Lecture 6 Communication Network PDF

Lecture6 Communication Network  y ’ s o a d ure T ec t Lecture Outline l of fi t s e n e d b a n...

Lecture6 Communication Network  y ’ s o a d ure T ec t Lecture Outline l of fi t s e n e d b a n i o n s : n i t u e fi. De orks i s s i g n w s n et r k d e t w o. Ne d i a Me logy To p o l o c o ot i n g P r e s s d r l e : A d i ng m p na m xa ee Networking ‘ Networks is a set of technologies – including hardware, software and media – that can be used ‘ to connect computers together, enabling them ’’ to communicate, exchange information and share resources in real time Benefits Resource sharing (cost savings) Personal communication Data backups Reliability (reduced errors/inconsistencies) Greater performance (distributed computing)  Network Design Issues Media; Topology; Protocol; Addressing; Naming; Example networking application. Transmission media Wired (or Guided) Media 1) Copper pair: Unshielded Twisted Pair (UTP) Shielded Twisted Pair (STP) 2) Coaxial Cable 3) Optical Fiber Transmission media Wireless (or Unguided) Media 1. Infrared 2. Radio 3. Microwave 4. Satellite Network Topology Network topology is the study of the physical (real) and logical (virtual) interconnections between nodes [Wikipedia] Topology types: Point to Point; Bus; Star; Ring; Mesh and Hybrid Network Topology (cont) Point to Bus Point Star Fully Tre Connect Parti e ed al Rin Mesh g  Protocol ‘ The rules governing the syntax, ’ semantics, and synchronization of communication. [Wikipedia] ‘ ‘ Protocol defines 1) format and 2) order of messages sent and ’ received among network entities ’ and 3) action(s) taken on ‘ transmission and receipt of message [Kurose and Protocol In this course, we will focus on protocols for data traffic only. TCP/IP is the most dominant suite of protocols and is used on the Internet. TCP/IP suite of protocols is often organized in a hierarchy of layers (OSI layers; to be covered next week) Some other protocol suites (no where as popular) include: NetBIOS/ NetBEUI and IPX/ SPX. Addressing Each station must be addressable Two kinds of addresses: 1) Physical addressing (MAC addresses) 2) Logical addressing (IP addresses) The communicating applications (source/ destination applications) must also be identifiable Identified through TCP ports A socket (IP address + TCP port) identifies both an application and Physical Addressing: MAC MAC Address: 48 bits (Ethernet) Flat addressing Usually non- configurable Logical Addressing: IP IP Version 4; Address: 4,294,967,2 32 bits IP Version 6; Address: 12896 possible addresses = bits 2 32 Hierarchical addressing 2 parts: a network part and a host part. Machines in a LAN have the same network part; they differ ? ??Subnet in host parts mask IP (Internet Protocol) IP Address 192.168.15.2 (decimal) 11000000 10101000 00001111 00000010 (binary) Subnet Mask: 255.255.255.0 (decimal) part Network Host part 11111111 11111111 Applications Identification How to identify source/ ? ?? destination application communicating The source/ destination applications are identified through TCP ports Common TCP Ports: HTTP: 80; SMTP:25; DNS: 53 Naming Machine addresses are difficult to memorize Solution: Provide recognizable names to numerically addressed Examples: Internet resources. ogle.com; stanford.edu; niit.edu.pk …, Third level domain, Second level domain; Top level domain (TLD); List of TLDs: http://en.wikipedia.org/wiki/List_of_Internet_top-leve _domains Naming How to manage address to 1) A hostsname file on mapping? each machine Unix/ Linux: /etc/hosts file Windows: %SystemRoot%\system32\ drivers\etc 2) A decentralized domain name server system Scalable solution The name to IP mapping is available at a DNS server DNS servers are of two types a) DNS Authoritative server (each domain has Example application To clarify concepts, let us assume a greatly simplified model of the W W P C LAN of NUST-SEECS W Network’s domain name: Let’s assume that a student (in niit.edu.pk the niit.edu.pk LAN) wishes to access NUST-SEECS website Example application Address Bar http://www.niit.edu.pk This is an example of a browser (Internet Explorer) Other browsers include Firefox, Opera. Browser acts as: 1 a client of webserver 2 fetches and displays user requested documents Example application (contd.) The HTTP request sent by the student PC (the machine pc.niit.edu.pk) to the webserver (the machine www.niit.edu.pk) would be something like “GET / HTML/1.1” GET / HTML/1.1 Packet so far: 1 Outstanding issues: 2 How to send this request to Webserver?  Example application (contd.) 1 But how to send this request to Webserver? To communicate with www.niit.edu.pk (hostname), its IP address must be known How to resolve hostnames to IP ? ? ? addresses Domain Name Service Example application (contd.) D N S W W W DNS Client/Server Exchange D N S Reque st W W W Tell me the IP address of www.niit.edu.pk? DNS Client/Server Exchange D Repl N y S W W W The IP address of www.niit.edu.pk is 202.125.157.196  Example application (contd.) 2 Which application at webserver must process this packet? In TCP/IP, each well-known application is identified using ports. The port of DNS is 53; HTTP is 80; SMTP is 25. In our considered example, HTTP server application (port 80) Source Port | Destination Port |would GET process the packet. / HTML/1.1 > 1024 | 80 |  Example application (contd.) The destination IP address (found through DNS) is 202.125.157.196. Let’s assume the source IP address is 202.125.157.150 (network must be same; to be explained later) Source IP | Destination IP | Source Port | Destination Packet so far: Port | GET / HTML/1.1 202.125.157.150 | 202.125.157.196 | > 1024 | 80 | Logical addressing: network and host parts *Assuming /24 subnet mask (to be explained  Example application (contd.) 3 How to send the created packet to Webserver? To communicate with any host, its physical address (called MAC address) must be known. ? ? How to resolve IP addresses to MAC addresses Address Resolution Protocol (ARP) ARP Client/Server Exchange D N S Reque st W W W Any one knows the MAC (physical) address of ARP Client/Server Exchange D N S W Repl W y W The MAC address of 202.125.157.196  Example application (contd.) Now that the physical (MAC) addresses are known, communication can take place The destination MAC address is 12:34:aa:bb:cc:dd The source MAC address (let’s assume) is 23:34:aa:bb:cc:dd Source IP | Destination IP | Source Port | Destination Port | GET / HTML/1.1 IP packet containing the data| 202.125.157.150 | 202.125.157.196 | > 1024 80 | Source MAC address | Destination MAC Payload FCS address MAC frame Encapsulation This topic is to be studied in more depth next lecture Application GET / HTML/1.1 data Source Port | Payloa TCP Destination Port d Segment > 1024 80 | IP Packet Source IP | Payloa Destination IP d MAC 202.125.157.150 | Frame 202.125.157.196 Source MAC address | Destination Payload FCS MAC address 23:34:aa:bb:cc:dd | 12:34:aa:bb:cc:dd HTTP Client/Server Exchang D N S Reque st W W W Send me the index.html page for the host www.niit.edu.pk using HTTP Client/Server Exchang D N S W Repl W y W The index.html page in the wwwroot directory configured for the www.niit.edu.pk webserver is sent  e’ ur c t L e s ary m of u m p e s S t y s i c b a s e d c u s d i s i a ; ’v e e d ) e k m k ) a W o r ; o r 1 e t w i e s ) e tiwn g on ta n l o g 2 re s ns lut i d a p o s ; ) d d s o o f t o me s. 3 a e r e p l e c h e u e ) a m a m s n i q 4 n e x c h a n te d i e d n a s tu wee ’v e b et b) We er er  x t Ne u r e c t Le Internetworkin g Interconnecting multiple networks Hierarchical addressing; Routing; Encapsulation/ References layered (today’s and next communication lecture): “Networking basics” and “Data ?? s / o n ? s t i s ? u e o n Q fusi C o n