1 / 35

Requirements

Requirements. Connectivity Resource Sharing Support for Common Services Performance. Performance Metrics. Bandwidth (throughput) data transmitted per time unit link versus end-to-end notation KB = 2 10 bytes Mbps = 10 6 bits per second Latency (delay)

shoushan-mccoy
Download Presentation

Requirements

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Requirements • Connectivity • Resource Sharing • Support for Common Services • Performance

  2. Performance Metrics • Bandwidth (throughput) • data transmitted per time unit • link versus end-to-end • notation • KB = 210 bytes • Mbps = 106 bits per second • Latency (delay) • time to send message from point A to point B • one-way versus round-trip time (RTT) • components Latency = Propagation + Transmit + Queue Propagation = Distance / c Transmit = Size / Bandwidth • Examples of RTT: LAN, Cross-country link, Satellite

  3. Delay x Bandwidth Product • Amount of data “in flight” or “in the pipe” • Example: 100ms x 45Mbps = 560KB • Why is it important to know Delay x Bandwidth product?

  4. Bandwidth versus Latency • Relative importance • 1-byte: 1ms vs 100ms dominates 1Mbps vs 100Mbps • 25MB: 1Mbps vs 100Mbps dominates 1ms vs 100ms • Infinite bandwidth • RTT dominates • Throughput = TransferSize / TransferTime • TransferTime = RTT + TransferSize /Bandwidth • 1-MB file to 1-Gbps link as 1-KB packet to 1-Mbps link

  5. Network Architecture • Layering and Protocols • ISO Architecture • Internet architecture

  6. Layering • Use abstractions to hide complexity • Abstraction naturally lead to layering • Alternative abstractions at each layer • Advantages: • Solve small problems vs. monolithic software • Modularity: easily add new services • Drawback: • May hide important information Application programs Request/reply Message stream channel channel Host-to-host connectivity Hardware

  7. Protocols • Building blocks of a network architecture • Each protocol object has two different interfaces • service interface: operations on this protocol (SAP) • peer-to-peer interface: messages exchanged with peer • Term “protocol” is overloaded • specification of peer-to-peer interface (rules) • module that implements this interface • Protocol stack: set of consecutive layers • Interoperability problems

  8. Interfaces Host1 Host2 Service High-level High-level interface object object Protocol Protocol Peer-to-peer interface

  9. Protocol Machinery • Protocol Graph • most peer-to-peer communication is indirect • peer-to-peer is direct only at hardware level Host 2 Host 1 Digital Digital Video Video File File library library application application application application application application RRP MSP RRP MSP HHP HHP

  10. Machinery (cont) • Multiplexing and Demultiplexing (demux key) • Encapsulation (header/body) Host 1 Host 2 Application Application program program Data Data RRP RRP RRP Data RRP Data HHP HHP HHP RRP Data

  11. OSI Architecture:Reference Model End host End host Application Application Presentation Presentation Session Session Transport Transport Network Network Network Network Data link Data link Data link Data link Physical Physical Physical Physical One or more nodes within the network

  12. Physical Layer • Function: provides a “virtual bit pipe” • How: maps bits into electrical/electromagnetic signals appropriate for the channel • The physical layer module is called a modem (modulator/demodulator) • Important issues: • Timing: synchronous, intermittent synchronous, asynchronous (characters) • Interfacing the physical layer and DLC (e.g., RS-232, X.21)

  13. Data Link Control Layer (DLC) • Receives packets from the network layer and transforms then into bits transmitted by the physical layer. Generally guarantees order and correctness. • Mechanisms of the DLC: • Framing: header, trailer to separate packets, detect errors… • Multiple access schemes: when the link is shared by several nodes there is a need for addressing and controlling the access (this entity is called MAC sublayer) • Error detection and retransmission (LLC sublayer)

  14. Network Layer • Provides naming/addressing, routing, flow control, and scheduling/queuing in a multi-hop network • Makes decisions based on packet header (e.g., destination address) and module stored information (e.g., routing tables) • General comment: each layer looks only at its corresponding header (here packet header) • Routing is different on virtual circuit networks than on datagram networks

  15. Transport Layer • Provides a reliable mechanism to transmit messages between two end-nodes through: • Message fragmentation into packets • Packets reassembly in original order • Retransmission of lost packets • End-to-end flow control • Congestion control

  16. Session Layer • Was intended to handle the interaction between two end points in setting up a session: • multiple connections • Service location (e.g., would achieve load sharing) • Control of access rights • For example, managing an audio and video stream in a teleconferencing application • In many networks these functionalities are inexistent or spread over other layers

  17. Presentation Layer • Concerned with the format of the data exchanged • Provides data encryption, data compression, and code conversion.

  18. Application Layer • What’s left over… • Examples:WWW, Email, Telnet, …

  19. FTP HTTP NV TFTP UDP TCP IP … NET NET NET 2 1 n Internet Architecture • Defined by Internet Engineering Task Force (IETF) • IETF requires working implementations for standard adoption • Application vs. Application Protocol (FTP, HTTP)

  20. Internet Architecture • Not quite layered Application TCP UDP IP Network

  21. Implementing Network Software • Success of the Internet is partially due to: • Minimal functionality within the network • Most of the functionality running is software over general-purpose computers • Simple Application Programming Interface • Efficient protocol implementation

  22. Application Programming Interface • Each OS can have a special interface exported by the network to the applications developer • Most widely used network API is: socket interface • Initially developed by the Berkeley Distribution of Unix and today ported to almost all OS

  23. Creating a Socket • int socket( int domain, /* PF_INET, PF_UNIX */ int type, /* SOCK_STREAM, SOCK_DGRAM */ int protocol)

  24. Active Open • Clients perform an active open operation using the connect routine • int connect (int socket, struct sockaddr *address, int addr_len)

  25. Passive Open • Servers perform a passive open • bind, listen, accept • int bind (int socket, struct sockaddr *address, int addr_len) • int listen (int socket, int backlog) • int accept (int socket, struct sockaddr *address, int *addr_len)

  26. Sending and Receiving Data • Once the connection is established, use send/recv functions to exchange data • int send (int socket, char *message, int msg_len, int flags) • int recv (int socket, char *buffer, int buf_len, int flags)

  27. Closing a Socket • void close (int socket)

  28. Client/Server Sockets • Client: • socket, connect, (send, recv)*, close • Server: • socket, bind, listen, (accept, (recv, send)*, close)*

  29. Exercise • Write the simplex-talk client and server programs given in Section 1.3.2 of text • Given in C • Run a client and server on same machine and test • Run client and server on different machines • Do Exercises 28, 29, and 30 of text

  30. Protocol Implementation Issues • The socket API is an interface between the application and the network subsystem (TCP, UDP, IP, etc.) • Could potentially be used as a protocol-to-protocol interface • Turns out that the socket interface, while clean, introduces a number of inefficiencies • Different protocol-to-protocol interfaces designed

  31. Process Models Process-per-protocol Process-per-message

  32. Context Switches • Inefficiency of process-per-protocol model: • Too many context switches, as the message is handed from one protocol to the next • Context switches become procedure calls in the process-per-message model • Sending a message: high-level protocol calls send on the low-level protocol • Receiving a message: high-level protocol calls receive on the low-level protocol

  33. Protocol-to-Protocol Interface • The receive operation replaced by deliver

  34. Message Buffer Handling • Copying messages between buffers expensive • Shared message abstraction • Adding and stripping headers • Fragmenting and reassembling messages

  35. Other Common Library Routines • Event library: commonly need to schedule an event in the future • Examples: timeout, garbage collection • A common event & event manager abstraction • Map library: For maintaining bindings between identifiers • Example: Mapping incoming messages to the connection that will process the message

More Related