EE 122 Lecture 18 Differentiated Services Ion Stoica Nov 8 2001 What is the Problem Goal provide support for wide variety of applications Interactive TV IP telephony on line gamming distributed simulations Virtual Private Networks VPNs etc Problem Best effort cannot do it see previous lecture Intserv can support all these applications but Too complex Not scalable istoica cs berkeley edu 2 Differentiated Services Diffserv Build around the concept of domain Domain a contiguous region of network under the same administrative ownership Differentiate between edge and core routers Edge routers Perform per aggregate shaping or policing Mark packets with a small number of bits each bit encoding represents a class subclass Core routers Process packets based on packet marking Far more scalable than Intserv but provides weaker services istoica cs berkeley edu 3 Diffserv Architecture Ingress routers Police shape traffic Set Differentiated Service Code Point DSCP in Diffserv DS field Core routers Implement Per Hop Behavior PHB for each DSCP Process packets based on DSCP DS 2 DS 1 Ingress Egress Egress Edge router Ingress Egress Egress Core router istoica cs berkeley edu 4 Differentiated Service DS Field 0 5 6 7 DS Filed 0 4 8 Version HLen TOS Identification TTL 16 19 31 Length Flags Fragment offset Protocol Header checksum Source address Destination address IP header Data DS filed reuse the first 6 bits from the former Type of Service TOS byte The other two bits are proposed to be used by ECN istoica cs berkeley edu 5 Administrative Stuff Review session for 2nd Project Friday November 9 6pm Soda Hall 306 4th homework available on line today due November 27 istoica cs berkeley edu 6 Differentiated Services Two types of service Assured service Premium service Plus best effort service istoica cs berkeley edu 7 Assured Service Defined in terms of user profile how much assured traffic is a user allowed to inject into the network Network provides a lower loss rate than best effort In case of congestion best effort packets are dropped first User sends no more assured traffic than its profile If it sends more the excess traffic is converted to besteffort istoica cs berkeley edu 8 Assured Service Large spatial granularity service Theoretically user profile is defined irrespective of destination All other services we learnt are end to end i e we know destination s apriori This makes service very useful but hard to provision why Traffic profile Ingress istoica cs berkeley edu 9 Premium Service Provides the abstraction of a virtual pipe between an ingress and an egress router Network guarantees that premium packets are not dropped and they experience low delay User does not send more than the size of the pipe If it sends more excess traffic is delayed and dropped when buffer overflows istoica cs berkeley edu 10 Edge Router Ingress Class 1 Traffic conditioner Marked traffic Traffic conditioner Data traffic Per aggregate Classification e g user Class 2 Classifier Best effort istoica cs berkeley edu Scheduler 11 Assumptions Assume two bits P bit denotes premium traffic A bit denotes assured traffic Traffic conditioner TC implement Metering Marking Shaping istoica cs berkeley edu 12 TC Performing Metering Marking Used to implement Assured Service In profile traffic is marked A bit is set in every packet Out of profile excess traffic is unmarked A bit is cleared if it was previously set in every packet this traffic treated as best effort r tokens b tps assured traffic Metering User profile token bucket Set A bit in profile traffic Clear A bit out of profile traffic istoica cs berkeley edu 13 TC Performing Metering Marking Shaping Used to implement Premium Service In profile traffic marked Set P bit in each packet Out of profile traffic is delayed and when buffer overflows it is dropped r bps User profile b bits token bucket premium traffic out of profile traffic delayed and dropped Metering Shaper Set P bit in profile traffic istoica cs berkeley edu 14 Scheduler Employed by both edge and core routers For premium service use strict priority or weighted fair queuing WFQ For assured service use RIO RED with In and Out Always drop OUT packets first For OUT measure entire queue For IN measure only in profile queue Dropping probability 1 OUT IN Average queue length istoica cs berkeley edu 15 Scheduler Example Premium traffic sent at high priority Assured and best effort traffic pass through RIO and then sent at low priority P bit set no yes high priority yes A bit set no RIO istoica cs berkeley edu low priority 16 Control Path Each domain is assigned a Bandwidth Broker BB Usually used to perform ingress egress bandwidth allocation BB is responsible to perform admission control in the entire domain BB not easy to implement Require complete knowledge about domain Single point of failure may be performance bottleneck Designing BB still a research problem istoica cs berkeley edu 17 Example Achieve end to end bandwidth guarantee 3 2 BB BB 1 9 8 profile 7 BB BB 6 profile 5 BB BB 4 profile receiver sender istoica cs berkeley edu 18 Comparison to Best Effort and Intserv Best Effort Diffserv Service Connectivity No isolation No guarantees Per aggregate isolation Per flow isolation Per aggregate guarantee Per flow guarantee Service scope End to end Domain End to end Complexity No setup Long term setup Per flow steup Scalability Highly scalable nodes maintain only routing state Scalable Not scalable each router maintains per edge routers maintains per aggregate state core flow state routers per class state istoica cs berkeley edu Intserv 19 Summary Diffserv more scalable than Intserv Edge routers maintain per aggregate state Core routers maintain state only for a few traffic classes But provides weaker services than Intserv e g Per aggregate bandwidth guarantees premium service vs per flow bandwidth and delay guarantees istoica cs berkeley edu 20
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