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An in-depth analysis of the network layer, focusing on datagram and virtual circuit packet switching. Topics include addressing, switching, routing, traffic control, connectionless vs. Connection-oriented services, and forwarding tables. It also covers the differences between ip and atm models.
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Introduction Datagrams and Virtual Circuits Routing Traffic Control
Transport Session
Presentation Application (^) TransportSession
Presentation
Application
Physical
Data Link Network
Physical
Data Link
Network
Physical Data Link
Network
Physical
Data Link
Network
Physical
Data Link
Network
Physical
Data Link
Network
Station (Host)
Node (Router)
Copyright by Jorg Liebeherr 98,
n Simple, unreliable, unordered delivery service n Different letters between the same parties are handled independently (connectionless model) n Stateless (no record of who’s corresponding with whom) n Intelligent end-user
n Concept of “connections” between conversing users n Reliable delivery (of voice) n State is maintained regarding active connections n Dumb end-device (phone)
Packet-switched network
1.3 1.2 1. 2.3 2.2 2.
1.^ 1.^
1.
**2.
2.**
A
B
C Copyright by Jorg Liebeherr 98,
A 1
2 3
6
4 5
B
C
2 1
2
1
3 3
Copyright by Jorg Liebeherr 98,
Copyright by Jorg Liebeherr 98,99VC #
Ethernet Switch (Link layer device) Cisco Router (Network layer device)
Port 0 Port 1
In Port In VCI Out Port Out VCI
Port 2
Copyright by Jorg Liebeherr 98,
0
1
2 0 1
2
(Port0,VCI1)‡ Port
3
(Port3,VCI5)‡ Port
4 (Port4,VCI7)
VCI
,VCI
VCI
,VCI
VCI
A establishes connection to D
Application TCP IP Network Access
Application TCP
IP NetworkAccess
Application protocol TCP protocol IP protocol IP protocol DataLink NetworkAccess
IP NetworkAccess NetworkAccess
IP Data^ NetworkAccess Link DataLink
IP protocol
Host Router Router Host
Copyright by Jorg Liebeherr 98,
n is 32 bits long. n encodes a network number and a host number
n 128.238.42.112 means 10000000 in 1st Byte 11101110 in 2nd Byte 00101010 in 3rd Byte 01110000 in 4th Byte Copyright by Jorg Liebeherr 98,
n Example: For how long will a 1M byte datagram tie up a T1 line (1.5Mbps)? n How about a 1 Gbps optical fiber?
Copyright by Jorg Liebeherr 98,
version (4 bits) header length Type of Service/TOS (8 bits) Total Length (in bytes) (16 bits) Identification (16 bits) (^) (3 bits)f l a g s Fragment Offset (13 bits)
Source IP address (32 bits) Destination IP address (32 bits) Options (if any, <40 bytes)
DATA
>= five 32-bit words
32-bit word
0 31
TTL Time-to-Live (8 bits)
Protocol (8 bits) Header Checksum (16 bits)
Copyright by Jorg Liebeherr 98,
n Security restrictions n Record Route: each router that processes the packet adds its IP address to the header. n Timestamp: each router that processes the packet adds its IP address and time to the header. n (loose) Source Routing: specifies a list of routers that must be traversed. n (strict) Source Routing: specifies a list of the only routers that can be traversed.
Copyright by Jorg Liebeherr 98,
FDDI Ring (^) Router Host A (^) Host B
Ethernet
MTUs: FDDI: 4352 Ethernet: 1500
Copyright by Jorg Liebeherr 98,
version (4 bits)
header length
Type of Service/TOS Total Length (in bytes) Identification f l a g s^ Fragment Offset
......
TTL Time-to-Live (8 bits) Protocol (8 bits) Header Checksum (16 bits)
Identification is the same in all fragments. Flags contains a “more fragments” bit (There is also a “don’t fragment bit” that can be set) Fragment offset contains the offset of current fragment in the original datagram Total length is changed by fragmentation Copyright by Jorg Liebeherr 98,
