Networking Systems (1)

Department of Computer EngineeringUniversity of California at Santa Cruz

Networking Systems (1)

Hai Tao


LANs, MANs, and WANs

LANs (Local area networks)• Extension over a local area typically within a few kilometers

• Usually owned by a single organization

• High data rate

• The number of stations connect to a LAN is usually less than 100

• Usually is based on broadcasting channels

• Some examples include Ethernet, Token Ring, Fiber Distributed Data Interface (FDDI), local ATM (asynchronous transfer mode) networks

MANs (Metropolitan Area Networks)• Covers an entire city with LAN technology

• Shared medium and distributed access control


LANs, MANs, and WANs

WANs (Wide Area Networks)• Typically span entire countries

• Point-to-Point communication

• Example: Internet


LANs, WANs, Layers, Protocols, and Services

Services provides a set of applications for the requesting application

Logically related services are grouped into layers• Each layer is a service provider to the layer lying above

Protocol consists of rules followed by two peers during any communications• Define protocol data units (PDU) in terms of format (syntax) and

meaning (semantics)


ISO-OSI Reference Model

(SearchNetworking.com)


Layers in ISO-OSI Reference Model

Physical Layer• Transmission method of individual bits over the physical medium

such as fiber optics, cables, phone lines, etc

• Concern with modulation, delay, etc

Data Link Layer• Transmission of data frame (block)

• Access protocols to the physical medium

• Error and recognition correction

• Flow control and block synchronization


Data Link Layer

Medium access protocol• Multi-access channels

- Medium access control (MAC) to determine access from competing parties+ Very important in LANs+ Timed Token Rotation Protocol+ Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

• Point-to-Point connection


Network Layers

Transports data packets from one station to another Provide services such as addressing, internetworking, error

handling, congestion control, packet sequencing For continuous media data, resource reservation and

guarantees for through put can be achieved using Quality of Service (QoS) parameters


Transport Layers

Provides process-to-process connection Bridge the gap between the requested transport and the

provided services from network layers Some functionalities include

• Divide and assemble packets

• Error handling between process (e.g. TCP)


Session Layer, Presentation Layer, and Application Layer

Session layer - Guarantee the existence of connection during a session• Point-to-point session

• Multi-cast session – a connection with many destinations

• Multi-drop session – a connection with many sources

Presentation layer – Definition, abstraction, and conversion of various data exchange formats• Examples: HTTP, TELNET, FTP, POP

Application Layer – Various applications based on the presentation layer (See figure for an example)


LANs - Ethernet

Bandwidth increases dramatically: 10Mbps to 100Mbps to 1GMbps to 10 Gbps

Bus-based network

Three kinds of Ethernet cabling.

(a) 10Base5, (b) 10Base2, (c) 10Base-T.


LANs - Ethernet

A simple example of switched Ethernet.


LANs - Ethernet

Cable topologies. (a) Linear, (b) Spine, (c) Tree, (d) Segmented.


LANs - Ethernet

(a) A two-station Ethernet. (b) A multistation Ethernet.


LANs - Ethernet

Using CSMA/CD protocol to solve the multiple access problem • Sender station checks the network state (Listen)

• Only send data when no other stations are transmitting data (Send)

• When multiple stations send data simultaneously, sending stations detect collisions by finding errors in their own data

• If collision detected, wait for randomly computed time and transmit again


Ethernet and Continuous Media

Ethernet does not explicitly guarantee end-to-end delay To transmit continuous media data on the Ethernet, several

methods can be used• Using fast Ethernet – end-to-end delay can be long if the network

is congested, using fast Ethernet will solve this problem under most situations

• Dynamic adaptation – Change the data rate of the media data according to the network load

• Dedicated Ethernet for media data – one network for discrete date, one network for continuous data


LANs – Token Ring

All stations are connected to a logical ring A special bit pattern (3Bytes) called a token circulate in

the ring A sender station will capture the token and break the ring.

The station sends the data in data frames. Each frame include sender address and destination address

Connect the ring once the transmission is finished A multiple priority scheme is used to control the network

access


LANs – Local ATM Networks

Asynchronous Transfer Mode use fixed length packet (cell)

ATM allows systems to operate at higher rate because• No error protection or flow control on a link-to-link basis (but can

be done in higher layers)

• Operate in connection oriented mode with a setup phase for resource reservation

• Information field is small to reduce the internal buffers in the switching nodes


WANs

Internet – DARPA experiment in 1973, see table 1 for illustration

Interconnection devices• Source and destination are connected by a sequence of

interconnection devices (packet switches)

• Packet switches cooperatively compute the path in the network. They are called routers in network layer

• Routing protocols- Distance vector – each router keeps tracking and informing its

neighbors of its distance to each destination. Slow propagation.

- Link State - Each router determines the identities of its neighbors and the associated distance and constructs link state packet (LPS). LPS is sent to all all the other routers

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Networking Systems (1)

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