Unit 4

Network Layer Overview

The network layer routes data packets from source to destination across multiple networks. It determines best path and ensures packets reach correct destination using IP addressing.

Logical addressing: IP addresses uniquely identify devices
Internetworking: Connects multiple networks (like Internet)
Tunneling: Secure data encapsulation across networks
Address mapping: Logical → Physical address conversion

ICMP & IGMP Protocols

ICMP: Error reporting + diagnostics (ping, traceroute)
IGMP: Manages multicast group memberships
Forwarding: Router-to-router packet sending

Unicast: Single destination | Multicast: Multiple receivers

Transport Layer (Layer 4)

Handles end-to-end communication between applications on different hosts. Sits above Network Layer (L3), below Application Layer (L5-7).

Main Protocols: TCP (reliable), UDP (fast), SCTP (multi-stream)

Process-to-Process Delivery

Delivery Types

Type	Layer	Scope	Example
Node-to-Node	L2	LAN	Switch→PC
Host-to-Host	L3	Internet	IP packet
Process-to-Process	L4	Apps	Port 80→80

Port Numbers (0-65535)

Well-known (0-1023): HTTP(80), FTP(21), SSH(22)
Registered (1024-49151): Custom apps
Dynamic (49152-65535): Client temp ports

Multiplexing:

Chrome+Email+VLC → 1 Transport Layer → Adds ports

Demultiplexing:

Reads dest port → Delivers to correct app

Transport Protocols

Protocol	Type	Features	Uses
UDP	Connectionless	Fast, unreliable	VoIP, Video, DNS
TCP	Connection-oriented	Reliable, ordered	HTTP, FTP, Email
SCTP	Multi-stream	TCP+UDP features	Telephony signaling

Data Traffic Management

Traffic Types

Type	Example	Requirements	Protocol
Constant Bit Rate	VoIP	Low jitter	UDP+RTP
Variable Bit Rate	Video stream	Adapt bitrate	UDP+RTP
Bursty	Web browsing	Reliability	TCP
Interactive	SSH typing	Low delay	TCP

Management Techniques

Segmentation: Large messages → Small segments
Flow Control: Prevent receiver overload
Congestion Control: Avoid network jam
Error Control: Detect/fix corrupt data

Quality of Service (QoS)

QoS Parameters

Parameter	Measures	For	Target
Throughput	bytes/sec	Video	5 Mbps min
Delay	End-to-end	VoIP	<150ms
Jitter	Delay variation	Video calls	<30ms
Packet Loss	% lost	Real-time	<1%

TCP vs UDP:

TCP: Reliable, VARIABLE delay (retransmits)
UDP: FIXED low delay, unreliable

Implementation:

Port identification (HTTP80, VoIP5060)
Traffic shaping, Priority queuing
Bandwidth allocation

Integrated Services (IntServ)

Per-Flow Reservation

Each flow (srcIP+dstIP+srcPort+dstPort) gets reserved bandwidth.

Process:

App sends RSVP message
All routers reserve bandwidth
Flow gets GUARANTEED QoS
End → Resources released

Components:

RSVP: Signaling
Admission Control: Bandwidth check
Classifier: Packet grouping
Scheduler: Priority queue

IntServ vs DiffServ

Feature	IntServ	DiffServ
Granularity	Per flow	Per class
Scalability	Poor	Excellent
Complexity	High	Low
Guarantees	Hard	Best effort
Best for	LANs	Internet