Re -Thinking Internet Architecture

1. Re-Thinking Internet Architecture • Today’s Internet • Original Design Goal, Philosophy and Principles • End-to-End Principle and “Hourglass” Architecture of Internet • Pros and Cons; Challenging Issues • What have changed? What may have yet to come? • Overlay Networks • Future Internet Architectures? • What are key challenges/issues? • E.g., mobility, security, “services-oriented” … • Diversity of “end systems”: laptops, cell phones, sensors, …

2. Network Architecture What is (Network) Architecture? • not the implementation itself • “design blueprint” on how to “organize” implementations • what interfaces are supported • where functionality is implemented • Two Basic Architectural Principles • Modularity (e.g., layering) • how to break network functionality into modules • End-to-End Argument • where to implement functionality

3. Architectural Principles (not unique to networks!) Zhi-Li’s version (synthesized from various sources) • End-to-end argument • functionality placement • Modularity • Increase inter-operability and manage complexity • vertical partition -> layered architecture • horizontal partition? • Keep it simple, stupid (KISS principle) • Occam’s Razor: choose simplest among many solutions! • complicated design increases system coupling (inter-dependence), amplifies errors, .. • don’t over-optimize! • Separating policies from mechanisms • decouple control from data • “semantics-free” • Design for scale • hierarchy, aggregation, …

4. Some Design/Implementation Principles • virtualization • indirection • soft state vs. hard state • fate sharing • randomization • expose faults, don’t suppress/ignore • caching • ……

5. Original Internet Design Goals[Clark’88] In order of importance: • Connect existing networks • initially ARPANET and ARPA packet radio network • Survivability • ensure communication service even with network and router failures • Support multiple types of services • Must accommodate a variety of networks • Allow distributed management • Allow host attachment with a low level of effort • Be cost effective • Allow resource accountability

6. Priorities • The effects of the order of items in that list are still felt today • E.g., resource accounting is a hard, current research topic • Different ordering of priorities would make a different architecture! • How well has today’s Internet satisfied these goals? • Let’s look at them in detail

7. Summary: Internet Architecture • Packet-switched datagram network • IP is the “compatibility layer” • Hourglass architecture • All hosts and routers run IP • Stateless architecture • No per flow state inside network TCP UDP IP Satellite Ethernet ATM

8. Summary: Minimalist Approach • Dumb network • IP provide minimal functionalities to support connectivity • Addressing, forwarding, routing • Smart end system • Transport layer or application performs more sophisticated functionalities • Flow control, error control, congestion control • Advantages • Accommodate heterogeneous technologies (Ethernet, modem, satellite, wireless) • Support diverse applications (telnet, ftp, Web, X windows) • Decentralized network administration • Beginning to show age • Unclear what the solution will be  probably IPv6?

9. Questions • What priority order would a commercial design have? • What would a commercially invented Internet look like? • What goals are missing from this list? • Which goals led to the success of the Internet?

10. Requirements for Today’s Internet Some key requirements (“-ities”) • Availability and reliability • “Always on”, fault-tolerant, fast recovery from failures, … • Quality-of-service (QoS) for applications • fast response time, adequate quality for VoIP, IPTV, etc. • Scalability • millions or more of users, devices, … • Mobility • untethered access, mobile users, devices, … • Security (and Privacy?) • protect against malicious attacks, accountability of user actions? • Manageability • configure, operate and manage networks • trouble-shooting network problems • Flexibility, Extensibility, Evolvability, ……? • ease of new service creation and deployment? • evolvable to meet future needs?

11. End System Based Overlay/P2P Services/Solutions • General Concept of Overlays • Some Examples • End-System Multicast • Rationale • How to construct “self-organizing” overlay • Performance in support conferencing applications • Internet Indirection Infrastructure (i3) • Motivation and Basic ideas • Implementation Overview • Applications

12. Overlay Networks

13. Focus at the application level Overlay Networks

14. Overlay Networks • A logical network built on top of a physical network • Overlay links are tunnels through the underlying network • Many logical networks may coexist at once • Over the same underlying network • And providing its own particular service • Nodes are often end hosts • Acting as intermediate nodes that forward traffic • Providing a service, such as access to files • Who controls the nodes providing service? • The party providing the service (e.g., Akamai) • Distributed collection of end users (e.g., peer-to-peer)

15. Routing Overlays • Alternative routing strategies • No application-level processing at the overlay nodes • Packet-delivery service with new routing strategies • Incremental enhancements to IP • IPv6 • Multicast • Mobility • Security • Revisiting where a function belongs • End-system multicast: multicast distribution by end hosts • Customized path selection • Resilient Overlay Networks: robust packet delivery

16. A B E F A B E F IP Tunneling • IP tunnel is a virtual point-to-point link • Illusion of a direct link between two separated nodes • Encapsulation of the packet inside an IP datagram • Node B sends a packet to node E • … containing another packet as the payload tunnel Logical view: Physical view:

17. Flow: X Src: A Dest: F data Flow: X Src: A Dest: F data Flow: X Src: A Dest: F data Flow: X Src: A Dest: F data C E B A D F F E B A tunnel Logical view: IPv6 IPv6 IPv6 IPv6 Physical view: IPv6 IPv6 IPv6 IPv6 IPv4 IPv4 Src:B Dest: E Src:B Dest: E A-to-B: IPv6 E-to-F: IPv6 B-to-C: IPv6 inside IPv4 B-to-C: IPv6 inside IPv4 6Bone: Deploying IPv6 over IP4

18. unicast multicast MBone: IP Multicast • Multicast • Delivering the same data to many receivers • Avoiding sending the same data many times • IP multicast • Special addressing, forwarding, and routing schemes • Not widely deployed, so MBone tunneled between nodes

19. End-System Multicast • IP multicast still is not widely deployed • Technical and business challenges • Should multicast be a network-layer service? • Multicast tree of end hosts • Allow end hosts to form their own multicast tree • Hosts receiving the data help forward to others

20. Premise: by building application overlay network, can increase performance and reliability of routing Princeton Yale application-layer router Berkeley RON: Resilient Overlay Networks Two-hop (application-level) Berkeley-to-Princeton route

21. RON Can Outperform IP Routing • IP routing does not adapt to congestion • But RON can reroute when the direct path is congested • IP routing is sometimes slow to converge • But RON can quickly direct traffic through intermediary • IP routing depends on AS routing policies • But RON may pick paths that circumvent policies • Then again, RON has its own overheads • Packets go in and out at intermediate nodes • Performance degradation, load on hosts, and financial cost • Probing overhead to monitor the virtual links • Limits RON to deployments with a small number of nodes

22. Secure Communication Over Insecure Links • Encrypt packets at entry and decrypt at exit • Eavesdropper cannot snoop the data • … or determine the real source and destination

23. www.cnn.com gateway Communicating With Mobile Users • A mobile user changes locations frequently • So, the IP address of the machine changes often • The user wants applications to continue running • So, the change in IP address needs to be hidden • Solution: fixed gateway forwards packets • Gateway has a fixed IP address • … and keeps track of the mobile’s address changes

24. Stanford Gatech CMU Berkeley End Systems Routers Unicast Emulation of Multicast

25. Routers with multicast support IP Multicast Gatech Stanford CMU Berkeley • No duplicate packets • Highly efficient bandwidth usage • Key Architectural Decision: Add support for multicast in IP layer

26. Key Concerns with IP Multicast • Scalability with number of groups • Routers maintain per-group state • Analogous to per-flow state for QoS guarantees • Aggregation of multicast addresses is complicated • Supporting higher level functionality is difficult • IP Multicast: best-effort multi-point delivery service • End systems responsible for handling higher level functionality • Reliability and congestion control for IP Multicast complicated • Deployment is difficult and slow • ISP’s reluctant to turn on IP Multicast

27. Berkeley Berk2 Overlay Tree Stan1 Gatech Stan2 CMU Berk1 Berk2 End System Multicast CMU Stan1 Gatech Stanford Stan2 Berk1

28. Potential Benefits • Scalability • Routers do not maintain per-group state • End systems do, but they participate in very few groups • Easier to deploy • Potentially simplifies support for higher level functionality • Leverage computation and storage of end systems • For example, for buffering packets, transcoding, ACK aggregation • Leverage solutions for unicast congestion control and reliability

29. Design Questions • Is End System Multicast Feasible? • Target applications with small and sparse groups • How to Build Efficient Application-Layer Multicast “Tree” or Overlay Network? • Narada: A distributed protocol for constructing efficient overlay trees among end systems • Simulation and Internet evaluation results to demonstrate that Narada can achieve good performance

30. Delay from CMU to Berk1 increases Stan1 Gatech Stan2 CMU Berk2 Berk1 Duplicate Packets: Bandwidth Wastage Gatech Stan1 Stan2 CMU Berk1 Berk2 Performance Concerns

31. The delay between the source and receivers is small Ideally, The number of redundant packets on any physical link is low Heuristic used: Every member in the tree has a small degree Degree chosen to reflect bandwidth of connection to Internet What is an efficient overlay tree? CMU CMU CMU Stan2 Stan2 Stan2 Stan1 Stan1 Stan1 Gatech Gatech Berk1 Berk1 Berk1 Gatech Berk2 Berk2 Berk2 High latency High degree (unicast) “Efficient” overlay

32. Why is self-organization hard? • Dynamic changes in group membership • Members may join and leave dynamically • Members may die • Limited knowledge of network conditions • Members do not know delay to each other when they join • Members probe each other to learn network related information • Overlay must self-improveas more information available • Dynamic changes in network conditions • Delay between members may vary over time due to congestion

33. Delay from CMU to Berk1 increases Stan1 Gatech Stan2 CMU Berk1 Berk2 Stan1 Stress = 2 Stan2 CMU Berk1 Performance Metrics • Delay between members using Narada • Stress, defined as the number of identical copies of a packet that traverse a physical link Gatech Berk2

34. ESM Conclusions • Proposed in 1989, IP Multicast is not yet widely deployed • Per-group state, control state complexity and scaling concerns • Difficult to support higher layer functionality • Difficult to deploy, and get ISP’s to turn on IP Multicast • Is IP the right layer for supporting multicast functionality? • For small-sized groups, an end-system overlay approach • is feasible • has a low performance penalty compared to IP Multicast • has the potential to simplify support for higher layer functionality • allows for application-specific customizations

35. Internet Indirection Infrastructure (i3) Motivations • Today’s Internet is built around a unicast point-to-point communication abstraction: • Send packet “p” from host “A” to host “B” • This abstraction allows Internet to be highly scalable and efficient, but… • … not appropriate for applications that require other communications primitives: • Multicast • Anycast • Mobility • …

36. Why? • Point-to-point communication  implicitly assumes there is one sender and one receiver, and that they are placed at fixed and well-known locations • E.g., a host identified by the IP address 128.32.xxx.xxx is located in Berkeley

37. IP Solutions • Extend IP to support new communication primitives, e.g., • Mobile IP • IP multicast • IP anycast • Disadvantages: • Difficult to implement while maintaining Internet’s scalability (e.g., multicast) • Require community wide consensus -- hard to achieve in practice

38. Application Level Solutions • Implement the required functionality at the application level, e.g., • Application level multicast (e.g., Narada, Overcast, Scattercast…) • Application level mobility • Disadvantages: • Efficiency hard to achieve • Redundancy: each application implements the same functionality over and over again • No synergy: each application implements usually only one service; services hard to combine

39. “Any problem in computer science can be solved by adding a layer of indirection” Key Observation • Virtually all previous proposals use indirection, e.g., • Physical indirection point  mobile IP • Logical indirection point  IP multicast

40. Application Build an efficient indirection layer on top of IP Indir. layer TCP/UDP IP i3 Solution • Use an overlay network to implement this layer • Incrementally deployable; don’t need to change IP

41. trigger data data data id id R id R Internet Indirection Infrastructure (i3): Basic Ideas • Each packet is associated an identifier id • To receive a packet with identifier id, receiver R maintains a trigger (id, R) into the overlay network Sender Receiver (R)

42. Service Model • API • sendPacket(p); • insertTrigger(t); • removeTrigger(t) // optional • Best-effort service model (like IP) • Triggers periodically refreshed by end-hosts • ID length: 256 bits

43. Receiver (R1) id id R1 R2 Receiver (R2) Mobility • Host just needs to update its trigger as it moves from one subnet to another Sender

44. data data data data R2 R1 id id Multicast • Receivers insert triggers with same identifier • Can dynamically switch between multicast and unicast id R1 Receiver (R1) Sender id R2 Receiver (R2)

45. p|a data p|a data Receiver (R1) data R1 R1 p|s1 R2 p|s2 Sender Receiver (R2) R3 p|s3 Receiver (R3) Anycast • Use longest prefix matching instead of exact matching • Prefix p: anycast group identifier • Suffix si: encode application semantics, e.g., location

46. idT,id T,id data data data data id R idT,id data Service Composition: Sender Initiated • Use a stack of IDs to encode sequence of operations to be performed on data path • Advantages • Don’t need to configure path • Load balancing and robustness easy to achieve Transcoder (T) Receiver (R) Sender id R T idT

47. id data idF,R F,R id data data data data R Service Composition: Receiver Initiated • Receiver can also specify the operations to be performed on data Firewall (F) Receiver (R) F Sender idF id idF,R

48. Quick Implementation Overview • i3 is implemented on top of Chord • But can easily use CAN, Pastry, Tapestry, etc • Each trigger t =(id, R) is stored on the node responsible for id • Use Chord recursive routing to find best matching trigger for packet p = (id, data)

49. S 0 2m-1 S 3 send(37, data) 20 [8..20] 7 7 [4..7] 3 [40..3] Chord circle 35 37 R [21..35] 41 41 [36..41] 20 trigger(37,R) 37 R 35 R send(R, data) R Routing Example • R inserts trigger t = (37, R); S sends packet p = (37, data) • An end-host needs to know only one i3 node to use i3 • E.g., S knows node 3, R knows node 35

50. 37 R data data 37 R cache node Optimization #1: Path Length • Sender/receiver caches i3 node mapping a specific ID • Subsequent packets are sent via one i3 node [8..20] [4..7] [42..3] [21..35] Sender (S) [36..41] Receiver (R)