Advanced Computer Networks: Lecture 3 - Dr. Amir Qayyum

Advanced Computer Networks: Lecture 3. This lecture will cover the following: protocol machinery; message transmission using layers; open system interconnect (OSI) architecture; TCP/IP architecture; protocol acronyms; elements of a protocol implementation; network application programming interface (API);...

CS716 Advanced Computer Networks By Dr. Amir Qayyum Lecture No. 3  Protocol Machinery Multiplexing and Demultiplexing (demux key) Encapsulation (header/body) in peer­to­peer interfaces indirect communication (except at hardware level) each protocol adds a header part of header includes demultiplexing field (e.g., pass up to  request/reply or to message stream?) Encapsulation Host Host Application program Application program Data Data RRP RRP RRP Data RRP Data HHP HHP HHP RRP Data Message Transmission Using Layers Standard Architectures • Open System Interconnect (OSI) Architecture – International Standards Organization (ISO) – International Telecommunications Union (ITU),  formerly CCITT – “X dot” series: X.25, X.400, X.500 – Primarily a reference model       OSI Architecture End host End host User  level OS  kernel Application Application Application Presentation Presentation Data formatting Session Session Connection management Transport Transport Process­to­process  communication channel Network Network Network Network Data link Data link Data link Data link Physical Physical Physical Physical Host­to­host packet  delivery Framing of data bits Transmission of raw bits One or more nodes within the network Internet Architecture • TCP/IP Architecture – Developed with ARPANET and NSFNET – Internet Engineering Task Force (IETF) • Culture: implement, then standardize • OSI culture: standardize, then implement – Became popular with release of Berkeley Software  Distribution (BSD) Unix; i.e. free software – Standard suggestions traditionally debated publically  through “Request For Comments” (RFC’s) Internet Architecture • Implementation and design done together • Hourglass Design (bottleneck is IP) • Application vs Application Protocol (FTP, HTTP) FTP HTTP NV TFTP UDP TCP IP NET1 NET2 … NETn Internet Architecture • Layering is not very strict Application TCP UDP IP Network 10 Protocol­to­Protocol Interface • A protocol interacts with a lower level  protocol like an application interacts with  underlying network • Why not using available network APIs for  PPI ? – Inefficiencies built into the socket interface • application programmer tolerate them to  simplify their task – inefficiency at one level • protocol implementers do not tolerate them 23 Protocol­to­Protocol Interface Issues • Configure multiple layers – static versus extensible • Process Model – avoid context switches • Buffer Model – avoid data copies 24 Process Model procedure  call inter­process  communication (a) Process­per­Protocol (b) Process­per­Message 25 Process Model (cont.) TCP send(IP, message) deliver(TCP, message) IP int send(Protocol llp, Msg *message) int deliver(Protocol hlp, Msg *message) 26 Buffer Model Application process buffer copy buffer copy send() deliver() Topmost protocol 27 Message Library • Add header m • Strip header m abcdefg abcdefg bcopy (“ xyz” , hdr , 3); msgAddHdr (m, hdr, 3); hdr =msgStripHdr (m, 3); m m defg + hdr = “ abc” xyzabcdefg 28 Message Library (cont) • Fragment message m m1 abcdefg m + m2 abcd msgFragment (m, new, 3); new defg • Reassemble messages abc efg msgReassemble(new, m1, m2) new abcdefg 29 Network Programming • Things to learn – Internet protocols (IP, TCP, UDP, …) – Sockets API (Application Programming Interface) • Why IP and sockets • allows a common name space across most of  Internet – IP (Internet Protocol) is standard • reduces number of translations, which incur  overhead – Sockets: reasonably simple and elegant Unix  interface (most servers run Unix) 30 OSI Model application layers Internet Protocols FTP network physical NV TFTP UDP TCP transport data link HTTP IP FDDI Ethernet … ATM 31 Programming transport network • learn to use Internet for  communication (with  focus on implementation  of networking concepts) data link physical Principles  and concepts • learn to build network  from ground up 32 Socket Programming • Reading: Stevens 2nd edition, Chapter 1­6 • Sockets API: a transport layer service interface – – – – introduced in 1981 by BSD 4.1 implemented as library and/or system calls similar interfaces to TCP and UDP can also serve as interface to IP (for super­user);  known as “raw sockets” – Linux also provides interface to MAC layer (for super­ user); known as “data­link sockets” 33 Outline • • • • • • Client­server model TCP connections UDP services Addresses and data Sockets API Example of usage 34 Client­Server Model • Asymmetric relationship • Server/daemon – well­known name – waits for contact – process requests, sends  replies • Client server client client client – initiates contact – waits for response 35 Client­Server Model • Bidirectional communication channel • Service models – sequential: server processes only one client’s requests at  a time – concurrent: server processes multiple clients’ requests  simultaneously – hybrid: server maintains multiple connections, but  processes requests sequentially • Server and client categories not disjoint – server can be client of another server – server as client of its own client (peer­to­peer  architecture) 36 Review Lecture 3 • • • • • • • • Protocol Machinery ­ Encapsulation Standard architectures: OSI, Internet Network models and layering Elements of protocol implementation Network software Network API – Socket API – PPI Process and buffer model Programming – Client server model 37 ... hdr , 3) ; msgAddHdr (m, hdr, 3) ; hdr =msgStripHdr (m, 3) ; m m defg + hdr = “ abc” xyzabcdefg 28 Message Library (cont) • Fragment message m m1 abcdefg m + m2 abcd msgFragment (m, new, 3) ; new... user); known as “data­link sockets” 33 Outline • • • • • • Client­server model TCP connections UDP services Addresses and data Sockets API Example of usage 34 Client­Server Model • Asymmetric relationship... server can be client of another server – server as client of its own client (peer­to­peer  architecture) 36 Review? ?Lecture? ?3 • • • • • • • • Protocol Machinery ­ Encapsulation Standard architectures: OSI, Internet