Computer Networks Miscellenous Topics, Study notes of Computer Networks

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Miscellaneous Topics

HCST@HOD-IT 2019

Service Access Point ( SAP )

 A Service Access Point ( SAP ) is an identifying label for network endpoints used in Open Systems interconnection (OSI) networking.

 The SAP is a conceptual location at which one OSI layer can request the services of another OSI layer.

 Relation between layers at an interface shown below-

Connection Less Services

 It is similar to the postal services, as it carries the full address where the message (letter) is to be carried.

 Each message is routed independently from source to destination.

 The order of message sent can be different from the order received.

 In connectionless the data is transferred in one direction from source to destination without checking that destination is still there or not or if it prepared to accept the message.  Authentication is not needed in this.

 Example of Connectionless service is UDP (User Datagram Protocol) protocol.

Difference between Connection oriented service and Connectionless service

 In connection oriented service authentication is

needed while connectionless service does not need any authentication.

 Connection oriented protocol makes a connection

and checks whether message is received or not and sends again if an error occurs connectionless service protocol does not guarantees a delivery.

 Connection oriented service is more reliable than

connectionless service.

 Connection oriented service interface is stream

based and connectionless is message based.

Differentiate between OSI and TCP/IP

model

OSI TCP/IP

1 It has 7 layers It has 4 layer

2 Transport layer guarantee delivery of packets

Does not guarantee

4 Horizontal approach Vertical approach

5 Separate session layer No session layer ; characteristics provided by TCP

5 Protocols are hidden and replace as technology changes

Not easy to replace

6 OSI is a general model It can not be used for any other applications

7 Offers both connectionless and connection oriented connection in network layer

Offers only connection oriented service in IP layer but offer both services in Transport.

Introduction to devices-

 Bridge

 Hub

 Switch

HUB

 Hubs are used in Ethernet networks.

 A signal received at any port on the hub is retransmitted on all other ports.

 Network segments that employ hubs are often described as having a star topology, in which the hub forms the wiring center of the star.

 Using a hub provides a degree of fault tolerance, because each network device has its own connection to the hub, and if a connection fails, only a single device is affected.

 Expanding the network is also easier, because many additional devices can be added to the network using a single hub, which is itself often connected to a network backbone.

 Hubs can be either active or passive.

Switch

 The switch is a relatively new network device that has replaced both hubs and bridges in LANs.

 A switch uses an internal address table to route incoming data frames via the port associated with their destination MAC address.

 Switches can be used to connect together a number of end-user devices such as workstations, or to interconnect multiple network segments.

 A switch that interconnects end-user devices is often called a workgroup switch.

 Switches provide dedicated full-duplex links for every possible pairing of ports, effectively giving each attached device its own network segment This significantly reduces the number of intra-segment and inter-segment collisions..

BACKBONE NETWORKS

Figure - Bus backbone

Star backbone

Introduction -(ISDN)

ISDN is a digital transport and signaling systems

 ISDN defines a vendor independent interface between the user (telephones, PBXs, computers) and the network  The operations inside the network are typically governed by the common channel signaling system No. 7 (SS-7 Layer)

 ISDN was designed primarily for circuit-switched voice traffic and secondarily for all other aspects of data communication  Interfaces and Functional Groupings

 The ISDN user interface can be divided into two

areas

• Functional Groupings
• Reference Points

 Functional groupings (TE, TA, NT2, etc.) are a set of capabilities needed in an ISDN user access interface

Integrated Services Digital Network

 Reference points (R, S, T, and U) are the interfaces dividing the functional groupings.

 Usually a reference point is a physical interface between two pieces of equipment