The Integrated Services in the Internet: State of the Art

1. The Integrated Services in the Internet: State of the Art Paul P. White Jon Crowcroft Advanced Computer Networks

2. Motivation of the paper • To Study the Evolution of the Internet from a simple Data only Network into a true multiservice Network that supports multimedia applications and their protocols with appropriate performance and cost. Advanced Computer Networks

3. What is traditional services and what was the goal behind it ? • Point to point best effort service. • Goal – highly fault tolerant data network for the defense community. • So….. most of the attention was paid to dynamic route calculation, thus not too much attention was paid to performance of packet forwarding. • Assumptions…… not to share network with other users and let it become overloaded. • the amount of state shared between the network and end systems is minimized, just enough to calculate set to routes and determine best route. More importance given to dynamic and distributed route calculation. Advanced Computer Networks

4. What are typical old applications? • Telnet • FTP • http etc….. Advanced Computer Networks

5. What are new emerging applications ? • Real Audio • Real video • Net Meeting/ conferencing • White board etc…… Advanced Computer Networks

6. What do we need ? • A new service model • Applications that need higher assurance for bandwidth, packet loss and delay can ask for it. • Implies that we need networks to treat some packets differently from others. Advanced Computer Networks

7. What led the internet evolution and how ? • Traffic management for different applications. • Different users. Stages in internet evolution: • TOS (Type of Service) forwarding, obtained by spying at TCP port numbers. • TCP, enhances inherently unreliable IP, to provide ordered and reliable delivery, Advanced Computer Networks

8. cont.. • Mbone (multicast backbone), for group communication. Advantage – massive reduction in load. Advanced Computer Networks

9. How do we enhance internet to support various applications, users without overloading ? • Overengineering – always will be some applications that can exceed network capacity. • Resource Reservation – received most attention. • Usage based charging – very complex, hard to deploy and not global agreement on traffic. Advanced Computer Networks

10. What do these new applications require? Commitment to have • Real time delivery i.e. bounded jitter-no retransmission allowed. • Certain Bandwidth • Packet loss So, they are very sensitive to QOS their packet receives. • Also, these new applications are multipoint to multipoint. Advanced Computer Networks

11. How to fulfill these requirement ? • Not use the applications due to pricing and network congestion. • Use congestion avoidance RED, DEC bit … • Use congestion control and WFQ. None of above guarantee minimal packet forwarding rate, so…… dynamic specification of a source req. is preferable. Advanced Computer Networks

12. Two main classed of multimedia applications • Adaptive applications – guarantee for minimum capacity with reasonable probability. • Legacy constant rate applications – strong guarantee of service. Advanced Computer Networks

13. IETF (Internet Engineering Task Force) • Standardizing body. • Has Integrated Services Working group. http://www.ietf.org/html.charters/intserv-charter.html • Defined several services classes – provides certain QOS commitments • QOS is programmable on per flow basis by end applications. Advanced Computer Networks

14. How is it done ? • End applications makes requests. • Requests pass to routers by network management protocols or through Reservation Protocols (RSVP). • Requests dictate level of resources to e reserved and transmission scheduling behavior in the routers……. Thus providing end-to-end QOS. Advanced Computer Networks

15. Does having QOS between router provide end to end QOS ? • No…. Why ? • What about link layer technologies ? • Link layer to ensure that the link layer installs appropriate QOS support. • Defined by Integrated Services over Specific Link Layers Working Group of IETF(issll). http://www.ietf.org/html.charters/issll-charter.html Advanced Computer Networks

16. What is admission control and why is it required ? • Control mechanism. • Admission control looks at the Tspec and Rspec of the flow to determine if desired service can be provided to a flow given its currently available resources. • Not causing previously admitted flow to suffer. • If it can provide the service flow is admitted • Otherwise denied. Advanced Computer Networks

17. cont… • Also look at the maximum datagram size, it should not be greater than MTU maximum transmission unit of the link. • Assumption: Datagram receiving enhanced QOS are never fragmented. Advanced Computer Networks

18. What is Tspec ? • Traffic characteristics of the flow. Tspec parameters include: p peak rate of flow (bytes/sec) b bucket depth (bytes) r token bucket rate (bytes/sec) m minimum policed unit (bytes) M maximum datagram size (bytes) Advanced Computer Networks

19. What is Rspec ? • Reservation characteristics. R bandwidth, I.e. service rate (bytes/sec) S slack term (ms) Advanced Computer Networks

20. Classes of services: • Best effort Services And two Integrated Services: • Guaranteed service • Controlled load service • Predictive load service Advanced Computer Networks

21. What is controlled load service ? • Provides approximately the same QOS under heavy loads as under light loads. • Commits to offer a service equivalent to that seen by a best effort flow on a lightly loaded network. • Tspec is required without peak rate parameter. Advanced Computer Networks

22. How is it different from Best Effort Service ? • Does not noticeably deteriorate as the network load increases. • Best effort experiences worst services as the network load increases. • Best effort uses simple FIFO buffering schemes while it uses simple priority queuing Advanced Computer Networks

23. What are the applications that require controlled load services ? • Intended for class of applications that can tolerate certain amount of loss or delay. • Adaptive real-time applications • Existing Mbone applications over intranet • SNA or DEC local area terminal tunneling across a public internet service provider’s backbone network –both are delay sensitive. Advanced Computer Networks

24. What is guaranteed load service ? • Provides an assured level of bandwidth, a firm end-to-end delay bound. • No queuing loss for conforming packets of data flow. • Characterized by allocating a bandwidth R and buffer space B that flow consumes. Advanced Computer Networks

25. How to get end to end delay ? • In a perfect fluid model delay is bound by b/R provided R > r where R is bandwidth of wire between src – dst. b is depth of bucket. r is token bucket rate. Two errors arises due to finite packet sizes Any packet experiences an excess delay in the forwarding due to its size in the same queue Advanced Computer Networks

26. cont.. • Inaccuracies in the scheduling. So delay bound becomes b/R + C/R + D In guaranteed service limit on peak rate p results in reduction of the delay bound also due to packetization effect of the flow consider the maximum packet size M. Advanced Computer Networks

27. cont.. Qdelayend2end =(b-M) (p-R) + (M + Ctot) + Dtot R(p-r)R (case p> R > r) Qdelayend2end =(M + Ctot) + Dtot R (case R > P > r) Advanced Computer Networks

28. What is policy control ? Why ? • It is a function applied on a per-packet basis to make sure that a flow conforms to the Tspec that was used to make reservation. • Policy control should be done at network access point to traffic does not interfere with other flows. • Different from admission control ….. Advanced Computer Networks

29. cont.. • Non conforming flow should not be allowed to affect QOS if conforming flows. • Non conforming data should be treated as best effort traffic. • Routers should try to forward as many packets of nonconforming data as possible Advanced Computer Networks

30. Why need traffic reshaping ? Where ? • Requires the reshaping of traffic to the token bucket of the reserved Tspec. • Should be applied at places where it is possible for a data to exceed the reserved Tspec. Occurrences is possible in two cases: - branch pt in distribution tree where the reserved tspecs of the outgoing branches are not the same. Advanced Computer Networks

31. cont… - merge points in the distribution tree for sources sharing the same reservation. - reshaping incurs additional delay – slowing down early packets. Advanced Computer Networks

32. Killer Reservation problem • Occurs due to merging of heterogeneous reservation requests from receivers onto the tree from the same source. - large reservations made subsequent to an existing smaller reservation fails, and due to native implementation entire reservation fails - receivers continually making attempts to make large reservations, retrying quickly after failure block smaller reservation requests that might succeed. Advanced Computer Networks

33. What are the applications that require guaranteed service ? • Many military and commercial applications. • Real-time stock quotes. • Remote surgery using robotic arm. Any more applications ???? Advanced Computer Networks

34. Does all link layer technology support QOS ? • Token ring – yes (synchronous, asynchronous traffic) • LAN switches – yes (multiple queue based on 802.1p header) • Frame Relay - yes. • ATM – yes (CBR, VBR, ABR, GFR) • Ethernet – yes (802.1p header has 3 priority bits) Advanced Computer Networks

35. Why RSVP ? • Setup necessary router state to support the Integrated Services. • Why not ST-II or ST-II+ ? because RSVP has - receiver initiated reservation. - separating reservations from packet filtering - providing different reservation styles Advanced Computer Networks

36. cont… - maintaining soft state in the network. - protocol overhead control/ - modularity. Advanced Computer Networks

37. Why receiver oriented ? • To efficiently handle heterogeneous receivers. • Allow dynamic group membership. • Easier to commercial deployment - since receiver would pay for requested services.’ • similar to Deering’s Multicast routing approach. Advanced Computer Networks

38. Why use softstate ? • Tolerant to frequent routing changes. • Adds robustness • QOS routing can be deployed separately • gives straight forward way to increase or decrease the level of resource allocation. Advanced Computer Networks

39. RSVP is – is not Is • Signaling protocol • Is simplex – makes reservation for unidirectional flow only • Receiver –oriented approach • Maintains soft –state. • Traffic control and policy control parameters are opaque to it. • Is dependent on present routing protocols • Provides transparent operation through routers that do not support it. Advanced Computer Networks

40. cont…. Is not • A routing protocol. • Not duplex. • Not a sender oriented approach. • Does not use hard-state. Advanced Computer Networks

41. How RSVP works ? • Senders originate PATH message to install routing state in each router in the path • provide information to receiver of Sender’s traffic • Receivers send RESV messages towards senders to request reservation in intermediate routers • IP datagram protocol number is 46. Advanced Computer Networks

42. What are Directions of RSVP messages ? Resv ResvTear PathErr RCV1 S1 R1 R2 R3 RCV2 Path PathTear ResvErr ResvConf R4 RCV3 Rn router Advanced Computer Networks

43. What is filterspec and flowspec? • Associated with reservations at the routers • describes the packet to which reservation applies • obtained from merging process applied to selected Resv messages • style is (filterspec{flowspec}) used to summarize the request made by the Resv message. Advanced Computer Networks

44. What are different merging and reservation styles ? • Fixed Filter (Distinctive Reservation and Explicit sender selection) - filterspec consists of single sender only - effective flowspec of the reservation installed is the maximum of all FF reservation requests received for that particular sender. Advanced Computer Networks

45. cont... • Wildcard Filter (shared Reservation and Explicit Sender Selection) - filterspec is a wildcard and matches on any sender from upstream - effective flowspec installed is the maximum of all reservation requests received. Advanced Computer Networks

46. cont... • Shared Explicit (Shared reservation and explicit sender selection) - filterspec contains a specific set of senders from upstream and is obtained by taking the union of individual filterspecs. - effective flowspec installed is the maximum form all SE reservation requests received Advanced Computer Networks

47. Outgoing requests after merging Reserve S1{4B} S2{3B} S4{5B} S2{6B} S4{4B} S6{2B} S2{3B} S3{2B} S5{4B} incoming reservation requests FF(S1{2B}, S2{3B}, S4{5B}) FF(S1{4B}, S2{2B}) FF(S1{4B},S2{6B}) I Towards S1, S2 FF(S4{4B}) FF(S2{6B}, S4{2B}, S6{2B}) FF(S3{2B},S4{5B}) I Towards S3, S4 FF(S5{4B},S6{6B}) FF(S2{3B}, S3{2B}, S5{4B}) I Towards S5, S6 FF Reservation example Outgoing requests after merging incoming reservation requests Reserve (* {5B}) (* {3B}) (* {4B}) WF(* {5B}) WF(* {2B}) WF(* {5b}) I I Towards S1, S2 WF(* {3B}) WF(* {2B}) WF(* {5b}) I I Towards S3, S4 WF(* {5b}) WF(* {4B}) I I Towards S5, S6 WF Reservation example Advanced Computer Networks

48. Outgoing requests after merging incoming reservation requests Reserve (S1, S2, S4){5B} (S4, S6){3B} (S2, S3, S5){4B} SE((S2, S4){5B}) SE((S1, S2){2B}) SE((S1,S2){5B}) I I Towards S1, S2 SE((S4{3B}) SE((S4, S6{2B}) SE((S3, S4){5B}) I I Towards S3, S4 SE((S5, S6{5B}) SE((S2, S3, S5){4B}) I I Towards S5, S6 SE Reservation example Advanced Computer Networks

49. What information is in PATH messages ? • phop - the address of the last RSVP capable node, updated at every RSVP capable router. • Sender template - the filter specification identifying sender, IP addr, sender port • sender Tspec - sender traffic characteristics • adspec - OPWA information, updated at every RSVP capable router. Advanced Computer Networks

50. How PATH messages are processed and propagated ? • Update/Create its PATH state entry. • Setup cleanup timer equal to timeout interval and restart timer. • Router generates the PATH messages based on its PATH state and forwarding down the tree. • PATH messages forwarded on any change in PATH state or on change of outgoing interfaces in the data forwarding path. Advanced Computer Networks