Routing e QoS

1
Routing e QoS

• Francesco Santini
• IMT-Lucca
• venerdì 9 novembre 2007

2
Contenuti

• Applicazioni real-time e QoS
• IntServ e RSVP
• DiffServ
• MPLS

3
Contenuti

• Applicazioni real-time e QoS
• IntServ e RSVP
• DiffServ
• MPLS

4
Best effort

• Consegno i pacchetti al meglio che posso
• Conseguenze
• Tutti i dati vengono trattati alla stessa maniera
• Non è possibile avere delle garanzie per un
  flusso
• Difficile offrire servizi su tale schema
• Non avendo garanzie ed essendo trattati alla
  stesa maniera, in caso di congestione posso
  scartare i pacchetti

5
Dati real-time

• Audio, Voce, Video
• Ma anche dati che devono essere consegnati con
  una certa precisione
• Posizione e azioni nei giochi
• Tele operazioni in medicina (robot)
• Controllo industriale (robot)
• Quotazioni azioni
• Negli ultimi anni, aumento banda dei link e
  miglioramento algoritmi compressione

6
Real-time applications

• Applicazioni sensibili alla tempesitivtà dei
  dati (timeliness)
• Deve essere supportato da tutta la rete,
  nativamente

7
Why we need QoS?

• Common issues in networks are
• Loss / packet drop
• Drop above certain will influence experience
• On congestion different drop algorithms are used.
• RED, RIO, WRED, tail drop
• Jitter (variation in delay)
• Jitter buffer can handle some jitter (used i.e in
  VoIP).
• Misordering (different routes) (delay)
• Delay (queuing)
• QoS is basically a set of techniques to handle
  these issues for selected services.

8
Delay Four sources of delay

• 1. processing
• check bit errors
• determine output link (routing table lookup)
• CPU, architecture etc

• 2. queueing
• time waiting at output link for transmission
• depends on congestion level of router and queue
  size

9
Four sources of packet delay

• 3. Transmission delay
• Rlink bandwidth (bps)
• Lpacket length (bits)
• time to send bits into link L/R

• 4. Propagation delay
• d length of physical link
• s propagation speed in medium (2x108 m/sec)
• propagation delay d/s

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Nodal delay

• dproc processing delay
• Usually small though depending on the processor,
  a few microsecs?
• dqueue queuing delay
• depends on the congestion level
• dtrans transmission delay
• L/R, significant for low-speed links
• dprop propagation delay
• a few microsecs to hundreds of msecs

11
Traceroute
12
Playback

• Playback Buffer

13
Esemio VoIP
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Classificazione applicazioni
Perdita pacchetti
Applications
Spostare playback point / Cambiare compressione
Elastic
Real Time
Intolerant
Tolerant
Adaptive
Non-Adaptive
Robot/ Audio
Delay Adaptive
Rate Adaptive
Robot medico
www email
15
Delay Adaptive
Density
100
99
97
msec
50
150
250
16
Why Not TCP

• Dont want reliable transmission
• TCP is purely byte oriented
• TCP relies on saturating the net
• Retransmitting end-to-end is not a solution

17
La soluzione

• Obiettivo è avere un modello di servizi che
• Mi garantisca effettivamente le richieste
• Mi risponda che non è possibile soddisfare tale
  richiesta al momento
• Bisogno di più classi di servizio differenti
• Mantenere best effort! ?

18
Soluzioni esistenti

• Architetture
• Integrated Services
• Differentiated Services
• Protocolli
• Multi-Protocol Label Switching (MPLS)
• Metodologie più generiche
• Traffic Engineering
• Constraint Based Routing

19
Soluzioni esistenti(2)
20
Alcune definizioni

• Service Level Agreement (SLA) A service contract
  between a customer and a service provider that
  specifies the forwarding service a customer
  should receive. A customer may be a user
  organization or another provider domain (upstream
  domain).
• Traffic profile A description of the properties
  of a traffic stream such as rate and burst size.
• Scheduling The process of deciding which packet
  to send first in a system of multiple queues
• Shaping The process of delaying packets within
  traffic stream to cause it to conform to some
  defined traffic profile.

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Definizione di flusso

• Flow A stream of packets with the same source IP
  address, source port number, destination IP
  address, destination port number and protocol ID
  (unicast or multicast).

• Omogeneo
• Eterogeneo

22
Contenuti

• Applicazioni real-time e QoS
• IntServ e RSVP
• DiffServ
• MPLS

23
Integrated Service (IntServ)

• IntServ framework was developed within IETF to
  provide individualized QoS guarantees to
  individual sessions
• provides services on a per flow basis where a
  flow is a packet stream with common source
  address, destination address and port number
• IntServ routers must maintain per flow state
  information

24
Riferimenti

• RFC 1633 - Integrated Services in the Internet
  Architecture an Overview
• RFC 2211 - Specification of the Controlled-Load
  Network Element Service
• RFC 2212 - Specification of Guaranteed Quality of
  Service
• RFC 2215 - General Characterization Parameters
  for Integrated Service Network Elements
• RFC 2205 - Resource ReSerVation Protocol (RSVP)

25
IntServ

• two key IntServ features
• Reserved Resources
• the router must know the amount of its resources
  currently reserved for on-going sessions
• standard resources link capacity, router buffers
• Call Setup
• A flow requiring QoS guarantees must be able to
  reserve sufficient resources at each router on
  path to ensure QoS requirements are met

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Role of RSVP

• Rides on top of unicast/multicast routing
  protocols
• Must be present at sender(s), receiver(s), and
  routers
• Carries resource requests all the way through the
  network
• At each hop consults admission control and sets
  up reservation

27
Esempio semplice
28
RSVP Service Model

• Make reservations for simplex data streams.
• Receiver decides whether to make reservation
• Control messages in IP datagrams (proto 46).
• PATH/RESV messages sent periodically to refresh
  soft state on the router
• Failed requests return error messages - receiver
  must try again
• No end to end ack for success

29
Flow Specification

• Session must first declare its QoS requirement
  and characterize the traffic it will send through
  the network
• R-spec defines the QoS being requested by
  receiver
• T-spec defines the traffic characteristics of
  sender
• RSVP is the signaling protocol is needed to carry
  the R-spec and T-spec to the routers

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Filter Specification

• The router needs to recognize the packets
  belonging to that flow
• IP of the sender
• IP destination
• Port number generating the packets
• Port number of the receiver
• Protocol ID
• Any field of the header
• flowspec filterspec flowdescriptor

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PATH Messages

• PATH messages carry senders Traffic
  Specifications (TSpec)
• Carries also the FilterSpec
• Routers note the direction PATH messages arrived
  and set up reverse path to sender
• Receivers send RESV messages that follow reverse
  path and setup reservations
• If reservation cannot be made, user gets an error

32
RESV Messages

• RESV messages carry receivers QoS needs (R-spec)
• Forwarded via reverse path of PATH
• Queuing delay and bandwidth requirements
• Source traffic characteristics (from PATH)
• Filter specification
• Which transmissions can use the reserved
  resources?
• Reservation style.
• Router performs admission control and reserves
  resources

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Router Handling of RESV Messages

• If new request rejected, send error message.
• If admitted
• Install packet filter into forwarding dbase.
• Pass flow parameters to scheduler.
• Activate packet policing if needed.
• Forward RESV message upstream.

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Integrated Services - RSVP

• Mechanisms
• Flow specification
• Tell the network what the flow wants
• Admission control
• Network decides if it can handle flow
• Reservation
• Enable admission control
• Packet classification
• Map packets to flows
• Scheduling
• Forwarding policy

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Integrated Services - RSVP

• Example
• Flowspec
• 100 msec guaranteed to www.nsf.gov
• Reservation
• Spec travels down path for approval
• Delay guarantee approved by all routers, so
  admitted
• Classification
• Packets marked as guaranteed
• EXAMPLE policy
• guaranteed packets sent first

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RSVP Functional Diagram
Host
Router
RSVPD
D A T A
DATA
DATA
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Soft State

• Routers keep state about reservation
• Periodic messages refresh state, with PATH and
  RESV messages
• Non-refreshed state times out automatically
• Alternative Hard state
• No periodic refresh messages.
• State is guaranteed to be there.
• State is kept till explicit removal.
• Properties of soft state
• Adapts to changes in routes, sources, and
  receivers.
• Recovers from failures
• Cleans up state after receivers drop out

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RSVP Reservation (1)
R3
R2
R4
R1
Host B 128.32.32.69
Host A 24.1.70.210
R5
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RSVP Reservation (2)
R3
R2
R4
PATH
R1
PATH
Host B 128.32.32.69
PATH
PATH
Host A 24.1.70.210
R5
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RSVP Multicast Reservation (1)
Sender
R1
R3
R2
R5
R6
R4
R7
Receiver
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RSVP Multicast Reservation (2)
Sender
R1
R3
R2
R5
R6
R4
R7
Receiver
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Reservation Merging
(3) 50Kbs
R1
Reservations merge as they travel up tree.
(6) 100 Kbs
R3
(2) 50Kbs
(5) 100 Kbs
(9) 60Kbs
R4
R6
R7
(1) 50Kbs
(4) 100 Kbs
(8) 60Kbs
Receiver 1
Receiver 2
Receiver 3
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Token Bucket (TSpec)
Drops packets if token is not available
Buffers data until tokens become available
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Token Bucket (2)
r
b bucket size in tokens r rate tokens are
added to bucket
b
Data Queue
Data

• Beta mi consente di rappresentare i burst di
  traffico, limitandoli
• Sigma di descrive il normale rate previsto dei
  pacchetti
• I dati vengono trasmessi quando esistono
  sufficienti token per mandarli
• Es bucket 40 token, 1 token 1 byte implica
  che posso mandare burst di 40 byte
• Nel tempo t, la quantità di traffico e limitata a
  ß ?t

45
In words

• Tspec describe flows traffic characterization
• Average bandwidth burstiness token bucket
  filter
• Token rate r
• Bucket depth B
• Must have a token to send a byte
• Must have n tokens to send n bytes
• Start with no tokens
• Accumulate tokens at rate of r per second
• Can accumulate no more than B tokens

46
Two Service Classes

• RSVP supports three service classes
• Guaranteed service
• Specified maximum delay
• Controlled load services
• For delay tolerant, adaptive applications
• Network shields this traffic from congestion
• Best effort

47
RSVP Routing Problems

• IntServ does not specify any route selection of
  its own
• It relies on existing routing protocols to
  forward its control packets further
• Routing is separated from admission control
• If route changes, reservation must be made along
  new route
• New reservation takes time to setup
• New reservation might fail
• Old route could still be working fine
• Route pinning
• Always use the route where reservation is in
  place

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Problemi IntServ

• Complessità/Scalabilità problema centrale per
  grandi reti backbone
• End-to-end
• Stato replicato su tutti i router, per ciascun
  flusso
• Le informazioni devono essere rinfrescate
  periodicamente
• Il processo di controllo ammissione avviene per
  ogni flusso
• La richiesta di QoS avviene dinamicamente

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Contenuti

• Applicazioni real-time e QoS
• IntServ e RSVP
• DiffServ
• MPLS

50
Differential Service (DiffServ)

• In DiffServ, flows are aggregated into classes
  that receive treatment by class.
• More complex operations are pushed out to edge
  routers and simpler operations done by core
  routers.
• motivated by
• scalability, flexibility, and better-than-best-eff
  ort service without RSVP signaling
• Flexibility Flow A better than flow B

51
Riferimenti

• RFC 2474Definition of the Differentiated
  Services Field (DS Field) in the IPv4 and IPv6
  Headers
• RFC 2475An Architecture for Differentiated
  Services
• RFC 2597Assured Forwarding PHB Group
• RFC 3140Per Hop Behavior Identification Codes
• RFC 3246An Expedited Forwarding PHB

52
DiffServ functional elements

• Edge functions
• packet classification
• packet marking
• traffic conditioning
• Core functions
• forwarding based on per-hop behavior (PHB)
  associated with packets class, no more
  end-to-end as in IntServ

53
DiffServ edge functions

• packet classification
• classifier selects packets based on values in
  packet header fields and steers packet to
  appropriate marking function
• how classifier obtains the rules for
  classification not yet addressed RFC 2475 uses
  term behavior aggregate rather than class of
  traffic.
• administrator could load table of source
  addresses
• done under control of TBA signaling protocol

54
Traffic Conditioner Block (TCB)
Classification selects a packet in a traffic
stream based on the content of some portion of
the packet header
55
Traffic Conditioner Block (TCB)
Metering checks whether the traffic falls within
the negotiated profile.
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Traffic Conditioner Block (TCB)
Marking marks packet to a particular DS behavior
aggregate
57
Traffic Conditioner Block (TCB)
Shaper/Droper delays if necessary and then
forwards or discards the packets .
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DS field

• Former ToS Byte new DS field

59
DiffServ core routers

• Routers define packet classes and separate
  incoming packets into classes.
• Treatment is done per class.
• Per-hop behavior (PHB) defines differences in
  performance among classes.
• externally observable performance criteria that
  do not specify internal implementation mechanisms
  at router.

60
Router interni

• No reservation ma provisioning
• La qualità del servizio dipende da provisioning e
  da come sono gestire le risorse nella rete
• Scalabilità deriva da aggregazione di più flussi
  in un numero limitato di classi (DSCP)

61
PHB types
The DSCP (6 bit) pattern is 000000

• Default PHB
• Traditional best effort treatment.
• Must be implemented
• Used for unsupported DSCP

62
PHB types
The DSCP (6 bit) pattern is 101110

• Expedited Forwarding PHB
• Providing low loss, low latency, low jitter,
  assured bandwidth, end-to-end service through DS
  domains
• Implies isolation guarantee for the EF traffic
  should not be influenced by the other traffic
  classes
• Non-conformant traffic is dropped or shaped.
• Possible service providing a virtual wire

63
PHB types

• Assured Forwarding (AF)
• A method by which Behavior Aggregates can be
  given different forwarding assurances.
• The intent is that it will be used to implement
  services that differ relative to each other
  (e.g., gold, silver,).
• AF defines 4 classes with some bandwidth and
  buffers allocated to them.
• Within each class, there are three drop
  priorities, which affect which packets will get
  dropped first if there is congestion.
• Non-conformant traffic is remarked.

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AF table
The DSCP (6 bit) pattern is xyzab0 xyz is the
class 001-class1 010-class2 011-class3
100-class4ab is the drop precedence 01-low
10-medium 11-high
ClassDropprecedence Class 1 Class 2 Class 3 Class 4
Low Drop 001010(AF11) 010010(AF21) 011010(AF31) 100010(AF41)
Medium Drop 001100(AF12) 010100(AF22) 011100(AF32) 100100(AF42)
High Drop 001110(AF13) 010110(AF23) 011110(AF33) 100110(AF43)
65
Service

• A service describes the overall treatment of a
  customers traffic within a DS domain.
• Customers see services, not PHBs.
• To support a service, many components must work
  together
• Mapping of service to PHBs, traffic conditioning,
  network provisioning, PHB-based forwarding.
• Services in the DiffServ architecture is defined
  in the form of Service Level Agreement (SLA).

66
Putting it all together
67
Assured Forwarding (AF) PHB

• Determining resource allocation per class of
  service must be done with knowledge about traffic
  demands for the various traffic classes.

68
Conclusioni

• Una via di mezzo tra best effort e IntServ
• Si basa su provisioning, ma è difficile da
  effettuare. Più facile con reservation
• Più flussi in una sola classe. Meno possibilità
  rispetto a IntServ

69
IntServ e DiffServ riassunto
70
IntServ e DiffServ insieme

• Approcci complementari
• IntServ forti garanzie ma limiti scaling
• DiffServ garanzie deboli, ma buon scaling
• La soluzione è unirli!
• IntServ sui router
• DiffServ su tutti gli altri router backbone
• Mapping tra classi di servizio IntServ a livello
  di servizio DiffServ

71
IntServ e DiffServ insieme(2)
72
Contenuti

• Applicazioni real-time e QoS
• IntServ e RSVP
• DiffServ
• MPLS

73
Multi Protocol Label Switching

• Uso di unetichetta di lunghezza fissa per
  instradare
• MPLS è un forwarding scheme
• Evoluto da Cisco Tag Switching
• Tra Layer 2 (L2, link layer) a Layer 3 (L3,
  network layer) 2.5 level
• RFC 3031
• Si chiama multi-protocol perché, in linea di
  principio, è in grado di operare con qualunque
  protocollo di livello 3 (rete) anche se lo si
  applica tipicamente ad IP.
• Permette ai nodi che lo utilizzano di realizzare
  una communtazione su base etichetta e anche un
  instradamento tipo Circuito Virtuale su base
  flusso.

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MPLS and ISO model
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Termonologia

• I nodi (router) che operano usando MPLS vengono
  chiamati Label Switching Router (LSR)
• La parte di rete che questi nodi compongono viene
  chiamata Dominio MPLS (MPLS Domain)
• I nodi al confine del Dominio, ossia i nodi che
  ricevono/trasmettono traffico allesterno del
  Dominio vengono chiamati Edge Label Switching
  Router (ELSR)

76
MPLS Cloud
LER
L3 Routing
LER
LER
L3 Routing
L3 Routing
LSR
LSR
LER
Label Swapping
Label Swapping
LER
L3 Routing
L3 Routing
IP Packet IP Packet w/ Label
77
Funzionamento

• Lidea di base è che una certa tipologia di
  pacchetti che raggiungono un ELSR debbano venir
  trasportati allinterno del Dominio tramite MPLS
  ad un altro ELSR.
• In corrispondenza di un indirizzo di destinazione
  e di un tipo di trattamento richiesto (QoS) viene
  definita una specifica Forwarding Equivalent
  Class (FEC).
• Una FEC individua quindi un aggregato di
  pacchetti diretto ad una stessa destinazione
  (intesa o come destinazione finale ocome ELSR)
  che devono avere lo stesso trattamento

78
Funzionamento (2)

• Quanto un ELSR riceve un pacchetto IP
• compie una operazione di Classificazione, ossia
  in base a quanto contenuto nellintestazione
  identifica leventuale FEC di appartenenza
• inserisce fra lintestazione di livello 2 e il
  pacchetto IP una Label.
• Tale Label
• Identifica la FEC a cui il pacchetto appartiene
• Ha una lunghezza costante e breve
• Ha un significato locale alla linea

79
Funzionamento (3)

• DallELSR di ingresso a quello di uscita tutte le
  operazioni di forwarding verranno effettuate
  utilizzando solo la Label e quindi lintestazione
  del pacchetto IP non verrà più letta fino
  allELSR di destinazione.
• Gli LSR attraversati leggono la Label, trovano
  tramite essa in una tabella il FEC corrispondente
  ossia linformazione sulla porta di uscita, la
  Label successiva ed il tipo di trattamento
  richiesto.
• LELSR di uscita (quindi lultimo nodo
  attraversato allinterno del Dominio MPLS)
  elimina la Label ed instrada il pacchetto
  nuovamente sulla base dellindirizzo IP.

80
Label Switched Path
81
Passi fondamentali

• MPLS prevede in sostanza 4 passi fondamentali
• La definizione di una FEC
• Lindividuazione del percorso LSP.
• La creazione (associazione al FEC) e
  distribuzione delle Label lungo il LSP (si
  osservi che questa operazione e la precedente si
  svolgono in modo parallelo e coordinato).
• Il meccanismo di forwarding che comprende
  linserimento della Label, la commutazione sulla
  base di essa e la sua rimozione.

82
Etichette

• Per distribuire
• Label Distribution Protocol (LDP)
• RSVP-TE (Traffic Engineering)
• Minimizzare il loro numero (tabelle piccole)
  anche ridurre il traffico di segnalazione
• Aggregation FEC diversi con la stessa label, per
  esempio se destinazione è uguale
• Label Merging pacchetti da diversi LSR hanno
  label diversa per la stessa FEC

83
Operazioni

• Le operazioni che vengono effettuate sul
  pacchetto in transito nei LSR in relazione alle
  Label sono sostanzialmente tre
• Pushing, ossia linserimento della Label, che
  viene realizzata dallELSR di ingresso.
• Swapping, ossia conversione delletichetta,
  realizzata contestualmente alloperazione di
  commutazione
• Popping, ossia leliminazione di etichetta
  effettuata dallultimo o dal penultimo LSR

84
Header
S the current label is the last in the stack
85
Label popping

• Conviene fare il popping al penultimo LSR
  (Penultimate Popping), perché
• Allutimo nodo il forwarding viene eseguito sulla
  base del pacchetto IP e quindi losservazione
  della Label è inutile
• Lasciarlo significa costringere il nodo a cercae
  nella tabella MPLS per scoprire che deve
  eliminare la Label e quindi usare IP
• Non sempre si può fare il Penultimate Popping in
  quanto non è detto che lLSR sia in grado di
  accorgersi di essere il penultimo del LSP.

86
Multidominio
87
Vantaggi

• La procedura di forwarding richiede solo
  lispezione di una etichetta (Label) di
  dimensioni ridotte e lesplorazione di una
  tabella relativamente semplice
• Instradamento effettuato anche con altre
  informazioni, non solo header come IP
• Possibile scegliere percorsi per traffic
  engineering e QoS
• Tunneling efficiente

88
Riferimenti

• G. Chaffee, RSVP The ReSerVation Protocol,
  Multimedia Research Berkeley Center, (ppt online)
  
• E. Rot and I. Poleg DiffServ QoS in internet,
  Presentation for ATM Networks course (EE-046992)
  (ppt online)
• R. Bolla, Servizi Multimediali e Qualità del
  Servizio (QdS) su IP MPLS, appunti di
  Telematica 2, università di Genova.

89
Contatti f.santini_at_imtlucca.it