Network Layer | Computer Networks - Computer Science Engineering (CSE) PDF Download

1. TRANSPORT LAYER

  • provide logical communication between app processes running on different hosts
  • transport protocols run in end systems
    • send side: breaks app messages into segments, passes to network layer
    • rcv side: reassembles segments into messages, passes to app layer
  • more than one transport protocol available to apps
    • Internet: TCP and UDP
  • network layer: logical communication between hosts
  • transport layer: logical communication between processes relies on, enhances, network layer services  reliable, in-order delivery (TCP) congestion control (distributed control)
    • flow control
    • connection setup
  • unreliable, unordered delivery: UDP no-frills extension of “best-effort” IP services not available:
    • delay guarantees

    • bandwidth guarantees

2. USER DATAGRAM PROTOCOL (UDP)

“no frills,” “bare bones” Internet transport protocol  best effort” service, UDP segments may be:

  • lost
  • delivered out of order to app  

     

connectionless:

  • no handshaking between UDP sender, receiver
  • each UDP segment handled independently of others
  • no connection establishment (which can add delay)
  • simple: no connection state at sender, receiver
  • small segment header
  • no congestion control: UDP can blast away as fast as desired  

often used for streaming multimedia apps

  • loss tolerant
  • rate sensitive

other UDP uses

  • DNS
  • SNMP

reliable transfer over UDP: add reliability at application layer

  •  application-specific error recovery!

 

Network Layer | Computer Networks - Computer Science Engineering (CSE)

3. TRANSMISSION CONTROL PROTOCOL

point-to-point:

  • one sender, one receiver  reliable, in-order byte steam: 
  • no “message boundaries” 

pipelined:

  • TCP congestion and flow control set window size send & receive buffers

 

Network Layer | Computer Networks - Computer Science Engineering (CSE)

full duplex data:

  • bi-directional data flow in same connection
  • MSS: maximum segment size

connection-oriented:

  • handshaking (exchange of control msgs) init’s sender, receiver state before data exchange

flow controlled: sender will not overwhelm receiver

3.1.TCP segment structure

 

Network Layer | Computer Networks - Computer Science Engineering (CSE)

3.2. TCP seq. #’s and ACKs

 

Seq. #’s: byte stream “number” of first byte in segment’s data

ACKs: seq # of next byte expected from other side cumulative ACK

how receiver handles out-of-order segments. TCP spec doesn’t say, - up to implementor longer than RTT. but RTT varies

too short: premature timeout unnecessary retransmissions

too long: slow reaction to segment loss

SampleRTT: measured time from segment transmission until ACK receipt ignore retransmissions

SampleRTT will vary, want estimated RTT “smoother” average several recent measurements, not just current SampleRTT TCP Round Trip Time and Timeout EstimatedRTT = (1-a )*EstimatedRTT +a *SampleRTT Exponential weighted moving average influence of past sample decreases exponentially fast typical value: a =0.125

4. CONGESTION CONTROL

Congestion:

  • informally: “too many sources sending too much data too fast for network to handle” different from flow control!
  • manifestations:
    • lost packets (buffer overflow at routers)
    • long delays (queueing in router buffers)
  • a top-10 problem!

Causes/costs of congestion: scenario 1

  • two senders, two receivers
  • one router, infinite buffers
  • no retransmission

Causes/costs of congestion: scenario 2

  • one router, finite buffers
  • sender retransmission of lost packet
  • always: (goodput)
  • “perfect” retransmission only when loss: retransmission of delayed (not lost) packet makes larger (than perfect case) for same
  • “costs” of congestion: more work (retrans) for given “goodput” unneeded retransmissions: link carries multiple copies of pkt

Causes/costs of congestion: scenario 3

  • four senders multihop paths timeout/retransmit
  • Another “cost” of congestion: when packet dropped, any “upstream transmission capacity used for that packet was wasted!. Approaches towards congestion control End-end congestion control: no explicit feedback from network congestion inferred from end-system observed loss, delay approach taken by TCP Network-assisted congestion control: routers provide feedback to end systems
    • single bit indicating congestion (SNA, DECbit, TCP/IP ECN, ATM)
    • explicit rate sender
The document Network Layer | Computer Networks - Computer Science Engineering (CSE) is a part of the Computer Science Engineering (CSE) Course Computer Networks.
All you need of Computer Science Engineering (CSE) at this link: Computer Science Engineering (CSE)
21 videos|107 docs|66 tests

Up next

FAQs on Network Layer - Computer Networks - Computer Science Engineering (CSE)

1. What is the purpose of the network layer in computer science engineering?
Ans. The network layer is responsible for routing and forwarding data packets across different networks. It ensures that data is correctly delivered from the source to the destination by establishing logical paths, choosing the best route, and controlling congestion.
2. How does the network layer handle addressing in computer science engineering?
Ans. The network layer uses IP (Internet Protocol) addressing to assign unique addresses to devices connected to a network. These addresses are used to identify the source and destination of data packets, allowing routers to correctly forward them to the intended recipient.
3. What are the key protocols used in the network layer of computer science engineering?
Ans. Some of the key protocols used in the network layer include IP (Internet Protocol), ICMP (Internet Control Message Protocol), ARP (Address Resolution Protocol), and OSPF (Open Shortest Path First). These protocols play crucial roles in addressing, routing, error reporting, and network discovery.
4. How does the network layer handle congestion control in computer science engineering?
Ans. The network layer implements various congestion control mechanisms to manage network congestion and prevent packet loss. These mechanisms include traffic shaping, traffic policing, and queuing algorithms such as Random Early Detection (RED) and Weighted Fair Queuing (WFQ).
5. What are the challenges faced by the network layer in computer science engineering?
Ans. The network layer faces challenges such as scalability, security, and quality of service (QoS) management. As networks grow larger and more complex, ensuring efficient routing, protecting against threats, and maintaining desired service levels become increasingly difficult tasks for the network layer.
21 videos|107 docs|66 tests
Download as PDF

Up next

Explore Courses for Computer Science Engineering (CSE) exam
Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev
Related Searches

Free

,

Network Layer | Computer Networks - Computer Science Engineering (CSE)

,

Semester Notes

,

Summary

,

Objective type Questions

,

Sample Paper

,

Extra Questions

,

video lectures

,

mock tests for examination

,

Viva Questions

,

ppt

,

Network Layer | Computer Networks - Computer Science Engineering (CSE)

,

MCQs

,

practice quizzes

,

Network Layer | Computer Networks - Computer Science Engineering (CSE)

,

past year papers

,

study material

,

pdf

,

shortcuts and tricks

,

Exam

,

Previous Year Questions with Solutions

,

Important questions

;