Quality of Service Monitoring and Delivery Part 01 ICT Technical Update Module
Presentation Outline Introduction to IP-QoS IntServ Architecture DiffServ Architecture Post Graduate Certificate in Professional Development Slide 2
Evolution of QoS Architectures Best effort service: 1981 RFC-791 Integrated Services (IntServ)/RSVP: 1997 Differentiated Services (DiffServ): 1998/99 DiffServ-Aware Traffic Engineering (DS-TE) Post Graduate Certificate in Professional Development Slide 3
Resource Allocation Packets get Dropped Delayed because the resources in the network cannot meet all of the traffic demands. Internet does not support any active resource allocation methodology. A network that supports QoS must take an active role in the resource allocation process and decide who gets resources and how much they should receive. Post Graduate Certificate in Professional Development Slide 4
ATM QoS Definitions QoS Parameters CBR Service Category rt_vbr nrt-vbr Cell Delay Variation Max Cell Transfer Delay Cell Loss Ratio Traffic Parameters Peak Cell Rate Specified Specified Specified Specified Specified Not specified Not specified Sustainable Cell Rate Maximum Burst Size Cell Delay Variation Tolerance n/a n/a Specified Specified Specified Source: Table 2.1, ATM Forum Traffic Management Specification v4.1 Post Graduate Certificate in Professional Development Slide 5
IP QoS Definitions? QoS Parameters Gold Service Category Silver Bronze Packet Delay Variation (Jitter) Packet Transfer Delay (Latency) Packet Loss Ratio Traffic Parameters Peak Throughput Specified Specified Specified Specified Specified Not specified Not specified Guaranteed Throughput Maximum Burst Size Max Packet Delay Variation n/a n/a Specified Specified Specified Post Graduate Certificate in Professional Development Slide 6
Four technologies for IP-QoS 1. Integrated Services 2. Differentiated Services 3. Multi-protocol Label Switching 4. Traffic Engineering Two resource allocation architectures for the Internet Give Service Providers a set of management tools for bandwidth provisioning and performance optimisation The above technologies have become the core building blocks for enhancing the Internet with QoS capabilities. The early days of the Internet centred around providing a best effort service and treating all packets in an identical manner. With the advent of real-time services and other critical services it became necessary to re-think the BE strategy in order top address the requirement that IP networks ( the Internet ) should be become the universal service network. Post Graduate Certificate in Professional Development Slide 7
IntServ Architecture RFCs 2210, 2211, 2212 & 2215
Summary IntServ is based upon the idea of a per-flow resource reservation To receive resource assurance, an application must: Make a reservation before transmitting traffic onto network Reservation steps are: Application must characterise its source and resource requirements. The network uses a routing protocol to install the reservation state along the path based on the requested resources at each hop admission control checks When reservation is confirmed, application can send. Exclusive use of the resources is available to application Enforced by packet classification and scheduling mechanism Post Graduate Certificate in Professional Development Slide 9
IntServ Ideas and Concepts - 1 Preservation of the End to End semantics of IP for QoS The key end points are the senders and the receivers Applications request desired service from the network for a set of Microflows Microflows are defined as a 5-tuple, viz: Source address Destination address Transport protocol Source port # Destination port # Note that for a VoIP call, we need to establish two Microflows one in each direction! Post Graduate Certificate in Professional Development Slide 10
IntServ Ideas and Concepts - 2 There are basically three key components to IntServ: Specification of what the sender is sending Rate, MTU, etc this is the TSpec (Transmitter Specification) Specification of what the receiver needs: Bandwidth, path MTU, etc this is the RSpec (Receiver Specification) Specification as to how the signalling is done to the network by the sender and the receiver: RSVP is the Signalling Protocol for IntServ RSVP = Resource ReSerVation Protocol Post Graduate Certificate in Professional Development Slide 11
Resource ReserVation Protocol - RSVP Signalling protocol to request specific QoS service from the network Admission control Policy control Filter spec / Flow spec Post Graduate Certificate in Professional Development Slide 12
RSVP Setup With best effort we can send packets where-ever and whenever we like! With Integrated Services the architecture requires an application to set up a reservation before traffic can be transmitted. New protocol needed to do this: RSVP Used by hosts to communicate service requirements to the network Used by routers to establish a reservation state along the path. RSVP is an add-on protocol to the existing IP suite. Post Graduate Certificate in Professional Development Slide 13
RSVP - Simplex Reservation RSVP used to establish resource reservation between sender and receiver. Reservation is established in one direction only Simplex flow In a two way communication, both ends need to establish reservation RSVP treats a sender as logically different from a receiver. Post Graduate Certificate in Professional Development Slide 14
RSVP Operation Overview RSVP supports multicast communications RSVP is receiver oriented Receivers responsible for deciding what resources will be reserved Receivers must initiate the reservation Post Graduate Certificate in Professional Development Slide 15
RSVP at the Routers - 1 Soft-State State Soft-State: RSVP uses this approach to maintaining a connection: Timer associated with state When timer expires, state is automatically deleted RSVP periodically refreshes the reservation state along the paths of the communication Assists multicast communication adaptability Post Graduate Certificate in Professional Development Slide 16
RSVP at the Routers - 2 Routing Independence Decision to select path for a flow is done separately by routing RSVP simply consults a forwarding table and sends appropriate messages. With TE extensions, RSVP an explicit route object can be carried in the message body to specify the entire path over which the reservation can be made Reservation Style RSVP has a number of different reservation styles that characterise how the reservation should be treated. Post Graduate Certificate in Professional Development Slide 17
IntServ Basic Approach Steps: Sender Sender starts the setup of a reservation Describes characteristics of flow and resource requirements Network accepts flow Assuming sufficient resources available for new request Establish reservation Receiver After reservation established, application sends packets along the reserved path. Post Graduate Certificate in Professional Development Slide 18
IntServ Reference Models - 1 QoS Routing Agent Admission Control Reservation Set up Agent Resource Reservation Table Control Plane Flow Identification Packet Scheduler Data Plane Post Graduate Certificate in Professional Development Slide 19
IntServ Reference Models - 2 Reservation Agent Management Agent Routing Agent Admission Control Traffic Control Database Routing Database Input Scheduler Classifier Forwarder Output Scheduler Post Graduate Certificate in Professional Development Slide 20
IntServ Disadvantages All routers must maintain per state flow Constant refresh messages High overhead for low rate connections: Per-flow classification, policing, queueing and scheduling All routers must perform Call Admission Control Poor scalability Post Graduate Certificate in Professional Development Slide 21
IntServ Advantages QoS is relatively automatic Just have to provision the RSVP bandwidth on interfaces Integrates well with a policy infrastructure Micro-flow granularity for QoS Post Graduate Certificate in Professional Development Slide 22
Differentiated Services (DiffServ) RFCs 2474, 2475, 2597 & 2598
The DiffServ Idea Offer service levels for packets: Gold Silver Bronze Service: Some significant characteristics of packet transmission in one direction across a set of one or more paths within a network (eg Bandwidth, Latency, etc) RFC 2475 Packets of a particular service are said to be packets of a class Services constructed using Per-Hop Behaviours Post Graduate Certificate in Professional Development Slide 24
Traffic Conditioner Block Meter Classifier Marker Shaper/ Dropper Main components of the Traffic Conditioner Block: Classifier Assignment of packets to classes Meter Checking of compliance to traffic parameters. Actions: Marker Writes or rewrites the DSCP value Shaper Delays some packets to bring them into the profile Dropper Drops packets that exceed the profile Post Graduate Certificate in Professional Development Slide 25
Creation of Services At the Ingress Network-Edge (Traffic Conditioning Block TCB) 1. Classify packets into classes 2. Mark ( colour ) packets for classification in the core 3. Optionally meter a class 4. If doing 3, police or shape the class (at network ingress or egress) 5. Queue and/or drop packets toward the core In the core (doing PHB) Queue and/or drop packets Post Graduate Certificate in Professional Development Slide 26
Differentiated Services Architecture (DiffServ) Scalable architecture (RFC2475) Packets classified into aggregated traffic classes at the edge of the network Packets Marked at DSCP (RFC2474) Different Per Hop behaviours are applied Post Graduate Certificate in Professional Development Slide 27
How Does DiffServ Operate? Classification in IPv4 1 2 3 01234567890123456789012345678901 Version IHL Type of service Total Length Identification Flags Fragment Offset Time to live Protocol Source Address Header Checksum Destination Address Options Padding Packets are marked at the edge using the ToS Byte Post Graduate Certificate in Professional Development Slide 28
Precedence and Type of Service Field The type of service field actually carries two subfields Precedence An indication of priority Type of service An indication for routing 0 1 2 3 4 5 6 7 Precedence Type of service D T R C D - Delay; T - Throughput; R - Reliability; C - Cost Post Graduate Certificate in Professional Development Slide 29
Precedence The precedence indicator affects queueing. If several packets are awaiting transmission on the same channel, the one with the highest precedence is supposed to be sent first. There are eight preference values, viz: 111 - Network Control 110 - Inter-network Control 101 - CRITIC-ECP 100 - Flash Override 011 - Flash 010 - Immediate 001 - Priority 000 - Routine Post Graduate Certificate in Professional Development Slide 30
Type of Service Often there is more than one route to a destination. These routes may have quite different characteristics. Eg telephone circuits, satellite links, radio channels, We want to indicate to the routing protocols how we would like the packet to be routed. As indicated above, the four types of service are D, T, R and C: D - Delay: This is a mechanism for requesting low delays (avoid satellite links) T - Throughput: Select path with highest throughput (avoid telephone links) R - Reliability: Highest reliability (avoid radio channels) C - Cost: Cheapest route Post Graduate Certificate in Professional Development Slide 31
IPv4 ToS to new DS-Field D - Delay; T - Throughput; R - Reliability Currently Unused DSCP Differentiated Services CodePoint Post Graduate Certificate in Professional Development Slide 32
Marking of Packets Marking can take place at either layer 2 or 3 Common marking techniques: IP DSCP Layer 3 MPLS EXP bits Layer 2½ ATM CLP bit Layer 2 Frame Relay DE bit Layer 2 IEEE802.1Q/p user priority bits Layer 2 Post Graduate Certificate in Professional Development Slide 33
Metering (Optional) Tokens Incoming packet stream Accepted packet stream Rejected or marked packets Tokens pour into bucket at predefined average rate If token available, transmit packet Post Graduate Certificate in Professional Development Slide 34
Token Bucket Tokens Token Bucket Data Queue Regulator Post Graduate Certificate in Professional Development Slide 35
Metering Policing/Dropping Traffic Policing Traffic Time Time Traffic Shaping Traffic Time Time Post Graduate Certificate in Professional Development Slide 36
Policing of Packet Flows Policing is used to Drop out-of-profile packets Re-mark packets to ensure that they are dropped ahead of in-profile packets Traffic Flow Post Graduate Certificate in Professional Development Slide 37
Shaping of Packet Flows Used where there are speed mismatches Involves buffering Various queueing and scheduling techniques may be used when the shaped rate is achieved. Destination office FR/ATM/WAN Central site Bottleneck Shaping Traffic flow Post Graduate Certificate in Professional Development Slide 38
Per Hop Behaviour by Queueing and Dropping - 1 Queueing involves: Buffering packets when the interface experiences congestion Scheduling packets out of the buffer onto the link Different queues Scheduler Outgoing packets Algorithms may include: FIFO, CBQ, WFQ etc Post Graduate Certificate in Professional Development Slide 39
Per Hop Behaviour by Queueing and Dropping - 2 Dropping occurs: At the edge when policing In the edge/core when buffers full and they indicate congestion to the end-nodes for back-off (Tail Drop) In the edge/core when trying to avoid congestion and signal to the end-nodes that they can back-off. Post Graduate Certificate in Professional Development Slide 40
Queueing Packet networks are networks of queues-based Queue manipulation is a simple extension to the basic Internet architecture Many styles of queueing have been proposed: Post Graduate Certificate in Professional Development Slide 41
Priority Queueing Separate traffic according to priority Simple to implement no state Requires careful engineering Post Graduate Certificate in Professional Development Slide 42
Random Early Discard (RED) Discard packets randomly once queue threshold exceeded Triggers TCP congestion avoidance to slow flows No effect on UDP traffic This method targets the biggest flows Many variations have been developed in recent years, including Blue, Green, etc! Prob(drop) Queue size Post Graduate Certificate in Professional Development Slide 43
Fair Queueing Flows serviced fairly on packet by packet basis Prevents flows interfering State information per queues Variations: weighted FQ, stochastic FQ Post Graduate Certificate in Professional Development Slide 44
Class Based Queueing Round robin servicing of classes Flexible pre-assigned allocation to traffic classes Rotation time trade off between jitter and fairness Post Graduate Certificate in Professional Development Slide 45
The Various Per Hob Behaviours Using Queueing and Dropping: Expedited Forwarding (EF): RFC2598 Very low delay, low jitter, assured bandwidth Assured Forwarding (AF): RFC2597 Assured amount of bandwidth IETF has defined four AF classes Class Selector: Compatible with IP Precedence for Forwarding Probability Default: Best effort Post Graduate Certificate in Professional Development Slide 46
DiffServ Ingress Router DiffServ Policy Manager Admission Control Marker Control Meter Routing Agent Routing Database Marker Scheduler Input Classifier Forwarder DSCP Output Classifier Scheduler Post Graduate Certificate in Professional Development Slide 47
DiffServ Interior Router Routing Agent Routing Database Input Forwarder DSCP Classifier Scheduler Scheduler Output Post Graduate Certificate in Professional Development Slide 48
DiffServ Advantages No hop by hop signalling No per flow or per customer state Aggregate classification state only Small set of forwarding behaviours Complex classification/conditioning functions at boundary routers only Simple packet classification at interior routers Post Graduate Certificate in Professional Development Slide 49
Multi-Protocol Label Switching (MPLS) Add label to packet with link specific significance Arbitrary mapping of IP flows to Forwarding Equivalence Classes (FEC) Separate Forwarding (label based) from Routing (address based) Multiprotocol Label Switching Architecture (RFC 3031) Post Graduate Certificate in Professional Development Slide 50
ATM / Frame Relay Labels L2 Header L3Header L4 Header and Data PPP / Ethernet etc L2 Header Label L3Header L4 Header and Data Post Graduate Certificate in Professional Development Slide 51
MPLS Network LER LSR Label Edge Router (LER) LSR LSR Label Switch Router (LSR) Post Graduate Certificate in Professional Development Slide 52
MPLS Protocols OSPF/ ISIS Routing LDP TCP UDP CR LDP/ RSVP-TE IP Forwarding Link State Information MPLS Forwarding Physical Post Graduate Certificate in Professional Development Slide 53
MPLS Advantages Explicit Control of Routing on a per Flow basis Traffic Engineering - efficiency Complex mapping of IP attributes to FECs VPNs services End to end signalling along Label Switched Paths Protection / Recovery Post Graduate Certificate in Professional Development Slide 54
Conclusions A wide variety of different techniques have been proposed for QoS in the Internet. Experimentation and new proposals are emerging on a daily basis. DiffServ and MPLS are the current favourites, but others are waiting to be considered. MPLS has been generalised to wavelength networks. It is called GMPLS. Post Graduate Certificate in Professional Development Slide 55