CS 447 Network & Data Communication QoS (Quality of Service) & DiffServ Introduction Department of Computer Science Southern Illinois University Edwardsville Fall, 2013 Dr. Hiroshi Fujinoki QOS_PART1/001

CS 447 Network & Data Communication QOS_PART1/002 What are QoS & DiffServ? QoS = Quality of Service Techniques and standards developed for controlling ways network traffic (= “packets”) is handled in a network. DiffServ = Differentiated Service A standard that implements QoS in the Internet

CS 447 Network & Data Communication QOS_PART1/003 Background Before the concept of QoS was introduced to the Internet, all what the Internet could provide was “best-effort service”. What is “best-effort service”? Sender Receiver The Internet  No guarantee for transmitted packets to reach the destination  No guarantee for available transmission bandwidth - They could be dropped at anytime anywhere - Tx bandwidth dynamically changes

CS 447 Network & Data Communication QOS_PART1/004 No guarantee for successful transmissions nor Tx bandwidth Time Tx-Rate (in bps) Time Tx-Rate (in bps) packet is lost No guaranteed Tx rate (observed at the receiver) No guarantee for successful Tx (observed at the receiver) Sharp drop in Tx rate Unpredictable Tx-rate

CS 447 Network & Data Communication QOS_PART1/005 Background Before the concept of QoS was introduced to the Internet, all what the Internet could provide was “best-effort service”. What is “best-effort service”? Sender Receiver The Internet  End-to-end delay dynamically fluctuates - This is a result of  in the previous slide

CS 447 Network & Data Communication QOS_PART1/006 Sender Receiver Dynamically fluctuating E2E delay R1R1 RNRN Physical Distance Sender transmits a packet Router Delay E2E Delay Router delay dynamically fluctuates The longer the physical distance, the longer E2E delay The larger the E2E hop-count, the longer E2E delay

CS 447 Network & Data Communication QOS_PART1/007 Background Before the concept of QoS was introduced to the Internet, all what the Internet could provide was “best-effort service”. What is “best-effort service”? Sender Receiver The Internet  Unpredictable (no control for) delay jitter - Delay jitter = variance in E2E delay for arriving packets

CS 447 Network & Data Communication QOS_PART1/008 Sender Receiver R1R1 RNRN Sender transmits a packet Router Delay E2E Delay    Time packet Unpredictable (no control for) delay jitter

CS 447 Network & Data Communication QOS_PART1/009 Background Before the concept of QoS was introduced to the Internet, all what the Internet could provide was “best-effort service”. What is “best-effort service”? Sender Receiver The Internet  Unpredictable (no control for) packet-loss rate - Packet-loss rate = (number of lost packets)/(number of packets sent) - Because router resources (memory buffers) are shared

CS 447 Network & Data Communication QOS_PART1/010 Sender Receiver R1R1 RNRN Unpredictable (no control for) packet-loss rate A large # of senders might be transmitting packets through a router (Router buffers’ are shared resource in the Internet) We can not predict which senders transmit how much and when (Senders do not reserve resources in advance in the Internet)

CS 447 Network & Data Communication QOS_PART1/011 QoS parameters and various network applications So far, we defined “best-effort service” as lack of controls for Tx-rate, E2E delay, delay jitter and packet-loss rate. Question Which network applications need a good control for which parameters? Applications Control required for HTTP (web) FTP (No MIME) Telnet VoIP

CS 447 Network & Data Communication QOS_PART1/012 QoS parameters and various network applications So far, we defined “best-effort service” as lack of controls for Tx-rate, E2E delay, delay jitter and packet-loss rate. Question Which network applications need a good control for which parameters? Applications Control required for Online chatting On-line game (Real-Time) Problem The best-effort Internet service can not handle for network applications with various QoS requirements

CS 447 Network & Data Communication QOS_PART1/013 Existing QoS controlling components  Admission Control  Traffic Classifier  Traffic Policing and Shaper  Packet Scheduler

CS 447 Network & Data Communication QOS_PART1/014  Admission Control Network Router Request for reserve resources Positive ACK Admitted “signaling” Reserve resources Reserve resources Reserve resources Reserve resources

CS 447 Network & Data Communication QOS_PART1/015  Admission Control Network Router Request for reserve resources Reserve resources I don’t have enough resource Rejected Reserve resources Negative ACK On rejection, the requesting host:  Give up now and try again later  Reduce the requested resources and try again

CS 447 Network & Data Communication QOS_PART1/016  Admission Control Admission control is a mechanism that prevents overloading a network Each host must reserve network resources before it starts transmission (This is exactly what “virtual-circuit” networks do) Router resources are reserved by signaling messages On success, a positive ACK from the destination On fail, a negative ACK from a rejecting router The Internet does not perform admission control (The Internet is a datagram packet-switching network)

CS 447 Network & Data Communication QOS_PART1/017  Traffic Classifier Sender Receiver R1R1 RNRN Receiving NIC Routing Classifier Policing Scheduler Transmitting NIC Decide which transmitting NIC each packet is directed Detect the type of packet so that a different policing and scheduling can be applied for each different type

CS 447 Network & Data Communication QOS_PART1/018 Classifier Traffic Type-A Traffic Type-B    Traffic Type-X Shaper Policing Shaper Policing    Shaper Policing Queues Routing  Traffic Classifier    The classifier “classifies” incoming packets to groups, each of which holds packets that have the same “requirements (demands)”

CS 447 Network & Data Communication QOS_PART1/019  -a Traffic Policing If some hosts (or a group of network applications) are transmitting more network traffic than they are supposed to, drop the traffic.  -b Traffic Shaping Reduce delay jitter Control on transmission rate (in bps) Reduce transmission burst

CS 447 Network & Data Communication QOS_PART1/020  -a Traffic Policing Traffic Load (in bps) Time Upper Threshold

CS 447 Network & Data Communication QOS_PART1/020  -a Traffic Policing Traffic Load (in bps) Time Upper Threshold

CS 447 Network & Data Communication QOS_PART1/021  -b Traffic Shaper    packet Traffic Load (in bps) Transmission Burst Transmission Burst Transmission Burst Time (i) Jitter Reduction (micro-shaping) (Zero jitter) (High jitter) (Low jitter) (ii) Flattening transmission burst (macro-shaping)

CS 447 Network & Data Communication QOS_PART1/022 = an implementation of traffic policing/shaping Token Bucket Leaky Bucket Bursty Traffic (Average Traffic Rate = R 1 bps) Drain (Output Rate = R 2 bps) Incoming Link Bucket Capacity = B bits Must be: R 2  R 1 (memory buffer in a router) (network traffic with a high jitter) (outgoing drain with a constant rate)

CS 447 Network & Data Communication QOS_PART1/023  Packet Scheduler Classifier Traffic Type-A Traffic Type-B    Traffic Type-X Shaper Policing Shaper Policing    Shaper Policing Queues Transmitting NIC Scheduler Decide from which queue packets will be forwarded to the transmitting NIC Routing

CS 447 Network & Data Communication QOS_PART1/000