41902 Lecture Notes - Lecture 3: Single-Mode Optical Fiber, Network Layer, Transport Layer
Network Fundamentals:
Chapter 1.5: Protocols layer, service models
Networks are complex with many components. Hosts, routers, links of various media, applications,
protocols, hardware, software. Protocol laying is used to organise and deal with complex systems.
Explicit structure allows identification, relationship of complex systems pieces (layered reference
model), modularization eases maintenance and updating of system. Change of implementation of
layers serie trasparet to rest of syste (e.g. hage i gate proedure doest affet rest of
system).
Internet Protocol stack:
5. Application: supporting network applications (FTP, SMTP, HTTP)
4. Transport: process-process data transfer (TCP, UDP)
3. Network: routing of datagrams from source to destination (IP, routing, protocols)
2. Link: data transfer between neighbouring network element (Ethernet, 802.111(Wifi), PPP)
1. Physical: its o the ire
How a packet changes as it moves between layers:
The application layer is where network applications and their protocols reside. Protocols include
HTTP (provides for Web document request and transfer), SMTP (provides for the transfer of files
between two end systems) and FTP (provides for the transfer of files between two end systems). The
application of one end system uses protocols to exchange packets of information with another
application in another end system. At the application layer, the packet is a message.
The transport-layer transports application-layer messages between application endpoints. Protocols
include TCP and UDP, wither of which can transport application-layer messages. TCP provides
connection-oriented service to its applications, including guaranteed delivery of messages to the
destination and flow control (sender/receiver speed is matched). TCP also breaks long messages into
shorter segments and provides a congestion-control mechanism to increase transmission rate. UDP
is a connectionless service that is unreliable, has no flow control and no congestion control. At the
transport layer, the packet is a segment.
The network-layer is responsible for moving packets (known as datagrams at this layer) from one
host to another. Transport layer protocol in a source host passes a transport-layer segment and a
destination address to the network layer. The network layer then provides the service of delivering
the segment to the transport layer in the destination host. Network layer includes IP protocol, which
defines the fields in the datagram and how the end systems and routers act on these fields.
The network layer routs a datagram through a series of routers between source and destination. To
move a packet from one node (host or router) to the next node, the network layer relies on the
services of the link-layer. At each node, the network layer passes a datagram down to the link layer,
which delivers the datagram to the next node along the route. Protocols include Ethernet, WiFi, and
cable access networks DOCSIS protocol. Packets at this layer are frames. The link layers moves entire
frames one network element to an adjacent network element.
The physical layer moves individual bits within the frame from one node to the next. Protocols are
link dependant and depend on actual transmission medium (e.g. twister pair, copper wire, single-
mode fiber optics). Ethernet has many physical layer protocols.
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Document Summary
Hosts, routers, links of various media, applications, protocols, hardware, software. Protocol laying is used to organise and deal with complex systems. Explicit structure allows identification, relationship of complex systems pieces (layered reference model), modularization eases maintenance and updating of system. Change of implementation of layer(cid:859)s ser(cid:448)i(cid:272)e tra(cid:374)spare(cid:374)t to rest of syste(cid:373) (e. g. (cid:272)ha(cid:374)ge i(cid:374) gate pro(cid:272)edure does(cid:374)(cid:859)t affe(cid:272)t rest of system). How a packet changes as it moves between layers: The application layer is where network applications and their protocols reside. Http (provides for web document request and transfer), smtp (provides for the transfer of files between two end systems) and ftp (provides for the transfer of files between two end systems). The application of one end system uses protocols to exchange packets of information with another application in another end system. At the application layer, the packet is a message. The transport-layer transports application-layer messages between application endpoints.
