1. Lect3..ppt - 09/13/04 CIS 4100 Systems Performance and Evaluation Lecture 4 by Zornitza Genova Prodanoff

2. ZGP002 Lecture Outline Chapter 2: Types of networks Network protocols Client/Server Model Peer-to-Peer Model Web services protocols

3. ZGP003 The client (process) Runs on a desktop Makes requests for services Executes a portion of the application code The server (process) Executes a set of functionally related services Never initiates a message exchange with a client Implements a queue to hold client requests as they arrive Request-reply protocol: client sends requests and server replies Queue of client requests at the server Server throughput is the number of requests served per unit time Client/Server Communication

4. ZGP004 Client/Server Communication (continued)

5. ZGP005 Fig. 2.14a shows that if only one request is served at a time, the resources at the server machine may be underutilized, the server throughput (number of requests served per time unit) may be low, and response time to clients will increase as the load on the server increases Fig. 2.14b shows that most servers create multiple processes or multiple threads of execution in a single process to handle the queue of incoming requests Client/Server Communication (continued)

6. ZGP006 Client/Server Communication (continued)

7. ZGP007 Using multiple threads or processes has an interesting effect on response time as shown in Fig. 2.15. The figure shows two response time curves: one for an arrival rate of 2.5 requests/sec and the other for 3.6 requests/sec. It is assumed that each request uses 0.07 sec of CPU time and 0.2 sec of disk time. Client/Server Communication (continued)

8. ZGP008 Client/Server Communication (continued)

9. ZGP009 As the curves illustrate, when the number of threads increases from one to two, the response time decreases because of the decrease in the time spent by a request waiting for an available thread. However, as the number of threads increases beyond this point, the additional time spent by a request contending for the same hardware resource dominates the decrease in thread waiting time, leading to a net increase in response time. The average number of active threads will not increase. When the number of threads becomes large enough, the thread waiting time becomes negligible (given a constant arrival rate) Response time does no longer vary with the number of threads Client/Server Communication (continued)

10. ZGP0010 Two-tier vs. three-tier model “Fat” vs. “thin” clients Use caches to relieve the server from some of the load. −If 30% of 900 requests are serviced by the cache, then only (1-.30) x 900 = 630 requests are serviced by the server. −Trade-offs are: −Updates of cache content are needed to maintain consistency (a fresh copy of the files) −Overhead processing for misses: first check the cache then request from server vs. request from server directly Client/Server Communication (continued)

11. ZGP0011 Client/Server Communication (continued)

12. ZGP0012 Server Types: File servers Database servers Application servers Groupware servers Object servers Web servers Software servers Client/Server Communication (continued)

13. ZGP0013 Hypertext Markup Language (HTML) −Integrate images and other multimedia objects, as well as software applications Application layer protocol Runs on top of TCP/IP Hyper Text Transfer Protocol (HTTP)

14. ZGP0014 HTTP 1.0 vs. HTTP 1.1 HTTP 1.0 −Allows for embedded documents in the HTML file −The client browser opens a separate connection with the server for each requested file: html, image, etc. −Client does not need to wait for connection termination before another connection request is sent −Images are downloaded transparent to user: HTTP response, containing the URL for the image is parsed before a new connection request is made Hyper Text Transfer Protocol (HTTP) (continued)

15. ZGP0015 HTTP 1.1 −Allows for embedded documents in the HTML file −“Persistent connections”: The client browser opens a (single) connection with the server for the html file. Then, embedded documents are requested within this same TCP connection −Pipelined requests: multiple requests are sent without waiting for response (ACK) −Pipelined HTTP 1.1 outperforms parallel connection based HTTP 1.0 Hyper Text Transfer Protocol (HTTP) (continued)

16. ZGP0016

17. ZGP0017 Figure 2.17: HTTP 1.1 vs. HTTP 1.0 −HTTP 1.1. results in 3 RTTs (vs. 4 RTTs with HTTP 1.0) −Improving performance with HTTP 1.1 −Reducing the number of packets sent −Better affect on network performance (less congestion) It has been shown that pipelined request based HTTP 1.1 outperforms HTTP 1.0 even if parallel TCP connections are initiated with HTTP 1.0 Hyper Text Transfer Protocol (HTTP) (continued)

18. ZGP0018 Peer-to-Peer Model Problems with C/S model −Server seen as a central node: − Scalability − Reliability Peer-to-Peer model: a collaborative and distributed approach to computing A study conducted at a major company with 10,000 workstations −75% of CPU cycles in the workstations or network nodes such as routers are idle −50% of disk space is free

19. ZGP0019 Peer-to-Peer Model (continued) 10 billion MHz & 10,000 TB not utilized at the edges of the Internet (see openP2P.com) The size of the networks and the complexity/requirements from the protocols steadily increase Bandwidth consumption attributed to popular file sharing applications reaches 60% of the total Internet traffic Must be able to locate the resources efficiently

20. ZGP0020 Peer-to-Peer model: sharing of resources available at the edges of the Internet In a P2P system, distributed computing nodes of equal roles or capabilities exchange information directly with each other Resources could be content, storage, CPU-cycles, bandwidth P2P paradigm has many plausible characteristics: −Scalability −No centralized authority, −Robustness −Cooperation, sharing −Anonymity Peer-to-Peer Model (continued)

22. ZGP0022 Routing Indexes No-indexing (Gnutella) Centralized index (Napster) Distributed index (FreeNet) Peer-to-Peer Model (continued)

23. ZGP0023 Advantages of Peer-to-Peer model: Performance gain with much less cost Self-organization Load balancing Adaptation Fault-tolerance Mobile devices Peer-to-Peer Model (continued)

24. ZGP0024 Open problems: Locating and addressing Caching of passing through objects How to identify an Object Network usage and participation Peer-to-Peer Model (continued)

25. ZGP0025 Queries propagate across nodes, each node does some processing and uses resources Bandwidth: The average over a set of representative queries of the aggregate BW consumed (in bytes) over each edge on behalf of the query Processing: The average over a set of representative queries of the aggregate processing power consumed at each node on behalf of the query Peer-to-Peer Model (continued)

26. ZGP0026 Gnutella: BFS technique is used with depth limit of D, where D= TTL of the message. At all levels < D query is processed by each node and results are sent to source and at level D query is dropped. Freenet: uses DFS with depth limit D. Each node forwards the query to a single neighbor and waits for a definite response from the neighbor before forwarding the query to another neighbor (if the query was not satisfied), or forwarding the results back to the query source (if query was satisfied). Peer-to-Peer Model (continued)

27. ZGP0027 Services provided to users via the Web Web service architecture: Provider Registry Requester A service is an application available for use by requesters that fit the prerequisites specified by the service provider Web services can be composed with other services Services are deployed on the Web by service providers Web Service Protocols

28. ZGP0028 Examples: Stock Quotes User Authentication Payment Authorization Airplane Ticket Purchase Hotel Reservations Web Service Protocols (continued)

29. ZGP0029 Automating: Service Discovery Service Execution Service Composition Service Interoperation Web Service Protocols (continued)

30. ZGP0030 What is Web Service Discovery? Automatically locating services that perform given task and exhibit the requested properties What is Web Service Composition and Interoperation? Includes selection of adequate Web services to perform a given task Web Service Protocols (continued)

31. ZGP0031 Web Service Protocols (continued) Uniform service description format Uniform service discovery protocols Upper layers represent service interoperability protocols

32. ZGP0032 Simple Object Access Protocol (SOAP) A World Wide Web Consortium (W3C) draft Specifies how to use Extended Markup Language (XML) and HTTP together A uniform way of disseminating XML-encoded structured data Web Service Protocols (continued)

33. ZGP0033 SOAP consists of three parts: An envelop that defines a framework – specifies message fields A set of encoding rules – how to represent instances of application defined data types Syntax for remote procedure calls and responses - SOAP results in no need to share a common programming language or distributed object infrastructure Web Service Protocols (continued)