Differentiated Services 2007

Two Approaches for Providing QoS on the Internet u “Freeway model” -- integrated services Internet (intserv) – Build a dedicated highway or “circuit” between communicating points (VIP) u “Doctor’s model” -- differentiated services (diffserv) – Mark a doctor’s vehicle (e. g.,ambulance) or “packet” to get priority the road and limit the percentage of such high- priority vehicles in the total traffic mix (fire-engine, policeman)

Difficulties with Intserv and RSVP Intsev –A connection-oriented solution –QoS on a per-flow basis –Depends on resource reservation (RSVP) - signaling Scalability – Keeping a state (and using it!) for each flow overloads the routers – Periodic messages to refresh the states create more traffic Router complexity increases How to satisfy heterogeneous QoS requirements for different receivers Ambitious signaling is not practical

Differentiated Services (Diff-Serv) Motivations –Don’t want end-to-end signaling and per-flow state, for scalability, complexity and quick-to-deploy reasons Connectionless mode QoS for aggregates of traffic, such as premium, assured and best- effort –Avoid strong assumptions about traffic types Keep the forwarding path simple –Push complexity to network edge -> Differentiated Services Domain (DS Domain) Per-Hop-Behavior (PHB) –Define behavior of individual routers rather than end- to-end services –forwarding behavior

Differentiated Service (DS) Field Diff-Serv Approach: Use the TOS field to sort packets into classes and routers treat them differently – e.g., delay requirement, drop precedence etc. DS filed reuse the first 6 bits from the TOS byte –Diff- Service Code Point (DSCP) The other two bits are proposed to be used by ECN VersionHLen TOSLength Identification Fragment offset Flags Source address Destination address TTLProtocolHeader checksum Data IP header DS Filed

Differentiated Services (Diffserv) Build around the concept of domain Domain – a contiguous region of network under the same administrative ownership Differentiate between edge and core routers Edge routers –Perform per aggregate shaping or policing –Mark packets with a small number of bits; each bit encoding represents a class (subclass) Core routers –Process packets based on packet marking Far more scalable than Intserv, but provides weaker services

Diffserv Architecture Ingress routers –Police/shape traffic –Set Diff- Service Code Point (DSCP) in Diffserv (DS) field Core routers –Implement Per Hop Behavior (PHB) for each DSCP –Process packets based on DSCP Ingress Egress Ingress Egress DS-1 DS-2 Edge router Core router

Differentiated Services Two types of QoS service –Two PHBs defined so far  Premium service EF - Expedited forwarding (type P)  Assured service AF - Assured forwarding (type A) – 4 classes, each guaranteed a minimum amount of bandwidth and buffering – each with three drop preference partitions Plus, best-effort service

Premium Service EF - Expedited Forwarding Provides guaranteed peak bandwidth service with negligible delay / jitter –Provides the abstraction of a virtual pipe between an ingress and an egress router Network: guarantees that premium packets are not dropped and they experience low delay with requested profile User: sends within profile. User does not send more than the size of the pipe –If it sends more, excess traffic is delayed, and dropped when buffer overflows Rate limiting of EF packets at edges only, using token bucket to shape transmission

Assured Service (1) AF -- Assured Forwarding Provides an expected level of bandwidth with delay Permits flows to use any additional available bandwidth Network: provides lower loss rate than best-effort –In case of congestion best-effort packets are dropped first User: sends no more assured traffic than its profile –If it sends more, the excess traffic is converted to best-effort

Assured Service (2) User and network agree to some traffic profile (how much traffic is a user allowed to send) –Edges mark packets up to allowed rate as “in- profile” or low drop precedence –Other packets are marked with higher drop precedence A congested DS node tries to protect packets with a lower drop precedence value from being lost by preferably discarding packets with a higher drop precedence value –Implemented using buffer management, e. g., RIO -- RED (random early detection) with In and Out

Assured Service (3) Large spatial granularity service Theoretically, user profile is defined irrespective of destination –All other services we learnt are end-to-end, i.e., we know destination(s) apriority This makes service very useful, but hard to provision (why ?) Ingress Traffic profile

Components of Diff-Serv (1) Edge node algorithms –Classification, policing, shaping, metering, marking, etc. (2) Router algorithms –Packet discard algorithms: RED-like methods for in-profile and out-of- profile traffic – Priority, low-latency queueing

Ingress Edge Router Classifier Traffic conditioner Scheduler Class 1 Class 2 Best-effort Marked traffic Ingress Per aggregate Classification (e.g., user) Data traffic

Traffic Conditioning Wait for token Set EF bit Packet input Packet output Test if token Set AF “in” bit token No token Packet input Packet output Drop on overflow Traffic conditioner (TC) implement –Metering –Marking –Shaping

Scheduler Employed by both edge and core routers For premium service – use strict priority, or weighted fair queuing (WFQ) For assured service – use RIO (RED with In and Out) –Has two classes, “In” and “Out” (of profile) –Always drop OUT packets first –For OUT measure entire queue –For IN measure only in-profile queue

RIO (RED with In and Out) Drop Probability P(drop) 1.0 MaxP Min inin Max in Max out Min out AvgLen

Scheduler Example Premium traffic sent at high priority Assured and best-effort traffic pass through RIO and then sent at low priority P-bit set? A-bit set?RIO yes no yes no high priority low priority

Core Router Output Processing What DSCP? If “in” set incr in_cnt High-priority Q Low-priority Q If “in” set decr in_cnt RIO queue management Packets out EF AF

Control Path Each domain is assigned a Bandwidth Broker (BB) –Usually, used to perform ingress-egress bandwidth allocation BB is responsible to perform admission control in the entire domain BB not easy to implement –Require complete knowledge about domain –Single point of failure, may be performance bottleneck –Designing BB still a research problem

Example Achieve end-to-end bandwidth guarantee BB sender receiver 8 profile 6 4

Comparison Service Service Scope Complexity Scalability Connectivity No isolation No guarantees End-to-end No set-up Highly scalable (nodes maintain only routing state) Best-Efforts Per aggregation isolation Per aggregation guarantee Domain Long term setup Scalable (edge routers maintains per aggregate state; core routers per class state) Diffserv Per flow isolation Per flow guarantee End-to-end Per flow setup Not scalable (each router maintains per flow state) Intserv

Summary Diffserv more scalable than Intserv –Edge routers maintain per aggregate state –Core routers maintain state only for a few traffic classes But, provides weaker services than Intserv –Per aggregate bandwidth guarantee (premium service) vs. per flow bandwidth and delay guarantee BB is not an entirely solved problem –Single point of failure –Handle only long term reservations (hours, days)

Intserv over Diffserv -- Integrated Services Operation over Diffserv Networks Intserv enables per-flow end-to-end QoS –enables hosts to request per-flow, quantifiable resources, along end-to-end data paths and to obtain feedback regarding admissibility of these requests Diffserv enables scalability across large networks => Intserv over Diffserv –Integrated Services Operation over Diffserv Networks

Network Configuration _______ ___________ ______ / \ / \ / \ |----| | |-----| |-----| |------| |-----| | |-----| |Tx |-| |ER1|---|BR1| |BR2|---|ER2| |-|Rx | |----| | |-----| |-----| |------| |-----| | |-----| \ / \ / \ / \________/ \____________/ \_______/ Non-Diffserv region Diffserv region Non-Diffserv region ER -- edge routers which are adjacent to the Diffserv region BR -- border routers within the Diffserv region

QoS over Next Generation Networks Concluding Remark by H. T. Kung 1998: –In 1993 ATM was in, but it was out of favor in 1997 –In 1995 IP switching was in, but it was out of favor in 1997 –In 1996 RSVP was in, but it is out of favor in 1998 –In 1998 Diff-Serv and MPLS are in, but will they also be out of favor soon? IWQoS2000 panel discussion: –ATM is on its way out. –Intserv is dead. –Diffserv is dying. –MPLS is in misguiding. Growing use of Multi-Protocol Label Switching now

Topics Integrated and Differentiated Services Active Buffer Management techniques, ex. RED. Multiprotocol Label Switching QoS in 3G wireless multimedia networks QoS based routing QoS management in multi-bearer IP networks including PSTN Impact of media compression in QoS networks QoS over Mobile IP QoS enabled MAC design