Telecommunications Network Management
Types of Networks

Choosing a Network

•	1st -- what is your business need?
•	2nd -- think about architecture
•	internet connecting LANs?
•	centralized, hierarchical WAN?
•	can you use public switched network and/or Internet?
•	combinations of all?
•	what can be outsourced?

Classification of Networks

•	Type of information transmitted
•	voice; data; special purpose; multimedia
•	Type of underlying technology
•	cable; microwave; satellite
•	Type of ownership
•	public; private; semipublic, semiprivate VAN
•	Geographic scope
•	LANs; MANs; WANs; International
•	Type of topology
•	star; bus; ring; mesh; hybrid LAN; backbone

Type of Information Transmitted

•	Once, networks were dedicated to one particular type of information
•	public telephone system was only voice
•	private networks were separate for voice, data, and video
•	In recent years, public systems handle voice, fax, e-mail and file transfer
•	Current trend is away from classifying networks by type of information

Type of Underlying Technology

•	Type of switching method
•	packet-switched, circuit-switched, tandem-switched
•	Type of transmission media
•	fiber-optic, satellite, microwave
•	Currently, trend is away from classifying by underlying technology
•	increasing use of mixed media and mixed technology within one network

Type of Ownership

•	Public (owned and managed by authorized common carriers): AT&T
•	Private (owned and managed by private companies), but still leases long distance transmission and local access
•	Semi-public (VANs: value-added networks): Yahoo, Google
•	Semi-private (VPNs: virtual private networks, and SDNs: software-defined networks)
•	Relatively prevalent classification

Geographic Scope

•	Local area network (LAN) -- high speed client/server or contention data network in no larger than a campus environment
•	Metropolitan area network (MAN) -- high speed voice and data network that links LANs throughout a metropolitan area -- often used to “bypass” local providers
•	Wide area network (WAN) -- regional, national or international network transmitting full range of information at 9600 bps to 1.544 mbps (T1), or maybe 45 mbps (T3), or maybe more (OC?) and Gigabit Ethernet

Type of Topology

•	Topology -- the physical configuration of the various nodes and the manner in which they are linked -- generally used to describe LANs and satellite networks
•	Almost all networks, except for the smallest LANs, are mixtures of various topologies
•	In most LANs, the topology is not physical, but virtual -- it’s a card contained in the wiring hub

Star Topology

•	All terminals connect directly to a central node -- host computer or file server
•	Facilitates central control and reduces the need for intelligence in terminals
•	Central node may become overloaded at peak periods or otherwise fail
•	Used in some LANs, but best suited for VSAT network applications -- remote nodes are simple and easy to use

Mesh Topology

•	Ideally, all nodes are directly connected to each other
•	Best solution from a performance standpoint -- lower response time and reduced chance of errors
•	As the number of nodes increases, the cost of the network becomes prohibitive
•	Most mesh networks directly link only the major nodes in the network

Hierarchical Topology 

•	Similar to a layered organizational chart
•	End-user nodes are linked to lower-level intermediate nodes, which are linked to higher-level nodes, and so on
•	Number of layers determined by overall size of network
•	Tradeoff: performance vs. efficiency 
•	Best example is the public switched telephone network

Bus Topology

•	Uses a single length of guided transmission medium -- the bus
•	Terminals are connected directly to the bus -- no single point of control
•	Provides for high transmission speeds, but only for a limited distance -- thus, usually found only in LANs
•	In its purest form, difficult to find points of failure, but one failure generally doesn’t affect the network

Ring Topology

•	Similar to a bus network, except the ends of the bus are connected to form a continuous loop
•	Each terminal regenerates the signal, which eliminates attenuation and allows for a much larger network
•	Failure of just one node will cause the network to crash
•	Solution is to have parallel rings transmitting in opposite directions

Local Area Networks

•	Basic LAN concept:  real-time interconnection of end-user devices in a local environment for the purpose of sharing information, files, software, and hardware peripheral devices.

•	Three factors in LAN development
•	powerful and inexpensive PCs
•	failure of IS departments to meet the applications needs of workgroups
•	the need to share software, files and peripheral devices among users
•	Key feature:  all end-user devices are given equal status -- no slave/host or hierarchical arrangements -- distributed processing power through low-cost PCs

Characteristics of LANs

•	No common carrier involvement
•	Customer owned and maintained
•	Supports users with:
•	services, applications, data
•	access to and from the LAN
•	peripheral sharing
•	flexible expansion
•	heterogeneous products
•	Requires strategy to plan and manage

LAN Technology

•	Three broad categories of LANs
•	circuit-switched -- PBXs and data switches, based on a star topology, but not usually spoken of as a LAN
•	broadband -- multiplexed, multichannel analog transmission incorporates voice, data, video
•	baseband -- workstations connected directly to a transmission medium -- one or more nodes are designated as general purpose or specialized servers
•	Entire bandwidth is dedicated to each transmission
•	Creates potential for congestion and interference among transmissions
•	Therefore, transmission speeds must be high and there must be a way to manage access to the network
•	Must also be a structure for specifying standards, including naming and addressing devices, provision of network services, and methods for connection
•	The big two: Ethernet and Token Ring

Ethernet LANs

•	Developed by Xerox Corporation
•	Operates in a broadcast mode
•	Architecture corresponds to layers one and two of the OSI model
•	Layer 1 (physical interface) is the plug in the socket
•	Layer 2 (data link) -- two sublayers
•	logical link control (LLC) -- typical data protocol
•	medium access control (MAC) -- manages access to the network
•	Standard: IEEE 802.3: CSMA/CD
•	Access to the shared medium is performed by system called Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
•	Effective when traffic is light, but slows the network down when traffic is heavy
•	Therefore, CSMA/CD is inappropriate for applications that require uniform access time
•	Ethernet architecture specifies:
•	topology -- bus
•	medium -- coaxial cable, twisted pair or fiber operating at 10 mbps or 100 mbps or more
•	Physical configuration is not the same as logical configuration -- all nodes connected directly to a hub
•	Easier to isolate the location of network faults

Token Ring LANs

•	Developed by IBM
•	IEEE 802.5: Token Passing Ring
•	Similar to the Ethernet architecture in the physical and LLC layers, but totally different in the MAC layer
•	Electronic token (certain sequence of bits meaning the network is available) is passed to each node
•	When a node transmits, the bit sequence is changed to mean “unavailable” -- then only that node has a transmission on the network
•	Lower variability in response time, even at peak traffic
•	Response time is a function of number of nodes and average message size
•	Token ring architecture specifies:
•	ring topology
•	shielded twisted pair at 16 mbps, or
•	unshielded twisted pair at 4 mbps
•	Logical architecture contained on the NIU card, actual is a star configuration

Fiber Distributed Data Interface

•	Developed to provide very high speed LANs and backbone links 
•	FDDI architecture specifies:
•	token passing
•	ring topology with two rings transmitting in opposite directions at 100 mbps
•	medium is generally optical fiber
•	Enables prioritized workstations
•	Enables larger network -- up to 200 km
•	Makes networked multimedia possible

Performance Tradeoffs

•	Ethernet -- simplest and least expensive, but variable and sometimes slow response if there are a large number of users
•	Token Ring -- reliable and less variable response, but more complex and expensive than Ethernet -- failure of a station or break in the ring without backups can bring down entire network
•	FDDI -- clearly better and much faster responsiveness with backups built in
•	ATM -- the promise never realized

Wide Area Networks

•	Private or semi-private networks whose reach extends beyond a metro area
•	Regional, national, or international
•	May be restricted to one medium or may be a mix of media -- one type of info or voice, data, and audio/video
•	Trend is towards high capacity, digital backbone links that interconnect LAN subnetworks and provide long distance integrated voice, data, and video

WAN Technology and Services

•	Typical private network historically incorporated leased T1 (1.54 mbps) or fractional T1 (increments of 56 or 64 kbps) lines
•	Whenever possible, fast packet (frame and cell relay) switching and trans-mission methods are incorporated
•	Trend is toward SDN/VPN systems
•	more efficient use of carrier facilities
•	more flexible and easily modified
•	less expensive than leased lines
•	company has control, but carrier has responsibility for operations

Public Switched Networks

•	Oldest, and once the only, form of net
•	Once, each country had only one public switched network
•	Had to be used by everyone -- at tariffed prices, but couldn’t be all things to everyone, which limited the available services
•	Flexible, high-speed networks have changed that, along with a trend toward outsourcing telecommunications

PSN Technology and Services

•	Trend from analog to digital has brought:
•	Basic access ISDN -- 2B + D
•	two 64 kbps bearer channels
•	one 16 kbps signaling (delta) channel
•	available in homes and offices w/ 2X wire
•	Primary access ISDN -- 23B + D
•	23 64 kbps bearer channels
•	one 16 kbps signaling (delta) channel
•	almost the capacity of a T1 circuit
•	Asymmetric Digital Subscriber Line (ADSL)
•	There are a variety of xDSL services for home and business
•	The next step is BISDN (broadband integrated digital services network)
•	transmission speeds of 500 mbps and up
•	includes standards for SONET and ATM
•	Also happening:
•	frame relay (1.54 mbps and up) has replaced X.25 (64 kbps)
•	local carriers are instituting switched multimegabit data services (SMDS), a fast packet, cell relay service similar to ATM  

Trends in Networks

•	Distributed processing and client/server models of computing
•	supported by LANs and internets of LANs connected through backbone WANs
•	further integration of high speed switching
•	Development of the BISDN
•	the universal information utility -- full reach, range, and responsiveness on demand in the home, office, or on the move.