Review of Topology and Access Techniques / Switching Concepts BSAD 141 Dave Novak Sources: Network+ Guide to Networks, Dean 2013

Overview Three base wired topologies Bus, star, ring Two wireless topologies Ad-hoc, infrastructure Three basic access techniques CSMA/CD, CSMA/CA, and token passing Packet switching versus circuit switching

Architecture Basic level – any topology will support any architecture Star topology may support client – server (CS) or peer-to-peer (P2P) architecture Likewise, P2P architecture may be implemented using star, bus, or ring topology

Architecture / Topology Topology –physical or logical design or layout of the network What is the difference between a physical star and logical star topology? Architecture – describes the functionality and administrative structure of the network How devices interact Whether there are servers and exactly what these devices do

Access Technique The access technique describes how the devices using a particular networking technology coordinate the use of, or share, the communication medium How is CSMA and how does it work?

Access Technique What about CSMA/CD? CSMA/CA?

Access Technique Token Passing?

Packet Concept Computer networks do not transfer data as a string or stream of continuous bits Bits or data are divided into small generic blocks called packets Dividing data into small packets helps determine which blocks have errors and which do not Packets promote equity

Packets –vs- frames What is the difference between a packet and a frame?

Switching Determines how connections are established between different nodes on the network Focus on 2 types of switching 1) 2)

Switching Many / most LAN technologies use baseband communication Why would this generally be the case?

Switching To enable many devices to share the medium, transmission data are broken up into packets

Circuit switching A connection-based telecommunications transmission technology where 2 nodes establish a dedicated connection / communication channel for the duration of the communication session Requires that the sending node contact receiving node and establish a connection (what is a potential drawback to this type of connection?)

Circuit switching Concept is a dedicated path that provides non- stop transfer Bandwidth on circuit is dedicated and remains available until connection is terminated Not shared While nodes connected, all data follow same path Data arrive in order

Circuit switching Misconception that circuit switching only used for connecting voice circuits (either analog or digital)

Advantages of Circuit Switching Dedicated connection between 2 hosts – full use of communication channel for duration of communication session Highly reliable (with respect to path, variation in delay, and constant bit rate) Requires little packet overhead during transmission because path / communication circuit is dedicated and known Makes optimal use of available bandwidth (ratio of overhead to data is very small) during communication

Disadvantages of Circuit Switching Inflexible with respect to many internet-based applications (data are bursty) Involves a lot of communication overhead and time with respect to ESTABLISHING communication channel Can waste a lot of bandwidth if data are not continually being sent In event of failure, data are not packetized and do not seek an alternate path – path may be lost

Packet switching A digital networking communication method where data are broken into small packets Delivers variable rate data streams During transmission packets are buffered and queued which leads to variable delay and throughput No communication is needed with receiving node ahead of time - asynchronous

Packet switching Two modes 1) Connectionless (datagram) 2) Connection-based (virtual circuit) Implication is that data-oriented, digital, packet-switched networks can take advantage of both connectionless and connection-based transfer

Packet switching 1) Connectionless (datagram concept) Asynchronous communication – no coordination Each packet much include complete routing information because each packet can be routed individually Out-of-order delivery, different paths

Packet switching 2) Connection-based (virtual circuit concept) Protocols establish a connection between sender and receiver A connection is established via software rather than physically Connection set up and torn down as needed Packets include connection identifier Packets are typically delivered in order

Advantages of Packet switching Bandwidth from end-to-end is optimized Unused circuits are torn down and reallocated Supports variable data transfer rates In event of failure, packets can reroute Designed to support bursty data transfer

Disadvantages of Packet switching Variable delay Packets can be lost or corrupt Sophisticated protocols are needed to provide some level of reliability during transfer Not good for certain types of applications that require constant bit rates, limited variation in delay, or no data loss (e.g. real-time video)

Distance limitation and LANs Distance is a fundamental consideration in the design of any network – particularly LAN technologies Why?

LAN extension Why cant the length of an Ethernet network continually be increased adding new segments using hubs or repeaters?

Ethernet and Delay CSMA/CD (and CSMA/CA for that matter) designed to function with limited latency Scheme fails if length is too long or too many segments are connected Serious performance problems if you string a bunch of Ethernet segments together with repeaters

Summary Three base wired topologies Bus, star, ring Two wireless topologies Ad-hoc, infrastructure Three basic access techniques CSMA/CD, CSMA/CA, and token passing Packet switching versus circuit switching