Quality of ServiceENEE 426 | Communication Networks | Spring 2008 Lecture 22Motivation• Quality of Service (QoS)• Provide circuit-switched features in a packet-switched network• Guarantees on rate, latency, and jitter• Two approaches– Differentiated Services– Integrated ServicesENEE 426 | Communication Networks | Spring 2008 Lecture 22Differentiated Services (DiffServ)• IP provides “best effort” service– All packets treated equally– Anyone’s packets can be dropped when network is congested• DiffServ– Class-based QoS– Coarse-grained– Each packet assigned a service class• Prioritizes packets• Higher priority ones sent first• Lower priority ones sent last or dropped• Priority FIFO queuesENEE 426 | Communication Networks | Spring 2008 Lecture 22DiffServ Implementation• Differentiation based on Flow• Assigned traffic class• 8-bit DS field in IP header (TOS field)– 6-bit DiffServe Code Point (DSCP)– Theoretically 26= 64 different traffic classes– Default per-hop behavior (PHB) = 000000– Expedite Forwarding PHB (highest priority)– Assured Forwarding PHBClass 1Class 2Class 3Class 4Low DropAF11AF21AF31AF41Med DropAF12AF22AF32AF42High DropAF13AF23AF33AF43ENEE 426 | Communication Networks | Spring 2008 Lecture 22DiffServ RouterENEE 426 | Communication Networks | Spring 2008 Lecture 22DiffServ Pros/Cons• Prioritization is flexible, each administrative domain can reclassify or ignore• No advanced setup or registration required• Different routers can treat DSCP very differently• May waste resources getting packets through with highest priority only to have the dropped later on by a non DiffServ routerENEE 426 | Communication Networks | Spring 2008 Lecture 22Integrated Services (IntServ)• Fine-grained QoS• Requires additional protocols• Token Bucket Flow ControlENEE 426 | Communication Networks | Spring 2008 Lecture 22Token Bucket• Token bucket is like cell-phone roll over minutes• If you get 500 min/month, normally if you don’t use them they get thrown out– This caps you to 500 min/month• With roll over minutes, let’s say you can roll-over up to 1000 minutes– If you don’t use all your minutes one month, you can save them for next month – perhaps you have a “burst” of calls the next month– You can only save up to 1000 minutes (size of your bucket)– This means that in the long term your average phone use will be 500 min/month, but some months may be larger, others smaller, but the long-term average will be under 500 min/monthENEE 426 | Communication Networks | Spring 2008 Lecture 22Resource reSerVation Protocol (RSVP)• Provides admission control– Applications ask for guaranteed simplex service• Hosts or Routers can make requests– Routers decide whether the request can be accommodated• Each flow receives a service class and a label• Intermediate routers enforce reserved bandwidthENEE 426 | Communication Networks | Spring 2008 Lecture 22IntServ Pros/Cons• Fine-grained control• Enforce complex QoS• Requires state on routers, preconfiguration, complex