McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Chapter 23 Congestion Control and Quality of Service

McGraw-Hill©The McGraw-Hill Companies, Inc., Data Traffic Traffic Descriptor Traffic Profiles

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 23.1 Traffic descriptors

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 23.2 Constant-bit-rate traffic

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 23.3 Variable-bit-rate traffic

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 23.4 Bursty traffic

McGraw-Hill©The McGraw-Hill Companies, Inc., Congestion Network Performance

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 23.5 Incoming packet

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 23.6 Packet delay and network load

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 23.7 Throughput versus network load

McGraw-Hill©The McGraw-Hill Companies, Inc., Congestion Control Open Loop Closed Loop

McGraw-Hill©The McGraw-Hill Companies, Inc., Two Examples Congestion Control in TCP Congestion Control in Frame Relay

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 TCP assumes that the cause of a lost segment is due to congestion in the network. Note:

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 If the cause of the lost segment is congestion, retransmission of the segment does not remove the cause—it aggravates it. Note:

McGraw-Hill©The McGraw-Hill Companies, Inc., Quality of Service Flow Characteristics Flow Classes

McGraw-Hill©The McGraw-Hill Companies, Inc., Techniques to Improve QoS Scheduling Traffic Shaping Resource Reservation Admission Control

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure Flow characteristics

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure FIFO queue

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure Priority queuing

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure Weighted fair queuing

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure Leaky bucket

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure Leaky bucket implementation

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 A leaky bucket algorithm shapes bursty traffic into fixed-rate traffic by averaging the data rate. It may drop the packets if the bucket is full. Note:

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure Token bucket

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 The token bucket allows bursty traffic at a regulated maximum rate. Note:

McGraw-Hill©The McGraw-Hill Companies, Inc., Integrated Services Signaling Flow Specification Admission Service Classes RSVP

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Integrated Services is a flow-based QoS model designed for IP. Note:

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure Path messages

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure Resv messages

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure Reservation merging

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Quality of service QoS = provide the service the application needs Requirements of common applications:

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 QOS: techniques No magic bullet: many techniques used Overprovisioning Provide more than enough Router capacity, buffer space,bandwidth Expensive Ex. Telephone system: dial tone nearly always there Buffering Traffic shaping: leaky/token bucket Resource reservation Admission control Proportional routing Packet scheduling

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 QOS: techniques Buffering Buffer flow before delivering to application Reduces jitter Increases delay

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 QOS: techniques Traffic shaping Smooth output traffic at server side Agreement between customer & carrier Traffic pattern = SLA or Service Level Agreement

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 QoS: techniques Traffic shaping Main cause of congestion: bursty traffic Open loop solution: force transmission at a predictable rate Agreement between client and carrier Client: my traffic look like … Carrier: accepts and reserves resources Carrier will monitor traffic generated by client Leaky bucket algorithm Token bucket algorithm

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 QoS: techniques - leaky bucket Approach: strict flow regulation Transmit 1 packet /time unit Finite queue

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Environment: o Communication line supports: 25 MB/sec o Limit set at: 2 MB/sec o Bucket capacity: 1 MB Example: Computer sends burst of 1 MB o Completely stored in bucket o Flow to network: 2 MB/sec for 500 msec

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Too rigid output pattern?

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 QoS: techniques - token bucket Approach: Bucket holds tokens Token generated at every clock tick Transmission of packet destroys token Bucket has limited capacity for tokens

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 QoS: techniques - token bucket Environment: o Communication line supports: 25 MB/sec o Limit set at: 2 MB/sec o Bucket capacity?  Initially full  Max:

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Why not? 250 KB / 25 MB/sec = 10 msec 250 KB 500 KB 750 KB

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 QoS: techniques - token bucket Parameters: o Communication line supports: M Bytes/sec o token arrival rate:  Bytes/sec o Bucket capacity: C Bytes? o Burst length: S sec

McGraw-Hill©The McGraw-Hill Companies, Inc., MB/sec 2 MB / sec 250 KB S = C / ( M -  ) C +   S = M  S 250 KB 500 KB 750 KB

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 QoS: techniques - token bucket Token bucket high peak = line transfer rate Combined approach: Token bucket followed by leaky bucket Peak is limited by leaky bucket

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Resource reservation Regulate the shape of load is useless if routers, lines are overloaded Scattering packets over various lines? Create route for a flow!! “connection oriented” Bandwidth Never oversubscribe an output line Buffer space Reserve some buffers per flow How to compute? CPU cycles: mean delay T = 1 / (  - ) QoS: techniques  = mean processing capacity = mean arrival rate in packets/sec

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 QoS: techniques Admission control Only accept flows that can be handled! Flow specification? How to transform into needed resources?

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 QoS: techniques Proportional routing Split a flow over multiple paths How? Which info is available?

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 QoS: techniques Packet scheduling In router for each output line: A queue for each router Round robin handling of queues Problem: favours large packets Simulated byte-by byte round-robin Find finishing time for each packet Sort packets using increasing finishing times Send packets in that order Problem: same priority for all hosts Weighted fair queueing Give some hosts more bytes per clock tick

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 QoS: Techniques

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Network Layer Design issues Routing Congestion Quality of service Internetworking Internet Protocols Requirements Techniques Integrated services Differentiated services Label switching & MPLS

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 QoS: Integrated Services Problem: Handle multicasts From multiple senders To multiple destinations Allow for dynamically changing groups Examples: Video conferencing Television RSVP: Resource reSerVation Protocol Multicast routing Spanning tree Group address example

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 QoS: Integrated Services

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 QoS: Integrated Services RSVP: Resource reSerVation Protocol Multicast routing Spanning tree Group address Example Receivers can send reservation messages up the tree to the sender To get better reception To eliminate congestion Example Sharing of channels possible

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 QoS: Integrated Services

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 QoS: Integrated Services Conclusion for flow-based algorithms: Good quality of service possible Downside Advanced setup needed State/flow in routers Complex algorithms in routers Complex router-to-router exchanges Few implementations Solution: class-based QoS Differentiated services

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Network Layer Design issues Routing Congestion Quality of service Internetworking Internet Protocols Requirements Techniques Integrated services Differentiated services Label switching & MPLS

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Differentiated Services Class-based Offered by a set of routers forming an administrative domain Administration defines Classes + forwarding rules Customers sign up (&pay) for a class IETF has standardised an architecture Network-independent service classes

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Differentiated Services 2 classes only: expedited regular

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Reserved bandwidth for expedited class: 10% packets 20% bandwidth Low delay Implementation: weighted fair queueing Expedited forwarding Most packets!

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Differentiated Services 4 priority classes Each having its own resources 3 discard probabilities: Low – Medium - High

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Assured forwarding Processing steps for a packet: Classify it Mark it (header field needed) Discard? Queue packet To be executed at host or ingress router Most packets!

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Network Layer Design issues Routing Congestion Quality of service Internetworking Internet Protocols Requirements Techniques Integrated services Differentiated services Label switching & MPLS

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Label switching & MPLS How to improve forwarding in a router? Based on address: slow lookup Based on label: used a index in a table Fast! Connections? Various names: Label switching Tag switching Standardization by IETF: MPLS MultiProtocol Label Switching

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Label switching & MPLS Extra layer between Datalink Network Belongs to … layer?

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Local significance only Fields in header Label QoS service classes S hierarchy of labels TTL

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Label switching & MPLS Data-driven First packet (without a flow) on router triggers construction of a FEC Router Requests next router to assign a label; this router recursively does the same Used on ATM networks Control-driven Booting router creates FECs for all the hosts for which it is the destination Forwards the labels to its neighbours Other variants exist Construction of forwarding tables  FEC forwarding equivalence class group of flows under a single label

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Network Layer Design issues Routing Congestion Quality of service Internetworking Internet Protocols

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure Reservation styles

McGraw-Hill©The McGraw-Hill Companies, Inc., Differentiated Services An Alternative to Integrated Services

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Differentiated Services is a class-based QoS model designed for IP. Note: