Derek,
Redundant? No way. The TCP header information is very unique
in itself. Think about this..
IP (layer 3) is connectionless and therefore makes no guarantee that the
data will received by the destination, whereas TCP (layer 4) is
connection-oriented and is there to provide the appearance of a
point-to-point connection.
Further investigation reveals that a point-to-point connection has two
characteristics;
1. The data flow must be the same path to and from it's destination.
2. Packet arrive in the order they're sent.
TCP uses 3 mechanisms to achieve connection-oriented service on top of a
conectionless service.
1. The packet are labeled with sequence number so order can be determined.
2. The system of acknowledgment, checksum, and timers to provide
reliability. Where if a packet if corrupted
the receiver will notify the sender to retransmit, or if the sender
doesn't receive an *ack* from the receiver
a specified amount of time, the sender will assume the packet did not
arrive.
3. Windowing..regulate the flow of packets..
---------------------
Whereas IP two primary responsibilities; providing connectionless
best-effort delivery of datagrams(remember your five-step process of
encapsulation) through the internetwork. IP provides fragmentation and
reassembly of datagrams to support the different Maximum Transmission
Unit(MTU) sizes.
last but not least there's a protocol field in the IP header so when IP
processing is complete it can pass the packet onto the upper layer protocol
indicated.
HTH this helps..
For more info check out Jeff Doyle's TCP/IP Routing and the Internetwoking
Technologies Handbook.. and all will be revealed..
Nigel...
----- Original Message -----
From: Derek CHUNG <[EMAIL PROTECTED]>
Newsgroups: groupstudy.cisco
To: <[EMAIL PROTECTED]>
Sent: Sunday, August 20, 2000 11:59 AM
Subject: Is a TCP packet encapsulated by a IP packet which is inside a Layer
2 frame?
> Is a TCP packet (layer 4) encapsulated by a IP packet (layer 3) which is
> inside a Layer 2 frame?
> If so, why the headers of a IP packet and TCP packet look so similar and
> redundant?
>
>
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