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NETE0510Network and Protocol

Architecture

Supakorn Kungpisdan

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Outline

RequirementsNetwork ArchitecturePerformance

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Links, Nodes, and Clouds

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Switched Network

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Switched Network (cont’d)

Circuit-switched network: telephone system Establish a dedicated circuit across a sequence of links

Packet-switched network: data network Store-and-forward Packet or message

Efficiency of circuit-switched VS packet-switched networks

Cloud: any type of network e.g. point-to-point, multiple access, switched

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Internetwork

A set of independence networks are interconnected to form an internetwork

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Internetwork (cont’d)

Internet VS internet Router or gateway:

a node connecting to two or more networks Address:

a byte string that identifies a node; used to distinguish a node from others

Routing A process of determining systematically how to forward

messages toward the destination node based on its address

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Unicast, Multicast, Broadcast

Unicast: a source node sends a message to a single destination node

Broadcast: a source node sends a message to all the nodes on the network

Multicast: a source node sends a message to some subset of nodes

Network: two or more nodes connected by a physical link, or Two or more networks connected by a node

A large message is divided into packets Why?

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Cost-effective Resource Sharing Efficiency How do all the hosts that want to communicate at the

same time share the network? Multiplexing : a system resource is shared among multiple

users Analogous to time sharing computer: CPU is shared among

multiple job Multiplexing Techniques

Synchronous Time-Division Multiplexing (STDM) Frequency-Division Multiplexing (FDM)

Same concept as TV transmission Statistical Multiplexing

Share physical link only when more than one node transmit data at the same time

Transmit data on demand rater than during a predetermined time slot

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Multiplexing

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Switch Multiplexing Packets

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Switch Multiplexing Packets (cont’d)

Switch makes decision on a packet-by-packet basis FIFO Round robin STDM Quality of Service (QoS)

Congestion Switch receives packets faster than the share link can

accommodate need a buffer Running out of buffer packet loss

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Additional Benefits of Statistical Multiplexing

Cost effective for multiple users to share network resources Define the packet as the granularity with which the links

of the network are allocated to different flows Decide the flow with per packet basis Fairly allocating capacity to different flows Dealing with congestion when it occurs

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Support for Common Services

Network supports application-level processes to communicate with each other Viewed as logical “channel”

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Support for Common Services (cont’d)

What functionality the channels should provide to application programs? Delivery guarantee? In-order delivery? Secure from eavesdropping? Etc.

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Identifying Common Communication Patterns

Two general types of channels Request/reply channel

Used in file transfer and digital library apps Need security/privacy protection

Message stream channel Used in video-on-demand and videoconferencing apps No 100% delivery guarantee, but in-order Unicast/multicast/broadcast

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Reliability

3 classes of failures Bit errors or burst errors

Occurred from outside forces e.g. lightning strikes, power surges, and microwave ovens

Rare 1/106-107 bits on copper-based cable and 1/1012-1014 bits on optical fiber

Packet errors Packet loss because there are bit errors Congestion Software error e.g. forward packet to the wrong link

Node and link errors Physical link is cut, computer crashes by software, power failure Need time to fix

Need to understand application’s requirements and recognize limitations of underlying technology

Semantic gap: the gap between that application expects and what the underlying technology can provide

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Outline

RequirementsNetwork ArchitecturePerformance

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Network Architecture

A network must provide general, cost-effective, fair, and robust connectivity among a large number of computers

Network architecture: a general blueprint that guide design and implementation of networks OSI and Internet (TCP/IP) architecture

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Layering and Protocols

When the system gets complex, abstraction is needed Abstraction leads to layering Start by services offered by the underlying hardware and

then add a sequence of layers of services The services provided at the higher layers are

implemented in terms of the ones provided by the low layers

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Layering

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Protocols

Protocols: abstract objectives that make up the layers of a network system

Protocol provides a communication service that higher-level objects use to exchange messages

Each protocol defines two different interfaces: Service interface to other objects on the same computer Peer interface to another computer

Indirect communications: protocol in each layer passes a message to lower layer-protocol which in turn deliver the message to its peer

Multiple protocols provide a different communication service Protocol graph: a suite of protocol that make up a network

system

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Protocols (cont’d)

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Example of Protocol Graph

Request/Reply Message Stream

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Encapsulation

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OSI Architecture

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OSI Architecture (cont’d)

Physical layer: handle the transmission of raw bits over a communications link

Data-link layer: collect a stream of bits into a large aggregate called a frame

Network layer: handle routing among nodes within a packet-switched network.

Transport layer: implement a process-to-process channel Session layer: provide a name space used to tie together the

potential different transport streams Presentation layer: concern with the format of data exchanged

between peers Application layer: include network applications

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OSI Model Analogy

Create document (paper + pen, pencil, etc, used for separate rooms)

Translate, arrange format (dictionary, translator)

Doorman, enter and leave the room Check document condition and bring

document to each room (port number) living room (80), dining room (21), art studio (23)

Postal address (IP address) front door , post office

How to deliver document trucks, ships, planes (ID card = MAC address))

Street, ocean, air

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Ethernet and the OSI Model

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Network Layer Devices in Data Flow

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Internet (TCP/IP) Architecture

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TCP/IP Layers

no official model but a working one Application layer Host-to-host, or transport layer Internet layer Network access layer Physical layer

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concerned with physical interface between computer and network

concerned with issues like: characteristics of transmission medium signal levels data rates other related matters

Physical Layer

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exchange of data between an end system and attached network

concerned with issues like : destination address provision invoking specific services like priority access to & routing data across a network link between

two attached systems

Network Access Layer

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routing functions across multiple networks for systems attached to different networks using IP protocol implemented in end systems and routers routers connect two networks and relays data

between them

Internet Layer (IP)

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Transport Layer (TCP)

common layer shared by all applications provides reliable delivery of data in same order as sent commonly uses TCP

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Application Layer

provide support for user applications need a separate module for each type of

application

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OSI v TCP/IP

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Operation of TCP and IP

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Addressing Requirements

two levels of addressing required each host on a subnet needs a unique global

network address its IP address

each application on a (multi-tasking) host needs a unique address within the host known as a port

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Operation of TCP/IP

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Transmission Control Protocol (TCP)

usual transport layer is (TCP) provides a reliable connection for transfer of

data between applications a TCP segment is the basic protocol unit TCP tracks segments between entities for

duration of each connection

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TCP Header

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an alternative to TCP no guaranteed delivery no preservation of sequence no protection against duplication minimum overhead adds port addressing to IP

User Datagram Protocol (UDP)

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UDP Header

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IP Header

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IPv6 Header

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TCP/IP Applications

have a number of standard TCP/IP applications such as Simple Mail Transfer Protocol (SMTP) File Transfer Protocol (FTP) Telnet

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Some TCP/IP Protocols

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Features of Internet Architecture

Does not imply strict layering Free to bypass the defined transport layers and directly use IP or

one of the underlying networks Hourglass shape

IP serves as the focal point of the architecture – common method for exchanging packets among a wide collection of networks

(According to IETF) If someone propose a new protocol to be included in the architecture, they must produce both a protocol specification and representative implementation of the specification Ensure that the protocols can be efficiently implemented

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Outline

RequirementsNetwork ArchitecturePerformance

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Bandwidth

Bandwidth: the number of bits that can be transmitted over the network in a certain period of time Bandwidth of a single physical link Bandwidth of a logical process-to-process channel

At the physical level, transmitting 1 bit of data on a 1-Mbps link takes 1 µs

For logical process-to-process channels, bandwidth is also influenced by other factors

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Latency

Latency: time taken a message to travel from one end of a network to the other E.g. transcontinental network has a latency of 24 ms.

Round-trip Time (RTT): time taken to send a message from one end of a network to the other and back

Components of latency: Speed-of-light propagation delay:

3 x 108 m/s in a vacuum, 2.3 x 108 m/s in a cable, 2 x 108 m/s in a fiber

Transmission delay: time taken to transmit a unit of data Queuing delay

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Latency (cont’d)

TotalLatency = Propagation + Transmit + Queue Propagation = Distance/SpeedOfLight Transmit = Size/Bandwidth

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Delay X Bandwidth Product

A channel where latency is the length of the pipe and the bandwidth is diameter of the pipe Then the product gives the volume of the pipe the number

of bits it holds

E.g. a transcontinental channel with a one-way latency of 50 ms and a bandwidth of 45 Mbps is able to hold 50 x 103 s x 45 x 106 bps = 2.25 x 106 bits or approx 280 KB

Important when constructing high performance networks because it tells how many bits the sender must transmit before the first bit arrives at the receiver.

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Delay X Bandwidth Product (cont’d)

The sender sends 2 delay X bandwidth of data before hearing from the receiver

The bits are said to be “in flight” If the receiver tells the sender to stop transmitting, it will

takes up to a delay X bandwidth before the sender can respond. Takes 5.5 x 106 bits (671 KB) of data

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Questions?

Next LectureIntroduction to Transmission

Technologies