EEL 4781 Computer Communication Networks

Lecture 2

Protocol Layering, Protocol Stack, Example Networks

Protocol Layering

Protocol An agreement between the communication parties on how to standardize communication

Most networks are organized as a stack of layers to reduce design complexity

Protocol layers use interfaces to interact with each other Reference models include OSI, TCP/IP, and a modified one for this class

Protocol Layering

Principles that guided the OSI model: A layer should be created where a different abstraction is needed Each layer should perform a well-defined function The function of each layer should be chosen with an eye toward defining internationally standardized

protocols

The layer boundaries should be chosen to minimized the information flow across the interfaces The number of layers should be large enough that distinct functions need not be thrown together in

the same layer out of necessity and small enough that the architecture does not become unwieldy

Protocol Layering

Why wasnt the OSI model successful Bad timing standards need to be written after research but before investments

OSI came too late and TCP/IP had already taken over Bad technology the model and protocols were flawed, the session and presentation

layers are nearly empty while data link and network are overfull

Bad implementations people associated OSI with poor quality while TCP was quite good and free

Bad politics educational research communities vs government agencies

Protocol Layering

Transport

Network

Link

Physical

Application

Example of the protocol stack used in this bookHeaders with additional data are added at each layer

H4

H4

H4

H4

H3

H3H2

H3H2H1

Transport

Network

Link

Physical

Application

H4

H4

H4

H4

H3

H3H2

H3H2H1

User 1 User 2

Physical Medium

Protocol Stack

Physical Layer how to transmit raw bits over a communication channel Modulation and multiplexing (AM, FM, PM, QAM, QPSK, FDMA, TDMA, CDMA)

Link Layer how to send finite-length messages between users Ethernet, 802.11, 802.16

Protocol Stack

Network Layer how to combine multiple links into networks and how to combine multiple networks into internetworks IPv4, IPv6, ICMP, RIP, IGMP

Transport Layer how services in the network layered are guaranteed TCP, UDP, RSVP

Application Layer how programs make use of the network HTTP, DHCP, FTP, DNS, IMAP, SMTP, XMPP, SSH, BGP, Telnet

Whos who

ISO International Standards Organization Voluntary nontreaty organization issuing standards on a variety of subjects from fishing nets to the internet

IEEE Institute of Electrical and Electronics Engineers Lagest professional organization in the world that hosts conferences, published journals, and developes

standards. ie: IEEE 802.11 WIFI

W3c World Wide Web Consortium Developes protocols and guidelines to facilitate the long-term growth of the web

RFC Request for Comments Where standards are proposed, critiqued, and implemented

Whos who

Please refer to handwritten notes Mobile Phone Networks

AMPS, GSM, CDMA2000, HSPA, LTE, frequency reuse, soft handover vs hard handover Sample problems from the back 4, 6, 10, 13, 17, 22, 32 (UCF)

EEL 4781 Computer Communication NetworksProtocol LayeringProtocol LayeringProtocol LayeringProtocol LayeringProtocol StackProtocol StackWhos whoWhos who