combination of hardware and software that sends data from one location to another

Hardware consists of physical equipment that carries signals

Software consists of instruction sets that make possible the services that we expect from a network

International Standards Organization (ISO) introduced the Open Systems Interconnection model in the late 1970s

OSI model ISO/IEC 7498-1

Open system – a set of protocols that allows any two different systems to communicate regardless of the underlying architecture

OSI is not a protocol; it is a model for understanding and designing a network architecture that is flexible, robust, and interoperable

Physical

Data Link

Network

Transport

Session

Presentation

Application

1

2

3

4

5

6

7

Application

Application

Presentation

Presentation

Session

Session

Transport

Transport

Network

Network

Data Link

2 - 1 Interface

Physical​

Physical​

Data Link

3 - 2 Interface

4 - 3 Interface

5 - 4 Interface

6 - 5 Interface

7 - 6 Interface

Physical​

Physical​

Data Link

Data Link

Network

Network

7 - 6 Interface

6 - 5 Interface

5 - 4 Interface

4 - 3 Interface

3 - 2 Interface

3 - 2 Interface

3 - 2 Interface

2 - 1 Interface

2 - 1 Interface

2 - 1 Interface

D7

H7

D6

H6

D7

H7

H5

H4

H3

H2

H1

H6

H5

H4

H3

H2

H1

D6

Defines the connector and interface specifications as well as the medium (cable) requirements

Electrical, mechanical, functional and procedural specifications are provided for sending a bit stream on a computer network

Physical characteristics of interfaces and medium

Representation of bits - encoding

Data rate - number of bits sent each second

Synchronization of bits - timing

Line configuration – point-to-point, multipoint

Physical topology – bus, star, ring, mesh, hybrid

Transmission mode – simplex, half-duplex, duplex

Transforms the physical layer to a reliable link

Makes the physical layer appear error-free to the upper layer

Framing – defining frames

Physical addressing – defines sender/receiver

Flow control – prevents overwhelming the receiver

Error control – detect and retransmit damaged or lost frames, use of trailers

Access control – defines which device has control over the link when it is shared by devices

Source-to-destination delivery of packets, possibly across multiple networks

No need for network layer if two systems are connected to the same link

Logical addressing – distinguish source and destination systems if packets pass network boundary

Routing – makes possible the delivery of packets in internetworks, connecting devices are called routers and switches

Responsible for process-to-process delivery

Ensures that the whole message arrives intact and in order

Service-point addressing – several programs can use the network, uses ports

Segmentation and reassembly – message divided into transmittable segments (uses sequence numbers)

Connection control – maybe connectionless or connection-oriented

Flow control – end-to-end flow control rather than a single link

Error control – process-to-process flow control rather than single link

Network dialog controller

Establishes, maintains, and synchronizes interactions among communicating systems

Dialog control – dialog between two systems

Synchronization – add checkpoints

Concerned with the syntax and semantics of the information exchanged between two systems

Translation – apply encoding schemes

Encryption – provides privacy

Compression – reduce the number of bits contained in the information

Enables the user (human or software) to access the network

Provides user interfaces and support services: email, remote file access and transfer, shared DBM, distributed information services

Network virtual terminal – software version of a software terminal

File transfer, access, and management – access files remotely

Mail services – email forwarding and storage

Directory services – distributed database sources

To transmit bits over a medium; to provide mechanical and electrical specifications

To organize bits into frames; to provide hop-to-hop delivery

To move packets from source to destination; to provide internetworking

To provide reliable process-to-process message delivery and error recovery

To establish, manage and terminate sessions

To translate, encrypt and compress data

To allow access to network resources

Developed prior to the OSI model

Originally defined as having four layers: host-to-network, internet, transport, application

DCN views it as having five layers: physical, data link, network, transport, application

Hierarchical protocol made up of interactive modules – upper-level protocol is supported by one or more lower-level protocols

Does not define any specific protocol

Supports all standard and proprietary protocols

May be LAN or WAN

Internet Protocol (IP)

Address Resolution Protocol (ARP)

Reverse Address Resolution Protocol (RARP)

Internet Control Message Protocol (ICMP)

Internet Group Message Protocol (IGMP)

IP is host-to-host, UDP and TCP are process-to-process

User Datagram Protocol (UDP)

Transmission Control Protocol (TCP)

Physical Addresses

Logical Addresses

Port Addresses

Specific Addresses

Lowest-level address defined by a node's LAN or WAN

Size and format varies depending on network

Example: Ethernet uses 6-byte physical addresses written as 12 hexadecimal digits separated by a colon
68:a3:c4:ce:8c:e2

Necessary for universal communications – internetworks

Internet (IP) address is 32 bits

No two publicly addressed and visible host on the Internet can have the same IP address

Data

A|P

10 | 20

T2

Data

A|P

Data

Upper Layers

Network Layer

Data Link Layer

10 | 20

A|P

Data

T2

A|P

Data

A|P

Data

Data

A|P

T2

A|P

A|P

Data

Data

T2

T2

Data

A|P

66 | 95

99 | 33

99 | 33

A|P

Data

Data

Data

A|P

A|P

66 | 95

T2

Data

objective of Internet communication is a process communicating with another (peer) process running on a remote computer

TCP/IP Port address – assigned to a process,16 bits