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T-110.5110 Computer Networks II
Quality of Service
19.10.2009
Prof. Sasu Tarkoma
Based on slides by Dr. Matti Siekkinen
(Primary sources: C. Hota: “Quality of Service in the Internet” and J. Manner: IP Quality
of Service)
Outline
 What is QoS?
 QoS mechanisms
 QoS architectures
 Integrated Services (IntServ)
 Differentiated Services (DiffServ)
 Multiprotocol Label Switching (MPLS)
 Generalized Multiprotocol Label Switching (GMPLS)
 QoS architectures for mobile networks
 Next Steps in Signaling (NSIS)
 Overlay Solutions
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What is Quality of Service?
 Many applications are sensitive to delay, jitter, and packet loss
 Too high values makes utility drop to zero
 Some mission-critical applications cannot tolerate disruption
 VoIP
 high-availability computing
 Charge more for business applications vs. consumer applications
 Related concept is service availability
 How likely is it that I can place a call and not get interrupted?
 requires meeting the QoS requirements for the given application
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QoS Requirements
Sensitive
Personal
voice
over
IP
CEO Video
conference
with analysis
Network
monitorin
g
Unicast
radio
Financial
Transactions
Interactive
whiteboar
d
Delay
Public web
traffic
Extranet
web traffic
Network
management
traffic
Push
news
Personal
e-mail
Busines
s
e-mail
Server
backups
Insensitive
Casual
4
Mission
Criticality
Critical
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QoS and the Internet
 The existing Internet architecture provides a best effort service.
 All traffic is treated equally (generally, FIFO queuing with tail drop)
 No mechanism for distinguishing between delay sensitive and best
effort traffic
 No guarantees for end-to-end QoS 
 Originally IPv4 has TOS (type-of-service byte) in packet header
 RFC 795: defined multiple axes (delay, throughput, reliability)
 rarely used in practice (DiffServ)
 We try to minimize delay and loss
 …and try to mitigate the effects with different techniques
 E.g. adapt application (video stream) based on QoS feedback (RTCP)
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Outline
 What is QoS?
 QoS mechanisms
 QoS architectures
 Integrated Services (IntServ)
 Differentiated Services (DiffServ)
 Multiprotocol Label Switching (MPLS)
 Generalized Multiprotocol Label Switching (GMPLS)
 QoS architectures for mobile networks
 Next Steps in Signaling (NSIS)
 Overlay Solutions
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QoS Mechanisms
Packet
Scheduling
Traffic
Shaping
(Users get their share
of bandwidth)
(Amount of traffic
users can inject
into the network)
Admission
Control
(To accept or reject
a flow based on
flow specifications)
7
Core
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QoS Mechanisms: classification
 Provisioning
 Admission control
o
Prohibit or allow new flows to enter the nw
 Resource reservation
o
E.g. Over provisioning
 Control
 Operate on short time scales
 Real-time traffic or flow control
o
E.g. scheduling, shaping, policing...
 Management
 Monitor the QoS
 Longer time scales than control
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QoS Control Mechanisms
 Application-level techniques
 Application adapts to network conditions
 E.g. adapt media stream to a lower quality based on RTCP feedback
 Transport-layer techniques
 Adapt transport protocols to application requirements and network
conditions
 TCP, DCCP
 Network-layer techniques
 QoS routing
 Non-FIFO scheduling (like WFQ)
 Something else than tail drop (like RED)
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QoS Control Mechanisms (cont.)
IP addresses, net mask,
port numbers, protocol id
N
Full
Arrival
Packet Classifier
Y
Processor
Departure
Queue
Discard
Scheduling (FIFO Queuing)
Flow identifier
Full
Arrival
Classifier
The switch turns to other queue
when the current one is empty
N
High Priority Queue
Y
Discard
Full
Processor
Departure
N
Y
Discard
Low Priority Queue
Scheduling (Priority Queuing)
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QoS Control Mechanisms (cont.)
Full
Arrival
Classifier
The turning switch selects 2 packets
from 1st queue, then 1 packet from 2nd
queue and the cycle repeats
N
Weight: 2
Y
Discard
Full
Processor
Departure
N
Y
Discard
Weight: 1
Scheduling (Weighted Fair Queuing)
Leaky Bucket (Regulate the traffic)
11
Token Bucket (Credit an idle host)
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QoS Control Mechanisms (cont.)
Arriving Packet
Arriving Packet
Queue
Queue
Accepted
Dropped
Dropped from front
Full
Full
(Tail-drop scheme)
(Drop-from-front scheme)
Drop probability
Queue
1
Avg. TCP
Traffic
Drop
MAXth
MINth
MAXdrop
MINth
(Random Early Detection with Drop function)
12
MAXth
Avg. queue size
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Random Early Detection
Source: Leonardo Balliache, Differentiated
Service on Linux HOWTO
http://www.opalsoft.net/qos/DS.htm
QoS Control Mechanisms (cont.)
 QoS routing
 Routing based on QoS related metrics, not just shortest path
o
E.g. available bandwidth
 (Multi-)constrained path computation
o
Can be computationally complex
 Widest-Shortest Path
o
Select the shortest path that is feasible according to the bandwidth
constraint
 Shortest-Widest Path
o
o
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Find paths with the most available bandwidth (i.e. widest paths)
Break ties by selecting the shortest path (#hops or delay)
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Where to implement QoS mechanisms?
 Core routers
 Link speeds fast
 Lot of traffic
Cannot do much more than over provisioning or treat limited nb of
flow classes
 Access routers
 Generally, not so high rates
 Feasible to do complex operations (filtering, classification, policing…)
Could do per-flow packet handling
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Outline
 What is QoS?
 QoS mechanisms
 QoS architectures
 Integrated Services (IntServ)
 Differentiated Services (DiffServ)
 Multiprotocol Label Switching (MPLS)
 Generalized Multiprotocol Label Switching (GMPLS)
 QoS architectures for mobile networks
 Next Steps in Signaling (NSIS)
 Overlay Solutions
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QoS Architectures
 Use the QoS mechanisms to provide application to application QoS
 Many different proposals over the years
 YESSIR, IntServ, DiffServ, Mobile RSVP, OMEGA, QoS-A...
 We will look at a few ones in more detail
 Integrated Services (IntServ)
 Differentiated Services (DiffServ)
 Multiprotocol Label Switching (MPLS)
 Generalized MPLS (GMPLS)
 QoS for mobile networks
 Next Steps in Signaling (NSIS)
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IntServ
 Resource reservation and admission control
 Source describes its desired flow rate and sends this information
to the routers and the receiver
 Network admits requests and reserves resources
 Source must send at this rate (controlled by network)
 Provides a sort of “dedicated” connection within an IP packetswitched network
 Reservation of resources is done with the Resource Reservation
Protocol (RSVP)
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RSVP
 Supports both multicast and unicast
 Sender-to-network signaling
 path message: make sender presence known to routers
 path teardown: delete sender’s path state from routers
 Receiver-to-network signaling
 reservation message: reserve resources from senders to receiver
 reservation teardown: remove receiver reservations
 Network-to-end-system signaling
 path error, -reservation error
 Soft state protocol
 Need to refresh state
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RSVP (cont.)
 Reservations are for unidirectional data flows
 Provides several reservation models or "styles" to fit a variety of
applications (shared and dedicated reservations)
 Transparent to routers that do not support it
 RSVP packets are just normal IP packets
 Not a routing protocol but depends upon present and future
routing protocols
 Supports both IPv4 and IPv6
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IntServ: Scalability Issues
 RSVP signaling Overhead
 One PATH/RESV per flow for each refresh period
 Processing overhead
 Routers have to classify, police and queue each flow
 State information stored in routers
 Flow identification (using IP address, port etc)
 Previous hop identification
 Reservation Status
 Reserved Resources
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DiffServ
 No signalling, no resource reservation
 Complex processing is moved from core to edge
 Per flow service (IntServ) is replaced by per aggregate or per class
service with a SLA with the provider
 Mark packets with a code (DSCP) to differentiate between
pkts/flows
 e.g. a priority stamp
 Uses IP type of service field (TOS)
 Core uses the codes to select appropriate service level
 Premium, priority, best effort
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DiffServ
 Two types of services standardized, operators may define other
services and code points
 Does not necessarily provide end-to-end QoS:
 Operators may have different meanings and implementations for classes and
code points,
 The code points can change, thus, may not remain the same on the whole
end-to-end path.
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DiffServ Schema
 Source sends request message to first hop router
 First hop router sends request to Bandwidth Broker (BB) that replies with either
accept or reject
 If the request is accepted, either the source or the first hop router will mark DSCP
and will start sending packets
 Edge router checks compliance with the SLA and will do policing. It may drop or
mark the packet with low priority to match the SLA
 Core routers will look into DSCP and decide the PHB
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Expedited Forwarding
25
•
Expedited packets experience a traffic-free network (low loss, low latency, low jitter,
and assured bandwidth (premium service)
•
Strict priority queuing
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Assured Forwarding
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•
A possible implementation of the data flow for assured forwarding is shown below.
•
AF PHB delivers the packet with high assurance as long as its class does not exceed the a
subscribed rate
•
Use e.g. WFQ scheduling with RED
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Bandwidth Brokers
U1
BB
S1
U2
BB
C1
S2
C2
ISP 2
D
Server 3
C3
C6
Core Network
C7
Server 2
Server 1
U1
U2
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BB
C5
C4
ISP 1
BB
BB
U3
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Integrated Solution
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Multiprotocol Label Switching (MPLS)
 Traffic engineering tool
 Allocate specific path and network resources to specific types of traffic ensuring QoS
 Supports multiple protocols
 IPv4, IPv6, IPX, AppleTalk at the network layer

Ethernet, Token Ring, FDDI, ATM, Frame Relay, PPP at the link layer
 Forwarding behavior independent of layer 2 and layer 3
 Data transmission occurs on Label Switched Paths (LSP)
 Labels are distributed using Label Distribution Protocol (LDP), or RSVP, or piggybacked on
BGP and OSPF
 FEC (Forward Equivalence Class) is a representation of group of packets that share the same
requirements for their transport
 Assignment of FEC to a packet is done once only as it enters into the network
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Model for MPLS Network
• Convergence of connection oriented forwarding techniques and Internet’s routing protocols
LER
LSR = Label Switched Router
LER = Label Edge Router
LSP = Label Switched Path
LSR
LSP
LSP
Route at edge and Switch at core
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Separate forwarding and control
• Exact match instead of
longest prefix match (like IP)
 faster forwarding
IP Router
Control:
IP Router
Software
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MPLS
Control:
IP Router
Software
ATM Switch
Control:
ATM Forum
Software
Forwarding:
Forwarding:
Forwarding:
Longest-match
Lookup
Label Swapping
Label Swapping
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MPLS Forwarding
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MPLS Operation
1a. Routing protocols (e.g. OSPF-TE)
exchange reachability to destination networks
4. LER at egress
removes label and
delivers packet
1b. Label Distribution Protocol (LDP)
establishes label mappings to destination
network
IP
Ingress
IP
Egress
MPLS
Domain
2. Ingress LER receives packet and
“label”s packets
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3. LSR forwards packets
using label swapping
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MPLS Labels
• Label assignment decisions are based on forwarding criteria like
•Destination unicast routing
•Traffic engineering
•Multicast
•Virtual Private Network
•Quality of Service
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A Label could be embedded
in the header of the DL layer
like ATM (VPI/VCI) and FR
(DLCI) or could be between
DL and IP as shown below:
of Stack (first label in stack)
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Label and FEC Relationship
R4 could send
a packet with
Label=L1, but it
would mean a
different FEC
Assignment of
FEC to a packet is
done by ingress
router
•FEC (Forwarding Equivalence Class): Assigned on the basis of IP addresses,
port numbers or TOS bits.
•FEC could be associated with all the flows destined to an egress LSR.
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Label Merging
 Label Switched Path (LSP): A unidirectional connection through multiple LSRs.
 Label Merging: The replacement of multiple incoming labels for a particular FEC with a
single outgoing label.
 Labels are "downstream-assigned", and label bindings are distributed in the
"downstream to upstream“ direction.
Multi-point to
Single point tree
routed at Egress
router
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LSP Hierarchy

A Packet can have several labels one after the other before the IP header.
(Why? Tunneling)
(Multiple Levels of Nesting)
(Tunnel 1 may be for the Enterprise with
1a for VoIP data, 1b for billing, and 1c for
alarm & provisioning)
Push
Swap & Push
R1
R2
R2A
Swap
R2B
Pop & Swap
Pop
R2C
R3
R4
IP
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3
2 7
2256May 2017
2 8
4
IP
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Label Distribution
 Establishes and Maintains a LSP that includes establishment of Label/FEC bindings between LSRs
in the LSP.
 A downstream LSR can directly distribute Label/FEC (unsolicited downstream).
 An upstream LSR requests a downstream for Label/FEC (downstream on demand).
 Protocols like LDP, RSVP-TE are used to distribute Labels in the LSP
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Label Distribution
 Label Distribution Protocol (LDP) [RFC 3036]

An LSR sends HELLO messages over UDP periodically to its’ neighbors to discover LDP peers
(routing protocol tells about peers)

Upon discovery, it establishes a TCP connection to its peer

Two peers then may negotiate Session parameters (label distribution option, valid label ranges,
and valid timers)

They may then exchange LDP messages over the session (label request, label mapping, label
withdraw etc)
 RSVP-TE (Resource Reservation Protocol-Traffic Extension) [RFC 3209]
39

Path message includes a label request object, and Resv message contains a label object

Follows a downstream-on-demand model to distribute labels

Path message could contain an Explicit Route Object (ERO) to specify list of nodes

Priorities can be assigned to LSPs, where a higher one can preempt a lower one
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MPLS Protection
 Dynamic routing restores the traffic (upon a failure) based on the
convergence time of the protocol
 Convergence can be slow
 Set up secondary backup paths in addition to primary working
paths
 End-to-end protection
 May need really fast recovery for mission critical or high priority
data
 Fast reroute: Setup detour paths around failed links/nodes
 Temporary recovery until backup path takes over
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IntServ, DiffServ and MPLS
 An RSVP request (say guaranteed service) from one domain could be mapped to an appropriate
DiffServ PHB at another domain that again could be mapped to a possible MPLS FEC at the edge of
another MPLS domain.
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Generalized MPLS (GMPLS)
 MPLS – the base technology (for packet switched nws)
 GMPLS – extension of MPLS to provide the control plane
(signaling and routing) for devices that switching in any of these
domains: packet, time, wavelength and fiber.
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MPLS vs. GMPLS
MPLS
 For packet-switching nw only
 Focuses mainly on the data
plane
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GMPLS
 For packet switched capable
(PSC) as well as non-PSC
interfaces.
 Focuses on the control plane
that performs connection
management for the data plane
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MPLS vs. GMPLS (cont.)
MPLS
GMPLS
 Requires Label Switched Path
(LSP) to be set up b/w routers
at both ends
44
 LSP can be set up b/w any similar
types of Label Switched Routers
(LSR) e.g. b/w SONET/SDH ADM
to form a TDM LSP
 Scale better by forming a forwarding
hierarchy
 Functions specific to optical nw such
as suggested label and bi-directional
LSP setup
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Goals of GMPLS
 A common control plane promises to simplify network operation
and management by:
 Automating end-to-end provisioning of connections
 Managing network resources
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Summary of the GMPLS Protocol Suite
 Extended the signaling (RSVP-TE, CR-LSP) and routing
protocols (OSPF-TE, IS-IS-TE) to accommodate the
characteristics of TDM/SONET & optical networks.
 A new protocol, Link Management Protocol (LMP) has been
introduced to manage and maintain the health of the control and
data planes between two neighboring nodes.
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LSP Creation in GMPLS-Based
Networks / Hierarchical LSP
47
1.
LSP (LSPλ) is established between OXC1 and OXC2 and capable of
delivering OC-192 wavelength to tunnel in TDM LSPs.
2.
LSP (LSPtdi) is established between DCSi and DCSe.
3.
LSP (LSPtdm) is established between DCS1 and DCS2.
4.
LSP (LSPpi) is established between LSR2 and LSR3 (LSPpi).
5.
LSP (LSPpc) is established between LSR1 and LSR4.
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QoS for Mobile Networks
 Problems:




Current IP QoS Signaling is not mobility aware (RSVP, DiffServ etc)
Resources may not be available for the new path
Handoff latency
Different QoS mechanisms
 Requirements/challenges:




Minimize disruption in QoS during handover
Localize the QoS re-establishment to only the effected parts of the packet path
Release any old QoS state after handover as early as possible
Deal with multiple QoS mechanisms deployed

Multi-path routing
 Mobile RSVP (MRSVP)
 Use advance resource reservations
 Common path identification
 Mobile proxy: refresh RSVP state instead of energy constrained mobile device
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QoS for MANETs
 More problems:
 No infrastructure, all mobile battery limited devices
 Frequent topology changes and high mobility
 INSIGNIA
 Support for the delivery of adaptive services in mobile ad hoc
networks
 See Seoung-Bum Lee et al. INSIGNIA: An IP-Based Quality of
Service Framework For Mobile Ad Hoc Networks, Journal of
Parallel and Distributed Computing, 2000.
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Next Steps in Signaling (NSIS)
 RSVP not widely used for resource reservation
 Used for MPLS path setup
 Security an open issue
 Limited support for IP mobility
 IETF NSIS working group is looking at new ways to do QoS
signaling
 Re-use, where appropriate, the mechanisms of RSVP
 See e.g. rfc4080
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Overlay Solutions
 QoS can also be provided by using overlay solutions (application
layer)
 Idea is to determine paths through the overlay network and then
utilize one or more paths with characteristics that meet the
requirements
 Given a good overlay node placement, network topology can be
taken into account and multiple paths across the network can be
determined
 Example: RON Reliable Overlay Network
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Reliable Overlay Routing
RON Example: Reliable Routing
N2
N3
ISP2
ISP1 X
N1
ISP3
Overload
N4
N5
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 Consider a native link failure in CE
 Only overlay link AE is affected.
 The native path AE is rerouted over F
(ACE → ACFDE)
G
3
A
I
3
2
OVERLAY
2
4
E
NATIVE
G
B
∞
F
C
Cost
Overlay
recovery: 8
Original: 2
Native
Recovery
+
H
E
D
Native
Rerouting: 2
Overlay
rerouting: 4
Native
Failure
53
I
A
Time
Native
Repair
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References
1.
Andrew S. Tanenbaum, Computer Networks, Fourth Edition, Pearson Education, 2006.
2.
James F. Kurose, and Keith W. Ross: Computer Networking: A Top-Down Approach Featuring the Internet, Third Edition, Pearson Education, 2006.
3.
Alberto Leon-Garcia and Indra Widjaja, Communication Networks: Fundamental Concepts and Key Architectures, Second Edition, Tata McGraw-Hill, 2005.
4.
IP QoS Architectures and Protocols, Packet Broadband Network Handbook, Digital Engineering Library, McGraw Hill, 2004.
5.
Congestion Control and Quality of Service, Data Communication and Networking, Digital Engineering Library, McGraw Hill, 2006.
6.
Curado, M. and Monteiro, E. , "A Survey of QoS Routing Algorithms", in Proc. of the International Conference on Information Technology (ICIT2004),
December 2004
7.
Manner Jukka, Lopez A, Mihailovi A, Velayos H, Hepworth E, and Y Khouaja, Evaluation of Mobility and QoS Interaction, Computer Networks Volume 38,
Issue 2, 5 Feb 2002, pp. 137-163.
8.
Anup Kumar Talukdar, B. R. Badrinath, and Arup Acharya, MRSVP: A Resource Reservation Protocol for an Integrated Services Network with Mobile Hosts,
Wireless Networks, 7, 5–19, 2001.
9.
Rajeev Koodli, and Charles E. Perkins, Fast Handovers and Context Transfers in Mobile Networks, ACM SIGCOMM Computer Communications Review,
Special Issue on Wireless Extensions to Internet, 2001.
10.
J. Hillebrand, C.Prehofer, R. Bless, M. Zitterbart, Quality-of-Service Signaling for Next-Generation IP-based Mobile Networks, IEEE Communications
Magazine, June 2004.
11.
Seoung-Bum Lee, G. Ahn, X. Zhang and A. T. Campbell, INSIGNIA: An IP-Based Quality of Service Framework For Mobile Ad Hoc Networks, Journal of
Parallel and Distributed Computing, 2000.
12.
Chittaranjan Hota, Sanjay Jha, G Raghurama, Distributed Dynamic Resource Management in IP VPNs to Guarantee Quality of Service, IEEE ICON 2004,
Singapore.
13.
RFC 2205: Resource Reservation Protocol, Braden, Zhang et al.
14.
RFC 3031: Multiprotocol Label Switching (MPLS), Rosen, Viswanathan and Callon.
15.
RFC 2475: An Architecture for Differentiated Services, S. Blake, D. Black et al.
16.
RFC 4080: Next Steps in Signaling (NSIS): Framework, R. Hancock, G. Karagiannis et al., 2005.
17.
RFC 2326: Real Time Streaming Protocol (RTSP), H. Schulzrinne et al., 1998
18.
GMPLS tutorial: http://www.iec.org/online/tutorials/gmpls/
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