Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.



Published on

  • Be the first to comment

  • Be the first to like this


  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:
  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>