Transcript lect25 - Department of Computer and Information Sciences

Special Session PDCS’2000
Interworking of Diffserv, RSVP
and MPLS for achieving QoS in
the Internet
Junaid Ahmed Zubairi
Department of Mathematics and Computer Science
SUNY at Fredonia
November 2000
Overview of Presentation
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The Evolution of Internet
Performance Issues in Packet Switching
The World Wide Web
Changing Traffic on the Internet
IETF’s RSVP and DiffServ Models
MPLS
Interworking of Diffserv, RSVP and MPLS
The Evolution of Internet
 The Internet was initially used for
connecting academic campuses together
until the mid 80’s
 Applications on the Internet included email, ftp, telnet and newsgroups
 The traffic generated by these
applications demanded reliable delivery
of data
Types of Traffic on the Internet
 The protocols were expected to deliver all the
data no matter how long it took
 With high error rate, the elapsed time simply
increased but the transmissions were
completed
 The traffic was bursty and with distributed
routing, the network behavior was
unpredictable because congested routers
could drop additional incoming packets
Performance Issues in Packet
Switching
 The network made its best effort to
deliver the data however it did not give
any guarantees of performance
 Meanwhile, in 1990’s, HTML and HTTP
transformed the Internet into a useroriented information repository
 The open ended HTTP supports the
linking of various types of data into the
web published documents
The World Wide Web
 HTTP makes it possible for web sites to
offer binary files, images, and
multimedia documents to the users with
the click of a button
 A significant change in the type of traffic
on the Internet started to take place
The Changing Traffic on the
Internet
 Now more applications are generating
traffic that is time-sensitive and
requires on-time delivery
 For example, consider the case of realtime audio based applications
 For such applications, users did not get
a consistent performance from the best
effort network.
QoS
 These applications needed certain QoS
(quality of service) from the network
 In simple words, a quantifiable
consistent delay through the network,
within the bounds set by the application
and an error rate within set limits
 ATM meets QoS requirements but it is
too complex to manage and too
expensive
IETF’s Models
 It was felt that instead of focussing on
coping with congestion, Internet should
be run in a way that there is no
congestion
 Applications should be able to reserve
network resources at a given QoS
 IETF has been working on developing
new models and protocols for the
Internet and private networks
IETF’s Models
 IntServ and RSVP provide quantitative
guarantees to each flow. RSVP requires
all intermediate routers to keep track of
each flow through “soft state”.
 RSVP involves signaling and soft state
overhead and RSVP does not scale well
to the Internet. It may be successfully
deployed in a campus network
IETF’s DiffServ Model
 IETF has developed a model to provide
differing levels of service to different
applications without the overhead of signaling
and state maintenance
 The DiffServ model uses the TOS field in IPv4
header to affix labels on packets belonging to
different service levels (EF, AF and DF)
 DiffServ has the potential to offer QoS on the
Internet, at last!!
MPLS
 MPLS is another recently developed protocol
to provide virtual circuit (like ATM)
functionality in the packet switching network
 MPLS installs Label Switched Paths (LSP) in
a domain to provide same path and treatment
to flows
 Using diffserv, EF, AF and BE PDB’s can be
treated in the MPLS domain
MPLS
 Thus the flows directed towards a
common point can be provided
consistent treatment in the domain
 MPLS can handle IP overlay model and
implements traffic engineering by
evenly distributing load across all the
links within the domain
Interworking of MPLS, Diffserv
and RSVP
 MPLS, Diffserv and RSVP can work
together to achieve QoS in the Internet
 Diffserv provides the DSCP labels in IP
headers that may be examined by MPLS
and it then finds an LSP that matches
the requirements and meets TE rules
 The selected LSP can then be installed
using RSVP or CR-LDP
Interworking of MPLS, Diffserv
and RSVP
 All these protocols are very new and may
interact in ways that have not been fully
explored or understood yet
 This session brings together the people
involved in studying, understanding,
analyzing and experimenting with these
protocols for achieving QoS in the Internet
 Thus we can share our experience and take
new leads for our work