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Packet Voice Backbone Network Design Matt Kolon February 23rd, 2004 APRICOT 2004 - Kuala Lumpur Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 1 Agenda Packet voice essentials • Quick background: VoIP Applications • Customer Goals for Voice • VoIP Traffic Characteristics Packet voice backbone design • Class of service • High Availability • MPLS Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 2 Business: IP Voice Trunking Service Provided: Point-to-Point “IP trunk” with low-latency QoS and guaranteed bandwidth. Usually to replace a pure FR service. SP implements it with circuit-oriented access network(s) and a Traffic Engineered MPLS tunnel in the IP/MPLS backbone All VoIP “application” intelligence resides in enterprise private devices (e.g. IAD/Media Gateway, IP PBX, SIP phones, etc) IP trunk Enterprise HQ Enterprise Remote Site MPLS LSP FR/TDM DSLAM IP PBX SIP IAD ATM IP/MPLS Copyright © 2003 Juniper Networks, Inc. POTS ETH/VLAN Proprietary and Confidential www.juniper.net 3 Business: [Vo]IP transport VPNs Service Provided: Multipoint IP VPN with low-latency QoS and guaranteed bandwidth, suitable for voice traffic. Often part of a multi traffic class IP VPN offering (VoIP being only one traffic class). SP implements it with circuit-oriented access network(s) and a mesh of Traffic Engineered MPLS tunnels in the backbone. Or pure Diffserv approach with traffic trend monitoring. Or Layer 2 VPLS. Or IPSec… All VoIP “application” intelligence resides in enterprise private devices Enterprise Remote Sites (Vo)IP VPN Enterprise HQ DSLAM FR/TDM IAD POTS IAD POTS IP PBX SIP Copyright © 2003 Juniper Networks, Inc. DSLAM IP VPNs ETH/VLAN Proprietary and Confidential www.juniper.net 4 Business: IP VPNs + Managed VoIP Service Provided: Multipoint IP VPN with low-latency QoS and guaranteed bandwidth; Managed VoIP equipment in customer premises. SP implements it with circuit-oriented access network(s) and a mesh of Traffic Engineered MPLS tunnels in the backbone. Or pure Diffserv approach with traffic trend monitoring. Or Layer 2 VPLS. Or IPSec. Or private line (e.g. FR) links. Etc. All VoIP “application” intelligence resides in managed devices (e.g. IAD/Media Gateway, IP PBX, etc) located in customer premises. IP Telephony Enterprise Remote Sites (Vo)IP VPN Enterprise HQ DSLAM FR/TDM IAD POTS IAD POTS IP PBX SIP Copyright © 2003 Juniper Networks, Inc. DSLAM IP VPNs ETH/VLAN Proprietary and Confidential www.juniper.net 5 Business: TDM/telephony, VoIP core Service Provided: regular TDM Telephony (transport and application) SP implements it with a TDM access network, Media Gateways, an IP Core, a PSTN core, and PSTN mediation mechanisms. This is a Class 4/5 replacement application, not directly visible to the end users. VoIP “application” intelligence (servers and gateways) hosted by the SP, overlaid on IP backbone, coupled with PSTN “intelligence”. Enterprise Site 1 TDM / Telephony TDM / Telephony Enterprise Site 2 IP/MPLS POTS GE CSU/DSU MPLS LSP TDM GE TDM TDM PBX TDM POTS TDM Softswitch SIP Softphone Copyright © 2003 Juniper Networks, Inc. PSTN/SS7 Proprietary and Confidential www.juniper.net 6 Carrier: signaling transport Service Provided: IP VPN to convey IP-based signaling & control messages (SS7-over-IP, SIP, H.323, MGCP/Megaco, TCAP/IN, etc) with proper CoS and insulation. SP implements it with an IP/MPLS Core. Could be operated by the voice carrier, or outsourced to an IP provider. VoIP “application” intelligence (servers and gateways) hosted by the SP, overlaid on IP backbone, coupled with PSTN intelligence. Media Gateway Softswitch Class 4/5 Signaling IP/MPLS Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 7 Carrier: inter-domain VoIP peering Service Provided (to end users): public telephony (VoIP or POTS) Main goal is to create a VoIP peering point between carriers SP implements it with “virtual” IP-to-IP gateways, plus inter-domain signaling (e.g. SIP or SS7). May require true media/codec transcoding, or “simple” IP forwarding. Complex business peering issues are addressed by the signaling layer. IP-to-IP “Virtual” Gateways IP/MPLS IP/MPLS MPLS LSPs SIP/H.323 Gatekeeper MPLS LSPs Softswitch Softswitch SIP/H.323 Gatekeeper Peering Signaling Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 8 Business: IP Centrex, Softswitch Service Provided: IP Centrex (a.k.a. Hosted IP Telephony) to Small & Medium VoIP-enabled Businesses. SP implements it with a broadband access network(s), a VPN enabled IP/MPLS backbone, softswitches with Centrex intelligence, and PSTN gateways (transport & signaling). All VoIP “application” intelligence is hosted by the SP, as well as PSTN gateway mechanisms. “Virtual PBX” IP Centrex Enterprise Site IP VPN SIP Sig. Gateway MG Modem DSLAM Softswitch FR/TDM IP/MPLS with VPNs SS7 PSTN Media Gateway POTS Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 9 Residential: VoIP / telephony Service Provided: regular telephony services (transport and application), via VoIP, in addition to regular Broadband Internet. SP implements it with a broadband access network, an IP/MPLS Core, a PSTN core, and PSTN mediation mechanisms. VoIP “application” intelligence hosted by the SP, overlaid on IP backbone, and coupled with PSTN “intelligence” CPE could be a mere bridge, or an IP router, or a full-blown media gateway (POTS phones). Home network could be ETH, WLAN, etc. Household/SOHO IP / Telephony INTERNET IP / Telephony Household/SMB IP/MPLS CPE CPE MPLS LSP (hierarchical) SIP or H.323 DSLAM POTS DSLAM CMTS CMTS SIP or H.323 POTS Softswitch PSTN/SS7 Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 10 Agenda Packet voice essentials • Quick background: VoIP Applications • Customer Goals for Voice • VoIP Traffic Characteristics Packet voice backbone design • Class of service • High Availability • MPLS Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 11 Goals for Packet Voice Networks Quality • Deliver a grade of voice service equivalent to that provided by the current Public Switched Telephone Network (PSTN). Multiservice • Voice service must live on a common IP backbone with a set of other services. Flexibility • Must be capable of supporting future applications that may not yet be fully defined. Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 12 Quality: MOS Model Voice quality in the PSTN network has historically been measured using ‘mean opinion score’ (MOS). The mean opinion score measures the subjective quality of a voice call. Historically the telephony providers invited people and used various call types (with delay, echo etc.) and recorded the results. MOS scores for “acceptable” voice have been dropping, but quality is still important. Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 13 Quality: Voice-worthy IP Backbones Sufficient bandwidth for voice + other services Delay: Less than 40msec Jitter: Less than 20msec Loss: Less than 2% Availability: Better than 4 9s, less than 1% blocking Security: No unauthorized intrusion or DoS effects Predictability: None of this changes in unforseeable ways Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 14 Engineering VoIP Experience Levels Over-Provisioned Network Best Effort Over-Subscribed Network Enhanced Delivery Carrier-Grade Multi-Service Network Assured Experience Experience Levels None (State-less) Planning/Reporting (Historical) Reactive (Real-time) Service Level State Best Effort Diff-Serv MPLS (Core) / Static (Access) MPLS (Core) / Dynamic (Access) QoS Flat Access / Core Integrated End-to-End Network Resources Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 15 Core Domain VoIP Solutions Over-Provisioned Network Core Access Copyright © 2003 Juniper Networks, Inc. Best Effort Access Proprietary and Confidential www.juniper.net 16 Core Domain VoIP Architecture Best Effort A Best Effort Experience is achieved by transporting voice over IP networks without special treatment • All packets delivered according to equal prioritization router queuing throughout network Best effort engineered networks require over-provisioning to account for peak traffic bursts associated with data applications and busy voice hours Studies and experience both show that today’s well engineered overprovisioned networks based on current routing technologies can support most voice services Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 17 Core Domain VoIP Architecture Best Effort Failure Detection ~ 300 ms – 1+ sec (without optimizations) Route Convergence ~ 10+ sec (area size dependant) Causes temporary service interruption, degradation of capacity Router Failure Copyright © 2003 Juniper Networks, Inc. O Proprietary and Confidential www.juniper.net 18 Core Domain VoIP Architecture Best Effort Routing protocols unable to detect route around congestion Causes temporary service interruption, degradation of capacity O Link Congestion Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 19 Core Domain VoIP Architecture Best Effort – Pros & Cons Pros Inexpensive Simple Studies show that overprovisioning provides satisfactory delay and jitter performance Sufficient strategy for voice-only and over-provisioned networks Cons Performance levels not maintainable across failures and congestion Not adequate for oversubscribed networks Challenges inherent with building over-provisioned networks Does not provide admission control constructs Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 20 Core Domain VoIP Solutions Over-Subscribed Network Core Access Copyright © 2003 Juniper Networks, Inc. Enhanced Delivery Differentiated Services Access Proprietary and Confidential www.juniper.net 21 Core Domain VoIP Architecture Enhanced Delivery Differentiated Services (Diff-Serv) facilitates the ability to provision separate service classes such that they receive particular treatment levels Packets marked accordingly before entering the network Participating routers process packets according to Diff-Serv marking Router Diff-Serv processing variables • Queuing (priority levels) • Scheduling (strict, weighted, round-robin, etc) • Congestion avoidance (RED, WRED) Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 22 Core Domain VoIP Architecture Enhanced Delivery DiffServ markings (DSCP) scale well DSCP’s can be AS-Dependant • Router DSCP mediation requirement DSCP may be mapped to other QoS technologies across network • QoS migration • Network segment QoS interworking DiffServ adds deterministic behavior to packet class transport • This benefit enhances transport behavior in secondary path re-route optimizations Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 23 Core Domain VoIP Architecture Enhanced Delivery •Cycle through output queues emptying from highest to lowest priority •DiffServ markings map to queue level Copyright © 2003 Juniper Networks, Inc. High Priority Queue Medium Priority Queue Low Priority Queue •Queuing schedulers typically allow for variable weighting/emptying •Queue sizes typically variable/provisionable Proprietary and Confidential www.juniper.net 24 Core Domain VoIP Architecture Enhanced Delivery Failure Detection ~ 300 ms – 1+ sec (without optimizations) Route Convergence ~ 10+ sec (area size dependant) Re-Route performance doesn’t benefit from DiffServ treatment Causes temporary service interruption, degradation of capacity Router Failure Copyright © 2003 Juniper Networks, Inc. O Proprietary and Confidential www.juniper.net 25 Core Domain VoIP Architecture Enhanced Delivery Routing protocols unable to detect route around congestion High-priority-marked VoIP flows will take longer to be affected by congestion than lower priority flows May cause temporary VoIP service interruption, degradation of capacity, will affect other services O Link Congestion Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 26 Core Domain VoIP Architecture Enhanced Delivery – Pros & Cons Pros Cons Adequate for oversubscribed networks Performance levels not guaranteed across failures and congestion Enhanced flow treatment for VoIP across failure reroute paths Lowers per-router hop latency Link bandwidth statistics not maintained or usable Does not enable admission control constructs Adds flow-based traffic engineering model Scales easily Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 27 Core Domain VoIP Solutions Carrier-Grade MultiService Network Core Access Copyright © 2003 Juniper Networks, Inc. Assured Experience MPLS-TE Access Proprietary and Confidential www.juniper.net 28 Core Domain VoIP Architecture Assured Experience Assured Experience networks are built upon an intelligent network resource plane Allow the service provider to guarantee deterministic performance to its customers under all network conditions • Even during network congestion and element failures Facilitate multi-service network infrastructures Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 29 Core Domain VoIP Architecture Assured Experience The Intelligent Network Resource Plane… • Maintains resource state, such as • Link Bandwidth – up/down, total and current allocation • Facilitates connection-oriented traffic engineering constructs, such as… • Constraint Based Routing Control • Flow Classification and Forwarding • Supports fault tolerance constructs, such as • Fail-over Resources – routes, network elements Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 30 Core Domain VoIP Architecture Assured Experience – MPLS MPLS supports the requirements of Intelligent Network Resource Plane MPLS was designed to ease the provisioning and maintenance of efficient packet data networks IGP and BGP routing protocols building forwarding tables based on shortest path only MPLS separates the route control and packet forwarding such that policy-based paths may be constructed Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 31 Core Domain VoIP Architecture Assured Experience – MPLS MPLS is based on… • Label Switched Paths (LSP) • Link Attribute Distribution (IGP/BGP protocol extensions) • Traffic Engineering Databases (TED) • Constrained-Shortest-Path-First Algorithm (CSPF) • Label Distribution Protocols (LDP) • Label Edge Routers (LER) and Label Switch Routers (LSR) MPLS-TE facilitates constraint-based routing We’ll talk more about MPLS items later… Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 32 Core Domain VoIP Architecture Assured Experience – MPLS Route Protection Primary LSP / Secondary LSP Configuration • Allows for backup physical path TE Fast Rerouting • Facilitates dynamic routing around link / node failures Fate Sharing • Limit backup LSP crossing of the same physical elements as primary LSP Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 33 Core Domain VoIP Architecture Assured Experience – MPLS •Traffic Engineering creates LSP’s •Labels are distributed to construct LSP’s LER •Packets are classified / Labels added •L2/L3 policy application •Upstream flows policed, downstream flows shaped LSR LER •LSR’s only inspect label •Label is removed from packets •Label and interface table lookup •Packets are routed to destination •Output label and interface •Queue and drop accordingly Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 34 Core Domain VoIP Architecture Assured Experience – MPLS Failure Detection ~ 20 – 30 ms Fast Reroute < 50 ms Small amount of packet loss during failover Service interruption not noticeable, minimal capacity degradation Router Failure Copyright © 2003 Juniper Networks, Inc. O Proprietary and Confidential www.juniper.net 35 Core Domain VoIP Architecture Assured Experience – Pros & Cons Pros Cons State-full, intelligent network resource plane Fully meshed topologies suffer from n2 scaling issues Designed to ease TE design, maintenance and management Facilitates class-based forwarding for multi-service networks Interworks with disparate QoS mechanisms and transport technologies Supports hierarchical forwarding Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 36 Multiservice: Service Classes From this… Control To this…. Data Control Internet Voice VPN Easy to think of as “CoS”, but actually involves much more than traditional router CoS or QoS mechanisms. Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 37 Multiservice: Bundled Service Offerings Plain VoIP service model is proven to be non-sustainable • First generation of pure VoIP carriers are gone • Price of 1 min of voice has fallen through the floor VoIP with other services is the way to go • Value-add: Unified messaging, voice accessible content, video telephony • Additional non-voice: Broadcast video, surveillance, etc. VPNs and other business services • Generate more revenue, key differentiator from competitors • Can be offered at minimum additional cost Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 38 Final Thought on Goals: Who Really Knows? Future service revenue • By definition unknowable, will always surprise us… • Immense possibility in diverse areas such as mobile, micropayment, handheld videoconferencing… • Infrastructure must have: • Unrestricted future service rollout – Vendors must design flexible hardware and software platforms • Upgradeable without forklift • Capability to support many services at one time, without the services affecting each other Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 39 Agenda Packet voice essentials • Quick background: VoIP Applications • Customer Goals for Voice • VoIP Traffic Characteristics Packet voice backbone design • Class of service • High Availability • MPLS Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 40 QoS: Bandwidth VoIP traffic is constant bit stream, bandwidth required varies with which codec used, # of voice sample per packet, and transport media used. Even G.711 packets are only ~80 bytes, each call only ~112 kbps. VoIP packet is very small for compressed codecs • G.729 with two 10ms samples/frame yields 24Kbps without layer2 headers Line rate processing of VoIP packets is crucial! Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 41 QoS: Delay ITU G.114: <150ms for one-way, e2e Delay Budget: • T f Packet formation delay, O(10ms) • Tsf Packet switching delay, O(10us) per Hop Si • Serialization delay, (#bits/link rate*#Hop) Pi • Q Propagation delay, (1ms/100mile) • Queuing delay, (variable) typical backbone delay requirement: <30ms max Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 42 QoS: Jitter Definition: Variations in packet arrival time Causes: • Queuing variation under changing network load condition • Load sharing over changing paths De-jitter (“playout”) buffer in gateways • Static or dynamic • Adds to the overall delay Best to avoid causes of Jitter rather than trying to buffer it away. Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 43 QoS: Packet Loss UDP as transport • no flow control • doesn’t tolerate packet loss very well <1% to avoid quality degradation <5% if VoIP gateway provides concealment mechanism Higher compression rates demand lower loss budgets Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 44 Network Availability & Recovery Availability • Common SLA for VoIP network: 99.995% or 26 min/yr • Availability needs continue to increase Recovery • O(sub-second) to avoid session timeout and new call setup • VoIP gateway to gateway recovery usually spans over several segments • Layer 3 based network recovery is generally unacceptable Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 45 Network Security Guard against un-trusted network elements and networklevel attacks Stateful and stateless firewall capabilities may be necessary Authentication to Prevent Fraud • RADIUS most common deployment Confidentiality is emerging as another basic security requirement for VoIP • Carry VoIP traffic within VPN, such as IPsec tunnel or MPLS VPN • Increased security vs. encryption overhead for VoIP packet Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 46 Agenda Packet voice essentials • Quick background: VoIP Applications • Customer Goals for Voice • VoIP Traffic Characteristics Packet voice backbone design • Class of service • High Availability • MPLS Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 47 Topological Assumptions Routers deployed in pairs at each site • Primarily for fault tolerance • Also useful for load sharing Intra-site connections required in all topologies • Must be at least same capacity as inter-site trunk links Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 48 Core Topologies Star-connected Core • “Outer core” connected to two “super-routers” • Simple routing and forwarding • Probably least expensive • Concerns about redundancy Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 49 Core Topologies Fully-connected Mesh • Each router connected to every other site • Also simple routing and forwarding • Perhaps most expensive • Mesh can always be reduced! Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 50 Core Topologies Half-mesh router groups • Each router connected to ~half of other sites • More complex routing and forwarding • Many full-mesh benefits without the expense • Success depends on engineering to particular needs Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 51 Edge-core Topologies 1 Single uplink per router edge site • Two connections to two routers in one core site • Availability largely dependent on physical layout Core Router Site 1 Ed g e Ro u ter S it e D Co re Ro u ter • Usually lowest cost Copyright © 2003 Juniper Networks, Inc. S it e 2 Proprietary and Confidential www.juniper.net 52 Edge-core Topologies 2 Single uplink per router edge site • Two site connections to two separate routers • Availability depends on physical media • Somewhat low cost Core Router Site 1 Ed g e Ro u ter S it e C Co re Ro u ter S it e 2 Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 53 Edge-core Topologies 3 Partially duplicated edge router uplinks • Three connections to three separate routers • One dual-homed, Edge one not Router Site B • Particularly useful in MPLS topologies • High availability • Somewhat high cost Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential Co re Ro u ter S it e 1 Co re Ro u ter S it e 2 www.juniper.net 54 Edge-core Topologies 4 Fully duplicated edge router uplinks • Four connections to four separate routers • Both edge routers dual-homed • Highest availability Ed g e Core Router Site 1 Ro u ter S it e A Co re Ro u ter S it e 2 • Highest cost Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 55 Site Connection to Edge Routers Many variants on dual-homed designs possible Essential idea is suitable for gateway or softswitch sites Media Best-effort traffic may enter through separate aggregation points Copyright © 2003 Juniper Networks, Inc. Gateways Proprietary and Confidential www.juniper.net 56 IGP Selection Two options: • ISIS • OSPF Very close race! Biggest issue is probably legacy deployment in current network, and customer comfort. ISIS has slight edge in terms of sub-second failure detection Main point is that a successful network can be built with either. Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 57 IGP Configuration Issues to consider • Hierarchy (areas or levels) • Hello Timers •BFD changes things here! • Authentication for security • Addressing plan •ISIS requires ISO NET lo0 addresses • Metrics • Load balancing Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 58 Load-balancing Considerations Two approaches to load balancing • Per-destination • Single path chosen from equal-cost next hops • Simpler to predict • Per-flow • Flow distributed between equal-cost next hops • Policy can restrict potential traffic path Choice depends primarily on topology and other requirements Most voice engineers more comfortable with per-destination Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 59 Forwarding Protection Protocol Options Link Redundancy • MLPPP – T1/E1 Link aggregation • 802.3ad – Ethernet aggregation • SONET/SDH aggregation SONET/SDH APS/MPS Virtual Router Redundancy Protocol (VRRP) Standard IGP protocols • OSPF • ISIS Bidirectional Forwarding Detection (BFD) Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 60 Bidirectional Forwarding Detection (BFD) IETF Draft co-authored by Juniper and Cisco Optimized timer-based link failure detection protocol • Brings link failure detection in line with today’s highspeed transport technologies Reduces link failure recognition from seconds to 10’s of milliseconds • Provisionable for link/service requirements Operates at packet forwarding plane • Independent from routing protocols and applications When run between edge router and media gateway, provides network resource to VoIP service link Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 61 MG to Router Connection with BFD VoIP Line Cards MG BFD-A1bu BFD-B1bu BFD-B2 BFD-A2 BFD-B2bu BFD-A2bu Line Cards BFD-B1 Line Cards BFD-A1 VoIP Line Card Failure • Connectivity of A1 protected by B1 (vice-versa) • Call preserved only under specific MG application control Router PIC Failure • Connectivity of A1 and B1 protected by A2 and B2 respectively (vice-versa) • Call preserved with packet-loss period (dependant on detection and re-route times) Router System Failure • Connectivity of A and B protected by Abu and Bbu respectively (vice-versa) Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 62 Agenda Packet voice essentials • Quick background: VoIP Applications • Customer Goals for Voice • VoIP Traffic Characteristics Packet voice backbone design • Class of service • High Availability • MPLS Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 63 IP CoS Functions Per-flow Rate Policing Traffic Classification & Marking Priority Queuing Congestion Avoidance W R R RED • IP Flow • IP Precedence bits, DSCP Byte • MPLS CoS bits 100% Stream • Incoming Physical Interface • Incoming Logical Interface • Destination IP address Copyright © 2003 Juniper Networks, Inc. 100% 100% PLP=1 Proprietary and Confidential PLP=0 www.juniper.net 64 Converged Network CoS Design In a voice / best effort network, three classes (at least) of service are necessary: • IP network control traffic • Low bandwidth requirements, not sensitive to latency, jitter • Must not be starved • Voice signaling and bearer traffic • Highest latency and jitter requirements • Best effort data traffic • Whatever capacity is left More complex configurations may or may not be needed in other network designs (e.g. with VPN service) More classes = more complexity, no way around this. Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 65 Converged Network CoS Design Queue 0 : IP Network Control traffic • Allocated bandwidth : 5% (the default for NC) • Priority: High; this guarantees that NC traffic will never be starved of bandwidth. • No RED drop profile assigned, as NC traffic should never be dropped. Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 66 Converged Network CoS Design Queue 3 : Voice Signaling and Bearer traffic • Initial requirement is 50% of total traffic. • Allocated bandwidth: 20%; although doesn’t really matter as this queue gets strictly high priority. • Strictly High Priority: voice can take as much bandwidth as it needs. RED drop profile: drop nothing until queue is full, then drop everything. • Dropping packets randomly is not very suitable on voice traffic. • Forces head dropping (rather than tail dropping) once queue is full. Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 67 Converged Network CoS Design Queue 1 : Best effort • Allocated bandwidth: remaining 75%. • Not guaranteed • Priority: Low; this traffic is served only if there is no voice traffic, and there is bandwidth available. • RED drop profile: medium. This can be fine tuned, perhaps start to drop when queue is 70%, with a probability of 30%, then drop 100% of the traffic when queue fullness reaches 90%. • Medium RED drop profile will limit the TCP congestion synchronization phenomena that would occur otherwise. Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 68 More Services Possible! Multiservice queuing • Service VoIP Queue Aggressively to Avoid Filling the Queue Best Effort Traffic Queue 0 = 50% WRR Service Rate = 15% VPN Traffic Queue 1 = 35% WRR Service Rate = 15% VoIP Traffic Queue 2 = 10% WRR Service Rate = 65% Network Control Traffic Queue 3 = 5% WRR Service Rate = 5% Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 69 Agenda Packet voice essentials • Quick background: VoIP Applications • Customer Goals for Voice • VoIP Traffic Characteristics Packet voice backbone design • Class of service • High Availability • MPLS Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 70 Don’t Stop Sending the Voice! It doesn’t matter what happens otherwise… • Customers only notice when the call is interrupted Many call this idea “Non-Stop Forwarding” Main Principles of NSF • Data Plane should not be disrupted • Control plane failures should not effect forwarding • Failures happen but the infrastructure can recover gracefully • Management/Routing sessions can be re-connected unnoticed Many Vendors Adopting this approach • Not all, some favor fully redundant protocol state mirroring Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 71 Graceful Restart - How ? Restarting node preserves the forwarding state Control plane failure known only to the Routing peers Routing peers preserve routing information of restarting node Restarting node (re)learns its routing information from its routing peers No preservation of any of the protocol-related state across the restart on restarting node Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 72 Graceful Restart - How ? Separate control and data planes P P PE 2 When router recovers, neighbors sync up without disturbing forwarding. PE 1 If router’s control plane fails, data plane can keep forwarding packets Copyright © 2003 Juniper Networks, Inc. PE 3 P Neighbors hide failure from all others routers in the network P Other routers are never made aware of failure Proprietary and Confidential www.juniper.net 73 Graceful Restart - How ? (cont.) Graceful restart mechanisms are protocol specific: • BGP for Interdomain routing • ISIS and OSPF for IGPs • LDP and RSVP for LSP management • BGP/MPLS specific to MPLS VPN management • RIP – already built in, but a draft nonetheless All these are currently IETF drafts, but implemented by major vendors (this isn’t an unusual situation, many examples of this these days) Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 74 Hitless RE Switchover Routing Engines Protects against Single Node Hardware Failure Primary (REP) and Secondary (RES) utilize keepalive process Keep Alive • Automatic failover to RES • Synchronized Configuration REP and RES share: • Forwarding info + PFE config Packet Forwarding Engines REP failure does not reset PFE • No forwarding interruption • Only Management sessions lost • Alarms, SNMP traps on failover Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 75 Agenda Packet voice essentials • Quick background: VoIP Applications • Customer Goals for Voice • VoIP Traffic Characteristics Packet voice backbone design • Class of service • High Availability • MPLS Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 76 IP-only Path Selection Largely dependent on routing protocols Adjustable only through metrics • Changes tend to be global • Difficult on per-application basis • Extremely manual and labor-intensive in nature • Requires offline path computation Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 77 IP-only Network Reliability Mechanisms •Connection-oriented transport (TCP) •Not used for realtime traffic like voice •Dependence on underlying network infrastructure •E.g. SONET/SDH APS, Ethernet VRRP, ATM •Not IP-based, therefore not network-wide •Routing protocol recovery •Relatively slow convergence •Potential system-wide effects •BFD improves this, but not enough by itself Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 78 Enter MPLS •Low-overhead virtual circuits for IP! •Gives many Voice-friendly attributes to IP •DiffServ-compatible CoS •Deterministic path selection •Failure recovery via: •Fast reroute •Secondary LSPs •Planning and determinism through circuit-like traffic engineering Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 79 MPLS-TE network optimization •Traffic engineering allows deterministic paths for Voice and other realtime data, similar to circuit switched networks •Constraint-based routing can dynamically choose paths best suited to applications or types of traffic label-switched-path HK_to_Tokyo { to Tokyo; from Hong_Kong; admin-group {exclude red} cspf} Seoul Tokyo Hong Kong Taipei Kuala Lumpur Manilla Singpore Jakarta Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 80 MPLS CoS Capabilities •EXP field (and label) can be used for CoS Label (20-bits) L2 Header MPLS Header CoS S TTL IP Packet 32 bits •DiffServ-compatible •Consistent meanings can exist for MPLS EXP (and label) and IP DiffServ per-hop behaviors •Core (MPLS) and edge (IP/DiffServ) PHBs can be related and consistent Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 81 What is Diff-Serv TE ? Diff-Serv: scheduling/queueing behaviour at each node depends on traffic type (indicated by DSCP/EXP setting) MPLS TE: use of constraints to control placement of LSPs. Typically, various traffic classes share the same LSP. Bandwidth reservations do not take account of the classes of traffic involved. MPLS Diff-Serv TE: • Traffic divided into up to eight Class-Types. • CSPF and RSVP take the Class-Type into account when computing path of LSP. • Results in More granular bandwidth reservation. On each link in network, can have separate bandwidth constraints for each type of traffic • E.g. limit the bandwidth taken by voice LSPs on a link to a maximum of 40%, data LSPs take the rest. Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 82 CoS / QoS & Forwarding Diff-Serv-aware MPLS Traffic Engineering Guaranteed bandwidth for MPLS • Combines MPLS Diffserv and Diffserv TE • Provides strict point to point QoS guarantees Aggregated State (DS) Aggregate Admission Control (DS-TE) Aggregate Constraint-based Routing (DS-TE) No state Aggregated state Per-Flow state MPLS Diff-Serv + MPLS DS-TE Best effort Diff-Serv MPLS Guaranteed Bandwidth Copyright © 2003 Juniper Networks, Inc. RSVP v1 & Int-Serv Proprietary and Confidential www.juniper.net 83 How DS-TE Operates Extended IGP Routing Table Traffic Engineering Database (TED) Operations Performed by the Ingress LSR Constrained Shortest Path First User Constraints 1) Store information from IGP flooding 2) Store traffic engineering information Explicit Route 3) Examine user defined constraints 4) Calculate the physical path for the LSP 5) Represent path as an explicit route Copyright © 2003 Juniper Networks, Inc. RSVP Signaling Proprietary and Confidential www.juniper.net 84 MPLS failure recovery •Fast reroute allows rapid switching to alternate link segments while longer-term repairs are made •Secondary LSPs provide deterministic alternate paths during link failure •Possible in a consistent, network-wide manner Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 85 MPLS Fast Reroute Single user command at head end to enable Fast Reroute. Detour Detour Primary LSR1 Primary LSR2 Detour Primary LSR3 Primary LSR4 LSR5 • Fast reroute is signaled to each LSR in the path • Each LSR computes and sets up a detour path that avoids the next link and next LSR • Each LSR along the path uses the same route constraints used by head-end LSR Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 86 MSeconds MPLS Fast Reroute:Recovery Times 400 350 300 250 200 150 100 50 0 Max Average Min 5.0 5.1 5.2 5.3+ JUNOS version Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 87 Summary •VoIP deployments are going ahead •Good for provider profits •Good for customer services and needs •The question is no longer “if”, but rather “how” •Luckily: •There are tools that make voice backbones •Possible •High-quality •Profitable •Diff-serv, NSF, and MPLS are up to the job Copyright © 2003 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 88 Thank You