89-850 Communication Networks:
Protocols for QoS Support:
RSVP and MLPS
Source and ©: Stallings Hi-Speed Networks and Internets, Ch. 18
Last updated: Monday, July 31, 2017
Prof. Amir Herzberg
Dept of Computer Science, Bar Ilan University
http://AmirHerzberg.com
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Chapter 18 Protocols for QoS Support
Resource Reservation: RSVP
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Dynamic routing, WFQ, diff-serv (RED, ECN):
use available resources for existing traffic
RSVP: reserve resources to ensure QoS
Unicast: appl reserves resources (@routers)
– If QoS unavailable: wait or try at reduced QoS

Multicast: ditto, plus…
– Some recipients may not want to `tune in`
– Others may want only some of the traffic

E.g. basic and enhanced video components, select channel
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Chapter 18 Protocols for QoS Support
Resource Reservation
Problems on an Internet

Must interact with dynamic routing
– Reservations must follow changes in route
– Implicit assumption: new route is `better` 
would usually have resources

Soft state – a set of state information at a
router that expires unless refreshed
– End users periodically renew resource
requests
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Chapter 18 Protocols for QoS Support
Resource ReSerVation Protocol
(RSVP) Design Goals

Enable receivers to make reservations
– Allow different reservations in same multicast group

Deal gracefully with changes in group membership
– Dynamic reservations, separate for each member of group

Aggregate for group should reflect resources needed
– Take into account common path to different members of group

Receivers can select one of multiple sources
– E.g. to select `channel` to view

Deal gracefully with changes in routes
– Re-establish reservations
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Minimize, aggregate control protocol overhead
Independent of routing protocol
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Chapter 18 Protocols for QoS Support
RSVP Characteristics
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Unicast and Multicast
Simplex
– Unidirectional data flow
– Separate reservations in two directions

Receiver initiated
– Receiver knows which subset of source transmissions it wants

Maintain soft state in internet
– Responsibility of end users

Providing different reservation styles
– Users specify how reservations for each group are aggregated

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Transparent operation through non-RSVP routers
Support IPv4 (ToS field) and IPv6 (Flow label field)
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Chapter 18 Protocols for QoS Support
Data Flows - Session
Data flow identified by destination
 Resources allocated by router for duration
of session
 Defined by

– Destination IP address

Unicast or multicast
– IP protocol identifier

TCP, UDP etc.
– Destination port

May not be used in multicast
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Flow Descriptor
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Reservation Request issued by destination
– Flow spec
Desired QoS
 Used to set parameters in node’s packet scheduler
 Service class, Rspec (reserve), Tspec (traffic)

– Filter spec
Set of packets for this reservation
 Source address, source UDP/TCP port

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Treatment of Packets of One
Session at One Router
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RSVP Operation Diagram
G1, G2
sent
filter spec
w/o S2
G3
sent
filter
spec
w/o
grey
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Chapter 18 Protocols for QoS Support
Reservation Styles
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How resource requirements from members of
group are aggregated
Reservation attribute
– Reservation shared among all senders (shared)

Characterizing entire flow received on multicast address
– Allocated to each sender (distinct)


Simultaneously capable of receiving flow from each sender
Sender selection
– List of sources (explicit)
– All sources, no filter spec (wild card)
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Chapter 18 Protocols for QoS Support
Reservation Styles in RSVP

Reservation Attribute:
– Distinct
Sender selection explicit = Fixed filter (FF) style
 Sender selection wild card = none

– Shared
Sender selection explicit= Shared-explicit (SE) style
 Sender selection wild card = Wild card filter (WF)

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Chapter 18 Protocols for QoS Support
Fixed Filter Style
Distinct reservation for each sender
 Explicit list of senders
 FF(S1{Q1}, S2{Q2},…)
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– Q = flow spec

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E.g. nB for n units of resource B
Example usage: video distribution
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Chapter 18 Protocols for QoS Support
Shared Explicit Style
Single reservation shared among specific
list of senders
 SE(S1, S2, S3, …{Q})
 Multicast data sources
 Unlikely to transmit simultaneously
 E.g. primary and backup sources

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Chapter 18 Protocols for QoS Support
Wild Card Filter Style
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Single reservation shared by all senders
If used by all receivers: shared pipe whose
capacity is largest of resource requests from
receivers downstream from any point on tree
Independent of number of senders using it
Propagated upstream to all senders
WF(*{Q})
– * = used for (wild card) sender

Audio teleconferencing with multiple sites
– Assuming one speaker at any given time
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Chapter 18 Protocols for QoS Support
Reservation Style Examples
If
shorter
route
from
S2, S3
to R1
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RSVP Protocol Mechanisms

Two message types
– Resv

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Originate at multicast group receivers
Propagate upstream
Merged when appropriate
Create soft states
Reach sender
– Allow host to set up traffic control for first hop
– Path



Provide upstream routing information
Issued by sending hosts (to allow Resv to reach sources)
Transmitted through distribution tree to all destinations
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RSVP Host Model
5
2
6
4
3
1
7
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RSVP Router Model
From multicast routing:
N(group)
RSVP in Router
Rcv(m,u,style)
(message m from neighbor u;
m{path(g),rsv(g,amt,)})
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Chapter 18 Protocols for QoS Support
Multi-Protocol Label Switching
(MPLS) : Background

Mid-1990s: Efforts to marry IP and ATM
– Motivation: ATM switches were much faster than routers
– IP switching (Ipsilon), Tag switching (Cisco), …


Routing (e.g. OSPF) define path between end points
Assign packets to flow & path as they enter network
–
–
–
–
–
Simpler, faster routing/switching of packets
Connection-oriented QoS support
Traffic engineering: choose and change path for each flow
Virtual private networks
Multi-Protocol support
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Chapter 18 Protocols for QoS Support
MPLS: Connection Oriented
QoS Support
Guarantee fixed capacity for specific
applications
 Control latency/jitter

– Ensure capacity for voice
Provide specific, guaranteed quantifiable
SLAs
 Configure varying degrees of QoS
 MPLS imposes connection oriented
framework on IP based internets

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Chapter 18 Protocols for QoS Support
MPLS Traffic Engineering


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Traffic Eng: select routes, reserve resources to
optimize utilization based on known demands
Basic IP: per-packet routing/forwarding decision
MPLS: aware of flow traffic, QoS req’
– Load-balance – select (different) route for flows
– Intelligent re-routing (of flows) when congested
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Chapter 18 Protocols for QoS Support
MPLS Operation

Label Switched Routers (LSR)
– Forward packets based on appended label
– IP header not examined
Labels define flow of packets between end
points or multicast destinations
 Connection oriented: each flow has…

– Specific path through LSRs
– Specific QoS requirements
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MPLS Domain Operation
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Explanation - Setup
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Labelled Switched Path (LSP) established prior
to routing and delivery of packets
QoS parameters established along LSP:
–
–
–
–
Resource commitment
Queuing and discard policy at LSR (Per-Hop Behav.)
Interior routing protocol e.g. OSPF used
Labels assigned

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Local significance only
Manually or using protocol
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Explanation – Packet Handling
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Packet enters domain through edge LSR
– Edge LSR determines flow, LSP
– Append label
– Forward packet

LSR within domain:
– Remove label from incoming packet
– Attach outgoing label and forward

Egress LSR:
– Strips label, reads IP header and forwards
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MPLS Packet Forwarding
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MPLS Labels Stack

Packet may carry a stack of MPLS labels
– Processing based on top label
– Any LSR may push or pop label

Unlimited levels
– Push label of aggregate (tunnel) LSP, pop at exit
– Fewer labels  smaller, more efficient tables
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Chapter 18 Protocols for QoS Support
Label Format Diagram
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Label value: Locally significant 20 bit
Exp: 3 bit reserved for experimental use
– E.g. DS information or PHB guidance

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S: 1 for oldest entry in stack, zero otherwise
Time to live (TTL): from (& to!) IP header
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Chapter 18 Protocols for QoS Support
Constraint Based Routing

Take into account traffic requirements of flows
and resources available along hops
– Current utilization, existing capacity, committed
services
– Additional metrics over and above traditional routing
protocols (e.g. OSPF, BGP)

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Maximum link data rate
Current capacity reservation
Packet loss ratio
Link propagation delay
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Label Distribution
Setting up LSP for a flow… each LSR:
 Assign in-label to incoming packets
 Inform all upstream LSRs of in-label
 Receive out-label from downstream LSR
 Manually or by label-setup protocol

– RFC 3031: enhanced RSVP/BGP or new
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Chapter 18 Protocols for QoS Support
Summary - QOS
Queuing to prefer/guarantee QoS (e.g. WFQ)
 Signal congestion to slow TCP (fairly)

– RED, ECN

Reserve resources – RSVP
– For unicast, multicast
– Traditional IP dynamic routing or…
Fixed paths, label switching – MPLS
 More… (e.g. RTP – in book)

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