台北科技大学：《计算机网络》（英文版） NP04 16 server

Server software design Algorithms and Issues Chuan-Ming LIu Computer Science and Information Engineering Spring 2004, NTUT TAIWAN CSIE NTUT Taiwan

1 CSIE, NTUT, Taiwan Server Software Design Algorithms and Issues Chuan-Ming Liu Computer Science and Information Engineering Spring 2004, NTUT TAIWAN

●。 Conceptual Server Algorithm o Simple server Algorithm 1. Create a socket 2. Bind the socket to the port 3. Enter an infinite loop Accept request Process request Reply request o Not enough in practice generall SIE, NTUT, Taiwan

2 CSIE, NTUT, Taiwan Conceptual Server Algorithm  Simple Server Algorithm 1. Create a socket 2. Bind the socket to the port 3. Enter an infinite loop • Accept request • Process request • Reply request  Not enough in practice generally

●。 Conceptual Server Algorithm o Consider file transfer first client needs a 200 Mb file o Second client needs a 20 byte file If the server processes them in Fifo fashion The second client will wait an unreasonable amount of time for a small transfer Server usually handles more than one request at a time SIE, NTUT, Taiwan

3 CSIE, NTUT, Taiwan Conceptual Server Algorithm  Consider file transfer ⚫ First client needs a 200 MB file ⚫ Second client needs a 20 byte file ⚫ If the server processes them in FIFO fashion The second client will wait an unreasonable amount of time for a small transfer  Server usually handles more than one request at a time

。。 Concurrent vs. Iterative o Iterative server: one request at a time o Concurrent server: multiple requests at one time o Note: the concurrency is conceptual and generally will use one thread for one request o Concurrent server refers to whether the server permits multiple requests to proceed concurrently, not whether the underlying implementation uses multiple and concurrent threads 4 CSIE. NTUT. Taiwan

4 CSIE, NTUT, Taiwan Concurrent v.s. Iterative  Iterative server: one request at a time  Concurrent server: multiple requests at one time  Note: the concurrency is conceptual and generally will use one thread for one request  Concurrent server refers to whether the server permits multiple requests to proceed concurrently, not whether the underlying implementation uses multiple and concurrent threads

●。 Concurrent vs. Iterative o Concurrent servers are difficult to design and build o Why concurrency? o Long delay caused by iterative servers o Performance bottleneck resulted from iterative servers effects many clients 5 SIE NTUT. Taiwan

5 CSIE, NTUT, Taiwan Concurrent v.s. Iterative  Concurrent servers are difficult to design and build  Why concurrency? ⚫ Long delay caused by iterative servers ⚫ Performance bottleneck resulted from iterative servers effects many clients

●。 Connection Access or not o Two major transport protocols o TCP(Transmission Control protocol) UDP (USer Datagram Protocol) o tCP is connection-oriented and udp is connectionless o The corresponding servers are o Connection-oriented servers o Connectionless serves 6 SIE, NTUT, Taiwan

6 CSIE, NTUT, Taiwan Connection Access or Not  Two major transport protocols: ⚫ TCP (Transmission Control Protocol) ⚫ UDP (User Datagram Protocol)  TCP is connection-oriented and UDP is connectionless  The corresponding servers are ⚫ Connection-oriented servers ⚫ Connectionless serves

●。 TCP Semantics o Point-to-point communication o Reliable connection establishment o Reliable delivery o Flow controlled transfer o Full-duplex transfer o Stream paradigm SIE, NTUT, Taiwan

7 CSIE, NTUT, Taiwan TCP Semantics  Point-to-point communication  Reliable connection establishment  Reliable Delivery  Flow controlled transfer  Full-duplex transfer  Stream paradigm

●。 UPD Semantics o Many-to-many communication o Unreliable service o Lack of flow control o Message paradigm SIE, NTUT, Taiwan

8 CSIE, NTUT, Taiwan UPD Semantics  Many-to-many communication  Unreliable Service  Lack of flow control  Message paradigm

TCP or UDP o Because the semantics of TcP and UDP differ sharply, a designer cannot choose between connection-oriented and connectionless transport protocols without considering the semantics required by the application protocol o Depends on the applications, not the pes SIE, NTUT, Taiwan

9 CSIE, NTUT, Taiwan TCP or UDP?  Because the semantics of TCP and UDP differ sharply, a designer cannot choose between connection-oriented and connectionless transport protocols without considering the semantics required by the application protocol  Depends on the applications, not the types

●。 Connection- Oriented servers o Easier to program since tCP provide all the reliabili o Drawbacks o Need a separate socket for each connection o cares about the socket allocation and resource consuming o Resource limitation problem-due to the clients crash often 10 SIE, NTUT, Taiwan

10 CSIE, NTUT, Taiwan Connection-Oriented Servers  Easier to program since TCP provide all the reliability  Drawbacks: ⚫ Need a separate socket for each connection ⚫ Cares about the socket allocation and resource consuming ⚫ Resource limitation problem – due to the clients crash often