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T-110.5110 Computer Networks II Quality 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 2 25 May 2017 22.10.2007 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 3 25 May 2017 22.10.2007 QoS Requirements Sensitive Personal voice over IP CEO Video conference with analysis Network monitorin g Unicast radio Financial Transactions Interactive whiteboar d Delay Public web traffic Extranet web traffic Network management traffic Push news Personal e-mail Busines s e-mail Server backups Insensitive Casual 4 Mission Criticality Critical 25 May 2017 22.10.2007 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) 5 25 May 2017 22.10.2007 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 6 25 May 2017 22.10.2007 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) 7 Core 25 May 2017 22.10.2007 QoS Mechanisms: classification Provisioning Admission control o Prohibit or allow new flows to enter the nw Resource reservation o E.g. Over provisioning Control Operate on short time scales Real-time traffic or flow control o E.g. scheduling, shaping, policing... Management Monitor the QoS Longer time scales than control 8 25 May 2017 22.10.2007 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) 9 25 May 2017 22.10.2007 QoS Control Mechanisms (cont.) IP addresses, net mask, port numbers, protocol id N Full Arrival Packet Classifier Y Processor Departure Queue Discard Scheduling (FIFO Queuing) Flow identifier Full Arrival Classifier The switch turns to other queue when the current one is empty N High Priority Queue Y Discard Full Processor Departure N Y Discard Low Priority Queue Scheduling (Priority Queuing) 10 25 May 2017 22.10.2007 QoS Control Mechanisms (cont.) Full Arrival Classifier The turning switch selects 2 packets from 1st queue, then 1 packet from 2nd queue and the cycle repeats N Weight: 2 Y Discard Full Processor Departure N Y Discard Weight: 1 Scheduling (Weighted Fair Queuing) Leaky Bucket (Regulate the traffic) 11 Token Bucket (Credit an idle host) 25 May 2017 22.10.2007 QoS Control Mechanisms (cont.) Arriving Packet Arriving Packet Queue Queue Accepted Dropped Dropped from front Full Full (Tail-drop scheme) (Drop-from-front scheme) Drop probability Queue 1 Avg. TCP Traffic Drop MAXth MINth MAXdrop MINth (Random Early Detection with Drop function) 12 MAXth Avg. queue size 25 May 2017 22.10.2007 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 o E.g. available bandwidth (Multi-)constrained path computation o Can be computationally complex Widest-Shortest Path o Select the shortest path that is feasible according to the bandwidth constraint Shortest-Widest Path o o 14 Find paths with the most available bandwidth (i.e. widest paths) Break ties by selecting the shortest path (#hops or delay) 25 May 2017 22.10.2007 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 15 25 May 2017 22.10.2007 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 16 25 May 2017 22.10.2007 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) 17 25 May 2017 22.10.2007 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 packetswitched network Reservation of resources is done with the Resource Reservation Protocol (RSVP) 18 25 May 2017 22.10.2007 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 19 25 May 2017 22.10.2007 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 20 25 May 2017 22.10.2007 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 21 25 May 2017 22.10.2007 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 22 25 May 2017 22.10.2007 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. 23 25 May 2017 22.10.2007 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 24 25 May 2017 22.10.2007 Expedited Forwarding 25 • Expedited packets experience a traffic-free network (low loss, low latency, low jitter, and assured bandwidth (premium service) • Strict priority queuing 25 May 2017 22.10.2007 Assured Forwarding 26 • 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 25 May 2017 22.10.2007 Bandwidth Brokers U1 BB S1 U2 BB C1 S2 C2 ISP 2 D Server 3 C3 C6 Core Network C7 Server 2 Server 1 U1 U2 27 BB C5 C4 ISP 1 BB BB U3 25 May 2017 22.10.2007 Integrated Solution 28 25 May 2017 22.10.2007 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 29 25 May 2017 22.10.2007 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 30 25 May 2017 22.10.2007 Separate forwarding and control • Exact match instead of longest prefix match (like IP) faster forwarding IP Router Control: IP Router Software 31 MPLS Control: IP Router Software ATM Switch Control: ATM Forum Software Forwarding: Forwarding: Forwarding: Longest-match Lookup Label Swapping Label Swapping 25 May 2017 22.10.2007 MPLS Forwarding 32 25 May 2017 22.10.2007 MPLS Operation 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 IP Ingress IP Egress MPLS Domain 2. Ingress LER receives packet and “label”s packets 33 25 May 2017 3. LSR forwards packets using label swapping 22.10.2007 MPLS Labels • Label assignment decisions are based on forwarding criteria like •Destination unicast routing •Traffic engineering •Multicast •Virtual Private Network •Quality of Service 34 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: of Stack (first label in stack) 25 May Bottom 2017 22.10.2007 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. 35 25 May 2017 22.10.2007 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 36 25 May 2017 22.10.2007 LSP Hierarchy A Packet can have several labels one after the other before the IP header. (Why? Tunneling) (Multiple Levels of Nesting) (Tunnel 1 may be for the Enterprise with 1a for VoIP data, 1b for billing, and 1c for alarm & provisioning) Push Swap & Push R1 R2 R2A Swap R2B Pop & Swap Pop R2C R3 R4 IP 37 3 2 7 2256May 2017 2 8 4 IP 22.10.2007 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 38 25 May 2017 22.10.2007 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] 39 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 25 May 2017 22.10.2007 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 40 25 May 2017 22.10.2007 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. 41 25 May 2017 22.10.2007 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. 42 25 May 2017 22.10.2007 MPLS vs. GMPLS MPLS For packet-switching nw only Focuses mainly on the data plane 43 GMPLS For packet switched capable (PSC) as well as non-PSC interfaces. Focuses on the control plane that performs connection management for the data plane 25 May 2017 22.10.2007 MPLS vs. GMPLS (cont.) MPLS GMPLS Requires Label Switched Path (LSP) to be set up b/w routers at both ends 44 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 25 May 2017 22.10.2007 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 45 25 May 2017 22.10.2007 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. 46 25 May 2017 22.10.2007 LSP Creation in GMPLS-Based Networks / Hierarchical LSP 47 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. 25 May 2017 22.10.2007 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 48 25 May 2017 22.10.2007 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. 49 25 May 2017 22.10.2007 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 50 25 May 2017 22.10.2007 Overlay Solutions QoS can also be provided by using overlay solutions (application layer) Idea is to determine paths through the overlay network and then utilize one or more paths with characteristics that meet the requirements Given a good overlay node placement, network topology can be taken into account and multiple paths across the network can be determined Example: RON Reliable Overlay Network 51 25 May 2017 22.10.2007 Reliable Overlay Routing RON Example: Reliable Routing N2 N3 ISP2 ISP1 X N1 ISP3 Overload N4 N5 52 25 May 2017 22.10.2007 Consider a native link failure in CE Only overlay link AE is affected. The native path AE is rerouted over F (ACE → ACFDE) G 3 A I 3 2 OVERLAY 2 4 E NATIVE G B ∞ F C Cost Overlay recovery: 8 Original: 2 Native Recovery + H E D Native Rerouting: 2 Overlay rerouting: 4 Native Failure 53 I A Time Native Repair 25 May 2017 22.10.2007 References 1. Andrew S. Tanenbaum, Computer Networks, Fourth Edition, Pearson Education, 2006. 2. James F. Kurose, and Keith W. Ross: Computer Networking: A Top-Down Approach Featuring the Internet, Third Edition, Pearson Education, 2006. 3. Alberto Leon-Garcia and Indra Widjaja, Communication Networks: Fundamental Concepts and Key Architectures, Second Edition, Tata McGraw-Hill, 2005. 4. IP QoS Architectures and Protocols, Packet Broadband Network Handbook, Digital Engineering Library, McGraw Hill, 2004. 5. Congestion Control and Quality of Service, Data Communication and Networking, Digital Engineering Library, McGraw Hill, 2006. 6. Curado, M. and Monteiro, E. , "A Survey of QoS Routing Algorithms", in Proc. of the International Conference on Information Technology (ICIT2004), December 2004 7. Manner Jukka, Lopez A, Mihailovi A, Velayos H, Hepworth E, and Y Khouaja, Evaluation of Mobility and QoS Interaction, Computer Networks Volume 38, Issue 2, 5 Feb 2002, pp. 137-163. 8. Anup Kumar Talukdar, B. R. Badrinath, and Arup Acharya, MRSVP: A Resource Reservation Protocol for an Integrated Services Network with Mobile Hosts, Wireless Networks, 7, 5–19, 2001. 9. Rajeev Koodli, and Charles E. Perkins, Fast Handovers and Context Transfers in Mobile Networks, ACM SIGCOMM Computer Communications Review, Special Issue on Wireless Extensions to Internet, 2001. 10. J. Hillebrand, C.Prehofer, R. Bless, M. Zitterbart, Quality-of-Service Signaling for Next-Generation IP-based Mobile Networks, IEEE Communications Magazine, June 2004. 11. Seoung-Bum Lee, G. Ahn, X. Zhang and A. T. Campbell, INSIGNIA: An IP-Based Quality of Service Framework For Mobile Ad Hoc Networks, Journal of Parallel and Distributed Computing, 2000. 12. Chittaranjan Hota, Sanjay Jha, G Raghurama, Distributed Dynamic Resource Management in IP VPNs to Guarantee Quality of Service, IEEE ICON 2004, Singapore. 13. RFC 2205: Resource Reservation Protocol, Braden, Zhang et al. 14. RFC 3031: Multiprotocol Label Switching (MPLS), Rosen, Viswanathan and Callon. 15. RFC 2475: An Architecture for Differentiated Services, S. Blake, D. Black et al. 16. RFC 4080: Next Steps in Signaling (NSIS): Framework, R. Hancock, G. Karagiannis et al., 2005. 17. RFC 2326: Real Time Streaming Protocol (RTSP), H. Schulzrinne et al., 1998 18. GMPLS tutorial: http://www.iec.org/online/tutorials/gmpls/ 54 25 May 2017 22.10.2007