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AETA_2004_VOIP.ppt

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AETA_2004_VOIP.ppt

  1. 1. Voice and Video over IP (The No Spin Zone) Rick Bagwell AREN Network Engineer
  2. 2. Talking Points Memo <ul><li>VoIP --- does it really work, do I need it? </li></ul><ul><li>Distance Learning (education speak for Video Teleconferencing) How good is this video over IP thing? </li></ul><ul><li>Common beliefs (some facts and some Misconceptions) </li></ul>
  3. 3. VoIP (Voyeep) <ul><li>Voice over IP (Ethernet phones and IP transport) </li></ul><ul><li>Stable technology (yes it really works now) </li></ul><ul><li>Proper deployment requires: </li></ul><ul><ul><li>VLAN and QoS capable infrastructure </li></ul></ul><ul><ul><li>Powered Ethernet for cleanest installations </li></ul></ul><ul><ul><li>Comprehensive dial-plan and backup plan </li></ul></ul><ul><li>Robust deployment requires: </li></ul><ul><ul><li>Redundant LAN and WAN connections </li></ul></ul><ul><ul><li>SRST (or equivalent to handle outages) </li></ul></ul>
  4. 4. Cisco’s “five nines” Network Reference: http://www.cisco.com/en/US/customer/netsol/ns340/ns394/ns165/ns268/networking_solutions_white_paper09186a00800a113e.shtml
  5. 5. So I have to have GigE right? <ul><li>Nope…. You have to have QoS </li></ul><ul><li>Common misperception: Voice and Video require fiber optic infrastructure </li></ul><ul><li>What is required? --- Adequate bandwidth, low latency, low jitter, proper QoS, and appropriate queueing (sounds like engineering doesn’t it ;-) </li></ul>
  6. 6. Bandwidth, Latency, and Jitter <ul><li>Default Codec for VoIP is G.729 </li></ul><ul><ul><li>8kbps per voice call </li></ul></ul><ul><ul><li>1500kbps/8kbps = 192 calls per T1 line </li></ul></ul><ul><ul><ul><li>But you would NEVER try this! </li></ul></ul></ul><ul><li>Latency: how long it takes the packet to traverse the network. </li></ul><ul><ul><li>ITU Standard G.114 states that a one-way delay of 150ms is OK </li></ul></ul><ul><li>Jitter: The change in delay or latency of successive packets… </li></ul><ul><ul><li>40ms is a good rule of thumb for max jitter </li></ul></ul><ul><ul><li>This all depends on Jitter buffers and other stuff </li></ul></ul>
  7. 7. Queueing and QoS
  8. 8. What’s the Problem Here?
  9. 9. Queueing <ul><li>Without some sort of priority queuing, high bandwidth transmissions from the server to clients could easily fill egress queues in the switches </li></ul><ul><li>Weighted Fair Queueing helps alleviate this problem </li></ul><ul><li>Class Based Weighted Fair Queueing (CBWFQ) is better and allows more customization </li></ul>
  10. 10. So what does QoS do? <ul><li>Classify traffic (by TCP port, IP address, pre-defined tag etc.) </li></ul><ul><li>Police traffic, queue traffic, shape traffic </li></ul><ul><li>Tag traffic for specific treatment by peers </li></ul><ul><ul><li>Part of an end to end QoS design </li></ul></ul>
  11. 11. Types of QoS Tagging <ul><li>Layer2: CoS (Class of Service field) </li></ul><ul><ul><li>Defined in 802.1p (part of 802.1Q) </li></ul></ul><ul><ul><li>Ethernet frame is altered </li></ul></ul><ul><ul><li>3 bits = 8 levels </li></ul></ul><ul><li>Layer3: ToS (Type of Service) </li></ul><ul><ul><li>IP packet tagging </li></ul></ul><ul><ul><li>ToS field as 3bits for precedence = 8 levels </li></ul></ul><ul><li>Layer3: DiffServ (Differentiated Services) </li></ul><ul><ul><li>DSCP allows for 64 levels of prioritization </li></ul></ul>
  12. 12. Distance Learning <ul><li>The Wide-Area Challenge </li></ul><ul><ul><li>How do I provide good Quality Video Conferencing over my WAN? </li></ul></ul><ul><li>Many of the same issues that need to be addressed with VoIP also need to be addressed here </li></ul><ul><li>H.323 can provide good quality video if properly and methodically deployed </li></ul><ul><ul><li>H.264 codec makes it work even better  </li></ul></ul>
  13. 13. Common Problems with H.323 <ul><li>Many Education Networks have limited bandwidth connections with little funding for upgrades (Small Pipes) </li></ul><ul><li>Most school system networks are behind firewalls and NAT (Can be Tricky.. strange audio/video problems) </li></ul><ul><li>Duplex and Speed !!!! </li></ul>
  14. 14. The Small Pipe Issue <ul><li>In Alabama, many schools connect to their system’s network (and then the Internet) through point to point DS1 (T1s) – 1.5Mbps </li></ul><ul><li>A single H.323 VTC connection with decent quality uses 384kbps (+overhead) </li></ul><ul><li>Conservative Rule of Thumb recommended by Cisco is 20% overhead  ~460kbps </li></ul><ul><li>So… a single H.323 session at 384kbps uses almost 1/3 of a T1 line (for design purposes) </li></ul><ul><li>And the real problem…. Most large schools fill the pipe with just Internet traffic </li></ul>
  15. 15. Solution: Quality of Service (QoS) <ul><li>QoS enabled using DSCP tagging and CBWFQ on routers and layer3 switches </li></ul><ul><ul><li>Differentiated Services Code Point (DSCP) </li></ul></ul><ul><ul><li>Class-Based Weighted Fair Queueing (CBWFQ) </li></ul></ul><ul><li>Traffic is classified and tagged at routers based on source/destination IP address </li></ul><ul><li>Schools often don’t use VLANs and have switches (or hubs!) with no QoS support at layer2 </li></ul><ul><ul><li>So No CoS 802.1p can be used </li></ul></ul>
  16. 16. Problems With Firewalls (and NAT) <ul><li>H.323 uses multiple tcp connections and udp ports simultaneously for VTC </li></ul><ul><li>The H.323 standard assigns ports dynamically from 1024 to 65535 </li></ul><ul><li>During call setup, the IP address of the calling party is sent to the called party in the data field of the IP packet (so NAT can’t translate it) </li></ul>
  17. 17. Solutions to the Firewall Problem <ul><li>Don’t NAT H.323 clients </li></ul><ul><ul><li>Well…. what’s the firewall doing then? </li></ul></ul><ul><ul><li>May or may not open the H.323 client to all ports </li></ul></ul><ul><ul><ul><li>Probably not a good idea to open everything! </li></ul></ul></ul><ul><li>NAT H.323 and rely on the client to be “smart” enough to work through the firewall/NAT </li></ul><ul><ul><li>Polycom and Tandberg clients can be told to use specific ports. These clients can also be configured to know their real “outside address” and can use this address in handshaking </li></ul></ul><ul><li>NAT H.323 and rely on the firewall to be “smart” enough to work everything out </li></ul><ul><ul><li>Application Proxy, “Fixup protocol” - Must turn off encryption </li></ul></ul><ul><li>Use an additional device to perform the Application Proxy </li></ul><ul><ul><li>May be useful when deploying a standard solution across diverse networks </li></ul></ul>
  18. 18. Duplex and Speed Issues <ul><li>This is the single most common problem with VoIP and H.323 VTC implementations </li></ul><ul><li>Do NOT use AUTO setting </li></ul><ul><ul><li>It seems like it never really works </li></ul></ul><ul><li>Manually set Speed and Duplex between all switches and routers (switch to switch, or router to switch). </li></ul><ul><li>Manually set Speed and Duplex between VTC equipment or VoIP equipment and switches </li></ul><ul><li>Auto should only be used on switch interfaces connecting to PCs not used for Voice or Video </li></ul>
  19. 19. AREN Provides Support <ul><li>AREN Network is designed to support video through Quality of Service Guarantees (QoS). </li></ul><ul><ul><li>If both ends of the call are inside AREN, we can prioritize the call. </li></ul></ul><ul><ul><li>If the call is to an Internet2 member the quality will be good. </li></ul></ul><ul><ul><li>If the call goes through the Public Internet….. </li></ul></ul><ul><li>AREN staff is experienced in VTC troubleshooting (duplex, speed, firewalls, droped packets, etc..) </li></ul>
  20. 20. The Gold Standard Advantage <ul><li>Quality of Service </li></ul><ul><ul><li>ASA/AREN can prioritize traffic and guarantee quality video </li></ul></ul><ul><li>Technical Support </li></ul><ul><ul><li>Onsite and telephone support of schools’ video conferencing initiatives </li></ul></ul><ul><li>Contact Kim Carroll at kcarroll @ asc . edu to receive a quote for support services </li></ul><ul><li>Contact the AREN NOC (800-338-8320) to inquire about or activate QoS </li></ul>

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