISP ,such as regional or local ISPs within a country.

Stub ASes are non-transit ASes that are customers of any ISP (Tier-1, Tier-2, or Tier-3)

Example:In Figure 36

- ISPs such as AS11, AS12, AS21, AS23, and AS31 would be classified as Tier-2 ISPs,- while AS22 represents a Tier-3 ISP.

An important corollary of this hierarchical structure is that the diameter of the Internet is verysmall in terms of AS hops.

3.3.4 General definitions

Hierarchy:- backbone network, - autonomous systems, - networks, subnetworks, hosts

- Autonomous System(AS) ( Domain) logical portion of larger IP networks administeredby a sin

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