Transcript Network Service Models: Introduction

Network Service Models
Based on:
Dr. Jon Crowcroft’s
www.cs.ucl.ac.uk/staff/jon/mmbook/book/node35.html
CECS401- Multimedia Systems
Prof. Dr. Xinhua Zhang
University of Missouri-Columbia
Presented by: Othoniel Rodriguez-Jimenez
Arturo Guillen
Network Service Models:
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Arturo Guillen
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Introduction
Sharing and Caring
Service Scheduling and Queues
Evolution of the Internet Service Model
Otho Rodriguez
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Outline
RSVP
Service Classes and Assurance
Detailed Analysis of the Integrated Services
Host Functions
Resource ReSerVation Protocol (RSVP)
QoS Routing
Futures
Arturo Guillen
– IP and ATM
– Conclusions
Network Service Models:
Introduction
Definition: Service Model refers both to the interface
and to the performance that the network gives us.
In this talk we are going to take a look at:
- Components of user and network that must interact to
provide a network service.
- The way internet provides these components and how
they can fit together to make the service model that a
user requires.
- Network service models for supporting multimedia.
- Mechanisms to provide varying levels of assurance
about performance in terms of delay, throughput, loss
and standard protocols.
Network Service Models:
Introduction - User and Network Service Interface
The user
The network
Type of service (Parameters, Dimensioning or
Payments)
Provisioning
Service Possible Shaped
Reservation
Service Policing
Policing
Control Service congestion
Congestion Indications
Routing Packets
Scheduling of Packets
Monitoring
Control of Session
Network Service Models:
Sharing and Caring I
Situation of the Internet:
- At the beginning the Internet was intended to support multiple
types of service.
- Nowadays the “Best effort” service model is the most used in
the Internet. In this type of model, each request to send is
honored by the network as best as it can.
- The most problematic characteristic of the Best effort service
model is the lack of contract between the network and the user.
- The way users access the Internet made this model the most
useful service model so far. Essentially any computer may
attempt to communicate with any other computer at any
moment.
Network Service Models:
Sharing and Caring II
Traditional telecommunication networks:
- The actual situation of the Internet is in direct
contrast with the traditional telecommunication
networks. For example, in telephony system, the
network can be provisioned for the expected # of
calls at any time.
- call blocking: congestion or overload. Here the
degradation of service is to the users who get none,
rather than to users who have established access to
the network.
- leased line: strong resource commitment between
the network and the user.
Network Service Models:
Sharing and Caring III
Internet vs Traditional telecomm. Networks:
Type of network Congestion
Manifestation
Internet based
Elastic: congestion
leads to lower rate of
quality
Circuit based
Brittle: congestion
leads to call blocking
Network Service Models:
Sharing and Caring IV
How do we specify a “contract” between the user and the network?
- In networks we have different types of traffic from different
applications. We can specify a “contract” with the network in
terms of a set of performance parameters.
Table of service “contract” models:
Model
What defines
Type of service
High or low values of
throughput, delay and loss
Class of service
Several externally specified
service models, selected by
class parameter.
Exact service selected inline
by specific signaling.
Quality of service
Network Service Model:
Sharing and Caring V - User Expectation and Service Models
- The service model that a network provides has a
profound effect on user expectations.
- It’s very important to consider users’ expectations,
when considering QoS requirements.
- Modern phone network vs mobile phone.
- In today’s Internet users have a lack of expectation of
quality. Users accept low quality of audio and video
communication.
Network Service Model:
Service Schedules and Queues
- Performance of a comm. path is made up of contributions from many
places:
- technology used:
- throughput of each link.
- error rate (due to noise).
- delay for the path:
- propagation time.
- Store/forward time. <-- Here is were we can improve performance
- To change “Best effort” service used in the Internet we need to:
- recognize the user traffic.
- give different treatment in the queues to that traffic.
- There are different proposed queuing systems:
- for example: Fair Queuing: round robin scheduler for each sourcedestination.
- A given device can implement several different queuing mechanisms and
sort packets into the appropriate queue based on some notion of
packet classification.
Network Service Models:
Evolution of the Internet Service Model
- The “best effort” Internet has provided the worst service possible
for multimedia:
- packets are forwarded by routers solely on the basis that there
is any known route, irrespective of the traffic along the route.
- Routers overloaded discard packets (typically at the tail of the
queue).
- Other types of digital networks have been built. The most notably
(for wide public access) it is based on the Integrated Services
Digital Network architecture:
- gives constant rate from source to sink, irrespective of whether
you have something ready to send at any moment or not.
- inconvenient: It’s narrow band service.
- Most recently, we have seen an evolution towards a more
flexible support for multimedia service: Multiservice IP and
broadband ISDN (the last one provided by ATM).
- At this point, the notion of Traffic Classes (each of which have a
range of parameters = QoS parameters) have being designed.
Network Service Models:
Evolution of the Internet Service Model Classification and Admission I
CLASSIFICATION:
- A class is supported by some queuing discipline being applied
especially to a particular flow of traffic.
- This is set up using a signaling protocol by:
- network manager.
- programmed into a router.
- request by user.
- In the Internet the signaling protocol has to provide:
- traffic flow category.
- the QoS parameters.
- a way for a router to recognize the packets belonging to the
flow.
Network Service Models:
Evolution of the Internet Service Model Classification and Admission II
- The classification is simply based on a set of packet fields that
remain constant for a flow:
- UDP and TCP port #.
- IP level transport identifier.
- source and destination IP host addresses.
- To dynamically create this classification, and map it into routers
queues, the Internet has devised RSVP, the Resource
Reservation Protocol.
ADMISSION:
- When a service request is made it can deny access to a flow.
Right now a normal IP router cannot do this.
Network Service Models:
Evolution of the Internet Service Model - Integrated
Service Model
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Key features of Integrated Servs. Arch.
– Reserved Resources
• router must know resources committed for ongoing sessions
– Call Setup (call admission)
• requires participation of all routers in path
• router determines available local resources
required for the flow
Network Service Models:
Evolution of the Internet Service Model - Integrated
Service Model
- Right now there are 5 classes of service:
Service Name Description
Best effort
This is the traditional service model of the
Internet. It is typically implemented
through FIFO queueing in routers.
Fair
Enhancement of Best effort model. The
routers try to partition up network
resources in some fair share sense:
- drop randomly packets
- use round robin.
The traffic admitted to the network is
limited.
Delay of each flow is controlled.
The source should “tell” the routers that a
particular throughput is required
Controlled load
Predictive or
controlled delay
Guaranteed
The delay a source perceives is bounded
within some absolute limit (the most
expensive of all five).
Network Service Models:
Evolution of the Internet Service Model Differentiated Services
- Differentiated Services have emerged in the Internet as a Class
of Service to provide better than “Best effort” quality, in contrast
to Integrated Services which uses more stringent and complex
QoS approach.
- Essentially, through pricing and understanding of user
requirements, it appears that we can control a repertoire of
quality of service parameters for each application.
- A class of service is selected (by subscription or by marking using
class of service bits in each packet header) and the routers
along the path have programmed the parameters for each class.
- There is great enthusiasm for this approach nowadays.
Network Service Models
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Outline
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RSVP, an Overview
Service Classes and Assurance
Detailed Analysis of Integrated Services Internet (ISI)
Host Functions to Support ISI
Resource ReSerVation Protocol (RSVP), in Detail
QoS Routing
Futures
Network Service Models
Resource ReSerVation Protocol
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An Overview, will discuss in detail later
– RSVP [Zhang-94]
– Establishes resources reservations in the
network routers for different flow classes
– Dual Function Protocol:
• Installs knowledge on classes of flows
– This is known as the FilterSpec
• Details QoS needed by those flows
– This is known as the FlowSpec
Network Service Models
Resource ReSerVation Protocol
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RSVP motivation:
– fill the needs of multimedia applications
distributed using Multicast Procotocol
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Important Concepts of Multicast Prot.:
– On each multicast address (MC-IP/port),
several senders (identified by their IP/port)
source packets and an unspecified and
anonymous number of receivers subscribe
Network Service Models
Resource ReSerVation Protocol
– Filter Specs. are re-usable in two ways:
• Senders and Receivers can independently
specify flow characteristics
– Receivers can select sub-band rates or sub-set of
senders most convenient to them
– Similar to people choosing among B&W/Color,
mono/stereo, NTSC/HDTV
• Wild-card filterSpec refers to groups of sources
– A user in a teleconference only needs 1 voice chan.
that may originate at any of the participants
– More when we discuss traffic Merging Styles later
Network Service Models
Resource ReSerVation Protocol
– Flow Specs
• Used for Admission Control and Traffic Re-shaping
• For each class of service specify quantitative parameters
– mean rate, and burstiness,
– modeled through the token-bucket parameters
fixed token rate, r associated with mean rate
L bytes
x
b (depth) associated to peak burst
Yes
L <= x ? No
Conforming
Non-conforming
To traffic shaper
– Tokens are credits that accumulate at rate r, and are
expended 1:1 with each byte of packet traffic
admitted
Network Service Models
Service Classes and Assurance
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Service Classes and Assurance
– Associated with all proposed service
classes we find two functions:
• Admission control: (before admission)
– Can serv. be traffic supported with current resources
– Refusal control, or call reservation blocking
• Policing action: (after admission)
– Does actual flow violates requirements or capacity?
– If yes, do we use queue tail packet dropping or
Random Early Detection (RED) dropping , or others?
Network Service Models
Detailed Analysis of Integrated Services Internet
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IETF and Integrate Services Internet
– Services classes are defined with QoS
commitments from routers traversed by flow.
– End applications request QoS on a per flow basis
– Requests specify level of resources, as well as
Routers transmission scheduling behavior
– Packets in flow are to receive QoS committed
– Session identifies flow; a generalized port spec:
Session: Destination MC-IP address and Port num,
Transport protocol, and List of Senders to session
with their IP and Port number
Network Service Models
Detailed Analysis of Integrated Services Internet
– Integrated Services Over Specific Lower
Layers (ISSLL)
• Specify how router negotiates service
guarantees from “QoS-active” lower layers
– Example: ISSLL required to use ATM as LL
• Router receives application’s flow “traffic
envelope”, a.k.a. traffic arrival pattern, for
example MTU parameter is data link layer
media dependent.
• Otherwise, Router controls passive link layers
directly
Network Service Models
Detailed Analysis of Integrated Services Internet
– Installed reservations on Routers along path will
not change as long as:
• no path changes, no router fails, and requested
resources are not exceeded during flow lifetime.
• RSVP senders refresh timers allow restablishment
– Behaving data flows are protected from nonconforming flows which trigger policy enforcement
activity in the Router
– IETF has considered many but formally specified
two classes: Guaranteed Svc., Controlled Load
Network Service Models
Host Functions for Integrated Service Internet
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Host Functions needed to Support ISI
– Controlled Load Service
– Guaranteed Service
– Policing and Conformance
– Integrated Services on Specific Link
Technology
Network Service Models
Host Functions for Integrated Service Internet
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Controlled-Load Service
– Same Tspec (traffic) as for Guaranteed but
without the peak-rate parameter.
– Service committed is equivalent to that of a
lightly loaded network under Best-Effort,
with little deterioration upon load increases
• Example: For applics. that can tolerate some limited loss
and delay:
– like existing MBONE applic. with adaptive playout
buffering,
– or some delay sensitive protocols like LAT, (assumes LANlike environment latencies, i.e.Local Area Transport)
Network Service Models
Host Functions for Integrated Service Internet
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Guaranteed Service
– Assured bandwidth (b/w)
– Firm end-to-end delay
– No queuing loss
• Suitable for legacy applic. expecting
delivery model similar to Telecom
circuits
• Router allocates b/w R and buff.spc. B
using “fluid model” of service
Network Service Models
Host Functions for Integrated Service Internet
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Guaranteed Service
• uses perfect Fluid Model:
– token bucket at rate r, and depth d, link rate R
– delay due to burst b is bounded by b/R when R >= r
• router model dev. from ideal, error terms C & D
– give delay bound of: b/R+ C/R+ D where C&D
correspond to packet size and scheduling delays
• GS further bounds the flow peak rate p and the
maximum packet size M for more precise bound
on delay,
• these are summed to obtain the bound on the
end to end path delay through all the routers.
Network Service Models
Host Functions for Integrated Service Internet
– Fluid Model equations (missing in Website)
• End to End Delay Bound ,
• Eq.(1) for case p > R >= r
 = (b-M)(p-R) / (R(p-r)) + (M + Ctot)/R + Dtot
• Eq.(2) for case
R >= p>= r
=
0
+ (M + Ctot)/R + Dtot
– In (2) with R>=p there is no peak rate shaping delay term
because there is no need to use queuing to re-shape traffic
– Reference: (McDysan, David; QoS & Traffic Management in IP &
ATM Networks, 2000, McGraw-Hill, ISBN 0-07-134959-6, available
at EBW Engineering Library
Network Service Models
Host Functions for Integrated Service Internet
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Guaranteed Service
– FlowSpec made up of:
• Tspec parameters: (traffic)
–
–
–
–
–
p: peak rate of flow (bytes/sec)
b: bucket depth (bytes)
r: token bucket rate (bytes/sec)
m: minimum policed unit (bytes)
M: maximum datagram size (bytes)
• Rspec parameters: (reservation)
– R: bandwidth, i.e. service rate (bytes/ sec)
– S: slack Term (ms), when end-to-end delay < applic req.
• Besides Rspec R & Tspec router needs terms Csum and Dsum since
last reshape point, uses these to calculate queuing buffer size B
Network Service Models
Host Functions for Integrated Service Internet
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Guaranteed Service
– Traffic policed at network Access points
– Traffic reshaping required at points where:
– possible to exceed the Tspec even though all senders
associated to data flow conform to their individual
Tspecs.
• at branch points in distribution tree
• at merge points in the distribution tree for sources
sharing the same reservation
• this reshaping incurs in additional queuing delay
Network Service Models
Host Functions for Integrated Service Internet

Policing and Conformance
– Routers must check flows for
conformance to Tspecs
• Prevent non-conforming flows from negatively
impacting QoS of conforming or best effort pkt
• Alternatives for handling non-conformance:
– handle as Best Effort traffic
– assign lower effort than Best Effort
– degrade individual packets or all packets in flow
• Pricing policies might force lesser service to
non-conforming traffic
Network Service Models
Host Functions for Integrated Service Internet

Integrated Srvcs with Specific Link Layer
– Routers must implement ISSLL:
• Queue servicing disciplines like Weighted Fair Queuing,
hierarchical round-robin are a baseline requirement to
support Guaranteed Service, while simple priority
queuing may suffice for Controlled Load.
• Need a mechanism for controlling the link interconnect
technology
• IP across ATM switches maps RSVP QoS requests into
AMT Q.2931 requests.
Network Service Models
Resource Reservation Protocol
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Resource ReSerVation Protocol (RSVP)
• Enables senders, receivers and routers of
communication sessions to communicate
– to setup the necessary router state to support the
services required by a session.
• Novel signaling protocol in three ways:
– multicast, receiver-driven request model
– uses soft-state
– low cost in implementation in end-sys. and routers
• RSVP operations apply to packets of a session
Network Service Models
Resource Reservation Protocol
– A signaling, not a routing protocol
• uses any pre-existing route set up by underlying routing
protocol, i.e. Multicast distribution tree
– Path message originates from traffic sender
• installs reverse-routing information for routers in path
• inform receivers of characteristics of path to sender
– Reservation message originates from traffic recvr
• carry reservation requests to routers along distribution
tree from receivers toward senders (upstream)
• receivers must periodically issue refresh reservation
message to their reservation upstream router
• Router issues periodic refresh Reservation msg to
upstream router, while reservation is active
Network Service Models
Resource Reservation Protocol
UPSTREAM
DOWNSTREAM
Resv
ResvTear
RC1
PathErr
S1
R1
R2
R3
RC2
R4
RC3
Path
PathTear
ResvConf
ResvErr
Network Service Models
Resource Reservation Protocol
Router Interface
Soft State
PathMsg
Refresh PathMsg
(from upstream)
merged RsvMsg
refreshRsvMsg
(periodic local origin)
PathTearMsg
RsvTearMsg
FlowSpec
FilterSpec
refresh
timers
clean-up
timers
FlowSpec
FilterSpec
modified PathMsg
refresh PathMsg
(periodic local origin)
RsvMsg
refreshRsvMsg
(from dowstream)
PathTearMsg
RsvTearMsg
Refresh Rsv/Path msgs originate locally while Reservation/Path exists.
Local Rsv state refreshed by downstream refresh Reservation msgs
Local Path state is refreshed by upstream refresh Path messages
Refresh messgs locally originated every refresh time-out interval
Received Reservation/Path messages reset respective clean-up timer
Network Service Models
Resource Reservation Protocol
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Reservation styles and Merging
– FilterSpec and FlowSpec are obtained by
• merging resource requests from arriving Resv messages
– Reservation style
• Determines the way Reservation Specification merging is
performed when reservation message arrives
– Three reservation styles:
• Fixed Filter (FF)
• Wildcard Filter (WF)
• Shared Explicit(SE)
Network Service Models
Resource Reservation Protocol
RSVP Reservation Options
Reservation
Distinct
Shared
Choice of Sender
Explicit
Fixed-Filter
(FF) Style
Shared-Explicit
(SE) Style
Not Defined
Wildcard Filter
(WF) Style
Wildcard
Merging can only occur with Resv of the same Style
and for the same Session
(Source: Multimedia Comm. Protocols and Applic,
Kuo,Effelsberg,Garcia-Luna)
Network Service Models
Resource Reservation Protocol
forwards
S  session sources
B  b/w units
Fixed Filter (FF) Reservation Example
Network Service Models
Resource Reservation Protocol
Wildcard Filter Reservation Example
WF reservation scope must apply to outgoing intrf to agregate
Network Service Models
Resource Reservation Protocol
Shared Explicit Reservation Example
Network Service Models
Resource Reservation Protocol
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Path Messages information
– Phop(previous hop): addr. of last RSVP-capable node
to forward this message, updated by routers
– Sender Template FilterSpec: sender IP/port
– Sender Tspec: sender source traffic characteristics
– Optional Adspec (OPWA) updated at routers along
path, and informs receivers of level of resources
required to obtain a given end-to-end QoS
Network Service Models
Resource Reservation Protocol

Processing and Propag. of Path Mssgs.
– Update, or create Path state within router
• Path state stored includes: Sender Tspec, the address
Phop of previous upstream router, and optional Adspec
• Sender Tspec provides ceiling to guard against
overspecified Reservation requests
• Reset cleanup-timer, used for soft-state time-out
– Router updates and forwards Path message
• periodically sends path message to refresh path state
– Reception of a PathTear messg removes path and
reservation state , usually at session-end
Network Service Models
Resource Reservation Protocol
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Adspec
– Optional service descriptor in Path mssgs
– Advertises to recvrs characteristics end-end path
– Consists of:
• Message header
• Default General Parameters part
• At least one of:
– Guaranteed Service part
– Controlled-Load Service part
Network Service Models
Resource Reservation Protocol
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Adspec: Default General Part contains:
– Minimum Path Latency: end-to-end link latency, needs
adding queuing delay to obtain real end-end delay
– Path Bandwidth: minimum link b/w along path
– Global Break bit: flags RSVP not supported by some router
– Integrated Svcs Hop Count: incremented by RSVP/IS router
– Path MTU: Max Trans. Unit, is minimum of links’ MTU.
Network Service Models
Resource Reservation Protocol

Adspec: Guaranteed Service Part
– Ctot and Dtot - end to end composed values for C and D
• C is rate dependent queuing delay
• D is rate independent queuing delay
– Csum and Dsum - composed value for C and D since last reshaping point, used/modified by flow reshaping processes
– Guaranteed Service Break bit - flags no support for G.Svc.
– Guaranteed Service General Parameters Headers/Values will override corresponding Default parameters with respect
to Guaranteed Service.
Network Service Models
Resource Reservation Protocol
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Adspec: Controlled Load Part
– Controlled-Load Service Break bit - set by any RSVP/IP
router that does not support Controlled -Load
– Controlled-Load Service Parameters Headers/Values Override specific General Parameters as far as receiver
wishing to make a Controlled-Load reservation is
concerned.
Omission of either Controlled Load Part or Guaranteed Service
part means that such QoS is not available. Can be used to force
receivers to choose the same service.
Network Service Models
Resource Reservation Protocol

Reservations using One Pass with
Advertising (OPWA)
– Sender must include Adspec on its Path message, otherwise
it is called One Pass (OP)
– RSVP goal is to minimize the number of handshakes either
for One Pass or OPWA
Network Service Models
Resource Reservation Protocol

OPWA (cont..)
– Sample Case, with Controlled-Load omitted
• Receiver can extract from Path Message:
– Sendr Tspec: r, b, p, m,
– Sendr Adspec: Min Path Latency, Ctot, Dtot, path MTU and B/W
• MaxQueuingDelayTolerated is calculated as QdelReq
– QdelReq = (Application end-end delay) - (Min Path Latency)
• Then estimate Resv Rspec R parameter by checking equ. (2)
– if Qdelreq <= ( (M + Ctot)/R + Dtot ) , assuming R=p
increase R up to min value that meets Qdelreq, use equ (2)
– else
decrease R down to max value that meets Qdelreq, use equ(1)
– if obtained value of R exceeds Path B/W it must be reduced to
that value
Network Service Models
Resource Reservation Protocol
– Sample Case, with Controlled-Load omitted (cont…)
• Recvr can create Resv Rspec comprising of:
– Calculated value of reservation rate R
– Slack Term set either to:
» zero,
– or when R equal to its min value of r
» Slack = r - (R for  equal Qdelreq)
–
–
–
–
Indication of reservation style FF,SE, WF
Filterspec, similar to Sendr Template in Path messg.
Flowspec, comprising Rspec and a Tspec where M equal PathMtu
ResvConf object, with Recvr address, to be returned to receiver
indicating “high probability” that end to end reservation is installed
– (Note: receiver and sender above are from Flow point of view,
their role is inverted during Reservation message transmission)
Network Service Models
Resource Reservation Protocol
– Sample Case, with Controlled-Load omitted (cont…)
• The Resv messg containing Rspec is sent to upstream Router
using the Phop previous hop address.
• The Flowspec within Rspec is passed to Router traffic control
module
• If reservation is denied ResvErr message is sent downstream
• If reservation is accepted Filterspec and Flowspec are installed
• This reservation could be merged to additional reservations and
sent to the next router upstream.
Network Service Models
Resource Reservation Protocol
– Slack Term
• Included within Rspec of Resv messg.
• Amount by which receiver end-to-end
application delay is below the end-to-end delay
bound assuming routers reserve b/w R
• Helps end-to-end reservation be successful by
allowing routers to take advantage of the slack
to reserve less bandwidth, differential must not
be larger than slack.
Network Service Models
Resource Reservation Protocol

Slack Term (cont..)
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Figure 2.7: R1=2.5Mb/s, S1=0. Reservation request denied
Network Service Models
Resource Reservation Protocol

Slack Term (cont..)
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Figure 2.8: R1=3Mb/s, S1>0, R2=2Mb/s, S2<S1. Reservation accepted
, slack used to accommodate the difference
Network Service Models
Resource Reservation Protocol

QoS Routing
– Any other way to change performance of
flow, besides changing Router schedule?
– Sln: Select a different path, “QoS routing”
– Problems:
• alternate path routing is very complex
• alternate paths used by other users
– Research topic
Network Service Models
Resource Reservation Protocol

Futures
– Internet has evolved from:
– Best Effort, FIFO, Dest. Routed, Unicast system
• To
– Multi-service, QoS Routed, multicast-capable
system
• RSVP with OPWA
– allow application to determine end to end QoS
in advance
Network Service Models
Resource Reservation Protocol

Futures (cont..)
– In the future more research needs to be done in:
– Research areas: per Jon Crowcroft (circa 1998)
•
•
•
•
•
•
Accounting and Billing integrated into the model
Aggregation of non-specifically related reservations
Authentication of users of RSVP for billing purposes
Usage accounting model must incorporate mirror servers
Scheme to permit settlements across service providers
Experience in using a mutiservice networks is needed
Network Service Models:
IP and ATM
- Two basic tasks of intermediate node in packet switched
networks:
- forwards packets, maintaining as economically as possible and
appropriate timing relationship between packets (to meet the
service contract).
- deliver packets along the appropriate route to destination.
- The Internet TCP/IP has defined a simple service model:
- It does not offer any definition of the timing model (the routers
have a single FIFO queue)
- The path selection mechanism is very rich. It has a rapid
response to changes in traffic patterns.
Network Service Models:
IP and ATM II
- Recently, to add further services, the Internet standards have
been enhanced to provide signaling protocol. The new family of
service models are base on the theory in Parekh’s work:
- His work shows how a Weighted Fair Queueing System can
provide bounded delays, once the traffic is constrained by a
leaky bucket and an admission test is carried out.
- This is known as a “flow specification”. Subsequent packets
are matched to the admitted flow.
- In contrast to Parekh’s work, two other hybrid approaches to build
a fast Internet have been proposed:
1.- Frame Relay or ATM switch fabric:
- It will be provided by telecommunication carriers. It is
made up of traditional virtual circuit based on packet switching.
2.- Hybrid switch/router nodes:
- Is more integrated approach. It tries to capitalize on the
benefits of virtual circuits and the flexibility advantages of
dynamic IP routing.
Network Service Models:
IP and ATM - Mapping Classes and QoS
- The integrated service model has an initial deployment scenario
of routers connected together by point to point links. In this
situation only the routers need to know how to do the packet
scheduling for service classes.
- However, there are part of the Internet using other interconnection
technologies between routers:
- routers interconnected via LAN
- routers interconnected by so-called “Non Broadcast Multiple
Access” (NBMA) like frame relay or ATM.
- The integrated services of some of the IP level services onto
services provided at the lower layer:
- in some cases the data link layer cannot guarantee the
services (case of Ethernet) and need kind of a “bandwidth
manager”.
- In the case of NBMA networks (particularly ATM) a much richer
variety is available at the lower layer.
Network Service Models:
IP and ATM - Topology Control
- One of the main reasons for the success of IP is the flexibility for
addressing and routing. But it also has some problems:
- stability of routing is getting worse.
- exhaustion of global IPv4 address space.
- These problems are being solved by the introduction of IPv6, but it seems
that it also introduces new problems:
- the performance for route lookup.
- The work of Degermark and others, shows that it is feasible to construct a
new data structure that:
- permits fast routing lookup.
- reduces the size of the routing tables.
- This permits us to consider using IP addresses for deciding what to do
with a packet as well as where to send it. This gives high degrees of
flexibility. One can change:
- QoS in the middle of the flow.
- the route of the packet.
Network Service Models:
IP and ATM - QoS Control
- QoS control requires:
- some number of alternate queues.
- some form of admission and policing.
- Assuming that admission and policing can be done on
small number of flows when ingress into the network,
we can aggregate flows as they approach the core of
the network.
- The only problem left is the performance of queue
insertion.
Network Service Models:
IP and ATM - Queue Insertion/Lookup Performance
- Queue insertion for WFQ is typically a sort
algorithm: basically it is swapping packets
in the queue.
- Hui Zhang’s work shows that for CBR
(guarantee Service in Integrated Service
Internet), a different algorithm called Worst
Case Fair Weight Fair Queueing achieves
better delay jitter bounds and can have
O(1) insertion time.
Network Service Models:
IP and ATM - Conclusions
- It appears that a purist IP architecture for
all switching nodes in the Internet is both
feasible, and for management reasons
(and therefore cost), attractive.
- The work done on QoS and scalable ATM
switch design, seems to be unnecessary
for general Internet, but useful at modest
speed links, where the reduced latency for
voice/video may be cut through cell size.
Network Service Models:
Conclusions
- We have looked at network service models and discovered that it is a
complex area. There are a lot of debate on how to provide what is
perceived as the need for guarantees for multimedia networked
applications.
- A network offers services which provide probabilities of meeting some
performance requirements. The performance of a service may be
applied to:
- individual offerings (i.e.: to pair of groups of users).
- to a set of typical users.
- The contract concerning performance may be made:
- sometime in advance through subscription.
- immediately before (or remade during) each session.
- This area is extremely active in terms of research, standard development
and technology deployment.
- The very important aspect of this area is the effect of pricing.
- Also is important to realize that the best technical solutions are often
swept away by marketing.