Queue Management

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Quality of Service in IP Networks (2)

CH-1015 Ecublenshttp://icawww.epfl.ch

Prof. Jean-Yves Le BoudecProf. Andrzej DudaProf. Patrick Thiran

LCA-ISC-I&C, EPFL

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Integrated Services

o An architecture for providing QOS guarantees in IP networks for individual application sessions

o relies on resource reservation, and routers need to maintain state info (Virtual Circuit??), maintaining records of allocated resources and responding to new Call setuprequests on that basis

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Call Admission

o Session must first declare its QOS requirement and characterize the traffic it will send through the network

o R-spec: defines the QOS being requestedo T-spec: defines the traffic characteristicso A signaling protocol is needed to carry the R-spec and T-spec to the

routers where reservation is required; RSVP is a leading candidate for such signaling protocol

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Call Admission

o Call Admission: routers will admit calls based on their R-spec and T-spec and base on the current resource allocated at the routers to other calls.

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Integrated Services: Classes

o Guaranteed QOS: this class is provided with firm bounds on queuing delay at a router; envisioned for hard real-time applications that are highly sensitive to end-to-end delay expectation and variance

o Controlled Load: this class is provided a QOS closely approximatingthat provided by an unloaded router; envisioned for today’s IP network real-time applications which perform well in an unloaded network

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RSVP

o Performs resource reservation for unicast and multicast applicationo RSVP session = IP data flow identified by destination

l destination IP address (unicast or multicast)l IP protocol number l (optional) destination port (TCP, UDP, …)

o Flow descriptors:l Flowspec = QoS =

– R-SPEC (reserved QoS)– T-SPEC (Source traffic description)

l Filterspec = Data = Set of packets that can use the reservation in the session (source IP address, source port)

o Ad-SPEC = information about the state of a router (rate, latency). Modified by intermediate systems to give cumulative values through a path (total latency, minimal rate

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RSVP session establishment

o Advertizment with a PATH message = l Address of previous hop RSVP nodel RSVP session identifierl T-SPECl Ad-SPEC

path

S R1 R2 D

path path

(S,S-D,T-Spec,Ad-Spec)

(R1,S-D,T-Spec,Ad-Spec)

(R2,S-D,T-Spec,Ad-Spec)

path

S R1 R2 D

path path

(D,S-D,R-Spec)

resv resv resv(R2,S-D,R-Spec)

(R1,S-D,R-Spec)

o Reservation with a RESV message = l Address of previous hop RSVP nodel RSVP session identifierl R-SPEC

o RESV and PATH messages must follow the same route

Reservations can be merged

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RSVP session establishment

o Routers must send error message when reservation rejected o Sources may send a confirmation of reservation

path

S R1 R2 D

path path

resv resv resv

resvconf resvconf resvconf

Reservations can be merged

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Reservation styles

o Shared vs separate reservations l Some applications can share reservations among multiple sources (audio-conference)l Other applications cannot share reservations among multiple sources (video-conference)

o Explicit vs wildcard sender reservationsl Some applications want to make reservations from some sources only (tele-teaching)l Other applications want to make reservations from any source only (videa-conference)

Separate Shared

Wildcard

Explicit

- Wildcard WF

Share-Explicit SE

Fixed-Filter FF

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Soft state

o Reservations need to be periodically refreshed by PATH and RESV messages to be maintained

o Allows to cope with change of routeso End of RSVP session:

l Do nothing and wait for time-outl Send a PATH-Teardown message or a RESV-Teadown message

path

S R1 R2D

path

resv

resv

R3

path

resv

released after time-out

new reservation

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RSVP packet header

Ver IHL ToS Total length

identification Flags Fragment offset

TTL Protocol 46 checksum

Source IP address

Destination IP address

Ver Flags Type RSVP checksum

RSVP lengthreservedSend_TTL

IP

RSVP

o Send_TTL different from IP TTL if some routers are not RSVP enabledo Message types are PATH, RESV, PathTear, PathErr, ResvConf ,…o RSVP Ver = 1o Flags not used

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Differentiated Services

o Intended to address the following difficulties with Intservand RSVP;o Scalability: maintaining states by routers in high speed networks is

difficult sue to the very large number of flows o Flexible Service Models: Intservhas only two classes, want to provide

more qualitative service classes; want to provide ‘relative’ service distinction (Platinum, Gold, Silver, …)

o Simpler signaling : (than RSVP) many applications and users may only want to specify a more qualitative notion of service

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Differentiated Services

o Approach: l Only simple functions in the core, and relatively complex functions at edge routers

(or hosts)l Do not define service classes, instead provides functional components with which

service classes can be built

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Edge Functions

o At DS-capable host or first DS-capable routero Classification: edge node marks packets according to classification

rules to be specified (manually by admin, or by some TBD protocol)o Traffic Conditioning : edge node may delay and then forward or may

discard

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Core Functions

o Forwarding: according to “Per-Hop-Behavior” or PHB specified for the particular packet class; such PHB is strictly based on class marking (no other header fields can be used to influence PHB)

o BIG ADVANTAGE:No state info to be maintained by routers!

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Classification and Conditioning

o It may be desirable to limit traffic injection rate of some class; user declares traffic profile (eg, rate and burst size); traffic is metered and shaped if non-conforming

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Forwarding (PHB)

o PHB result in a different observable (measurable) forwarding performance behavior

o PHB does not specify what mechanisms to use to ensure required PHB performance behavior

o Examples: l Class A gets x% of outgoing link bandwidth over time intervals of a specified

lengthl Class A packets leave first before packets from class B

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Forwarding (PHB)

o Expedited Forwarding : departure rate of packets from a class equals or exceeds a specified rate (logical link with a minimum guaranteed rate).

l Premium service: equivalent to a virtual leased linel The PHB is specified, but the mechanism to implement it (see network calculus)

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Forwarding (PHB)

o Assured Forwarding : 4 classes, each guaranteed a minimum amount of bandwidth and buffering; each with three drop preference partitions

l Olympic service: gold (class 1), silver (class 2) and bronze (class 3).l If customer sends more than its traffic profile, then the excess traffic may be

dropped following the drop perference optionsl Afij = class i and drop precedence j. AF1i has lower loss proabability than AF2j,

AFi1 has lower loss probability than AFi2 l Different drop precedence level RIO (modification of RED with different drop

probabilities and threshold).

1

p

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Diffserv packet header

Ver IHL DSCP Total length

identification Flags Fragment offset

TTL Protocol checksum

Source IP address

Destination IP address

IP

o Differentiated Service Code Point (DSCP) determine PHB that the packet will receive (6 bits).

l Default: 000000l EF: 101110l AFij: xxxxx0 depending on the class i and drop precedence j Ex: AF12 = 001100l xxxxx1 can be used locally

o 2 bits are currently unused (reserved for ECN)

CU

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Differentiated Services Issues

o AF and EF are not even in a standard track yet… research ongoingo “Virtual Leased lines” and “Olympic” services are being discussed o Impact of crossing multiple ASs and routers that are not DS-capable

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MPLS

o IETF work on Multi-Protocol Label Swappingl originally proposed by CISCO as Tag Switching

o (Initial) Purpose:l increase router performance in WANs (global Internet) by reducing complexity of

packet forwardingreduce number of entries in look-up tablesreduce real time processing of packet header (exact vs. longest prefix match )

l support scalable flow based packet forwarding (ex: reserved flow s)

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Principle

o LSR = Label Swiched Router (integrates routing and switching)o LSP = Label Switched Patho LER (Label Edge Router) binds label with IP packeto Egress LSR removes label

LSR1

LSR2

LSR3

IPIP 1

IP address -> label L1

LER IP 3

L1 W L3 NEL2 W L2 SE

L3 W L5 EL7 W L4 S

IP 5LSR4

IP

L5 W E

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Label binding

o All IP packets in the same FEC (Forwarding Equivalent Class) receive the same label

LSR1

LSR2

LSR3

IPIP 1

IP address -> label L1

LER IP 3

L1 W L3 NEL2 W L2 SE

L3 W L5 EL7 W L4 S

IP 5LSR4

IP

L5 W E

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Label Stack

o Two (or more) MPLS domainso Allows tunnelling

LSR1

LSR2

LSR3

IPIP 1LER IP 3

IP 1LSR4

IP1

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IP packet...

Label Format

o 32-bit label appended to packeto at LSR

l label swapping l TTL is decremented

label

32 bits = 20 3 1 8

cos: class of serviceS = 1 if bottom of stack

cos S TTLlabel

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Label Distribution

o Label distribution is either l Explicit: done by a special protocol :

– LDP (Label Distribution Protocol)– RSVP

l Destination based – Label mapping piggybacked in routing protocol messages (BGP)

o Label mappings are sent by downstream LSR towards upstream LSR

R2R1

R4

23: 128.178/16

875: 10/8

10/8875

2

3

1

128.178/1610/8

23399

Label Inf. Base

21

128.178/1623

23399

23875

23

input table

233: 128.178/1699: 10/8

R3

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Label Distribution

o Downstream label distribution l On demand (following a request from an upstream LSR)l Unsollicited

o Which LSR initiates label distribution ?l Egress LSR (ordered control)l Any LSR (independent control)

R2R1

R4

23: 128.178/16

875: 10/8

10/8875

2

3

1

128.178/1610/8

23399

Label Inf. Base

21

128.178/1623

23399

23875

23

input table

233: 128.178/1699: 10/8

R3

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Example: Packet Forwarding

o Packets forwarded from upstream LSR towards downstream LSRo Label mappings are sent by downstream LSR towards upstream LSR

R2

R3

R4

2

3

121

da=128.178.156.24233 da=128.178.156.24

23 da=128.178.156.24

da=10.149.231.65

99 da=128.178.156.24

875 da=128.178.156.24

R1

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MPLS

o Initial purpose:l increase router performance in WANs (global Internet) by reducing complexity of

packet forwardingreduce number of entries in look-up tablesreduce real time processing of packet header (exact vs. longest prefix match )

l support scalable flow based packet forwarding (ex: reserved flow s)

o Main (other) purposes:l Explicit routing for traffic engineering (load balancing)l Fast restorationl Virtual Private Networks

o Well fit for packet switched logical topology on top of a circuit switched physical topology:

l IP/WDM networks: label is replaced by a wavelength (MPλS)