ee 706: computer communication networksmazum/ece610/networking.pdf · 2005-11-24 · the bit...

EE 706: ComputerCommunication Networks

Networking Technologies

D. [email protected]

IIT-Bombay

Manjunath: Computer Communicatin Networks – p.1

Networking

� Information technology is as much aboutmanipulating information as about moving ortransporting information.

Networking deals with Information Transport.More specifically, the mechanisms that governthe sharing of the resources in the bit carrierinfrastructure.


Networking

� Information technology is as much aboutmanipulating information as about moving ortransporting information.

� Networking deals with Information Transport.More specifically, the mechanisms that governthe sharing of the resources in the bit carrierinfrastructure.


Technology: Discussion Outline

� Identify functional elements ofnetworking—Multiplexing, Switching, Routingand Management.

Current practice in networking where we describethe Bit Carrier Infrastructure and the seven layerISO-OSI model for networking.

Finally, an overview of the three dominantnetworking technologies—Telephone Network,Internet and Asynchronous Transfer ModeNetworks.

Quick overview of ‘other’ networks like X.25 andFrame Relay.




� Current practice in networking where we describethe Bit Carrier Infrastructure and the seven layerISO-OSI model for networking.

Finally, an overview of the three dominantnetworking technologies—Telephone Network,Internet and Asynchronous Transfer ModeNetworks.






� Finally, an overview of the three dominantnetworking technologies—Telephone Network,Internet and Asynchronous Transfer ModeNetworks.






� Finally, an overview of the three dominantnetworking technologies—Telephone Network,Internet and Asynchronous Transfer ModeNetworks.

� Quick overview of ‘other’ networks like X.25 andFrame Relay.


Preliminaries

� Points at which networked information servicesconnect to generators and absorbers ofinformation flow, called sources and sinksrespectively

Example sources: telephone transmitters, videocameras, file on a disk, etc

Example sinks: telephone receivers, videomonitors, storage devices,

source/sink

source/sink

source/sink

source/sink

source/sink

source/sink

distributedinformation applications


Preliminaries


� Example sources: telephone transmitters, videocameras, file on a disk, etc

Example sinks: telephone receivers, videomonitors, storage devices,

source/sink

source/sink

source/sink

source/sink

source/sink

source/sink



Preliminaries


� Example sources: telephone transmitters, videocameras, file on a disk, etc

� Example sinks: telephone receivers, videomonitors, storage devices, � � �

source/sink

source/sink

source/sink

source/sink

source/sink

source/sink



A Layered View

Bit Carrier Infrastructure

Resource Sharing Mechanisms

sources and/or sinksnetworked applications

Common Information Services

Multiplexing, scheduling, routing,network management

Information Services

Communication Links

infrastructure and traffic flow:

buffering, jitter removal, etc.browsers, source compression, storage,User interfaces, transducers, servers,

Dynamic and intelligent control of

"NETWORKING"

WDM, Optical Crossconnects, SDH, DSL,"cable", Ethernet, satellite, fixed or mobilewireless links

A three-layered view of a communication network.“Networking” is concerned with resource sharingmechanisms that efficiently share the bit carrierinfrastructure, and control the quality of serviceprovided to the various applications using the network


A Layered View

� A layered view helps in identifying anddistinguishing different classes of functions.

Similar to the concept of subroutines or functionsin programming.

Three layersInformation Services LayerBit Carrier Infrastructure Layer“Networking” Layer


A Layered View


� Similar to the concept of subroutines or functionsin programming.

Three layersInformation Services LayerBit Carrier Infrastructure Layer“Networking” Layer


A Layered View



� Three layers

Information Services LayerBit Carrier Infrastructure Layer“Networking” Layer


A Layered View



� Three layers

� Information Services Layer

Bit Carrier Infrastructure Layer“Networking” Layer


A Layered View



� Three layers


� Bit Carrier Infrastructure Layer

“Networking” Layer


A Layered View



� Three layers


� Bit Carrier Infrastructure Layer

� “Networking” Layer


Information Services LayerH/W and S/W to facilitate the transport serviceand attach the source and sink.

� Encode information from source into atransportable form and decode receivedinformation into usable form.

ExamplesVoice coding, packet buffering and playout,and voice decoding for packet telephony;Mail preparation and forwarding software forelectronic mail;Browser for the WWW.




� Examples

Voice coding, packet buffering and playout,and voice decoding for packet telephony;Mail preparation and forwarding software forelectronic mail;Browser for the WWW.




� Examples

� Voice coding, packet buffering and playout,and voice decoding for packet telephony;

Mail preparation and forwarding software forelectronic mail;Browser for the WWW.




� Examples

� Voice coding, packet buffering and playout,and voice decoding for packet telephony;

� Mail preparation and forwarding software forelectronic mail;

Browser for the WWW.


Information Services Layer

� Handle network induced imperfections—loss,delay, delay variations

Define the allowable imperfections from thenetwork—Quality of Service (QoS) as statistical(mean, percentiles) or deterministic (bounds)guarantees

Example QoS measures: service denial(blocking), delay, delay variations, loss,reordering, etc.




� Define the allowable imperfections from thenetwork—Quality of Service (QoS) as statistical(mean, percentiles) or deterministic (bounds)guarantees

Example QoS measures: service denial(blocking), delay, delay variations, loss,reordering, etc.




� Define the allowable imperfections from thenetwork—Quality of Service (QoS) as statistical(mean, percentiles) or deterministic (bounds)guarantees

� Example QoS measures: service denial(blocking), delay, delay variations, loss,reordering, etc.


Bit Carrier InfrastructureThe raw material for building the informationtransport superstructure.

� The issues here are those from a classicalcommunication course—modulation, capacity,channel coding, medium characteristics, etc.

Reasonable to assume that the channel is digital.

We assume that the communication links areimperfect bit pipes in the sense that these pipescan delay, lose or modify the bits that they carry.




� Reasonable to assume that the channel is digital.

We assume that the communication links areimperfect bit pipes in the sense that these pipescan delay, lose or modify the bits that they carry.




� Reasonable to assume that the channel is digital.

� We assume that the communication links areimperfect bit pipes in the sense that these pipescan delay, lose or modify the bits that they carry.


NetworkingUses the raw material of communication links andprovides the networking services that the informationservices assumes.

� The link design problem is concerned with the bitflow—extract the maximum bit rate possible,Networking is concerned with information flow.


Computer System Analogy

DistributedInformation Applications

DistributedAlgorithms for

Information Transport(e.g., X.25, Internet, ATM)

Applications

ComputerOperating System

(e.g., Unix, Linux, Windows)

disk drives, sound card)

analogy with the operating systemof a computer

Communication Links

Network of

Hardware

(e.g.,calculation, accounting, database)

(e.g., processor, memory,

(e.g., www, e−commerce, teleconf)

Networking is concerned with distributed algorithmsfor efficient sharing of bit carrier network resources.Very similar to OS of a computer helping applicationsto use and share hardware resources.


Functional Elements

� Consider a sample information flow.

After source prepares the bits for transportation,“network” decides how to route flow overphysical network.

Infrastructure is shared by many such flows.Hence network has to decide how to multiplexedthis flow with other flows.

Flow may traverse multiple links. At junction oftwo links, switch flow elements to target link.

Need to monitor network behaviour and collectstatus information; possibly handle situations forwhich network is not engineered. i.e., performnetwork management.


Functional Elements


� After source prepares the bits for transportation,“network” decides how to route flow overphysical network.

Infrastructure is shared by many such flows.Hence network has to decide how to multiplexedthis flow with other flows.




Functional Elements



� Infrastructure is shared by many such flows.Hence network has to decide how to multiplexedthis flow with other flows.




Functional Elements




� Flow may traverse multiple links. At junction oftwo links, switch flow elements to target link.



Functional Elements




� Flow may traverse multiple links. At junction oftwo links, switch flow elements to target link.

� Need to monitor network behaviour and collectstatus information; possibly handle situations forwhich network is not engineered. i.e., performnetwork management.


Multiplexing

� Communications links or bit pipes are expensiveresources and possibly imperfect.

Need to amortise cost among a large number ofsources—need mechanism to share efficiently.

Assume information flow requirements—sourceand destination and capacity required, is a time avarying process.

Sharing the communication link ismultiplexing—technique used for systematicallymerging several data flows into one bit-pipe.

Two types of multiplexing:Circuit multiplexing.Packet multiplexing.


Multiplexing


� Need to amortise cost among a large number ofsources—need mechanism to share efficiently.

Assume information flow requirements—sourceand destination and capacity required, is a time avarying process.




Multiplexing



� Assume information flow requirements—sourceand destination and capacity required, is a time avarying process.




Multiplexing




� Sharing the communication link ismultiplexing—technique used for systematicallymerging several data flows into one bit-pipe.



Multiplexing





� Two types of multiplexing:

Circuit multiplexing.Packet multiplexing.


Multiplexing






� Circuit multiplexing.

Packet multiplexing.


Multiplexing






� Circuit multiplexing.

� Packet multiplexing.Manjunath: Computer Communicatin Networks – p.13

Circuit Multiplexing on a Link

� Link capacity is statically partitioned intochannels (possibly differentcapacities)—Frequency, Time, Space and CodeDivision Multiplexing.

Standards specify partitioning details, e.g.,CCITT and North American standards for TDM.

Each conversation (flow) is allocated to a channelfor the entire duration of call—the call holds thechannel.

Connection setup is required to allocateresources.

Fixed rate allocated at time of connection setupdetermines the peak rate at which the source cantransmit data.




� Standards specify partitioning details, e.g.,CCITT and North American standards for TDM.

Each conversation (flow) is allocated to a channelfor the entire duration of call—the call holds thechannel.







� Each conversation (flow) is allocated to a channelfor the entire duration of call—the call holds thechannel.








� Connection setup is required to allocateresources.







� Connection setup is required to allocateresources.

� Fixed rate allocated at time of connection setupdetermines the peak rate at which the source cantransmit data. Manjunath: Computer Communicatin Networks – p.14

Circuit Multiplexing on a Link(contd)

� A call (request for resources) can be blocked if allthe channels are busy.

Performance measures: Connection setup delayand call blocking probability.

A typical design problem: What should be thelink capacity for a given load and specifiedblocking probability.

The link may also have to handle different classesof flows each with a different blockingprobability requirement.




� Performance measures: Connection setup delayand call blocking probability.

A typical design problem: What should be thelink capacity for a given load and specifiedblocking probability.






� A typical design problem: What should be thelink capacity for a given load and specifiedblocking probability.






� A typical design problem: What should be thelink capacity for a given load and specifiedblocking probability.

� The link may also have to handle different classesof flows each with a different blockingprobability requirement.


Circuit multiplexing: ResourceAllocation Model

time

link c

apacity

channelslink

Static partitioning of bandwidth in a circuit switchednetwork


Circuit Multiplexing Ineffi-ciency

� Most sources generate data in bursts:

Voice: Talk and silence spurtsVideo: Scene changesTelnet: Typing behaviourWeb browsing patterns: Think times betweendownloads




� Voice: Talk and silence spurts

Video: Scene changesTelnet: Typing behaviourWeb browsing patterns: Think times betweendownloads





� Video: Scene changes

Telnet: Typing behaviourWeb browsing patterns: Think times betweendownloads






� Telnet: Typing behaviour

Web browsing patterns: Think times betweendownloads






� Telnet: Typing behaviour

� Web browsing patterns: Think times betweendownloads


Motivating Packet Multiplexing

data emitted by a computer

PCM voice with activity detection

variable bit rate video

video frames (e.g., 30 frames/sec)

talk spurt silence

random epochs of data emission

bit rate

bits

in e

ach

fram

ebi

ts in

eac

h em

issi

on

scenechange

Traffic flow from sources is typically bursty

� Average rate is much lower than peak rate.

Capacity is wasted during “lean periods”.


Motivating Packet Multiplexing

data emitted by a computer

PCM voice with activity detection

variable bit rate video

video frames (e.g., 30 frames/sec)

talk spurt silence

random epochs of data emission

bit rate

bits

in e

ach

fram

ebi

ts in

eac

h em

issi

on

scenechange

Traffic flow from sources is typically bursty

� Average rate is much lower than peak rate.

� Capacity is wasted during “lean periods”.Manjunath: Computer Communicatin Networks – p.18

Packet Multiplexingtime

link ca

pacity

link

packets from various connections

Packet Multiplexing: No partitioning of the bit pipe

� Packets will need to contain header and trailerinformation to identify with a specificinformation flow (source, destination,application, etc.).

Apply entire bit rate to a source and hence, eachpacket gets the entire bit pipe for shorter periodsof time.


Packet Multiplexingtime

link ca

pacity

link

packets from various connections

Packet Multiplexing: No partitioning of the bit pipe

� Packets will need to contain header and trailerinformation to identify with a specificinformation flow (source, destination,application, etc.).

� Apply entire bit rate to a source and hence, eachpacket gets the entire bit pipe for shorter periodsof time.


Packet Multiplexing

� Source peak rate can exceed link rate—packetsmay need to be queued. If buffer capacity is notsufficient, packets may be dropped and hencelost.

Abstraction: Link is a server serving customerswaiting in a queue.

Performance measures: Packet delay and losscharacteristics.


Packet Multiplexing


� Abstraction: Link is a server serving customerswaiting in a queue.

Performance measures: Packet delay and losscharacteristics.


Packet Multiplexing


� Abstraction: Link is a server serving customerswaiting in a queue.

� Performance measures: Packet delay and losscharacteristics.


Centralised Packet MultiplexingTERMINAL

TERMINAL

TERMINAL

TERMINAL

HOST

HOST

MUX MUX

multiplexer ports

full-duplex link

Centralised packet multiplexing: multiplexers havefull control over link’s transmission rate.

� Multiplexer stuffs packets on to link; hascomplete control over link.

Scheduler can decide sequence of transmissions.


Centralised Packet MultiplexingTERMINAL

TERMINAL

TERMINAL

TERMINAL

HOST

HOST

MUX MUX

multiplexer ports

full-duplex link

Centralised packet multiplexing: multiplexers havefull control over link’s transmission rate.

� Multiplexer stuffs packets on to link; hascomplete control over link.

� Scheduler can decide sequence of transmissions.Manjunath: Computer Communicatin Networks – p.21

Distributed Packet Multiplexing

link

NODES

Distributed packet multiplexing: sources share link ina distributed fashion.

� Sources (hosts/nodes) connected to a multipointlink (wiretap, wireless channel).



� Only one source can successfully transmit on thechannel at any time—multiple access channel.

Design Issue: Coordination among the sources.Random access: collision recognition andresolution.Controlled access: various flavours ofpolling—central or distributed.Reservation access: Usually for satellitechannels.




� Design Issue: Coordination among the sources.

Random access: collision recognition andresolution.Controlled access: various flavours ofpolling—central or distributed.Reservation access: Usually for satellitechannels.





� Random access: collision recognition andresolution.

Controlled access: various flavours ofpolling—central or distributed.Reservation access: Usually for satellitechannels.





� Random access: collision recognition andresolution.

� Controlled access: various flavours ofpolling—central or distributed.

Reservation access: Usually for satellitechannels.


Polling Based MultiplexingToken ring

node

node

node

node


Reservation Based MultiplexingA Satellite System Example (VSAT Network)

VSAT

VSAT

router

routercampusnetwork

campusnetwork

packetswitch

DIU

DIU

� Inbound channel to the hub is shared.

Propagation delay is large, no instantaneousfeedback of result of the transmission—cannotuse polling or contention based random access.


Reservation Based MultiplexingA Satellite System Example (VSAT Network)

VSAT

VSAT

router

routercampusnetwork

campusnetwork

packetswitch

DIU

DIU

� Inbound channel to the hub is shared.

� Propagation delay is large, no instantaneousfeedback of result of the transmission—cannotuse polling or contention based random access.


VSAT System

� Ask for reservations from the hub using somecontention mechanism

Successful reservations and the frame structuresare communicated on the outbound channel to theusers


VSAT System

� Ask for reservations from the hub using somecontention mechanism

� Successful reservations and the frame structuresare communicated on the outbound channel to theusers


Multiplexing Summary

multiplexing

circuit multiplexed packet multiplexed

centralised distributed

random access

polledaccess

reservationaccess

token passingmaster−slave


Hybrid solutions

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� � � � � � � � � � � � � � � � � � � � � � � � �circuitmultiplexed

packetmultiplexed

movableboundary

Hybrid link multiplexing; combining circuitmultiplexing and packet multiplexing on a link.

� Partition capacity into circuit & packetmultiplexing parts.

Important example: “2B+D” ISDN services

More complex solutions vary boundary; rarelyimplemented.


Hybrid solutions

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� � � � � � � � � � � � � � � � � � � � � � � � �

circuitmultiplexed

packetmultiplexed

movableboundary



� Important example: “2B+D” ISDN services

More complex solutions vary boundary; rarelyimplemented.


Hybrid solutions

� � � � � � � � � � � � � � � � � � � � � � � � �

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circuitmultiplexed

packetmultiplexed

movableboundary



� Important example: “2B+D” ISDN services

� More complex solutions vary boundary; rarelyimplemented.


Switching: Motivation

S2S1

S

(c)

(b)(a)

A six node network constructed in three ways—(a) Abrute force way. (b) Every node is connected to acentral switch

�that selectively establishes paths

between nodes and (c) Hierarchical network withinter-switch links with possibly multiplexing on it.


Switching

switchlink link

link

� Information flow will traverse more than one link.

Switch is required at junction of two or morelinks.

Switch is a device that selectively establishes andreleases connections between communicationlinks to allow sharing of these links among anumber of flows (connections).


Switching

switchlink link

link


� Switch is required at junction of two or morelinks.

Switch is a device that selectively establishes andreleases connections between communicationlinks to allow sharing of these links among anumber of flows (connections).


Switching

switchlink link

link


� Switch is required at junction of two or morelinks.

� Switch is a device that selectively establishes andreleases connections between communicationlinks to allow sharing of these links among anumber of flows (connections).


Switching (contd)

� Switch moves information from link to link bydemultiplexing on the inbound link andmultiplexing on the selected outbound link.

A switch is required with circuit multiplexing andcentralised packet multiplexing.


Switching (contd)

� Switch moves information from link to link bydemultiplexing on the inbound link andmultiplexing on the selected outbound link.

� A switch is required with circuit multiplexing andcentralised packet multiplexing.


Functions of a Switch

� Two categories, also called planes offunctions—data plane and control plane

Data plane functionsDemultiplex the flow (e.g., packet or timeslot) on the input link.Switch the flow element onto the appropriateoutput link.Multiplex the flows on the output link.




� Data plane functions

Demultiplex the flow (e.g., packet or timeslot) on the input link.Switch the flow element onto the appropriateoutput link.Multiplex the flows on the output link.





� Demultiplex the flow (e.g., packet or timeslot) on the input link.

Switch the flow element onto the appropriateoutput link.Multiplex the flows on the output link.






� Switch the flow element onto the appropriateoutput link.

Multiplex the flows on the output link.






� Switch the flow element onto the appropriateoutput link.

� Multiplex the flows on the output link.



� This implies every packet or slot in a TDM frameneeds to be processed.

Thus these are fast timescalefunctions—performed per packet or per frame.

Specialised hardware may be used for these highspeed functions.




� Thus these are fast timescalefunctions—performed per packet or per frame.

Specialised hardware may be used for these highspeed functions.




� Thus these are fast timescalefunctions—performed per packet or per frame.

� Specialised hardware may be used for these highspeed functions.


Functions of a SwitchControl plane functions

� Connection setup and resourceallocation/reservation

Achieved through source-network andswitch-switch signalling

Functions performed over connection (flow)arrival timescales

General purpose processors can be used;Increasing interest in parallelisation

Routing and local conditions informationdissemination and computation, usuallyperformed at timescales at which trafficcharacteristics change




� Achieved through source-network andswitch-switch signalling

Functions performed over connection (flow)arrival timescales







� Functions performed over connection (flow)arrival timescales








� General purpose processors can be used;Increasing interest in parallelisation







� General purpose processors can be used;Increasing interest in parallelisation

� Routing and local conditions informationdissemination and computation, usuallyperformed at timescales at which trafficcharacteristics change


Design Issues in a Packet Switch

� Input and output lines could be slotted orunslotted—correspondingly, packets lengths andinterarrival time have a discrete or continuousdistributions

Packet lengths could be fixed or variable

Datagram packet switches: Every packet of aflow is treated independent of previous packets inthe flow

Control and signalling functions includepopulating the routing table, participating indistributed algorithms associated, for example,with routing.




� Packet lengths could be fixed or variable

Datagram packet switches: Every packet of aflow is treated independent of previous packets inthe flow






� Datagram packet switches: Every packet of aflow is treated independent of previous packets inthe flow






� Datagram packet switches: Every packet of aflow is treated independent of previous packets inthe flow

� Control and signalling functions includepopulating the routing table, participating indistributed algorithms associated, for example,with routing.



� Virtual circuit packets switches

Connection setup to allocate path andresources on links on path to the flowPackets are assigned link level labels andswitched based on labelsPerformance measures: Switching delay ingetting to the output queue, packet loss rate,




� Connection setup to allocate path andresources on links on path to the flow

Packets are assigned link level labels andswitched based on labelsPerformance measures: Switching delay ingetting to the output queue, packet loss rate,





� Packets are assigned link level labels andswitched based on labels

Performance measures: Switching delay ingetting to the output queue, packet loss rate,





� Packets are assigned link level labels andswitched based on labels

� Performance measures: Switching delay ingetting to the output queue, packet loss rate,


Components of a Packet Switch

processing

O/p Queue Scheduling,

processing

O/p Queue Scheduling,

Control and Signalling Functions

Switch

Fabric

Interface

Line

Input Processing& Forwarding

Queuing &Scheduling

Queuing &Scheduling

LineInterface

Line

Input Processing& Forwarding

Interface

InterfaceLine


Call Setup in a Circuit Switch

� Detect off hook, apply dial tone, accept digits,perform digit analysis

From routing algorithm determine next switch onpath to destination and perform signalling toreserve channel on link to the switch

If path is available reserve resources and“program” the pair “output port:TDM slot” forthe channel on the incoming port of the call

Maintain call

Release resources on completing the call andperform possible billing functions




� From routing algorithm determine next switch onpath to destination and perform signalling toreserve channel on link to the switch

If path is available reserve resources and“program” the pair “output port:TDM slot” forthe channel on the incoming port of the call

Maintain call






� If path is available reserve resources and“program” the pair “output port:TDM slot” forthe channel on the incoming port of the call

Maintain call







� Maintain call







� Maintain call

� Release resources on completing the call andperform possible billing functions



Call Teardown Delay

Call Processing Delay

Dial Tone Delay

Information Transfer

Calling Phone Switch

Call Complete Signal (On Hook)

Dial digits

Apply dial tone

Phone goes off hook

time

Call Accept (or Deny) Signal


Functions of a Circuit Switch

� Switching function like setting up circuit insideswitch between input and output and maintain itfor duration of call

Call processing functions like off-hook detection,digit acceptance and analysis, routing call andcorresponding signaling for path reservation andbilling functions

Background functions for executing the routingprotocols and algorithms, management andmaintenance of the switch.




� Call processing functions like off-hook detection,digit acceptance and analysis, routing call andcorresponding signaling for path reservation andbilling functions

Background functions for executing the routingprotocols and algorithms, management andmaintenance of the switch.




� Call processing functions like off-hook detection,digit acceptance and analysis, routing call andcorresponding signaling for path reservation andbilling functions

� Background functions for executing the routingprotocols and algorithms, management andmaintenance of the switch.


Circuit Switch: Logical View

Switc

h Fab

ricInput i x

TDM Frame TDM Frame

Control Processor

Output oy


Operation of a Circuit Switch

� Each slot on each input line contains theinformation flow unit for a circuit.

At the time of circuit set up, the switchingpattern—output port and the slot in the outputport, is determined.

The fabric will perform the switching operationwhich is repeated in every frame.

In figure, the contents of slot on input line areswitched to slot on line .




� At the time of circuit set up, the switchingpattern—output port and the slot in the outputport, is determined.

The fabric will perform the switching operationwhich is repeated in every frame.






� The fabric will perform the switching operationwhich is repeated in every frame.






� The fabric will perform the switching operationwhich is repeated in every frame.

� In figure, the contents of slot �� on input line

�

areswitched to slot �� on line �.


Routing

� A route is an ordered sequence of links between asource and a destination.

A network node, or a switch, performs therouting function along with multiplexing andswitching. However, routing is a “network wide”function and the nodes collaborate in makingrouting decisions.

Often, routing and forwarding are usedsynonymously and this is wrong!

An incoming packet is processed, its output portdetermined and then the packet is forwarded tothe output link. Thus forwarding is a fasttimescale operation and is a data plane function,meaning it operates on the data.


Routing


� A network node, or a switch, performs therouting function along with multiplexing andswitching. However, routing is a “network wide”function and the nodes collaborate in makingrouting decisions.

Often, routing and forwarding are usedsynonymously and this is wrong!



Routing



� Often, routing and forwarding are usedsynonymously and this is wrong!



Routing



� Often, routing and forwarding are usedsynonymously and this is wrong!

� An incoming packet is processed, its output portdetermined and then the packet is forwarded tothe output link. Thus forwarding is a fasttimescale operation and is a data plane function,meaning it operates on the data.


Routing

� The decision of which output port this packetshould be sent is made on slower timescale. Thisdepends on the route that the packet will take inthe network. Thus this is a control plane activity.

The forwarding function consults a routing tableto decide the output port for a packet. The routingfunction nopulates this routing table.


Routing

� The decision of which output port this packetshould be sent is made on slower timescale. Thisdepends on the route that the packet will take inthe network. Thus this is a control plane activity.

� The forwarding function consults a routing tableto decide the output port for a packet. The routingfunction nopulates this routing table.


Routing: Computation Models

� Objective of routing algorithm: Use networkresources efficiently—conflicts of providing QoSto a customers and utilise network resourcesefficiently needs to be addressed.

Network topology information and userrequirements need to be known.

Routing decisions can be centralised ordistributed.




� Network topology information and userrequirements need to be known.

Routing decisions can be centralised ordistributed.




� Network topology information and userrequirements need to be known.

� Routing decisions can be centralised ordistributed.



� In centralised routing the network topologyinformation is collected using a distributedalgorithm at a central node where the routes aredetermined for every possible source-destinationpair. These routing decisions communicated to allthe nodes in the network.

In distributed routing, distributed algorithms areused to collect topology information and makerouting decisions.

Information aggregation may be used to minimise“information explosion”. An obvious solution isuse of hierarchies.




� In distributed routing, distributed algorithms areused to collect topology information and makerouting decisions.

Information aggregation may be used to minimise“information explosion”. An obvious solution isuse of hierarchies.




� In distributed routing, distributed algorithms areused to collect topology information and makerouting decisions.

� Information aggregation may be used to minimise“information explosion”. An obvious solution isuse of hierarchies.


Distributed RoutingDecision Models

� Source Routing: The decision on the sequence ofthe links to the destination may be made at thesource.

The routing information is embedded into thepacket and is used by the intermediate nodes inthe network to forward the packet appropriately.

Hop-by-Hop Routing: Each node only knows the‘next node on the best route’ to the destination.The nodes need not know the entire route to thedestinations.




� The routing information is embedded into thepacket and is used by the intermediate nodes inthe network to forward the packet appropriately.

Hop-by-Hop Routing: Each node only knows the‘next node on the best route’ to the destination.The nodes need not know the entire route to thedestinations.




� The routing information is embedded into thepacket and is used by the intermediate nodes inthe network to forward the packet appropriately.

� Hop-by-Hop Routing: Each node only knows the‘next node on the best route’ to the destination.The nodes need not know the entire route to thedestinations.


Tasks in Routing

� Exchange of local topology information withneighbours at faster timescales.

This helps keep track of link status and and alsothe demands on the links. The latter helps indetermining QoS capabilities of the routes.

Perform any aggregation that may be required bythe algorithms and disseminate aggregatedinformation.

A Routing Protocol will be used to exchangeinformation that is necessary for the routingalgorithm


Tasks in Routing


� This helps keep track of link status and and alsothe demands on the links. The latter helps indetermining QoS capabilities of the routes.

Perform any aggregation that may be required bythe algorithms and disseminate aggregatedinformation.



Tasks in Routing



� Perform any aggregation that may be required bythe algorithms and disseminate aggregatedinformation.



Tasks in Routing



� Perform any aggregation that may be required bythe algorithms and disseminate aggregatedinformation.

� A Routing Protocol will be used to exchangeinformation that is necessary for the routingalgorithm


Tasks in Routing

� Route computations are based on the topologyinformation collected and use a routingalgorithm.

Topology information exchange always occurs.Route computation may be triggered and/or timedriven.

Granularity of route computationFine grained on demand routing on a persession basis.Coarse grained per flow routing where fatpipes are a priori set up.


Tasks in Routing


� Topology information exchange always occurs.Route computation may be triggered and/or timedriven.

Granularity of route computationFine grained on demand routing on a persession basis.Coarse grained per flow routing where fatpipes are a priori set up.


Tasks in Routing



� Granularity of route computation

Fine grained on demand routing on a persession basis.Coarse grained per flow routing where fatpipes are a priori set up.


Tasks in Routing




� Fine grained on demand routing on a persession basis.

Coarse grained per flow routing where fatpipes are a priori set up.


Tasks in Routing




� Fine grained on demand routing on a persession basis.

� Coarse grained per flow routing where fatpipes are a priori set up.


Design and Performance Issues

� Routing protocols: What information toexchange, how often, how to exchange

Routing Algorithms: Objective functions for besteffort routing and QoS routing

Multicast routing algorithms

Routing protocols and algorithms for rapidlychanging topologies, e.g., ad hoc networks




� Routing Algorithms: Objective functions for besteffort routing and QoS routing

Multicast routing algorithms






� Multicast routing algorithms






� Multicast routing algorithms

� Routing protocols and algorithms for rapidlychanging topologies, e.g., ad hoc networks



� Performance measures: Connection blockingprobability, load imposed on the network,adaptation to changes in the network conditions.

Connection blocking only relevant in connectionbased networks. Typically associated with circuitmultiplexed networks.

In datagram networks, connections are not set up.Hence no concept of connection blocking.

Virtual circuit based networks use packetmultiplexing but set up a connection before datatransfer begins to alert the switches of thecreation of a flow.




� Connection blocking only relevant in connectionbased networks. Typically associated with circuitmultiplexed networks.

In datagram networks, connections are not set up.Hence no concept of connection blocking.






� In datagram networks, connections are not set up.Hence no concept of connection blocking.






� In datagram networks, connections are not set up.Hence no concept of connection blocking.

� Virtual circuit based networks use packetmultiplexing but set up a connection before datatransfer begins to alert the switches of thecreation of a flow.


Network Management

� Handle conditions for which the network is notengineered. Different from ‘congestion control’where the overload conditions are short lived.

All operational networks define a managementarchitecture to collect and control the networkresources.

Performance data are collected by managednetwork devices these are in turn are gathered bya network management station in the network thatwill analyse the data that has been collected.


Network Management


� All operational networks define a managementarchitecture to collect and control the networkresources.

Performance data are collected by managednetwork devices these are in turn are gathered bya network management station in the network thatwill analyse the data that has been collected.


Network Management


� All operational networks define a managementarchitecture to collect and control the networkresources.

� Performance data are collected by managednetwork devices these are in turn are gathered bya network management station in the network thatwill analyse the data that has been collected.


Network Management

� The management architecture provides somecontrol functions that can be performed on remotemanaged devices by management stations eitherin a programmed manner or through an operator

Security issues are also handled by a networkmanagement architecture.


Network Management

� The management architecture provides somecontrol functions that can be performed on remotemanaged devices by management stations eitherin a programmed manner or through an operator

� Security issues are also handled by a networkmanagement architecture.


Traffic Controls and Timescales

� Network functions cover a wide variety oftimescales—of the order of a few microsecondsto minutes to months and years.Rather thanconsider absolute time we identify the followingfour relative timescales.

1. Packet timescale (packet transmission time;seconds or milliseconds)

2. Session, call or flow timescale (typicallyminutes)

3. Busy hour or traffic variation timescale(typically hours)

4. Provisioning timescale (usually hours to daysor weeks)



� Network functions cover a wide variety oftimescales—of the order of a few microsecondsto minutes to months and years.Rather thanconsider absolute time we identify the followingfour relative timescales.1. Packet timescale (packet transmission time;

�seconds or milliseconds)

2. Session, call or flow timescale (typicallyminutes)






�seconds or milliseconds)2. Session, call or flow timescale (typically

minutes)







minutes)3. Busy hour or traffic variation timescale

(typically hours)






minutes)3. Busy hour or traffic variation timescale

(typically hours)4. Provisioning timescale (usually hours to days

or weeks)



� Packet timescale controls discriminate betweentreatment of individual packets (e.g.,transmissionscheduling, buffer allocation).

Accepting and the routing of a call in connectionoriented networks are made on slower timescales,those of the order of session interarrival times.

Since traffic processes vary over a day/week andprobably have some cyclical patterns, resourceallocation algorithms and thresholds may need tochanged at the rate at which traffic processes inthe network change.

Resource provisioning occurs over longerperiods, of say months, to years.




� Accepting and the routing of a call in connectionoriented networks are made on slower timescales,those of the order of session interarrival times.

Since traffic processes vary over a day/week andprobably have some cyclical patterns, resourceallocation algorithms and thresholds may need tochanged at the rate at which traffic processes inthe network change.






� Since traffic processes vary over a day/week andprobably have some cyclical patterns, resourceallocation algorithms and thresholds may need tochanged at the rate at which traffic processes inthe network change.






� Since traffic processes vary over a day/week andprobably have some cyclical patterns, resourceallocation algorithms and thresholds may need tochanged at the rate at which traffic processes inthe network change.

� Resource provisioning occurs over longerperiods, of say months, to years.


ee 706: computer communication networksmazum/ece610/networking.pdf · 2005-11-24 · the bit...

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