T-110.5110 Computer Networks II Quality of Service

T-110.5110 Computer Networks IIQuality of Service 19.10.2009 Prof. Sasu Tarkoma Based on slides by Dr. Matti Siekkinen (Primary sources: C. Hota: “Quality of Service in the Internet” and J. Manner: IP Quality of Service)

Outline • What is QoS? • QoS mechanisms • QoS architectures • Integrated Services (IntServ) • Differentiated Services (DiffServ) • Multiprotocol Label Switching (MPLS) • Generalized Multiprotocol Label Switching (GMPLS) • QoS architectures for mobile networks • Next Steps in Signaling (NSIS) • Overlay Solutions

What is Quality of Service? • Many applications are sensitive to delay, jitter, and packet loss • Too high values makes utility drop to zero • Some mission-critical applications cannot tolerate disruption • VoIP • high-availability computing • Charge more for business applications vs. consumer applications • Related concept is service availability • How likely is it that I can place a call and not get interrupted? • requires meeting the QoS requirements for the given application

Sensitive CEO Video conference with analysis Personal voice over IP Network monitoring Financial Transactions Unicast radio Interactive whiteboard Network management traffic Delay Public web traffic Extranet web traffic Push news Business e-mail Server backups Personal e-mail Insensitive Mission Criticality Casual Critical QoS Requirements

QoS and the Internet • The existing Internet architecture provides a best effort service. • All traffic is treated equally (generally, FIFO queuing with tail drop) • No mechanism for distinguishing between delay sensitive and best effort traffic • No guarantees for end-to-end QoS  • Originally IPv4 has TOS (type-of-service byte) in packet header • RFC 795: defined multiple axes (delay, throughput, reliability) • rarely used in practice (DiffServ) • We try to minimize delay and loss • …and try to mitigate the effects with different techniques • E.g. adapt application (video stream) based on QoS feedback (RTCP)

QoS Mechanisms Packet Scheduling Traffic Shaping (Users get their share of bandwidth) (Amount of traffic users can inject into the network) Admission Control (To accept or reject a flow based on flow specifications) Core

QoS Mechanisms: classification • Provisioning • Admission control • Prohibit or allow new flows to enter the nw • Resource reservation • E.g. Over provisioning • Control • Operate on short time scales • Real-time traffic or flow control • E.g. scheduling, shaping, policing... • Management • Monitor the QoS • Longer time scales than control

QoS Control Mechanisms • Application-level techniques • Application adapts to network conditions • E.g. adapt media stream to a lower quality based on RTCP feedback • Transport-layer techniques • Adapt transport protocols to application requirements and network conditions • TCP, DCCP • Network-layer techniques • QoS routing • Non-FIFO scheduling (like WFQ) • Something else than tail drop (like RED)

IP addresses, net mask, port numbers, protocol id Packet Classifier Flow identifier Full Full Y Y QoS Control Mechanisms (cont.) Full N Processor Arrival Departure Queue Y Discard Scheduling (FIFO Queuing) The switch turns to other queue when the current one is empty N High Priority Queue Processor Classifier Discard Arrival Departure N Low Priority Queue Discard Scheduling (Priority Queuing)

The turning switch selects 2 packets from 1st queue, then 1 packet from 2nd queue and the cycle repeats N Weight: 2 Processor Classifier Discard Arrival Departure N Weight: 1 Discard Scheduling (Weighted Fair Queuing) Full Full Y Y QoS Control Mechanisms (cont.) Token Bucket (Credit an idle host) Leaky Bucket (Regulate the traffic)

Arriving Packet Arriving Packet Queue Queue Accepted Dropped Dropped from front Full Full (Tail-drop scheme) (Drop-from-front scheme) QoS Control Mechanisms (cont.) Drop probability Queue 1 Avg. TCP Traffic MAXth MINth Drop MAXdrop MINth MAXth Avg. queue size (Random Early Detection with Drop function)

Random Early Detection Source: Leonardo Balliache, Differentiated Service on Linux HOWTO http://www.opalsoft.net/qos/DS.htm

QoS Control Mechanisms (cont.) • QoS routing • Routing based on QoS related metrics, not just shortest path • E.g. available bandwidth • (Multi-)constrained path computation • Can be computationally complex • Widest-Shortest Path • Select the shortest path that is feasible according to the bandwidth constraint • Shortest-Widest Path • Find paths with the most available bandwidth (i.e. widest paths) • Break ties by selecting the shortest path (#hops or delay)

Where to implement QoS mechanisms? • Core routers • Link speeds fast • Lot of traffic • Cannot do much more than over provisioning or treat limited nb of flow classes • Access routers • Generally, not so high rates • Feasible to do complex operations (filtering, classification, policing…) • Could do per-flow packet handling

QoS Architectures • Use the QoS mechanisms to provide application to application QoS • Many different proposals over the years • YESSIR, IntServ, DiffServ, Mobile RSVP, OMEGA, QoS-A... • We will look at a few ones in more detail • Integrated Services (IntServ) • Differentiated Services (DiffServ) • Multiprotocol Label Switching (MPLS) • Generalized MPLS (GMPLS) • QoS for mobile networks • Next Steps in Signaling (NSIS)

IntServ • Resource reservation and admission control • Source describes its desired flow rate and sends this information to the routers and the receiver • Network admits requests and reserves resources • Source must send at this rate (controlled by network) • Provides a sort of “dedicated” connection within an IP packet-switched network • Reservation of resources is done with the Resource Reservation Protocol (RSVP)

RSVP • Supports both multicast and unicast • Sender-to-network signaling • path message: make sender presence known to routers • path teardown: delete sender’s path state from routers • Receiver-to-network signaling • reservation message: reserve resources from senders to receiver • reservation teardown: remove receiver reservations • Network-to-end-system signaling • path error, -reservation error • Soft state protocol • Need to refresh state

RSVP (cont.) • Reservations are for unidirectional data flows • Provides several reservation models or "styles" to fit a variety of applications (shared and dedicated reservations) • Transparent to routers that do not support it • RSVP packets are just normal IP packets • Not a routing protocol but depends upon present and future routing protocols • Supports both IPv4 and IPv6

IntServ: Scalability Issues • RSVP signaling Overhead • One PATH/RESV per flow for each refresh period • Processing overhead • Routers have to classify, police and queue each flow • State information stored in routers • Flow identification (using IP address, port etc) • Previous hop identification • Reservation Status • Reserved Resources

DiffServ • No signalling, no resource reservation • Complex processing is moved from core to edge • Per flow service (IntServ) is replaced by per aggregate or per class service with a SLA with the provider • Mark packets with a code (DSCP) to differentiate between pkts/flows • e.g. a priority stamp • Uses IP type of service field (TOS) • Core uses the codes to select appropriate service level • Premium, priority, best effort

DiffServ • Two types of services standardized, operators may define other services and code points • Does not necessarily provide end-to-end QoS: • Operators may have different meanings and implementations for classes and code points, • The code points can change, thus, may not remain the same on the whole end-to-end path.

DiffServ Schema • Source sends request message to first hop router • First hop router sends request to Bandwidth Broker (BB) that replies with either accept or reject • If the request is accepted, either the source or the first hop router will mark DSCP and will start sending packets • Edge router checks compliance with the SLA and will do policing. It may drop or mark the packet with low priority to match the SLA • Core routers will look into DSCP and decide the PHB

Expedited Forwarding • Expedited packets experience a traffic-free network (low loss, low latency, low jitter, and assured bandwidth (premium service) • Strict priority queuing

Assured Forwarding • A possible implementation of the data flow for assured forwarding is shown below. • AF PHB delivers the packet with high assurance as long as its class does not exceed the a subscribed rate • Use e.g. WFQ scheduling with RED

Bandwidth Brokers U1 BB S1 BB U2 BB BB C5 C1 C4 D ISP 1 ISP 2 Server 3 C3 BB C2 C6 C7 S2 Core Network Server 2 Server 1 U1 U3 U2

Integrated Solution

Multiprotocol Label Switching (MPLS) • Traffic engineering tool • Allocate specific path and network resources to specific types of traffic ensuring QoS • Supports multiple protocols • IPv4, IPv6, IPX, AppleTalk at the network layer • Ethernet, Token Ring, FDDI, ATM, Frame Relay, PPP at the link layer • Forwarding behavior independent of layer 2 and layer 3 • Data transmission occurs on Label Switched Paths (LSP) • Labels are distributed using Label Distribution Protocol (LDP), or RSVP, or piggybacked on BGP and OSPF • FEC (Forward Equivalence Class) is a representation of group of packets that share the same requirements for their transport • Assignment of FEC to a packet is done once only as it enters into the network

Model for MPLS Network • Convergence of connection oriented forwarding techniques and Internet’s routing protocols LER LSR = Label Switched Router LER = Label Edge Router LSP = Label Switched Path LSR LSP LSP Route at edge and Switch at core

MPLS ATM Switch IP Router Control: Control: Control: IP Router Software IP Router Software ATM Forum Software Forwarding: Forwarding: Forwarding: Longest-match Lookup Label Swapping Label Swapping Separate forwarding and control • Exact match instead of longest prefix match (like IP) • faster forwarding

MPLS Forwarding

1a. Routing protocols (e.g. OSPF-TE) exchange reachability to destination networks 4. LER at egress removes label and delivers packet 1b. Label Distribution Protocol (LDP) establishes label mappings to destination network 10 20 40 IP IP IP IP IP 2. Ingress LER receives packet and “label”s packets 3. LSR forwards packets using label swapping MPLS Operation Ingress Egress MPLS Domain

MPLS Labels • Label assignment decisions are based on forwarding criteria like • Destination unicast routing • Traffic engineering • Multicast • Virtual Private Network • Quality of Service A Label could be embedded in the header of the DL layer like ATM (VPI/VCI) and FR (DLCI) or could be between DL and IP as shown below: Bottom of Stack (first label in stack)

Label and FEC Relationship R4 could send a packet with Label=L1, but it would mean a different FEC Assignment of FEC to a packet is done by ingress router • FEC (Forwarding Equivalence Class): Assigned on the basis of IP addresses, port numbers or TOS bits. • FEC could be associated with all the flows destined to an egress LSR.

Label Merging • Label Switched Path (LSP): A unidirectional connection through multiple LSRs. • Label Merging: The replacement of multiple incoming labels for a particular FEC with a single outgoing label. • Labels are "downstream-assigned", and label bindings are distributed in the "downstream to upstream“ direction. Multi-point to Single point tree routed at Egress router

(Multiple Levels of Nesting) 4 3 2 2 2 8 7 6 LSP Hierarchy • A Packet can have several labels one after the other before the IP header. (Why? Tunneling) (Tunnel 1 may be for the Enterprise with 1a for VoIP data, 1b for billing, and 1c for alarm & provisioning) Swap Push Swap & Push Pop & Swap Pop R1 R2 R2A R2B R2C R3 R4 IP IP

Label Distribution • Establishes and Maintains a LSP that includes establishment of Label/FEC bindings between LSRs in the LSP. • A downstream LSR can directly distribute Label/FEC (unsolicited downstream). • An upstream LSR requests a downstream for Label/FEC (downstream on demand). • Protocols like LDP, RSVP-TE are used to distribute Labels in the LSP

Label Distribution • Label Distribution Protocol (LDP) [RFC 3036] • An LSR sends HELLO messages over UDP periodically to its’ neighbors to discover LDP peers (routing protocol tells about peers) • Upon discovery, it establishes a TCP connection to its peer • Two peers then may negotiate Session parameters (label distribution option, valid label ranges, and valid timers) • They may then exchange LDP messages over the session (label request, label mapping, label withdraw etc) • RSVP-TE (Resource Reservation Protocol-Traffic Extension) [RFC 3209] • Path message includes a label request object, and Resv message contains a label object • Follows a downstream-on-demand model to distribute labels • Path message could contain an Explicit Route Object (ERO) to specify list of nodes • Priorities can be assigned to LSPs, where a higher one can preempt a lower one

MPLS Protection • Dynamic routing restores the traffic (upon a failure) based on the convergence time of the protocol • Convergence can be slow • Set up secondary backup paths in addition to primary working paths • End-to-end protection • May need really fast recovery for mission critical or high priority data • Fast reroute: Setup detour paths around failed links/nodes • Temporary recovery until backup path takes over

IntServ, DiffServ and MPLS • An RSVP request (say guaranteed service) from one domain could be mapped to an appropriate DiffServ PHB at another domain that again could be mapped to a possible MPLS FEC at the edge of another MPLS domain.

Generalized MPLS (GMPLS) • MPLS – the base technology (for packet switched nws) • GMPLS – extension of MPLS to provide the control plane (signaling and routing) for devices that switching in any of these domains: packet, time, wavelength and fiber.

For packet-switching nw only Focuses mainly on the data plane For packet switched capable (PSC) as well as non-PSC interfaces. Focuses on the control plane that performs connection management for the data plane MPLS vs. GMPLS MPLS GMPLS

Requires Label Switched Path (LSP) to be set up b/w routers at both ends LSP can be set up b/w any similar types of Label Switched Routers (LSR) e.g. b/w SONET/SDH ADM to form a TDM LSP Scale better by forming a forwarding hierarchy Functions specific to optical nw such as suggested label and bi-directional LSP setup MPLS vs. GMPLS (cont.) MPLS GMPLS

Goals of GMPLS • A common control plane promises to simplify network operation and management by: • Automating end-to-end provisioning of connections • Managing network resources

Summary of the GMPLS Protocol Suite • Extended the signaling (RSVP-TE, CR-LSP) and routing protocols (OSPF-TE, IS-IS-TE) to accommodate the characteristics of TDM/SONET & optical networks. • A new protocol, Link Management Protocol (LMP) has been introduced to manage and maintain the health of the control and data planes between two neighboring nodes.

LSP Creation in GMPLS-Based Networks / Hierarchical LSP 1. LSP (LSPλ) is established between OXC1 and OXC2 and capable of delivering OC-192 wavelength to tunnel in TDM LSPs. 2. LSP (LSPtdi) is established between DCSi and DCSe. 3. LSP (LSPtdm) is established between DCS1 and DCS2. 4. LSP (LSPpi) is established between LSR2 and LSR3 (LSPpi). 5. LSP (LSPpc) is established between LSR1 and LSR4.

QoS for Mobile Networks • Problems: • Current IP QoS Signaling is not mobility aware (RSVP, DiffServ etc) • Resources may not be available for the new path • Handoff latency • Different QoS mechanisms • Requirements/challenges: • Minimize disruption in QoS during handover • Localize the QoS re-establishment to only the effected parts of the packet path • Release any old QoS state after handover as early as possible • Deal with multiple QoS mechanisms deployed • Multi-path routing • Mobile RSVP (MRSVP) • Use advance resource reservations • Common path identification • Mobile proxy: refresh RSVP state instead of energy constrained mobile device

QoS for MANETs • More problems: • No infrastructure, all mobile battery limited devices • Frequent topology changes and high mobility • INSIGNIA • Support for the delivery of adaptive services in mobile ad hoc networks • See Seoung-Bum Lee et al. INSIGNIA: An IP-Based Quality of Service Framework For Mobile Ad Hoc Networks, Journal of Parallel and Distributed Computing, 2000.

Next Steps in Signaling (NSIS) • RSVP not widely used for resource reservation • Used for MPLS path setup • Security an open issue • Limited support for IP mobility • IETF NSIS working group is looking at new ways to do QoS signaling • Re-use, where appropriate, the mechanisms of RSVP • See e.g. rfc4080

T-110.5110 Computer Networks II Quality of Service