Transcript H_IP QoS for 3G

IP QoS for 3G
A Possible Solution
• The main focus of this network QoS
mechanism is to provide one, real time,
service in addition to the normal best effort
service.
• This real-time service requires that data be
transmitted across the entire network in
less than 200 ms, and that no losses due
to network congestion should occur.
Admission Control Descriptions
• Call admission may be based on a number
of parameters that describe the traffic.
• Increasing the number of parameters
enables more accurate admission
decisions, leading to more efficient
network usage.
• A user can minimise their bill by doing
traffic shaping to keep the required peak
bandwidth as low as possible.
Proposed Internet QoS Mechanisms
•
•
•
•
Integrated Services (IntServ)
Multi-Protocol Label Switching (MPLS)
Differentiated Services (DiffServ)
Integrated Services over Specific Link
Layers (ISSLL)
• Resource ReserVation Protocol (RSVP)
IntServ
• The Guaranteed Service gives hard QoS
guarantees with quantified delay and jitter
bounds for the traffic. It also guarantees that
there will be no packet loss from data buffers,
thus ensuring near-lossless transmission. This
Service is intended to support real-time traffic.
• The Controlled Load Service makes the network
appear to be a lightly loaded best-effort network.
This class is aimed at delay-tolerant
applications.
• Best Effort (no reservation required).
MPLS
• MPLS was originally presented as a way of improving
the forwarding speed of routers.
• It appears particularly suited to carrying IP traffic over
fast ATM networks.
• The basic principle of MPLS is that routers at the edge of
the MPLS domain mark all packets with a fixed-length
label that acts as shorthand for the information contained
in the IP packet header.
• It is usually used as a Layer 2 rather than a Layer 3
solution.
• It cannot provide end-to-end QoS configurable on a flowby-flow basis.
DiffServ
• DiffServ provides a simple and coarse method of
classifying services of various applications.
• Two standard Per Hop Behaviors (PHB) defined
that effectively represent two service levels
– Expedited Forwarding (EF): Has a single codepoint
(DiffServ value).EF minimizes delay and jitter and
provides the highest level of aggregate quality of service.
– Assured Forwarding (AF): Has four classes and three
drop precedences within each class (so a total of twelve
codepoints).
Each AF class is allocated a certain amount of
forwarding resources.
ISSLL
• ISSLL working group was initially formed to consider
how to provide IntServ over specific link technologies,
such as a shared Ethernet cable.
• One of the key ideas to come from this working group
is an approach to provide IntServ QoS by using
DiffServ network segments.
ISSLL architecture
RSVP
• It is a key element of both IntServ and ISSLL
approaches described above.
• It is important to minimise the amount of
signalling to save both wireless network
bandwidth and mobile battery power.
• RSVP is an out-of-band signalling system that
operates in a soft-state mode.
• Initially, RSVP was designed to operate on a
hop-by-hop basis, but the ISSLL community has
now considered the use of RSVP across
DiffServ domains, where only the edge nodes
interpret the RSVP messages.
Details of RSVP Signalling
Establishing a uni-directional RSVP reservation.
Use of RSVP in a Mobile
Environment
Context Transfer Protocol and RSVP
Overall Architecture
• It is based upon the ISSLL architecture.
• Core network operators are implementing DiffServ based
core networks. In keeping with this, RSVP is used as the
signalling protocol for real-time services.
Architecture for QoS in mobile network.
Overall Architecture (cont.)
Summary of generic design decisions
Overall Architecture (cont.)
Shows mobility and wireless design choices
Bounded Delay Differentiated
Service
• One of the key differences between this solution and
standard ISSLL IntServ over DiffServ is that DiffServ
routers are used in the domain at the edge.
• DiffServ requires simpler scheduling and admission
control mechanisms than traditional IntServ.
• The BD service has been proposed as a means to
provide scalable, guaranteed real-time data transport
within the Internet.
• It does not require any per-flow state to be held at
routers, and admission control is based on a bandwidth
sum.
Basic Operation of Bounded Delay
Service
• All traffic for this service can be scheduled using
simple FIFO queuing algorithms.
• This worst-case delay is fixed for that output port.
• N is the number of active BD flows destined for
the output port.
• MTUBD and MTUBE are the Maximum
Transmission Units of the bounded delay and
best effort flows respectively.
• R is the link speed of the output port.
Building a Network Behaviour from
the Bounded Delay DS
• This is known as a per-hop behaviour.
• To build a real-time service, the end-to-end
transmission delay budget is 200 ms.
• The use of a wireless network can
increase this transmission latency.
• Internet packets have a maximum number
of routers – usually 30.
Building a Network Behaviour from
the Bounded Delay DS (cont.)
Minimum bounded delay of a node is determined by size.
Buffer sizes required if jitter is not controlled independently from delay
Mobility Management
• This eliminates scalability concerns and allows
this service to be used throughout a core
network to provide hard real time QoS.
• BD is still considerably less complex than true
IntServ routers, where more complex scheduler
techniques and more complex admission control
decisions would be needed.
• BD does not guarantee flow isolation: flows are
treated as aggregate flows.
Signalling
• Building a system that is naturally
compatible with end-to-end Internet QoS
• RSVP is scalable, but its use hop by hop
throughout a network with regular refresh
messages as described in pure IntServ is
not scalable.
Signalling (cont.)
• The D parameter to represent the fixed worstcase delay of the node.
• C is the bandwidth dependent delay (in bytes)
and D is the bandwidth independent delay (in
microseconds).
Discussions
• The QoS solution finally proposed integrates
easily with the ISSLL framework.
• A fundamental difference between this design
and that of current mobile systems is that it
assumes that the data receiver is responsible for
requesting, and paying for, the QoS provided.
• Actual model for RSVP is ‘receiver pays, but
sender is ultimately responsible’, in the hope that
this would prevent junk traffic.
Discussions (cont.)
• One of the main differences between this
discussion and current mobile QoS systems is
that the emphasis has been on how end-to-end
QoS, including end-to-end reservation-based
QoS, may be achieved.
• None of the QoS solutions considered have
addressed the soft handover problem of CDMA
networks.
• One way to manage the problem is to devolve
this to Layer 2, as in CDMA networks.
‘‘Extended link layer’’
Conclusions
• One particular outstanding issue for IP over wireless
QoS is the poorly understood problem concerning
interactions between the wireless link and the network
layer QoS mechanisms.
• Critics of IP networks believe that achieving the same
level of QoS for voice-over-IP as current telephony will
always be more expensive than the telephony networks.
• Conversely, critics of the telephony network claim that
those networks are over-engineered, and that they would
rather have significantly worse QoS, at a significantly
cheaper price!
• There is clearly some way to go before these issues are
resolved.