Transmission mode

• Simplex – communication is unidirectional as a one way street. Only one of the two stations on a link can transmit, other can only receive.
• Half-duplex – each station can both transmit and receive, but not at the same time, when one device is sending, other can only receive or vice versa.
• Full-duplex – both stations can transmit and receive simultaneously.

Categories of Network

• LAN (Local Area Network) – usually privately owned and links the devices in a single office buildings or compress, depending on the needs of organization the type of technology used.
• MAN (Metropolitan Area Network) – is designed to extend over city. It may be a single network such as a cable TV network, or it may be beans of connecting a number of LAN’s into a large networks. So that resources may be shared as LAN-to-LAN as device-to-device.
• WAN (Wide Area Network) – provides a long distance transmission of data (voice, image, video) that may comprise a country, continent or whole world.
• Intenetworks (Internet) – when 2 or more networks are connected they become a internetwork or internet.

Summary of OSI model

• Application – to allow access to network resources.
• Presentation – to translate encrypt and compress data
• Session – to establish, manage, terminate session.
• Transport – to provide reliable end-to-end message delivery and error recovery.
• Network – to move packets from resource to destination, to provide internetworking.
• Data-link – to organize bits into frames, node-to-node delivery.
• Physical – to transmit bits over medium, to provide mechanical & electrical specifications.

Transmission of Digital Data (interfaces)

Data Transmission

1. Parallel – binary data consisting 1’s and 0’s maybe organized in 2 groups of n-bits each. Computer produce a consume data in groups of bits much as we consume of and use spoken language in the form of words rather than letters by grouping we can end data n-bits at a time instead of one this is called parallel transmission.
2. Serial – one bit follows another, so we need only one communication channel rather than n to transmit data between 2 communicating devices.
1. Synchronous – the bit stream combined into longer frames. This may contain multiple bytes. Each byte however is introduced to transmission link, without a gap between it and next one.
2. Asynchronous – we send one start bit 0 at the beginning and one or more stop bits at the end of each bit. There may be a gap between data.

DTE-DCE

Bit includes any unit that functions either as a source or a destination of binary digital data. At the physical layer it can be a terminal microcomputer.

• DTE (Data Terminal Equipment) – is any device that is the source of or a destination for binary digital data
• DCE (Data Circuit Equipment) – is any device that transmits or receives data in their form of any analog or digital signal through a network

Network and Internetworking Devices

Connecting device

1. Networking device

a. Repeaters

b. Bridges

2. Internetworking device

a. Routers

b. Gateways

Digital Subscriber Lines (DSL)

DSL – a new technology that uses an existing telecommunication networks such as the local loop telephone line to accomplish high speed delivery data, voice and multimedia.

ADSL

ADSL2+

VDSL

VDSL2

HDSL

SHDSL

SHDSL bis

SDSL

ADSL (Asymmetric DSL) – is asymmetrical which means, it provides higher rates in the downstream, lower rates in upstream.

HDSL (High bit rate DSL)

VDSL (Very high bit rate DSL) – an alternative approach that’s similar to ADSL. It uses coaxial fiber optic or twisted pair cable for more distances (300m-1800m). Downstream might be (50-55Mb/s), upstream (1.5-2.5Mb/s).

ISP (Internet Service Provider) – offers the end users to access internet backbone networks. The ISP is the downstream ret aver reseller of IP-transport services.

IBP (The Internet backbone Provider) – offers IP connectivity to the internet cloud for the ISP and provides backbone transport, including routing and basic transport. The IBS is the upstream whaleback of internet services to the ISP

Multiprotocol Label Switching (MPLS) – mechanism in high-performance telecommunications networks which directs and carries data from one network node to the next. MPLS makes it easy to create "virtual links" between distant nodes. It can encapsulate packets of various network protocols.

Label Edge Routers (LER) – the entry and exit points of an MPLS network; push an MPLS label onto an incoming packet and pop it off the outgoing packet.

Label Switch Routers (LSR) – routers that perform routing based only on this label.

Label Distribution Protocol (LDP) – a protocol in which two Label Switch Routers (LSR) exchange label mapping information. Labels are distributed between LERs and LSRs using this protocol.

Ingress router – a Label Switch Router that is a starting point (source) for a given Label Switched Path (LSP)

Virtual private network (VPN) – a computer network that is layered on top of an underlying computer network. The private nature of a VPN means that the data traveling over the VPN is not generally visible to, or is encapsulated from, the underlying network traffic.

Radio frequency allocation – the section of the electromagnetic spectrum defined as radio communication is divided into 8 ranges called bands each regulated by government authorities. These bands are rated Very Low Frequency (VLF) to Extremely High Frequency (EHF).

VLF

LF

MF

HF

VHF

UHF

SHF

EHF