Advanced Computer Networks: Lecture 2 - Dr. Amir Qayyum

Advanced Computer Networks: Lecture 2. This lecture will cover the following: multiplexing and statistical multiplexing; inter-process communication; IPC abstractions; abstract channel functionality; performance metrics; bandwidth versus latency; bandwidth requirements; protocol interfaces;...

CS716 Advanced Computer Networks

By Dr. Amir Qayyum

Lecture No. 2 

• An application needs to break­up its message in packets,  and re­assemble at the receiver

• Turn host­to­host connectivity into process­to­process 

communication, making the communication  meaningful.

• Fill gap between what applications expect and what the  underlying technology provides.

Application

Host Application

Channel Abstraction for 

application­level  communication

• information retrieval

• Message stream

– video on­demand – video conferencing

1 second (a)

1 second (b)

1Mbps, 1µs/bit

2Mbps, 0.5µs/bit

Bandwidth related to “bit width”

• Large data (file transfer) is bandwidth critical

• Small data (HTTP) is latency critical

• Amount of data “in flight” or “in the pipe”

• This much data must be buffered before the sender responds to slowdown the request

Bandwidth

Delay

• Latency (RTT) dominates instead of throughput

– Throughput = TransferSize / TransferTime

– TransferTime = RTT + 1/Bandwidth x TransferSize

• Request/reply type applications may agree for as much bandwidth as is available

• Message stream type applications often require a certain bandwidth: not more not less

• Established a comprehensive set of requirements for network design

• Networks evolve to accommodate changes in 

underlying technologies and user demands

• However, hardware and user expectations are 

moving targets …

Application programs

Application programs Request/reply

channel Message streamchannel

Host 1 Host 2

Service interface

Peer-to-peer interface

Protocol Interfaces

High-level object

High-level

object

Protocol Protocol

Digital library application

Video application

File application

Digital library application

Video application