Quality of Service Support in Packet Networks

Quality of Service Support in Packet Networks
Tiziana Ferrari Italian National Institute for Nuclear Physics INFN - CNAF Tiziana Ferrari Quality of Service Support in Packet Networks

Tiziana Ferrari Quality of Service Support in Packet Networks
Overview Problem statement technical solutions: ATM RSVP and RSVP to ATM SVC mapping differentiated services (diffserv) Diffeserv in detail Diffserv: a case study Diffserv test activities (TF-TANT) comments Tiziana Ferrari Quality of Service Support in Packet Networks

Heterogeneous networks capacity transmission technology bottlenecks congestion and lack of transmission guarantees heterogeneous application requirements interactive: telnet, remote X sessions, web browsing non-interactive and packet loss tolerant: ftp, mailing delay sensitive: real time applications (e.g. remote control) delay variation sensitive and packet loss: voice over IP, videoconferencing ... Quality of Service Tiziana Ferrari Quality of Service Support in Packet Networks

Quality of Service: basic concepts
Service: a pre-defined type of packet treatment during transmission across the network qualitative quantitative delay instantaneous delay variation packet loss probability throughput MTU (Maximum Transfer Unit) priority (e.g. for congestion treatment) Class: set of packets to which a given service applies. Classification is based on traffic filters. A filter defines a set of packet matching rules. Matching is based on the content of packet fields. E.g. filter := (pack(src) = SRC) && (pack(dest) = DEST) && (pack(pro) = TCP) Tiziana Ferrari Quality of Service Support in Packet Networks

Quality of Service: benefits
network. congestion management, congestion independent QoS parameters, traffic engineering differentiated allocation of expensive network resources e.g. over intercontinental connections multiple services application: within a single application: differentiated treatment of streams according to their requirements and priority multiple applications: applications hierarchy according to priorities today: single service, best-effort Tiziana Ferrari Quality of Service Support in Packet Networks

Solutions Cell based networks: ATM (permanent and/or switched connections) IP based networks: RSVP (resource ReSerVation Protocol) and integrated services heterogeneous networks: RSVP to ATM SVC mapping (IP and ATM) differentiated services Tiziana Ferrari Quality of Service Support in Packet Networks

ATM (Asynchronous Transfer Mode)
Cell based pre-defined classes of services: Constant Bit Rate (peak cell rate - PCR-) Variable Bit Rate (sustainable cell rate, PCR, maximum burst size -MBS-) real time non real time Available Bit Rate (minimum cell rate -MCR-, PCR, rate increase/decrease factors) Unspecified bit rate (PCR) today: deployed as backbone technology (GARR, European national research networks, TEN-155, ESnet), not common as LAN technology. Only permanent connections are commonly deployed to support traffic engineering. Tiziana Ferrari Quality of Service Support in Packet Networks

ATM (cont) Permanent and/or dynamic connections (PVC, SVC) 1-to-1 or 1-to-many end-to-end signalling protocol for ATM connection set-up traffic engineering Disadvantages: not widely deployed as LAN technology (no end-to-end connectivity) no native ATM applications IP over ATM: overhead few applications supporting traffic profile definition addressing scheme not compatible with IP signalling only in few backbones -> lack of interoperability Tiziana Ferrari Quality of Service Support in Packet Networks

RSVP RSVP: signalling protocol for IP based applications traffic profile definition - source - reservation profile specification - destination - 3 classes of service: best-effort, controlled load, guaranteed reservation: (soft state) QoS support in heterogeneous network multicast is supported QoS support to the application Advantage: IP compatible Disadvantages: requires RSVP support on each router on the path from tx to rx lack of scalability admission control and policy management Tiziana Ferrari Quality of Service Support in Packet Networks

RSVP to ATM SVC mapping ATM signalling in the core RSVP signalling at the edge (access networks) reservation parameter mapping at the boundary Advantages: deploys ATM features in the backbones QoS support in heterogeneous environments QoS to the application interim solution -> intserv - diffserv (scalability) Disadvantages: application: RSVP capable, traffic profile specification RSVP support at both edges connection set-up latency: not convenient for delay sensitive applications transmitting small chunks of data still relays on ATM signalling in the core Tiziana Ferrari Quality of Service Support in Packet Networks

RSVP to ATM mapping: features
Translation of intserv classes of services and parameters into ATM classes of services and parameters deployment of best-effort connections (UBR in the ATM core) for initial transmission of RSVP messages (PATH, RESV) combination of RSVP and ATM admission control ATM: tx initiated signalling vs RSVP: rx initiated reservation request Tiziana Ferrari Quality of Service Support in Packet Networks

Scenarios Mapping in the end-system mapping in the router LIS 2 LIS 3 LIS 1 ATM ATM ATM RSVP -> ATM NRN - TEN NRN RSVP RSVP 1. PATH ATM 4. SVC 2. RESV 3. RSVP -> ATM Tiziana Ferrari Quality of Service Support in Packet Networks

Differentiated Services: Architecture
Tiziana Ferrari Quality of Service Support in Packet Networks

Differentiated services
cont. Why diffserv? new technology independent of layer 2 technologies interoperability between independent national research networks (different requirements, infrastructures, policies and management) traffic aggregation scalability: no reservation state maintained in the routers no signalling QoS for networks not ATM based RFC 2474: Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 headers RFC 2475: An Architecture for Differentiated Services RFC 2598: An Expedited Forwarding PHB RFC 2597: Assured Forwarding PHB Group Tiziana Ferrari Quality of Service Support in Packet Networks

Diffserv architecture: building blocks
Label: DS field (1 byte), DS Code Point (6 bits) packet classification packet scheduling traffic conditioning: metering marking policing shaping 6 7 DSCP CU Tiziana Ferrari Quality of Service Support in Packet Networks

DS building blocks: logical view
meter Shaper/ policer scheduler classifier marker Tiziana Ferrari Quality of Service Support in Packet Networks

Diffserv: traffic aggregation and (re)marking

Terminology Per Hop Behaviour (PHB): the externally observable forwarding behaviour applied to a DS-compliant node to packets with same label (DS codepoint) PHB Group: set of PHBs which can only meaningfully specified and implemented simultaneously (e.g. with common constraints on queue servicing and queue management). E.g. 4 PHB each associated to a different drop priority. A single PHB is a special case of PHB Group. Service: quantitative or statistical definition of significant characteristics of packet transmission in one direction across the network in terms of throughput, delay, jitter, loss, priority in access to network resources. Services are implemented through PHBs. The service describes the overall treatment end-to-end. Tiziana Ferrari Quality of Service Support in Packet Networks

Terminology (cont) DS codepoint: specific value of the DSCP field DS behaviour aggregate: packets with same code point DS domain: contiguous set of nodes with same service provisioning policies and same code point numbering scheme DS region: set of contiguous DS domains DS ingress/egress node: DS node handling packets entering/leaving the DS domain it belongs to classifier: entity selecting packets according to the content of packet headers according to a defined rule BA classifier: a classifier which only takes into account the DS field content Interior/Ingress/Egress Node DS Region DS Domain Tiziana Ferrari Quality of Service Support in Packet Networks

Terminology (cont) Conditioning: metering, marking Policing: packet discard according to the state of a corresponding meter enforcing a traffic profile Metering: the process of measuring the temporal properties of a traffic stream selected by a classifier Marking: the process of setting the DS codepoint in a packet based on defined rules Service Level Agreement: traffic contract between a customer and service provider specifying the forwarding service the customer’s traffic should receive Service Provisioning Policy: specification of microflow mapping into a DS Behaviour Aggregate conditioning configuration Tiziana Ferrari Quality of Service Support in Packet Networks

Diffserv architecture: network model for TEN-155
DS domain NRN DS domain MPLS Non DS capable domain DS domain NRN Marking policing scheduling TEN-155 marking shaping DS domain DS domain Tiziana Ferrari Quality of Service Support in Packet Networks

Diffserv architecture: PHBs
Standardised PHBs: Expedited Forwarding (low delay, low delay variation, guaranteed bandwidth) Assured Forwarding (Behaviour Aggregate, 4 classes, 3 drop priorities per class) Experimental PHBs PHB class selectors 3 7 precedence Tiziana Ferrari Quality of Service Support in Packet Networks

PHB: Expedited Forwarding
For the implementation of services requiring a reservation profile like: low loss, low latency, low jitter, assured bandwidth loss, latency and jitter  queue management (small queues) in order to prevent a queue from building up, in the EF queue of each transit node, the aggregate maximum arrival rate < departure rate EF implementation based on scheduling (for traffic isolation and support of bandwidth guarantees) policing shaping EF traffic can preempt other classes, for this reason the maximum EF rate has to be limited through policing EF codepoint: 101|110 Tiziana Ferrari Quality of Service Support in Packet Networks

PHB: Assured Forwarding
4 independent AF forwarding classes 3 drop priorities in each AF class given two packets in node with drop precedence p and q respectively, with p < q, pack(p) is always transmitted BEFORE pack(q) at the boundary between two AF domains, traffic conditioning can apply: shaping, per class discarding, drop precedence remarking and AF class reassignment. Traffic conditioning has to avoid REORDERING -> performance gain on the rx side Tiziana Ferrari Quality of Service Support in Packet Networks

PHB: Assured Forwarding (cont)
In case of long term congestion AF packets are dropped drop algorithm: WRED (Weighted Random Early Discard) for the implementation of a gradual discard mechanism based on congestion levels and proportional to the drop precedence of a given microflow Codepoints: class class2 class3 class4 low drop prec 001| | | |010 medium drop prec 001| | | |010 high drop prec 001| | | |110 Tiziana Ferrari Quality of Service Support in Packet Networks

PHB: Class Selectors and Experimental PHBs
XXX000 where x = 1 or 0 for backward compatibility with precedence field of the old so called TOS (Type Of Service) byte. TOS was replaced by the DS field. Precedence = [0, 7] if pred(pack1) < pred(pack2) then p_drop(pack1) > p_drop(pack2) Experimental PHB: not standardised codepoint and packet forwarding behaviour definition up to the ISP requires PHB mapping at the boundary precedence TOS byte 3 7 Tiziana Ferrari Quality of Service Support in Packet Networks

Diffserv architecture: scheduling policing and classification traffic metering Tiziana Ferrari Quality of Service Support in Packet Networks

Scheduling Scheduling: queue service policy for differentiated treatment of packets among queues Examples of packet scheduling algorithms: simple priority queue (high priority queues have the highest priority, arrival rate < departure rate, low priority traffic starvation is possible) weighted round robin queuing (queues serviced in round robin fashion, service time proportional to the weight) weighted fair queuing (minimum rate guaranteed per class, service time of each packet in each queue is a function of the packet size and of the queue weight. Current service time is updated every time a packet is sent) class based queuing (maximum rate per class is configured) Tiziana Ferrari Quality of Service Support in Packet Networks

Congestion management and service enforcement: policing
Policing: traffic which exceeds a given rate threshold is treated differently from conforming traffic. E.g. Exceeding packets can be dropped, re-marked, transmitted as best-effort etc. Policing is deployed for service level agreement enforcement: - to limit the input rate at the edge - at the boundary between domains to guarantee a fair deployment of the service among different domains Network Edge Packet Classifier and Policer Customer Premise Policy Specification Tiziana Ferrari Quality of Service Support in Packet Networks

Policing: token bucket
Policing is based on traffic metering. A typical algorithm is called token bucket. Input pack stream drop probability = 1 Exceed burst 0 < drop probability < 1 Normal burst (number of tokens available), drop probability = 0 R: departure rate at which tokens are replenished output pack stream Tiziana Ferrari Quality of Service Support in Packet Networks

Token bucket: algorithm
tokens replenished at regular intervals Normal burst: max number of tokens which can be in the bucket (in bytes) Exceed burst: to avoid tail drop in favour of gradual drop Actual debt AD =  ADi where is the number of borrowed tokens, ADi decreases of R tokens per time unit Compounded debt CD =  ADi where ADi CD = 0 after a packet drop packi is dropped if CB > exceed burst Tiziana Ferrari Quality of Service Support in Packet Networks

Token bucket: algorithm (cont)
Example (by BoB Olsen) token rate = 1 data_unit/time_unit normal burst size = 2 data_units (DUs) extended burst = 4 DUs. rate = 2 DUs arrive per time unit. After 2 time units, the stream has used up its normal burst and must begin borrowing one DU per time unit, beginning at time unit 3. Time tocken available DU arrivals Actual Debt Compounded Debt = = = = = (temp) (temp) > 4 Tiziana Ferrari Quality of Service Support in Packet Networks

Token bucket: algorithm (cont)
At this time a packet is dropped because the new compounded debt (6) would exceed the extended burst limit (4). This causes CD to effectively become 0, and lowers AD back down to 2. The values 3 and 6 were only temporary and do not remain valid in the case where a packet is dropped. The final values for time unit 5 are given below. Time tocken available DU arrivals Actual Debt Compounded Debt = (temp) (temp) > 4 drop (*) = = (temp) (temp) Tiziana Ferrari Quality of Service Support in Packet Networks

Congestion Avoidance: Weighted Random Early Discard (WRED)
Goal: to avoid congestion before it occurs by dropping isolated packets among different streams. Packets are dropped according to the current amount of data into a buffer. If buffer_level < thr1 p(drop) = 0 case 1 thr1 < buffer_level < thr2 0 < p(drop) < 1 case 2 otherwise p(drop) = 1 case 3 (W)RED is a congestion avoidance algorithm for TCP traffic based on the TCP flow control features (TCP reduces the output rate when a single packet is dropped before real congestion occurs) WRED: like RED but p(drop) in case 2 depends on the DS codepoint of the packet. Packets with low priority experience packet drop before packets with higher priority with both RED and WRED packet drop is randomly distributed among several flows Tiziana Ferrari Quality of Service Support in Packet Networks

Weighted Random Early Discard (WRED) - cont -
Class 6 gets 50% minimum Class 4 gets 30% minimum Class 2 gets 20% minimum The remaining traffic gets 10% Packet Drop Probability Bronze Standard Packet Drop Probability Silver Gold Queue Length 40% 60% 70% 90% Max Gold Class 6 will never get drop unless extreme congestion : 90%of queue depth Silver Class 4 will not get dropped unless severe congestion :70%of queue depth Bronze Class 2 will start drop at 60%queue occupancy Standard The remaining traffic will start drop at 40% of queue occupancy Tiziana Ferrari Quality of Service Support in Packet Networks

Differentiated Services: Case Study

Characterisation of the application
Characterisation needed to identify the requirements of the application: service definition 1. Hardware of the trigger: remote control - ROBIN - few transactions (low bandwidth), TCP traffic on a limited well-known set of TCP ports, IP address of the server known client - server, one connection to a server at a time  low paket loss, delay sensitive application, reliability, burst tolerance 2. Monitoring of quality and correctness of the results of the analysis - ROOT - exchange of analysis results (root object) low bandwidth consumption client - server, IP address of the server is known  bandwidth guarantee, more tolerance to packet loss Tiziana Ferrari Quality of Service Support in Packet Networks

Models of network deployment
1. Trigger hardware control Power PC VME Client 1 Server 1 Client 2 VME Server 2 Client 3 ... ... VME Client n Server m bottlenecks 1. Monitoring of analysis Browser 1 server Browser 2 Browser 3 ... Browser n Tiziana Ferrari Quality of Service Support in Packet Networks

Service for trigger control packets
low drop probability delay bound (minimum queue size) precedence: highest precedence, higher than monitoring packets precedence Capacity: a minimum network capacity guaranteed, in case of spare capacity, more bandwidth can be allocated. No upper limit in rate for maximum burst tolerance Tiziana Ferrari Quality of Service Support in Packet Networks

Service 1: implementation
If pack(src/dest) = (s1 || s2 || … || s m) && pack(TCP_port) in [x, y] then pack(label) = max precedence policing: always transmit delay: buffer size of 2*MTU minimum service rate = m * r * Nclient or rate = m * R * Nclient m: overbooking factor r: estimated rate consumed by 1 client, R: estimated rate consumed by 1 server Nclient : number of clients downstream VME Server 1 Server 2 ... Client 1 Client 2 Client 3 Client 4 r R 2*m*r r R 4*m*r r R 2*m*r r Server 8 Marking client -> server Marking server -> client Scheduling client -> server Scheduling server -> client Tiziana Ferrari Quality of Service Support in Packet Networks

Service for monitoring traffic
precedence: higher than best effort, lower than service 1 packets drop probability: packets can be dropped in case of congestion. Label: lower precedence capacity: minimum guaranteed bandwidth, more bandwidth can be allocated if available maximum upper rate threshold: for fair bandwidth allocation between several clients Tiziana Ferrari Quality of Service Support in Packet Networks

Service 2: implementation
If pack(src/dest) = s1 then if rate < max, pack(label) = medium prcedence (marking) else drop (policing) shaping: buffer size > server or client burst size minimum service rate = r * Nclient (client), or rate = R * Nclient (server) r: estimated rate needed for 1 client, R: estimated rate needed by the server to support m clients Nclient : number of clients downstream precedence: < precedence(service 1) r Client 1 2*r r Client 2 R 4*r Server r Client 3 ... 2*r r Policing client -> server Policing server -> client Client 4 Marking client -> server Marking server -> client Scheduling client -> server Scheduling server -> client Tiziana Ferrari Quality of Service Support in Packet Networks

Diffserv testing and QoS measurement

Test network Tiziana Ferrari Quality of Service Support in Packet Networks

LAN layout (example) Tiziana Ferrari Quality of Service Support in Packet Networks

Equipment Test workstations traffic generators (3 SmartBits, Netcom System loan) ATM switches in the test sites cabletron ethernet switch DS capable platforms: CISCO: C7200 or C7500 (partial CISCO loan) IBM: IBM 2212 and IBM 2216 (2 routers in 5 sites, IBM donation) Linux Cabletron (LAN switch) (Nortel, Torrent) Tiziana Ferrari Quality of Service Support in Packet Networks

CISCO: traffic policing (CAR)
CAR: Committed Access Rate Multi-field classification: OK packet marking (precedence setting): OK exceed action testing: OK policing (at a configurable rate): two parameters token bucket for TCP performance optimisation normal burst exceed burst --> parameter tuning Tiziana Ferrari Quality of Service Support in Packet Networks

CAR: test of exceed actions
Throughput: SWITCH: 1.20 Mbps DANTE: Mbps Tiziana Ferrari Quality of Service Support in Packet Networks

CAR: TCP burst tolerance
Normal and exceed burst tuning with TCP traffic single and multiple TCP streams optimum values are functions of the rate R at which traffic is policed, in particular: normal burst = 0.5 sec * R exceed burst = 2 * normal burst Tiziana Ferrari Quality of Service Support in Packet Networks

CAR: TCP burst tolerance (cont)

CISCO: scheduling (CB-WFQ)
Scheduling mechanism to provide minimum bandwidth guarantees to classes class definition: precedence or MF classification --> OK bandwidth allocation: no starvation, no bandwidth consumption --> OK traffic isolation: scenarios UDP high priority + UDP best-effort TCP high priority + UDP best-effort TCP high priority + TCP best-effort UDP --> OK (always) TCP: inconsistent results with 1 TCP stream due to cell shaping problems in the ATM part of the network, good results with several TCP strams Tiziana Ferrari Quality of Service Support in Packet Networks

CB-WFQ: set-up Tiziana Ferrari Quality of Service Support in Packet Networks

IBM: scheduling (Self Clocked Fair Queuing)
Policy = (traffic profile, validity period, diffserv action) diffserv action = (type of marking, queue type, bandwidth) optimum traffic isolation (tests only with UDP) Premium: Kbps guaranteed (8% PPP link bw) Assured: Kbps (40% PPP bw) Tiziana Ferrari Quality of Service Support in Packet Networks

IBM: EF policing Small TCP burst tolerance in a policer can completely starve a TCP stream. Token bucket depth is key parameter --> tuning need according to the rate at which traffic is policed Tiziana Ferrari Quality of Service Support in Packet Networks

IBM: EF policing (cont)
EF with TCP traffic, target rate = 163 Kbps Tiziana Ferrari Quality of Service Support in Packet Networks

QoS measurement Resource allocation monitoring for resource allocation and network dimensioning performance measurement passive active (invasive traffic) for service validation to understand the effect on end-to-end performance of buffering in one router or in a chain Tiziana Ferrari Quality of Service Support in Packet Networks

Performance measurement
parameters of interest: one-way delay, requirements: clock synchronisation GPS based synchronisation SmartBits (Netcom Systems) NTP (Network Time Protocol) NTP client / server hierarchy one-way delay variation packet loss throughput RTT Tiziana Ferrari Quality of Service Support in Packet Networks

Services: examples Virtual leased line: point to point one to many capacity allocation on congested links (e.g. US links) better-than-best-effort (qualitative definition) delay bound and delay variation sensitive traffic classes rate limiting of invasive traffic ... Tiziana Ferrari Quality of Service Support in Packet Networks

More information at diffserv: QoS measurement: QBONE: US initiative for testing, validation and deployment of services based on the expedited forwarding PHB of the pr Tiziana Ferrari Quality of Service Support in Packet Networks

Comments Diffserv building blocks: already supported by several vendors diffserv: no changes in applications required diffserv goal: simplified approach to QoS for its support in backbones from today good interim test results diffserv in the future: Packet Over Sonet (POS) vs ATM VLL vs ATM permanent connections Tiziana Ferrari Quality of Service Support in Packet Networks

Comments (cont) diffserv still requires QoS support end-to-end (but diffserv can be implemented in some domains, provided that the end-to-end service is homogeneous) Dedicated connection diffserv diffserv ATM/POS Production network diffserv diffserv diffserv Production network Tiziana Ferrari Quality of Service Support in Packet Networks

Comments (cont) Issues effects of high degree aggregation? More testing needed interoperability between different platforms: effect on end-to-end services? performance of marking, classification and scheduling at high speed? Tools for service monitoring…. Diffserv in production? 1 year? Tiziana Ferrari Quality of Service Support in Packet Networks

Discussion Deployment of diffserv in HEP Issues in diffserv deployment in HEP recommendations Tiziana Ferrari Quality of Service Support in Packet Networks

Quality of Service Support in Packet Networks

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