Lecture 3: State of the Art

Lecture 3:State of the Art www.psirp.org D.Sc. Arto Karila Helsinki Institute for Information Technology (HIIT) arto.karila@hiit.fi T-110.6120 – Special Course on Data Communications Software: Publish/Subscribe Internetworking

Contents • Introduction • Guiding Principles • Future Internet Architecture • Protocols • Mechanisms • Publish/Subscribe paradigm • Design Considerations • Economics • Security • Trust • Privacy

Introduction • The PSIRP project aims to solve some major issues of the current Internet by applying… • information-centric • publish/ subscribe … paradigm throughout the layers • In fact, many current applications are inherently pub/sub in nature: • Distribution of software and anti-virus updates • IPTV • BitTorrent • RSS feeds and more! • A clean-slate pub/sub architecture could serve such applications very well

Introduction • To succeed, we must know the current state of the art, make use of it, and extend it in many areas of communication • In early 2008 a rather thorough state-of-the-art study was conducted and collected to a report (D2.1) • Development has not stopped there and the wiki used has lived on but D2.1 presents a snap-shot of the situation two years ago • Because of the breadth of the area, we had to focus on promising sub-areas

Guiding Principles • Our vision is based on these concepts: • Everything is information, which can be organized hierarchically to build complicated structures from simple elements • There are different forms of information reachability on all levels of the design and they can change in real-time • Control is given to the recipient of information, fixing the imbalance of powers inherent in TCP/IP • The state-of-the-art study was focused on issues that appear to serve these ideas

Scope • The goals were mapped into areas of investigation that seemed to be relevant • Future Internet Architecture • Protocols • Naming • Addressing • Routing • Multicast • Mechanisms • Compensation • Caching • Security • Network Coding

Scope (cont’d) • Publish Subscribe • Design considerations • Economics • Socio-economic aspects • Security must be designed into the architecture • Trust is an important aspect of networking • Privacy is of increasing importance

Methodology • The methodology of the SoA study was dictated by the envisioned scope • The SoA was simply the first step towards understanding the relevant prior work • “A system as complex as the Internet can only be designed effectively if it is based on a core set of design principles, or tenets, that identify points in the architecture where there must be common understanding and agreement” [Cla2003]

Methodology • The original Internet was created by people who share the common goal of interconnecting their computing equipment • Computers were physically large, with extremely limited resources • You kept your data with you and not on the system  Communication was modeled to share resources point-to-point… NOT for many-to-many content sharing and retrieval • As the Internet has grown well out of its envisioned scope, several of its limitations have become apparent • From the socio-economic point of view, solving tussles (conflicts of interest) is one of the key problems facing future Internet • This leads to design for change [Cla2003] and the requirement of evolvability [Rat05] • The importance of trust (E2E => T2T)

Naming • Currently naming usually happens at the service-level: • domain names, • e-mail addresses, • URIs etc. • The Domain Name System (DNS) defines a static, hierarchical namespace organized into a tree, where ICANN manages the top-level domains • The DNS namespace is decoupled from the (also hierarchical) IP address space

Quick Discussion • What is good about DNS? • What is bad about DNS? • Why is DNS is insufficient to support host mobility?

Naming • DONA replaces domain names with self-certifying, two-part, hash-based names, naming data (not hosts or interfaces) • [Ram2004a] proposes a new design for name resolution • [Ram2004b] proposes prefix-matching DHT • In [Cal2007] on channels are named with unique identifiers without hierarchy or centralized control • [Cro2003] introduces contexts – collections of homogeneous network elements • There are lots of different proposals

Addressing • Traditionally IP addresses are divided into classes A, B, and C • In 1993 Classless Inter-Domain Routing (CIDR) was introduced, with variable-length prefixes and aggregation of blocks • [And2007] proposes an address structure where the subnet prefix is replaced with a self-certifying Autonomous Domain identifier (AD) and the suffix with a self-certifying Host Identifier (EID), adresses now being of form: AD:EID • ROFL proposes routing on flat labels, in a totally topology-independent way (this does not scale)

Addressing • In [Cal2007] nodes are anonymous and addressed through their incoming channels • In [Cro2003] specific addresses are bound to different addresses in different contexts • [Han2004] proposes seven steps towards an Internet resistant against DoS attacks – the first two calling for separation of client and server addresses and removal of globally reachable client addresses

Inter-Domain Routing • Border Gateway Protocol (BGP) is suffering from serious scaling problems • Default-free zone • In June 2007, APNIC router in Tokyo had ~225,000 routes! • Any change in a globally visible prefix causes Internet-wide route updates • The number of globally visible prefixes is growing for a number of reasons, such as: • Provider-independent addressing • Multi-homing of sites • Protecting against prefix hijacking

Domain-Level Routing • To tackle BGP’s scaling issues [And2007] proposes to route at the domain level • Removal of path selection from packet-forwarding-level routing has been proposed • Explicit domain-level path construction fits with name-based routing (e.g. TRIAD) • [Lak2006] proposes providing the path selection function as a separate routing service • [Key2006] lets the sending host optimize path selection based on congestion information • NIRA [Yan2007] proposes a separate path discovery protocol for the up-graph, Name-to-Route Lookup Service (NRLS) for the downhill route, and allowing the endpoints to further negotiate end-to-end path selection

Domain-Level Routing • Some of these functionalities are needed by multi-path capable transport protocols, such as the Stream Control Transmission Protocol (SCTP) [Ste2000] • [Fea2004] proposes removing the routing function from routers to allow for better domain-level control of routing policies and allow a more direct domain-level mechanism for inter-domain routing • ROFL uses domain-level source routes as the means to route packets between endpoints – the first packet of a session uses hierarchical DHT routing, but after that the endpoints can use NIRA-like [Yan2007] end-to-end domain-level path control

Compact Routing • Routing table sizes and communication cost of BGP are increasing exponentially with the number of global prefixes [Kri2007] • Routing on AS numbers doesn’t offer a real solution to the growing complexity • Compact Routing aims to decrease the size of routing tables while allowing non-shortest paths to be used • Traditional shortest-path algorithms yield routing tables of size O[n*log(n)] [Gav1996]

Compact Routing • A routing scheme is said to be compact if it produces: • Logarithmic address and header sizes • Sub-linear routing table sizes • Stretch bounded by a constant • A compact routing scheme can be.: • Specialized or universal (works on all graphs) • Name-dependent or name-independent • Two compact routing schemes with small stretch (3) are the non-hierarchical Cowen [Cow1999] and the Thorup-Zwick (TS) [Tho2001] schemes • [Kri2004] focuses on the TZ scheme with Internet-like graphs

Overlay Routing • In overlay routing the topology is formed over an underlying (usually IP) network • DHTs are examples of overlay routing • DHT techniques can be utilized e.g. in implementing non-hierarchical rendezvous • An example of DHT-based solutions is the Content Addressable Network (CAN) • CAN is based on a d-dimensional Cartesian space, each node having a coordinate zone that it is responsible for

CAN • A two-dimensional example

Chord Ring • Greedy forwarding (cmp w/ ROFL)

Pastry DHT • An example with hexadecimal identifiers

Content-Based Pub/Sub Routing • Hosts subscribe to content by specifying filters on the events • The content of the message defines its ultimate destination • Subscribers use interest registration facility which sets up data delivery paths • Pub/sub has been proposed as a replacement for TCP/IP • This would change the economic model too

Content-Based Pub/Sub Routing • Filter-based event routing – pub/sub servers are organized into an acyclic tree • Multicast-based event routing – a multicast tree is build for every interest group • Kyra [Cao2004] combines the approaches using a two-level hierarchy • Within a clique (based on proximity) all nodes know each other • On a higher level minimum spanning trees to the cliques are built for various events

Content-Based Pub/Sub Routing • Siena is a classic example of distributed content-based routing implemented in the application layer, coexisting with TCP/IP [Car2001] • Overlay networks allow more complex functionality to be implemented on top of IP • Good overlay routing configuration follows the placement of network-level routers

Multicast • Multicast is vital for the efficient distribution of media (such as video) • IPv4 has class D addresses for multicast • DVRMP is and early mcast routing protocol • The topological map of OSPF allows MOSPF to operate with little overhead • Protocol Independent Multicast (PIM) works with any routing protocol in two modes: sparse (PIM-SM) and dense (PIM-DM) • In the local network, IGMP is used

Multicast • Multicast is considered valuable but it is not supported in the Internet • The main reasons for this are its security and scalability issues • DVRMP and PIM-DM initially flood the n/wk • Each multicast router requires a lot of state • The sender runs the risk of getting traffic back from a large group of recipients • [PAS1998] provides a summary of approaches emphasizing different goals

Recent Trends in Multicast • There are many proposals for more scalable or more easily deployable multicast • These can be roughly divided into three groups: • Router-based • Host-based • Overlay (DHT) -based

Mechanisms • Compesation • Cacheing • Security • Network Coding

Compensation • To facilitate efficient use of resources by providing the “owner” with some assurance that he will eventually benefit from the use of his resource • Different forms of compensation: • Authorization • Community membership • Resource exchange • Sacrifice or evidence of deliberate waste of the user’s own resources • Payment or promise of future reimbursement

Compensation • Types of transaction-related costs: • Immediate technical costs • Information search costs • Collateral costs associated with the use • Compare w/ Transaction Cost Economics: • Researching potential suppliers • Collecting information on prices • Negotiating contracts • Monitoring the supplier’s output • Legal costs incurred (contract breaches)

Compensation • Weber, Biggard and Delbridge: exchange = voluntary agreement involving the offer of any sort of present, continuing, or future utility in exchange for utilities of any sort offered in return • Four categories of exchange systems: • Price System • Associative System • Moral System • Communal System

Caching • [PIT2008] studies caching performance in nodes of a Delay Tolerant Network (DTN), providing ad-hoc communication services within (sparse) mobile user communities when end-to-end IP service is unavailable • The network acting as a distributed cache • Caching is needed to handle heavy traffic • The price of storage is dropping faster than the price of communication => caching is getting more tempting

2009 $100/MB $10/MB $1/MB Raw Disk Space $100/GB $10/GB Tier-1 Internet Transit $1/GB $0.1/GB Storage vs. Transit Price

Scope Security • In pub/sub architectures scopes control the spreading of information • [Fie2004] proposes an extension to a large pub/sub system Rebeca to support scopes • In [Far2002] access control is implemented with attribute certificates (ACs) used to identify nodes and their privileges

Packet Layer Authentication • Each packet (or PDU at any layer) can be signed and the public key included • The authenticity of the packet can now be determined by any node on its route • This prevents the attacker from consuming a lot of resources with falsified packets • This area will be covered more on the PSIRP Security Architecture lecture

Transparency and Information Accountability • Social rules ted to more often cause compliance than abuse • This is due to the fact that the consequences of compliance usually are more pleasant than those of violation • If we can build this into the architecture, a large-scale system can be made reliable, robust, secure, trusted, and efficient • [Wei2007] introduces transparency and accountability as the attributes of information systems that could result in compliance and collaboration

Network Coding • Communication through an unreliable and unpredictable channel is difficult • Transmission errors can lead to long delay and large number of retransmissions • Network coding includes Forward Error Correction (FEC) as well as more modern rateless codes – i.e. digital fountain codes

Reed-Solomon Codes • Among the most significant traditional codes is the Reed-Solomon code (N,K), with qm symbols in its alphabet, can be decoded after receiving K out of N symbols sent • The message consists of K original symbols and N-K parity symbols

Fountain Codes • Fountain techniques send randomly all the parts of a message with added redundancy • They are rateless since there is no limit on the number of encoded packets generated from the source message and it can change on the fly • The source can send as many encoded packets as necessary for the destination to decode the data • Among fountain codes are: • Random Linear Fountain Code, • Tornado Codes and • LT Fountain Code

XOR Coding • Intelligent mixing of packets can be used to increase network throughput • An example is the situation where two users of a wifi base station (router) exchange two messages • Without network coding we need four transmissions • With simple XOR coding we can do with only three transmissions

XOR Coding • Message exchange without network coding – four transmissions

XOR Coding • Message exchange with network coding – three transmissions

Linear Network Coding • Linear network coding is rather like XOR coding, except that the XOR operation is replaced with linear combination of data • The recipient can decode the information having received m out of the n messages • Linear coding appears to work well with multicast, which makes it interesting for PSIRP

Publish/Subscribe Paradigm • The starting point of our work is that event-based computing and the pub/sub paradigm are crucial for future services • RSS feeds can be seen as pub/sub • SIP is an example of event-based comp. • Formal modeling of pub/sub systems and correctness of content-based routing protocols are examined in [Müh2002b] • A routing protocol is correct if it satisfies the safety and liveliness requirements

Design Considerations • Economics • Security • Formal Modeling

Lecture 3: State of the Art