Advanced network architecture ppt

advanced network architecture ppt and cdma network architecture diagram ppt and network management architecture ppt
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Dr.ShivJindal,India,Teacher
Published Date:19-07-2017
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Review of Networking and Design Concepts (I) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1Overview  Connectivity:  direct (pt-pt, N-users),  indirect (switched, inter-networked)  Concepts: Topologies, Framing, Multiplexing, Flow/Error Control, Reliability, Multiple-access, Circuit/Packet- switching, Addressing/routing, Congestion control  Data link/MAC layer:  SLIP, PPP, LAN technologies …  Interconnection Devices  Chapter 1,2,11 in Doug Comer book  Reading: Saltzer, Reed, Clark: "End-to-End arguments in System Design"  Reading: Clark: "The Design Philosophy of the DARPA Internet Protocols": Shivkumar Kalyanaraman Rensselaer Polytechnic Institute  Reading: RFC 2775: Internet Transparency: In HTML 2Connectivity...  Building Blocks links: coax cable, optical fiber... nodes: general-purpose workstations...  Direct connectivity: point-to-point multiple access Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 3Connectivity… (Continued)  Indirect Connectivity switched networks = switches inter-networks = routers Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 4What is “Connectivity” ?  Direct or indirect access to every other node in the network  Connectivity is the magic needed to communicate if you do not have a link. Tradeoff: Performance characteristics worse Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 5Connectivity …  Internet: Best-effort (no performance guarantees) Packet-by-packet  A pt-pt link: Always-connected Fixed bandwidth Fixed delay Zero-jitter Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 6Point-to-Point Connectivity Issues A B  Physical layer: coding, modulation etc  Link layer needed if the link is shared bet’n apps; is unreliable; and is used sporadically  No need for protocol concepts like addressing, names, routers, hubs, forwarding, filtering … Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 7Link Layer: Serial IP (SLIP)  Simple: only framing = Flags + byte-stuffing  Compressed headers (CSLIP) for efficiency on low speed links for interactive traffic.  Problems:  Need other end’s IP address a priori (can’t dynamically assign IP addresses)  No “type” field = no multi-protocol encapsulation  No checksum = all errors detected/corrected by higher layer.  RFCs: 1055, 1144 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 8Link Layer: PPP  Point-to-point protocol  Frame format similar to HDLC  Multi-protocol encapsulation, CRC, dynamic address allocation possible key fields: flags, protocol, CRC  Asynchronous and synchronous communications possible Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 9Link Layer: PPP (Continued)  Link and Network Control Protocols (LCP, NCP) for flexible control & peer-peer negotiation  Can be mapped onto low speed (9.6Kbps) and high speed channels (SONET)  RFCs: 1548, 1332 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 10Reliability Mechanisms  Mechanisms:  Checksum: detects corruption in pkts & acks  ACK: “packet correctly received”  Duplicate ACK: “packet incorrectly received”  Sequence number: identifies packet or ack 1-bit sequence number used both in forward & reverse channel  Timeout only at sender  Reliability capabilities achieved:  An error-free channel  A forward & reverse channel with bit-errors  Detects duplicates of packets/acks  NAKs eliminated  A forward & reverse channel with packet-errors (loss) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 11Stop and Wait Flow Control t frame U= 2t +t prop frame t Data frame 1 = t prop 2 + 1 U Ack Data  Light in vacuum Ack = 300 m/s Light in fiber t Distance/Speed of Signal prop  = = = 200 m/s Frame size /Bit rate t frame Electricity Distance  Bit rate = 250 m/s = Frame size Speed of Signal Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 12Sliding Window Protocols Nt frame U= 2t +t prop frame t frame Data N t prop 2+1 = 1 if N2+1 Ack Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 13List of Issues  Connectivity (direct/indirect)  Pt-Pt connectivity: Framing Error control/Reliability (optional) Flow control (optional) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 14Connecting N users: Directly… A B  Pt-pt: connects only two users directly…  How to connect N users directly ? . . . Bus Full mesh  What are the costs of each option?  Does this method of connectivity scale ? Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 15Multiplexing vs Have it all  Multiplexing = sharing  Allows system to achieve “economies of scale”  Cost: waiting time (delay), buffer space & loss  Gain: Money () = Overall system costs less Full Mesh Bus Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 16Virtualization  The multiplexed shared resource with a level of indirection will seem like a unshared virtual resource  I.e. Multiplexing + indirection = virtualization A B . . . = A B Physical Bus Virtual Pt-Pt Link  We can “refer” to the virtual resource as if it were the physical resource. Eg: virtual memory, virtual circuits…  Connectivity: a virtualization created by the Internet  Indirection requires binding and unbinding… Eg: use of packets, slots, tokens etc Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 17Statistical Multiplexing  Reduce resource requirements (eg: bus capacity) by exploiting statistical knowledge of the system.  Eg: average rate = service rate = peak rate  If service rate average rate, then system becomes unstable First design to ensure system stability  Then, for a stable multiplexed system: Gain = peak rate/service rate. Cost: buffering, queuing delays, losses.  Useful only if peak rate differs significantly from average rate.  Eg: if traffic is smooth, fixed rate, no need to play games with capacity sizing… Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 18Stability of a Multiplexed System Average Input Rate Average Output Rate = system is unstable How to ensure stability ? 1. Reserve enough capacity so that demand is less than reserved capacity 2. Dynamically detect overload and adapt either the demand or capacity to resolve overload Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 19What’s a performance tradeoff ? • A situation where you cannot get something for nothing • Also known as a zero-sum game.  R=link bandwidth (bps)  L=packet length (bits)  a=average packet arrival rate Traffic intensity = La/R Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 20