1 An Introduction to Computer Networks University of Tehran Dept. of EE and Computer Engineering By: Dr. Nasser Yazdani Lecture 2: Foundation

Univ. of TehranIntroduction to computer Network2 Outline Introduction Statistical Multiplexing Inter-Process Communication Network Architecture Performance Metrics

Univ. of TehranIntroduction to computer Network3 Introduction Building a network to support diverse ranges of applications Distributed computing. Multimedia. Telecommunication. E-commerce, etc. What kind of technology do we need? Hardware. Software.

Univ. of TehranIntroduction to computer Network4 First Step What is computer Network? Different views. Differences from other networks, Its generality. What is requirements? Different perspective: Network provider Network designer Application programmer

Univ. of TehranIntroduction to computer Network5 Design goals Connectivity Scalability Simplicity For designers. Most importantly for users. Efficiency cost performance Support for common user services.

Univ. of TehranIntroduction to computer Network6 Building Blocks Nodes: PC, special-purpose hardware… hosts switches, routers and gateways Links: coax cable, optical fiber… point-to-point multiple access …

Univ. of TehranIntroduction to computer Network7 Switched Networks two or more nodes connected by a link, or two or more networks connected by two or more nodes A network can be defined recursively as...

Univ. of TehranIntroduction to computer Network8 Strategies Circuit switching: carry bit streams Connection oriented. original telephone network Dedicated resource. Packet switching: store-and-forward messages Connectionless (IP) or connection oriented (ATM) Internet Shared resource. Packet switching is the focus of computer Networks.

Univ. of TehranIntroduction to computer Network9 Addressing and Routing Address: byte-string that identifies a node usually unique Routing: process of forwarding messages to the destination node based on its destination address Types of addresses unicast: node-specific broadcast: all nodes on the network multicast: some subset of nodes on the network

Univ. of TehranIntroduction to computer Network10 Multiplexing (resource sharing) Time-Division Multiplexing (TDM) Frequency-Division Multiplexing (FDM) L1 L2 L3 R1 R2 R3 Switch 1Switch 2

Univ. of TehranIntroduction to computer Network11 Statistical Multiplexing On-demand time-division Schedule link on a per-packet basis Packets from different sources interleaved on link scheduling fairness, quality of service Buffer packets that are contending for the link Buffer (queue) overflow is called congestion …

Univ. of TehranIntroduction to computer Network12 Packet Switching A node in a packet switching network incoming linksoutgoing links Node Memory

Univ. of TehranIntroduction to computer Network13 Inter-Process Communication Turn host-to-host connectivity into process- to-process communication regardless where the process are. Give a unified view and fill gaps between what applications expect and what the underlying technology provides. Host Application Host Applicatio n Host Channel

Univ. of TehranIntroduction to computer Network14 IPC Abstractions 1. Request/Reply (Client-server) distributed file systems (NFS) digital libraries (web) File Transfer (FTP) Guarantee delivering data, and might protect privacy and integrity also. We should identify the common communication patterns. Two general patterns are:

Univ. of TehranIntroduction to computer Network15 IPC Abstractions(Cont) 2.Stream-Based- sequence or stream of bits.  Video on demand: sequence of frames. Delay constrained, but can be fetched before hand. For example, a Monitor with 352 x 240 pixels and 24 bit color. (352 x 240 x 24)/8=247.5KB Assuming 30 frame per second => 7500KBps = 60Mbps  video Conferencing - tightly delay bounded. VIC From Berkeley.  Both application can tolerate packet loss. Questions? What functionality each channel should provide? Where the functionality has to be implemented? In the end points or in the network?

Univ. of TehranIntroduction to computer Network16 Reliability in the network? What Goes Wrong in the Network? Bit-level errors (electrical interference), a bit is corrupted or a burst error. Packet-level errors (congestion) Messages are delayed Messages are deliver out-of-order Third parties eavesdrop, (lost packets) Link and node failures

Univ. of TehranIntroduction to computer Network17 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) 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 (light speed) Transmit = Size / Bandwidth

Univ. of TehranIntroduction to computer Network18 Bandwidth versus Latency Relative importance Latency bounded- sending 1-byte by client, 1ms vs 100ms dominates sending a message on a 1Mbps or 100Mbps link Bandwidth Bounded- sending 25MB image: 1Mbps vs 100Mbps dominates 1ms vs 100ms delayed channel. Infinite bandwidth RTT dominates Throughput = TransferSize / TransferTime TransferTime = RTT + 1/Bandwidth x TransferSize 1-MB file to 1-Gbps link the same as 1-KB packet to 1-Mbps link.

Univ. of TehranIntroduction to computer Network19 Delay x Bandwidth Product Amount of data “in flight” or “in the pipe” Example: 100ms x 45Mbps = 560KB We are usually more interested in 2 times of this value Since it take RTT to hear from receiver.

Univ. of TehranIntroduction to computer Network20 Layering Use abstractions to hide complexity and decompose to manageable components. Abstraction naturally lead to layering Alternative abstractions at each layer Request/reply channel Message stream channel Application programs Hardware Host-to-host connectivity

Univ. of TehranIntroduction to computer Network21 Layering Advantages Modularity – protocols easier to manage and maintain Abstract functionality –lower layers can be changed without affecting the upper layers Reuse – upper layers can reuse the functionality provided by lower layers Disadvantages Information hiding – inefficient implementations

Univ. of TehranIntroduction to computer Network22 Protocols Building blocks of a network architecture, or layer abstraction. Each protocol object has two different interfaces service interface: operations on this protocol peer-to-peer interface: messages exchanged with peer Term “protocol” is overloaded specification of peer-to-peer interface module that implements this interface

Univ. of TehranIntroduction to computer Network23 Host 1 Protocol Host 2 Protocol High-level object High-level object Service interface Peer-to-peer interface Interfaces

Univ. of Tehran24 Protocol Machinery Protocol Graph Nodes are protocols and edges are depend on. most peer-to-peer communication is indirect peer-to-peer is direct only at hardware level Digital library application Video application RRP MSP HHP File application Host 1 Digital library application Video application RRP MSP HHP File application Host 2

Univ. of Tehran25 Protocol Machinery (cont) Multiplexing and Demultiplexing (demux key) Encapsulation (header/body) RRPData HHP Application program Application program Host 1 Host 2 Data RRP Data HHP Data RRP Data HHP

Univ. of TehranIntroduction to computer Network26 ISO OSI Reference Model ISO – International Standard Organization OSI – Open System Interconnection Started to 1978; first standard 1979 ARPANET started in 1969; TCP/IP protocols ready by 1974 Goal: a general open standard allow vendors to enter the market by using their own implementation and protocols

Univ. of TehranIntroduction to computer Network27 ISO Architecture Application Presentation Session Transport End host One or more nodes within the network Network Data link Physical Network Data link Physical Network Data link Physical Application Presentation Session Transport End host Network Data link Physical Telnet, FTP, TFTP MSB, integer Manage TCP streams Message, P2P(process) Packet, routing Frame, CRC Raw bit pipe The last 3 protocols are implemented in all elements in the Network.

Univ. of TehranIntroduction to computer Network28 Encapsulation A layer can use only the service provided by the layer immediate below it Each layer may change and add a header to data packet data

Univ. of TehranIntroduction to computer Network29 OSI Model Concepts Service – says what a layer does Interface – says how to access the service Protocol – Says how the communication is done and how is the service implemented a set of rules and formats that govern the communication between two peers

Univ. of TehranIntroduction to computer Network30 Physical Layer (1) Service: move the information between two systems connected by a physical link Interface: specifies how to send a bit Protocols: coding scheme used to represent a bit, voltage levels, duration of a bit Examples: coaxial cable, optical fiber links; transmitters, receivers

Univ. of TehranIntroduction to computer Network31 Datalink Layer (2) Service: framing, i.e., attach frame separators send data frames between peers others: arbitrate the access to common physical media ensure reliable transmission provide flow control Interface: send a data unit (packet) to a machine connected to the same physical media Protocols: layer addresses, implement Medium Access Control (MAC) (e.g., CSMA/CD)…

Univ. of TehranIntroduction to computer Network32 Network Layer (3) Service: deliver a packet to specified destination perform segmentation/reassemble others: packet scheduling buffer management Interface: send a packet to a specified destination Protocols: define global unique addresses; construct routing tables

Univ. of TehranIntroduction to computer Network33 Transport Layer (4) Services: provide an error-free and flow-controlled end-to-end connection multiplex multiple transport connections to one network connection split one transport connection in multiple network connections Interface: send a packet to specify destination Protocols: implement reliability and flow control Examples: TCP and UDP

Univ. of TehranIntroduction to computer Network34 Session Layer (5) Service: full-duplex access management, e.g., token control synchronization, e.g., provide check points for long transfers Interface: depends on service Protocols: token management; insert checkpoints, implement roll-back functions

Univ. of TehranIntroduction to computer Network35 Presentation Layer (6) Service: convert data between various representations Interface: depends on service Protocol: define data formats, and rules to convert from one format to another

Univ. of TehranIntroduction to computer Network36 Application Layer (7) Service: any service provided to the end user Interface: depends on the application Protocol: depends on the application Examples: FTP, Telnet, WWW browser

Univ. of TehranIntroduction to computer Network37 Internet Architecture Defined by Internet Engineering Task Force (IETF). Developed in mid 60s in the ARPANET project. No assumption about the network tech. … FTPHTTPNV TFTP TCP UDP IP NET 1 2 n

Univ. of TehranIntroduction to computer Network38 Internet Architecture Hourglass Design, IP is the focual point. Delivery is separated from end-to-end process channel. No restrict layering Application vs Application Protocol (FTP, HTTP) Network IP TCP UDP Application

Univ. of TehranIntroduction to computer Network39 OSI vs. TCP/IP OSI: conceptually define services, interfaces, protocols Internet: provide a successful implementation Application Presentation Session Transport Network Datalink Physical Internet Host-to- network Transport Application IP LAN Packet radio TCPUDP TelnetFTPDNS OSITCP