Voice Over IP Performance Assurance Transforming the WAN into a voice-friendly using Exinda WAN OP 2.0 Integrated Performance Assurance Platform Document version 2.0
Voice over IP Performance Assurance Transforming the WAN into a voice-friendly using Exinda Integrated Performance Assurance Platform Executive Summary Exinda offers a comprehensive offering on a single integrated platform which enables enterprises to easily and cost-effectively deploy VoIP to branch offices. Exinda 360 s performance assurance modules combine data reduction techniques with L7 signature based traffic shaping and Quality of Service, compression, and loss mitigation all tuned jointly to ensure VoIP is can be deployed and assured high quality performance across most WAN links. VoIP converts analogue voice signals into IP packets and distributes these packets across a WAN. Voice over Internet Protocol (VoIP) is a delay-sensitive application. For high quality voice, the network must be fine-tuned from end to end before implementing VoIP. Finetuning to support VoIP incorporates a series of protocols and features that improve quality of service (QoS). Furthermore, traffic shaping is required to ensure the reliability of VoIP. VoIP quality can be mainly affected by either end-to-end delay or jitter. One of the most crucial factors in implementing VoIP is minimizing one-way, end-to-end delay. VoIP traffic is real-time traffic; if delay is too high, speech becomes unrecognizable. Jitter is the variation delay between the times a voice packet is expected to be received and when it actually is received. Jitter causes discontinuity in the real-time voice stream. Excessive jitter can result from congestion on LANs, Access Links, and low bandwidth WAN links or from the transmission of large data packets on the same link. As a first step Exinda automatically detects all VoIP calls that are traversing the WAN using L7 signatures for the state full signalling protocols and intercepting the random UDP sessions classified all under a single application. Configuration efforts FREE which eliminates any prior knowledge of the customers VoIP system, network VLAN setup or protocol used. Voice calls traversing the WAN through Exinda will automatically by score using MOS which the industry standard for marking VoIP calls quality. The second step in Key Features & Benefits Real Time reporting and scoring of VoIP calls over the WAN using Industry standard MOS scheme. Layer 7 Signatures for all VoIP protocols - H323, SIP, IAX, H.248, RTCP, RTP, Megaco, Skype, Skype Video, Skype Voice, Facetime Latency aware L7 QoS and shaping for VoIP traffic IPv4 and IPv6 DSCP/TOS classification and packet marking Wan Memory & Compression Reducing non VoIP traffic load on the WAN to reduce congestion scenarios and enable higher concurrent VoIP calls at the same time. Physical or Software product delivery addressing installation challenges in rural areas and supporting Virtualised branches or datacentres. the Exinda solution is to apply SLA and Shaping policies around the areas in the network were VoIP delivery is reported as poor and its performance is lacking assurance.
Real-Time and Historical View of VoIP Calls VoIP is a UDP based real-time application which uses TCP based signalling protocols to establish and manage the calls. Anyone looking to deploy VoIP combined with WAN Optimisation networking solutions must consider the use of a specifically structured Wan Optimisation product to support UDP and in particular state full applications such as VoIP which utilises in most cases random UDP ports. Traditional approach of VoIP management requires prior knowledge of the VoIP setup in order to best match detection policies on routers and switches. Some deployments are using dedicated VLAN IDs to ease the detection of VoIP traffic an approach that is challenged when a need for Softphone software is required to be used on the same desktop or laptop which also is used for data applications. Exinda uses application signatures to detect VoIP calls by tracking both the signalling protocols and the VoIP data over the UDP phone calls sessions. Exinda provides an immediate automatic report which shows calls quality over time and real time. The report automatically includes any RTP based VoIP call, including SIP, H.323 and Cisco Skinny. In addition all the calls are being shown using 3 series, the number of "Good", "Tolerable" and "Bad" calls over time. The table below lists the worst quality inbound and outbound VoIP calls over the selected time period. Green (Good) Number of calls with a MoS greater than 4. Yellow (Tolerable) Number of calls with a MoS between 2 and 4. Red (Bad) Number of calls with a MoS less than 2.
VoIP Traffic Acceleration/Compression Exinda doesn t compress nor applies any TCP/UDP acceleration algorithms on the VoIP traffic. Unfortunately there are vendors in the networking and WAN OP market who claim to provide high compression ratios on VoIP traffic however in most networks byte-utilisation of VoIP traffic diminishes in comparison to the vast volume of other application TCP based traffic. Albeit substantial compression results could be realized, still there will be no substantial amount of bandwidth saved when looking at the total volume of all traffic in the network. In fact most of the vendors who claim to accelerate or compress VoIP lacks fundamental VoIP detection and classification which limits their ability to pick up all the different types of VoIP protocols and be able to granularly display it to the customer. Accelerated WAN Bandwidth compared to Adding Telco Bandwidth VoIP traffic takes small and foreseeable bandwidth from the WAN links compared to the TCP based applications. Increasing the WAN bandwidth needs to be considered should VoIP performance, quality and reliability creates an issue or concern. Traditional WAN upgrades are common an option to consider however in many cases the cost somewhat doesn t justify it as the amount of bandwidth required to support a given call is not that significant in the first place a few kbps per call. On the other hand when delivering VoIP over a network alongside applications it is clear that this traffic contains significant amounts of repetitive data information which in many cases is highly compressible. Exinda WAN Memory is a proven way to reduce the volume all those applications. As a result from applying Exinda s WAN Memory substantial amounts of bandwidth resources are becoming available for the VoIP calls. While Exinda is better choice in order to address on demand bandwidth for VoIP calls it is critical to understand that a given latency of a WAN is not changeable by a WAN OP solution therefore if WAN bandwidth is not a limitation to a successful VoIP roll out, link and WAN latency needs to be examined.
VoIP Assurance Using Traffic Shaping Traffic shaping (also known as packet shaping ) is the control of network traffic in order to optimize or improve application performance, reduce network latency, and increase usable bandwidth on a wide area network. Traffic shaping provides a means to control the volume of traffic being sent into a network (bandwidth throttling), and the maximum rate at which the traffic is sent (rate limiting). Traffic shaping or traffic management involves controlling the flow of traffic on the network so that the highest priority applications such as VoIP always have adequate bandwidth and no delay. Exinda uses variety of techniques to gain visibility and shape network traffic. Policies provide bandwidth guarantees to critical applications such as VoIP to ensure they receive the network resources they need in order to operate effectively. Policies also, limit and constrain recreational or non-business critical applications. This minimizes the negative impact non-sanctioned applications can have on the network and VoIP calls quality. In addition, traffic discard or blocking can allow the IT organization to completely block applications if required. This is very effective in reducing congestion and protecting an organization from the dangers of file sharing, P2P, and other rogue applications that may appear on a network. Policy based shaping helps prevent network congestion by ensuring network services align with the policies set by the network manager to meet user expectations. To deliver the VoIP performance guarantees in today s networks several different technologies must be employed together. When control is decentralized, computers and the applications they run will attempt to achieve the maximum available bandwidth. The result is many non-critical applications consume resources at the expense of VoIP. Exinda supports an automatic fully customised policy to assure the performance of VoIP by guaranteeing enough bandwidth and eliminating any delay and jitter with serving it high priority. When such policy shaping is employed organizations are able to improve the utilization of existing bandwidth. Controlling the non-critical applications and enforcing bandwidth guarantees that will increase application performance such as. Using Exinda s shaping policies VoIP can be deployed and delivered with a consistent high quality of calls.
VoIP Assurance Using TOS/DSCP on IPv4/IPv6 Networks The ToS (type of service) or DiffServ (differentiated services) field in the IPv4 header, and the Traffic Class field in the IPv6 header are used to classify IP packets so that routers can make QoS (quality of service) decisions about what path packets should traverse across the network. For example, users may want ensure that VoIP utilizes high quality, low latency (and expensive) links, or, they might want to ensure email or recreational traffic uses cheaper (but less reliable) links. Previously, there were 5 different categories that users could classify their traffic with using the IP ToS field (see RFC 791). Normal Service Minimize Cost Maximize Reliability Maximize Throughput Minimize Delay These have since been replaced by a new set of values called DSCP (DiffServ Code Points, see RFC 2474). A DSCP is a 6-bit number; therefore, there are 64 possible DSCP combinations, of which, only a portion have been standardized and are listed below. IPv6 contains an 8 bit Traffic Class field. The 6 most significant bits are treated the same as IPv4 DSCP. The least 2 significant bits are not modified by the appliance. How Exinda uses the ToS / DiffServ Field All Exinda products can read and write the ToS/DiffServ field, allowing users to: Match packets with a ToS/DSCP value and apply optimizer polices to this traffic. Mark the packets with a ToS/DSCP value based on source/destination host/subnet, source/destination port, layer 7 application, time of day, vlan id, etc. Matching Packets - when defining Optimizer Policies on the Exinda appliance, there is a ToS/DSCP drop down that allows users to match only those packets with the specified ToS/DSCP value. Users can select the appropriate DSCP/ToS value from this drop down field and any packets that match this ToS/DSCP value will be applied to this policy. Example: VoIP equipment in a user s network may be configured to mark all outgoing packets as DSCP EF (decimal 46). VoIP is a real-time application and the user wishes to prioritize this with a high priority policy that guarantees VoIP a certain amount of WAN bandwidth. To achieve this, the user selects DSCP 46 from the ToS/DSCP drop down and configures the appropriate bandwidth allocation in this policy.
Marking Packets - Users may want to mark certain packets with a ToS/DSCP value so that external routers can treat the traffic appropriately. The same policy configuration screen above (see Figure 1) allows users to configure such an action. When the policy action is set to Optimize, several options are available on the right-hand side, one of which is the ToS/DSCP Mark checkbox. Users will need to enable this feature by checking the box and selecting the appropriate ToS/DSCP mark from the drop down. Any traffic that matches the corresponding filter rules will then be marked with the specified value and should be treated appropriately by routing equipment down the line. Example: Service Providers may provide users with a table similar to the one below (example only). Each class has different guaranteed service and pricing levels. This information should be used in conjunction with optimizer policies to implement and ensure quality of service. See Table 1 to convert the DSCP Settings to a decimal value that can be used in the Optimizer Policies. North AmerRDP EMEA Asia Pacific +1 877 439 4632 +44 808 120 1996 +61 3 9415 8332 www.exinda.com 2009 Exinda Networks. All rights reserved. Exinda is a registered trademark of Exinda Networks PTY Ltd. Facebook is a registered trademark of Facebook Inc. All other product names, company names, trademarks, registered trademarks, logos and symbols are the property of their respective owners.