The possibilities of congestion control mechanisms in FAN networks Dominik Najder Jakub Palider

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks Presentation plan 1. Current network quality requirements 2. What is congestion? 3. What are the current QoS solutions? 4. Int- and DiffServ 5. Features of FAN 6. FAN – pros and cons… 7. How does congestion control is implemented in DiffServ? 8. Traffic conditioning mechanisms 9. Scheduling mechanisms 10. Is it possible to implement DiffServ congestion solutions into FAN? 11. What DiffServ congestion control ideas may be used in FAN? 12. Measurement Based Admission Control (MBAC) 13. Cross-protect in FAN router 14. Priority Fair Queuing 15. Priority Deficit Round Robin 16. PFQ vs PDRR 17. Future

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks Current network quality requirements Nowadays networks are expected to support a variety of services beyond the best-effort service available today New applications already rely on the network ability to guarantee such services

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks What is congestion? Simple definition: congestion occurs when traffic coming into one link exceeds its capacity e.g. motorway Main reason: lack of bandwidth Demand bigger than capacity Suddenly changing demands Network failures Changes in routing

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks What are the current QoS solutions? Already Implemented: Integrated Services – IntServ, the first model defining whole concept of QoS Differentiated Services – DiffServ – later conception, opposite (in majority) to IntServ New Idea: Flow Aware Networking

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks Int- and DiffServ

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks Main differences between IntServ and DiffServ Bilateral agreementsMultilateral agreementsInter domain deployment Scalable and robustInformation held in each network node – not scalable Scalability Cannot provide low delay and high bandwith guarantee simultaneously Per flow - bandwidth and delay guarantee Quality guarantees Similar to IP networksSimilar to network switching (e.g. phone calls) Network management Based on class usageBased on flow characteristics and QoS requirement Network accounting Limited by number of classes of service Limited by number of flowsClassification of traffic Per hopEnd to endCoordination for service differentation DiffServIntServParameter

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks Features of FAN No reservation Classification based on flows 2 flow classes - stream (audio, video, real-time) and elastic (digital documents) Idea of cross-protect router – accurate relation between admission control and scheduling “Good enough” performance Cost effectiveness and accountability $$$

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks FAN – pros and cons… AdvantagesDisadvantages Good scalability Ease of admission control in each network node (MBAC) Only small amounts of data stored in network node memory No strict guarantees of network performance Not yet implemented

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks How does congestion control is implemented in DiffServ? Network traffic entering a DiffServ domain is subjected to classification and conditioning AC realized only in edge routers, controlled by Bandwidth Broker PHB define packet forwarding properties inside domain

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks Traffic conditioning mechanisms Traffic conditioning is performed only in edge routers – the assumption is that inside DiffServ domain the bandwidth is even overestimated

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks Scheduling mechanisms Assures differential quality in routing packets assigned to different flows Different packet typesDifferent quality of service Many algorithms (FCFS, PS, FQ etc.)

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks Is it possible to implement DiffServ congestion solutions into FAN? Differences in congestion control ideas: DiffServFAN AC, classifier, traffic conditioner, scheduler blocks Only AC and scheduler blocks – cross protect router Admission control performed only in edge routers Admission control performed in every router No information about flows inside router memory – QoS based on information about agregates Router holds only flow list, without declaration info for traffic class Domain agent Bandwidth BrokerNo central agents No info about network state hold in routers Information based on measurements held in every router

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks What DiffServ congestion control ideas may be used in FAN? The only common mechanisms are admission control and scheduling, but the admission control is realized in different way Scheduling algorithms may be implemented in FAN There are many elementary conceptions common to both architectures – but these are mostly basics of QoS idea

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks Measurement Based Admission Control (MBAC)

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks Cross-protect in FAN router Incoming packets Outgoing packets

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks Priority Fair Queuing Modified version of Start-time Fair Queuing Push-In First-Out queue, each element has timestamp Active Flow list Virtual Time counter

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks SFQ algorithm Packet arrival: 1. on arrival of l-byte packet p of flow f: 2. if f is a registered in ActiveList do 3. p.TimeStamp = f.FinishTag 4. f.FinishTag += l 5. else 6. add f to ActiveList 7. p.TimeStamp = VirtualTime 8. f.FinishTag = VirtualTime + l Packet departure: 1. transmit packets in increasing TimeStamp order 2. at the start of transmission of packet p: 3. VirtualTime = p.TimeStamp 4. for all flows f registered in ActiveList 5. if (f.FinishTag < VirtualTime) 6. remove f 7. if no packets in scheduler VirtualTime = 0

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks PFQ algorithm Packet arrival: 1. if PIFO congested, reject packet p at head of longest backlog 2. if f is registered in flow list F 3. if bytes >= MTU 4. p.TimeStamp = f.FinishTag 5. else begin 6. p.TimeStamp = virtual time 7. put behind P, update P 8. f.FinishTag += l 9. else 10. p.TimeStamp = VirtualTime 11. put behind P, update P 12. if flow list is not saturated 13. add flow 14. f.FinishTag = virtual time + l Main disadvantage: SCALABILTY Per packet computational complexity is O (logQ), where: Q – number of flows server by the router Q – number of flows server by the router

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks Priority Deficit Round Robin Based on standard DRR Per flow f state: f.Identier - the flow identifier (possibly a hash of the relevant header fields) f.Queue - current length in bytes of flow f queue f.Quantum - value of flow f quantum ( >= MTU bytes) f.Deficit - current flow deficit f.FIFO - addresses of head and tail packets of a linked list forming the flow f FIFO f.Next - the next flow in the DRR schedule following flow f

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks Priority Deficit Round Robin simplified algorithm Packet enqueue: If no free buffers left then dropPacket(); i = ExtractFlow(p); If (i is not registered in AFL) InsertActiveList(i); i.DC = 0; i.ByteCount = size(p); Enqueue(PQ, p) Else i.ByteCount += size(p); If (i.ByteCount <= i.Q) then Enqueue(PQ, p); Else Enqueue(i.Queue, p); Packet dequeue: 1. While (PQ not empty) do 2. p = Dequeue(PQ); i = ExtractFlow(p); 3. Send(p); i.DC -= Size(p); 4. If (AFL is not empty) then 5. Get head of AFL - flow i; 6. i.DC += i.Q; 7. While ((i.DC >= 0) and (Queue i not empty)) do 8. PacketSize = Size (Head(i.Queue)); 9. If (PacketSize <= i.DC) then 10. Send(Dequeue(i.Queue)); 11. i.DC -= PacketSize; 12. Else 13. break; 14. RemoveActiveList(i); 15. If (Queue i is not empty) then 16. InsertActiveList(i);

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks PFQ vs PDRR Which solution is better?PFQ: -simple -but higher computational complexity O(logQ) – not well scalablePDRR: -more complex, bigger amount of data to be held inside router -computation complexity O(1) – very scalable, main FAN feature over DiffServ

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks What is the future? Redesign of IPv6 packet Minimized header overhead and reduced header process for the majority of packets Less essential fields removed or moved to extension headers Traffic class in IPv6= TOS in IPv4 New Flow Label

Optical IP Networks D. Najder & J. Palider The possibilities of congestion control mechanisms in FAN networks Which QoS solution is better? FAN takes the best of DiffServ and IntServ It’s idea is closer to current traffic characteristics FAN is more scalable and flexible FAN is not yet implemented – improvements are still possible However FAN is not yet implemented – and may never be…